全文获取类型
收费全文 | 1456篇 |
免费 | 111篇 |
国内免费 | 2篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 21篇 |
2021年 | 42篇 |
2020年 | 25篇 |
2019年 | 23篇 |
2018年 | 38篇 |
2017年 | 27篇 |
2016年 | 51篇 |
2015年 | 106篇 |
2014年 | 96篇 |
2013年 | 107篇 |
2012年 | 182篇 |
2011年 | 141篇 |
2010年 | 88篇 |
2009年 | 58篇 |
2008年 | 99篇 |
2007年 | 88篇 |
2006年 | 77篇 |
2005年 | 60篇 |
2004年 | 61篇 |
2003年 | 54篇 |
2002年 | 38篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1569条查询结果,搜索用时 15 毫秒
221.
The cranchiid Teuthowenia pellucida, like many deep-sea squid species, possesses large eyes that maximise light sensitivity in a nearly aphotic environment. To assess ontogenetic changes in the visual system, we conducted morphometric and histological analyses of the eyes using specimens from New Zealand collections. While the ratio between eye diameter and mantle length maintained a linear relationship throughout development, histological sections of the retina revealed that the outer photoreceptor layer became proportionally longer as the animal aged, coincident with a habitat shift into deeper, darker ocean strata. Other retinal layers maintained the same absolute thickness as was observed in paralarvae. Granules of the pigment ommin, normally located in the screening layer positioned at the base of the photoreceptors, were also observed at the outer end of the photoreceptor segments throughout the retina in young and mid-sized specimens. Early developmental stages of this species, dwelling in shallow waters, may therefore rely on migratory ommin to help shield photoreceptors from excess light and prevent over-stimulation. The oldest, deeper-dwelling specimens of T. pellucida examined had longer photoreceptors, and little or no migrated ommin was observed; we suggest therefore that short-term adaptive mechanisms for bright light conditions may be used primarily during epipelagic, early life stages in this species. 相似文献
222.
Fabienna Arends Constantin Nowald Kerstin Pflieger Kathrin Boettcher Stefan Zahler Oliver Lieleg 《PloS one》2015,10(2)
The migration of cells within a three-dimensional extracellular matrix (ECM) depends sensitively on the biochemical and biophysical properties of the matrix. An example for a biological ECM is given by reconstituted basal lamina gels purified from the Engelbreth-Holm-Swarm sarcoma of mice. Here, we compare four different commercial variants of this ECM, which have all been purified according to the same protocol. Nevertheless, in those gels, we detect strong differences in the migration behavior of leukocyte cells as well as in the Brownian motion of nanoparticles. We show that these differences correlate with the mechanical properties and the microarchitecture of the gels which in turn arise from small variations in their biochemical composition. 相似文献
223.
Bioprocess and Biosystems Engineering - Polymersomes are hollow, spherical vesicles that are surrounded by a polymer membrane. The applied polymer must be amphiphilic to promote self-assembly in... 相似文献
224.
225.
Nathan D. Mathewson Orr Ashenberg Itay Tirosh Simon Gritsch Elizabeth M. Perez Sascha Marx Livnat Jerby-Arnon Rony Chanoch-Myers Toshiro Hara Alyssa R. Richman Yoshinaga Ito Jason Pyrdol Mirco Friedrich Kathrin Schumann Michael J. Poitras Prafulla C. Gokhale L. Nicolas Gonzalez Castro Marni E. Shore Kai W. Wucherpfennig 《Cell》2021,184(5):1281-1298.e26
- Download : Download high-res image (226KB)
- Download : Download full-size image
226.
227.
Ann-Katrin Hopp Federico Teloni Lavinia Bisceglie Corentin Gondrand Fabio Raith Kathrin Nowak Lukas Muskalla Anna Howald Patrick G.A. Pedrioli Kai Johnsson Matthias Altmeyer Deena M. Leslie Pedrioli Michael O. Hottiger 《Molecular cell》2021,81(2):340-354.e5
- Download : Download high-res image (198KB)
- Download : Download full-size image
228.
Kathrin F. Stanger Barbara S. Coffman M. Kay Izard 《American journal of primatology》1995,36(3):223-237
Most nocturnal Malagasy primates, as well as many diurnal species, are highly endangered in their natural habitat. Captive breeding programs have been established for many species, but detailed information on reproduction is only available for three nocturnal taxa: the mouse lemur (Microcebus murinus), the dwarf lemur (Cheirogaleus medius), and the greater dwarf lemur (Cheirogaleus major). In this study, we present data for another nocturnal Malagasy primate, Coquerel's dwarf lemur (Mirza coquereli), which has been propagated since 1982 at the Duke University Primate Center. Unlike all other Malagasy primates bred in captivity, M. coquereli cycles throughout the year, and is clearly less seasonal in its birth distribution than is C. medius or M. murinus. Estrous intervals ranged between 19 and 30.5 days. Estrus lasted no longer than 1 day. After an average gestation length of 89.2 days, litters of one or two were born. Females cycled for the first time between 8 and 15 months of age, and gave birth for the first time between 12.8 and 33.5 months of age. The earliest mating of a male leading to conception was observed at the age of 17 months. For males and females, an increase in daylength appears to trigger pubertal development. Males had seasonal changes in testicular volume which were not explained by covariation with body weight. Maximum testis size occurred in spring, when breeding activity was highest. The occurrence of year-round reproduction in M. coquereli, and the absence of seasonal fattening and/or hibernation, along with their specialized winter diet, may be correlated. © 1995 Wiley-Liss, Inc. 相似文献
229.
230.
Simone S. Riedel Congcong Lu Hongbo M. Xie Kevin Nestler Marit W. Vermunt Alexandra Lenard Laura Bennett Nancy A. Speck Ichiro Hanamura Julie A. Lessard Gerd A. Blobel Benjamin A. Garcia Kathrin M. Bernt 《Molecular cell》2021,81(11):2332-2348.e9
- Download : Download high-res image (137KB)
- Download : Download full-size image