全文获取类型
收费全文 | 2750篇 |
免费 | 295篇 |
出版年
2023年 | 17篇 |
2022年 | 25篇 |
2021年 | 71篇 |
2020年 | 32篇 |
2019年 | 44篇 |
2018年 | 53篇 |
2017年 | 49篇 |
2016年 | 88篇 |
2015年 | 168篇 |
2014年 | 167篇 |
2013年 | 163篇 |
2012年 | 245篇 |
2011年 | 202篇 |
2010年 | 125篇 |
2009年 | 115篇 |
2008年 | 145篇 |
2007年 | 165篇 |
2006年 | 134篇 |
2005年 | 151篇 |
2004年 | 110篇 |
2003年 | 106篇 |
2002年 | 125篇 |
2001年 | 37篇 |
2000年 | 32篇 |
1999年 | 34篇 |
1998年 | 28篇 |
1997年 | 18篇 |
1996年 | 30篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 31篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 19篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1974年 | 6篇 |
1973年 | 10篇 |
1969年 | 7篇 |
1967年 | 6篇 |
1962年 | 6篇 |
排序方式: 共有3045条查询结果,搜索用时 15 毫秒
1.
2.
Gray Flycatchers (Empidonax wrightii) breed in a variety of habitats in the arid and semi‐arid regions of the western United States, but little is known about their breeding biology, especially in the northern portion of their range where they nest in ponderosa pine (Pinus ponderosa) forests. From May to July 2014 and 2015, we conducted surveys for singing male Gray Flycatchers along the eastern slope of the Cascade Range in Washington, U.S.A, monitored flycatcher nests, and quantified nest‐site vegetation. We used a logistic‐exposure model fit within a Bayesian framework to model the daily survival probability of flycatcher nests. During the 2 yr of our study, we monitored 141 nests, with 93% in ponderosa pines. Mean clutch size was 3.6 eggs and the mean number of young fledged per nest was 3.2. Predation accounted for 90% of failed nests. We found a positive association between daily nest survival and both nest height and distance of nest substrates from the nearest tree. Flycatchers that locate their nests higher above the ground and further from adjacent trees may be choosing the safest alternative because higher nests may be less exposed to terrestrial predators and nests in trees that are farther from other trees may be less exposed to arboreal predators such as jays (Corvidae) that may forage in patches with connected canopies. Nests in trees farther from other trees may also allow earlier detection of approaching predators and thus aid in nest defense. 相似文献
3.
4.
5.
6.
S D Kroll J Chen M De Vivo D J Carty A Buku R T Premont R Iyengar 《The Journal of biological chemistry》1992,267(32):23183-23188
7.
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
8.
9.
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
10.
An extended hamstring V-Y myocutaneous advancement flap is described that may be used to cover unusually large defects in the ischial region. Technical points that allow a large amount of flap advancement are discussed. Because of its large size, the flap can be raised and used on repeated occasions to repair defects from recurrent ischial pressure sores. Two patients are presented in whom the same flap was used repeatedly on multiple occasions, demonstrating the potential for preservation of future options in such patients when this flap is used. 相似文献