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203.
Cariillo M.Belen; Milner Caroline M.; Ball Simon T.; Snoek Margriet; Campbell R.Duncan 《Glycobiology》1997,7(7):975-986
The Neu1 locus, in the S region of the murine histocompatibility-2complex, regulates the sialic acid content of several liverlysosomal enzymes. Three alleles, Neu1a, Neu1b, and Neu1c, havebeen described on the basis of differential sialylation of theenzyme liver acid phosphatase. The Neu1a allele occurs in asmall number of mouse strains, e.g., SM/J and is associatedwith sialidase deficiency. We recently described G9, a sialidasegene in the human major histocompatibility complex (Milner etal. (1997) J. Biol. Chem., 272, 45494558), and we nowreport the characterization of the equivalent gene in mouse.The protein product of the murine G9 gene is 409 amino acidsin length and is 83% identical to its human orthologue. Expressionof the murine G9 protein in insect cells has confirmed thatit is a sialidase, with optimal activity at pH 5. To elucidatethe basis of sialidase deficiency in mouse strains carryingthe Neu1a allele, we have sequenced the G9 coding regions frommice carrying the three Neu1 alleles and hence defined the aminoacid sequence characteristic of each allotype. Of particularinterest is a Leu-209 to Ile mutation that is unique to theNeu1a allotype and is associated with reductions in sialidaseactivity of 68% and 88% compared to the Neu1b and Neu1c allotypes,respectively, when these three protein variants are expressedin insect cells. Additional factors, such as differential expression,may also influence the activities of the Nen1 allotypes in vivo.We have observed that the level of G9 mRNA is substantiallyreduced in mice carrying the Neu1a allele compared to the Neu1b(8595% reduction) and Neu1c (70% reduction) alleles. H2 complex MHC Neu1 sialidase 相似文献
204.
Cinnamoyl CoA reductase, the first committed enzyme of the lignin branch biosynthetic pathway: cloning, expression and phylogenetic relationships 总被引:15,自引:3,他引:12
205.
The male determinant of self-incompatibility in Brassica oleracea is located in the pollen coating 总被引:2,自引:0,他引:2
Andrew G. Stephenson James Doughty Suzanne Dixon Carole Elleman Simon Hiscock Hugh G. Dickinson 《The Plant journal : for cell and molecular biology》1997,12(6):1351-1359
An in vitro bioassay has been developed to explore the role of the pollen coating in the pollen/stigma interaction in Brassica oleracea . In the assay, coating is removed from pollen grains, supplemented with protein fractions isolated from coatings of different S (self incompatibility) haplotypes, and then—using micromanipulation—interposed between individual pollen grains and the stigmatic surface. Normally, the coating used is of the same haplotype as the pollen in the experiment—thus constituting an 'extension' of its own coat—but carrying the supplemented protein fractions. Initial experiments confirmed preliminary data that the pollen coating contained the male determinant of self incompatibility (SI); not only did the addition of 'self' coating (i.e. that with the same S -haplotype as the stigma) prevent the success of a compatible cross pollination, but a 'cross' coating (i.e. that with a different S -haplotype from the stigma) could induce the germination and growth of self pollen. Protein supplementation experiments demonstrated that the pollen-held determinant is contained within the water soluble component of the pollen coat, while further analysis revealed that the active molecular species possesses an Mr 10 kDa. More extensive fractionation by gel filtration and reverse phase HPLC was used to isolate a family of basic, cysteine-rich proteins (PCP-A: P ollen C oat P roteins-class A)—one of which is known to bind to stigmatically-expressed components of the S -locus in Brassica . Introduction of the PCP-A protein fraction into the bioassay confirmed the male determinant of SI as a protein, and probably a member of the PCP-A protein family. 相似文献
206.
Cohen Shabtai; Moreshet Samuel; Guillou Loic Le; Simon Jean-Christophe; Cohen Moises 《Journal of experimental botany》1997,48(1):35-44
Citrus trees are characterized by a large canopy and low hydraulicconductivity. In Israel's semi-arid summer climate this couldcause transpiration to exceed water uptake and cause temporaryexcessive water deficits. It was hypothesized that reductionof radiative load would reduce transpiration and thus reducedeficits. Net radiation of lemon trees in the hottest season was reducedby shading hedgerows with reflective nets for approximatelyone month in both 1994 and 1995. Stem sap flow and climate variableswere measured continuously. Daily courses of leaf conductanceand leaf water potentials were measured on selected days. Midday net radiation below the dense and sparse shade net treatmentswas 47% and 73% of that above the control trees. Midday sunlitleaf temperatures below the nets were reduced by 2.7 and 1.6C,respectively. The reduction in net radiation caused large changes in leafconductance. Average midday sunlit leaf conductance measuredin 1995 under the dense and sparse treatments and control were4.1, 2.9 and 1.8mm s1, respectively (significantly differentat P <0.01). Similar differences in sunlit leaf conductancewere found in 1994. Shade leaf conductance was not affectedby the treatments. Daily total and midday sap flow under the dense net were reducedby 67% and 1011%, respectively. Sap flow underthe sparse net did not change significantly in 1994, but in1995 daily and midday sap flows were reduced by 6% and 7%, respectively.Midday leaf water potentials increased by 0.2 and 0.1 MPa underdense shade in 1994 and 1995, respectively. Under sparse shademidday leaf water potentials increased by 0.1 MPa in 1994, butdid not change significantly in 1995. A modified Penman-Monteith model evaluated transpiration ifleaf conductance were constant in the different radiation environments.At leaf conductance levels found in the unshaded trees, denseshade was estimated to cause a 25% reduction in transpiration,while leaf conductance values found in trees under the denseshade would lead to an increase in transpiration of more than35% in unshaded trees. The ability of the tree to maintain almost constant transpirationin different radiation environments and thus avoid water deficitby adjusting the conductance of sunlit leaves is discussed interms of environmental influences and significance to the plant'swater balance. Key words: Tree transpiration, stomatal closure, climate modification, citrus 相似文献
207.
Francesco Frati Chris Simon Jack Sullivan David L. Swofford 《Journal of molecular evolution》1997,44(2):145-158
The sequence of the mitochondrial COII gene has been widely used to estimate phylogenetic relationships at different taxomonic
levels across insects. We investigated the molecular evolution of the COII gene and its usefulness for reconstructing phylogenetic
relationships within and among four collembolan families. The collembolan COII gene showed the lowest A + T content of all
insects so far examined, confirming that the well-known A + T bias in insect mitochondrial genes tends to increase from the
basal to apical orders. Fifty-seven percent of all nucleotide positions were variable and most of the third codon positions
appeared free to vary. Values of genetic distance between congeneric species and between families were remarkably high; in
some cases the latter were higher than divergence values between other orders of insects. The remarkably high divergence levels
observed here provide evidence that collembolan taxa are quite old; divergence levels among collembolan families equaled or
exceeded divergences among pterygote insect orders. Once the saturated third-codon positions (which violated stationarity
of base frequencies) were removed, the COII sequences contained phylogenetic information, but the extent of that information
was overestimated by parsimony methods relative to likelihood methods. In the phylogenetic analysis, consistent statistical
support was obtained for the monophyly of all four genera examined, but relationships among genera/families were not well
supported. Within the genus Orchesella, relationships were well resolved and agreed with allozyme data. Within the genus Isotomurus, although three pairs of populations were consistently identified, these appeared to have arisen in a burst of evolution from
an earlier ancestor. Isotomurus italicus always appeared as basal and I. palustris appeared to harbor a cryptic species, corroborating allozyme data.
Received: 12 January 1996 / Accepted: 10 August 1996 相似文献
208.
Early cytokine and chemokine gene expression in lymph nodes of macaques infected with simian immunodeficiency virus is predictive of disease outcome and vaccine efficacy. 总被引:4,自引:4,他引:0
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W Zou A A Lackner M Simon I Durand-Gasselin P Galanaud R C Desrosiers D Emilie 《Journal of virology》1997,71(2):1227-1236
Competitive PCR was used to evaluate the expression of cytokine, granzyme B, and chemokine genes in lymph nodes of macaques recently infected with the simian immunodeficiency virus (SIV) pathogenic molecular clone SIVmac239 (n = 16), the nonpathogenic vaccine strain SIVmac239 delta nef (n = 8), and the nonpathogenic molecular clone SIVmac1A11 (n = 8). For both SIVmac239 and its nef-deleted derivative, strong expression was observed as early as 7 days postinfection for interleukin 1beta (IL-1beta), IL-6, tumor necrosis factor alpha, gamma interferon, and IL-13. The levels of gene induction were equally intense for both viruses despite a lower viral load for SIVmac239 deltanef compared with that for SIVmac239. However, the nature of the cytokine network activation varied with the viral inocula. Primary infection with SIVmac239 was characterized by a higher level of IL-4, IL-10, MIP-1alpha, MIP-1beta, MCP-1, and RANTES gene expression and a lower level of IL-12 and granzyme B gene expression compared with infection with SIVmac239 delta nef. Thus, infection with nef-deleted SIV was associated with a preferential Th1 versus Th2 pattern of cytokine production. Infection with SIVmac1A11 was characterized by a delayed immune response for all markers tested. The unique patterns of cytokine and chemokine gene expression in lymph nodes correlated nicely with the pathogenic potential of the SIV strains used as well as with differences in their ability to serve as protective vaccines. 相似文献
209.
Susceptibility of human immunodeficiency virus type 1 group O isolates to antiretroviral agents: in vitro phenotypic and genotypic analyses. 总被引:10,自引:4,他引:6
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D Descamps G Collin F Letourneur C Apetrei F Damond I Loussert-Ajaka F Simon S Saragosti F Brun-Vzinet 《Journal of virology》1997,71(11):8893-8898
210.