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Biological destruction of coral reefs   总被引:10,自引:3,他引:7  
The major agents of biological destruction of coral reefs can be divided into grazers, etchers and borers. Each of these groups is reviewed on a world wide basis, together with the mechanisms by which they destroy the coral substrate. Rates of bioerosion attributed to major agents of grazers, etchers and borers are given, together with limitations of some of the measurements. Recent work is highlighting the variability in rates of bioerosion both over time and space. Factors which may be responsible for this variability are discussed. Bioerosion is a major factor influencing reef morphology and the ways in which this is achieved is discussed in some detail. Although the review concentrates mainly on present day reefs, some attempt is made to consider the impact of bioerosion on older reefs.  相似文献   
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A function-sparing pectoralis major muscle flap is presented. The flap is a medially based segmental transfer of a single intercostal portion of the pectoralis major muscle supplied by a single perforating branch of the internal thoracic artery. The segmental terminal nerve distribution of the medial and lateral pectoral nerves permits preservation of the remainder of the muscle in situ. Six cases of this procedure are presented with five successful outcomes. The single exception was in the loss of the distal tip when used to cover an irradiated carotid sheath to the base of the skull.  相似文献   
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The effect of 2-deoxyguanosine (dGuo) on the generation in vitro of nonspecific suppressor cells in murine spleen cell cultures by concanavalin A (Con A) is examined. The experiments indicate that dGuo abrogates the generation of nonspecific suppressor activity by lectin stimulation of murine spleen cells. When comparisons were made between the effect of this nucleoside on the generation of suppressor and cytotoxic cells by Con A stimulation of murine spleen cells, it was found that dGuo only affected the generation of suppressor cells. The development of lectin-stimulated cytotoxicity was not affected by dGuo. In addition it was found that dGuo does not affect the NK activity of murine spleens.  相似文献   
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The immune response to bovine herpesvirus 1 (BHV-1) infection can protect cattle from subsequent challenge with the virus. This protection involves a variety of defensive strategies, and the activation of most of these defenses requires the recognition of viral proteins by the cellular immune system. To identify some of the BHV-1 proteins recognized by T lymphocytes, we measured in vitro proliferative responses to individual proteins. Viral proteins were separated by gel electrophoresis followed by Western immunoblotting, and immunoblots were evaluated for serological reactions. Unstained blotted fractions were processed into antigen-bearing particles for analysis in blastogenesis assays. Purified BHV-1 proteins obtained by immunoadsorbent chromatography were processed and included for comparison in both enzyme-linked immunosorbent and proliferation assays. The tegument protein VP8 and the glycoprotein gIV appeared to be the antigens which most consistently stimulated the proliferation of lymphocytes from BHV-1-immunized animals. Positive blastogenic responses were also detected to gI, gIII, and to one or more uncharacterized, low-molecular-weight proteins in some of the cattle tested. These results indicate that T-lymphocyte proliferative responses to BHV-1 proteins are detectable in immune cattle and may be important in protection from BHV-1 infection.  相似文献   
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The evolution of alternative mating strategies in variable environments   总被引:6,自引:0,他引:6  
Summary We assessed the influence of phenotypic plasticity in age at maturity on the maintenance of alternative mating strategies in male Atlantic salmon,Salmo salar. We calculated the fitness,r, associated with the parr and the anadromous strategies, using age-specific survival data from the field and strategy-specific fertilization data from the laboratory. The fitness of each strategy depended largely on mate competition (numbers of parr per female, i.e. parr frequency) and on age at maturity. Fitness declined with increasing numbers of parr per female with equilibrium frequencies (at which the fitnesses of each strategy are equal) being within the range observed in the wild. Equilibrium parr frequencies declined with decreasing growth rate and increasing age at maturity. Within populations, the existence of multiple age-specific sets of fitness functions suggests that the fitnesses of alternative strategies are best represented as multidimensional surfaces. The points of intersection of these surfaces, whose boundaries encompass natural variation in age at maturity and mate competition, define an evolutionarily stable continuum (ESC) of strategy frequencies along which the fitnesses associated with each strategy are equal. We propose a simple model that incorporates polygenic thresholds of a largely environmentally-controlled trait (age at maturity) to provide a mechanism by which an ESC can be maintained within a population. An indirect test provides support for the prediction that growth-rate thresholds for parr maturation exist and are maintained by stabilizing selection. Evolutionarily stable continua, maintained by negative frequency-dependent selection on threshold traits, provide a theoretical basis for understanding how alternative life histories can evolve in variable environments.  相似文献   
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Molecular systematists need increased access to nuclear genes. Highly conserved, low copy number protein-encoding nuclear genes have attractive features for phylogenetic inference but have heretofore been applied mostly to very ancient divergences. By virtue of their synonymous substitutions, such genes should contain a wealth of information about lower-level taxonomic relationships as well, with the advantage that amino acid conservatism makes both alignment and primer definition straightforward. We tested this postulate for the elongation factor-1 alpha (EF-1 alpha) gene in the noctuid moth subfamily Heliothinae, which has probably diversified since the middle Tertiary. We sequenced 1,240 bp in 18 taxa representing heliothine groupings strongly supported by previous morphological and allozyme studies. The single most parsimonious gene tree and the neighbor-joining tree for all nucleotides show almost complete concordance with the morphological tree. Homoplasy and pairwise divergence levels are low, transition/transversion ratios are high, and phylogenetic information is spread evenly across gene regions. The EF-1 alpha gene and presumably other highly conserved genes hold much promise for phylogenetics of Tertiary age eukaryote groups.   相似文献   
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