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671.
Three prenyl transferases in Micrococcus luteus were recovered in the soluble fraction following cell disruption. Undecaprenyl pyrophosphate (C55-PP) synthetase chromatographed on DEAE-cellulose independently from geranylgeranyl-PP and octaprenyl-PP synthetases. Further purification of C55-PP synthetase resulted in an approximate 250-fold purification over the crude lysate. The molecular weight of the synthetase was estimated to be between 47,000 and 49,000 by Sephadex G-100 chromatography. The enzyme had a broad specificity toward the allylic pyrophosphate substrate. The reactivities of the allylic substrates increased with chain length, C10 < C15 < C20, except for trans-solanesyl-PP, which was unreactive. Moreover, the enzyme was active on allylic substrates having both cis- and trans-stereochemistry. Although C55-PP and C50-PP were the major products, some shorter chain products were also produced, when t,t-farnesyl pyrophosphate and Δ3sopentenyl pyrophosphate (IPP) were used as substrates. The stereochemistries of the products formed with C55-PP synthetase were established, using [14C]IPP and 2R-[2-3H] and 2S-[2-3H]IPP. Each new isoprene unit added had a cis-configuration. The enzyme was inactive in the absence of added effectors. It was stimulated by Triton X-100, egg lecithin, and a whole phospholipid extract from M. luteus. Cardiolipin and deoxycholate were poor activators of the enzyme. The product chain length distribution observed with the phospholipid-activated enzyme showed highly favored production of the C55-PP product over the C50-PP product. 相似文献
672.
Calcium ion is a secondary messenger that mediates a variety of physiological responses of neurons, including cell survival
responses. To determine the role of calcium in regulating neuronal survival and death, we examined whether chelation of extracellular
calcium with EGTA induces caspase-dependent apoptotic cell death and whether glycogen synthase kinase-3 is involved in EGTA-induced
cell death in PC12 cells. EGTA increased apoptotic cell death with morphological changes characterized by cell shrinkage and
nuclear condensation and fragmentation accompanied by caspase activation. EGTA increased GRP78 protein expression, suggesting
that EGTA induces ER stress. Glycogen synthase kinase-3 inhibitors prevented EGTA-induced apoptosis. In addition, nerve growth
factor and insulin growth factor-I completely blocked EGTA-induced cell death. Moreover, caspase-3 activation was inhibited
by glycogen synthase kinase-3 inhibitors. These results suggest that chelation of extracellular calcium with EGTA induces
caspase-dependent apoptosis, and the activation of glycogen synthase kinase-3 is involved in the death of PC12 cells. 相似文献
673.
Ordus chiayiensis isolated from discolored red pine needles is redescribed and illustrated. 相似文献
674.
Eishi Nagai Takahiro Ogawa Tammy Kielian Akashi Ikubo Tsuneo Suzuki 《Cancer immunology, immunotherapy : CII》1998,47(2):72-80
The specific aim of this study was to examine the prophylactic as well as the therapeutic efficacies of irradiated mouse
CT26 colon cancer cells, infected with recombinant adenoviruses harboring cDNAs specific for granulocyte macrophage-colony-stimulating
factor (GM-CSF), interferon (IFN-γ) and monocyte chemotactic protein1 (MCP-1). Results showed that tumor cells secrete the
respective cytokines for several days after infection and subsequent irradiation. Vaccination with irradiated GM-CSF-secreting
CT26 cells protected 90% of syngeneic mice challenged with live parental cells. On the other hand, vaccination with irradiated
IFNγ or MCP-1-secreting CT26 cells totally failed to protect mice from tumor development after challenge with parental cells.
None of the tumor-free mice initially vaccinated with irradiated GM-CSF-producing CT26 cells developed tumor upon repeated
challenge with parental cells during the entire observation period. The establishment of specific and long-lasting antitumor
immunity following vaccination with GM-CSF-producing tumor cells requires the simultaneous presence of GM-CSF and tumor antigen
at the vaccine site. Depletion of CD8+ cells, but not CD4+ cells, blocked the vaccine efficacy of GM-CSF-producing tumor cells. Subcutaneous injection of irradiated GM-CSF-producing
CT26 cells also effectively prevented the growth of a small load of parental tumor that was implanted 3 days earlier or the
development of metastatic foci in the lung from intravenously injected parental cells either 7 days before or 3 days after
vaccination. Our data thus show that, in these experimental tumor models, subcutaneous injection of irradiated tumor cells
adenovirally, transduced with the GM-CSF gene leads not only to prevention of growth of subsequently implanted tumor but also
to elimination of pre-existing and metastatic tumors. 相似文献
675.
676.
Gene regulation of steroidogenesis 总被引:11,自引:0,他引:11