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101.
The capacity of CD4+ T cells to induce IgG synthesis in B cells has been known to be radioresistant for more than 20 years. However, the radiation sensitivity of helper T cells with regard to their ability to induce the synthesis of isotypes other than IgG has not been studied. We therefore irradiated KLH-primed lymph node T cells and examined their capacity to induce IgG, IgM, and IgE synthesis in hapten-primed B cells. We demonstrated that while the capacity of KLH-primed lymph node cells to induce IgG synthesis was not affected by irradiation, the capacity of such T cells to induce IgE synthesis was greatly reduced by γ-irradiation. This was consistent with our observations that IL-4 and IL-5 synthesis in such cells was greatly diminished by irradiation, whereas IL-2 synthesis was only minimally affected. A similar differential sensitivity to irradiation of the helper activity of Th1 and Th2 clones was observed with regard to their ability to induce IgE and IgG synthesis under cognate conditions. Irradiation greatly inhibited the capacity of Th2 clones to induce IgE synthesis, but only minimally affected the capacity of Th1 clones to induce IgG synthesis in primed B cells. The capacity of irradiated Th2 clones to induce IgE synthesis was restored by the addition of IL-4 and IL-5. These results taken together indicated that the sensitivity to irradiation of T helper cells with regard to the induction of IgE but not IgG synthesis was due to the sensitivity to irradiation of the production of IL-4 but not of IL-2. Thus, although some functions of CD4+ T cells are resistant to radiation, other functions, particularly those that depend on the production of IL-4 and IL-5, are greatly diminished by ionizing radiation. 相似文献
102.
Extracellular polysaccharide of Nostoc commune (Cyanobacteria) inhibits fusion of membrane vesicles during desiccation 总被引:6,自引:0,他引:6
Donna R. Hill Thomas W. Keenan Richard F. Helm Malcolm Potts Lois M. Crowe John H. Crowe 《Journal of applied phycology》1997,9(3):237-248
Cells of the cyanobacterium Nostoc commune secrete a complex, high molecular weight, extracellular polysaccharide (EPS) which
accumulates to more than 60% of the dry weight of colonies. The EPS was purified from the clonal isolate N. commune DRH1.
The midpoint of the membrane phase transition (Tm) of desiccated cells of N. commune CHEN was low (Tm
dry = 8 °C) and was comparable to the Tm of rehydrated cells((Tm)H20 = 6 °C). The EPS was not responsible for the depression of Tm. However, the EPS, at low concentrations, inhibited specifically the fusion of phosphatidylcholine membrane vesicles when
they were dried in vitro at0% relative humidity (−400 MPa). Low concentrations of a trehalose:sucrose mixture, in a molar
ratio which corresponded with that present in cells in vivo, together with small amounts of the EPS, were efficient in preventing
leakage of carboxyfloroscein (CF) from membrane vesicles. Freeze-fracture electron microscopy resolved complex changes in
the structure of the EPS and the outer membrane in response to rehydration of desiccated cells. The capacity of the EPS to
prevent membrane fusion, the maintenance of a low Tm
dry in desiccated cells, and the changes in rheological properties of the EPS in response to water availability, constitute what
are likely important mechanisms for desiccation tolerance in this cyanobacterium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
103.
Dale J. Kennedy Douglas C. Montgomery Dwayne A. Rollier J. Bert Keats 《The International Journal of Life Cycle Assessment》1997,2(4):229-239
A methodology is presented to develop and analyze vectors of data quality attribute scores. Each data quality vector component represents the quality of the data element for a specific attribute (e.g., age of data). Several methods for aggregating the components of data quality vectors to derive one data quality indicator (DQI) that represents the total quality associated with the input data element are presented with illustrative examples. The methods are compared and it is proven that the measure of central tendency, or arithmetic average, of the data quality vector components as a percentage of the total quality range attainable is an equivalent measure for the aggregate DQI. In addition, the methodology is applied and compared to realworld LCA data pedigree matrices. Finally, a method for aggregating weighted data quality vector attributes is developed and an illustrative example is presented. This methodology provides LCA practitioners with an approach to increase the precision of input data uncertainty assessments by selecting any number of data quality attributes with which to score the LCA inventory model input data. The resultant vector of data quality attributes can then be analyzed to develop one aggregate DQI for each input data element for use in stochastic LCA modeling. 相似文献
104.
Fermentation of corn fibre sugars by an engineered xylose utilizing Saccharomyces yeast strain 总被引:2,自引:0,他引:2
Moniruzzaman M. Dien B.S. Skory C.D. Chen Z.D. Hespell R.B. Ho N.W.Y. Dale B.E. Bothast R.J. 《World journal of microbiology & biotechnology》1997,13(3):341-346
The ability of a recombinant Saccharomyces yeast strain to ferment the sugars glucose, xylose, arabinose and galactose which are the predominant monosaccharides found in corn fibre hydrolysates has been examined. Saccharomyces strain 1400 (pLNH32) was genetically engineered to ferment xylose by expressing genes encoding a xylose reductase, a xylitol dehydrogenase and a xylulose kinase. The recombinant efficiently fermented xylose alone or in the presence of glucose. Xylose-grown cultures had very little difference in xylitol accumulation, with only 4 to 5g/l accumulating, in aerobic, micro-aerated and anaerobic conditions. Highest production of ethanol with all sugars was achieved under anaerobic conditions. From a mixture of glucose (80g/l) and xylose (40g/l), this strain produced 52g/l ethanol, equivalent to 85% of theoretical yield, in less than 24h. Using a mixture of glucose (31g/l), xylose (15.2g/l), arabinose (10.5g/l) and galactose (2g/l), all of the sugars except arabinose were consumed in 24h with an accumulation of 22g ethanol/l, a 90% yield (excluding the arabinose in the calculation since it is not fermented). Approximately 98% theoretical yield, or 21g ethanol/l, was achieved using an enzymatic hydrolysate of ammonia fibre exploded corn fibre containing an estimated 47.0g mixed sugars/l. In all mixed sugar fermentations, less than 25% arabinose was consumed and converted into arabitol. 相似文献
105.
Interactions between VirB9 and VirB10 membrane proteins involved in movement of DNA from Agrobacterium tumefaciens into plant cells. 总被引:3,自引:1,他引:2 下载免费PDF全文
The 11 VirB proteins from Agrobacterium tumefaciens are predicted to form a membrane-bound complex that mediates the movement of DNA from the bacterium into plant cells. The studies reported here on the possible VirB protein interactions in such a complex demonstrate that VirB9 and VirB10 can each form high-molecular-weight complexes after treatment with a chemical cross-linker. Analysis of nonpolar virB mutants showed that the formation of the VirB10 complexes does not occur in a virB9 mutant and that VirB9 and VirB10 are not components of the same cross-linked complex. VirB9, when stabilized by the concurrent expression of VirB7, was shown to be sufficient to permit VirB10 to cross-link into its usual high-molecular-weight forms in the absence of other Vir proteins. Randomly introduced single point mutations in virB9 resulted in Agrobacterium strains with severely attenuated virulence. Although some of the mutants contained wild-type levels of VirB9 and displayed an unaltered VirB9 cross-linking pattern, VirB10 cross-linking was drastically reduced. We conclude that specific amino acid residues in VirB9 are necessary for interaction with VirB10 resulting in the capacity of VirB10 to participate in high-molecular-weight complexes that can be visualized by chemical cross-linking. 相似文献
106.
A Mitosis-specific Phosphorylation of the Gap Junction Protein Connexin43 in Human Vascular Cells: Biochemical Characterization and Localization 总被引:3,自引:0,他引:3 下载免费PDF全文
Han-qing Xie Dale W. Laird Tsg-Hui Chang Valerie W. Hu 《The Journal of cell biology》1997,137(1):203-210
Western blotting studies revealed that connexin43 (Cx43), one of the major gap junction proteins in human vascular endothelial cells, is posttranslationally modified during mitosis. This mitosis-specific modification results in a Cx43 species that migrates as a single protein band and was designated Cx43m. Cx43m was shown to be the result of additional Ser/Thr phosphorylation as indicated by: (a) the increased gel mobility induced by both alkaline phosphatase and the Ser/ Thr-specific protein phosphatase-2A (PP2A) and (b) the removal of virtually all 32Pi from Cx43m by PP2A. Immunofluorescent confocal microscopy of mitotic cells revealed that Cx43 is intracellularly located, while in nonmitotic cells Cx43 is located at regions of cell–cell contact. Dye coupling studies revealed that mitotic endothelial cells were uncoupled from each other and from nonmitotic cells. After cytokinesis, sister cells resumed cell coupling independent of de novo protein synthesis. The mitosis-specific phosphorylation of Cx43 correlates with the transient loss of gap junction intercellular communication and redistribution of Cx43, suggesting that a protein kinase that regulates gap junctions is active in M-phase. 相似文献
107.
Jerzy K. Kulski Silvana Gaudieri Matthew Bellgard Lois Balmer Keith Giles Hidetoshi Inoko Roger L. Dawkins 《Journal of molecular evolution》1997,45(6):599-609
Sequence analysis of a 237 kb genomic fragment from the central region of the MHC has revealed that the HLA-B and HLA-C genes
are contained within duplicated segments peri-B (53 kb) and peri-C (48 kb), respectively, and separated by an intervening
sequence (IF) of 30 kb. The peri-B and peri-C segments share at least 90% sequence homology except when interrupted by insertions/deletions
including Alu, L1, an endogenous retrovirus, and pseudogenes. The sequences of peri-B, IF, and peri-C were searched for the
presence of Alu elements to use as markers of evolution, chromosomal rearrangements, and polymorphism. Of 29 Alu elements,
14 were identified in peri-B, 11 in peri-C, and 4 in IF. The Alu elements in peri-B and peri-C clustered phylogenetically
into two clades which were classified as ``preduplication' and ``postduplication' clades. Four Alu J elements that are shared
by peri-B and peri-C and are flanked by homologous sequences in their paralogous locations, respectively, clustered into a
``preduplication' clade. By contrast, the majority of Alu elements, which are unique to either peri-B or peri-C, clustered
into a postduplication clade together with the Alu consensus subfamily members ranging from platyrrhine-specific (Spqxcg)
to catarrhine-specific Alu sequences (Y). The insertion of platyrrhine-specific Alu elements in postduplication locations
of peri-B and peri-C implies that these two segments are the products of a duplication which occurred in primates prior to
the divergence of the New World primate from the human lineage (35–44 mya). Examination of the paralogous Alu integration
sites revealed that 9 of 14 postduplication Alu sequences have produced microsatellites of different length and sequence within
the Alu 3′-poly A tail. The present analysis supports the hypothesis that HLA-B and HLA-C genes are products of an extended
segmental duplication between 44 and 81 million years ago (mya), and that subsequent diversification of both genomic segments
occurred because of the mobility and mutation of retroelements such as Alu repeats.
Received: 21 May 1997 / Accepted: 9 July 1997 相似文献
108.
Endogenous nitric oxide decreases xanthine oxidase-mediated neutrophil adherence: role of P-selectin
Terada Lance S.; Repine John E.; Piermattei Dale; Hybertson Brooks M. 《Journal of applied physiology》1997,82(3):913-917
Terada, Lance S., John E. Repine, Dale Piermattei, andBrooks M. Hybertson. Endogenous nitric oxide decreases xanthine oxidase-mediated neutrophil adherence: role of P-selectin.J. Appl. Physiol. 82(3): 913-917, 1997.The oxygen radical-producing enzyme xanthine oxidase (XO) canpromote neutrophil adherence to endothelium. Recognizing that a balanceoften exists in inflammatory processes, we sought to determine whetherXO initiates antiadherent pathways. We found that bovine pulmonaryarterial endothelial cells (EC) exposed to XO released increasedamounts of nitrite into the media, reflecting an increased productionof nitric oxide (NO). When EC were subjected to shear stress, treatmentwith XO and/or the NO synthase inhibitorN-nitro-L-arginine(L-NNA) increased neutrophilrolling behavior and firm neutrophil adherence to EC in an additivefashion. Both rolling and adherent interactions were abolished bymonoclonal antibodies directed against P-selectin. In addition,treatment of EC with XO and/orL-NNA increased both surfaceexpression of P-selectin and release of von Willebrand factor intomedia. Finally, treatment of EC with the NO donor sodium nitroprussidedecreased XO-mediated neutrophil rolling and adherence. We concludethat XO stimulates EC to produce NO and that NO decreases theP-selectin-dependent neutrophil adhesion initiated by XO. Suchincreases in endogenous NO may constitute an importantnegative-feedback response to the acute proadhesive effects of XO. 相似文献
109.
Genetic and functional evidence that Type IV pili are required for social gliding motility in Myxococcus xanthus 总被引:19,自引:12,他引:7
The social gliding behaviour of Myxococcus xanthus has previously been associated with the presence of polar pili. A Tn 5 transposon insertion was isolated which introduces a defect in social gliding and is genetically linked to a known sgl locus; this insertion was found also to cause a piliation defect. A 2.7 kb section of DNA was isolated from either side of this transposon and sequenced, revealing three genes which encode amino acid sequences with substantial similarity to components of the Type IV pilus biogenesis pathway in Pseudomonas aeruginosa . The myxococcal pilA gene encodes a putative pilin precursor with a short signal sequence and processing site similar to those of other Type IV pilins. Myxococcal pilS and pilR encode amino acid sequences with similarity to PilS and PilR of P. aeruginosa , as well as to other members of the NtrB/C family of two-component regulators. Mutations within pilR and pilA that have no polar effect were demonstrated to be responsible for pilus and social motility defects. These results indicate that the pili of M. xanthus belong to the Type IV family of pili, and demonstrate that these pili are actually required for social motility. 相似文献
110.
The metabolism of radiolabeled arachidonic acid (AA) by the intact bovine retina
has been studied. Synthesis of prostaglandins (PGs) and hydroxyeicosatetraenoic acids (HETEs), and incorporation of AA into glycerolipids has been measured by reverse-phase and straight-phase high performance liquid chromatography with flow scintillation detection, and by thin-layer chromatography. AA was actively acylated into glycerolipids, particularly triglycerides, phosphatidylcholine and phosphatidylinositol. AA was also converted to the major PGs, PGF2α, PGE2, PGD2, 6-keto-PGF1α and TXB2, and to the lipoxygenase reaction products, 12-HETE, 5-HETE, and other monohydroxy isomers. Approximately 6% of the radiolabeled AA was converted to eicosanoids. The synthesis of HETEs was inhibited in a concentration-dependent manner (IC50 = 8.3 NM) by nordihydroguaiaretic acid (NDGA). PG synthesis was inhibited by aspirin (10 μM), indomethacin (1 μM) and NDGA (IC50 = 380 nM). Metabolism of AA via lipoxygenase, cyclooxygenase and activation-acylation was inhibited by boiling retinal tissue prior to incubation. These studies demonstrate an active system for the uptake and utilization of AA in the bovine retina, and provide the first evidence of lipoxygenase-mediated metabolism of AA, resulting in the synthesis of mono-hydroxyeicosatetraenoic acids, in the retina. 相似文献