全文获取类型
收费全文 | 1274篇 |
免费 | 154篇 |
出版年
2023年 | 13篇 |
2022年 | 16篇 |
2021年 | 28篇 |
2020年 | 18篇 |
2019年 | 35篇 |
2018年 | 22篇 |
2017年 | 24篇 |
2016年 | 35篇 |
2015年 | 63篇 |
2014年 | 67篇 |
2013年 | 92篇 |
2012年 | 92篇 |
2011年 | 80篇 |
2010年 | 56篇 |
2009年 | 40篇 |
2008年 | 73篇 |
2007年 | 77篇 |
2006年 | 74篇 |
2005年 | 82篇 |
2004年 | 64篇 |
2003年 | 58篇 |
2002年 | 40篇 |
2001年 | 27篇 |
2000年 | 14篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1979年 | 12篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1972年 | 9篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1969年 | 6篇 |
1967年 | 5篇 |
排序方式: 共有1428条查询结果,搜索用时 281 毫秒
1.
2.
Sexually selected infanticide is an important source of infant mortality in many mammalian species. In species with long-term male-female associations, females may benefit from male protection against infanticidal outsiders. We tested whether mountain gorilla (Gorilla beringei beringei) mothers in single and multi-male groups monitored by the Dian Fossey Gorilla Fund’s Karisoke Research Center actively facilitated interactions between their infants and a potentially protective male. We also evaluated the criteria mothers in multi-male groups used to choose a preferred male social partner. In single male groups, where infanticide risk and paternity certainty are high, females with infants <1 year old spent more time near and affiliated more with males than females without young infants. In multi-male groups, where infanticide rates and paternity certainty are lower, mothers with new infants exhibited few behavioral changes toward males. The sole notable change was that females with young infants proportionally increased their time near males they previously spent little time near when compared to males they had previously preferred, perhaps to encourage paternity uncertainty and deter aggression. Rank was a much better predictor of females’ social partner choice than paternity. Older infants (2–3 years) in multi-male groups mirrored their mothers’ preferences for individual male social partners; 89% spent the most time in close proximity to the male their mother had spent the most time near when they were <1 year old. Observed discrepancies between female behavior in single and multi-male groups likely reflect different levels of postpartum intersexual conflict; in groups where paternity certainty and infanticide risk are both high, male-female interests align and females behave accordingly. This highlights the importance of considering individual and group-level variation when evaluating intersexual conflict across the reproductive cycle. 相似文献
3.
Myriam R. Hirt Marlee Tucker Thomas Müller Benjamin Rosenbaum Ulrich Brose 《Ecology and evolution》2020,10(14):7094-7105
- Realized trophic niches of predators are often characterized along a one‐dimensional range in predator–prey body mass ratios. This prey range is constrained by an “energy limit” and a “subdue limit” toward small and large prey, respectively. Besides these body mass ratios, maximum speed is an additional key component in most predator–prey interactions.
- Here, we extend the concept of a one‐dimensional prey range to a two‐dimensional prey space by incorporating a hump‐shaped speed‐body mass relation. This new “speed limit” additionally constrains trophic niches of predators toward fast prey.
- To test this concept of two‐dimensional prey spaces for different hunting strategies (pursuit, group, and ambush predation), we synthesized data on 63 terrestrial mammalian predator–prey interactions, their body masses, and maximum speeds.
- We found that pursuit predators hunt smaller and slower prey, whereas group hunters focus on larger but mostly slower prey and ambushers are more flexible. Group hunters and ambushers have evolved different strategies to occupy a similar trophic niche that avoids competition with pursuit predators. Moreover, our concept suggests energetic optima of these hunting strategies along a body mass axis and thereby provides mechanistic explanations for why there are no small group hunters (referred to as “micro‐lions”) or mega‐carnivores (referred to as “mega‐cheetahs”).
- Our results demonstrate that advancing the concept of prey ranges to prey spaces by adding the new dimension of speed will foster a new and mechanistic understanding of predator trophic niches and improve our predictions of predator–prey interactions, food web structure, and ecosystem functions.
4.
5.
6.
The bias due to incomplete matching 总被引:8,自引:0,他引:8
Observational studies comparing groups of treated and control units are often used to estimate the effects caused by treatments. Matching is a method for sampling a large reservoir of potential controls to produce a control group of modest size that is ostensibly similar to the treated group. In practice, there is a trade-off between the desires to find matches for all treated units and to obtain matched treated-control pairs that are extremely similar to each other. We derive expressions for the bias in the average matched pair difference due to the failure to match all treated units--incomplete matching, and the failure to obtain exact matches--inexact matching. A practical example shows that the bias due to incomplete matching can be severe, and moreover, can be avoided entirely by using an appropriate multivariate nearest available matching algorithm, which, in the example, leaves only a small residual bias due to inexact matching. 相似文献
7.
Nataly Mancette Rijensky Netta R. Blondheim Shraga Eilon Barnea Nir Peled Eli Rosenbaum Aron Popovtzer Solomon M. Stemmer Alejandro Livoff Mark Shlapobersky Neta Moskovits Dafna Perry Eitan Rubin Itzhak Haviv Arie Admon 《Molecular & cellular proteomics : MCP》2020,19(8):1360-1374
Highlights
- •Sufficient tumor tissues are often unavailable large HLA peptidome discovery.
- •Using patient derived xenograft (PDX) tumors can overcome this limitation.
- •The large PDX HLA peptidomes expand significantly those of the original biopsies.
- •The HLA peptidomes of the PDX tumors included many tumor antigens.
8.
Chlamydomonas alpha-tubulin is posttranslationally modified by acetylation on the epsilon-amino group of a lysine 总被引:25,自引:0,他引:25
Previous work has shown that the principal alpha-tubulin within Chlamydomonas reinhardtii flagellar axonemes differs from the major alpha-tubulin in the cell body. These two variants of alpha-tubulin are related to one another since posttranslational modification of the cell body form converts it to the axonemal form. When flagella are induced to assemble in the absence of de novo protein synthesis, tritiated acetate can be used to posttranslationally label alpha-tubulin in vivo, and under these conditions, no other flagellar polypeptides exhibit detectable labeling [L'Hernault, S. W., & Rosenbaum, J. L. (1983) J. Cell Biol. 97, 258-263]. In the present report, this labeling method has been used to provide material for chemical analysis of the tritiated moiety that is posttranslationally added to flagellar alpha-tubulin. This radioactivity was volatile after acid hydrolysis, suggesting that the posttranslational modification is the addition of neither an amino acid nor carbohydrate. Treatment of posttranslationally 3H-labeled alpha-tubulin with hydrazine yields radioactive acetylhydrazine, indicating that the moiety involved in posttranslational modification is an acetyl group. Analysis of complete proteolytic digests by thin-layer chromatography has revealed that this acetyl group is located on the epsilon-amino group of a flagellar alpha-tubulin lysine residue. 相似文献
9.
10.