首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   33230篇
  免费   1755篇
  国内免费   148篇
耳鼻咽喉   360篇
儿科学   736篇
妇产科学   582篇
基础医学   6295篇
口腔科学   743篇
临床医学   2631篇
内科学   6283篇
皮肤病学   855篇
神经病学   3441篇
特种医学   1424篇
外科学   4602篇
综合类   152篇
一般理论   14篇
预防医学   1670篇
眼科学   721篇
药学   2319篇
中国医学   21篇
肿瘤学   2284篇
  2022年   161篇
  2021年   347篇
  2020年   295篇
  2019年   493篇
  2018年   574篇
  2017年   439篇
  2016年   566篇
  2015年   653篇
  2014年   784篇
  2013年   1171篇
  2012年   1643篇
  2011年   1760篇
  2010年   1185篇
  2009年   1134篇
  2008年   1891篇
  2007年   1930篇
  2006年   1798篇
  2005年   1925篇
  2004年   1804篇
  2003年   1766篇
  2002年   1845篇
  2001年   349篇
  2000年   273篇
  1999年   393篇
  1998年   503篇
  1997年   414篇
  1996年   369篇
  1995年   338篇
  1994年   291篇
  1993年   258篇
  1992年   213篇
  1991年   206篇
  1990年   170篇
  1989年   165篇
  1988年   170篇
  1985年   161篇
  1984年   181篇
  1983年   161篇
  1982年   198篇
  1981年   169篇
  1978年   135篇
  1933年   170篇
  1932年   180篇
  1931年   167篇
  1930年   169篇
  1929年   147篇
  1928年   163篇
  1927年   144篇
  1926年   158篇
  1925年   139篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
Widespread depletion of forebrain noradrenaline, produced by the intracerebral injection of 4 g of 6-hydroxydopamine into the fibres of the dorsal noradrenergic bundle, potentiated the catalepsy induced by 20 mg/kg of morphine and severely attenuated the catalepsy induced by two separate cholinergic agonists, arecoline and pilocarpine. It did not, however, affect haloperidol catalepsy at any of the four doses tested. These results suggest that cholinergic catalepsy may be critically dependent on an intact noradrenergic substrate, perhaps through cholinergic receptors located either presynaptically on noradrenergic terminals or on the cell bodies of origin in the locus coeruleus. Noradrenaline appears to play a modulatory role in morphine catalepsy, although other sites of action must also be involved. Ascending noradrenergic systems do not appear to influence haloperidol catalepsy.  相似文献   
202.
Zusammenfassung Der standardisierte Fragebogen zur Erfassung muskuloskeletaler Beschwerden des japanischen Komitees zum Studium arbeitsbedingter Gesundheitsstörungen im Hals-Arm-Gebiet wurde auf Deutsch übertragen und seine Reliabilität und Validität überprüft. Im Fragebogen wird anhand eines Körperschemas nach der Häufigkeit (nie/selten, gelegentlich, fast täglich) von Beschwerden (Schmerzen, Steifigkeit, Müdigkeit) in 12 Körperregionen gefragt. Der Fragebogen wurde gleichzeitig mit ärztlichen Palpationsuntersuchungen bei 644 Personen aus zwölf Berufsgruppen im Dienstleistungssektor eingesetzt. Auf Grund einer Faktoranalyse der Fragebogenresultate kann festgestellt werden, dass Beschwerden regional getrennt (nämlich im Nacken-Schultergebiet, dem Rücken und je der rechten und linken oberen Extremität) auftreten und für diese Regionen die Symptome zu Indizes zusammengefasst werden können. Diese Indizes sind reliabel (Cronbach 0.8). Mit zunehmenden Indexwerten nehmen schmerzhafte Palpationsbefunde stetig zu. Beschwerden korrelieren mit vermehrtem Medikamentenkonsum und Arztkonsultationen. Der Fragebogen stellt folglich ein valides Untersuchungsinstrument für muskuloskeletale Beschwerden am Arbeitsplatz dar.
Summary The standardized illustrated questionnaire on musculoskeletal disorders of the Japanese Committee on Occupational Cervico-brachial Disorders was translated into German. This questionnaire, composed of 37 items about the occurrence (never/seldom, occasionally, almost daily) of symptoms (pain, stiffness, fatique) in twelve body regions, was used together with medical examinations (pressure points), and further information was gathered on the consumption of analgetics and medical visits prompted by musculoskeletal symptoms. The questionnaire's reliability and validity were tested in 644 persons from twelve occupational groups within the service sector. Factoranalyses showed that symptoms can be grouped into four distinct regions of occurrence: neck/shoulder/area, back/low back, and both left and right upper extremities. Indices based on these regions are consistent (Cronbach 0.8). Palpation findings steadily increase with increasing index values. The consumption of medicaments and medical visits positively correlate with the indices. Consequently the questionnaire is judged to be a valid instrument for studying musculoskeletal disorders at the workplace.

Résumé Le questionnaire illustré et standardisé sur les symptômes musculaires et osseux du comité japonais sur la cervico-brachialgie professionelle a été traduit en allemand et sa reliabilité et validité ont été testées. Le questionnaire est composé de 37 variables sur la fréquence (jamais/rarement, par occasion, presque toujours) des symptômes (douleur, raideur, fatigue) dans douze régions du corps. Il était distribué simultanément aux examens médicaux parmi 644 personnes de douze groupes d'employés dans le secteur de service. D'autres informations concernent la fréquence de la consommation des analgésiques et des visites médicales pour des douleurs musculaires. Une analyse factorielle a montré que les symptômes peuvent être groupés en quatre régions du corps: nuque/épaules, dos et les extrémités supérieurs. Les indices sur ces régions sont consistant (Cronbach 0.8). Les douleurs provoquées par la palpation augmentent avec la valeur de l'index. La consommation des analgésiques et les consultations sont correlées avec les indices. Par conséquent, le questionnaire illustré est un instrument valable pour étudier les problèmes musculaires sur les lieux de travail.
  相似文献   
203.
Various N--hydroxyalkyl derivatives of N-acyl amino acids and di- and tripeptides were prepared by hydrolysis or aminolysis of N-acyl 5-oxazolidinones. The stability of these derivatives was studied in aqueous solution as a function of pH. The compounds were all degraded quantitatively to their parent N-acylated amino acid or peptide and aldehyde but with vastly different rates. At pH 7.4 and 37°C the half-lives of decomposition ranged from 4 min to 1500 hr. The structural factors influencing the stability included both steric and polar effects within the acyl and N--hydroxyalkyl moieties as well as within the amino acid attached to the N--hydroxyalkylated N-acyl amino acid. Whereas the N-benzyloxycarbonyl (Z) derivatives of the dipeptides Gly-L-Leu and Gly-L-Ala were readily hydrolyzed by carboxypeptidase A, the N-hydroxymethylated compounds, i.e., Z-Gly(CH2OH)-Leu and Z-Gly(CH2OH)-Ala, were resistant to cleavage by the enzyme as revealed by their similar rates of decomposition in the presence or absence of the enzyme at pH 7.4 and 37°C. The results suggest that N--hydroxyalkylation of a peptide bond protects not only this bond but also an adjacent peptide bond against proteolytic cleavage. Since the N--hydroxyalkyl derivatives are readily bioreversible, undergoing spontaneous hydrolysis at physiological pH, this prodrug approach promises to overcome the enzymatic barrier to absorption of various peptides.  相似文献   
204.
The M current, I M, a voltage-dependent non-inactivating K+ current, was recorded in NG108-15 neuroblastoma × glioma hybrid cells, using the whole-cell mode of the patch-clamp technique. We studied the effect of arachidonic acid, other fatty acids and inhibitors of the arachidonic acid metabolism. In relatively high concentrations (25–50 M) arachidonic acid first increased and later decreased the current, I h, which holds the membrane potential at –30 mV and mainly flows through open M channels. It shifted the midpoint potential, V o, of the relation between M conductance, g M, and membrane potential, V, to more negative values and decreased the maximum conductance ¯g M and the time constant M. In smaller concentrations (5–10 M) arachidonic acid merely decreased I h and ¯g M with little effect on V o and M. Eicosatetraynoic acid and docosa-hexaenoic acid acted similarly to arachidonic acid whereas stearic acid had no effect. Of the three enzyme inhibitors studied, nordihydroguaiaretic acid acted similarly to arachidonic acid. i. e. caused a biphasic change in I h. Indomethacin and quinacrine caused, respectively, a pure increase and a pure decrease of I h and ¯g M. Possible explanations are build-up of internally produced arachidonic acid, depletion of eicosanoid products or an inhibitory effect unrelated to arachidonic acid metabolism.  相似文献   
205.
Summary Oral MPA 1.5 g/day leads to plasma concentrations between 1 and 12 g/ml, with a broad intra-and interindividual variance. The plateau state is reached in between 4 and 16 days. Plasma concentrations in the plateau state are very sensitive to dose modifications. After cessation of administration, the decline in plasma levels seems to proceed in two phases, with half-times of about 20 h and 4 days. Extraction procedures reveal no benefit in discriminating between MPA and its metabolites.  相似文献   
206.
Addition of [3H]-benzo(a)pyrene to the perfusion medium of isolated rat livers results in irreversible binding of radioactivity to DNA, RNA and protein. Binding to DNA accounted for about 0.1% of the total radioactivity which was bound in livers from animals treated with oil or saline and was increased by a factor of 3–5 after pretreatment of the animals with -naphthoflavone or with phenobarbital. When the inhibitiors of monooygenase activity, -naphthoflavone or metyrapone, were present in the perfusion medium, irreversible binding was reduced in livers from both -naphthoflavone- and phenobarbital-pretreated animals, irrespective of the inhibitor used.In livers from animals treated with oil or saline protein and a RNA fraction containing tightly associated protein were able to bind [3H]-benzo(a)pyrene metabolites to about the same extent but after induction by pretreatment with -naphthoflavone binding to the RNA fraction was enhanced to a much higher extent than binding to the protein fraction. Pretreatment with phenobarbital did not result in an increased irreversible binding to RNA and protein.A considerable amount of 15–25% of the total radioactivity added to the perfusion medium was excreted into the bile after treatment of the animals with the tested inducers of monooxygenase activity compared to an excretion of 3% in animals treated with oil or saline.The results indicate that nucleic acid and protein adduct formation in the liver is controlled by the action of the cytochrome P-450-dependent monooxygenases.In part subject of the doctoral thesis of Erik Klaus, Fachbereich Biologie, University of Mainz  相似文献   
207.
This study was designed to determine which objective acoustic or aerodynamic parameters allowed a homogeneous group of patients with unilateral vocal fold paralysis (UVFP) to be distinguished from an age-matched and smoking-matched control group and to search for linear correlations between the objective parameters and the subjective breathiness ratings. Eight patients with recent-onset UVFP and 12 controls were prospectively studied. The acoustic parameters measured for the vowel /a/ at a comfortable frequency and intensity were: jitter, shimmer, harmonics-to-noise ratio, cepstral peak prominence, the difference between the levels of the first two harmonics and the relative energy above 6 kHz. Aerodynamic parameters included the mean flow rate during a sustained /a/ and intraoral pressure during the production of the phoneme /pi/. The long-term average spectrum was calculated for 40 s of text, and the relative average energies in four frequency bands were compared. Six judges rated a mid-/a/ sample using a five-parameter scale with four levels of severity. Nonparametric statistical analysis revealed significant differences ( P<.05) between the UVFP group and the control group for 14 of the 19 parameters studied. Correlations between the objective parameters and perceived breathiness differed in the two groups. Correlations were not always as expected as based on previous literature reports. These measurements provided an objective qualification of voice in patients with UVFP and successfully distinguished them from the normal controls. The objective acoustic and aerodynamic measurements had generally low linear correlations with breathiness ratings in the control group. Higher correlations were seen in the UVFP group, in which breathiness was best correlated with airflow measurements.  相似文献   
208.
SSR181507 ((3-exo)-8-benzoyl-N-[[(2S)7-chloro-2,3-dihydro-1,4-benzodioxin-1-yl]methyl]-8-azabicyclo[3.2.1]octane-3-methanamine monohydrochloride) is a novel tropanemethanamine benzodioxane derivative that possesses high and selective affinities for D2-like and 5-HT(1A) receptors (K(I)=0.8, 0.2, and 0.2 nM for human D(2), D(3), and 5-HT(1A), respectively). In vivo, SSR181507 inhibited [(3)H]raclopride binding to D(2) receptors in the rat (ID(50)=0.9 and 1 mg/kg, i.p. in limbic system and striatum, respectively). It displayed D(2) antagonist and 5-HT(1A) agonist properties in the same concentration range in vitro (IC(50)=5.3 nM and EC(50)=2.3 nM, respectively, in the GTPgammaS model) and in the same dose range in vivo (ED(50)=1.6 and 0.7 mg/kg, i.p. on striatal DA and 5-HT synthesis, respectively, and 0.03-0.3 mg/kg, i.v. on dorsal raphe nucleus firing rate). It selectively enhanced Fos immunoreactivity in mesocorticolimbic areas as compared to the striatum. This regional selectivity was confirmed in electrophysiological studies where SSR181507, given acutely (0.1-3 mg/kg, i.p.) or chronically (3 mg/kg, i.p., o.d., 22 days), increased or decreased, respectively, the number of spontaneous active DA cells in the ventral tegmental area, but not in the substantia nigra. Moreover, SSR181507 increased both basal and phasic DA efflux (as assessed by microdialysis and electrochemistry) in the medial prefrontal cortex and nucleus accumbens, but not in the striatum. This study shows that the combination of D(2) receptor antagonism and 5-HT(1A) agonism, in the same dose range, confers on SSR181507 a unique neurochemical and electrophysiological profile and suggests the potential of this compound for the treatment of the main dimensions of schizophrenia.  相似文献   
209.
For the first time the human intestinal effective permeability, estimated from the luminal disappearance and intestinal metabolism of phytochemicals, sulforaphane and quercetin-3,4'-glucoside, as well as the simultaneous changes in gene expression in vivo in enterocytes, has been studied in the human jejunum in vivo (Loc-I-Gut). Both compounds as components of an onion and broccoli extract could readily permeate the enterocytes in the perfused jejunal segment. At the physiologically relevant, dietary concentration tested, the average effective jejunal permeability (Peff) and percentage absorbed (+/- S.D.) were 18.7 +/- 12.6 x 10-4 cm/s and 74 +/- 29% for sulforaphane and 8.9 +/- 7.1 x 10-4 cm/s and 60 +/- 31% for quercetin-3,4'-diglucoside, respectively. Furthermore, a proportion of each compound was conjugated and excreted back into the lumen as sulforaphane-glutathione and quercetin-3'-glucuronide. The capacity of the isolated segment to deconjugate quercetin from quercetin-3,4'-diglucoside during the perfusion was much higher than the beta-glucosidase activity of the preperfusion jejunal contents, indicating that the majority (79-100%) of the beta-glucosidase capacity derives from the enterocytes in situ. Simultaneously, we determined short-term changes in gene expression in exfoliated enterocytes, which showed 2.0 +/- 0.4-fold induction of glutathione transferase A1 (GSTA1) mRNA (p < 0.002) and 2.4 +/- 1.2-fold induction of UDP-glucuronosyl transferase 1A1 (UGT1A1) mRNA (p < 0.02). The changes in gene expression were also seen in differentiated Caco-2 cells, where sulforaphane was responsible for induction of GSTA1 and quercetin for induction of UGT1A1. These results show that food components have the potential to modify drug metabolism in the human enterocyte in vivo very rapidly.  相似文献   
210.
Risk factors for postoperative complications of benign goiter surgery have not been investigated systematically. To this end, a prospective multicenter study (January 1 through December 31, 1998) was conducted involving 7266 patients with surgery for benign goiter from 45 East German hospitals. High-volume providers (>150 operations per year) performed 69% (5042/7266), intermediate-volume providers 27% (50–150), and low-volume providers 4% (258/7266) of operations. Among the hospital groups, the pattern of thyroid disease did not vary significantly, but there was a trend that small-volume providers tended to perform more operations for uninodular goiter and high-volume providers treated more patients with Graves' disease and recurrent goiter. Extent of resection (p < 0.0001) and remnant size (multinodular goiter and recurrent goiter, p < 0.001), differed significantly, with total thyroidectomy being performed more often in hospitals with more than 150 operations compared to hospitals with an operative volume of less than 150 procedures per year. Despite the larger extent of resection and smaller remnant size, rates of recurrent laryngeal nerve (RLN) palsy or hypoparathyroidism were not increased. When the logistic regression analyses were fitted to evaluate the impact of risk factors on transient and permanent RLN palsy and hypoparathyroidism, larger extent of resection [relative risk (RR) 1.5–2.1] and recurrent goiter (RR 1.8–3.4) consistently evolved as independent risk factors. With hypoparathyroidism, additional significant factors included patient gender (RR 2.1–2.4), hospital operative volume (RR 0.8–1.5), and Graves' disease (RR 2.8). Unlike parathyroid gland identification during hypoparathyroidism, RLN identification (RR 1.6) significantly (p= 0.01) reduced permanent RLN palsy rates. The multivariate analyses clearly confirmed the pivotal role of routine RLN identification, independent of the extent of the thyroid resection. These findings might help hospitals with lower operative volumes to identify patients at increased risk whom they might consider for specialist care.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号