全文获取类型
收费全文 | 1882篇 |
免费 | 152篇 |
国内免费 | 1篇 |
出版年
2022年 | 21篇 |
2021年 | 31篇 |
2020年 | 14篇 |
2019年 | 18篇 |
2018年 | 27篇 |
2017年 | 37篇 |
2016年 | 55篇 |
2015年 | 65篇 |
2014年 | 80篇 |
2013年 | 117篇 |
2012年 | 114篇 |
2011年 | 140篇 |
2010年 | 75篇 |
2009年 | 81篇 |
2008年 | 109篇 |
2007年 | 110篇 |
2006年 | 92篇 |
2005年 | 93篇 |
2004年 | 89篇 |
2003年 | 81篇 |
2002年 | 69篇 |
2001年 | 28篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 31篇 |
1997年 | 18篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 16篇 |
1982年 | 9篇 |
1980年 | 13篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1975年 | 7篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1971年 | 7篇 |
1968年 | 6篇 |
1939年 | 6篇 |
排序方式: 共有2035条查询结果,搜索用时 296 毫秒
41.
42.
43.
The spindle is a microtubule-based structure that facilitates chromosome segregation during mitosis and meiosis. Spindle assembly from dynamic microtubule building blocks is a major challenge for the dividing cell and a process that critically requires microtubule motors. In this review we focus on the mechanisms by which microtubule motors shape the spindle. Specifically, we address how motors are thought to move and arrange microtubules to form the characteristic bipolar morphology shared by all eukaryotic spindles as well as motor-dependent mechanisms of microtubule length regulation. 相似文献
44.
Andrew J. MacDonald Sofie McComb Craig ONeill Kerry A. Padgett Ashley E. Larsen 《Global Change Biology》2020,26(10):5459-5474
Global environmental change is having profound effects on the ecology of infectious disease systems, which are widely anticipated to become more pronounced under future climate and land use change. Arthropod vectors of disease are particularly sensitive to changes in abiotic conditions such as temperature and moisture availability. Recent research has focused on shifting environmental suitability for, and geographic distribution of, vector species under projected climate change scenarios. However, shifts in seasonal activity patterns, or phenology, may also have dramatic consequences for human exposure risk, local vector abundance and pathogen transmission dynamics. Moreover, changes in land use are likely to alter human–vector contact rates in ways that models of changing climate suitability are unlikely to capture. Here we used climate and land use projections for California coupled with seasonal species distribution models to explore the response of the western blacklegged tick (Ixodes pacificus), the primary Lyme disease vector in western North America, to projected climate and land use change. Specifically, we investigated how environmental suitability for tick host‐seeking changes seasonally, how the magnitude and direction of changing seasonal suitability differs regionally across California, and how land use change shifts human tick‐encounter risk across the state. We found vector responses to changing climate and land use vary regionally within California under different future scenarios. Under a hotter, drier scenario and more extreme land use change, the duration and extent of seasonal host‐seeking activity increases in northern California, but declines in the south. In contrast, under a hotter, wetter scenario seasonal host‐seeking declines in northern California, but increases in the south. Notably, regardless of future scenario, projected increases in developed land adjacent to current human population centers substantially increase potential human–vector encounter risk across the state. These results highlight regional variability and potential nonlinearity in the response of disease vectors to environmental change. 相似文献
45.
Charles D. Waters Jeffrey J. Hard David E. Fast Curtis M. Knudsen William J. Bosch Kerry A. Naish 《Molecular ecology》2020,29(4):658-672
Genomic approaches permit direct estimation of inbreeding and its effect on fitness. We used genomic‐based estimates of inbreeding to investigate their relationship with eight adult traits in a captive‐reared Pacific salmonid that is released into the wild. Estimates were also used to determine whether alternative broodstock management approaches reduced risks of inbreeding. Specifically, 1,100 unlinked restriction‐site associated (RAD) loci were used to compare pairwise relatedness, derived from a relationship matrix, and individual inbreeding, estimated by comparing observed and expected homozygosity, across four generations in two hatchery lines of Chinook salmon that were derived from the same source. The lines are managed as “integrated” with the founding wild stock, with ongoing gene flow, and as “segregated” with no gene flow. While relatedness and inbreeding increased in the first generation of both lines, possibly due to population subdivision caused by hatchery initiation, the integrated line had significantly lower levels in some subsequent generations (relatedness: F2–F4; inbreeding F2). Generally, inbreeding was similar between the lines despite large differences in effective numbers of breeders. Inbreeding did not affect fecundity, reproductive effort, return timing, fork length, weight, condition factor, and daily growth coefficient. However, it delayed spawn timing by 1.75 days per one standard deviation increase in F (~0.16). The results indicate that integrated management may reduce inbreeding but also suggest that it is relatively low in a small, segregated hatchery population that maximized number of breeders. Our findings demonstrate the utility of genomics to monitor inbreeding under alternative management strategies in captive breeding programs. 相似文献
46.
Evolutionary Ecology - Understanding how environmental conditions affect trait expression in animals is important for estimating the evolutionary potential of that trait. Two different mechanisms... 相似文献
47.
Andrew D. Stephens Cory W. Quammen Binny Chang Julian Haase Russell M. Taylor II Kerry Bloom 《Molecular biology of the cell》2013,24(24):3909-3919
In mitosis, the pericentromere is organized into a spring composed of cohesin, condensin, and a rosette of intramolecular chromatin loops. Cohesin and condensin are enriched in the pericentromere, with spatially distinct patterns of localization. Using model convolution of computer simulations, we deduce the mechanistic consequences of their spatial segregation. Condensin lies proximal to the spindle axis, whereas cohesin is radially displaced from condensin and the interpolar microtubules. The histone deacetylase Sir2 is responsible for the axial position of condensin, while the radial displacement of chromatin loops dictates the position of cohesin. The heterogeneity in distribution of condensin is most accurately modeled by clusters along the spindle axis. In contrast, cohesin is evenly distributed (barrel of 500-nm width × 550-nm length). Models of cohesin gradients that decay from the centromere or sister cohesin axis, as previously suggested, do not match experimental images. The fine structures of cohesin and condensin deduced with subpixel localization accuracy reveal critical features of how these complexes mold pericentric chromatin into a functional spring. 相似文献
48.
Adam J. Golman Kerry A. Danelson James P. Gaewsky 《Computer methods in biomechanics and biomedical engineering》2013,16(10):1044-1055
This study's purpose was to implement injury metrics into the Total Human Model for Safety (THUMS) mirroring the spinal accelerometers, rib accelerometers and chest band instrumentation from two lateral post-mortem human subject sled test configurations. In both sled configurations, THUMS contacted a flat rigid surface (either a wall or beam) at 6.7 m/s. Sled A maximum simulated wall forces for the thorax, abdomen and pelvis were 7.1, 5.0 and 10.0 kN versus 5.7 ± 0.8, 3.4 ± 1.2 and 6.2 ± 2.7 kN experimentally. Sled B maximum simulated beam forces for the torso and pelvis were 8.0 and 7.6 kN versus 8.5 ± 0.2 and 7.9 ± 2.5 kN experimentally. Quantitatively, force magnitude contributed more to variation between simulated and experimental forces than phase shift. Acceleration-based injury metrics were within one standard deviation of experimental means except for the lower spine in the rigid wall sled test. These validated metrics will be useful for quantifying occupant loading conditions and calculating injury risks in various loading configurations. 相似文献
49.
50.