全文获取类型
收费全文 | 1409篇 |
免费 | 76篇 |
国内免费 | 39篇 |
出版年
2024年 | 3篇 |
2023年 | 28篇 |
2022年 | 41篇 |
2021年 | 45篇 |
2020年 | 39篇 |
2019年 | 23篇 |
2018年 | 37篇 |
2017年 | 31篇 |
2016年 | 37篇 |
2015年 | 31篇 |
2014年 | 40篇 |
2013年 | 81篇 |
2012年 | 33篇 |
2011年 | 31篇 |
2010年 | 34篇 |
2009年 | 52篇 |
2008年 | 68篇 |
2007年 | 63篇 |
2006年 | 47篇 |
2005年 | 45篇 |
2004年 | 63篇 |
2003年 | 42篇 |
2002年 | 52篇 |
2001年 | 36篇 |
2000年 | 47篇 |
1999年 | 45篇 |
1998年 | 46篇 |
1997年 | 30篇 |
1996年 | 32篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 30篇 |
1987年 | 11篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有1524条查询结果,搜索用时 15 毫秒
141.
Christopher T. Dawes Jaime E. Settle Peter John Loewen Matt McGue William G. Iacono 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2015,370(1683)
Civic engagement is a classic example of a collective action problem: while civic participation improves life in the community as a whole, it is individually costly and thus there is an incentive to free ride on the actions of others. Yet, we observe significant inter-individual variation in the degree to which people are in fact civically engaged. Early accounts reconciling the theoretical prediction with empirical reality focused either on variation in individuals’ material resources or their attitudes, but recent work has turned to genetic differences between individuals. We show an underlying genetic contribution to an index of civic engagement (0.41), as well as for the individual acts of engagement of volunteering for community or public service activities (0.33), regularly contributing to charitable causes (0.28) and voting in elections (0.27). There are closer genetic relationships between donating and the other two activities; volunteering and voting are not genetically correlated. Further, we show that most of the correlation between civic engagement and both positive emotionality and verbal IQ can be attributed to genes that affect both traits. These results enrich our understanding of the way in which genetic variation may influence the wide range of collective action problems that individuals face in modern community life. 相似文献
142.
143.
We have re-investigated the organization of ocelli in honeybee workers and drones. Ocellar lenses are divided into a dorsal and a ventral part by a cusp-shaped indentation. The retina is also divided, with a ventral retina looking skywards and a dorsal retina looking at the horizon. The focal plane of lenses lies behind the retina in lateral ocelli, but within the dorsal retina in the median ocellus of both workers and drones. Ventral retinula cells are ca. 25 μm long with dense screening pigments. Dorsal retinula cells are ca. 60 μm long with sparse pigmentation mainly restricted to their proximal parts. Pairs of retinula cells form flat, non-twisting rhabdom sheets with elongated, straight, rectangular cross-sections, on average 8.7 μm long and 1 μm wide. Honeybee ocellar rhabdoms have shorter and straighter cross-sections than those recently described in the night-active bee Megalopta genalis. Across the retina, rhabdoms form a fan-shaped pattern of orientations. In each ocellus, ventral and dorsal retinula cell axons project into two separate neuropils, converging on few large neurons in the dorsal, and on many small neurons in the ventral neuropil. The divided nature of the ocelli, together with the particular construction and arrangement of rhabdoms, suggest that ocelli are not only involved in attitude control, but might also provide skylight polarization compass information. 相似文献
144.
The 12th HLPP workshop was held in conjunction with the 9th HUPO 2010 World Congress on September 20th in Sydney, Australia. This 2‐h workshop was chaired by Prof. Fuchu He (Beijing Proteome Research Center). Highlights included: (i) progress of the post‐translational modification of liver proteome; (ii) construction of the human liver protein interaction and localization maps; (iii) progress made in terms of identifying biomarker for liver diseases; and (iv) discussion on the second phase of the initiative. This was followed by a lively discussion related to the project. 相似文献
145.
Pollen is the male gametophyte of seed plants and its tube growth is essential for successful fertilization. Mounting evidence
has demonstrated that actin organization and regulation plays a central role in the process of its germination and polarized
growth. The native structures and dynamics of actin are subtly modulated by many factors among which numerous actin binding
proteins (ABPs) are the most direct and significant regulators. Upstream signals such as Ca2+, PIP2 (phosphatidylinositol-4,5-bis-phosphate) and GTPases can also indirectly act on actin organization through several ABPs.
Under such elaborate regulation, actin structures show dynamically continuous modulation to adapt to the in vivo biologic functions to mediate secretory vesicle transportation and fusion, which lead to normal growth of the pollen tube.
Many encouraging progress has been made in the connection between actin regulation and pollen tube growth in recent years.
In this review, we summarize different factors that affect actin organization in pollen tube growth and highlight relative
research progress. 相似文献
146.
Blinks and saccades cause transient interruptions of visual input. To investigate how such effects influence our perceptual
state, we analyzed the time courses of blink and saccade rates in relation to perceptual switching in the Necker cube. Both
time courses of blink and saccade rates showed peaks at different moments along the switching process. A peak in blinking
rate appeared 1,000 ms prior to the switching responses. Blinks occurring around this peak were associated with subsequent
switching to the preferred interpretation of the Necker cube. Saccade rates showed a peak 150 ms prior to the switching response.
The direction of saccades around this peak was predictive of the perceived orientation of the Necker cube afterwards. Peak
blinks were followed and peak saccades were preceded by transient parietal theta band activity indicating the changing of
the perceptual interpretation. Precisely-timed blinks, therefore, can initiate perceptual switching, and precisely-timed saccades
can facilitate an ongoing change of interpretation. 相似文献
147.
Probing the architecture, mechanism, and dynamics of genome folding is fundamental to our understanding of genome function in homeostasis and disease. Most chromosome conformation capture studies dissect the genome architecture with population‐ and time‐averaged snapshots and thus have limited capabilities to reveal 3D nuclear organization and dynamics at the single‐cell level. Here, we discuss emerging imaging techniques ranging from light microscopy to electron microscopy that enable investigation of genome folding and dynamics at high spatial and temporal resolution. Results from these studies complement genomic data, unveiling principles underlying the spatial arrangement of the genome and its potential functional links to diverse biological activities in the nucleus. 相似文献
148.
149.
Efe Pygmies in northeast Zaire exhibit features of social organization (small group size, flexible but predominantly patrilocal residence, close relations with kin, and pair bonds) that are common to many hunting and gathering societies. This study uses methods commonly employed in studies of nonhuman primates to investigate the associations of Efe men with other individuals as a function of their age, sex, and kinship, and it tests the hypothesis that Efe are patrilocal because hunting efficiency is improved by hunting with male relatives. The analyses of 376 hours of focal behavior observations on 16 Efe men and observations of 71 cooperative group hunts show that the majority of associations between Efe men were with other adult men. Men associated preferentially with kin over nonkin, and they associated with close kin more than with distant kin. Men's close relationships (what we call “Companionships” sensu Smuts' “Friendships” in baboons) were predominantly with other adult men, but each man who cohabited with a woman had his strongest Companionship by far with that woman. Neither the efficiency of hunts nor the hunting success of individual men were found to be related to the degree of relatedness of hunters nor the proportion of relatives on the hunt. Alternative hypotheses concerning the functional significance of patrilocality and male kin groups are considered. We conclude that strong affiliative bonds between male kin and between males and females may arise as much from the need for strong allies in the face of competitive social situations as from economic or ecological necessity. 相似文献
150.
Venzke D Domgall I Köcher T Féthière J Fischer S Böttcher B 《Journal of molecular biology》2005,349(3):659-669
V-ATPases are membrane protein complexes that pump protons in the lumen of various subcellular compartments at the expense of ATP. Proton pumping is done by a rotary mechanism that requires a static connection between the membrane pumping domain (V(0)) and the extrinsic catalytic head (V(1)). This static connection is composed of several known subunits of the V-ATPase, but their location and topological relationships are still a matter of controversy. Here, we propose a model for the V-ATPase of Neurospora crassa on the basis of single-particle analysis by electron microscopy. Comparison of the resulting map to that of the A-ATPase from Thermus thermophilus allows the positioning of two subunits in the static connecting region that are unique to eukaryotic V-ATPases (C and H). These two subunits seem to be located on opposite sides of a semicircular arrangement of the peripheral connecting elements, suggesting a role in stabilizing the stator in V-ATPases. 相似文献