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   3520篇
  免费   158篇
  国内免费   3篇
  3681篇
  2023年   36篇
  2022年   73篇
  2021年   111篇
  2020年   69篇
  2019年   74篇
  2018年   112篇
  2017年   94篇
  2016年   140篇
  2015年   162篇
  2014年   174篇
  2013年   270篇
  2012年   309篇
  2011年   293篇
  2010年   169篇
  2009年   166篇
  2008年   171篇
  2007年   178篇
  2006年   139篇
  2005年   108篇
  2004年   99篇
  2003年   96篇
  2002年   55篇
  2001年   52篇
  2000年   36篇
  1999年   30篇
  1998年   18篇
  1997年   17篇
  1996年   19篇
  1995年   13篇
  1994年   11篇
  1993年   8篇
  1992年   25篇
  1991年   20篇
  1990年   22篇
  1989年   17篇
  1988年   24篇
  1987年   18篇
  1986年   22篇
  1985年   23篇
  1984年   21篇
  1983年   24篇
  1982年   13篇
  1981年   14篇
  1979年   19篇
  1978年   9篇
  1977年   12篇
  1974年   12篇
  1972年   18篇
  1971年   12篇
  1969年   10篇
排序方式: 共有3681条查询结果,搜索用时 0 毫秒
61.
Different from canonical ubiquitin-like proteins, Hub1 does not form covalent conjugates with substrates but binds proteins noncovalently. In Socchoromyces cerevisioe, Hub1 associates with spUceosomes and mediates alternative splicing of SRCI, without affecting pre-mRNA splicing generaity. Human Hub1 is highty similar to its yeast homotog, but its cellular function remains largely unexplored. Here, we show that human Hub1 binds to the spliceosomal protein Snu66 as in yeast; however, unlike its 5. cerevisioe homolos, human Hub1 is essential for viability. Prolonged in vivo depletion of human Hub1 leads to various cellular defects, including splicing speckle abnormalities, partial nuclear retention of mRNAs, mitotic catastrophe, and consequently cell death by apoptosis. Early consequences of Hub1 depletion are severe splicing defects, however, only for specific splice sites leading to exon skipping and intron retention. Thus, the ubiquitin-iike protein Hub1 is not a canonlcal spliceosomal factor needed generally for splicing, but rather a modulator of spliceosome performance and facilitator of alternative splicing.  相似文献   
62.
Co-degradation of resorcinol and catechol was studied in a catechol acclimated up flow anaerobic sludge blanket (UASB) reactor. Synthetic binary aqueous solution having a total concentration of 1000 mg/L with the resorcinol/catechol (R/C) ratio of 1/19, 1/9, 3/17, 1/4, 1/3, 3/7, 2/3 and then 1/3 was fed at various time intervals to the UASB reactor with a fixed organic loading rate of 5.7 kg COD/m(3) d and hydraulic retention time of 8h. The reactor was operated over a period of 145 days after its acclimation with catechol bearing synthetic wastewater at a constant feed rate of 1.2 L/h. When the resorcinol concentration was increased to have a R/C ratio of 1/4, the COD removal efficiency and the biogas production increased to the maximum levels. Pseudo steady state condition for COD removal was achieved at each of the stepped-up loading condition. An increase in the R/C ratio above 1/4 in the binary feed solution led to a decrease in the COD removal efficiency and the biogas production rate.  相似文献   
63.
Post-translational modifications (PTMs) of histones play an important role in many cellular processes, notably gene regulation. Using a combination of mass spectrometric and immunobiochemical approaches, we show that the PTM profile of histone H3 differs significantly among the various model organisms examined. Unicellular eukaryotes, such as Saccharomyces cerevisiae (yeast) and Tetrahymena thermophila (Tet), for example, contain more activation than silencing marks as compared with mammalian cells (mouse and human), which are generally enriched in PTMs more often associated with gene silencing. Close examination reveals that many of the better-known modified lysines (Lys) can be either methylated or acetylated and that the overall modification patterns become more complex from unicellular eukaryotes to mammals. Additionally, novel species-specific H3 PTMs from wild-type asynchronously grown cells are also detected by mass spectrometry. Our results suggest that some PTMs are more conserved than previously thought, including H3K9me1 and H4K20me2 in yeast and H3K27me1, -me2, and -me3 in Tet. On histone H4, methylation at Lys-20 showed a similar pattern as H3 methylation at Lys-9, with mammals containing more methylation than the unicellular organisms. Additionally, modification profiles of H4 acetylation were very similar among the organisms examined.  相似文献   
64.
Endophytic fungi from Nyctanthes arbor-tristis were isolated and evaluated for their antimicrobial activity. A total of 19 endophytic fungi were isolated from 400 segments of healthy leaf and stem tissues of N. arbor-tristis. Eighteen endophytic fungi were obtained from leaf, while only ten from stem. Alternaria alternata had the highest colonization frequency (15.0%) in leaf, whereas Cladosporium cladosporioides ranked first in stem with a colonization frequency of 12%. The diversity and species richness were found higher in leaf tissues than in stem. The similarity indices between leaf and stem were 0.473 for Jaccard’s and 0.642 for the Sorenson index, respectively. Of 16, 12 (75%) endophytic fungal extracts showed antibacterial activity against either one or more pathogenic bacteria. The endophytic Nigrospora oryzae showed maximum inhibition against Shigella sp. and Pseudomonas aeruginosa. The leaf endophytes Colletotrichum dematium and Chaetomium globosum exhibited a broad range of anibacterial activity and were active against Shigella flexnii, Shigella boydii, Salmonella enteritidis, Salmonella paratyphi, and P. aeruginosa. Nine out of 16 (56.25%) endophytic fungi exhibited antifungal activity to one or more fungal pathogens. Colletotrichum dematium inhibited 55.87% of the radial growth of the phytopathogen Curvularia lunata. The antimicrobial activity of these endophytic microorganisms could be exploited in the biotechnological, medicinal, and agricultural industries.  相似文献   
65.
Cervical cancer is the second most common cause of cancer-related death among women worldwide, especially in developing countries. Oxidative stress has been associated with cervical cancer. Many studies demonstrated that the low level of antioxidants induces the production of free radicals that cause lipid peroxidation, DNA, and protein damage leading to mutations that favors malignant transformation. This is a case-control institutional study conducted to evaluate the level of oxidative stress in cervical cancer patients and the age-matched healthy controls. We measured level of TBARS expressed as MDA, activity of SOD and GSH level by the spectrophotometric method, and level of 8-OHdG was estimated using a competitive sandwich ELISA assay. Our results showed a significant increase in the level of lipid peroxidation in group IV when compared to the control, group II and group III (p < 0.001). The activity of SOD was also significantly higher in group IV when compared to the control group (p < 0.001), group II (p < 0.001), and group III (p < 0.001). The level of GSH was also significantly lower in group IV when compared to the control group (p < 0.01), group II (p < 0.01), and group III (p < 0.01). The level of 8-OHdG was significantly higher in group IV than in the other groups (p < 0.01). The results suggest that oxidative stress is involved in the pathogenesis of cervical cancer, which is demonstrated by an increased level of lipid peroxidation and higher levels of 8-OHdG and an altered antioxidant defense system.  相似文献   
66.
67.
Abstract

In Anbetracht der weitreichenden Bedeutung des VIII. Internationalen Pflanzenschutzkongresses, der in der Zeit vom 22. bis 26. August 1975 in Moskau stattfand, hält es die Redaktion für erforderlich, die anläßlich des Kongresses verabschiedete Resolution im Wortlaut wiederzugeben.  相似文献   
68.
Human matrix metalloproteinase-8 (hMMP-8) plays a important role in the progression of colorectal cancer, metastasis, multiple sclerosis and rheumetoid arthritis. Extensive MD-simulation of the PDB and solvated structures of hMMP-8 has revealed the presence of few conserved water molecules around the catalytic and structural zinc (ZnC and ZnS) ions. The coordination of two conserved water molecules (W and WS) to ZnS and the H-bonding interaction of WS to S151 have indicated the plausible involvement of that metal ion in the catalytic process. Beside this the coupling of ZnC and ZnS metal ions (ZnC – WH (W1)…..W2 ….H162 - ZnS) through two conserved hydrophilic centers (occupied by water molecules) may also provide some rational on the recognition of two zinc ions which were separated by ~13 Å in their X-ray structures. This unique recognition of both the Zn+2 ions in the enzyme through conserved water molecules may be implemented/ exploited for the design of antiproteolytic agent using water mimic drug design protocol.  相似文献   
69.
A remarkable improvement in the emulsifying properties of proteins was observed in mixtures of serum albumin-dextran sulfate, lysozyme-dextran sulfate, serum albumin-chondroitin sulfate, α-lactalbumin-chondroitin sulfate and lysozyme-chondroitin sulfate. The emulsifying properties of these protein-polysaccharide complexes were affected by the molecular size of the polysaccharide and by such conditions as the presence of salt, acidic or alkaline pH, and heating. On the other hand, the emulsifying properties of ovalbumin-dextran hybrids prepared by covalent attachment were more enhanced in alkaline pH or by heating. The molecular size of the ovalbumin-dextran hybrids greatly affected the emulsifying properties.  相似文献   
70.
Russian Journal of Bioorganic Chemistry - In the present studies, novel pyrazole derivatives have been synthesized linked through various linkers for the anti-inflammatory evaluation. The...  相似文献   
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