全文获取类型
收费全文 | 3341篇 |
免费 | 195篇 |
国内免费 | 4篇 |
出版年
2024年 | 9篇 |
2023年 | 11篇 |
2022年 | 49篇 |
2021年 | 66篇 |
2020年 | 46篇 |
2019年 | 68篇 |
2018年 | 111篇 |
2017年 | 70篇 |
2016年 | 137篇 |
2015年 | 191篇 |
2014年 | 218篇 |
2013年 | 243篇 |
2012年 | 303篇 |
2011年 | 273篇 |
2010年 | 189篇 |
2009年 | 182篇 |
2008年 | 218篇 |
2007年 | 189篇 |
2006年 | 135篇 |
2005年 | 141篇 |
2004年 | 112篇 |
2003年 | 109篇 |
2002年 | 82篇 |
2001年 | 72篇 |
2000年 | 82篇 |
1999年 | 53篇 |
1998年 | 17篇 |
1997年 | 17篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 13篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 3篇 |
排序方式: 共有3540条查询结果,搜索用时 15 毫秒
941.
Park YC Kim SJ Choi JH Lee WH Park KM Kawamukai M Ryu YW Seo JH 《Applied microbiology and biotechnology》2005,67(2):192-196
Coenzyme Q10 (CoQ10) is a quinine consisting of ten units of the isoprenoid side-chain. Because it limits the oxidative attack of free radicals to DNA and lipids, CoQ10 has been used as an antioxidant for foods, cosmetics and pharmaceuticals. Decaprenyl diphosphate synthase (DPS) is the key enzyme for synthesis of the decaprenyl tail in CoQ10 with isopentenyl diphosphate. The ddsA gene coding for DPS from Gluconobacter suboxydans was expressed under the control of an Escherichia coli constitutive promoter. Analysis of the cell extract in recombinant E. coli BL21/pACDdsA by high performance liquid chromatography and mass spectrometry showed that CoQ10 rather than endogenous CoQ8 was biologically synthesized as the major coenzyme Q. Expression of the ddsA gene with low copy number led to the accumulation of CoQ10 to 0.97 mg l–1 in batch fermentation. A high cell density (103 g l–1) in fed-batch fermentation of E. coli BL21/pACDdsA increased the CoQ10 concentration to 25.5 mg l –1 and its productivity to 0.67 mg l–1 h–1, which were 26.0 and 6.9 times higher than the corresponding values for batch fermentation. 相似文献
942.
Hwang DY Cho JS Kim CK Shim SB Jee SW Lee SH Seo SJ Cho JY Lee SH Kim YK 《Neurochemical research》2005,30(9):1171-1177
Insulin-degrading enzyme (IDE) is a 110-kDa thiol zinc-methalloendopeptidase that can cleave small Aβ peptides and the APP
intracellular domain (AICD). The aim of this study was to examine aging-related correlation of IDE with γ-secretase-generated
products involving insulin and glucose levels in transgenic brains expressing neuron-specific enolase (NSE)-controlled human
mutant presenilin-2 (hPS2m). Herein, we concluded that the levels of IDE expression in transgenic brains were decreased relative
to those of control mice at 15 months of age. In parallel, inhibition in the IDE expression at this age underlies to the levels-up
of Aβ-42, AICD, γ-secretase, and glucose with a level-down of insulin. Thus, IDE expression is critical target for the therapeutic
trials. 相似文献
943.
Facilitation of expression and purification of an antimicrobial peptide by fusion with baculoviral polyhedrin in Escherichia coli 总被引:3,自引:0,他引:3
Wei Q Kim YS Seo JH Jang WS Lee IH Cha HJ 《Applied and environmental microbiology》2005,71(9):5038-5043
Several fusion strategies have been developed for the expression and purification of small antimicrobial peptides (AMPs) in recombinant bacterial expression systems. However, some of these efforts have been limited by product toxicity to host cells, product proteolysis, low expression levels, poor recovery yields, and sometimes an absence of posttranslational modifications required for biological activity. For the present work, we investigated the use of the baculoviral polyhedrin (Polh) protein as a novel fusion partner for the production of a model AMP (halocidin 18-amino-acid subunit; Hal18) in Escherichia coli. The useful solubility properties of Polh as a fusion partner facilitated the expression of the Polh-Hal18 fusion protein ( approximately 33.6 kDa) by forming insoluble inclusion bodies in E. coli which could easily be purified by inclusion body isolation and affinity purification using the fused hexahistidine tag. The recombinant Hal18 AMP ( approximately 2 kDa) could then be cleaved with hydroxylamine from the fusion protein and easily recovered by simple dialysis and centrifugation. This was facilitated by the fact that Polh was soluble during the alkaline cleavage reaction but became insoluble during dialysis at a neutral pH. Reverse-phase high-performance liquid chromatography was used to further purify the separated recombinant Hal18, giving a final yield of 30% with >90% purity. Importantly, recombinant and synthetic Hal18 peptides showed nearly identical antimicrobial activities against E. coli and Staphylococcus aureus, which were used as representative gram-negative and gram-positive bacteria, respectively. These results demonstrate that baculoviral Polh can provide an efficient and facile platform for the production or functional study of target AMPs. 相似文献
944.
Enhanced antioxidant enzymes are associated with reduced hydrogen peroxide in barley roots under saline stress 总被引:5,自引:0,他引:5
Kim SY Lim JH Park MR Kim YJ Park TI Seo YW Choi KG Yun SJ 《Journal of biochemistry and molecular biology》2005,38(2):218-224
Antioxidant enzymes are related to the resistance to various abiotic stresses including salinity. Barley is relatively tolerant to saline stress among crop plants, but little information is available on barley antioxidant enzymes under salinity stress. We investigated temporal and spatial responses of activities and isoform profiles of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), non-specific peroxidase (POX), and glutathione reductase (GR) to saline stress in barley seedlings treated with 200 mM NaCl for 0, 1, 2, 5 days, respectively. In the control plant, hydrogen peroxide content was about 2-fold higher in the root than in the shoot. Under saline stress, hydrogen peroxide content was decreased drastically by 70% at 2 d after NaCl treatment (DAT) in the root. In the leaf, however, the content was remained unchanged by 2 DAT and increased about 14 % at 5 DAT. In general, the activities of antioxidant enzymes were increased in the root and shoot under saline stress. But the increase was more significant and consistent in the root. The activities of SOD, CAT, APX, POX, and GR were increased significantly in the root within 1 DAT, and various elevated levels were maintained by 5 DAT. Among the antioxidant enzymes, CAT activity was increased the most drastically. The significant increase in the activities of SOD, CAT, APX, POX, and GR in the NaCl-stressed barley root was highly correlated with the increased expression of the constitutive isoforms as well as the induced ones. The hydrogen peroxide content in the root. 相似文献
945.
Biodegradable cross-linked poly(beta-amino ester) (CLPAE) was synthesized by Michael addition of pentaerythritol triacrylate and N,N-dimethylethylenediamine and modified with aminohexanoic acid and lysine to CLPAE-Ahx and CLPAE-Lys, respectively, for a gene delivery system. They could self-assemble with plasmid DNA, forming nanosized polyplexes, and CLPAE-Ahx polyplex released plasmid DNA slowly during a week through stepwise degradation. The polymers showed minimal cytotoxicity on 293 cells due to their biodegradability and biocompatibility. Transfection efficiencies of CLPAE-Ahx and CLPAE-Lys were comparable to that of PEI in 293 cells and C2C12 cells. Additionally, high transfection of CLPAE-Ahx on primary rat aorta vascular smooth muscle cells (SMC) and primary mouse embryonic fibroblast cells (MEF) shows a potential for a gene delivery system on primary cells, restenosis treatment of human SMC, and MEF cell function research. In conclusion, CLPAE-Ahx could be used as a nontoxic and highly efficient gene delivery system. 相似文献
946.
947.
Thirty-five strains of Burkholderia cenocepacia from clinical and environmental sources were characterized genotypically by repetitive sequence PCR (ERIC- and BOX-PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the flagellin gene (fliC). In cluster analysis based on the repetitive PCR profiles the strains were composed of five clusters, of which clusters 1, 2 and 3 were more closely related to each other than to clusters 4 and 5. It has been reported that the majority of Burkholderia cepacia complex strains can be separated into two types on the basis of fliC size (types I and II correspond to 1.4 and 1.0 kb, respectively). When the strains were analysed by PCR of fliC, all strains yielded amplified products of 1.0 kb except for three strains. The latter strains gave PCR products of 0.7 kb (atypical type), which belonged to repetitive PCR cluster 5. These results indicated that the majority of B. cenocepacia strains belonged to flagellin type II. In the RFLP analysis of the large fliC amplicons with HaeIII, 10 patterns were observed indicating remarkable variation. Strains grouping in repetitive PCR cluster 4 had a unique fliC RFLP pattern. The results of repetitive PCR typing and PCR-RFLP analysis of fliC showed a strong correlation. Strains belonging to the repetitive PCR clusters 4 or 5 were distinctly different from other B. cenocepacia strains as shown by PCR-RFLP analysis of the fliC gene and phenotypic assays. 相似文献
948.
The human pseudoautosomal region 1 (PAR1) is essential for the obligatory X-Y crossover in male meiosis. Despite its critical role, comparative studies of human and mouse pseudoautosomal genes have been limited owing to the scarcity of genes conserved between the two species. Human CD99 is a 32-kDa cell surface protein that is encoded by the MIC2 gene localized to the PAR1. Although several sequences such as CD99L2, PBDX, and CD99L1 are related to CD99, its murine ortholog, Cd99, has not yet been identified. Here we report a novel mouse Cd99, designated D4, which shows overall sequence homology to CD99, with the highest conservation between the two genes being found in the transmembrane regions. In addition, the D4 protein displays biochemical characteristics, functional homology, and expression patterns similar to those of CD99. The D4 gene is localized on an autosome, chromosome 4, reflecting a common mapping feature with other mouse orthologs of human PAR1 genes. Furthermore, a phylogenetic analysis of CD99-related genes confirmed that the D4 gene is indeed an ortholog of CD99 and exhibits the accelerated evolution pattern of CD99 orthologs, as compared to the CD99L2 orthologs. On the basis of these findings, we suggest that CD99 belongs to the ancient PAR genes, and that the rapid interspecies divergence of its present sequence and map position is due to a high recombination frequency and the occurrence of chromosomal translocation, supporting the addition-attrition hypothesis for PAR evolution. 相似文献
949.
950.
Lee YI Seo M Kim Y Kim SY Kang UG Kim YS Juhnn YS 《The Journal of biological chemistry》2005,280(23):22044-22052
Changes in plasma membrane electrical potential evoke signals that regulate the expressions of various genes in the nervous system. However, the role of glycogen synthase kinase 3beta (GSK-3beta) in this process has not been elucidated. Thus, this study was performed to examine whether membrane depolarization can regulate the phosphorylation of GSK-3beta and to identify the molecular mechanisms involved in this regulation. The depolarization by treating with 100 mm KCl for 5 min resulted in the undulating phosphorylation of GSK-3beta at Ser-9 in SH-SY5Y human neuroblastoma cells, in H19 -7/IGF-IR rat embryonic hippocampal cells, and in PC12 rat pheochromocytoma cells, but not in A172 human glioblastoma cells. Cellular beta-catenin contents showed a temporal pattern similar to that of the Ser-9 phosphorylation of GSK-3beta. Treatment with wortmannin or calphostin C or the expression of dominant negative Akt inhibited phosphorylation of GSK-3beta at Ser-9 following the KCl-induced depolarization of SH-SY5Y cells. Moreover, pretreatment with okadaic acid or cyclosporin A blocked the dephosphorylation of GSK-3beta at Ser-9 at 0, 15, and 30 min after KCl-induced depolarization, and the activity of protein phosphatases (PP) 2A and 2B increased at these times. Treatment with nifedipine or calcium-free medium inhibited GSK-3beta dephosphorylation following membrane depolarization, and the amounts of co-immunoprecipitated GSK-3beta and PP2A changed in parallel with GSK-3beta dephosphorylation. Our study demonstrated that KCl-induced depolarization caused undulating GSK-3beta phosphorylation/dephosphorylation, which was regulated for the most part by phosphatidylinositol 3-kinase and Akt (phosphorylation) and PP2A and PP2B (dephosphorylation), respectively. 相似文献