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   194102篇
  免费   18699篇
  国内免费   7429篇
耳鼻咽喉   1198篇
儿科学   4545篇
妇产科学   2692篇
基础医学   37267篇
口腔科学   3767篇
临床医学   12141篇
内科学   32836篇
皮肤病学   3272篇
神经病学   16038篇
特种医学   3707篇
外国民族医学   58篇
外科学   14133篇
综合类   23953篇
现状与发展   31篇
预防医学   8485篇
眼科学   2268篇
药学   25989篇
  20篇
中国医学   6756篇
肿瘤学   21074篇
  2024年   312篇
  2023年   2898篇
  2022年   3762篇
  2021年   7896篇
  2020年   6766篇
  2019年   7785篇
  2018年   7374篇
  2017年   7297篇
  2016年   7152篇
  2015年   8572篇
  2014年   11974篇
  2013年   13441篇
  2012年   12294篇
  2011年   14573篇
  2010年   12376篇
  2009年   11736篇
  2008年   11131篇
  2007年   9911篇
  2006年   8961篇
  2005年   7645篇
  2004年   6679篇
  2003年   5665篇
  2002年   4381篇
  2001年   3743篇
  2000年   3091篇
  1999年   2805篇
  1998年   2409篇
  1997年   2177篇
  1996年   1576篇
  1995年   1582篇
  1994年   1383篇
  1993年   1165篇
  1992年   967篇
  1991年   868篇
  1990年   717篇
  1989年   600篇
  1988年   514篇
  1987年   416篇
  1986年   424篇
  1985年   797篇
  1984年   822篇
  1983年   576篇
  1982年   644篇
  1981年   509篇
  1980年   418篇
  1979年   366篇
  1978年   281篇
  1977年   222篇
  1976年   206篇
  1975年   142篇
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
991.
本文研究了小儿糜烂性口腔炎的病毒病因,用人胚肾细胞及Hep—2细胞分离病毒,26例患儿有21例阳性(80.7%),从中取五株病毒进行鉴定,细胞病变特点属疱疹病毒,且均可被抗HSV—I抗体中和,结果表明HSV—I是本病的主要病原。体外实验证明,白细胞干扰素对新分离的HSV—I有较强的抑制病变作用,2.4~2.9Iu/ml白细胞干扰素即可抑制病毒的50%CPE。临床上试用干扰素局部治疗必获得显著的疗效。  相似文献   
992.
晶体结构分析显示环戊二烯-甲萘醌加合物的C4-C14键被它的角甲基空间效应所弱化,热分析(TG-DSC)研究显示在130℃该加合物的逆Diels-Alder反应趋势得到加强。根据这些结果,推论并证实了环戊二烯-维生素K1加合物具有更强的逆Diels-Alder反应趋势。  相似文献   
993.
Conventional MRI (cMRI) has shown that brain abnormalities without clinical stroke can manifest in patients with sickle cell disease (SCD). We used quantitative MRI (qMRI) and psychometric testing to determine whether brain abnormalities can also be present in patients with SCD who appear normal on cMRI. Patients 4 years of age and older with no clinical evidence of stroke were stratified by cMRI as normal (n = 17) or abnormal (n = 13). Spin-lattice relaxation time (T1) of gray and white matter structures was measured by the precise and accurate inversion recovery (PAIR) qMRI method. Patient cognitive ability was assessed with a standard psychometric instrument (WISC-III or WISC-R). In all 30 patients with SCD, qMRI T1 was lower than in 24 age- and race-matched controls, in cortical gray matter (P < .0006) and caudate (P < .0009), as well as in the ratio of gray-to-white matter T1 (P < .008). In the 17 patients who were shown to be normal by cMRI, qMRI T1 was still lower than in controls, in both cortical gray matter (P < .02) and caudate (P < .004). Histograms of voxel T1 show that the proportion of voxels with T1 values intermediate between gray and white matter (ie, consistent with encephalomalacia) was 9% higher than controls in patients shown to be normal by cMRI (P < .05) and 15% higher than controls in patients shown to be abnormal by cMRI (P < .0005). The full scale intelligence quotient (FSIQ) of all patients with SCD was 75, compared to the FSIQ of 88 in a historical control group of patient siblings (P < .001). The FSIQ of patients shown to be normal by cMRI was 79, significantly lower than the FSIQ of patient siblings (P < .04). The FSIQ of 71 in patients shown to be abnormal by cMRI was significantly lower than both the patient siblings (P < .005) and the patients shown to be normal by cMRI (P < .04). Patients shown to be abnormal by cMRI scored lower than patients shown to be normal by cMRI, specifically on the subtests of vocabulary (P = .003) and information (P = .03). Cognitive impairment is thus significant, even in patients with SCD who were shown to be normal by cMRI, suggesting that cMRI may be insensitive to subtle neurologic damage that can be detected by qMRI. Because cognitive impairment can occur in children normal by cMRI, our findings imply that prophylactic therapy may be needed earlier in the course of SCD to mitigate neurologic damage.  相似文献   
994.
The aim was to study firstly, the motor effects of a new 5-HT1A antagonist, NDL-249 [(R)-3-(N-cyclopentyl-N-propylamino)-8-fluoro-3,4-dihydro-2H-1-benzopyran-5-carboxamide hydrochloride] and of the reference 5-HT1A antagonist WAY-100 635 [N-(2-(1-(4-(2-methoxyphenyl)piperazinyl))ethyl)-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride], in comparison to the 5-HT1A agonist (±)-8-OH-DPAT [(8-hydroxy-2-(di-N-propylamino) tetralin, hereafter 8-OH-DPAT], in rats acclimatised to the automated activity cages; secondly, to study whether the behavioural effects of NDL-249 and 8-OH-DPAT are sensitive to the 5-HT depleting effects of p-chlorophenylalanine (PCPA); thirdly, to characterise the nature of the antagonist-induced activation seen in the automatic activity cages with the aid of a behavioural observation analysis; fourthly, to examine the interaction between the 5-HT1Areceptors mediating the behavioural effects and dopamine (DA) receptors. NDL-249 was found to bind in vitro to rat hippocampal 5-HT1A receptors with high affinity and selectivity. In second messenger studies, it was devoid of agonist-like effects. In the locomotor activity studies, each antagonist significantly increased the incidence of horizontal activity, peripheral activity and rearing. 8-OH-DPAT, while significantly increasing peripheral and horizontal activities, decreased the incidence of rearing. PCPA blocked the motor effects of NDL-249 but did not affect those of 8-OH-DPAT. Observational analyses indicated that NDL-249 induced significant increases at one or more doses in sniffing, rearing and locomotion together with a significant reduction in stillness. WAY-100 635 significantly increased the incidence of rearing, intense grooming and vacuous chewing. The significant increases in sniffing, grooming and intense grooming and the significant decrease in stillness induced by the DA D1 agonist, SK&F 38393 [(±)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrochloride], were not altered by concomitant pre-treatment with NDL-249. Pre-treatment of rats with either the DA D1 antagonist SCH-23390 (2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol) or the DA D2 antagonist, raclopride, blocked the reduced stillness and increased sniffing and rearing induced by NDL-249. In conclusion, 5-HT1A antagonists including the new selective antagonist, NDL-249, induce mild behavioural activation in rats, which is mediated probably indirectly via DA systems. Received: 3 April 1997/Final version: 23 February 1998  相似文献   
995.
Summary— Acidosis affects multiple steps in the excitation-contraction coupling pathway of myocardium, producing decreased calcium sensitivity of myofibrils and modification of the function of the sarcoplasmic reticulum. Our aim was to evaluate the effectiveness of three different classes of inotropic agents under acidotic conditions: 1) forskolin, an adenylate cyclase activator that enhances cellular cyclic AMP concentrations, 2) elevated extracellular Ca2+ and 3) endothelin-1, an activator of the inositol triphosphate, diacylglycerol pathway. Ferret papillary muscles were mounted in organ baths containing normal physiological solution (pH = 7.4). After baseline tension was measured, the muscles were bathed in an acidotic solution (pH = 6.98) that decreased tension to 40% of the control; subsequently, the muscles were washed with normal physiological solution until they returned to baseline. Each inotropic agent was added to the bathing solution in a concentration sufficient to increase tension by 40% above the baseline. Then the solution was made acidotic (pH = 6.98) in the continuous presence of that concentration of inotropic agent and the resultant steady-state developed tension measured. The increases in tension induced by each inotropic agent at normal pH were adjusted to be similar; in contrast, the response to each drug in acidosis was significantly different. Under acidotic conditions, endothelin-1 was the most effective inotropic agent in restoring the depressed developed tension. This was possibly due to enhancement of the myofilament sensitivity to Ca2+, which was more effective than increasing [Ca2+]i through elevating extracellular Ca2+ or the addition of forskolin which increased [Ca2+]i but desensitized the myofilaments to Ca2+.  相似文献   
996.
Peripheral and central injections of recombinant human interleukin-1β (IL-1β) have been shown to decrease social exploration and to induce body weight loss in rats. To characterize the receptor mechanisms of these effects, we used as a tool a specific antagonist of the receptors of IL-1, IL-1ra. Intraperitoneal (i.p.) administration of IL-1ra (8 mg/kg) blocked the effect of i.p. injection of IL-1β (4 μg/rat) on social behaviour but not on body weight. Central administration of IL-1ra (60 μg/rat, i.c.v.) abrogated the effects of centrally administered IL-1β (30 ngn/rat, i.c.v.) on both social behaviour and body weight. Central injection of IL-1ra (4 μg/rat, i.c.v.) also attenuated the effects of i.p. administered IL-1β (4 μg/rat) on social behaviour but not on body weight. These results suggest that the effects of IL-1β on social behavior are mediated centrally and that its effect on the loss of body weight involves different receptor mechanisms.  相似文献   
997.
Summary The polymorphism of the D1S80 locus has been analyzed in a population sample of 203 unrelated individuals living in Madrid (central Spain) by PCR and subsequent semi-dry discontinuous polyacrylamide gel electrophoresis (Tris-chloride/Tris-glycine buffer system) followed by silver staining, The electrophoretic system described in this study offers high resolution in the separation of the different D1S80 alleles allowing the detection of microvariability around the allele T22 in the spanish population. Twenty different alleles containing 17–40 repeats of the basic 16bp unit were distinguished. The alleles T18 and T24 were found to be relatively common in Spain, as in other populations:, with frequencies of 0.224 and 0.372, respectively. No evidence of significant deviations from Hardy-Weinberg equilibrium was found in these preliminary population data.  相似文献   
998.
Summary We have studied the effect of serotonin on synaptic transmission in rat hippocampal subiculum slices. Electrical stimulation of the alveus induced a field potential in the subiculum. The non-NMDA glutamate receptor antagonist, NBQX (3 × 10–6 mol/l) suppressed the response by 78%, indicating that the signal involves glutamatergic neurons. Application of serotonin suppressed (EC50 = 3.6 × 10–6 mol/l) the amplitude of he evoked potentials in a reversible, concentration-dependent manner. The responses to 5-HT were not altered after pretreatment with the 5-HT uptake blocker, fluvoxamine (10–5 mol/l) or a combination of the MAO inhibitor pargyline (10–5 mol/l) and ascorbic acid (10–4 mol/l). The responses to 5-HT were also unaffected by pretreatment with the 5-HT1A selective antagonist NAN-190 (10–6 mol/l), the 5-HT2A antagonist ketanserin (10–6 mol/l) or the 5-HT3/5-HT4 antagonist ICS 205–930 (10–6 mol/l).The 5-HT1B selective agonist CP 93,129 mimicked the effects of serotonin, but was more potent (EC50 4.1 × 10–7 mol/l). The 5-HT1B receptor antagonist, (±)21-009 (3 × 10–7 mol/l), antagonized the response to 5-HT and CP 93,129 with a pKB value of 7.1 and 7.2, respectively. These results suggest that the effect of 5-HT in the rat subiculum is mediated by 5-HT1B receptors.Correspondence to: H.W.G.M. Boddeke at the above address  相似文献   
999.
Homeostasisof11ematopoiesisiscontrollednotoillybytheproliferationanddifferentiationofcells,butalsobycelldeath.Inadditiontolossofcontrolofcellproliferation,disruptionofapoptosis--inducedf[lnctionalsocontributestotumordevelopment.Althoughdiversesignalscaninduceapoptosisinawidevarietyofcelltypes,anumberofevolutionarilyconservedgenesregulateafinalcommoncelldeathpathway,thatisconservedinmanyspeciesfromwormstohumansll].Thehcf--2proto--oncogeneisoneofthecrucialapoptosisantagonizinggenes.Highlevelofhc…  相似文献   
1000.
The aim of the present study was to elucidate if the potentiating effect of neuropeptide Y on various vasoactive agents in vitro is (1) altered in mesenteric arteries from rats with congestive heart failure and (2) mediated by the neuropeptide Y Y1 receptor. The direct vascular effects of neuropeptide Y and its modulating effects on the contractions induced by endothelin-1-, noradrenaline-, 5-hydroxytryptamine (5-HT)-, U46619-(9, 11-dideoxy-11, 9-epoxymethano-prostaglandin F2) and ATP, and acetylcholine-induced dilatations were studied in the presence and absence of the neuropeptide Y Y1 antagonist, BIBP3226 (BIBP3226{(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]- -arginine-amide}). Neuropeptide Y, per se, had no vasoactive effect in the arteries. The potency of endothelin-1 was significantly decreased in congestive heart failure rats. Neuropeptide Y and neuropeptide Y-(13–36) potentiated the endothelin-1-induced contraction in congestive heart failure mesenteric arteries. In 20% of the congestive heart failure rats, sarafotoxin 6c induced a contraction of 31±4%. Neuropeptide Y also potentiated U46619- and noradrenaline-induced contractions but not 5-HT-induced contractions in congestive heart failure arteries. In sham-operated animals neuropeptide Y potentiated noradrenaline- and 5-HT-induced contractions. These potentiations were inhibited by BIBP3226. Acetylcholine induced an equipotent relaxation in both groups which was unaffected by neuropeptide Y. In conclusion, neuropeptide Y responses are altered in congestive heart failure rats. The potentiating effect differs between vasoactive substances. Neuropeptide Y Y1 and non-neuropeptide Y1 receptors are involved.  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