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   2892篇
  免费   114篇
  国内免费   2篇
  2023年   6篇
  2022年   23篇
  2021年   44篇
  2020年   27篇
  2019年   35篇
  2018年   58篇
  2017年   46篇
  2016年   48篇
  2015年   120篇
  2014年   131篇
  2013年   224篇
  2012年   195篇
  2011年   232篇
  2010年   113篇
  2009年   125篇
  2008年   189篇
  2007年   178篇
  2006年   148篇
  2005年   179篇
  2004年   184篇
  2003年   160篇
  2002年   142篇
  2001年   18篇
  2000年   14篇
  1999年   23篇
  1998年   44篇
  1997年   38篇
  1996年   22篇
  1995年   22篇
  1994年   21篇
  1993年   18篇
  1992年   20篇
  1991年   16篇
  1990年   14篇
  1989年   17篇
  1988年   5篇
  1987年   20篇
  1986年   5篇
  1985年   6篇
  1984年   13篇
  1983年   9篇
  1982年   6篇
  1981年   9篇
  1980年   7篇
  1977年   6篇
  1976年   4篇
  1975年   3篇
  1974年   4篇
  1973年   5篇
  1970年   3篇
排序方式: 共有3008条查询结果,搜索用时 15 毫秒
771.
We analyzed the SCA8 CTA/CTG repeat in a large group of Japanese subjects. The frequency of large alleles (85-399 CTA/CTG repeats) was 1.9% in spinocerebellar ataxia (SCA), 0.4% in Parkinson disease, 0.3% in Alzheimer disease, and 0% in a healthy control group; the frequency was significantly higher in the group with SCA than in the control group. Homozygotes for large alleles were observed only in the group with SCA. In five patients with SCA from two families, a large SCA8 CTA/CTG repeat and a large SCA6 CAG repeat coexisted. Age at onset was correlated with SCA8 repeats rather than SCA6 repeats in these five patients. In one of these families, at least one patient showed only a large SCA8 CTA/CTG repeat allele, with no large SCA6 CAG repeat allele. We speculate that the presence of a large SCA8 CTA/CTG repeat allele influences the function of channels such as alpha(1A)-voltage-dependent calcium channel through changing or aberrant splicing, resulting in the development of cerebellar ataxia, especially in homozygous patients.  相似文献   
772.
A high-performance anion-exchange liquid chromatography system was constructed to identify sugar phosphates and nucleotides involved in photosynthetic metabolism. First sugar phosphates and nucleotides were separated by a gradient elution with boric acid and sodium phosphate, then they were detected by a fluorescence detector (as fluorescent derivatives with arginine) and UV detector, respectively. Eight authentic sugar phosphates and 11 authentic nucleotides could be analyzed using the system. The applicability of the system to the determination of the corresponding sugar phosphates and nucleotides in extracts from only five soybean leaf discs (8.95 cm2) was shown.  相似文献   
773.
In this study, we attempted to assess the incorporable potential of vascular endothelial cells derived from adult organ blood vessels into tumor blood vessels. Two kinds of adult organ-derived vascular endothelial cells, human aorta endothelial cells (HAEC) and umbilical vein endothelial cells (HUVEC), were administered into murine tumors inoculated to SCID mice. Many human blood vessel networks were visualized in the murine tumors. These cells in solid tumor not only survived and proliferated, but also incorporated into tumor endothelium. These results suggest that adult organ-derived vascular endothelial cells possess the potential to form the neovascular network in various tissues such as vascular endothelial progenitor-like cells in vivo. We propose that these cells can be regarded as a congenic (autologous) vector for vascular regeneration cell therapy and tumor vascular targeting gene therapy.  相似文献   
774.
Proteinuria is an independent risk factor for progression of renal diseases. Glia maturation factor-beta (GMF-beta), a 17-kDa brain-specific protein originally purified as a neurotrophic factor from brain, was induced in renal proximal tubular (PT) cells by proteinuria. To examine the role of GMF-beta in PT cells, we constructed PT cell lines continuously expressing GMF-beta. The PT cells overexpressing GMF-beta acquired susceptibility to cell death upon stimulation with tumor necrosis factor-alpha and angiotensin II, both of which are reported to cause oxidative stress. GMF-beta overexpression also promoted oxidative insults by H2O2, leading to the reorganization of F-actin as well as apoptosis in non-brain cells (not only PT cells, but also NIH 3T3 cells). The measurement of intracellular reactive oxygen species in the GMF-beta-overexpressing cells showed a sustained increase in H2O2 in response to tumor necrosis factor-alpha, angiotensin II, and H2O2 stimuli. The sustained increase in H2O2 was caused by an increase in the activity of the H2O2-producing enzyme copper/zinc-superoxide dismutase, a decrease in the activities of the H2O2-reducing enzymes catalase and glutathione peroxidase, and a depletion of the content of the cellular glutathione peroxidase substrate GSH. The p38 pathway was significantly involved in the sustained oxidative stress to the cells. Taken together, the alteration of the antioxidant enzyme activities, in particular the peroxide-scavenging deficit, underlies the susceptibility to cell death in GMF-beta-overexpressing cells. In conclusion, we suggest that the proteinuria induction of GMF-beta in renal PT cells may play a critical role in the progression of renal diseases by enhancing oxidative injuries.  相似文献   
775.
776.
777.

Background  

The hallmarks of age-related macular degeneration, the leading cause of blindness in the developed world, are the subretinal deposits known as drusen. Drusen identification and measurement play a key role in clinical studies of this disease. Current manual methods of drusen measurement are laborious and subjective. Our purpose was to expedite clinical research with an accurate, reliable digital method.  相似文献   
778.
A series of the comb-type poly(N-isopropylacrylamide) (NIPAM) gel beads were prepared by inverse suspension polymerization techniques. The comb-type NIPAM gel beads exhibited large volume change at 30 degrees C, and their deswelling rate, defined as the time required for half-shrinking, was 10 times faster than that of the normal-type NIPAM gel beads. The gel beads were utilized to concentrate dilute aqueous solutions of albumin, gamma-globulin, and vitamin B(12). The separation efficiencies of albumin and gamma -globulin with the comb-type NIPAM gel were 80% and 85%, respectively. Whereas those with normal-type NIPAM gel were 55% and 60%, respectively. The incorporation of grafted chains into gel makes the effective mesh size smaller. Therefore it induces the additional obstruction effects between the solutes and network and excludes the high molecular weight solutes. After they have extracted water, their rapid deswelling property makes the gel regenerate effectively by warming to release the absorbed water.  相似文献   
779.
A new series of diphenyl piperazine derivatives containing the phenyl substituted aminopropanol moiety, which were modified at sites between the diphenyl and piperazine moieties, was prepared and evaluated for dopamine transporter binding affinity with [(3)H]GBR12935 in rat striatal membranes. These synthesized compounds showed apparent dopamine transporter binding affinities (IC(50)<30 nM) and some of them were approximately equivalent in activity to GBR12909 known as a potent dopamine uptake inhibitor, showing the activities with IC(50) values of nanomolar range. Among them, 1-[4,4-bis(4-fluorophenyl)butyl]-4-[2-hydroxy-3-(phenylamino)propyl]piperazine 2 was evaluated for extracellular dopamine levels in rat striatum using in vivo brain microdialysis. The intraperitoneal administration of 2 (0.01, 0.03, or 0.1 mmol/kg) induced dose-dependent increases of dopamine levels in rat striatal dialysates. The maximum increases in dopamine levels induced by 2 were greater than those by GBR12909. The pharmacological data of these novel diphenyl piperazine derivatives show that the compounds have potent dopamine uptake inhibitory activities in the central nervous system.  相似文献   
780.
It is well documented that several cell surface molecules of T lymphocytes are altered by immune activation. We previously reported that feline immunodeficiency virus (FIV) infection induces a reduction in CD8beta chain expression of peripheral blood lymphocytes (PBLs) in cats. In this study, we performed three-color flow-cytometric analysis for activation-associated cell surface molecules (CD2, CD11a, CD45RA-like and major histocompatibility complex antigen class II (MHC II)) and light scatters (cellular size and complexity) to examine whether phenotypic changes also occurred in CD4(+) PBLs in addition to CD8(+) PBLs, of five FIV-infected cats and one uninfected cat. It was shown that (i) CD8alpha(+) PBLs, but not CD4(+) PBLs, had a distinct subpopulation with increased CD11a expression accompanying a reduced CD8beta chain and increased intracellular granules (ii) CD8alpha(+) PBLs, but not CD4(+) PBLs, expressed CD45RA-like antigen with diverse expression levels and (iii) MHC II expression was greater in CD8alpha(+) PBLs than CD4(+) PBLs, and the CD8beta chain reduction was correlated with the MHC II decrease within CD8alpha(+) PBLs. These results suggest that FIV infection induces phenotypically heterogeneous subpopulations in CD8(+) PBLs, including activated phenotypes, rather than in CD4(+) PBLs.  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