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   788篇
  免费   44篇
  2023年   2篇
  2022年   2篇
  2021年   15篇
  2020年   3篇
  2019年   9篇
  2018年   9篇
  2017年   9篇
  2016年   16篇
  2015年   23篇
  2014年   37篇
  2013年   42篇
  2012年   54篇
  2011年   52篇
  2010年   25篇
  2009年   26篇
  2008年   58篇
  2007年   42篇
  2006年   41篇
  2005年   56篇
  2004年   57篇
  2003年   38篇
  2002年   46篇
  2001年   15篇
  2000年   10篇
  1999年   18篇
  1998年   9篇
  1997年   8篇
  1996年   4篇
  1995年   10篇
  1994年   2篇
  1993年   2篇
  1992年   10篇
  1991年   10篇
  1990年   2篇
  1989年   8篇
  1988年   3篇
  1987年   6篇
  1986年   5篇
  1985年   8篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1980年   3篇
  1979年   7篇
  1978年   3篇
  1977年   4篇
  1976年   4篇
  1975年   3篇
  1963年   1篇
  1962年   1篇
排序方式: 共有832条查询结果,搜索用时 703 毫秒
801.
Regenerating islet-derived protein (Reg)3β belongs to a member of the Reg family of proteins and has pleiotropic functions, including antimicrobial activity and tissue repair. However, whether Reg3β plays a protective role in the development of colitis and ileitis has not been fully investigated. We generated transgenic mice expressing a short form of cellular FLICE-inhibitory protein (cFLIPs) that promotes necroptosis, a regulated form of cell death. cFLIPs transgenic (CFLARs Tg) mice develop severe ileitis in utero. Although Reg3β is undetectable in the small intestine of wild-type embryos, its expression is aberrantly elevated in the small intestine of CFLARs Tg embryos. To test whether elevated Reg3β attenuates or exacerbates ileitis in CFLARs Tg mice, we generated a Reg3b?/? strain. Reg3b?/? mice grew to adulthood without apparent abnormalities. Deletion of Reg3b in CFLARs Tg mice exacerbated the embryonic lethality of CFLARs Tg mice. Dextran sulfate sodium-induced colitis, characterized by body weight loss and infiltration of neutrophils, was exacerbated in Reg3b?/? compared to wild-type mice. Moreover, the expression of Interleukin 6, an inflammatory cytokine and Chitinase-like 3, a marker for tissue repair macrophages was elevated in the colon of Reg3b?/? mice compared to wild-type mice after DSS treatment. Together, these results suggest that attenuation of colitis and ileitis is a result of Reg3β′s real function.  相似文献   
802.
The formation of vascular structures requires precisely controlled proliferation of endothelial cells (ECs), which occurs through strict regulation of the cell cycle. However, the mechanism by which EC proliferation is coordinated during vascular formation remains largely unknown, since a method of analyzing cell-cycle progression of ECs in living animals has been lacking. Thus, we devised a novel system allowing the cell-cycle progression of ECs to be visualized in vivo. To achieve this aim, we generated a transgenic zebrafish line that expresses zFucci (zebrafish fluorescent ubiquitination-based cell cycle indicator) specifically in ECs (an EC-zFucci Tg line). We first assessed whether this system works by labeling the S phase ECs with EdU, then performing time-lapse imaging analyses and, finally, examining the effects of cell-cycle inhibitors. Employing the EC-zFucci Tg line, we analyzed the cell-cycle progression of ECs during vascular development in different regions and at different time points and found that ECs proliferate actively in the developing vasculature. The proliferation of ECs also contributes to the elongation of newly formed blood vessels. While ECs divide during elongation in intersegmental vessels, ECs proliferate in the primordial hindbrain channel to serve as an EC reservoir and migrate into basilar and central arteries, thereby contributing to new blood vessel formation. Furthermore, while EC proliferation is not essential for the formation of the basic framework structures of intersegmental and caudal vessels, it appears to be required for full maturation of these vessels. In addition, venous ECs mainly proliferate in the late stage of vascular development, whereas arterial ECs become quiescent at this stage. Thus, we anticipate that the EC-zFucci Tg line can serve as a tool for detailed studies of the proliferation of ECs in various forms of vascular development in vivo.  相似文献   
803.
1. Tryptophan was administered to rats under various nutritional conditions: fasted for 24 hr, fasted and refed with glucose or corn-oil, fasted and administered glycerol intramuscularly, and nonfasted. 2. The changes in the contents of glycolytic intermediates in the livers indicated that the phosphoenolpyruvate carboxykinase [EC 4.1.1.32] reaction is inhibited by tryptophan administration in all groups of rats. The inversely related changes in the contents of malate and phosphoenolpyruvate were associated with the accumulation of quinolinate in the livers. The content of quinolinate which exhibited the half-maximal effect on the contents of both metabolites was 0.1-0.2 mumole per g liver. 3. The rate of incorporation of 3H from 3H2O into the total hepatic fatty acids was increased about 2-fold by the administration of this amino acid to the fasted rats. The enhancement of the rate was closely related to the increase in the citrate content. The hyperlipogenesis was also related to the decrease of acetyl-CoA and the increase of malonyl-CoA. The content of long-chain acyl-CoA was not affected. These effects of tryptophan administration on the hepatic fatty acid metabolism were found in all groups of rats. The liver content of glycerol 3-phosphate was decreased by tryptophan administration was markedly increased by glycerol injection. The injection of glycerol into the control and the tryptophan-treated rats produced a marked increase of glycerol 3-phosphate but did not affect the rate of fatty acid synthesis in the livers of either group. 4. It may be concluded that, in the livers of rats under various nutritional conditions, the short-term control of fatty acid synthesis by tryptophan administration is most likely due to the activation of acetyl-coenzyme A carboxylase [EC 6.4.1.2] by citrate.  相似文献   
804.
Journal of Plant Research - To understand genetic diversity in focal species, it is important to consider the possibility of speciation with gene flow, especially in species with porous genomes...  相似文献   
805.
In the Joetsu region of central Honshu, Japan, snow lies on the ground 2–3 m deep from January to February every year. To test the effects of snow cover on the social and foraging behaviors of the great tit (Parus major Linnaeus) in the region, the following parameters were compared between the pre-snowy period (November and December) and the snowy period (January and February) at the individual level: population size, monospecific flock size and the stability of its membership, home range size, attendance rate with mixed-species flocks, and foraging height. Great tits lived alone or in pairs, but often joined mixed-species flocks. Throughout the study period, individuals exhibited strong site fidelity, which resulted in a stable population size. Neither the size of a monospecific flock nor its membership was affected by snow cover. The home range expanded when birds joined mixed-species flocks during both periods. Birds more frequently joined mixed-species flocks during the snowy period, and the size of mixed-species flocks was significantly larger than during the pre-snowy period. During the snowy period, birds shifted their foraging position from the ground to the upper parts of trees. They also used the upper parts of trees when they joined mixed-species flocks. These results suggest that the intraspecific sociality of great tits is relatively insensitive to snow cover, but that the home range size and foraging positions are affected by joining mixed-species flocks, rather than by snow cover.  相似文献   
806.
The purpose of this commentary is to provide information on the present status of the racemate/enantiomer debate in Japan and current industrial and regulatory attitudes to chiral drugs in Japan. It provides an update of our previous paper (Shindo and Caldwell, Chirality 3:91–93, 1991), and the interested reader is referred to this for background information. © 1995 Wiley-Liss, Inc.  相似文献   
807.
In total, 404 variants resistant to the antimicrotubule agent benomyl were isolated from UV-irradiated oidia of the basidiomyceteCoprinus cinereus. Part of the variants showed, in addition to benomyl resistance, heat sensitivity or heat dependence. Fifteen variants selected on the basis of different phenotypes were subjected to further analyses. All of the 15 variations were due to single-gene mutations, and the mutations comprised four groups (benA, benB, benC, andbenD) in terms of genetic linkage. Some of the 15 mutations affected nuclear migration in dikaryosis and/or fruiting processes.  相似文献   
808.
We aimed to determine the coacervation properties of high-molecular-weight (HMW) tissue-derived elastin (TDE) and to examine the potential use of TDE particles as a cosmetic biomaterial. TDE solutions were filtered and divided into three fractions (1–3) according to the molecular weight of the elastin. The turbidity of fraction 2, which contained a large portion (58%) of HMW elastin polypeptides (>100 kDa), was measured under several pH values (3.0–11.0) and NaCl concentrations (0–1000 mM) to examine its coacervation ability. HMW TDE exhibited coacervation under the physiological conditions (temperature, pH, and NaCl concentration) of the skin surface. We performed inclusion and release experiments using three model chemicals with different molecular weights and measured the size and zeta potential of the fraction 3 particles to investigate the suitability of HMW elastin polypeptides. Fraction 3, which contained a larger portion (64%) of HMW elastin polypeptides, displayed a strong coacervation property at a phase transition temperature of 19.8 ± 0.1°C. The inclusion ratio of the model chemical Biebrich Scarlet (BS) with a molecular weight of <600 was approximately 92.1 ± 0.7%. The release profiles of BS from the particles linearly increased and reached a plateau after 15 days. Moreover, the average size of the particles with BS was 474.2 ± 24.6 nm. The low-molecular-weight (LMW) elastin peptides have moisturizing and whitening functions for the skin. We concluded that TDE, as a mixture of HMW polypeptides and LMW peptides, can potentially serve as a multifunctional and effective cosmetic biomaterial.  相似文献   
809.
810.
Matsumoto  Asako K. 《Hydrobiologia》2004,530(1-3):389-397
Melithaea flabellifera (Kükenthal, 1909) (Octocorallia, Gorgonacea), an endemic and predominant gorgonian in Japanese shallow waters, grows mostly in one plane and ramifies in a dichotomous way. The growth rates of all branches and of the colony were measured from photographs of tagged gorgonian corals for approximately 1 year from June 1995 to May 1996 on the western Pacific coast of Japan (34° 39′ N, 138° 56′ E). The most rapid growth occurred when the water temperature was less than 20 °C. Mean growth ranged from 2.9 to 11.4 mm year−1. Linear growth of individual branches ranged between −30.4 and 24.8 mm year -1−1. Both seasonal and non-seasonal variations in growth rate were observed in each colony. When branches were lost, the adjacent branches grew faster, filling the open space in the fan. Heterogeneity in growth rate within a colony was partly caused by this compensatory growth. This indicates that the regular branching pattern of gorgonians is due to irregular and heterogeneous growth. The compensatory growth suggests that M. flabellifera is constrained by some potential optimal size or form.  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