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   862篇
  免费   47篇
  2023年   14篇
  2022年   20篇
  2021年   34篇
  2020年   23篇
  2019年   20篇
  2018年   26篇
  2017年   31篇
  2016年   40篇
  2015年   53篇
  2014年   37篇
  2013年   67篇
  2012年   73篇
  2011年   68篇
  2010年   48篇
  2009年   30篇
  2008年   41篇
  2007年   28篇
  2006年   30篇
  2005年   25篇
  2004年   36篇
  2003年   7篇
  2002年   27篇
  2001年   7篇
  2000年   6篇
  1998年   2篇
  1997年   2篇
  1995年   5篇
  1994年   4篇
  1993年   2篇
  1991年   3篇
  1990年   4篇
  1989年   4篇
  1987年   3篇
  1986年   3篇
  1985年   2篇
  1984年   2篇
  1981年   8篇
  1980年   5篇
  1979年   6篇
  1978年   9篇
  1977年   7篇
  1976年   3篇
  1975年   6篇
  1974年   7篇
  1973年   5篇
  1972年   3篇
  1971年   2篇
  1970年   2篇
  1969年   4篇
  1966年   2篇
排序方式: 共有909条查询结果,搜索用时 15 毫秒
11.
Salinity had a varying effect on stomatal frequency, size and pore in barley (Hordeum vulgare L.). This variation in stomatal frequency, size and pore under salinity offers a scope of selecting cultivars with lesser increase in stomatal number to avoid excessive loss of water due to transpiration without effecting photosynthetic efficiency.  相似文献   
12.
Abstract: The effect of a number of nucleotides and related compounds on glutamine synthetase (GS) induction in retina from 12-day chick embryo was studied with both biochemical and immunohistochemical techniques. A number of these compounds gave rise to GS activity comparable to that induced by treatment with cortisol, which is known to give rise to precocious induction of the enzyme in this system. Of the cyclic nucleotides examined, cAMP (0.5-1.2 × 10?3 M) gave essentially no increase in GS activity. In contrast, dibutyryl cAMP (0.8 × 10?3 M) had a more significant effect on GS activity, as did 8-bromo-cAMP and cGMP at the same concentration. The activity elicited by these nucleotides was generally half that obtained by treatment with 2.8 × 10?7 M-cortisol for the same length of time, 8-Bromo-cGMP (0.8 × 10?3 M) had an effect comparable to the aforementioned concentration of cortisol. Since phosphodiesterase activity is minimal in the chick retina at 12 days of development, addition of isobutylmethylxanthine (1 × 10?5 M) to this system had, as would be expected, little effect on GS activity. Of the noncyclic compounds, 8-bromoguanosine often gave rise to GS activity comparable to that obtained with cortisol. The other compounds (8-bromo-5′-GMP, guanosine, adenosine, and 5′-AMP) generally had less of an effect on GS. In general, the degree of staining in the immunohistochemical localization of GS corresponded well with the biochemical results and showed the enzyme to be present in regions consistent with the distribution of Muller cells and their processes. Thin-layer chromatography and radioimmunoassay of the nucleotides did not show any steroid impurity in any of the compounds used in the study, even when determinations were carried out at five times the concentration of nucleotide used in the experiments.  相似文献   
13.
14.
15.
International Journal of Peptide Research and Therapeutics - Bioactive peptides have been reported to exhibit opioid-like activity and are termed as opioid peptides. Either these are produced...  相似文献   
16.
In Vitro Cellular & Developmental Biology - Plant - Full-length and 5′ deletion fragments of three constitutively expressed gene promoters identified from the Citrus sinensis L. genome...  相似文献   
17.
18.
The recent outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has impacted the world severely. The binding of the SARS-CoV-2 virus to the angiotensin-converting enzyme 2 (ACE2) and its intake by the host cell is a necessary step for infection. ACE2 has garnered widespread therapeutic possibility as it is entry/interactive point for SARS-CoV-2, responsible for coronavirus disease 2019 (COVID-19) pandemic and providing a critical regulator for immune modulation in various disease. Patients with suffering from cancer always being on the verge of being immune compromised therefore gaining knowledge about how SARS-CoV-2 viruses affecting immune cells in human cancers will provides us new opportunities for preventing or treating virus-associated cancers. Despite COVID-19 pandemic got center stage at present time, however very little research being explores, which increase our knowledge in context with how SARS-CoV-2 infection affect cancer a cellular level. Therefore, in light of the ACE-2 as an important contributor of COVID-19 global, we analyzed correlation between ACE2 and tumor immune infiltration (TIL) level and the type markers of immune cells were investigated in breast cancer subtypes by using TIMER database. Our findings shed light on the immunomodulatory role of ACE2 in the luminal A subtype which may play crucial role in imparting therapeutic resistance in this cancer subtype.  相似文献   
19.
20.
Vertebrate Hedgehog signals are transduced through the primary cilium, a specialized lipid microdomain that is required for Smoothened activation. Cilia-associated sterol and oxysterol lipids bind to Smoothened to activate the Hedgehog pathway, but how ciliary lipids are regulated is incompletely understood. Here we identified DHCR7, an enzyme that produces cholesterol, activates the Hedgehog pathway, and localizes near the ciliary base. We found that Hedgehog stimulation negatively regulates DHCR7 activity and removes DHCR7 from the ciliary microenvironment, suggesting that DHCR7 primes cilia for Hedgehog pathway activation. In contrast, we found that Hedgehog stimulation positively regulates the oxysterol synthase CYP7A1, which accumulates near the ciliary base and produces oxysterols that promote Hedgehog signaling in response to pathway activation. Our results reveal that enzymes involved in lipid biosynthesis in the ciliary microenvironment promote Hedgehog signaling, shedding light on how ciliary lipids are established and regulated to transduce Hedgehog signals.  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