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1.
Andrea J Webster Andy Purvis 《Proceedings. Biological sciences / The Royal Society》2002,269(1487):143-149
Many methods are available for estimating ancestral values of continuous characteristics, but little is known about how well these methods perform. Here we compare six methods: linear parsimony, squared-change parsimony, one-parameter maximum likelihood (Brownian motion), two-parameter maximum likelihood (Ornstein-Uhlenbeck process), and independent comparisons with and without branch-length information. We apply these methods to data from 20 morphospecies of Pleistocene planktic Foraminifera in order to estimate ancestral size and shape variables, and compare these estimates with measurements on fossils close to the phylogenetic position of 13 ancestors. No method produced accurate estimates for any variable: estimates were consistently less good as predictors of the observed values than were the averages of the observed values. The two-parameter maximum-likelihood model consistently produces the most accurate size estimates overall. Estimation of ancestral sizes is confounded by an evolutionary trend towards increasing size. Shape showed no trend but was still estimated very poorly: we consider possible reasons. We discuss the implications of our results for the use of estimates of ancestral characteristics. 相似文献
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Sign language studies of cross-fostered chimpanzees measure the effect of special rearing conditions on the development of
very young chimpanzees. Cross-fostered chimpanzees, like human children, develop gradually in a process that takes many years.
Here we discuss details of the procedure, the overlap between human and chimpanzee infants in the contents of the first 50-item
vocabularies, and the ways in which the signs of the chimpanzees exhibit the fuzziness of natural language categories. We
also compare the cross-fostering approach with more traditional modular approaches to the study of language-like behavior
in nonhuman animals.
Project Washoe was originally supported by grants MH-12154 from the National Institute of Mental Health and GB-7432 from the
National Science Foundation. We gratefully acknowledge this support and the support that later sign language studies of chimpanzees
have received since then from NIH, NSF, the National Geographic Society, the Grant Foundation, the Spencer Foundation, the
University of Nevada, and the UNR Foundation. 相似文献
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A method for identifying cysteine-containing peptides in proteins is presented using 2-bromoacetamido-4-nitrophenol (BNP) to introduce an easily detectable probe. The formation of a covalent bond between the protein sulfhydryl group and the acetamido moiety of BNP introduces a chromophore with an absorbance maximum at 410 nm. The modified protein can then be cleaved with appropriate proteases and the resulting peptides separated by chromatographic methods. Monitoring the effluent at a single wavelength (405 nm) provides a rapid and simple method of detecting and isolating only those peptides which contain cysteine residue(s). The nitrophenol derivative is stable under conditions required for protease cleavage. The reagent is therefore useful for locating cysteine-containing peptides in protein digests and can be used to explore the accessibility of different cysteines under a variety of conditions. The ease of modification, specificity of reaction, product stability, and simple detection of modified peptides make BNP ideal for investigation of cysteine residues. 相似文献
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A neonate with aniridia was found to have a one band paracentric inversion of the short arm of chromosome 4. This was initially difficult to interpret on high resolution banding. The inversion was present in three generations of the family. 相似文献
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Plants often suffer reductions in fecundity due to insect herbivory. Whether this loss of seeds has population-level consequences
is much debated and often unknown. For many plants, particularly those with long-lived seedbanks, it is frequently asserted
that herbivores have minimal impacts on plant abundance because safe-site availability rather than absolute seed number determines
the magnitude of future plant recruitment and hence population abundance. However, empirical tests of this assertion are generally
lacking and the interplay between herbivory, spatio-temporal variability in seed- or safe-site-limited recruitment, and seedbank
dynamics is likely to be complex. Here we use a stochastic simulation model to explore how changes in the spatial and temporal
frequency of seed-limited recruitment, the strength of density-dependent seedling survival, and longevity of seeds in the
soil influence the population response to herbivory. Model output reveals several surprising results. First, given a seedbank,
herbivores can have substantial effects on mean population abundance even if recruitment is primarily safe-site-limited in
either time or space. Second, increasing seedbank longevity increases the population effects of herbivory, because annual
reductions in seed input due to herbivory are accumulated in the seedbank. Third, population impacts of herbivory are robust
even in the face of moderately strong density-dependent seedling mortality. These results imply that the conditions under
which herbivores influence plant population dynamics may be more widespread than heretofore expected. Experiments are now
needed to test these predictions.
Received: 3 November 1999 / Accepted: 15 February 2000 相似文献