全文获取类型
收费全文 | 891篇 |
免费 | 81篇 |
国内免费 | 104篇 |
出版年
2024年 | 1篇 |
2023年 | 29篇 |
2022年 | 53篇 |
2021年 | 25篇 |
2020年 | 35篇 |
2019年 | 42篇 |
2018年 | 26篇 |
2017年 | 32篇 |
2016年 | 50篇 |
2015年 | 68篇 |
2014年 | 99篇 |
2013年 | 131篇 |
2012年 | 63篇 |
2011年 | 79篇 |
2010年 | 34篇 |
2009年 | 19篇 |
2008年 | 30篇 |
2007年 | 33篇 |
2006年 | 22篇 |
2005年 | 18篇 |
2004年 | 20篇 |
2003年 | 13篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 29篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有1076条查询结果,搜索用时 140 毫秒
71.
Vincent J. Lynch 《Evolution; international journal of organic evolution》2009,63(9):2457-2465
The identification of adaptations and key innovations has long interested biologists because they confer on organisms the ability to exploit previously unavailable ecological resources and respond to novel selective pressures. Although it can be extremely difficult to test for the effects of a character on the rate of lineage diversification, the convergent evolution of a character in multiple lineages provides an excellent opportunity to test for the effect of that character on lineage diversification. Here, I examine the effect of parity mode on the diversification of vipers, which have independently evolved viviparity in at least 13 lineages. I find strong statistical evidence that viviparous species diversify at a greater rate than oviparous species and correlate major decreases in the diversification rate of oviparous species with periods of global cooling, such as the Oligocene. These results suggest that the evolution of viviparity buffered live-bearing species against the negative effects of global climate change during the Cenozoic, and was a key innovation in the evolution and diversification of live-bearing vipers. 相似文献
72.
73.
Polypteriformes (or Cladistia) and Lepisosteiformes (or Ginglymodi) are two groups of freshwater fishes with ganoid scales. The earliest fossil records of these taxa are Albian (Lepisosteiformes) and Cenomanian (Polypteriformes) respectively in Gondwana; they are still extant. The 'first' appearance of the two groups in the fossil record (explosive in polypteriforms, gradual in lepisosteiforms) as well as their evolutionary mode (diversification/disparity or replacement) is described in detail. The lepisosteiforms appear to show a rapid radiation of post-Palaeozoic clades immediately upon origination, while the polypteriforms represent a counter-example with their sudden diversification and their sudden acquisition of several 'key innovations'. 相似文献
74.
Reactive oxygen species (ROS) are activators of cell signaling and modify cellular molecules, including DNA. 8-Oxo-7,8-dihydroguanine (8-oxoG) is one of the prominent lesions in oxidatively damaged DNA, whose accumulation is causally linked to various diseases and aging processes, whereas its etiological relevance is unclear. 8-OxoG is repaired by the 8-oxoguanine DNA glycosylase-1 (OGG1)-initiated DNA base excision repair (BER) pathway. OGG1 binds free 8-oxoG and this complex functions as an activator of Ras family GTPases. Here we examined whether OGG1-initiated BER is associated with the activation of Rho GTPase and mediates changes in the cytoskeleton. To test this possibility, we induced OGG1-initiated BER in cultured cells and mouse lungs and used molecular approaches such as active Rho pull-down assays, siRNA ablation of gene expression, immune blotting, and microscopic imaging. We found that OGG1 physically interacts with Rho GTPase and, in the presence of 8-oxoG base, increases Rho–GTP levels in cultured cells and lungs, which mediates α-smooth muscle actin (α-SMA) polymerization into stress fibers and increases the level of α-SMA in insoluble cellular/tissue fractions. These changes were absent in cells lacking OGG1. These unexpected data and those showing that 8-oxoG repair is a lifetime process suggest that, via Rho GTPase, OGG1 could be involved in the cytoskeletal changes and organ remodeling observed in various chronic diseases. 相似文献
75.
76.
Recently, D.J. Hall et al. reported that ethidium (E+) is formed as a major product of hydroethidine (HE) or dihydroethidium reaction with superoxide (O2−) in intact animals with low tissue oxygen levels (J. Cereb. Blood Flow Metab. 32:23–32, 2012). The authors concluded that measurement of E+ is an indicator of O2− formation in intact brains of animals. This finding is in stark contrast to previous reports using in vitro systems showing that 2-hydroxyethidium, not ethidium, is formed from the reaction between O2− and HE. Published in vivo results support the in vitro findings. In this study, we performed additional experiments in which HE oxidation products were monitored under different fluxes of O2−. Results from these experiments further reaffirm our earlier findings (H. Zhao et al., Free Radic. Biol. Med. 34:1359, 2003). We conclude that whether in vitro or in vivo, E+ measured by HPLC or by fluorescence lifetime imaging is not a diagnostic marker product for O2− reaction with HE. 相似文献
77.
分别从产业经济、医院用药及零售终端这3 个方面对2013 年中国医药行业实际现况进行统计和分析,为企业明确发展方向、确定产品研发思路及制定市场策略提供参考。 相似文献
78.
Medwayella independencia, a new species of flea, is described from the tupaiid host Urogale everetti (Thomas) from Mindanao Island, Philippines. Several other species of fleas are also recorded from the Philippines including a single male of Lentistivalius philippinensis Hastriter and Bush, 2013 (previously known only from two males), the bat fleas Thaumapsylla breviceps orientalis Smit and Thaumapsylla longiforceps Traub, a single unidentified female species of Macrostylophora Ewing collected from the murid Bullimus bagobos Mearns, and a pair of Medwayella robinsoni ssp. from Sundasciurus hoogstraali (Sanborn) from Busuanga Island, Philippines. Representatives of Medwayella Traub, 1972 and Macrostylophora have not previously been recorded from the Philippines. A key to the male sex of Medwayella is provided. Phoretic mites of the genus Psylloglyphus (family Winterschmidtiidae) were present under the abdominal sclerites of several male and female specimens of M. independencia. This is the second report of a phoretic mite on a species of Medwayella Traub. The co-evolutionary implications between phoretic mites and fleas are discussed. 相似文献
79.
We provide a general overview of features and technical specifications of an online, interactive tool for the identification of scale insects of concern to the U.S.A. ports-of-entry. Full lists of terminal taxa included in the keys (of which there are four), a list of features used in them, and a discussion of the structure of the tool are provided. We also briefly discuss the advantages of interactive keys for the identification of potential scale insect pests. The interactive key is freely accessible on http://idtools.org/id/scales/index.php 相似文献
80.