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   9766篇
  免费   691篇
  国内免费   836篇
  11293篇
  2024年   19篇
  2023年   138篇
  2022年   363篇
  2021年   632篇
  2020年   357篇
  2019年   473篇
  2018年   464篇
  2017年   317篇
  2016年   447篇
  2015年   688篇
  2014年   799篇
  2013年   782篇
  2012年   930篇
  2011年   857篇
  2010年   497篇
  2009年   450篇
  2008年   502篇
  2007年   421篇
  2006年   328篇
  2005年   270篇
  2004年   232篇
  2003年   242篇
  2002年   197篇
  2001年   147篇
  2000年   113篇
  1999年   128篇
  1998年   72篇
  1997年   68篇
  1996年   63篇
  1995年   50篇
  1994年   36篇
  1993年   25篇
  1992年   39篇
  1991年   22篇
  1990年   21篇
  1989年   37篇
  1988年   14篇
  1987年   8篇
  1986年   9篇
  1985年   21篇
  1984年   4篇
  1983年   7篇
  1982年   2篇
  1981年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Ma  Guangzhen  Chen  Jirong  Wei  Tiantian  Wang  Jia  Chen  Wenshan 《Cytotechnology》2021,73(4):523-537
Cytotechnology - Forkhead box A2 (FOXA2) has emerged as a tumor inhibitor in several human malignancies. This work focused on the effect of FOXA2 on liver cancer (LC) cell invasion and migration...  相似文献   
102.
Gao  Kai  Liu  Meiyou  Li  Yuan  Wang  Lei  Zhao  Chao  Zhao  Xian  Zhao  Jinyi  Ding  Yi  Tang  Haifeng  Jia  Yanyan  Wang  Jingwen  Wen  Aidong 《Journal of molecular histology》2021,52(3):449-459
Journal of Molecular Histology - Currently, the excessive activation of N-methyl-D-aspartate receptors (NMDARs) is considered to be a crucial mechanism of brain injury. Lycium barbarum A (LyA) is a...  相似文献   
103.
目的:观察黑木耳多糖(APP)对急性脑缺血大鼠的保护作用并探讨其相关机制。方法:成年雄性SD大鼠给予不同浓度的AAP灌胃20d,每天1次,腹腔注射银杏叶提取物(ginkgo biloba extract,EGb671)作为阳性对照,20d后实施右侧大脑中动脉栓塞(MCAO)建立局灶性脑缺血模型。MCAO60min后复灌,复灌24h后进行Longa神经功能损伤评分,并用2,3,5-氯化三苯基四氮唑(TTC)染色法测定脑梗死面积。复灌48h后用TUNEL免疫组化检测神经元凋亡,测定脑组织线粒体内活性氧簇(ROS)的生成量判断氧化应激水平。结果:黑木耳多糖能降低神经功能损伤评分,减小脑梗死面积,减少神经元凋亡,并且能够使缺血复灌脑组织线粒体ROS生成显著减少。高剂量AAP组的凋亡神经元数量、ROS生成量和阳性对照组相比有显著性差异。结论:黑木耳多糖能够对抗大鼠的局灶性脑缺血损伤,其保护作用和减轻氧化应激水平有关,并优于银杏叶提取物。  相似文献   
104.
105.

Objective

KCa3.1 channel participates in many important cellular functions. This study planned to investigate the potential involvement of KCa3.1 channel in premature senescence, myofibroblast phenotype transition and proliferation of mesangial cells.

Methods & Materials

Rat mesangial cells were cultured together with TGF-β1 (2 ng/ml) and TGF-β1 (2 ng/ml) + TRAM-34 (16 nM) separately for specified times from 0 min to 60 min. The cells without treatment served as controls. The location of KCa3.1 channels in mesangial cells was determined with Confocal laser microscope, the cell cycle of mesangial cells was assessed with flow cytometry, the protein and mRNA expression of KCa3.1, α-smooth muscle actin (α-SMA) and fibroblast-specific protein-1 (FSP-1) were detected with Western blot and RT-PCR. One-way analysis of variance (ANOVA) and Student-Newman-Keuls-q test (SNK-q) were used to do statistical analysis. Statistical significance was considered at P<0.05.

Results

Kca3.1 channels were located in the cell membranes and/or in the cytoplasm of mesangial cells. The percentage of cells in G0-G1 phase and the expression of Kca3.1, α-SMA and FSP-1 were elevated under the induction of TGF-β1 when compared to the control and decreased under the induction of TGF-β1+TRAM-34 when compared to the TGF-β1 induced (P<0.05 or P<0.01).

Conclusion

Targeted disruption of KCa3.1 inhibits TGF-β1-induced premature aging, myofibroblast-like phenotype transdifferentiation and proliferation of mesangial cells.  相似文献   
106.
The importance of plant–soil feedback (PSF) has long been recognized, but the current knowledge on PSF patterns and the related mechanisms mainly stems from laboratory experiments. We aimed at addressing PSF effects on community performance and their determinants using an invasive forb Solidago canadensis. To do so, we surveyed 81 pairs of invaded versus uninvaded plots, collected soil samples from these pairwise plots, and performed an experiment with microcosm plant communities. The magnitudes of conditioning soil abiotic properties and soil biotic properties by S. canadensis were similar, but the direction was opposite; altered abiotic and biotic properties influenced the production of subsequent S. canadensis communities and its abundance similarly. These processes shaped neutral S. canadensis–soil feedback effects at the community level. Additionally, the relative dominance of S. canadensis increased with its ability of competitive suppression in the absence and presence of S. canadensis–soil feedbacks, and S. canadensis‐induced decreases in native plant species did not alter soil properties directly. These findings provide a basis for understanding PSF effects and the related mechanisms in the field conditions and also highlight the importance of considering PSFs holistically.  相似文献   
107.
端粒酶RNA反义基因对肝癌细胞的影响   总被引:1,自引:0,他引:1  
用RT-PCR的方法钓取端粒酶RNA基因的cDNA,并将其反向插入到逆转录病毒载体pLNCX上,构建hTR基因的反义表达质粒。将质粒经脂质体介导转染人肝癌SMMG-7721细胞中表达。结果表明hTR反义基因的表达有效地封闭或抑制肝癌细胞的端粒酶活性,抑制细胞的生长和增殖,延长细胞的倍增时间并促进细胞凋亡。  相似文献   
108.
鲨鱼软骨血管生成抑制因子的纯化和功能   总被引:25,自引:0,他引:25  
以中国东海鲸鲨软骨为原料,通过盐抽提、丙酮分级沉淀、离子交换层折、分子筛层析、高效液相色谱等步骤,获得鲨鱼软骨血管生成抑制因子-I(shark cartilgae angiogenesis inhibitory factor-I,SCAIF-I),对其分子量、抑制血管生成及抑制肿瘤生长活性进行了研究。结果显示SCAIF-I分子量18kD,在细胞和整体水平上显著抑制新血管生成,显著抑制小鼠肿瘤的生长  相似文献   
109.
Conservative Trp-to-Phe mutations were individually created in human thrombin at positions 60d, 96, 148, 207, and 215. Fluorescence intensities for these residues varied by a factor of 6. Residues 60d, 96, 148, and 215 transferred energy to the thrombin inhibitor 5-dimethylaminonaphthalene-1-sulfonylarginine-N-(3-ethyl-1,5- pentanediyl)amide efficiently, but residue 207 did not. Intensities correlated inversely with exposure to solvent, and measured and theoretical energy transfer efficiencies agreed well. Function was measured with respect to fibrinogen clotting, platelet and factor V activation, inhibition by antithrombin, and the thrombomodulin-dependent activation of protein C and thrombin-activable fibrinolysis inhibitor (TAFI). All activities of W96F and W207F ranged from 74 to 154% of the wild-type activity. This was also true for W148F, except for inhibition by antithrombin, where it showed 60% activity. W60dF was deficient by 30, 57, and 43% with fibrinogen clotting, platelet activation, and factor V cleavage (Arg(1006)), respectively. W215F was deficient by 90, 55, and 56% with fibrinogen clotting, platelet activation, and factor V cleavage (Arg(1536)). With protein C and TAFI, W96F, W148F, and W207F were normal. W60dF, however, was 76 and 23% of normal levels with protein C and TAFI, respectively. In contrast, W215F was 25 and 124% of normal levels in these reactions. Thus, many activities of thrombin are retained upon substitution of Trp with Phe at positions 96, 148, and 207. Trp(60d), however, appears to be very important for TAFI activation, and Trp(215) appears to very important for clotting and protein C activation.  相似文献   
110.
HLA haplotype analysis has important application value in human population genetics, anthropological research and HLA matching transplantation. Based on HLA-A, -B, -C, -DRB1 and -DQB1 genotyping data from 663 families including 663 leukemia patients and 991 related donors, the allele frequency (AF) and haplotype frequency (HF) of two-, three- and five-locus haplotype distribution patterns in the Chinese Han population were determined by family segregation. A total of 38 alleles at A locus, 75 alleles at B locus, 35 alleles at C locus, 53 alleles at DRB1 locus and 22 alleles at DQB1 locus were discovered in this population. The frequencies of these alleles were basically consistent with those of previous reports except for some tiny differences. The study found 11 A-C, 15 C-B, 4 B-DRB1 and 11 DRB1-DQB1 two-locus haplotypes with a frequency over 2%. The number of A-C-B and A-B-DRB1 three-locus haplotype with a frequency over 1% were 11 and 3 respectively. The most common HLA-A-C-B-DRB1-DQB1 haplotype (HF>1%) were A*3001-C*0602-B*1302-DR*0701-DQ*0202 (4.30%), A*0207-C*0102-B*4601-DR*0901-DQ*0303 (3.07%), A*3303-C*0302-B*5801-DR*0301-DQ*0201 (1.49%) and A*1101-C*0102-B*4601-DR*0901-DQ*0303 (1.01%). The results are helpful for finding matching donors for hematopoietic stem cell transplant patients and also contribute to transplant immunology, HLA-related diseases, research of human genetics and other fields.  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