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   6288篇
  免费   432篇
  国内免费   443篇
耳鼻咽喉   45篇
儿科学   93篇
妇产科学   140篇
基础医学   1190篇
口腔科学   55篇
临床医学   522篇
内科学   1920篇
皮肤病学   58篇
神经病学   326篇
特种医学   108篇
外科学   694篇
综合类   889篇
预防医学   164篇
眼科学   140篇
药学   502篇
中国医学   150篇
肿瘤学   167篇
  2024年   7篇
  2023年   37篇
  2022年   77篇
  2021年   138篇
  2020年   115篇
  2019年   83篇
  2018年   103篇
  2017年   135篇
  2016年   170篇
  2015年   215篇
  2014年   410篇
  2013年   445篇
  2012年   380篇
  2011年   501篇
  2010年   414篇
  2009年   440篇
  2008年   487篇
  2007年   483篇
  2006年   408篇
  2005年   387篇
  2004年   298篇
  2003年   269篇
  2002年   198篇
  2001年   158篇
  2000年   120篇
  1999年   87篇
  1998年   77篇
  1997年   60篇
  1996年   65篇
  1995年   59篇
  1994年   54篇
  1993年   49篇
  1992年   30篇
  1991年   28篇
  1990年   20篇
  1989年   18篇
  1988年   17篇
  1987年   20篇
  1986年   13篇
  1985年   21篇
  1984年   16篇
  1983年   6篇
  1982年   9篇
  1981年   7篇
  1980年   3篇
  1979年   5篇
  1978年   8篇
  1977年   3篇
  1976年   5篇
  1973年   2篇
排序方式: 共有7163条查询结果,搜索用时 187 毫秒
61.
Wu X  Zheng J  Fu J  You J  Cui X  Wang J  Fang W  Zhou A  Wu B 《中华病理学杂志》2000,29(5):363-366
目的 探讨反义血管内皮生长因子(VEGF)基因转染在抑制恶性肿瘤生长和转移的抗肿瘤血管基因治疗中的意义。方法 利用基因重组技术构建正义和反义VEGF121 cDNA真核表达载体,用脂质体法转染高转移性人巨细胞肺癌细胞(PG),经Northem杂交和Western印迹免疫化学检测VEGF mRNA和蛋白质的表达水平,并对转染前后细胞进行体外生长和裸鼠体内生长转移等多项生物学行为实验,结果 转染反义转  相似文献   
62.
目的:观察脂质过氧化对培养的人内皮细胞血管细胞粘附分子-1表达的影响。方法:培养的人脐静脉内皮细胞随机分为实验组和对照组。实验组与不同浓度联胺(1μmol/L、5μmol/L、10μmol/L)作用8h, 对照组不加联胺。细胞原位杂交和细胞酶联免疫吸附法分别测定内皮细胞血管细胞粘附分子-1mRNA和蛋白表达。结果:细胞原位杂交结果图像分析表明, 实验组平均吸光度值分别为0.147±0.013、0.292±0.020和0.396±0.022, 是对照组(0.077±0.011)的1.91倍、3.79倍和5.14倍。方差分析表明, 各组间两两比较有显著差异(P<0.01)。细胞酶联免疫吸附测定结果, 实验组平均吸光度值分别是0.158±0.008、0.220±0.017和0.321±0.023, 为对照组(0.104±0.016)的1.53倍、2.12倍和3.09倍。各组间两两比较有显著差异(P<0.01)。结论:人脐静脉内皮细胞脂质过氧化增加血管细胞粘附分子-1mRNA和蛋白表达, 这可能促进单核细胞粘附血管内皮, 在动脉粥样硬化发生发展中起重要作用。  相似文献   
63.
血管内皮生长因子促进小鼠胚胎干细胞的造血分化   总被引:1,自引:0,他引:1       下载免费PDF全文
目的:研究血管内皮生长因子(VEGF)体外促进小鼠胚胎干细胞系ES-D3向造血分化的能力。方法:先将ES-D3形成拟胚体,将拟胚体细胞转入含不同浓度的VEGF和VEGF+SCF的培养基中。实验分6组,分别为VEGF 5 μg/L组、VEGF 10 μg/L组、VEGF 20 μg/L组、VEGF 5 μg/L+SCF组、VEGF 10 μg/L+SCF组、VEGF 20 μg/L+SCF组,同时设不加因子的自发分化对照组。RT-PCR检测造血转录基因GATA-2和早期造血细胞基因c-kit和β-H1的表达,流式细胞仪检测CD34+细胞,甲基纤维素半固体培养法检测生成造血集落的能力。结果:经过1周的诱导培养,实验组生成的细胞可以表达GATA-2、c-kit和β-H1,CD34+细胞的比例也升高,并可形成造血祖细胞的集落。从诱导生成CD34+细胞的比例和生成的集落数量看,VEGF联合SCF组的诱导效率要高于VEGF单用组和对照组,其中以VEGF 20 μg/L+SCF组和VEGF 10 μg/L+SCF组的诱导效率最高。结论:VEGF能够促进ESC的早期造血分化,尤以与SCF合用时,其诱导效率更高。  相似文献   
64.
Smooth muscle cells have been isolated from human umbilical cord veins, characterized and cultured for the development of an endothelialsmooth muscle cell co-culture system. After harvesting endothelial cells, the umbilical cords were trimmed of amnion, connective tissue and arteries, split into pieces, cut open longitudinally and placed with the luminal surface of the explant down onto a culture plate, without the use of proteolytic enzymes. Adherent primary cells were sequentially passaged and various cytological/biochemical characterizations were performed between passages 2 and 10. Cells stained positive for antibodies against smooth muscle actin, negative for antibodies against factor VIII and displayed typical hill and valley morphology when confluent. Cell proliferation was stimulated and supported in a concentration-dependent manner by both human serum and fetal bovine serum over the range 1%–20%. The use of human serum at concentrations >10% decreased the population doubling time during exponential growth by circa 50%. The cells were also characterized by high seeding efficiencies (>70%) and retained their diploid karyotype for up to 3 months in culture. Endothelial cells and smooth muscle cells prepared from umbilical veins were then seeded at varying densities onto either side of porous tissue culture inserts coated with fibronectin. Utilising the measurement of electrical resistance, the optimal seeding density of 5×104 cells/cm2 for each cell type gave maximal resistance across the cell bi-layer already after 24 hours, which remaining essentially unaltered for up to 4 days of culture and which was always substantially higher than the resistance of filters seeded only with endothelial cells on one side. This was not substantially affected either by increasing passage of the HUVSM cells cultured with a fixed passage of endothelial cells, or by varying the donor origin of the endothelial cells. In terms of functionality of the selective permeability of the model, the calcium ionophore ionomycin (25 M), added to the endothelial side of the bi-layer, caused a 30% reduction in the electrical resistance across the co-culture within 60 minutes, with control resistance being re-established within 1 hour of removal of the ionophore by washing. These results clearly indicate that smooth muscle cells and endothelial cells prepared from the same human blood vessel can be reconstituted into a functional vascular model suitable for the study of biochemical, physiological and toxicological phenomena in the human vascular wall.Abbreviations BCA bicinchoninic acid - BSA bovine serum albumin - DMEM DMEM medium supplemented with 4.5 g/l glucose, 100 IU/ml penicillin, 100 g/ml streptomycin and 1.25 g/ml fungizone - DMEM-1 DMEM supplemented with 20% FBS, 300 IU/ml penicillin, 300 g/ml streptomycin and 3.75 mg/ml fungizone - DMEM-2 DMEM supplemented with 20% FBS, 100 IU/ml of penicillin, 100 g/ml of streptomycin and 1.25 g/ml of fungizone - DMSO dimethyl sulfoxide - FBS fetal bovine serum - HPF human pulmonary fibroblasts - HS human serum - HUVE human umbilical vein endothelial - HUVSM human umbilical vein smooth muscle - M199 M199 medium supplemented with 20% HS, 100 IU/ml penicillin, 100 g/ml streptomycin, 1.25 g/ml fungizone and 2 mM L-glutamine - P passage number - PBS phosphate buffered saline - TCA trichloroacetic acid - vwF von Willebrand factor (factor VIII)  相似文献   
65.
目的:探讨终末糖基化产物在糖尿病动脉粥样硬化(AS)形成中的作用机理。 方法: 分离正常人脐静脉内皮细胞(HUVECs),将终末糖基化终产物(AGE)修饰的人血清白蛋白(AGE-HSA)、人血清白蛋白(HSA)与HUVECs在体外共同培养,并用荧光单克隆抗体染色,流式细胞仪定量检测细胞间粘附分子-1(ICAM-1)、血管细胞粘附分子-1(VCAM-1)的表达。 结果: 正常人HUVEC表达ICAM-1和VCAM-1。AGE-HSA能以时间和剂量依赖的方式上调ICAM-1、VCAM-1的表达(P<0.05),而HSA对HUVECs上述粘附分子的表达均无影响。 结论: AGE能上调HUVECs粘附分子的表达,从而促进AS时单核/巨噬细胞的浸润。  相似文献   
66.
血管内皮生长因子和E26转录因子在乳腺癌中的表达及意义   总被引:19,自引:1,他引:19  
Wu H  Li Y  Zhang L  Zhu G  Cai J 《中华病理学杂志》2002,31(3):222-226
目的 试图揭示血管内皮生长因子(VEGF)和E26转录因子(E26 transformation-specificl,ETS-1)在乳腺癌组织中的表达规律,探讨其在血管生成和肿瘤浸润转移中的作用机制。方法 应用原位杂交和免疫组织化学链霉素抗生物系-过氧化物酶复合物法(SP)法,检测48例乳腺癌组织中VEGF和ETS-1的mRNA和蛋白的表达。结果 乳腺癌细胞高表达VEGF mRNA和蛋白,阳性率分别为75%(36/48),70.8%(34/48),而血管内皮细胞几乎不表达;ETS-1既表达在乳腺癌细胞,也表达在血管内皮细胞。癌细胞中mRNA和蛋白表达阳性率分别为85.4%(41/48),79.2%(38/48);VEGF和ETS-1高表达组的血管密度明显高于低表达组(均P<0.01);VEGF和ETS-1的表达与组织学分级和淋巴结转移密切相关,并且高表达组的微血管密度明显高于低表达组(P<0.01)。结论 VEGF和ETS-1可促进乳腺癌血管形成,同时也促进肿瘤的浸润和转移;检测VEGF和ETS-1的表达可做为乳腺癌恶性度,浸润转移等生物学行为的参考指标。  相似文献   
67.
右旋糖酐40、70对红细胞与内皮细胞粘附的影响   总被引:1,自引:0,他引:1  
采用流室显微观察系统,定量研究右旋糖酐40(DX40)和右旋糖酐70(DX70)对红细胞与内皮细胞动态粘附特性的影响。统计分析处理数据,得到反映切应力与细胞间动态粘附数关系的经验公式及粘附特征常数a,b值。a值反映红细胞的初始粘附数,b值反映随切应力增大,粘附数减小的速率。DX70实验组的a值大于DX40组的,而b值的情况相反。故结果显示切应力越大,粘附的红细胞越少;DX40使红细胞的粘附明显减少;DX70使红细胞粘附显著增加。由此提示不同长度的细胞桥接分子对红细胞的粘附影响不同,且临床上选用DX40作血浆扩容剂较DX70优越得多  相似文献   
68.
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   
69.
吴强  曾祖荫 《中国微循环》1998,2(3):154-156
目的:探讨自发性高血压大鼠(SHR)的微血管改变与血管内皮细胞(VEC)损伤的关系。方法:以10只成年Wistar-Kyoto大鼠(WKY)为正常对照组(WKY组)。观察、计数10只成年SHR的肠壁微动脉管径和分支数,同时测定血浆亚硝酸根(NO2-)和内皮素(ET)并与WKY组对照。结果:SHR组的肠壁各级微动脉管径较WKY组变细(P<0.01~0.001)、各级微动脉总条数较WKY组减少(P<0.001~0.0001);SHR组的血浆NO2-水平和K值[10g(NO2-/ET)」较WKY组低(P<0.05~0.001),而ET较WKY组高(P<0.05)。血压和K值分别与肠壁微动脉管径和条数呈负相关和正相关(P<0.005~0.001)。结论:高血压的微血管结构异常与VEC损伤有密切的关系。  相似文献   
70.
The objective of this study is to design a new apparatus to allow the control of the magnitude and frequency of dynamic stretch applied uniformly to cells cultured on a silicon elastic membrane. The apparatus is designed to produce equi-biaxial dynamic stretches with area changes ranging from 0% to 55% and frequencies ranging from 0 to 2 Hz. Homogeneous finite strain analysis using triangles of markers was performed to compute the symmetric two-dimensional Lagrangian strain tensor on the membrane. Measurements of strain in both static and dynamic conditions showed that the shear component of the strain tensor (Erc) was near zero, and that there was no significant difference between radial (Err) and circumferential (Ecc) components, indicating the attainment of equi-biaxial strain. Bovine aortic endothelial cells were transiently transfected with a chimeric construct in which the luciferase reporter is driven by TPA-responsive elements (TRE). The transfected cells cultured on the membrane were stretched. The luciferase activity increased significantly only when the cells were stretched by 15% or more in area. Cells in different locations of the membrane showed similar induction of luciferase activities, confirming that strain is uniform and equi-biaxial across the membrane. © 1998 Biomedical Engineering Society. PAC98: 8780+s, 8745-k, 8722-q  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