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   151423篇
  免费   24190篇
  国内免费   13339篇
  2024年   258篇
  2023年   1631篇
  2022年   3539篇
  2021年   6660篇
  2020年   6222篇
  2019年   8640篇
  2018年   8378篇
  2017年   7569篇
  2016年   9106篇
  2015年   11472篇
  2014年   12566篇
  2013年   13589篇
  2012年   13561篇
  2011年   12260篇
  2010年   9698篇
  2009年   7943篇
  2008年   7882篇
  2007年   6791篇
  2006年   6071篇
  2005年   4945篇
  2004年   4272篇
  2003年   3834篇
  2002年   3335篇
  2001年   2547篇
  2000年   2213篇
  1999年   2105篇
  1998年   1293篇
  1997年   1204篇
  1996年   1092篇
  1995年   955篇
  1994年   897篇
  1993年   739篇
  1992年   921篇
  1991年   700篇
  1990年   543篇
  1989年   496篇
  1988年   398篇
  1987年   390篇
  1986年   309篇
  1985年   356篇
  1984年   207篇
  1983年   191篇
  1982年   141篇
  1981年   126篇
  1980年   89篇
  1979年   97篇
  1978年   66篇
  1977年   79篇
  1975年   65篇
  1973年   73篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Pycnogenol® (PYC), a patented combination of bioflavonoids extracted from the bark of French maritime pine (Pinus maritima), scavenges free radicals and promotes cellular health. The protective capacity of PYC against ethanol toxicity of neurons has not previously been explored. The present study demonstrates that in postnatal day 9 (P9) rat cerebellar granule cells the antioxidants vitamin E (VE) and PYC (1) dose dependently block cell death following 400, 800, and 1600 mg/dL ethanol exposure (2) inhibit the ethanol‐induced activation of caspase‐3 in the same model system; and (3) reduce neuronal membrane disruption as assayed by phosphatidylserine translocation to the cell surface. These results suggest that both PYC and VE have the potential to act as therapeutic agents, antagonizing the induction of neuronal cell death by ethanol exposure. © 2004 Wiley Periodicals, Inc. J Neurobiol 59: 261–271, 2004  相似文献   
82.
83.
84.
Nacrein-like proteins have carbonic anhydrase (CA)-like domains, but their coding regions are flanked by inserted repeat sequence, such as Gly-X-Asn. Reportedly, nacrein-like proteins show the highest similarity to human carbonic anhydrase 1(α-CA1), possess CA catalytic functions, and play a key role in shell biomineralization. In the present study, two novel nacrein-like proteins were firstly identified from the shell-forming mantle of the Pacific oyster Crassostrea gigas. With numerous analyses, it was identified and characterized that both the nacrein-like proteins F1 and F2 were secreted and most closely related to the nacrein-like protein of California mussel Mytilus californianus via phylogenetic analysis. RT-PCR analysis showed that the nacrein-like proteins F1 and F2 were expressed in multiple tissues and the expression levels remarkably rose after entering the spat stage, which were basically consistent with the increase of calcite fractions in the total shell volume. Surprisingly, the Gly-X-Asn repeat domain, which is distinctive in most nacrein-like proteins, was absent in the two newly identified nacrein-like proteins in C. gigas and replaced with a series of acidic amino acids (D/E). Regardless, nacrein-like proteins in mollusks seem to be vital to the deposition of calcium carbonate and likely perform diverse functions.  相似文献   
85.
86.
Cytokinesis must be initiated only after chromosomes have been segregated in anaphase and must be terminated once cleavage is completed. We show that the fission yeast protein Etd1 plays a central role in both of these processes. Etd1 activates the guanosine triphosphatase (GTPase) Spg1 to trigger signaling through the septum initiation network (SIN) pathway and onset of cytokinesis. Spg1 is activated in late anaphase when spindle elongation brings spindle pole body (SPB)–localized Spg1 into proximity with its activator Etd1 at cell tips, ensuring that cytokinesis is only initiated when the spindle is fully elongated. Spg1 is active at just one of the two SPBs during cytokinesis. When the actomyosin ring finishes constriction, the SIN triggers disappearance of Etd1 from the half of the cell with active Spg1, which then triggers Spg1 inactivation. Asymmetric activation of Spg1 is crucial for timely inactivation of the SIN. Together, these results suggest a mechanism whereby cell asymmetry is used to monitor cytoplasmic partitioning to turn off cytokinesis signaling.  相似文献   
87.
The heritability of eating behavior and body weight–related traits in Asian populations has not been reported. The purpose of this study was to estimate the heritability of eating behavior and the body weight–related traits of current weight and self‐reported past weight among twins and their families. Study subjects were 2,144 Korean, adult, same‐sex twins and their families at the ages between 20 and 65 years (443 monozygotic (MZ) and 124 dizygotic (DZ) twin pairs, and 1,010 individuals of their family). The Dutch Eating Behavior Questionnaire (DEBQ) was used to assess three eating behavior subscales measuring restraint, emotional eating, and external eating. A variance component approach was used to estimate heritability. After consideration of shared environmental effects and adjustment for age and sex effects, the heritability estimates ± s.e. among twins and their family members were 0.31 ± 0.036 for restraint, 0.25 ± 0.098 for emotional eating, 0.25 ± 0.060 for external eating, 0.77 ± 0.032 for measured current body weight, and 0.70 ± 0.051 for self‐reported weight at 20 years old. The three DEBQ subscales were associated with all weight related traits after adjustment for age and sex. These results suggest eating behaviors and weight‐related traits have a genetic influence, and eating behaviors are associated with obesity indexes. Our findings from Korean twin family were similar to those reported in Western populations.  相似文献   
88.
Fertilized eggs of Sebastes schlegelii, Sebastes pachycephalus and Sebastes hubbsi are morphologically similar under stereomicroscope. However, under the scanning electron microscope, significant differences in the ultrastructures of the egg surface among the three species were observed, and herein, a taxonomic key was proposed for future applications. A clustering analysis based on the ultrastructures of the egg surface and the diameter of the oil globule suggested that among the three species, S. hubbsi and S. pachycephalus were more genetically similar, while S. schlegelii had diverged earlier. The results agree with the conclusions drawn from morphological and molecular analyses on adult samples of the same species.  相似文献   
89.
90.
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