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   12152篇
  免费   699篇
  国内免费   446篇
耳鼻咽喉   24篇
儿科学   256篇
妇产科学   79篇
基础医学   1590篇
口腔科学   127篇
临床医学   1140篇
内科学   2377篇
皮肤病学   128篇
神经病学   762篇
特种医学   193篇
外科学   592篇
综合类   1861篇
预防医学   655篇
眼科学   75篇
药学   2537篇
  6篇
中国医学   620篇
肿瘤学   275篇
  2024年   15篇
  2023年   81篇
  2022年   231篇
  2021年   338篇
  2020年   349篇
  2019年   240篇
  2018年   305篇
  2017年   279篇
  2016年   350篇
  2015年   280篇
  2014年   584篇
  2013年   874篇
  2012年   602篇
  2011年   705篇
  2010年   559篇
  2009年   499篇
  2008年   562篇
  2007年   567篇
  2006年   530篇
  2005年   493篇
  2004年   475篇
  2003年   428篇
  2002年   383篇
  2001年   324篇
  2000年   324篇
  1999年   279篇
  1998年   230篇
  1997年   238篇
  1996年   223篇
  1995年   193篇
  1994年   180篇
  1993年   152篇
  1992年   157篇
  1991年   129篇
  1990年   126篇
  1989年   113篇
  1988年   108篇
  1987年   89篇
  1986年   83篇
  1985年   109篇
  1984年   118篇
  1983年   69篇
  1982年   71篇
  1981年   54篇
  1980年   53篇
  1979年   27篇
  1978年   31篇
  1977年   26篇
  1976年   17篇
  1974年   15篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
DNA polymorphisms among independent isolates of herpes simplex virus (HSV) type 1 were studied from a 7-year-old male patient with recurrent infections of the skin and internal organs. In the patient's serum, HSV antibodies could not be detected by complement fixation, enzyme-linked immunosorbent assay (ELISA), or neutralization tests. ELISA tests for the presence of antibodies to human immunodeficiency virus were also negative. One HSV isolate was obtained from mesenteric nodes biopsied in 1983; one from skin in 1984; and three (postmortem) from brain, lungs, and liver in 1985. Restriction enzymes Eco RI, Bgl II, Hind III, Kpn I, and Bam H1 digestion patterns of the five isolates were similar. However, Sal I digests of isolates from skin, mesenteric nodes, lungs, and liver showed variations that were distinct from that of the brain isolate. Although Sal I digests of skin, mesenteric nodes, lungs, and liver isolates share a common variation in lacking F and G, the liver isolate can be further differentiated because of the gain of a restriction site on the H fragment. Thus, the three distinct variants observed were the isolates from brain (variant 1); from skin, mesenteric nodes, and lungs (variant 2); and from liver (variant 3). The fragments involved in variations among these isolates (presence or absence of Sal, G and H) are from the unique short and long regions (invariable regions) of the genome and therefore do not show heterogeneity in size. The extent of variation among these isolates is less than that seen among epidemiologically unrelated strains, suggesting that they originated from a single infecting strain, probably the brain isolate.  相似文献   
62.
人大脑内部微血管构筑——组织化学显示法研究   总被引:2,自引:0,他引:2  
本文应用碱性磷酸酶组织化学对血管内皮的染色方法,光镜观察了3例人大脑内部的微血管构型。结果,皮质短动脉进入皮质内的分枝去向有:1.皮质返枝;2.水平枝;3.下降支。皮质长动脉末端的分枝类型分为:1.血管栅栏样分枝型;2.烛台样或小锚样分枝型;3.树根样分枝型。看到了从微动脉、毛细血管到微静脉的连续性通路。论述了皮质动脉与静脉之间在形态学方面的差别及皮质内血管吻合的几种形式,为更好地理解大脑皮质内微循环类型提供了形态学依据。  相似文献   
63.
A new method has been developed to raise monoclonal anti-idiotypic antibodies. Monoclonal anti-idiotypic antibodies were obtained by fusion of NS-1 myeloma cells with splenocytes of mice immunised by intravenous injections of fixed hybridoma cells bearing a monoclonal antibody specific for beta-adrenergic ligands. New screening tests were developed to analyse the resulting hybridoma supernatants for different anti-idiotypic properties. Among 23 hybridoma supernatants recognising the idiotype, 6 were found to inhibit hapten binding and 3 of these recognised beta-adrenergic receptors.  相似文献   
64.
Anderson-Fabry disease (AFD) is an X-linked disorder caused by deficient activity of the lysosomal enzyme alpha-galactosidase A. The availability of enzyme replacement therapy (ERT) for this debilitating condition has led to the need for a convenient and sensitive instrument to monitor clinical effects in an individual patient. This study aimed to develop a scoring system--the Mainz Severity Score Index (MSSI)--to measure the severity of AFD and to monitor the clinical course of the disease in response to ERT. Thirty-nine patients (24 males and 15 females) with AFD were assessed using the MSSI immediately before and 1 year after commencing agalsidase alfa ERT. Control data were obtained from 23 patients in whom AFD was excluded. The MSSI of patients with AFD was significantly higher than that of patients with other severe debilitating diseases. The MSSI indicated that, although more men than women had symptoms classified as severe, overall, the median total severity scores were not significantly different between male and female patients. One year of ERT with agalsidase alfa led, in all patients, to a significant (p < 0.001) reduction in MSSI score (by a median of nine points). This study has shown that the MSSI score may be a useful, specific measure for objectively assessing the severity of AFD and for monitoring ERT-related treatment effects.  相似文献   
65.
The aim of the present study was to analyse quantitatively, on a cat gastrocnemius muscle preparation in vivo, the effects of local angiotensin-converting enzyme (ACE) inhibition by enalaprilat on total regional vascular resistance (tone) and its distribution to the large-bore arterial resistance vessels (>25 μm), the small arterioles (<25 μm) and the veins. Associated effects on capillary pressure and fluid exchange were also studied. Close-arterial infusion of enalaprilat (0.05–0.20 mg kg muscle tissue min-1) elicited a moderate dilator response in all three consecutive sections of the muscle vascular bed, an increase in capillary pressure and transcapillary fluid filtration. This dilation could be abolished by the selective bradykinin B2-receptor antagonist Hoe 140 (2 mg kg-1 min-1, i.a.), indicating that the dilator mechanism of ACE inhibition was an increased local concentration of bradykinin, and hardly at all a decreased concentration of angiotensin (AT) II. The generalized dilator response to ACE inhibition along the vascular bed suggested a relatively uniform distribution of ACE from artery to vein and this was further supported by the finding that a close-arterial infusion of AT I (0.04–0.32 μg kg-1 min-1), which was vasoactive only after conversion to AT II by local ACE, elicited a generalized constrictor response in all three vascular sections. In contrast, infused AT II (0.01–0.16 μg kg-1 min-1) constricted almost selectively the large-bore arterial vessels. The specific angiotensin AT1-receptor antagonist losartan (2 mg kg-1 min-1, i.a.) abolished the constrictor response to AT II but did not affect vascular tone under control conditions, indicating that AT II is not involved in the initiation of basal vascular tone in muscle. These results, taken together, indicate that under basal conditions vascular ACE contributes to the local control of vascular tone in skeletal muscle by degrading the endogenous dilator bradykinin, and not by converting AT I into vasoconstrictor AT II.  相似文献   
66.
67.
Anandamide (N-arachidonoylethanolamine, AEA) is a major endocannabinoid, known to impair mouse pregnancy and embryo development and to induce apoptosis in blastocysts. Here we show that mouse blastocysts rapidly (within 30 min of culture) release a soluble compound, that increases by approximately 2.5-fold the activity of AEA hydrolase (fatty acid amide hydrolase, FAAH) present in the mouse uterus, without affecting FAAH gene expression at the translational level. This "FAAH activator" was produced by both trophoblast and inner cell mass cells, and its initial biochemical characterization showed that it was fully neutralized by adding lipase to the blastocyst-conditioned medium (BCM), and was potentiated by adding trypsin to BCM. Other proteases, phospholipases A(2), C or D, DNAse I or RNAse A were ineffective. BCM did not affect the AEA-synthesizing phospholipase D, the AEA-binding cannabinoid receptors, or the selective AEA membrane transporter in mouse uterus. The FAAH activator was absent in uterine fluid from pregnant mice and could not be identified with any factor known to be released by blastocysts. In fact, platelet-activating factor inhibited non-competitively FAAH in mouse uterus extracts, but not in intact uterine horns, whereas leukotriene B(4) or prostaglandins E(2) and F(2)alpha had no effect. Overall, it can be suggested that blastocysts may protect themselves against the noxious effects of uterine endocannabinoids by locally releasing a lipid able to cross the cell membranes and to activate FAAH. The precise molecular identity of this activator, the first ever reported for FAAH, remains to be elucidated.  相似文献   
68.
The monoclonal antibody technology has provided a means to produce a supply of highly specific uniform antibody which is useful in the detection of plant viruses and which facilitates disease resistance screening. Because of the specificity of a monoclonal antibody to an epitope, a monoclonal antibody may not react to a partially degraded protein. Wheat streak mosaic virus (WSMV) is a member of the potyvirus group and is transmitted by the wheat curl mite Eriophyes tulipae Keifer. The capsid protein of WSMV, like many potyviruses, is degraded in planta. Monoclonal antibodies produced to WSMV reacted to native as well as trypsin treated virions. The antibodies were also useful for evaluation of hard red winter wheat cultivars inoculated with WSMV in the fall or in the spring under field conditions.  相似文献   
69.
The reaction of nitric oxide (NO) and superoxide results in the formation of peroxynitrite, a potent and relatively long-lived oxidant. In infectious diseases, these molecules are not only bactericidal but also toxic to host cells. Chorioamnionitis is often complicated by premature rupture of membranes and can be associated with placental abruption. These diseases are significant causes of premature low-birth-weight deliveries and consequently the morbidity and mortality of neonates. Lipopolysaccharide, bacterial endotoxin, is known to be elevated in the amniotic fluid of patients with chorioamnionitis. Lipopolysaccharide is known to induce the formation of NO and superoxide. We report here that nitrite/nitrate, stable metabolites of NO, were increased in serum from patients with chorioamnionitis. Immunohistochemical studies demonstrated enhanced expression of inducible NO synthase and formation of nitrotyrosine, a footprint of peroxynitrite, in the placentae from patients with chorioamnionitis and also in patients with placental abruption. Furthermore, apoptotic cell death was also increased in the placentae from patients with both diseases. These results suggest that chorioamnionitis and a portion of placental abruption may share a common cascade of placental injury. Nitric oxide and its metabolities may play an important role in this cascade.  相似文献   
70.
Mutations in APP are associated with familial early-onset Alzheimer disease (FAD). Examination of the genomic sequence in one patient with FAD revealed a change located in the axon 17 of the APP gene at position 275329G>A (GenBank accession number: D87675; GI: 2429080); cDNA sequence 2137G>A (GenBank accession number: X06989; GI: 28720). This corresponds to the mutation A713T in APP. AD stage VI of neurofibrillary degeneration and stage C of Aβ-amyloid burden was found at the post-mortem neuropathological examination. Previous studies have suggested that the mutation A713T in APP is a silent mutation or polymorphism. However, we have not found this change in APP in a control population analyzed by the amplification-refractory mutation system (ARMS). It is concluded that A713T in APP is implicated in the pathogenesis of AD. Since the immunohistochemical study indicates that A713T mutation is not likely to relate with Aβ-amyloid processing, the causative role of this rare mutation remains to be warranted.  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