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971.
Hodges RL Kelkar HS Xuei X Skatrud PL Keller NP Adams TH Kaiser RE Vinci VA McGilvray D 《Journal of industrial microbiology & biotechnology》2000,25(6):333-341
Echinocandin B (ECB), a lipopolypeptide used as a starting material for chemical manufacture of the anti-Candida agent LY303366,
is produced by fermentation using a strain of Aspergillus nidulans. In addition to ECB, the wild-type strain also produces a significant level of sterigmatocystin (ST), a potent carcinogen
structurally related to the aflatoxins. Characterization of a mutant designated A42355-OC-1 (OC-1), which is blocked in ST
biosynthesis, was the result of a chromosomal translocation. The chromosomal regions containing the breakpoints of the translocation
were isolated and DNA sequencing and PCR analysis of the chromosomal breakpoints demonstrated the translocation occurred within
the stcW gene of the ST biosynthetic pathway, resulting in disruption of the open reading frame for this gene. Biochemical feeding
studies indicate the involvement of this gene product in the conversion of averufin to 1-hydroxy versicolorone. This work
demonstrates an effective synergy between classical strain improvement methods and molecular genetics. Journal of Industrial Microbiology & Biotechnology (2000) 25, 333–341.
Received 27 April 2000/ Accepted in revised form 25 November 2000 相似文献
972.
Eichholtz-Wirth H Sagan D 《Apoptosis : an international journal on programmed cell death》2000,5(3):255-263
Fractionated -irradiation (15 × 2 Gy in 3 weeks) induces a cellular resistance in HeLa cells against cisplatin exposure but not against irradiation. The mechanisms underlying this cellular resistance are associated with major changes in the TNFR1-dependent transduction pathway. The resistant HeLa/B cells exhibit increased levels of NF-B with temporally independent regulation of the subunits NF-B50 and NF-B65. Blocking IB degradation by the proteasome inhibitor PSI, which abolishes the release of the active NF-B protein, induces cell death much more effectively in the parental than in the resistant HeLa/B cells. The translocation of NF-B does not seem to be affected in a similar manner since masking of the translocation sequence by NF-B SN50 enhances cisplatin toxicity to the same degree in both cell lines and overcomes drug resistance. Changes in upstream signaling are suggested by increased sensitivity of the parental HeLa cells to cisplatin in the presence of neutralizing anti-TNFR1. In HeLa/B cells, reduced expression of the 50 kDa silencer of death domain, SODD, is accompanied by constitutive overexpression of a 40–42 kDa SODD-like protein. A possible involvement of SODD in cisplatin resistance is discussed, which may shift the balance between life and death in the TNF receptor pathway to increased NF-B activation. 相似文献
973.
L. M. Simon M. Kotormn K. Marczi K. Lszl 《Journal of Molecular Catalysis .B, Enzymatic》2000,10(6):213
The bovine trypsin-catalysed synthesis of N-acetyl-
-arginine ethyl ester from N-acetyl-
-arginine and ethanol was studied in various organic solvents (dimethyl sulfoxide, dioxane, dimethylformamide, acetonitrile, acetone, tetrahydrofuran, chloroform, toluene, carbon tetrachloride, cyclohexane and n-hexane). The highest yield was achieved in acetonitrile after incubation for 6 or 24 h. The optimal conditions for ester synthesis in acetonitrile for 6 h were as follows: 5.0 mM N-acetyl-
-arginine, 10.0 M ethanol, 7.2 mg trypsin, 2.87% water, total volume 10.3 ml, pH 7.0 and 30°C. The hydrolytic activity of trypsin was determined after incubation for 6 days, when 87.7% of the original activity remained, suggesting that acetonitrile caused little inactivation of the enzyme. The synthetic reaction resulted in a maximal 79.3% conversion under optimized conditions after incubation for 48 h. 相似文献
974.
The electronic structures of small, odd-membered, all-trans polyenes doped with one Na atom at various positions have been investigated using Hartree-Fock and density functional (B3LYP) theory with a 6-31G(d) basis set. Two distinctly different structural motifs have been identified. In one motif, the dopant atom interacts with an allylic polyene unit in a 4-electron interaction that results in a planar polyene backbone. The other motif has the dopant atom interacting with a pentadienyl polyene unit in a 6-electron interaction, which produces a significantly warped polyene backbone. Independent of structural motif at the doping site, the portion of the polyene structure outside the interaction region remains largely undisturbed in terms of planarity and bond length alternation. For a particular formula unit and potential energy surface, the stationary points corresponding to minima and transition states are remarkably close in energy despite the pronounced changes that occur in the dihedral angles of the polyene backbone at the dopant sites. Whereas internal and external instabilities are found in the Hartree-Fock wavefunctions for NaC7H9 and NaC9H11 structures, the restricted B3LYP wavefunctions are stable for all structures investigated.Electronic Supplementary Material available. 相似文献
975.
The effects of schisandrin B (Sch B), a dibenzocyclooctadiene derivative isolated from the fruit of Schisandra chinensis, and dimethyl diphenyl bicarboxylate (DDB), a synthetic intermediate of schisandrin C (also a dibenzocyclooctadiene derivative), on hepatic mitochondrial glutathione redox status in control and carbon tetrachloride (CCl4)-intoxicated mice were examined. Treating mice with Sch B or DDB at a daily oral dose of 1 mmol/kg for 3 d did not produce any significant alterations in plasma alanine aminotransferase (ALT) and sorbital dehydrogenase (SDH) activities. CCl4 treatment caused drastic increases in both plasma ALT and SDH activities in mice. Pretreating mice with Sch B or DDB at the same dosage regimen significantly suppressed the CCl4-induced increase in plasma ALT activity, with the inhibitory effect of Sch B being much more potent. Sch B, but not DDB, pretreatment could also decrease the plasma SDH activity in CCl4-intoxicated mice. The lowering of plasma SDH activity, indicative of hepatoprotection against CCl4 toxicity, by Sch B pretreatment was associated with an enhancement in hepatic mitochondrial glutathione redox status as well as an increase in mitochondrial glutathione reductase (mtGRD) activity in both non-CCl4 and CCl4-treated mice. DDB pretreatment, though enhancing both hepatic mitochondrial glutathione redox status and mtGRD activity in control animals, did not produce any beneficial effect in CCl4-treated mice. The difference in hepatoprotective action against CCl4 toxicity between Sch B and DDB may therefore be related to their ability to maintain hepatic mitochondrial glutathione redox status under oxidative stress condition. 相似文献
976.
Under microaerophilic conditions Salmonella typhimurium LT2 synthesizes cobalamin, during which 5,6-dimethylbenzimidazole is formed from riboflavin. We report here that in an anoxic
environment S. typhimurium did not form cobalamin, but rather adenylcobamide, 2-methyladenylcobamide, and cobyric acid. This indicated that S. typhimurium, like other microorganisms that synthesize 5,6-dimethylbenzimidazole from riboflavin, requires oxygen for the formation of
the cobalamin base.
Received: 29 June 1999 / Accepted: 29 September 1999 相似文献
977.
McCarthy DO Glowacki N Schell K Emler CA Albertini MR 《Cancer immunology, immunotherapy : CII》2000,49(2):85-93
The aim of this study was to compare the antigenicity of human melanoma cells molecularly modified by particle-mediated gene
transfer to have transient or stable expression of the B7-1 co-stimulatory molecule (CD80). The unmodified melanoma cells
(mel5, m21) had no constitutive expression of B7-1, but 22%–28% of cells had transient B7-1 expression 24 h following transfection
with cDNA for B7-1 (mel5-B7, m21-B7). In addition, 85%–90% of cells had stable B7-1 expression following transfection with
cDNA for B7-1 and in vitro culture under selection conditions (mel5-B7neo, m21-B7neo). Allogeneic HLA-unmatched normal donor
peripheral blood mononuclear cells (PBMC) secreted greater amounts of granulocyte/macrophage-colony-stimulating factor (GM-CSF)
when incubated for 3 days with m21-B7neo than did PBMC incubated with m21-B7, which, in turn, secreted greater amount of GM-CSF
than PBMC incubated with m21. Similarly, cell-mediated cytotoxicity against unmodified melanoma cells by PBMC co-cultured
for 5 days with the modified or unmodified melanoma cells was proportional to the level of B7-1 expression on the stimulating
cells. This cytolytic activity had both an HLA-class-I-restricted and an HLA-class-I-unrestricted component. Following 5 days
of co-culture, PBMC expression of CD28, the ligand for B7-1, was down-regulated in proportion to the level of B7-1 expression
on the stimulating melanoma cells. Thus, particle-mediated gene delivery of cDNA for B7-1 into human melanoma cells increased
expression of functional B7-1 and enhanced the antigenicity of the gene-modified cells in proportion to their level of B7-1
expression.
Received: 14 October 1999 / Accepted: 3 December 1999 相似文献
978.
Reciprocal role of ERK and NF-kappaB pathways in survival and activation of osteoclasts 总被引:5,自引:0,他引:5
Miyazaki T Katagiri H Kanegae Y Takayanagi H Sawada Y Yamamoto A Pando MP Asano T Verma IM Oda H Nakamura K Tanaka S 《The Journal of cell biology》2000,148(2):333-342
To examine the role of mitogen-activated protein kinase and nuclear factor kappa B (NF-kappaB) pathways on osteoclast survival and activation, we constructed adenovirus vectors carrying various mutants of signaling molecules: dominant negative Ras (Ras(DN)), constitutively active MEK1 (MEK(CA)), dominant negative IkappaB kinase 2 (IKK(DN)), and constitutively active IKK2 (IKK(CA)). Inhibiting ERK activity by Ras(DN) overexpression rapidly induced the apoptosis of osteoclast-like cells (OCLs) formed in vitro, whereas ERK activation after the introduction of MEK(CA) remarkably lengthened their survival by preventing spontaneous apoptosis. Neither inhibition nor activation of ERK affected the bone-resorbing activity of OCLs. Inhibition of NF-kappaB pathway with IKK(DN) virus suppressed the pit-forming activity of OCLs and NF-kappaB activation by IKK(CA) expression upregulated it without affecting their survival. Interleukin 1alpha (IL-1alpha) strongly induced ERK activation as well as NF-kappaB activation. Ras(DN) virus partially inhibited ERK activation, and OCL survival promoted by IL-1alpha. Inhibiting NF-kappaB activation by IKK(DN) virus significantly suppressed the pit-forming activity enhanced by IL-1alpha. These results indicate that ERK and NF-kappaB regulate different aspects of osteoclast activation: ERK is responsible for osteoclast survival, whereas NF-kappaB regulates osteoclast activation for bone resorption. 相似文献
979.
Carpentier M Allain F Haendler B Slomianny MC Spik G 《Protein science : a publication of the Protein Society》2000,9(12):2386-2393
The immunosuppressant drug cyclosporin A (CsA) inhibits T-cell function by blocking the phosphatase activity of calcineurin. This effect is mediated by formation of a complex between the drug and cyclophilin (CyP), which creates a composite surface able to make high-affinity contacts with calcineurin. In vitro, the CyPB/CsA complex is more effective in inhibiting calcineurin than the CyPA/CsA and CyPC/CsA complexes, pointing to fine structural differences in the calcineurin-binding region. To delineate the calcineurin-binding region of CyPB, we mutated several amino acids, located in two loops corresponding to CyPA regions known to be involved, as follows: R76A, G77H, D155R, and D158R. Compared to wild-type CyPB, the G77H, D155R, and D158R mutants had intact isomerase and CsA-binding activities, indicating that no major conformational changes had taken place. When complexed to CsA, they all displayed only reduced affinity for calcineurin and much decreased inhibition of calcineurin phosphatase activity. These results strongly suggest that the three amino acids G77, D155, and D158 are directly involved in the interaction of CyPB/CsA with calcineurin, in agreement with their exposed position. The G77, D155, and D158 residues are not maintained in CyPA and might therefore account for the higher affinity of the CyPB/CsA complex for calcineurin. 相似文献
980.
A direct regional scale estimate of transgene movement from genetically modified oilseed rape to its wild progenitors 总被引:9,自引:0,他引:9
Wilkinson MJ Davenport IJ Charters YM Jones AE Allainguillaume J Butler HT Mason DC Raybould AF 《Molecular ecology》2000,9(7):983-991
One of the major environmental concerns over genetically modified (GM) crops relates to transgene movement into wild relatives. The pattern of hybridization ultimately affects the scale and rapidity of ecological change and the feasibility of containment. A new procedure for quantifying hybrid formation over large areas is described. Remote sensing was used to identify possible sites of sympatry between Brassica napus and its progenitor species across 15 000 km2 of south-east England in 1998. Two sympatric populations with B. rapa and one with B. oleracea were found over the entire survey area. Every newly recruited plant in these populations in 1999 was screened for hybrid status using flow cytometry and molecular analyses. One hybrid was observed from the 505 plants screened in the B. rapa populations but none of the nine B. oleracea recruits were hybrids. Measures to minimize gene flow are suggested, and a procedure for the post-release evaluation and containment of GM cultivars is proposed. 相似文献