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   1428篇
  免费   98篇
  国内免费   1篇
  2023年   14篇
  2022年   26篇
  2021年   51篇
  2020年   16篇
  2019年   24篇
  2018年   42篇
  2017年   39篇
  2016年   54篇
  2015年   101篇
  2014年   75篇
  2013年   122篇
  2012年   157篇
  2011年   104篇
  2010年   64篇
  2009年   70篇
  2008年   64篇
  2007年   71篇
  2006年   63篇
  2005年   56篇
  2004年   35篇
  2003年   44篇
  2002年   41篇
  2001年   17篇
  2000年   17篇
  1999年   10篇
  1998年   8篇
  1995年   3篇
  1994年   5篇
  1993年   4篇
  1992年   9篇
  1991年   7篇
  1990年   5篇
  1989年   10篇
  1988年   6篇
  1987年   4篇
  1986年   6篇
  1985年   4篇
  1984年   5篇
  1982年   7篇
  1981年   3篇
  1980年   3篇
  1979年   6篇
  1978年   7篇
  1976年   5篇
  1975年   3篇
  1974年   8篇
  1973年   9篇
  1971年   3篇
  1970年   3篇
  1965年   3篇
排序方式: 共有1527条查询结果,搜索用时 15 毫秒
951.
952.
An efficient synthesis of 2,5-diarylamino-3,6-dichloro-1,4-benzoquinone derivatives has been achieved by condensing mono substituted anilines with tetrachloro-p-benzoquinone in presence of fused sodium acetate as condensing agent under microwave irradiation without any solvent. All the synthesized compounds were tested for their antibacterial and antitumour activity using standard drugs.  相似文献   
953.
Over the last few decades wild population of Chitala chitala (HamiltonBuchanan) has been declined more than 50% due to various reasons and is presently listed under endangered (EN) category due to reduced abundance. In the present communication wild C. chitala were collected from natural habitats and induced to spawn under captivity during July 2002 by injecting three different doses of synthetic hormone Ovaprim. Intramuscular injections were administered to fishes using three different doses (1.5, 1.0 and 0.5 ml/kg body weight). Artificial breeding pool was prepared for each set by encircling area (20 × 5 m) with mosquito net, where wooden country boat (8 × 4 × 2.5 feet with surface area 48.5 sq. feet) was placed inside the breeding pool. Distinct spawning behavior was noticed in the experimental sets with different hormonal dose whereas no spawning activity was noticed in control set. The fertilization rate varied from 48.8680.2% and total numbers of spawned eggs in two sets of experiments were estimated to be 81,034. The average number of eggs deposited 15 ± 2.1/square inches. The fertilized eggs were large in size (4.5 ± 0.05 mm), adhesive and attached to the hard substratum. The eggs hatch out between 168192 h after fertilization and about 33,639 hatchlings were produced. Newly hatched larvae measured 10.23 ± 0.03 mm and 0.031± 0.008 gm in weight and the mean diameter of yolk sac was 4.1 ± 0.08 mm. The yolk sac remains attached up to a week. The percentage survival of hatchlings varied from 42.2 to 65.60. Statistical analysis was worked out to determine the relation between the hormone dosage with different breeding parameters like latency period, fertilization rate, egg output, hatching rate and hatchling production.  相似文献   
954.
Lysine epsilon-aminotransferase (LAT) is a PLP-dependent enzyme that is highly up-regulated in nutrient-starved tuberculosis models. It catalyzes an overall reaction involving the transfer of the epsilon-amino group of L-lysine to alpha-ketoglutarate to yield L-glutamate and alpha-aminoadipate-delta-semialdehyde. We have cloned and characterized the enzyme from Mycobacterium tuberculosisH37Rv. We report here the crystal structures of the enzyme, the first from any source, in the unliganded form, external aldimine with L-lysine, with bound PMP and with its C5 substrate alpha-ketoglutarate. In addition to interaction details in the active site, the structures reveal a Glu243 "switch" through which the enzyme changes substrate specificities. The unique substrate L-lysine is recognized specifically when Glu243 maintains a salt-bridge with Arg422. On the other hand, the binding of the common C5 substrates L-glutamate and alpha-ketoglutarate is enabled when Glu243 switches away and unshields Arg422. The structures reported here, sequence conservation and earlier mutational studies suggest that the "glutamate switch" is an elegant solution devised by a subgroup of fold type I aminotransferases for recognition of structurally diverse substrates in the same binding site and provides for reaction specificity.  相似文献   
955.
Copper-dependent co-internalization of the prion protein and glypican-1   总被引:1,自引:0,他引:1  
Heparan sulfate chains have been found to be associated with amyloid deposits in a number of diseases including transmissible spongiform encephalopathies. Diverse lines of evidence have linked proteoglycans and their glycosaminoglycan chains, and especially heparan sulfate, to the metabolism of the prion protein isoforms. Glypicans are a family of glycosylphosphatidylinositol-anchored, heparan sulfate-containing, cell-associated proteoglycans. Cysteines in glypican-1 can become nitrosylated by endogenously produced nitric oxide. When glypican-1 is exposed to a reducing agent, such as ascorbate, nitric oxide is released and autocatalyses deaminative cleavage of heparan sulfate chains. These processes take place while glypican-1 recycles via a non-classical, caveolin-associated pathway. We have previously demonstrated that prion protein provides the Cu2+ ions required to nitrosylate thiol groups in the core protein of glypican-1. By using confocal immunofluorescence microscopy and immunomagnetic techniques, we now show that copper induces co-internalization of prion protein and glypican-1 from the cell surface to perinuclear compartments. We find that prion protein is controlling both the internalization of glypican-1 and its nitric oxide-dependent autoprocessing. Silencing glypican-1 expression has no effect on copper-stimulated prion protein endocytosis, but in cells expressing a prion protein construct lacking the copper binding domain internalization of glypican-1 is much reduced and autoprocessing is abrogated. We also demonstrate that heparan sulfate chains of glypican-1 are poorly degraded in prion null fibroblasts. The addition of either Cu2+ ions, nitric oxide donors, ascorbate or ectopic expression of prion protein restores heparan sulfate degradation. These results indicate that the interaction between glypican-1 and Cu2+-loaded prion protein is required both for co-internalization and glypican-1 self-pruning.  相似文献   
956.
957.
The micro-eukaryotic diversity from the human gut was investigated using universal primers directed towards 18S rRNA gene, fecal samples being the source of DNA. The subjects in this study included two breast-fed and two formula-milk-fed infants and their mothers. The study revealed that the infants did not seem to harbour any microeukaryotes in their gut. In contrast, there were distinct eukaryotic microbiota present in the mothers. The investigation is the first of its kind in the comparative study of the human feces to reveal the presence of micro-eukaryotic diversity variance in infants and adults from the Indian subcontinent. The micro-eukaryotes encountered during the investigation include known gut colonizers like Blastocystis and some fungi species. Some of these micro-eukaryotes have been speculated to be involved in clinical manifestations of various diseases. The study is an attempt to highlight the importance of micro-eukaryotes in the human gut.  相似文献   
958.
Acute and chronic viral hepatitis infections are corresponding to increase the risk of different types of hematological malignancies especially with leukemia. In this study the serological and molecular markers of hepatitis viruses were evaluated in patients with different types of leukemia in comparing with control group. In this cross sectional study, 100 EDTA-treated blood samples were collected from leukemia patients and also from healthy control group, respectively. Serological and molecular markers of HBV, HCV and HDV viruses were analyzed for determination of the role of these hepatitis viruses in clinical outcomes of leukemia disorders. Increasing risk factors of leukemia were evaluated statistically in two studied groups by SPSS software. One of molecular and immunological markers of HBV, HDV and HCV was found in 24 of 100 (24%), 22 of 100 (22%), and 1 of 100 (1%) patients with leukemia and in 12 of 100 (12%), 6 of 100 (6%), and 2 of 100 (2%) control patients. Significant differences were detected in detection of HBsAg (P = 0.02), HBeAb (P = 0.009), and HCV-RNA (P = 0.05) between leukemia patients and control group, respectively. The high prevalence of HBV and HCV infective markers were detected in ALL and AML patients. Identification of high prevalence of HBV and HCV infective markers in leukemia patients proposed strong association between hepatitis viral infections and leukemia. Therefore, evaluation of the prevalence of viral hepatitis infections in larger groups of patients with long lasting follow up is suggesting.  相似文献   
959.

Background

Tuberculosis (TB) is the most threatening infectious disease globally. Although progress has been made to reduce global incidence of TB, emergence of multidrug resistant (MDR) TB threatens to undermine these advances. To combat the disease, novel intervention strategies effective against drug resistant and sensitive subpopulations of M. tuberculosis are urgently required as adducts in the present treatment regimen. Using THP-1 cells we have analyzed and compared the global protein expression profile of broth-cultured and intraphagosomally grown drug resistant and sensitive M.tuberculosis clinical isolates.

Results

On comparing the two dimensional (2-DE) gels, many proteins were found to be upregulated/expressed during intracellular state which were identified by matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). Four proteins (adenosylhomocysteinase, aspartate carbomyltransferase, putatitive thiosulfate sulfurtransferase and universal stress protein) were present in both intracellular MDR and sensitive isolates and three of these belonged to intermediary metabolism and respiration category. Two proteins (alanine dehydrogenase and adenosine kinase) of intracellular MDR isolate and two (glucose-6-phosphate isomerase and ATP synthase epsilon chain) of intracellular sensitive isolate belonged to intermediary metabolism and respiration category. One protein (Peroxidase/Catalase) of intracellular MDR and three (HSPX, 14 kDa antigen and 10 kDa chaperonin) of sensitive isolate belonged to virulence, detoxification and adaptation category. ESAT-6 of intracellular MDR belonged to cell wall and cell processes category. Two proteins (Antigen 85-C and Antigen 85-A) of intracellular sensitive isolate were involved in lipid metabolism while probable peptidyl-prolyl cis-trans isomerase A was involved in information pathways. Four (Rv0635, Rv1827, Rv0036c and Rv2032) of intracellular MDR and two proteins (Rv2896c and Rv2558c) of sensitive isolate were hypothetical proteins which were functionally characterized using bioinformatic tools. Bioinformatic findings revealed that the proteins encoded by Rv0036, Rv2032c, Rv0635, Rv1827 and Rv2896c genes are involved in cellular metabolism and help in intracellular survival.

Conclusions

Mass spectrometry and bioinformatic analysis of both MDR and sensitive isolates of M. tuberculosis during intraphagosomal growth showed that majority of commonly upregulated/expressed proteins belonged to the cellular metabolism and respiration category. Inhibitors of the metabolic enzymes/intermediate can therefore serve as suitable drug targets against drug-resistant and sensitive subpopulations of M. tuberculosis.  相似文献   
960.
The study of phytoremediation potential of Helianthus annuus L was conducted in the sewage-irrigated Indo-Gangetic alluvial soils, India. Calcium @ 1.0% and Zn @ 40 ppm enhanced the yield of H. annuus L and minimized the toxicity of Cr in the investigated soils. The study indicated that H. annuus L is highly sensitive to Cr and Zn in terms of metallic pollution; and may be used as indicator plant. For Cr-phytoremediation, humic acid treatment @ 500 mL/acre induced the Cr-accumulation in roots (p < 0.007) and in shoots (p < 0.015), which was recorded 3.21 and 3.16 mg/kg in root and shoot of H. annuus L, respectively. We suggest that H. annuus L fulfils the necessary condition for efficiently increasing species bioaccumulation after soil treatment with humic acid in Cr-polluted sewage-irrigated soils through soil- plant rhizospheric processes.  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