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491.
Skeletal and comparative evidence of mortality is combined with fertility estimates for the precontact Maori population of New Zealand to determine the implied rate of precontact population growth. This rate is found to be too low to populate New Zealand within the time constraints of its prehistoric sequence, the probable founding population size, and the probable population size at contact. Rates of growth necessary to populate New Zealand within the accepted time span are calculated. The differences between this minimum necessary rate and the skeletally derived rate are too large to result solely from inadequacies in the primary data. Four alternative explanations of this conundrum are proposed: 1) skeletal evidence of precontact mortality is highly inaccurate; 2) skeletal evidence of fertility is severely underestimating actual levels; 3) there was very rapid population growth in the earliest part of the sequence up to 1150 A.D., from which no skeletal evidence currently is available; or 4) the prehistoric sequence of New Zealand may have been longer than the generally accepted 1,000-1,200 years. These alternatives are examined, and a combination of the last two is found to be the most probable. The implications of this model for New Zealand prehistory and Oceanic paleodemography are discussed. 相似文献
492.
Birth order has been examined over a wide variety of dimensions in the context of modern populations. A consistent message
has been that it is better to be born first. The analysis of birth order in this paper is different in several ways from other
investigations into birth order effects. First, we examine the effect of birth order in an egalitarian, small-scale, kin-based
society, which has not been done before. Second, we use a different outcome measure, fertility, rather than outcome measures
of social, psychological, or economic success. We find, third, that being born late in an egalitarian, technologically simple
society rather than being born early has a positive outcome on fertility, and fourth, that number of older siblings and sibling
set size are even stronger predictors of fertility, especially for males.
Patricia Draper is a professor in the Department of Anthropology at the University of Nebraska. Her research interests are
in cross-cultural human development, evolutionary theory, hunter-gatherer society, and comparative family organization.
Raymond Hames is also a professor in the Department of Anthropology at the University of Nebraska. His research interests
are in behavioral and evolutionary ecology, exchange systems, and tropical forest peoples. 相似文献
493.
The broad determinants of fertility are thought to be reasonably well identified by demographers, though the detailed quantitative drivers of fertility levels and changes are less well understood. This paper uses a novel ecological index of malaria transmission to study the effect of child mortality on fertility. We find that temporal variation in the ecology of the disease is well-correlated to mortality, and pernicious malaria conditions lead to higher fertility rates. We then argue that most of this effect occurs through child mortality, and estimate the effect of child mortality changes on fertility. Our findings add to the literature on disease and fertility, and contribute to the suggestive evidence that child mortality reductions have a causal effect on fertility changes. 相似文献
494.
M. Dujardin W. Hanna 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1984,67(2-3):197-201
Summary Microsporogenesis, reproductive behavior, pollen fertility and seed set were studied in Pennisetum
basedowii Summerhayes and C. E. Hubbard, 2n = 54; P. macrostachyum (Brough.) Trin., 2n = 54; P. macrourum Trin., 2n = 36; P. polystachion (L.) Schult, 2n = 54; and P. squamulatum Fresen 2n = 54. Meiosis was regular in P. basedowii with primarily bivalent pairing. As many as 54 univalents were observed at metaphase I in P. macrostachyum. A high frequency of univalents at metaphase I in P. macrourum resulted in lagging chromosomes and micronuclei at anaphase I and telophase I, respectively. Pennisetum polystachion and P. squamulatum showed frequent multivalent chromosome associations. Studies of megasporogenesis and embryo sac development in P. basedowii showed sexual reproduction. Pennisetum
macrostachyum was highly male sterile with predominantly aposporous apomictic embryo sac development. Pennisetum macrourum, P. polystachion, and P.
squamulatum had only aposporous embryo sac development. Seed propagated progenies of these latter three species were uniform and matromorphic, confirming the obligate apomixis nature. 相似文献
495.
Floral development in bolting garlic 总被引:5,自引:0,他引:5
Garlic (Allium sativum L.) is a completely sterile plant, propagated only vegetatively. The aim of this research was to study the sequence of morphological
processes occurring during floral initiation and development of a number of bolting garlic accessions from the Allium gene bank in Israel by using SEM. The garlic inflorescence is an umbel-like flower arrangement, the branches (flower clusters)
of which arise from a common meristem. The numerous flowers have a distinct morphology typical of the genus Allium. Flower-stalk elongation precedes the swelling of the apical meristem and its subdivision into several centers of floral development.
Within clusters, floral primordia develop unevenly. Differentiation of topsets begins after floral differentiation on the
peripheral part of the apical surface, and their size, number and rate of development vary among genotypes. At least four
morphological types differing in flower/topset ratio were distinguished among the 12 clones studied in this investigation.
For further studies of flowering physiology and fertility restoration, only clones which can differentiate the greatest proportion
of normal flowers and the least of topsets in the apical meristem should be selected.
Received: 28 June 2000 / Revision accepted: 6 November 2000 相似文献