全文获取类型
收费全文 | 6651篇 |
免费 | 517篇 |
国内免费 | 457篇 |
专业分类
7625篇 |
出版年
2024年 | 32篇 |
2023年 | 109篇 |
2022年 | 159篇 |
2021年 | 248篇 |
2020年 | 235篇 |
2019年 | 267篇 |
2018年 | 228篇 |
2017年 | 207篇 |
2016年 | 238篇 |
2015年 | 227篇 |
2014年 | 247篇 |
2013年 | 361篇 |
2012年 | 229篇 |
2011年 | 260篇 |
2010年 | 218篇 |
2009年 | 304篇 |
2008年 | 337篇 |
2007年 | 374篇 |
2006年 | 305篇 |
2005年 | 284篇 |
2004年 | 221篇 |
2003年 | 225篇 |
2002年 | 224篇 |
2001年 | 167篇 |
2000年 | 144篇 |
1999年 | 141篇 |
1998年 | 149篇 |
1997年 | 147篇 |
1996年 | 150篇 |
1995年 | 120篇 |
1994年 | 120篇 |
1993年 | 99篇 |
1992年 | 100篇 |
1991年 | 118篇 |
1990年 | 77篇 |
1989年 | 91篇 |
1988年 | 54篇 |
1987年 | 53篇 |
1986年 | 61篇 |
1985年 | 56篇 |
1984年 | 45篇 |
1983年 | 42篇 |
1982年 | 46篇 |
1981年 | 27篇 |
1980年 | 29篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有7625条查询结果,搜索用时 15 毫秒
71.
Using data for 27 Texas counties from 1978-1987, it is shown that the incidence rates of suicide, homicide, and rape are significantly higher in counties whose drinking water supplies contain little or no lithium than in counties with water lithium levels ranging from 70-170 micrograms/L; the differences remain statistically significant (p less than 0.01) after corrections for population density. The corresponding associations with the incidence rates of robbery, burglary, and theft were statistically significant with p less than 0.05. These results suggest that lithium has moderating effects on suicidal and violent criminal behavior at levels that may be encountered in municipal water supplies. Comparisons of drinking water lithium levels, in the respective Texas counties, with the incidences of arrests for possession of opium, cocaine, and their derivatives (morphine, heroin, and codeine) from 1981-1986 also produced statistically significant inverse associations, whereas no significant or consistent associations were observed with the reported arrest rates for possession of marijuana, driving under the influence of alcohol, and drunkenness. These results suggest that lithium at low dosage levels has a generally beneficial effect on human behavior, which may be associated with the functions of lithium as a nutritionally-essential trace element. Subject to confirmation by controlled experiments with high-risk populations, increasing the human lithium intakes by supplementation, or the lithiation of drinking water is suggested as a possible means of crime, suicide, and drug-dependency reduction at the individual and community level. 相似文献
72.
John C. Mitani 《International journal of primatology》1990,11(5):411-424
Demographic processes and the structure of a population of agile gibbons (Hylobates agilis) were investigated over 6 years in the Gunung Palung Reserve, Indonesia. Estimates of population size, density, and biomass revealed a population whose groups were stable in size and composition. Demographic processes place gibbons at risk, however, to short-term changes in their environment. Patterns of survival, fecundity, mortality, and dispersal combined to produce negative rates of growth. In addition, a top-heavy age-class distribution, with adults forming a large fraction of animals, makes it unlikely that this population could recover rapidly from a decline in numbers. Two behavioral factors, territoriality and monogamy, account for the size and stability of gibbon groups. Monogamy imposes limits on group size, while mating patterns and territoriality decrease the impact of sources of high mortality common in other primate species. These relationships underscore the fundamental importance of behavioral influence on demographic processes and social structure. 相似文献
73.
Effect of CryIC toxin from Bacillus thuringiensis on larval feeding behavior of Spodoptera exigua 总被引:1,自引:0,他引:1
Mariano Berdegué John T. Trumble William J. Moar 《Entomologia Experimentalis et Applicata》1996,80(2):389-401
The lack of data on the effect of Bacillus thuringiensis (B.t.) toxins on larval feeding behavior of the pest Spodoptera exigua (Hübner) (Noctuidae: Amphypyrini) prompted us to investigate the effect of three delivery systems of CryIC, a commercial formulation, inclusion bodies, and the activated CryIC toxin. The commercial formulation was the least and CryIC toxin the most lethal form to neonates of susceptible colonies. All but two of the treatments in choice tests with neonates and third instars showed significant avoidance of B.t. treated diet, with greater proportion of larvae from susceptible (UCR-S and AUBURN-S) and resistant (AUBURN-R) colonies on untreated diet than on diet treated with any of the CryIC forms and concentrations tested. Furthermore, third instars consumed significantly more control than treated diet for all CryIC forms, colonies and concentrations. The avoidance of CryIC toxin by neonates and third instars strongly suggests that CryIC, which also is present in the commercial formulation and in the inclusion bodies, is responsible for eliciting avoidance behavior by S. exigua larvae. Behavioral observations of third instars in a no-choice test on either treated or control diet indicated that questing behavior in susceptible larvae appears to be positively related with presence of CryIC toxin in the diet. Furthermore, resistant third instars were on the whole more active than susceptible thirds on both treated and control diet. Resistant thirds raised on CryIC treated diet (AUBURN-RC) spent more time eating treated diet than resistant larvae raised on control diet (AUBURN-R), suggesting that diet conditioning plays an important role on feeding behavior of S. exigua. The implications of these results are discussed. 相似文献
74.
Lisa Gould 《International journal of primatology》1996,17(3):331-347
I examined the vigilance behavior of adult males and females in two groups of ring-tailed lemurs(Lemur catta)during the birth and lactation season at the Beza-Mahafaly Reserve, southwestern Madagascar. I found no sex difference with
respect to the rates of overall vigilance, rates of vigilance toward a potential predator or unfamiliar sound, or rates of
vigilance toward conspecifics from other social groups, nor were there sex differences in the percentage of time spent vigilant
in any of the above categories. Higher-ranking females were vigilant significantly more often toward predators or potential
predators than lower-ranking females were. I detected no relationship between vigilance behavior and dominance rank among
adult males. The alpha female in each group exhibited significantly more vigilance behavior than all other members of her
group. It was predicted that males should exhibit more vigilance behavior than females do, particularly during the birth and
lactation season, when predator pressure is high, if they are benefiting females in this respect. I discuss the results in
the context of this prediction and in terms of how ring-tailed lemur males benefit females, and why they may be tolerated
in social groups. 相似文献
75.
Observations of the potto (Perodicticus potto),a nocturnal prosimian primate,indicated a limited behavioral repertoire and prompted renovation of their exhibit at the Frankin Park Zoo (Boston, MA). We
used the natural history of this species to direct the exhibit modifications, which used only nonsynthetic items. We added
live plants, soil, bamboo, shelf fungi, grapevines, a hollow tree, and a log containing an insect dispenser to the exhibit
at little expense. They provided new textures, odors, pathways, stimulation and cover for this secretive species. The changes
produced a heightened aesthetic appeal to the nocturnal exhibit and improved its educational value by representing the animals’
habitat more accurately. The exhibit modifications also resulted in a significant increase in activity, an expansion of the
pottos’ behavioral repertoire,the emergence of sexual behaviors, and an increased visibility to the public. 相似文献
76.
Mike H. Jurke 《Primates; journal of primatology》1996,37(1):109-119
The fate of most nonhuman primate species is intimately related to man. The increasing encroachment on the natural habitat
has resulted in the decimation and even near extinction of some species. Along with this development, the basic concept in
many modern zoos has changed from one of merely display to self-perpetuating units. Primate research facilities are orienting
their research programs towards reproductive physiology and behavior in an effort to provide basic knowledge of reproduction
in these species. This increased emphasis in the area of reproductive biology and the various efforts to improve breeding
of these mostly endangered primates in captivity has stimulated the author to write this review. It represents an attempt
to provide the reader with basic background information relating to the endocrinology and behavior of reproduction in the
clawed New World monkeys as it exists at the time of publication.
The intermediate evolutionary position ofCallimico goeldii between the clawed New World monkeys and the ‘true New World monkeys’ and our relatively poor knowledge about reproduction
and behavior in this particular species fully justifies the focus on Goeldi’s monkey in this essay. This review is an attempt
to provide a brief history of previous studies but also the basis for research in the future. The current status of knowledge
of the small-bodied clawed monkeys is also discussed in an evolutionary context, with an emphasis on the different reproductive
strategies in this dynamic group of primates.
The outcome, not surprisingly, confirms the unique position ofCallimico goeldii in its social, ecological, and evolutionary environment. 相似文献
77.
Behavioral strategies of aphid hyperparasitoids to escape aggression by honeydew-collecting ants 总被引:2,自引:0,他引:2
We analyzed the behavioral interactions between two species of honeydew-collecting ants (Lasius niger, Myrmica laevinodis) and foraging females of four species of aphid hyperparasitoids (Aphidencyrtus aphidivorus, Dendrocerus carpenteri, Pachyneuron aphidis, Asaphes vulgaris) usingAphis fabae ssp.cirsiiacanthoidis andLysiphlebus cardui on thistles as aphid and primary parasitoid, respectively. The observed interaction patterns and foraging parameters varied within hyperparasitoid species and revealed different strategies based upon behavioral and morphological constraints.D. carpenteri generally tried to avoid ant encounters. This avoidance strategy was successful in interactions withM. laevinodis but failed when encountering the more aggressiveL. niger, which caused about 26% adult mortality. In contrast,A. aphidivorus, P. aphidis, andA. vulgaris possess jumping ability and were hardly exposed to mortality risks. The escape reaction jump off was used as soon as ants made physical contact with foraging females. While the flight strategy ofP. aphidis is connected with cryptic movement patterns without avoidance behavior,A. aphidivorus first avoided ants and jumped off only as a last resort. Similar patterns, but less expressive, are displayed byA. vulgaris. We suggest that these different strategies are responsible for different foraging success in ant-attended resources in field. 相似文献
78.
Ronald J. Prokopy Ratana Poramarcom Manon Sutantawong Ranu Dokmaihom Jorge Hendrichs 《Journal of Insect Behavior》1996,9(1):133-142
Oriental fruit flies,Bactrocera dorsalis, cultured in the laboratory for six generations, were released when 12–14 days old in an orchard of nonfruiting host trees that were furnished with either food and water, nonpunctured host fruit, punctured host fruit, or no resources. Nearly all flies of both sexes, all sexual behavior of males, and all mating pairs were observed on trees with fruit. Moreover, on trees with fruit, nearly all flies of both sexes, nearly all sexual behavior of males, and nearly all mating pairs occurred on the fruit itself rather than on the foliage or branches. In a subsequent test, both sexes were found to be strongly attracted to the odor of host fruit. For a polyphagous species of a tropical tephritid, these findings are the first to show a high level of male aggregation and a high amount of male sexual behavior on the fruit of host trees. Findings are discussed in relation to current knowledge of tephritid mating behavior. An additional quality-control test for laboratory cultured males used in the sterile insect technique of fly management is recommended. 相似文献
79.
J. P. Michaud 《Journal of Insect Behavior》1996,9(5):683-694
Two-day-old mated females ofAphidius ervi Haliday andMonoctonus paulensis (Ashmead) were each provided with two sequential host patches. Patches were comprised of plastic petri dishes containing either 15 pea aphids,Acyrthosiphum pisum (Harris), or 15 alfalfa aphids,Macrosiphum creelii Davis. Both wasp species parasitized more hosts in patches containing pea aphids than in those containing alfalfa aphids, regardless of sequence. Females ofA. ervi also laid more eggs per aphid in patches containing pea aphids than in patches containing alfalfa aphids. When both patches contained alfalfa aphids,M. paulensis females parsitized more aphids in the second patch than in the first. Fewer alfalfa aphids were parasitized in the second patch when the first patch contained pea aphids, and fewer eggs were laid per alfalfa aphid. Parasitoid females of both species exhibited consistently higher rates of oviposition into their preferred host species and adjusted their reproductive allocation to hosts and host patches as a function of their experience in previous patches. 相似文献
80.
A group of serotonergic cells, located in the pedal ganglia ofHelix lucorum, modulates synaptic responses of neurons involved in withdrawal behavior. Extracellular or intracellular stimulation of these
serotonergic cells leads to facilitation of spike responses to noxious stimuli in the putative command neurons for withdrawal
behavior. Noxious tactile stimuli elicit an increase in background spiking frequency in the modulatory neurons and a corresponding
increase in stimulus-evoked spike responses in withdrawal interneurons. The serotonergic neurons have processes in the neuropil
of the parieto-visceral ganglia complex, consistent with their putative role in modulating the activity of giant parietal
interneurons, which send processes to the same neuropil and to the pedal ganglia. The serotonergic cells respond to noxious
tactile and chemical stimuli. Although the group as a whole respond to noxious stimuli applied to any part of the body, most
cells respond more to ipsilateral than contralateral stimulation, and exhibit differences in receptive areas. Intracellular
investigation revealed electrical coupling between serotonergic neurons which could underlie the recruitment of members of
the group not responding to a given noxious stimulus. 相似文献