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91.
An electron microscope comparison of plasma membrane vesicles from meristematic and mature soybean root tissue
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Plasma membrane vesicles were isolated from homogenates of meristematic and mature soybean root tissue by differential sucrose gradient centrifugation. Vesicles were positively identified by the phosphotungstic acid-chromic acid procedure (PACP). The two preparations were comparable in size class distribution, mitochondrial contamination, and per cent plasma membrane vesicles present. Purity levels were estimated to be greater than 75%. The specificity of PACP was observed for a variety of cell types from both regions. Some variability in PACP staining was offset by careful modulation of the stain protocol and was found to be independent of developmental stage in subcellular fractions. Patchy or discontinuous staining, observed in both intact tissue and in subcellular fractions from both regions, was found to be a function of stain time. 相似文献
92.
Previous research showed that addition of nutrient nitrogen to ligninolytic (stationary, nitrogen-starved) cultures of the wood-decomposing basidiomycete Phanerochaete chrysosporium causes a suppression of lignin degradation. The present study examined early effects on nitrogen metabolism that followed addition of NH
4
+
and l-glutamate at concentrations that yield similar patterns of suppression. Both nitrogenous compounds were rapidly assimilated (>80% in 6 h). Both caused an initial 80% or greater increase in the intracellular glutamate pool and had similar effects in increasing the specific activities of NADP- and NAD-glutamate dehydrogenases and glutamine synthetase. Differences between the effects of added NH
4
+
and glutamate showed that suppression was not correlated with intracellular pools of arginine or glutamine, nor was the maintenance of an elevated glutamate pool required to maintain the suppressed state. While a portion of the initial glutamate suppression could be attributed to an effect on central carbon metabolism through glutamate catabolism by NAD-glutamate dehydrogenase, the long term suppression by glutamate and the suppression by NH
4
+
were more specific. Suppression by NH
4
+
or glutamate in the presence or absence of protein synthesis (cycloheximide) followed essentially identical kinetics during 12 h. These results indicate that nitrogen additions cause a biochemical repression of enzymes associated with lignin degradation. Results are consistent with the hypothesis that nitrogen metabolism via glutamate plays a role in initiation of repression.Non-Standard Abbreviations DMS
2,2-dimethylsuccinate
- TCA
trichloroacetic acid 相似文献
93.
Transient electric birefringence studies have been made on bovine rhodopsin solubilized in the detergent lauryldimethylamine oxide from glutaraldehyde fixed rod outer segment (ROS) membranes. It was found that fixation caused no appreciable differences in the measured relaxation times when compared with unfixed ROS. On the basis of these findings a model for the orientation of rhodopsin in photoreceptor membranes is proposed which accounts for translational diffusion and two modes of rotational diffusion. The proposed model is related to a number of experimentally determined biophysical properties reported in the literature. 相似文献
94.
95.
96.
Timothy A. Reinhardt Ronald L. Horst E.Travis Littledike Donald C. Beitz 《Biochemical and biophysical research communications》1982,106(3):1012-1018
1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] receptor was characterized after partial purification of thymus cytosol by ammonium sulfate fractionation. The 1,25-(OH)2D3 receptor sediments at 3.7S in 5–20% sucrose gradients. The binding of 1,25-(OH)2D3 in thymic cytosol was a saturable process with high affinity (Kd = 0.12?0.48 nM) at 4°C. Competition for 1,25-(OH)2[3H]D3 receptor by nonradioactive analogs demonstrated the affinities of these analogs to be in order; 1,25-(OH)2D3 = 1,24R,25-(OH)3D3 = 1,25S,26-(OH)3D3 = 1,25R,26-(OH)3D3 > 1,25-(OH)2D3-26,23 lactone > 25-OHD3 > 23R,25-(OH)2D3 > 24R,25-(OH)2D3 > 23S,25-(OH)2D3 ? 25-OHD3-26,23 lactone. The receptor bound to DNA cellulose columns in low salt buffer and eluted as a single peak at 0.21 M KCl. These findings provide evidence that the thymus possesses a 1,25-(OH)2D3 receptor with properties indistinguishable from 1,25-(OH)2D3 receptors in other tissues. 相似文献
97.
Proteolytic inactivation of alpha-1-anti-chymotrypsin. Sites of cleavage and generation of chemotactic activity. 总被引:2,自引:0,他引:2
J Potempa D Fedak A Dubin A Mast J Travis 《The Journal of biological chemistry》1991,266(32):21482-21487
The effect of several microbial and mammalian proteinases on the inhibitory activity of human plasma alpha-1-anti-chymotrypsin (alpha-1-Achy) has been tested. Most of these enzymes caused rapid inactivation of the inhibitor by cleavage at single sites within the reactive-site loop between P5 Lys and P3' Leu, with additional cleavages also being detected in some cases near the NH2 terminus of the native protein. In contrast, two of the enzymes tested failed to inactivate alpha-1-Achy, although they could cause removal of peptides near the NH2 terminus. Studies of neutrophil chemotaxis revealed that native or NH2-terminally truncated alpha-1-Achy was not stimulatory. However, testing of two enzymatically inactivated forms of the inhibitor (alpha-1-Achy), cleaved at widely different positions within the reactive-site loop, indicated that they had become potent chemoattractants at concentrations within the nanomolar range. Competition studies using proteolytically inactivated alpha-1-proteinase inhibitor suggested that the chemotactic activity of the two inactivated serpins was probably mediated by the same mechanism. The physiological relevance of this chemotactic activity is underscored by the results of plasma elimination studies which indicate that alpha-1-Achy is eliminated at approximately the same rate as native alpha-1-Achy, thus prolonging chemotactic stimuli within the tissues. 相似文献
98.
A review of the salt sensitivity of the Australian freshwater biota 总被引:13,自引:7,他引:6
Barry T. Hart Paul Bailey Rick Edwards Kent Hortle Kim James Andrew McMahon Charles Meredith Kerrie Swadling 《Hydrobiologia》1991,210(1-2):105-144
In Victoria, Australia, both dryland salinity and salinity in irrigation regions are serious agricultural problems. One option
to control the latter is to pump groundwater to maintain it below the surface. However, this leaves a saline wastewater for
disposal, probably into local streams or wetlands. This review of the salt sensitivity of the biota of Australian streams
and wetlands gives information of interest to those responsible for developing controls on these discharges. The review addresses
the lethal and sub-lethal effects of salinity on microbes (mainly bacteria), macrophytes and micro-algae, riparian vegetation,
invertebrates, fish, amphibians, reptiles, mammals, and birds. Data suggest that direct adverse biological effects are likely
to occur in Australian river, stream and wetland ecosystems if salinity is increased to around 1 000 mg L−1. The review highlights a general lack of data on the sensitivity of freshwater plants and animals to salinity increases. 相似文献
99.
The location of CTP:phosphocholine cytidylyltransferase in Chinese hamster ovary (CHO) cells made deficient in phosphatidylcholine was determined by immunofluorescence techniques. A rabbit polyclonal antibody was raised against a synthetic peptide corresponding to the amino-terminal 17 amino acid residues of rat liver cytidylyltransferase. The antibody recognized both native and denatured cytidylyltransferase from both rat liver and CHO cells. CHO cells were treated with phospholipase C to alter the lipid composition of the plasma membrane and to elicit translocation of cytidylyltransferase from the less active soluble pool to an activated membrane fraction. Visualization of cytidylyltransferase by indirect immunofluorescence revealed staining of the nuclear envelope in phospholipase C-treated cells but not in untreated cells. CHO cells were also starved for choline and supplemented with a choline analogue to provide an alternative technique of rendering the cells phosphatidylcholine-deficient. Although this treatment should affect different cellular membranes than those affected by phospholipase C treatment, cytidylyltransferase still translocated to the nuclear envelope, as shown by indirect immunofluorescence. These results indicate that activated, membrane-bound cytidylyltransferase is associated with the nuclear membrane and suggest that the nuclear membrane may be a site of de novo phosphatidylcholine synthesis. 相似文献
100.
J J Mulé M C Custer W D Travis S A Rosenberg 《Journal of immunology (Baltimore, Md. : 1950)》1992,148(8):2622-2629
The systemic administration of human rIL-6 to mice resulted in the regression of established, 3-day pulmonary micrometastases from two weakly immunogenic tumors, but not from a nonimmunogenic tumor, in the absence of observable toxicity. Although IL-6 alone failed to have a significant therapeutic impact on advanced, 10-day pulmonary macrometastases from weakly immunogenic tumors, substantial cure rates of mice could be achieved when this cytokine was combined with cyclophosphamide. Histologic analysis of the lungs of mice receiving IL-6 revealed infiltration with lymphoid cells during the regression of pulmonary nodules from a weakly immunogenic tumor. IL-6-mediated tumor regression could be abrogated after selective in vivo depletion of either CD4 or CD8 T cell subsets by the systemic administration of specific mAb. In vivo generation of tumor-specific CTL, but not of lymphokine-activated killer cells, was detected in the lungs of IL-6-treated mice during regression of pulmonary metastases. Collectively, these findings demonstrate a role for IL-6 in the treatment of established solid tumors that have the capacity to elicit T cell responses in the host. Differences in host cellular mechanisms involved in tumor regression mediated by immunotherapy using IL-6 vs IL-2 are discussed. 相似文献