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51.
David M. Rothwarf V. Gary Davenport Pu-Tau Shi Jin-Lin Peng Harold A. Scheraga 《Biopolymers》1996,39(4):531-536
In order to examine the helix-coil transition of water-insoluble polypeptides, without requiring interspersion of charged or polar residues within the sequence, a tri-block copolymer strategy has been developed to determine the helix propensity of amino acids in short (15-residue) peptides. The method is also well suited to evaluate specific interactions that contribute to helix formation. In this approach, measurement is made of the helix content of the central block of tri-block copolymers of the type Lys15-X-Lys15, where X is the 15-residue peptide whose helix content is being investigated. The suitability of tri-block copolymers of this type has been verified experimentally by using the water-soluble peptide (Ala2GlnAla2)3 as the central block. The CD spectrum of the central block in the tri-block copolymer and of Ac-(Ala2GlnAla2)3-NH2 are indistinguishable within experimental error. © 1996 John Wiley & Sons, Inc. 相似文献
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54.
Penezina OP Fomovskaia GN Haddock TF Davenport RD 《Ukrainski? biokhimicheski? zhurnal》1999,71(6):56-61
L-selectin (CD62L) is the principal leukocyte adhesion molecule for the high endothelial venules of peripheral lymph nodes. This adhesion has an absolute requirement for calcium ions. Nevertheless, some studies have shown carbohydrate adhesion receptor interactions on lymphocytes and neutrophils, including the L-selectin molecule, that are Ca-independent. In the present study fucoidan, a reportedly Ca2+ independent ligand of L-selectin, and Mabs to human CD62L were coupled to magnetic polystyrene beads (MPB), as a model of leukocyte-surface interactions, and the efficiency of human leukocyte separation was investigated. 30% of Ficoll-purified human mononuclear cells and 75% of dextran-purified human leukocytes (DPHL) were specifically bound by fucoidan-modified MPB in the presence of Ca2+; 55% of dextran-purified leukocytes were specifically bound in the absence of Ca2+. The specific binding was inhibited by an excess of free fucoidan. The data obtained show the presence of Ca-independent adhesion determinants, specific to fucoidan on human leukocytes. No significant specific binding of leukocytes to fucoidan-modified MPB was found after the incubation with fresh human Ca(2+)-depleted whole blood. More than 90% of DPHL were specifically bound to MPB modified with Mabs to human CD62L irrespective of Ca2+ presence. The same degree of separation was achieved after the incubation with fresh human Ca(2+)-depleted-whole blood with anti-CD62L modified beads. 相似文献
55.
Cytotoxic T lymphocyte (CTL) responses are thought to be important for the control of many viral and other infections. Qualitative aspects of the CTL response, including the epitope specificity, affinity, and clonal composition, may affect the ability of T cells to mediate infection control. Although it is clear that the mode of introduction and the dose of antigen can affect these qualitative aspects of the response, little is understood of the mechanisms. We have developed an in silico model of the CTL response, which we use to study the impact of antigen dose, antigen kinetics and repeated antigen delivery on the response. The results suggest that recent observations on differences in response to killed antigen can be explained simply by differences in timing of T-cell activation. These findings may provide insight into how different vaccination strategies can quantitatively and qualitatively affect the outcome of the immune response. 相似文献
56.
Na+ tolerance and Na+ transport in higher plants 总被引:69,自引:0,他引:69
57.
Many external signals influence growth cone motility, pathfinding, and the formation of synapses that lead to the final map formation of the retinotectal system. Chick temporal retinal ganglion cell axons (RGCs) collapse and retract after encountering posterior tectal cells in vitro. During this process lateral extensions appear along the RGC axonal shaft. Lateral extensions appear as nascent interstitial axonal branches and also as defasciculating growth cones that are trailing along the pioneer axon. RGC branching controlled by repellent tectal cues has recently been shown to be the critical event in retinotectal map development. The intracellular mechanism underlying this phenomenon, however, is not understood. Inhibiting RhoA with either C3 toxin or inhibiting p160Rock kinase, an effector of RhoA, with Y27632 inhibited collapse, retraction, and the number of axons that showed lateral extensions. Lateral extension length increased significantly. Inhibiting Rac1A and cdc42 with cell permeable peptide inhibitors did not inhibit collapse of growth cones, but did inhibit axon retraction. In addition, the number of axons that showed lateral extensions and lateral extension length were significantly reduced. A dynamic cytoskeleton is necessary to react to incoming guidance information. This study addresses the problems of how growth cone motility and branching or defasciculation are affected by Rho-GTPases as extracellular signals are transmitted to the cytoskeleton. 相似文献
58.
Clonal selection, clonal senescence, and clonal succession: the evolution of the T cell response to infection with a persistent virus 总被引:7,自引:0,他引:7
Davenport MP Fazou C McMichael AJ Callan MF 《Journal of immunology (Baltimore, Md. : 1950)》2002,168(7):3309-3317
We have analyzed the CD8(+) T cell response to EBV and find that a larger primary burst size is associated with proportionally greater decay during the development of memory. Consequently, immunodominance and clonal dominance are less marked in memory than primary responses. An intuitive interpretation of this finding is that there is a limit to the number of cell divisions a T cell clone can undergo, and that the progeny of clones that have expanded massively during a primary immune response are more prone to die as a result of senescence. To test this hypothesis, we have derived a mathematical model of the response of different T cell clones of varying avidity for Ag in the primary and persistent phases of viral infection. When cellular survival and replication are linked to T cell avidity for Ag and Ag dose, then high-avidity T cells dominate both the primary and secondary responses. We then incorporated a limit in the number of cell divisions of individual T cell clones to test whether such a constraint could reproduce the observed association between cell division number and alterations in the contribution of clones to the response to persistent infection. Comparison of the model output with the experimental results obtained from primary and persistent EBV infection suggests that there is indeed a role for cellular senescence in shaping the immune response to persistent infection. 相似文献
59.
Hennessy MB Voith VL Young TL Hawke JL Centrone J McDowell AL Linden F Davenport GM 《Journal of applied animal welfare science : JAAWS》2002,5(4):253-273
This study examined the effects of 2 manipulations-a brief, regular period of human contact and diet-on the behavior of dogs confined in a public animal shelter. A behavioral battery designed to assess reactions to novel situations, and a test of responsiveness to an unfamiliar human were administered both prior to (pretest) and immediately following (posttest) the 8-week intervention period. Overall, the regular periods of increased human contact together with a diet that contained augmented levels of digestible protein, fat, calories, and animal-derived ingredients reduced signs of behavioral reactivity from pretest to posttest. In some cases, the comparison diet appeared more effective, but only for dogs receiving minimal human interaction. The results indicate that a combination of human interaction and high quality diet may positively affect the behavior of dogs in animal shelters. 相似文献
60.
Murray JM Kaufmann GR Hodgkin PD Lewin SR Kelleher AD Davenport MP Zaunders JJ 《Immunology and cell biology》2003,81(6):487-495
Analysing T-cell receptor excision circle numbers in healthy individuals we find a marked change in the source of naive T cells before and after 20 years of age. The bulk of the naive T cell pool is sustained primarily from thymic output for individuals younger than 20 years of age whereas proliferation within the naive phenotype is dominant for older individuals. Over 90% of phenotypically naive T cells in middle age are not of direct thymic origin. Moreover, this change in source of naive T cells is accompanied either by an increased death rate of T cells from the thymus or reduced thymic export. Modelling of these processes shows that new naive T cells of a thymic origin have a half-life of approximately 50 days before this change occurs, and that either the life-span of recent thymic emigrants (but not necessarily of all naive cells) decreases approximately threefold in middle age, or thymic production drops by this same amount. The decay rate of T-cell receptor excision circle levels for individuals over 20 years of age is consistent with the decay rate of the productive thymus. Our modelling suggests that at age 25, thymic export is responsible for 20% of naive T-cell production and that this percentage decreases with the 15.7 year half-life of the productive thymus so that by age 55 only 5% of naive production arises from thymic export. 相似文献