全文获取类型
收费全文 | 4391篇 |
免费 | 424篇 |
国内免费 | 87篇 |
出版年
2024年 | 12篇 |
2023年 | 86篇 |
2022年 | 71篇 |
2021年 | 147篇 |
2020年 | 191篇 |
2019年 | 219篇 |
2018年 | 194篇 |
2017年 | 193篇 |
2016年 | 246篇 |
2015年 | 302篇 |
2014年 | 287篇 |
2013年 | 440篇 |
2012年 | 168篇 |
2011年 | 224篇 |
2010年 | 186篇 |
2009年 | 223篇 |
2008年 | 229篇 |
2007年 | 199篇 |
2006年 | 131篇 |
2005年 | 106篇 |
2004年 | 112篇 |
2003年 | 97篇 |
2002年 | 99篇 |
2001年 | 69篇 |
2000年 | 54篇 |
1999年 | 67篇 |
1998年 | 54篇 |
1997年 | 52篇 |
1996年 | 58篇 |
1995年 | 33篇 |
1994年 | 47篇 |
1993年 | 38篇 |
1992年 | 30篇 |
1991年 | 29篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 10篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1970年 | 1篇 |
排序方式: 共有4902条查询结果,搜索用时 46 毫秒
61.
Summary Colonies and nests ofApoica pallens in the llanos region of Venezuela range from small foundress nests to large mature colonies. Nests are sited on small diameter, near-horizontal branches in a variety of shrub and tree species. During the day, adult wasps cluster on the face of the nest in an array that seems to be determined by orientation to gravity; defense of the colony against parasitoids and ants by the resting wasps may be more a passive than an active behavior. Wasps fan their wings to cool the colony during the day, but no foraging for water accompanies the fanning behavior. Nightly foraging activity begins with the explosive departure from the nest of hundreds of wasps, most of which rapidly return. Moderate foraging levels early at night give way to very low foraging levels in pre-dawn hours. The period of moderate foraging may be extended for longer hours during increased moonlight. Foraging wasps collect arthropod provisions for larvae. Larvae produce a trophallactic saliva; adults engage in inter-adult trophallaxis; brood are cannibalized. During cluster formation prior to swarm emigration, adult wasps do not appear to scent-mark substrates such as leaves. Instead,A. pallens exhibits a calling behavior, unique among polistine wasps studied to date, in which the gaster is held rigidly away from the thorax and metasomal sternal glands are exposed. Swarms can emigrate during the day.A. pallens may incorporate absconding and colony relocation as features of its colony cycle in the highly seasonal llanos. 相似文献
62.
Today, the search for new energy sources continues unabated throughout the North. At the same time, scientists are increasingly concerned over the degradation of the Arctic and sub-Arctic environment stemming from fossil fuel and other large-scale energy projects already underway. Similar apprehensions are expressed by indigenous peoples who have often suffered from the impact of such development. While the most dramatic evidence of environmental devastation and social disruption is found in the Russian North, serious problems are by no means confined to that area alone. Nor are these negative effects necessarily limited to the borders of the country in which they originated. Indeed, the deleterious environmental impact of our global industrial economy has become sufficiently profound that social analysts are beginning to ask whether development strategies that cause such harm to the Arctic and sub-Arctic region should continue; and if not, what should replace them. This article addresses these issues as they relate to questions of sustainability, equity, political empowerment, and human rights in northwest Siberia and northern North America. 相似文献
63.
QUANTITATIVE BEHAVIORAL STUDY OF BOTTLENOSE DOLPHINS IN SWIM-WITH-DOLPHIN PROGRAMS IN THE UNITED STATES 总被引:1,自引:0,他引:1
The behavior of dolphins in four Swim-With-Dolphin programs was compared by type of Swim encounter, defined by the presence ("Controlled") or absence ("Not-Controlled") of explicit trainer regulation of interactions between dolphins and human swimmers. Dolphin-swimmer interactions involving aggressive, submissive, or sexual behavior were designated as "high-risk" in the Swim context; sexual behavior was included as high-risk based on analyses that demonstrated co-occurrence of sexual and agonistic behaviors. High-risk activity comprised a substantial proportion of dolphin-swimmer social activity during Not-Controlled Swims. In contrast, high-risk activity rarely occurred during Controlled Swims, even though agonistic and sexual behaviors were normal components of the same dolphins' free-time social repertoire. These results indicated that direct trainer control of dolphin-swimmer interactions virtually eliminated high-risk activity from the Swim context, and thereby diminished the potential for dolphin distress, swimmer injury, and rejection of dolphins from Swim programs due to swimmer injury. This study illustrates effective use of quantitative behavioral sampling techniques for evaluation of captive management concerns and promotes broader use of these techniques for a better understanding of cetacean behavior. 相似文献
64.
M A Campbell C J Handley V C Hascall R A Campbell D A Lowther 《Archives of biochemistry and biophysics》1984,234(1):275-289
Proteoglycans in cultures of adult bovine articular cartilage labeled with [35S]sulfate after 5 days in culture and maintained in medium containing 20% fetal calf X serum had longer half-lives (average 11 days) compared with those of the same tissue maintained in medium alone (average 6 days). The half-lives of proteoglycans in cultures of calf cartilage labeled after 5 days in culture and maintained in medium with serum were considerably longer (average 21 days) compared to adult cartilage. If 0.5 mM cycloheximide was added to the medium of cultures of adult cartilage, or the tissue was maintained at 4 degrees C after labeling, the half-lives of the proteoglycans were greater, 24 and greater than 300 days, respectively. Analyses of the radiolabeled proteoglycans remaining in the matrix of the tissue immediately after labeling the tissue and at various times in culture revealed two main populations of proteoglycans; a large species eluting with Kav of 0.21-0.24 on Sepharose CL-2B, of high bouyant density and able to form aggregates with hyaluronate, and a small species eluting with a Kav of 0.63-0.70 on Sepharose CL-2B, of low buoyant density, containing only chondroitin sulfate chains, and unable to form aggregates with hyaluronate. The larger proteoglycan had shorter half-lives than the smaller proteoglycan; in cartilage maintained with serum, the half-lives were 9.8 and 14.5 days, respectively. Labeling cartilage with both [3H]leucine and [35S]sulfate showed the small proteoglycan to be a separate synthetic product. The size distribution of 35S-labeled proteoglycans lost into the medium was shown to be polydisperse on Sepharose CL-2B, the majority eluting with a Kav of 0.27 to 0.35, of high buoyant density, and unable to aggregate with hyaluronate. The size distribution of glycosaminoglycans from 35S-labeled proteoglycans appearing in the medium did not differ from that associated with labeled proteoglycans remaining in the matrix. 相似文献
65.
The effect of Type I interferon on bone resorption was studied by measuring its effect on parathormone-stimulated calcium release from neonatal murine calvaria in vitro. A pure human recombinant leukocyte interferon hybrid of the A and D subtypes was used, which has high antiviral activity on mouse cells. Calcium release was inhibited in a dose dependent fashion with 50% inhibition at about 10(-10) M or 600 U/ml, and the inhibition was reversible. The presence of interferon was required before or during the activation phase of the resorptive response, when the formation of osteoclasts from precursor cells would occur. When added to actively resorbing bone it had no effect. The data suggest that Type I interferon can inhibit the parathormone-regulated development of active osteoclasts, possibly by inhibiting osteoclast precursor differentiation. 相似文献
66.
Female transfer in primates 总被引:3,自引:0,他引:3
Jim Moore 《International journal of primatology》1984,5(6):537-589
Intergroup transfer by males is nearly universal among social primates. Furthermore, among the most frequently studied monkeys-savanna
baboons and Japanese and rhesus macaques—females typically remain in their natal groups, so troops are composed of related
matrilines. These facts strongly support two major theories: (l) that kin selection is a powerful force in patterning sociality
(if one is to live in a group, one should prefer a group of one’s relatives); and (2) that the ultimate explanation for intergroup
transfer is the avoidance of inbreeding depression (though both sexes would prefer to live with kin, one sex has to disperse
to avoid inbreeding and for a variety of reasons the losing sex is generally male). Substantial rates of transfer by females
in social species with routine male transfer would cast doubt on both ideas. In fact, evidence reviewed here indicates that
female transfer is not unusual and among folivorous primates (e.g., Alouatta,the Colobinae) it seems to be routine. In addition to casting doubt on the demographic significance of inbreeding avoidance
and favoring mutualistic and/or game theory interpretations of behavior over nepotistic ones, this finding supports the hypothesis
that predator detection is the primary selective pressure favoring sociality for many primates. Finally, while female bonding [sensuWrangham, R. W. (1980), Behaviour75:262–299] among primates appears to be less common than generally believed, the observed correlation between female transfer
and morphological adaptations to folivory provides empirical support for Wrangham’s model for the evolution of female-bonded
groups. 相似文献
67.
Robert Wasserstrom 《Human ecology: an interdisciplinary journal》1978,6(2):127-143
In a recent work on the Tzotzil (Maya) of Chiapas, Mexico, George Collier has suggested that indigenous groups frequently employ agricultural practices which are in obvious disequilibrium with their environment. As a result, he claims, such groups bring about the permanent destruction of their lands and forests. In this article, historical and demographic evidence is presented to demonstrate that the development of commencal agriculture outside of native communities, not overpopulation or technological conservatism within them, lies at the heart of such destruction. Finally, it is argued that anthropologists must consider the evolution of social classes in rural areas if they are to understand the difficulties which economic development entails. 相似文献
68.
69.
The behavior of orang-utans (Pongo pygmaeus)was observed in two captive groups (one adult group, one juvenile group). Activity profiles,animal interactions, and compartmental spatial use for both adult-group and juvenile-group individuals were recorded over
a 9-month period. Behavioral repertoires for both groups included large amounts of social activity. Equivalent amounts of
social activity were found for each group. The social behavior of juvenile animals involved more active behavior such as play.
The social behavior of the adult animals was more subtle, involving social monitoring and allogrooming. These results indicate
that orangutans, at least when group-living in captivity, exhibit the potential to display social behavior which is apparently
of greater frequency and complexity than that which has been observed in the wild. These findings suggest that the solitary
behavior of wild orangutans is not a necessary characteristic of orangutan behavior. Under different environmental conditions
orangutans appear to readily adapt socially, and, like other nonhuman primates,they have the capacity to exhibit complex and subtle social behavior.
This report is based on part of a senior thesis submitted by Sara D. Edwards 相似文献
70.
C. M. Berman 《International journal of primatology》1980,1(2):153-170
Several aspects of agonistic experience are described for freeranging infant rhesus monkeys (Macaca mulatta)on Cayo Santiago. Even before infants are fully integrated with peers in rank dominance based on maternal ranks,infants of highranking mothers tend to be threatened less frequently by other members of the group and are less likely to
be threatened by unfamiliar individuals than are infants of lowranking mothers. There is no evidence that fearful interactions
between pairs of infants are related to their mother’s ranks before 22 weeks of age. However, an imperfect hierarchy can be
constructed for infants between 27 and 30 weeks of age. At this age,infants of higherranking mothers are also more likely to receive protection when threatened than are infants of lowerranking
mothers. When protected, their protectors are less likely to emit fearful gestures to the infants’ threatener. Close female
relatives appear to play a large role in the protection of infants and may be more directly responsible for the differences
described above than the mother, other relatives, or other highranking members of the group. It is suggested that more than
one mechanism, including intervention by the mother and by close female relatives,may be important in rank acquisition among peers. 相似文献