全文获取类型
收费全文 | 2501篇 |
免费 | 268篇 |
专业分类
2769篇 |
出版年
2023年 | 19篇 |
2022年 | 30篇 |
2021年 | 68篇 |
2020年 | 32篇 |
2019年 | 44篇 |
2018年 | 52篇 |
2017年 | 42篇 |
2016年 | 84篇 |
2015年 | 161篇 |
2014年 | 161篇 |
2013年 | 152篇 |
2012年 | 229篇 |
2011年 | 185篇 |
2010年 | 124篇 |
2009年 | 102篇 |
2008年 | 138篇 |
2007年 | 159篇 |
2006年 | 129篇 |
2005年 | 142篇 |
2004年 | 108篇 |
2003年 | 97篇 |
2002年 | 117篇 |
2001年 | 22篇 |
2000年 | 16篇 |
1999年 | 20篇 |
1998年 | 25篇 |
1997年 | 16篇 |
1996年 | 23篇 |
1995年 | 13篇 |
1994年 | 17篇 |
1993年 | 10篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1970年 | 7篇 |
1969年 | 8篇 |
排序方式: 共有2769条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Johannes Schwerk Mario K?ster Hansj?rg Hauser Manfred Rohde Marcus Fulde Mathias W. Hornef Tobias May 《PloS one》2013,8(8)
Cell lines derived from the small intestine that reflect authentic properties of the originating intestinal epithelium are of high value for studies on mucosal immunology and host microbial homeostasis. A novel immortalization procedure was applied to generate continuously proliferating cell lines from murine E19 embryonic small intestinal tissue. The obtained cell lines form a tight and polarized epithelial cell layer, display characteristic tight junction, microvilli and surface protein expression and generate increasing transepithelial electrical resistance during in vitro culture. Significant up-regulation of Cxcl2 and Cxcl5 chemokine expression upon exposure to defined microbial innate immune stimuli and endogenous cytokines is observed. Cell lines were also generated from a transgenic interferon reporter (Mx2-Luciferase) mouse, allowing reporter technology-based quantification of the cellular response to type I and III interferon. Thus, the newly created cell lines mimic properties of the natural epithelium and can be used for diverse studies including testing of the absorption of drug candidates. The reproducibility of the method to create such cell lines from wild type and transgenic mice provides a new tool to study molecular and cellular processes of the epithelial barrier. 相似文献
5.
6.
P. Higgins R. J. Mathias 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,74(4):439-444
Summary Calli were initiated from immature embryos of nine lines of hexaploid wheat (Triticum aestivum L. em. Thell). These were the euploid lines Chinese Spring and Cappelle-Desprez, a line of Chinese Spring ditelocentric for the long arm of 4B, four substitution lines of Chinese Spring in which chromosome 4B has been replaced by its homologues from different wheat varieties and substituted into Chinese Spring and a substitution line of Besostaya I 4B into Cappelle-Desprez. The calli from these lines were found to differ in their growth rates and morphogenic and regenerative activities. The substitution of different 4B chromosomes into Chinese Spring significantly increased morphogenesis and shoot regeneration from callus. The potential for developing wheat lines with improved culture characteristics is discussed. 相似文献
7.
Prostaglandin synthesis shows dependence on lipid hydroperoxides and resultant oxygen derived radical formation. In view of the importance of dietary copper in cytosolic copper dependent superoxide dismutase (Cu/Zn SOD) activity and the role of SOD in oxygen radical formation, the influence of dietary copper on prostacylin (PGI2) synthesis and SOD activity in rat aorta was examined. Copper deficient (0.5 micrograms Cu/g diet) rats showed a significant 47% reduction in PGI2 synthesis rates by aortic ring incubations in comparison to copper adequate (6.0 micrograms Cu/g diet) animals. Aortic SOD activity was reduced by 46% in copper deficiency in comparison to copper adequate animals. Marginal dietary copper (1.6 micrograms Cu/g diet) significantly reduced aortic SOD activity by 32% but was without effect on aortic ring incubation PGI2 synthesis. These results indicate that dietary copper deficiency, and the resultant decrease in SOD activity, depresses aortic PGI2 synthesis. 相似文献
8.
9.
Mathias R. Fibi Michael Bröker Rainer Schulz Roloff Johannsen Gerd Zettlmeissl 《Applied microbiology and biotechnology》1991,35(5):622-630
Summary Experiments were carried out to assess the survival of recombinant plasmid DNA during large-scale production of recombinant human erythropoietin (rhuEPO) in a fermentation pilot plant. The analyses revealed DNA-degrading activities in the fermentation broth and in the waste-water, leading to rapid destruction of plasmid DNA added to medium or waste-water. The capability of the plasmid-DNA-spiked samples to transform competent bacteria was drastically reduced. The DNA-degrading activity in the waste-waters could be blocked by addition of EDTA or by boiling, indicating the presence of DNA-degrading enzymes (DNases). No plasmid-specific DNA sequences were detected in waste-water samples by in-vitro amplification with Taqpolymerase. Genomic DNA preparations of cell debris collected from waste-water samples only contained degraded plasmid DNA. Furthermore, it was shown that intact plasmid DNA could be degraded to fragments of less than 1000 bp by incubation at 121°C for 20 min, leading to a decrease in the plasmid-specific transforming capacity by a factor of 103 per minute. Thus, DNA from the rhuEPO production pilot plant was efficiently inactivated at three different levels: (i) in the fermentation medium (DNase), (ii) in the waste-water container (DNase), and (iii) by heat inactivation for 20 min at 120°C. These results indicate that the probability of delivery of recombinant DNA into the environment is extremely low in such biotechnological production processes.
Offprint requests to: M. R. Fibi 相似文献
10.
Steady-state current flow through gap junctions. Effects on intracellular ion concentrations and fluid movement. 总被引:1,自引:1,他引:0 下载免费PDF全文
Double voltage clamp studies were performed on gap junctions contained in septal membranes of the earthworm median giant axon. The gap junctions exhibited no conductance changes in response to voltages imposed across either the septal membrane or the plasma membrane. However, the trans-septal current displayed a slow (10 s) relaxation in response to transjunctional voltage steps. The experimental evidence suggests that this relaxation is a polarization of the septum due to local accumulation/depletion of permeant ions. A theoretical analysis of this observation suggests that the applied electric field causes accumulation of impermeant anions on one side of the junction and depletion on the other, which leads to a change in concentration of permeant ions to maintain macroscopic electroneutrality. The change in concentration of permeant ions generates a transjunctional equilibrium potential that opposes junctional current flow. These results indicate that currents flowing through gap junctions can have an influence on the distribution of intracellular ions. Moreover, the theoretical analysis suggests that such currents will be accompanied by significant intracellular and intercellular water flow. 相似文献