首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1747篇
  免费   119篇
  2022年   8篇
  2021年   17篇
  2020年   9篇
  2019年   19篇
  2018年   18篇
  2017年   20篇
  2016年   32篇
  2015年   37篇
  2014年   39篇
  2013年   82篇
  2012年   76篇
  2011年   85篇
  2010年   49篇
  2009年   40篇
  2008年   95篇
  2007年   70篇
  2006年   78篇
  2005年   90篇
  2004年   81篇
  2003年   66篇
  2002年   77篇
  2001年   82篇
  2000年   73篇
  1999年   62篇
  1998年   20篇
  1997年   25篇
  1996年   21篇
  1995年   22篇
  1994年   21篇
  1993年   15篇
  1992年   44篇
  1991年   41篇
  1990年   38篇
  1989年   51篇
  1988年   40篇
  1987年   19篇
  1986年   31篇
  1985年   16篇
  1984年   16篇
  1983年   10篇
  1982年   9篇
  1981年   8篇
  1980年   6篇
  1979年   10篇
  1978年   13篇
  1976年   7篇
  1975年   14篇
  1974年   8篇
  1973年   7篇
  1971年   9篇
排序方式: 共有1866条查询结果,搜索用时 312 毫秒
991.
Several studies have provided evidence that activation of antigen-specific T cells requires interactions between CD28 on T cells and its ligands, CD80 and CD86, on antigen-presenting cells (APCs). However, the effects of CD80 and CD86 on cytokine production in patients with Hymenoptera venom allergy who receive venom immunotherapy remain unclear. We examined the effects of CD80 and CD86 on Th1- and Th2-cytokine production before and after venom immunotherapy in patients with wasp-venom allergy. Peripheral blood mononuclear cells (PBMCs) were isolated from patients with wasp-venom allergy before and after three months of venom immunotherapy. CD4+ T cells and monocytes were isolated as APCs from PBMCs and were cocultured with wasp venom in the presence of anti-CD80 or -CD86 blocking antibodies. Interleukin (IL)-4, IL-10, and interferon (IFN)-gamma were measured by enzyme-linked immunosorbent assay. The expression of CD80 and CD86 on CD14+ PBMCs was detected by fluorescence-activated cell-sorter analysis. The expression of CD86, but not that of CD80, on CD14+ PBMCs cocultured with venom increased after three months of venom immunotherapy, but not before venom immunotherapy. Blockade of CD86 reduced IL-10 production after three months of venom immunotherapy. IL-10 production promoted by CD86 costimulation may be involved in the mechanism of venom immunotherapy in patients with venom allergy.  相似文献   
992.
High ethanol intake is considered to impair insulin sensitivity. In the present study, we investigated the acute and chronic effects of ethanol intake on glucose metabolism and insulin signal transduction. Hyperinsulinemic-euglycemic clamp studies revealed 70% and 51% decreases in the glucose infusion rate, 52% and 31% decreases in the glucose utilization rate, and 6.6- and 8.0-fold increases in hepatic glucose in continuous- and acute-ethanol-loaded rats, respectively. Despite the presence of insulin resistance, alcohol-fed rats showed enhanced tyrosine phosphorylation of insulin receptors, IRS-1 and IRS-2, induced by insulin injection via the portal vein. PI 3-kinase activities associated with IRSs and phosphotyrosine also increased significantly as compared with those of controls. These data suggest ethanol intake to be a factor leading to insulin resistance, regardless of whether it is a single or continuous intake. In addition, the insulin signaling step impaired by ethanol feeding is likely to be downstream from PI 3-kinase.  相似文献   
993.
Ethanol was produced by simultaneous saccharification and fermentation (SSF) from beech wood chips after bioorganosolve pretreatments by ethanolysis and white rot fungi, Ceriporiopsis subvermispora, Dichomitus squalens, Pleurotus ostreatus, and Coriolus versicolor. Beech wood chips were pretreated with the white rot fungi for 2-8 weeks without addition of any nutrients. The wood chips were then subjected to ethanolysis to separate them into pulp and soluble fractions (SFs). From the pulp fraction (PF), ethanol was produced by SSF using Saccharomyces cerevisiae AM12 and a commercial cellulase preparation, Meicelase, from Trichoderma viride. Among the four strains, C. subvermispora gave the highest yield on SSF. The yield of ethanol obtained after pretreatment with C. subvermispora for 8 weeks was 0.294 g g(-1) of ethanolysis pulp (74% of theoretical) and 0.176 g g(-1) of beech wood chips (62% of theoretical). The yield was 1.6 times higher than that obtained without the fungal treatments. The biological pretreatments saved 15% of the electricity needed for the ethanolysis.  相似文献   
994.
995.
A statistical method to evaluate data from the mouse lymphoma L5178Y/tk assay (MLA) using microwell method is proposed. This proposed method is designed for data obtained from a single culture protocol instead of the duplicate culture recommended by United Kingdom Environmental Mutagen Society (UKEMS). The proposed method consists of the following three steps: (1) to apply Dunnett type test for identifying clear negative; (2) to apply a Simpson-Margolin procedure for detecting downturn data; and (3) to apply a trend test to evaluate the dose-dependent increase in mutant frequency (MF). The performance of the proposed method was evaluated through a Monte Carlo study and a case study. False positive rates realized in the Monte Carlo study were comparable with the UKEMS method modified for a single culture protocol with the heterogeneity factors being kept at 1.0. False negative rates were less than those of the modified UKEMS method for dose response patterns with a sharp uprise in higher dose groups, whereas, they were comparable for other patterns. The results of evaluating the data from an International Collaborative Study by the proposed method seem comparable with the UKEMS method. The proposed method enables us to evaluate data from the microwell MLA with a single culture protocol.  相似文献   
996.
MOTIVATION: It is well understood that the successful clustering of expression profiles give beneficial ideas to understand the functions of uncharacterized genes. In order to realize such a successful clustering, we investigate a clustering method based on adaptive resonance theory (ART) in this report. RESULTS: We apply Fuzzy ART as a clustering method for analyzing the time series expression data during sporulation of Saccharomyces cerevisiae. The clustering result by Fuzzy ART was compared with those by other clustering methods such as hierarchical clustering, k-means algorithm and self-organizing maps (SOMs). In terms of the mathematical validations, Fuzzy ART achieved the most reasonable clustering. We also verified the robustness of Fuzzy ART using noised data. Furthermore, we defined the correctness ratio of clustering, which is based on genes whose temporal expressions are characterized biologically. Using this definition, it was proved that the clustering ability of Fuzzy ART was superior to other clustering methods such as hierarchical clustering, k-means algorithm and SOMs. Finally, we validate the clustering results by Fuzzy ART in terms of biological functions and evidence. AVAILABILITY: The software is available at http//www.nubio.nagoya-u.ac.jp/proc/index.html  相似文献   
997.
Vibrios are gram-negative gamma-proteobacteria which are ubiquitous in marine and estuarine environments. Recently, we demonstrated that some, if not all, Vibrio species have two circular chromosomes. The whole genome sequence of Vibrio cholerae N16961 has been reported. In this study, we constructed a physical and genetic map of the genome of Kanagawa phenomenon-positive Vibrio parahaemolyticus strain KX-V237 and compared it with those of V. parahaemolyticus AQ4673 and V. cholerae N16961. The genome of KX-V237 comprised two circular chromosomes (3.3 and 1.9 Mb), similar to the structure of the AQ4673 genome. The relative positions of the genes on the genomes were well conserved in the two strains, but a large inversion on the large chromosomes, probably symmetric around the replication origin, was suggested. Although the sizes of the large chromosomes of KX-V237 and V. cholerae N16961 were similar, the sizes of the small chromosomes were very different. Unlike N16961, the superintegron of KX-V237 was located on the large chromosome. Comparison of the genetic maps of the chromosomes of KX-V237 and V. cholerae N16961 revealed that most of the open reading frames (ORFs) present on the large chromosome of the V. cholerae strain had homologues on the large chromosome of the V. parahaemolyticus strain and that most of the ORFs on the small chromosome of N16961 were present on the small chromosome of KX-V237. The difference in the orders of the ORFs on the chromosomes of N16961 and KX-V237 implies that numerous and frequent genetic exchanges have occurred intrachromosomally rather than interchromosomally.  相似文献   
998.
The Crk-associated substrate (Cas) is a unique docking protein that possesses a repetitive stretch of tyrosine-containing motifs and an Src homology 3 (SH3) domain. Embryonic fibroblasts lacking Cas demonstrated resistance to Src-induced transformation along with impaired actin bundling and cell motility, indicating critical roles of Cas in actin cytoskeleton organization, cell migration, and oncogenesis. To gain further insight into roles of each domain of Cas in these processes, a compensation assay was performed by expressing a series of Cas mutants in Cas-deficient fibroblasts. The results showed that motifs containing YDxP were indispensable for actin cytoskeleton organization and cell migration, suggesting that CrkII-mediated signaling regulates these biological processes. The C-terminal Src-binding domain played essential roles in cell migration and membrane localization of Cas, although it was dispensable in the organization of actin stress fibers. Furthermore, the Src-binding domain was also a prerequisite for Src transformation possibly, because of its crucial role in the phosphorylation of Cas during transformation. Overall, differential uses of the Cas domains in individual biological processes were demonstrated.  相似文献   
999.
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号