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   9472篇
  免费   838篇
  国内免费   623篇
  2024年   16篇
  2023年   134篇
  2022年   199篇
  2021年   272篇
  2020年   278篇
  2019年   326篇
  2018年   419篇
  2017年   272篇
  2016年   288篇
  2015年   305篇
  2014年   649篇
  2013年   679篇
  2012年   418篇
  2011年   549篇
  2010年   586篇
  2009年   660篇
  2008年   676篇
  2007年   679篇
  2006年   633篇
  2005年   510篇
  2004年   420篇
  2003年   411篇
  2002年   341篇
  2001年   188篇
  2000年   181篇
  1999年   144篇
  1998年   155篇
  1997年   105篇
  1996年   61篇
  1995年   74篇
  1994年   65篇
  1993年   51篇
  1992年   33篇
  1991年   21篇
  1990年   17篇
  1989年   15篇
  1988年   10篇
  1987年   11篇
  1986年   11篇
  1985年   10篇
  1984年   12篇
  1983年   9篇
  1982年   14篇
  1981年   9篇
  1980年   4篇
  1979年   5篇
  1978年   3篇
  1975年   2篇
  1973年   1篇
  1972年   1篇
排序方式: 共有10000条查询结果,搜索用时 687 毫秒
111.
The evolution of taxodiaceous Cupressaceae has been discussed controversially, because phylogenetic analyses using non-molecular data show major differences to molecular analyses. To solve this problem, we used non-molecular data with a high probability of homology. With these type of data, we could show for the first time in taxodiaceous Cupressaceae that phylogenetic trees of molecular and non-molecular data share the same topology. Investigation of female cone development also contributes to better understanding of morphology and anatomy in taxodiaceous Cupressaceae. Additional developmental, fossil and cone configuration data support the topology constructed by using the molecular and non-molecular data.  相似文献   
112.
113.
114.
  1. Download : Download high-res image (327KB)
  2. Download : Download full-size image
  相似文献   
115.
116.
Nucleotide‐Binding Oligomerization Domain 2 (NOD2) has been reported to be a candidate gene for Mycobacterium avium subsp. paratuberculosis (MAP) infection in a Bos taurus × Bos indicus mixed breed based on a genetic association with the c.2197T>C single nucleotide polymorphism (SNP). Nevertheless, this SNP has also been reported to be monomorphic in the B. taurus species. In the present work, 18 SNPs spanning the bovine NOD2 gene have been analysed in a genetic association study of two independent populations of Holstein‐Friesian cattle. We found that the C allele of SNP c.*1908C>T, located in the 3′‐UTR region of the gene, is significantly more frequent in infected animals than in healthy ones, which supports the idea that the bovine NOD2 gene plays a role in susceptibility to MAP infection. However, in silico analyses of the NOD2 nucleotide sequence did not yield definitive data about a possible direct effect of SNP c.*1908C>T on susceptibility to infection and led us to consider its linkage disequilibrium with the causative variant. A more exhaustive genetic association study including all putative, functional SNPs from this gene and subsequent functional analyses needs to be conducted to achieve a more complete understanding of how different variants of NOD2 may affect susceptibility to MAP infection in cattle.  相似文献   
117.
118.
Pancreatic cancer has a dismal prognosis and to date there are no targeted therapies for this malignancy. Using shotgun proteomics, the mRNA binding protein cold shock domain containing E1 (CSDE1), also called upstream‐of‐N‐Ras, is detected in pancreatic cancer cell lines but not in normal pancreatic epithelial cells. The expression of CSDE1 in pancreatic cancer cells is confirmed by Western blotting and immunohistochemistry of human pancreatic tumors. In vitro functional assays show that siRNA downregulation of CSDE1 or gene knockout using CRISPR‐Cas9 significantly reduce the invasiveness of pancreatic cancer cells. Together, this study reveals that CSDE1 is overexpressed in pancreatic cancer and is a potential therapeutic target to inhibit pancreatic cancer cell invasion.  相似文献   
119.
During the scale‐up of a bioprocess, not all characteristics of the process can be kept constant throughout the different scales. This typically results in increased mixing times with increasing reactor volumes. The poor mixing leads in turn to the formation of concentration gradients throughout the reactor and exposes cells to varying external conditions based on their location in the bioreactor. This can affect process performance and complicate process scale‐up. Scale‐down simulators, which aim at replicating the large‐scale environment, expose the cells to changing environmental conditions. This has the potential to reveal adaptation mechanisms, which cells are using to adjust to rapidly fluctuating environmental conditions and can identify possible root causes for difficulties maintaining similar process performance at different scales. This understanding is of utmost importance in process validation. Additionally, these simulators also have the potential to be used for selecting cells, which are most robust when encountering changing extracellular conditions. The aim of this review is to summarize recent work in this interesting and promising area with the focus on mammalian bioprocesses, since microbial processes have been extensively reviewed.  相似文献   
120.
Large‐scale bioreactors for the production of monoclonal antibodies reach volumes of up to 25 000 L. With increasing bioreactor size, mixing is however affected negatively, resulting in the formation of gradients throughout the reactor. These gradients can adversely affect process performance at large scale. Since mammalian cells are sensitive to changes in pH, this study investigated the effects of pH gradients on process performance. A 2‐Compartment System was established for this purpose to expose only a fraction of the cell population to pH excursions and thereby mimicking a large‐scale bioreactor. Cells were exposed to repeated pH amplitudes of 0.4 units (pH 7.3), which resulted in decreased viable cell counts, as well as the inhibition of the lactate metabolic shift. These effects were furthermore accompanied by increased absolute lactate levels. Continuous assessment of molecular attributes of the expressed target protein revealed that subunit assembly or N‐glycosylation patterns were only slightly influenced by the pH excursions. The exposure of more cells to the same pH amplitudes further impaired process performance, indicating this is an important factor, which influences the impact of pH inhomogeneity. This knowledge can aid in the design of pH control strategies to minimize the effects of pH inhomogeneity in large‐scale bioreactors.  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