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41.
Extrapair paternity has been observed in many formally monogamous species. Male pursuit of extrapair fertilizations is explained by the advantages of having offspring that receive essential paternal care from other males. Since females are capable of exercising a degree of control over the post-copulatory sperm competition, extrapair paternity cannot persist unless it confers fitness benefits on cuckolding females. Thus, extrapair paternity involves cooperation between mated females and extrapair males. On the other hand, paired males frequently exhibit strategies that minimize their loss of paternity and/or conserve paternal investment if paternity is lost. Hence, extrapair attributes of diverse species and populations reported in the literature are particular solutions of evolutionary games involving gender-specific cuckolding/anti-cuckolding strategies. Here we use methods of evolutionary game theory to study the role of male paternity guarding strategies in situations where females seek extrapair fertilizations for reasons of genetic compatibility and/or in pursuit of genetic diversity for their offspring. Our results indicate that in these circumstances pursuit of extrapair fertilizations is the only evolutionary stable female strategy. Males, on the other hand, have two, mutually exclusive, evolutionary stable strategies: full time pursuit of extrapair fertilizations and a compromise strategy wherein they protect in-pair paternity during their mate's fertile periods and pursue extrapair paternity the rest of the time. The relative merits of these two strategies are determined by the efficiency of male in-pair paternity defense, breeding synchrony, fitness advantages of extrapair over in-pair offspring, and the intensity of competition for extrapair fertilizations from floater males. 相似文献
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43.
Słowińska-Klencka D Klencki M Sporny S Popowicz B Lewiński A 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》2003,25(1):39-46
OBJECTIVE: To assess whether the cytologic appearance of aspirates from toxic nodular goiter is substantially modified during the course of therapy with thyrostatic drugs. STUDY DESIGN: Morphometric features of thyrocyte nuclei in aspirates obtained from nontoxic nodular goiter (NTNG), toxic nodular goiter before treatment (TNG-untreated) and toxic nodular goiter during thyrostatic administration (TNG-treated) were examined. The relationship between the degree of morphologic changes and the duration of therapy was evaluated. An analysis of the composition of aspirates was also performed. RESULTS: The sizes of thyrocyte nuclei in the TNG-untreated group were larger than in the NTNG and TNG-treated groups, and treatment with thyrostatics was accompanied by a gradual decrease in the sizes of thyrocyte nuclei. However, karyometric features showed a tendency to increase again in patients treated for longer than 1 year, with the variability of nuclear size in a smear (anisokaryosis) increasing more markedly than the mean size of nuclei. Moreover, in those patients, nuclei with visible nucleoli were found. CONCLUSION: Only long-term therapy with thyrostatic drugs leads to changes in the microscopic appearance of smears obtained by fine needle aspiration biopsy (FNAB) of the thyroid relevant to cytologic diagnosis. Thus, FNAB can be performed successfully after the onset of treatment with thyrostatics if the cytologist is informed of the time scale of treatment in each case. 相似文献
44.
Bottom-up excitable models of phytoplankton blooms 总被引:1,自引:0,他引:1
A simple nutrient-phytoplankton model is used to explore the dynamics of phytoplankton blooms. The model exhibits excitable
behaviour in the sense that a large scale outbreak can only be triggered when a critical nutrient threshold is exceeded. The
model takes into account several features often neglected but whose combined effect proves very important: (i) rapid nutrient
recycling associated with the microbial loop and patch formation; (ii) self-shading; and (iii) a bottom-up approach, whereby
nutrient levels are responsible for both the triggering and the demise of the bloom. Although the literature is replete with
studies of ‘top-down’ models in which zooplankton grazing control the triggering and demise of the bloom, bottom-up models
are nevertheless appropriate in many circumstances. We provide a full mathematical investigation of the effects of these three
different features in an excitable system framework. 相似文献
45.
Almogy G Cohen N Stöcker S Stone L 《Proceedings. Biological sciences / The Royal Society》2002,269(1493):809-815
Based on the current understanding of the immune response, we present what we believe to be a new model of intrahost virus dynamics. The model takes into account the relationship between virus replication rate and the level of antigen displayed by infected cells, and shows how the cell-directed immune response controls both virus load and virus replication rate. In contrast to conventional wisdom, it shows that the predominant virus variant does not necessarily have the highest replication rate. A strong immune response produces a selective advantage for latent viruses, whereas a deteriorating immune response invites in viruses of higher replication rates. The model is analysed in light of the well-studied HIV/AIDS disease progression, and shows how a wide range of major, seemingly unrelated issues in the study of HIV may be accounted for in a simple and unified manner. 相似文献
46.
A simple model that describes the dynamics of nutrient-driven phytoplankton blooms is presented. Apart from complicated simulation studies, very few models reported in the literature have taken this "bottom-up" approach. Yet, as discussed and justified from a theoretical standpoint, many blooms are strongly controlled by nutrients rather than by higher trophic levels. The analysis identifies an important threshold effect: a bloom will only be triggered when nutrients exceed a certain defined level. This threshold effect should be generic to both natural blooms and most simulation models. Furthermore, predictions are given as to how the peak of the bloom Pmax is determined by initial conditions. A number of counterintuitive results are found. In particular, it is shown that increasing initial nutrient or phytoplankton levels can act to decrease Pmax. Correct predictions require an understanding of such factors as the timing of the bloom and the period of nutrient buildup before the bloom. 相似文献
47.
E Sewerynek M Szkudliński A Lewiński J Kunert-Radek 《Biochemical and biophysical research communications》1988,157(1):95-99
The effect of a single injection of cysteamine /CySH/ - a sulfhydryl substance, known to deplete tissue content of somatostatin /SS/ - on 3H-thymidine incorporation into DNA of rat adrenal explants incubated in vitro was investigated. It was shown that: 1/ Single in vivo injection of ACTH or of CySH increased 3H-thymidine incorporation into DNA of the organ-cultured adrenals, 2/ Dexamethasone reduced the 3H-thymidine uptake, but that decrease did not attain statistical significance versus controls. 相似文献
48.
Poliomyelitis is a disease which began to appear in epidemic proportions in the late 19th century, paradoxically, just at the time when living conditions and developments in health were transforming enormously for the better. We present a simple age-class model that explains this "disease of development" as a threshold phenomenon. Epidemics arise when improved conditions in hygiene are able to reduce disease transmission of polio amongst children below a critical threshold level. This generates a large susceptible adult population in which, under appropriate conditions, epidemics can propagate. The polio model is analysed in terms of its bifurcation properties and in terms of its non-equilibrium outbreak dynamics. 相似文献
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