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   6336篇
  免费   440篇
  国内免费   4篇
  6780篇
  2023年   24篇
  2022年   83篇
  2021年   160篇
  2020年   74篇
  2019年   99篇
  2018年   138篇
  2017年   125篇
  2016年   204篇
  2015年   290篇
  2014年   327篇
  2013年   421篇
  2012年   530篇
  2011年   604篇
  2010年   321篇
  2009年   281篇
  2008年   371篇
  2007年   437篇
  2006年   365篇
  2005年   333篇
  2004年   308篇
  2003年   316篇
  2002年   303篇
  2001年   56篇
  2000年   28篇
  1999年   44篇
  1998年   47篇
  1997年   43篇
  1996年   32篇
  1995年   31篇
  1994年   18篇
  1993年   21篇
  1992年   17篇
  1991年   16篇
  1990年   9篇
  1989年   16篇
  1988年   12篇
  1987年   10篇
  1986年   10篇
  1984年   11篇
  1982年   11篇
  1981年   10篇
  1980年   12篇
  1977年   22篇
  1976年   19篇
  1975年   13篇
  1973年   9篇
  1972年   12篇
  1969年   11篇
  1968年   14篇
  1966年   13篇
排序方式: 共有6780条查询结果,搜索用时 15 毫秒
81.
82.
Hemp (Cannabis sativa L.) was karyotyped using by DAPI/C-banding staining to provide chromosome measurements, and by fluorescence in situ hybridization with probes for 45 rDNA (pTa71), 5S rDNA (pCT4.2), a subtelomeric repeat (CS-1) and the Arabidopsis telomere probes. The karyotype has 18 autosomes plus a sex chromosome pair (XX in female and XY in male plants). The autosomes are difficult to distinguish morphologically, but three pairs could be distinguished using the probes. The Y chromosome is larger than the autosomes, and carries a fully heterochromatic DAPI positive arm and CS-1 repeats only on the less intensely DAPI-stained, euchromatic arm. The X is the largest chromosome of all, and carries CS-1 subtelomeric repeats on both arms. The meiotic configuration of the sex bivalent locates a pseudoautosomal region of the Y chromosome at the end of the euchromatic CS-1-carrying arm. Our molecular cytogenetic study of the C. sativa sex chromosomes is a starting point for helping to make C. sativa a promising model to study sex chromosome evolution.  相似文献   
83.
The FGF signaling pathway plays essential roles in endochondral ossification by regulating osteoblast proliferation and differentiation, chondrocyte proliferation, hypertrophy, and apoptosis. FGF signaling is controlled by the complementary action of both positive and negative regulators of the signal transduction pathway. The Spry proteins are crucial regulators of receptor tyrosine kinase-mediated MAPK signaling activity. Sprys are expressed in close proximity to FGF signaling centers and regulate FGFR-ERK-mediated organogenesis. During endochondral ossification, Spry genes are expressed in prehypertrophic and hypertrophic chondrocytes. Using a conditional transgenic approach in chondrocytes in vivo, the forced expression of Spry1 resulted in neonatal lethality with accompanying skeletal abnormalities resembling thanatophoric dysplasia II, including increased apoptosis and decreased chondrocyte proliferation in the presumptive reserve and proliferating zones. In vitro chondrocyte cultures recapitulated the inhibitory effect of Spry1 on chondrocyte proliferation. In addition, overexpression of Spry1 resulted in sustained ERK activation and increased expression of p21 and STAT1. Immunoprecipitation experiments revealed that Spry1 expression in chondrocyte cultures resulted in decreased FGFR2 ubiquitination and increased FGFR2 stability. These results suggest that constitutive expression of Spry1 in chondrocytes results in attenuated FGFR2 degradation, sustained ERK activation, and up-regulation of p21Cip and STAT1 causing dysregulated chondrocyte proliferation and terminal differentiation.  相似文献   
84.
We have used a systemic approach to establish a relationship between enzyme measures of glial glutamate and energy metabolism (glutamine synthetase and glutamine synthetase-like protein, glutamate dehydrogenase isoenzymes, brain isoform creatine phosphokinase) and two major glial proteins (glial fibrillary acidic protein and myelin basic protein) in autopsied brain samples taken from patients with schizophrenia (SCH) and mentally healthy subjects (23 and 22 cases, respectively). These biochemical parameters were measured in tissue extracts in three brain areas (prefrontal cortex, caudate nucleus, and cerebellum). Significant differences in the level of at least one of the glutamate metabolizing enzymes were observed between two studied groups in all studied brain areas. Different patterns of correlative links between the biochemical parameters were found in healthy and schizophrenic brains. These findings give a new perspective to our understanding of the impaired regulation of enzyme levels in the brain in SCH.  相似文献   
85.
86.
87.
Probiotics and Antimicrobial Proteins - The study aims at elucidating the effect of bacilli probiotic preparations on the physiology of laying hens and roosters. Probiotic formulations were...  相似文献   
88.
89.
90.

Objective

The purpose of this study was to compare the apolipoprotein composition of the three major lipoprotein classes in patients with metabolic syndrome to healthy controls.

Methods

Very low density (VLDL), intermediate/low density (IDL/LDL, hereafter LDL), and high density lipoproteins (HDL) fractions were isolated from plasma of 56 metabolic syndrome subjects and from 14 age-sex matched healthy volunteers. The apolipoprotein content of fractions was analyzed by one-dimensional (1D) gel electrophoresis with confirmation by a combination of mass spectrometry and biochemical assays.

Results

Metabolic syndrome patients differed from healthy controls in the following ways: (1) total plasma - apoA1 was lower, whereas apoB, apoC2, apoC3, and apoE were higher; (2) VLDL - apoB, apoC3, and apoE were increased; (3) LDL - apoC3 was increased, (4) HDL -associated constitutive serum amyloid A protein (SAA4) was reduced (p<0.05 vs. controls for all). In patients with metabolic syndrome, the most extensively glycosylated (di-sialylated) isoform of apoC3 was reduced in VLDL, LDL, and HDL fractions by 17%, 30%, and 25%, respectively (p<0.01 vs. controls for all). Similarly, the glycosylated isoform of apoE was reduced in VLDL, LDL, and HDL fractions by 15%, 26%, and 37% (p<0.01 vs. controls for all). Finally, glycosylated isoform of SAA4 in HDL fraction was 42% lower in patients with metabolic syndrome compared with controls (p<0.001).

Conclusions

Patients with metabolic syndrome displayed several changes in plasma apolipoprotein composition consistent with hypertriglyceridemia and low HDL cholesterol levels. Reduced glycosylation of apoC3, apoE and SAA4 are novel findings, the pathophysiological consequences of which remain to be determined.  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