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41.
Marco Sunder 《Economics & Human Biology》2004,2(1):75-86
Average height of the free population in the United States born in the mid-1830s began to decline despite growing per capita incomes. Explanations for this "antebellum puzzle" revolve around a possibly deteriorating disease environment promoted by urban agglomeration and increases in the relative price of protein-rich foods. However, several groups were immune to the effect, including members of the middle class, whose income was high enough, and increased enough to overcome the adverse developments and maintain their nutritional status. Although at the opposite end of the social spectrum, the height of male slaves also increased, as it was in their owners' interest to raise their slaves' food allotments. The height of Tennessee convicts, analyzed in this article, also increased in the late-1830s, being the third exception to the "antebellum puzzle." Mid-19th century Tennessee was integrated into interstate commerce in cotton and tobacco and experienced considerable movement of people who would have brought with them diseases from elsewhere, hence, it would have been integrated into the US disease pool, and the fact that heights did not decline in the 1830s is therefore an indication that the antebellum puzzle cannot be explained exclusively by the spread of diseases. Yet, Tennessee's economy was quite different to that of the rest of the country. Although it did export live swine to the South, these exports did not increase during the antebellum decades. Hence, Tennessee remained self-sufficient in pork, and consumption of pork did not decline. Thus, the evidence presented here is consistent with the economic interpretation of the "antebellum puzzle": self-sufficiency in protein production protected even the members of the lower-classes of Tennessee from the negative externalities associated with the onset of industrialization. 相似文献
42.
John Prenter Robert W. Elwood W. Ian Montgomery 《Evolution; international journal of organic evolution》1999,53(6):1987-1994
We investigate the association between female reproductive investment, absolute size, and sexual size dimorphism in spiders to test the predictions of the fecundity-advantage hypothesis. The relationships between absolute size and sexual size dimorphism and aspects of female reproductive output are examined in comparative analyses using phylogenetically independent contrasts. We provide support for the idea that allometry for sexual dimorphism is the result of variation in female size more so than male size. Regression analyses suggest selection for increased fecundity in females. We argue that fecundity selection provides the only general explanation for the evolution of sexual size dimorphism in spiders. 相似文献
43.
The arrangement of resources in patchy landscapes: effects on distribution, survival, and resource acquisition of chironomids 总被引:3,自引:0,他引:3
The spatial arrangement of resources in patchy habitats influences the distribution of individuals and their ability to acquire
resources. We used Chironomus riparius, a ubiquitous aquatic insect that uses leaf particles as an important resource, to ask how the dispersion of resource patches
influences the distribution and resource acquisition of mobile individuals in patchy landscapes. Two experiments were conducted
in replicated laboratory landscapes (38×38 cm) created by arranging sand and leaf patches in a 5×5 grid so that the leaf patches
were either aggregated or uniformly dispersed in the grid. One-day-old C. riparius larvae were introduced into the landscapes in one of three densities (low, medium, high). In experiment 1, we sampled larvae
and pupae by coring each patch in each landscape 3, 6, 12, or 24 days after adding larvae. In experiment 2, emerging adults
were collected daily for 42 days from each patch in each landscape. In aggregated landscapes, individuals were aggregated
in one patch type or the other during a particular developmental stage, but the ”preferred” type changed depending on developmental
stage and initial density. Adult emergence was lower by about 30% in all aggregated landscapes. In dispersed landscapes, individuals
used both types of patch throughout their life cycles at all initial densities. Thus, patch arrangement influences the distribution
of mobile individuals in landscapes, and it influences resource acquisition even when average resource abundance is identical
among landscapes. Regardless of patch arrangement, high initial density caused accumulation of early instars in edge patches,
75% mortality of early instars, a 25% increase in development time, and a 60% reduction in adult emergence. Because mortality
was extremely high among early-instar larvae in high-density treatments, we do not have direct evidence that the mechanism
by which patch arrangement operates is density dependent. However, the results of our experiments strongly suggest that dispersion
of resource patches across a landscape reduces local densities by making non-resource patches available for use, thereby reducing
intraspecific competition.
Received: 20 July 1999 / Accepted: 28 January 2000 相似文献
44.
Genetic relationship between Mongolian and Norwegian horses? 总被引:3,自引:0,他引:3
Human populations of Central Asian origin have contributed genetic material to northern European populations. It is likely that migrating humans carried livestock to ensure food and ease transportation. Thus, eastern genes could also have dispersed to northern European livestock populations. Using microsatellite data, we here report that the essentially different genetic distances DA and (deltamu)2 and their corresponding phylogenetic trees show close associations between the Mongolian native horse and northern European horse breeds. The genetic distances between the northern European breeds and Standardbred/Thoroughbred, representing a southern-derived source of horses, were notably larger. We suggest that contribution of genetic material from eastern horses to northern European populations is likely to have occurred. 相似文献
45.
SÖREN NYLIN 《Physiological Entomology》2013,38(2):96-104
The ‘choice’ of whether to enter diapause or to develop directly has profound effects on the life histories of insects, and may thus have cascading consequences such as seasonal morphs and other less obvious forms of seasonal plasticity. Present knowledge of the control of diapause and seasonal morphs at the physiological and molecular levels is briefly reviewed. Examples, mainly derived from personal research (primarily on butterflies), are given as a starting point with the aim of outlining areas of research that are still poorly understood. These include: the role of the direction of change in photoperiod; the role of factors such as temperature and diet in modifying the photoperiodic responses; and the role of sex, parental effects and sex linkage on photoperiodic control. More generally, there is still a limited understanding of how external cues and physiological pathways regulating various traits are interconnected via gene action to form a co‐adapted complete phenotype that is adaptive in the wild despite environmental fluctuation and change. 相似文献
46.
J. A. Sulikowski † J. Kneebone S. Elzey J. Jurek ‡ W. H. Howell P. C. W. Tsang § 《Journal of fish biology》2006,69(5):1449-1465
Age at size was linked to sexual maturity in 77 male and 93 female thorny skates Amblyraja radiata from the western Gulf of Maine using three criteria: 1) gross reproductive morphology, 2) histology and 3) steroid hormone concentrations. Age-bias plots and the coefficient of variation from vertebral band counts suggested that the ageing method represented a non-biased and precise approach to the age assessment of A. radiata . Maturity ogives for males, based on data gathered for clasper length, circulating testosterone concentrations and proportion of mature spermatocysts within the testes, predicted that 50% maturity occurred at a total length ( L T ) of 865 mm and c. 10·90 years of age. For females, maturity ogives, based on data gathered for ovary mass, shell gland mass, follicle size and circulating oestradiol concentrations, predicted that 50% maturity occurred at 875 mm L T and c. 11·00 years of age. Collectively, the results suggest that analysis of several contemporaneous reproductive variables offers an accurate determination of sexual maturity in the thorny skate. 相似文献
47.
Holocene vegetation history of the Sahel: pollen, sedimentological and geochemical data from Jikariya Lake, north-eastern Nigeria 总被引:1,自引:0,他引:1
Aim This study aims to separate regional and local controls on Holocene vegetation development and examine how well pollen records reflect climate change in a semi‐arid region. The relative importance of climate and human activity as agents of vegetation change in the Sahel during the late Holocene is also considered. Location Jikariya Lake, an inter‐dune depression in the Manga Grasslands of north‐eastern Nigeria. Methods Pollen and charcoal were used to provide a record of Holocene vegetation history. Palaeoclimate and hydrological changes were reconstructed from sedimentary and geochemical data. Regional and local influences were separated by comparing the evidence obtained from Jikariya Lake with previously published data from the Manga Grasslands. Results The Manga Grasslands experienced a prolonged wet period during the early and mid‐Holocene, during which swamp forest vegetation with Guinean affinities (Alchornea, Syzygium, Uapaca) occupied the inter‐dune depressions. However, variation in the pollen records between sites suggests that their establishment was dependent on conditions being locally favourable, rather than being directly coupled to regional climate. The pollen records from the Manga Grasslands are more consistent in suggesting the colonization of the dunefields by trees associated with Sudanian savanna (Combretaceae, Detarium) c. 8700 cal. yr bp . The Jikariya Lake pollen data are in accordance with the sedimentological and geochemical data from the region in indicating that the onset of arid conditions occurred progressively during the late Holocene (from c. 4700 cal. yr bp ). Abrupt changes in pollen stratigraphy, recorded at other Manga Grasslands sites 3500 cal. yr bp , appear to be the product of the local passing of ecological thresholds. The dunefield vegetation (Sahelian savanna) appears to have been resilient to (or at least palynologically silent regarding) to the climatic variability of the late Holocene. Main conclusions While climate appears to have been the primary control on vegetation development in the Manga Grasslands during the Holocene, local conditions (particularly depression size and sand influx) had a strong influence on the timing of pollen stratigraphic changes. Anthropogenic influences are difficult to detect, even during the late Holocene. 相似文献
48.
49.
Joseph H. Manson 《Human nature (Hawthorne, N.Y.)》1998,9(2):97-117
The human “environment of evolutionary adaptedness” can only be inferred indirectly. In contrast, the behavior of some nonhuman
animals can be compared among “natural” and various altered environments. As an example, male immigration tactics in unprovisioned
versus provisioned macaque (Macaca) populations are compared using Tooby and Cosmides’s (1992) framework for evolutionary functional analysis. In unprovisioned
populations, social groups contain few males, and immigrant male takeovers of alpha rank occur frequently. In provisioned
populations, groups contain many males, and males almost invariably enter social groups at very low rank and rise in rank
only as more dominant males emigrate or die. Male conformity to the “seniority rule” is hypothesized to represent the behavioral
output of an evolved decision-making algorithm (psychological mechanism) that takes into account (1) the net payoff of each
rank in the dominance hierarchy and (2) the power of male group size as a predictor of the likelihood of successful immigrant
takeover.
Joseph H. Manson is Assistant Professor of Anthropology at the University of California, Los Angeles. His research interests
are social relationships in nonhuman primates and humans, with particular emphases on mate choice, courtship tactics, intrasexual
competition, and (currently) mother-infant relationships and infant handling. He has conducted fieldwork on rhesus macaques
at Cayo Santiago and white-faced capuchins in Costa Rica. 相似文献
50.
Using field surveys and experimental infections, we investigated the influence of a trematode parasite on life history traits
of adult Lymnaea elodes snails. We found that parasitism significantly affected the growth, fecundity, and survival of host snails. Within five of
the six natural L. elodes populations we sampled, shell length of echinostome-infected hosts was significantly greater than for uninfected conspecifics.
Furthermore, we show that gigantism occurs among experimentally infected snails due to an accelerated growth rate and size-selective
mortality following an Echinostoma revolutum infection. The fecundity of infected snails sharply decreased beginning at 3 weeks post exposure (PE) and all egg production
eventually ceased for most hosts by 5–6 weeks PE. Energy constraints, imposed by parasite development, alter the host energy
budget. Early in the infection, parasite depletion of host energy reserves reduces host reproduction, but sufficient resources
remain to allow accelerated host growth. Mortality was increased among host snails at two distinct stages: shortly after exposure
and several weeks after cercariae were first released. We did not observe tissue degradation in snails during the first 4
weeks after exposure to the parasite, but destruction of host tissues was noted among snails dying later in the infection.
Received: 5 September 1997 / Accepted: 19 November 1997 相似文献