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   5695篇
  免费   320篇
  国内免费   43篇
耳鼻咽喉   31篇
儿科学   167篇
妇产科学   123篇
基础医学   856篇
口腔科学   35篇
临床医学   500篇
内科学   1438篇
皮肤病学   112篇
神经病学   715篇
特种医学   120篇
外科学   405篇
综合类   10篇
一般理论   1篇
预防医学   292篇
眼科学   48篇
药学   446篇
中国医学   13篇
肿瘤学   746篇
  2024年   1篇
  2023年   39篇
  2022年   104篇
  2021年   141篇
  2020年   86篇
  2019年   115篇
  2018年   133篇
  2017年   113篇
  2016年   140篇
  2015年   155篇
  2014年   197篇
  2013年   260篇
  2012年   412篇
  2011年   435篇
  2010年   256篇
  2009年   232篇
  2008年   399篇
  2007年   389篇
  2006年   390篇
  2005年   387篇
  2004年   393篇
  2003年   324篇
  2002年   290篇
  2001年   47篇
  2000年   36篇
  1999年   55篇
  1998年   77篇
  1997年   65篇
  1996年   51篇
  1995年   50篇
  1994年   42篇
  1993年   37篇
  1992年   25篇
  1991年   33篇
  1990年   25篇
  1989年   19篇
  1988年   15篇
  1987年   12篇
  1986年   8篇
  1985年   14篇
  1984年   17篇
  1983年   12篇
  1982年   9篇
  1981年   4篇
  1980年   10篇
  1979年   2篇
  1977年   1篇
  1966年   1篇
排序方式: 共有6058条查询结果,搜索用时 31 毫秒
11.
12.
The aim of this study was to evaluate: (1) the accumulation of leukocytes in the ileum and the lung during splanchnic artery occlusion (SAO) shock; (2) the role of platelet-activating factor (PAF) and tumor necrosis factor (TNF-) in this phenomenon. Untreated anesthetized rats subjected to total occlusion of the celiac, superior and inferior mesenteric arteries for 45 min, followed by reperfusion, uniformly died within 90 min after reperfusion. The mean survival time was 93±7 min. The neutrophilic infiltrate was quantitated in the ileum and in the lung using a myeloperoxidase (MPO) assay. MPO activity in the ileum and in the lung averaged 0.05±0.03 and 0.4±0.02 U×10–3/g protein in animals killed before occlusion. MPO activity did not change in rats killed immediately before reperfusion and was significantly elevated (0.11±0.02 and 1.7±0.6 U×10–3/g protein in the ileum and the lung, respectively) in those killed 80 min after the beginning of the reperfusion. The histological examination confirmed the accumulation of leukocytes in the mucosa of the ileum and the lung over the 80 min. SAO shocked rats exhibited leukopenia and increased serum levels of TNF-. In order to evaluate the role of PAF and TNF- in SAO shock, a powerful PAF receptor antagonist, TCV-309 (5 g/kg i.v.), was injected 5 min after reperfusion. TCV-309 increased survival time, lowered serum TNF-, reduced MPO activity in both the ileum and the lung and ameliorated leukopenia induced by SAO shock. In addition, the drug significantly reduced ileal necrosis and pulmonary morphological alterations induced by shock. These results suggest an important role for PAF in the adhesion of leukocytes in SAO shock.  相似文献   
13.
14.
The signaling pathways triggered by adherence of Candida albicans to the host cells or extracellular matrix are poorly understood. We provide here evidence in C. albicans yeasts of a p105 focal adhesion kinase (Fak)-like protein (that we termed CaFak), antigenically related to the vertebrate p125Fak, and its involvement in integrin-like-mediated fungus adhesion to vitronectin (VN) and EA.hy 926 human endothelial cell line. Biochemical analysis with different anti-chicken Fak antibodies identified CaFak as a 105-kDa protein and immunofluorescence and cytofluorimetric analysis on permeabilized cells specifically stain C. albicans yeasts; moreover, confocal microscopy evidences CaFak as a cytosolic protein that colocalizes on the membrane with the integrin-like VN receptors upon yeast adhesion to VN. The protein tyrosine kinase (PTK) inhibitors genistein and herbimycin A strongly inhibited C. albicans yeast adhesion to VN and EA.hy 926 endothelial cells. Moreover, engagement of alpha v beta 3 and alpha v beta 5 integrin-like on C. albicans either by specific monoclonal antibodies or upon adhesion to VN or EA.hy 926 endothelial cells stimulates CaFak tyrosine phosphorylation that is blocked by PTK inhibitor. A role for CaFak in C. albicans yeast adhesion was also supported by the failure of VN to stimulate its tyrosine phosphorylation in a C. albicans mutant showing normal levels of CaFak and VNR-like integrins but displaying reduced adhesiveness to VN and EA.hy 926 endothelial cells. Our results suggest that C. albicans Fak-like protein is involved in the control of yeast cell adhesion to VN and endothelial cells.  相似文献   
15.
Non-specific mental retardation (NSMR) is a common human disorder characterized by mental handicap as the only clinical symptom. Among the recently identified MR genes is GDI1, which encodes alpha Gdi, one of the proteins controlling the activity of the small GTPases of the Rab family in vesicle fusion and intracellular trafficking. We report the cognitive and behavioral characterization of mice carrying a deletion of Gdi1. The Gdi1-deficient mice are fertile and anatomically normal. They appear normal also in many tasks to assess spatial and episodic memory and emotional behavior. Gdi1-deficient mice are impaired in tasks requiring formation of short-term temporal associations, suggesting a defect in short-term memory. In addition, they show lowered aggression and altered social behavior. In mice, as in humans, lack of Gdi1 spares most central nervous system functions and preferentially impairs only a few forebrain functions required to form temporal associations. The general similarity to human mental retardation is striking, and suggests that the Gdi1 mutants may provide insights into the human defect and into the molecular mechanisms important for development of cognitive functions.  相似文献   
16.
A reduction in muscle mass, with consequent decrease in strength and resistance, is commonly observed with advancing age. In this study we measured markers of oxidative damage to DNA, lipids and proteins, some antioxidant enzyme activities as well Ca2+ transport in sarcoplasmic reticulum membranes in muscle biopsies from vastus lateralis of young and elderly healthy subjects of both sexes in order to evaluate the presence of age- and sex- related differences. We found a significant increase in oxidation of DNA and lipids in the elderly group, more evident in males, and a reduction in catalase and glutathione transferase activities. The experiments on Ca2+ transport showed an abnormal functional response of aged muscle after exposure to caffeine, which increases the opening of Ca2+ channels, as well a reduced activity of the Ca2+ pump in elderly males. From these results we conclude that oxidative stress play an important role in muscle aging and that oxidative damage is much more evident in elderly males, suggesting a gender difference maybe related to hormonal factors.This revised version was published online in September 2005 with corrections to the Cover Date.  相似文献   
17.
In order to assess the suitability of cryopreserved neoplastic tissues for xenografting into nude (nu/nu) mice, we compared the take rate in 28 samples of pancreatic ductal carcinoma. Eleven fresh samples were implanted in nu/nu mice, and 17 were frozen in cryopreserving solution and implanted at a later time. All samples were examined for the presence of neoplastic tissue in cryostat sections. A total of 15 tumors grew in the animals; five from the freshly implanted samples and ten from those cryopreserved. Ten xenografted tumors were characterized for alterations in p53, K-ras, and p16 genes, which were found in six, eight, and nine cases, respectively. Our results demonstrate that the take rate for xenografting is comparable between cryopreserved and fresh tissue samples. The procedure allows for the exchange of tumor material between institutions and permits the establishment of centralized facilities for the storage of an array of different primary tumor samples suitable for the production of in vivo models of cancers.  相似文献   
18.
The OPA1 gene, encoding a dynamin-related GTPase that plays a role in mitochondrial biogenesis, is implicated in most cases of autosomal dominant optic atrophy (ADOA). Sixty-nine pathogenic OPA1 mutations have been reported so far. Most of these are truncating mutations located in the GTPase domain coding region (exons 8-16) and at the 3'-end (exons 27-28). We screened 44 patients with typical ADOA using PCR-sequencing. We also tested 20 sporadic cases of bilateral optic atrophy compatible with ADOA. Of the 18 OPA1 mutations found, 14 have never been previously reported. The novel mutations include one nonsense mutation, 3 missense mutations, 6 deletions, one insertion and 3 exon-skipping mutations. Two of these are de novo mutations, which were found in 2 patients with sporadic optic atrophy. The recurrent c.2708_2711delTTAG mutation was found in 2 patients with a severe congenital presentation of the disease. These results suggest that screening for OPA1 gene mutations may be useful for patients with optic atrophy who have no affected relatives, or when the presentation of the disease is atypical as in the case of early onset optic atrophy.  相似文献   
19.
Objectives To evaluate uterine artery resistance during multiovulation induction in relation to the implantation rate in patients attendingin vitro fertilization (IVF) cycles.Patients Multiovulation induction for IVF was monitored by daily determination of the pulsatility index (PI) of the uterine arteries, obtained by a transvaginal probe (6.5 MHz) implemented with color-flow imaging. Doppler data were obtained from 5 days before hCG administration to the day of follicular aspiration. One IVF cycle was monitored in 70 patients. In 17 patients, 41 IVF cycles were monitored until a successful attempt occurred.Results In the 70 patients studied during one IVF attempt, the PI of the uterine arteries significantly varied (P < 0.001) in the different phases of the cycle. In the 24 patients who conceived, a significantly lower PI (P < 0.03) was found throughout the cycle. This result was mainly due to a highly significant difference of PI values observed the day after hCG administration (P < 0.005). In the 17 patients who conceived after 1 to 4 negativein vitro fertilizations, no significant difference in PI was observed in the uterine artery resistance in cycles in which implantation was or was not successful.Conclusions Uterine artery resistance varies significantly during phases of the induction therapy. Uterine artery resistance is lower throughout the course of multiovulation induction in patients with higher pregnancy rates. The PI on the day after hCG administration was the best index of pregnancy rate. Low uterine artery resistance was present even in negative attempts in patients who eventually achieved a successful implantation. PI values 3 can be considered a favorable prognostic factor for future IVF cycles.Presented at the 49th Annual Meeting of the American Fertility Society, Montreal, 1993 and the 50th Annual Meeting of the American Fertility Society, November 5–10, 1994, San Antonio, Texas.  相似文献   
20.
Summary The aim of the present study was to analyse the current epidemiological situation with respect to TBE in the new federal Länder of Germany and in Saarland through detection of the TBEV genome in unengorged ticks using an RT-PCR technique. 22,273 ticks (Ixodes ricinus) were collected in the five new Länder (and some in Bavaria and Baden-Württemberg) and divided into 294 pools. It was possible to detect TBEV RNA in six pools of ticks from Mecklenburg Western-Pomerania [4], Brandenburg [1], Thuringia [1] (and in three pools from Bavaria and Baden-Württemberg). The nucleotide sequence data of the PCR products were analysed and compared. In Saarland 8,780 ticks were collected in 70 habitats from all the geographic regions and analysed using the PCR in 21 pools; two pools produced positive PCR signals (Saarlouis, Perl). We cannot as a result make a general recommendation that TBE-immunization be introduced in Saarland and in the new federal Länder of Germany. In Germany, however, TBE immunoprophylaxis in Bavaria and Baden-Württemberg is very important.
Nachweis des Virus der Frühsommer-Meningoenzephalitis in Zecken einiger Bundesländer mittels Polymerase-Kettenreaktion und nähere Charakterisierung des Virus
Zusammenfassung Das Ziel der vorgelegten Studie ist die Einschätzung der aktuellen epidemiologischen Situation der Frühsommer-Meningoenzephalitis in den fünf neuen Bundesländern und im Saarland mit Hilfe des Nachweises von FSMEV-RNA in ungesogenen Zecken (Ixodes ricinus) durch eine RT-PCR-Technik. 22 273 Zecken wurden in den fünf neuen Ländern (einige auch in Bayern und Baden-Württemberg) gesammelt und in 294 Pools untersucht. Der spezifische RNA-Nachweis gelang viermal in Zecken aus Mecklenburg-Vorpommern, einmal in solchen aus Brandenburg und einmal aus Thüringen. In Bayern und Baden-Württemberg gelang der Virus-RNA-Nachweis dreimal. Die Sequenzdaten der PCR-Amplifikate zeigten, auch im Vergleich mit denen des Prototypstammes Neudoerfl, den hohen Grad der Konservierung im Bereich der 5 NCR. 8780 saarländische Zecken aus allen Gebieten des Bundeslandes wurden in 21 Pools untersucht, positive PCR-Signale konnten in zwei Pools aus Saarlouis und Perl und Umgebung gefunden werden. Der relativ seltene FSMEV-RNA-Nachweis in den neuen Ländern und im Saarland berechtigt nicht, eine generelle Impfempfehlung für diese Gebiete zu geben. Ein Impfschutz sollte jedoch vor Einreise in die Endemiegebiete Bayerns und Baden-Württembergs bestehen.
  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