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   18940篇
  免费   1378篇
  国内免费   1236篇
  21554篇
  2024年   41篇
  2023年   254篇
  2022年   538篇
  2021年   922篇
  2020年   563篇
  2019年   804篇
  2018年   797篇
  2017年   561篇
  2016年   830篇
  2015年   1101篇
  2014年   1346篇
  2013年   1441篇
  2012年   1672篇
  2011年   1519篇
  2010年   967篇
  2009年   934篇
  2008年   1045篇
  2007年   974篇
  2006年   795篇
  2005年   682篇
  2004年   530篇
  2003年   518篇
  2002年   437篇
  2001年   343篇
  2000年   299篇
  1999年   290篇
  1998年   164篇
  1997年   158篇
  1996年   155篇
  1995年   117篇
  1994年   84篇
  1993年   70篇
  1992年   110篇
  1991年   82篇
  1990年   68篇
  1989年   52篇
  1988年   43篇
  1987年   43篇
  1986年   38篇
  1985年   51篇
  1984年   8篇
  1983年   17篇
  1982年   9篇
  1981年   11篇
  1980年   7篇
  1979年   7篇
  1978年   6篇
  1977年   5篇
  1974年   5篇
  1969年   11篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
111.
This paper describes our medicinal chemistry efforts on 7-(cyclopentyloxy)-6-methoxy1,2,3,4-tetrahydroisoquinoline scaffold: design, synthesis and biological evaluation using conformational restriction approach and bioisosteric replacement strategy. Biological data revealed that the majority of the synthesized compounds of this series displayed moderate to potent inhibitory activity against PDE4B and strong inhibition of LPS-induced TNFα release. Among them, compound 19 exhibited the strongest inhibition against PDE4B with an IC50 of 0.88?µM and 21 times more potent selectivity toward PDE4B over PDE4D when compared to rolipram. A primary structure-activity relationship study showed that the attachment of CH3O group or CF3O group to the phenyl ring at the para-position was helpful to enhance the inhibitory activity against PDE4B. Moreover, sulfonamide group played a key role in improving the inhibitory activity against PDE4B and subtype selectivity. In addition, the attachment of the additional rigid substituents at the C-3 position of 1,2,3,4-tetrahydroisoquinoline ring was favored to subtype selectivity, which was consistent well with the observed docking simulation.  相似文献   
112.
The 300-kDa cation-independent mannose 6-phosphate receptor (CI-MPR), which contains multiple mannose 6-phosphate (Man-6-P) binding sites that map to domains 3, 5, and 9 within its 15-domain extracytoplasmic region, functions as an efficient carrier of Man-6-P-containing lysosomal enzymes. To determine the types of phosphorylated N-glycans recognized by each of the three carbohydrate binding sites of the CI-MPR, a phosphorylated glycan microarray was probed with truncated forms of the CI-MPR. Surface plasmon resonance analyses using lysosomal enzymes with defined N-glycans were performed to evaluate whether multiple domains are needed to form a stable, high affinity carbohydrate binding pocket. Like domain 3, adjacent domains increase the affinity of domain 5 for phosphomannosyl residues, with domain 5 exhibiting ∼60-fold higher affinity for lysosomal enzymes containing the phosphodiester Man-P-GlcNAc when in the context of a construct encoding domains 5–9. In contrast, domain 9 does not require additional domains for high affinity binding. The three sites differ in their glycan specificity, with only domain 5 being capable of recognizing Man-P-GlcNAc. In addition, domain 9, unlike domains 1–3, interacts with Man8GlcNAc2 and Man9GlcNAc2 oligosaccharides containing a single phosphomonoester. Together, these data indicate that the assembly of three unique carbohydrate binding sites allows the CI-MPR to interact with the structurally diverse phosphorylated N-glycans it encounters on newly synthesized lysosomal enzymes.  相似文献   
113.
114.
In inflamed joints of rheumatoid arthritis, PGE(2) is highly expressed, and IL-10 and IL-6 are also abundant. PGE(2) is a well-known activator of the cAMP signaling pathway, and there is functional cross-talk between cAMP signaling and the Jak-STAT signaling pathway. In this study, we evaluated the modulating effect of PGE(2) on STAT signaling and its biological function induced by IL-10 and IL-6, and elucidated its mechanism in THP-1 cells. STAT phosphorylation was determined by Western blot, and gene expression was analyzed using real-time PCR. Pretreatment with PGE(2) significantly augmented IL-10-induced STAT3 and STAT1 phosphorylation, as well as suppressors of cytokine signaling 3 (SOCS3) and IL-1R antagonist gene expression. In contrast, PGE(2) suppressed IL-6-induced phosphorylation of STAT3 and STAT1. These PGE(2)-induced modulating effects were largely reversed by actinomycin D. Pretreatment with dibutyryl cAMP augmented IL-10-induced, but did not change IL-6-induced STAT3 phosphorylation. Misoprostol, an EP2/3/4 agonist, and butaprost, an EP2 agonist, augmented IL-10-induced STAT3 phosphorylation and SOCS3 gene expression, but sulprostone, an EP1/3 agonist, had no effect. H89, a protein kinase A inhibitor, and LY294002, a PI3K inhibitor, diminished PGE(2)-mediated augmentation of IL-10-induced STAT3 phosphorylation. In this study, we found that PGE(2) selectively regulates cytokine signaling via increased intracellular cAMP levels and de novo gene expression, and these modulating effects may be mediated through EP2 or EP4 receptors. PGE(2) may modulate immune responses by alteration of cytokine signaling in THP-1 cells.  相似文献   
115.
The purpose of this paper is to investigate the current status and method of biotope mapping for practical use for landscape planning and environmental policy in urban ecosystem in Korea. We examine current ecological mapping of Seoul, Seongnam, Daegu, and Yongin. Ecological mapping is examined closely in terms of investigation methodology, investigation subject, classification of urban landscape, and the present condition of application. Biotope mapping in Seoul and Seongnam were carried out by the city governments concerned with the pre-set budgets earmarked for mapping. In order to promote the utilization of biotope maps for city planning in Korea, the following actions should be considered. First, the survey method should be standardized by introducing a uniform standard with respect to the scope of survey, the quality of primary data used, the survey method, and the level of the survey. Second, it is necessary to identify a basic category of biotope for each area by consolidating the outcome of the previous surveys. Third, it is highly desirable to minimize the differences between the evaluation criteria and the assessment factors. Fourth, it is ideal to apply the results of the biotope evaluation to city planning in an indirect manner through reflecting the results first in the landscape plans. In order to facilitate this alternative utilization, it is necessary to strengthen the control provisions contained in the ordinances of the city concerned or to enact a set of new provisions in the ordinances so that biotope mapping could be used more widely as a criterion for the spatial environmental impact assessment.  相似文献   
116.
117.
IL-35 subunit EBI3 is up-regulated in pulmonary fibrosis tissues. In this study, we investigated the pathological role of EBI3 in pulmonary fibrosis and dissected the underlying molecular mechanism. Bleomycin-induced pulmonary fibrosis mouse model was established, and samples were performed gene expression analyses through RNAseq, qRT-PCR and Western blot. Wild type and EBI3 knockout mice were exposed to bleomycin to investigate the pathological role of IL-35, via lung function and gene expression analyses. Primary lung epithelial cells were used to dissect the regulatory mechanism of EBI3 on STAT1/STAT4 and STAT3. IL-35 was elevated in both human and mouse with pulmonary fibrosis. EBI3 knockdown aggravated the symptoms of pulmonary fibrosis in mice. EBI3 deficiency enhanced the expressions of fibrotic and extracellular matrix-associated genes. Mechanistically, IL-35 activated STAT1 and STAT4, which in turn suppressed DNA enrichment of STAT3 and inhibited the fibrosis process. IL-35 might be one of the potential therapeutic targets for bleomycin-induced pulmonary fibrosis.  相似文献   
118.
Obesity and its associated metabolic disorders such as diabetes, hepatic steatosis and chronic heart diseases are affecting billions of individuals. However there is no satisfactory drug to treat such diseases. In this study, we found that alisol A, a major active triterpene isolated from the Chinese traditional medicine Rhizoma Alismatis, could significantly attenuate high‐fat‐diet‐induced obesity. Our biochemical detection demonstrated that alisol A remarkably decreased lipid levels, alleviated glucose metabolism disorders and insulin resistance in high‐fat‐diet‐induced obese mice. We also found that alisol A reduced hepatic steatosis and improved liver function in the obese mice model.In addition, protein expression investigation revealed that alisol A had an active effect on AMPK/ACC/SREBP‐1c pathway. As suggested by the molecular docking study, such bioactivity of alisol A may result from its selective binding to the catalytic region of AMPK.Therefore, we believe that Alisol A could serve as a promising agent for treatment of obesity and its related metabolic diseases.  相似文献   
119.
Three new mycophenolic acid derivatives, penicacids A-C (1-3), together with two known analogues, mycophenolic acid (MPA, 4) and 4'-hydroxy-MPA (5), were isolated from a fungus Penicillium sp. SOF07 derived from a South China Sea marine sediment. The structures of compounds 1-3 were elucidated on the basis of MS and NMR ((1)H, (13)C, HSQC and HMBC) data analyses and comparisons with the known compounds. Structure-activity relationship studies of compounds 1-5 focused on inosine-monophosphate dehydrogenase inhibition revealed that hydroxylation at C-4', methylation at C-7-OH, dual hydroxylation at C-2'/C-3' double bond of MPA diminished bioactivity whereas glucosyl hydroxylation at C-4' correlated to bioactivity comparable to that observed for MPA.  相似文献   
120.
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