全文获取类型
收费全文 | 9965篇 |
免费 | 851篇 |
国内免费 | 12篇 |
专业分类
耳鼻咽喉 | 204篇 |
儿科学 | 558篇 |
妇产科学 | 329篇 |
基础医学 | 1038篇 |
口腔科学 | 658篇 |
临床医学 | 885篇 |
内科学 | 1876篇 |
皮肤病学 | 269篇 |
神经病学 | 774篇 |
特种医学 | 446篇 |
外国民族医学 | 2篇 |
外科学 | 2098篇 |
综合类 | 43篇 |
一般理论 | 3篇 |
预防医学 | 475篇 |
眼科学 | 237篇 |
药学 | 551篇 |
中国医学 | 13篇 |
肿瘤学 | 369篇 |
出版年
2023年 | 153篇 |
2022年 | 116篇 |
2021年 | 277篇 |
2020年 | 226篇 |
2019年 | 273篇 |
2018年 | 476篇 |
2017年 | 374篇 |
2016年 | 470篇 |
2015年 | 497篇 |
2014年 | 554篇 |
2013年 | 928篇 |
2012年 | 508篇 |
2011年 | 520篇 |
2010年 | 523篇 |
2009年 | 324篇 |
2008年 | 270篇 |
2007年 | 190篇 |
2006年 | 349篇 |
2005年 | 297篇 |
2004年 | 190篇 |
2003年 | 182篇 |
2002年 | 214篇 |
2001年 | 279篇 |
2000年 | 251篇 |
1999年 | 253篇 |
1998年 | 190篇 |
1997年 | 126篇 |
1996年 | 154篇 |
1995年 | 100篇 |
1994年 | 123篇 |
1993年 | 93篇 |
1992年 | 102篇 |
1991年 | 104篇 |
1990年 | 80篇 |
1989年 | 63篇 |
1988年 | 69篇 |
1987年 | 69篇 |
1986年 | 63篇 |
1985年 | 48篇 |
1984年 | 50篇 |
1983年 | 41篇 |
1982年 | 41篇 |
1981年 | 42篇 |
1980年 | 36篇 |
1979年 | 44篇 |
1978年 | 28篇 |
1977年 | 35篇 |
1975年 | 23篇 |
1973年 | 33篇 |
1967年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Sven-Erik Larsson Hongming Cai P. Åke Öberg 《European journal of applied physiology》1993,66(6):483-488
Summary Microcirculation in the upper portion of the trapezius muscle was measured percutaneously by continuous laser-Doppler flowmetry (LDF) during two 10-min series of alternating 1-min periods of static contraction and rest determined electromyographically (EMG). Stepwise increased contraction was induced by keeping the arms straight and elevated at 30, 60, 90 and 135°, which was repeated with a 1-kg load carried in each hand. Thereafter, fatigue and recovery were recorded while the subject kept her arms straight and elevated at 45° carrying the 1-kg hand load as long as possible, followed by rest with arms hanging and no load. A group of 16 healthy women of different ages was studied. Signal processing was done on line using a 386 SX computer. The LDF- and root-mean-square (rms) EMG signals were normalized. Spectrum analyses of EMG mean power frequency (MPF) and median spectrum frequency were performed. The rms-EMG increased significantly with an increase in the calculated shoulder torque (r=0.75). Accumulated local fatigue was indicated by a decrease in MPF with increased shoulder angle and added load (r = –0.54). Blood flow increased with increased shoulder angle (r=0.82, with hand loadr=0.62) and with increased shoulder torque (r=0.72), and also showed a significant increase with increased EMG activity (r=0.74). The LDF showed a negative correlation to MPF (r= –0.67), with increased values when MPF was lowered. During the endurance test, a moderate increase of LDF occurred which reached its maximum during the 1st min of recovery. Then, a slow return to the base level was recorded. The ability to increase the flow in the microcirculation with increasing muscle load was not diminished with age. 相似文献
52.
Gert Baumann Stephan B. Felix Claus D. Heidecke Gotthard Rieß Ursula Loher Liesel Ludwig Prof. Dr Hans Blömer 《Inflammation research》1984,15(3-4):216-228
Left ventricular infarction (AMI) was produced in experimental animals and the contractile response to -adrenergic and H2-histaminergic stimulation by isoproterenol and impromidine tested in the isolated perfused heart preparation. Adenylate cyclase activity as well as binding characteristics of [3H]-dihydroalprenolol ([3H]-DHA), [3H]-methyl-tiotidine ([3H]-TIOT) and [3H]-quinuclidinyl benzilate ([3H]-QNB) to cardiac
1-, H2- and cholinergic muscarinic receptors were determined in sarcolemmal membrane preparations of the right ventricle of the same hearts. In addition, an attempt was made to elucidate the therapeutic value of post-AMI treatment with impromidine in the presence and absence of-sympathomimetic, in contrast to administration of prenalterol and the conventional therapy with -sympathomimetic drugs, e.g. dobutamine. Three days post-AMI the dose-response curve for isoproterenol of right ventriculardP/dt
max was significantly depressed, while the inotropic effect of impromidine was not impaired. Stimulation of adenylate cyclase activity by isoproterenol was reduced by 80% whereas impromidine and NaF stimulation rates were unaltered. Receptor-binding studies indicated a 90% loss and 10-times lowered affinity (K
D) of the remaining -receptors while specific [3H]-TIOT- and [3H]-QNB-binding was unchanged.Administration of dobutamine increased mortality rates and extension of infarct size, led to a further decrease in contractile response to isoproterenol, induced complete insensitivity of adenylate cyclase to isoproterenol stimulation and caused pronounced additional reduction of number and affinity of [3H]-DHA-binding sites. In contrast, all above alterations were prevented by treatment with either prenalterol or combined administration of impromidine plus metoprolol. It is concluded, that these alterations in the non-ischemic, uninvolved myocardium post-AMI are the result of catecholamine-induced specific damage of sarcolemmal -receptors. Furthermore, treatment with H2-agonists in combination with -blocking agents may have beneficial effects, whereas conventional therapy with -sympathomimetic drugs tends to worsen the already depressed function of the -adrenergic stimulation mechanism.Supported by grants Ba 666/1 and Ba 666/2-2 from the Deutsche Forschungsgemeinschaft (DFG).Data presented in this paper are part of a doctoral thesis by Dr S.B. Felix. 相似文献
53.
Ulf Träff Anna Levén Rickard Östergren Daniel Schöld 《Developmental neuropsychology》2020,45(3):139-153
ABSTRACT This study examined if children (Mage = 14.60) with Mild Intellectual Disabilities (MID) display weaknesses in number processing and verbal working memory. An age-matched and mental age-matched (MA, Mage = 6.17) design extended by a group of 9–10-year-olds, and a group of 11–12-year-olds were used. The MID children’s working memory was equal to the MA group but poorer than the other groups. On number tasks, the MID group was faster than the MA group but slower than the other groups. All groups obtained equal Weber fraction scores and distance effects on the number comparison tasks. The MID group performed subitizing and counting faster than the MA group, but slower than the 11–12-year-olds. The results demonstrate that number processing and working memory in children with MID is characterized by a developmental delay, not a deficit. Their main problem is to access the quantitative meaning of Arabic numerals. The development of different types of cognitive abilities is differently affected by educational experience and intellectual ability. The innate number system appears to be unaffected by intellectual capacity or educational experience, while the innate working memory ability is affected by intellectual capacity but not by educational experience. Culturally acquired symbolic number abilities are strongly affected by educational experience. 相似文献
54.
Özcan Özdamar Rafael E. Delgado Syed Rahman Carlos Lopez 《Annals of biomedical engineering》1998,26(5):883-891
An innovative acoustic noise canceling method using adaptive Wiener filtering (AWF) was developed for improved acquisition of distortion product otoacoustic emissions (DPOAEs). The system used one microphone placed in the test ear for the primary signal. Noise reference signals were obtained from three different sources: (a) pre-stimulus response from the test ear microphone, (b) post-stimulus response from a microphone placed near the head of the subject and (c) post-stimulus response obtained from a microphone placed in the subjects nontest ear. In order to improve spectral estimation, block averaging of a different number of single sweep responses was used. DPOAE data were obtained from 11 ears of healthy newborns in a well-baby nursery of a hospital under typical noise conditions. Simultaneously obtained recordings from all three microphones were digitized, stored and processed off-line to evaluate the effects of AWF with respect to DPOAE detection and signal-to-noise ratio (SNR) improvement. Results show that compared to standard DPOAE processing, AWF improved signal detection and improved SNR. © 1998 Biomedical Engineering Society.
PAC98: 4364Jb, 4360-c, 8790+y 相似文献
55.
Günther Vogel Heinz Krause Elisabeth Krämer 《Pflügers Archiv : European journal of physiology》1955,261(5):486-494
Ohne ZusammenfassungBenutzte Symbole und Abkürzungen NNR
Nebennierenrinde
- DOCA
Desoxycorticosteronacetat
-
K
i
intracelluläres Kalium (sinngemäß für Natrium)
-
K
a
extracelluläres Kalium (sinngemäß für Natrium)
-
Q
Ladung
-
E
m
Membranruhepotential
-
m
Zeitkonstante der Membran
-
R
m
Membranwiderstand
-
C
m
Membrankapazität 相似文献
56.
Volker Schmidt Susanne Schneider Julian Schlömer Maria-Elisabeth Krautwald-Junghanns Elvira Richter 《Avian pathology》2008,37(6):589-592
The present report describes a case of Mycobacterium tuberculosis infection in an African Grey parrot (Psittacus erithacus erithacus) kept as a pet bird. Diagnosis was confirmed by microbiologic and pathologic results, and indicated a human–avian transmission. Clinical signs included sublingual nodules resulting in anorexia and signs of osteolysis in the long bones. Proliferation consisted of several nodules with small greenish-caseous foci in cross-section and revealed a severe granulomatous inflammation without intralesional acid-fast rods. M. tuberculosis was cultured from a pooled sample of sublingual and liver nodules, and was confirmed via polymerase chain reaction. Transmission between men and parrot was proved by spoligotyping pattern analysis. The absence of facial skin lesions and acid-fast rods within the tubercles is contrary to previous publications of tuberculosis in birds. This disease in a common pet bird species is of zoonotic importance, and those parrots with close contact to owners suffering from tuberculosis may serve as a potential reservoir for human infection. 相似文献
57.
A. G. Fahrenkamp C. Wibbeke W. Böcker K. W. Schmid G. Winde D. Öfner R. Fischer-Colbrie 《Virchows Archiv : an international journal of pathology》1995,426(4):361-367
The aim of the present study was to investigate immunohistochemically the distribution of chromogranin A, chromogranin B, and secretogranin II in a series of 152 neuroendocrine tumours of the gastrointestinal tract. Tumour tissues from 25 argyrophil gastric carcinoids, 18 gastrin and 5 somatostatin-producing tumours, 4 gangliocytic paragangliomas, 49 classical argentaffin and 2 L cell appendiceal carcinoids, 27 classical ileal carcinoids, 17 rectal carcinoids, and 5 poorly differentiated neuroendocrine tumours of the stomach and rectum were immunostained with antibodies against chromogranin A, chromogranin B, and secretogranin II. Chromogranin A was the major granin expressed in gastric carcinoids and in serotonin-producing carcinoids of the appendix and the ileum. In contrast, strong chromogranin B and secretogranin II immunoreactivity was found in rectal carcinoids, in which chromogranin A was rarely expressed. Since chromogranin A is a widely used marker for neuroendocrine differentiation, it is of diagnostic importance that some gastrin-producing tumours, gangliocytic paragangliomas, poorly differentiated neuroendocrine carcinomas, and appendiceal L cell carcinoids completely lacked chromogranin A positivity. It is concluded that the various neuroendocrine tumours of the gastrointestinal tract show distinctly different patterns of granin expression, probably reflecting their histogenetical origin. 相似文献
58.
The concept of the accumulated O2 deficit (AOD) assumes that the O2 deficit increases monotonically with increasing work rate (WR), to plateau at the maximum AOD, and is based on linear extrapolation of the relationship between measured steady-state oxygen uptake (O2) and WR for moderate exercise. However, for high WRs, the measured O2 increases above that expected from such linear extrapolation, reflecting the superimposition of a "slow component" on the fundamental O2 mono-exponential kinetics. We were therefore interested in determining the effect of the O2 slow component on the computed AOD. Ten subjects [31 (12) years] performed square-wave cycle ergometry of moderate (40%, 60%, 80% and 90%
), heavy (40%), very heavy (80%) and severe (110% O2 peak) intensities for 10–15 min, where
is the estimated lactate threshold and is the WR difference between
and O2 peak. O2 was determined breath-by-breath. Projected "steady-state" O2 values were determined from sub-
tests. The measured O2 exceeded the projected value after ~3 min for both heavy and very heavy intensity exercise. This led to the AOD actually becoming negative. Thus, for heavy exercise, while the AOD was positive [0.63 (0.41) l] at 5 min, it was negative by 10 min [–0.61 (1.05) l], and more so by 15 min [–1.70 (1.64) l]. For the very heavy WRs, the AOD was [0.42 (0.67) l] by 5 min and reached –2.68 (2.09) l at exhaustion. For severe exercise, however, the AOD at exhaustion was positive in each case: +1.69 (0.39) l. We therefore conclude that the assumptions underlying the computation of the AOD are invalid for heavy and very heavy cycle ergometry (at least). Physiological inferences, such as the "anaerobic work capacity", are therefore prone to misinterpretation. 相似文献
59.
M. Vegfors L. -G. Lindberg P. Å. Öberg C. Lennmarken 《Medical & biological engineering & computing》1993,31(2):135-141
In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with
circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate
the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system
was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise
damage to red blood cells. The pulse oximeter readings (SpO2) were compared with oxygen saturation analyses by a haemoximeter (SaO2). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO2 range 60–100 per cent. At a haematocrit level of 41–44 per cent, there was no correlation between SaO2 and SpO2 readings. After diluting the blood with normal saline to a haematocrit of 10–11 per cent, a good correlation between SaO2 and SpO2 was found. Following haemolysis, the agreement between SaO2 and SpO2 was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may
be dependent on the haematocrit level. 相似文献
60.
O M Ariyürek F Balkanci Ü Aydingöz M Önerci 《Surgical and radiologic anatomy : SRA》1996,18(2):137-139
Summary Anatomic variations are important in preendoscopic CT evaluation of the paranasal sinuses. In this study, we investigated whether the superior turbinate could become pneumatised like the middle turbinate, pneumatisation of which is well-known. Images of 52 patients who underwent CT examination prior to endoscopic sinus surgery and who had normally aerated posterior ethmoidal cells and an unobscured nasal cavity were retrospectively evaluated. The patients were 12–68 years old (median age, 35 years); 28 were women and 24 were men. Pneumatisation of the superior turbinates was graded in two groups as minimal or marked. Pneumatisation was evident in 25 patients (48%). 13 unilateral (25%), 8 bilateral (15%) pneumatisations were detected in the group graded as minimal, whereas 1 unilateral and 3 bilateral pneumatisations were present in the markedly (8%) pneumatised group of patients. Superior turbinates were seemingly aerated through the posterior ethmoid cells. The superior turbinates can be pneumatised as the middle turbinate is a not frequent anatomic variation that should be taken into account in preendoscopic CT evaluation of the paranasal sinuses.
La pneumatisation du cornet nasal supérieur : une variation anatomique courante ?
Résumé Les variations anatomiques sont importantes à connaitre dans le cadre du bilan tomodensitométrique précédant une chirurgie endoscopique des sinus paranasaux. Dans cette étude, nous avons recherché si le cornet nasal supérieur pouvait être pneumatisé comme l'est le cornet nasal moyen, entité anatomique bien connue. Les images de 52 patients ayant eu une tomodensitométrie avant chirurgie endoscopique et montrant des cellules ethmoïdales postérieures normalement pneumatisées et une cavité nasale nonopaque, ont été évaluées rétrospectivement. Les patients, 28 femmes et 24 hommes, étaient âgés de 12 à 68 ans (moyenne : 35 ans). La pneumatisation du cornet nasal supérieur a été classée en deux groupes; minime et prononçée. Cette pneumatisation était patente chez 25 patients (48 %). Treize pneumatisations unilatérales (25 %) et 8 pneumatisations bilatérales (15 %) furent retrouvées dans le groupe présentant une pneumatisation minime alors que 1 pneumatisation unilatérale et 3 bilatérales (8 %) étaient présentes dans le groupe dont la pneumatisation était plus marquée. Les cornets nasaux supérieurs semblaient être aérés par les cellules ethmoïdales postérieures. Les cornets nasaux supérieurs peuvent être pneumatisés, comme le sont les cornets nasaux moyens, avec une fréquence non-exceptionnelle. Cette variation anatomique mérite d'être prise en considération dans le bilan tomodensitométrique précédant toute chirurgie endoscopique des sinus paranasaux.相似文献