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   1792篇
  免费   210篇
  2002篇
  2022年   19篇
  2021年   41篇
  2020年   26篇
  2019年   19篇
  2018年   37篇
  2017年   35篇
  2016年   42篇
  2015年   58篇
  2014年   61篇
  2013年   81篇
  2012年   83篇
  2011年   99篇
  2010年   70篇
  2009年   47篇
  2008年   82篇
  2007年   86篇
  2006年   72篇
  2005年   56篇
  2004年   55篇
  2003年   73篇
  2002年   48篇
  2001年   45篇
  2000年   52篇
  1999年   39篇
  1998年   21篇
  1996年   15篇
  1995年   14篇
  1993年   14篇
  1992年   31篇
  1991年   34篇
  1990年   26篇
  1989年   35篇
  1988年   32篇
  1987年   41篇
  1986年   30篇
  1985年   27篇
  1984年   22篇
  1983年   16篇
  1982年   16篇
  1981年   15篇
  1980年   15篇
  1979年   25篇
  1978年   23篇
  1977年   18篇
  1976年   16篇
  1975年   22篇
  1973年   21篇
  1972年   21篇
  1971年   14篇
  1970年   14篇
排序方式: 共有2002条查询结果,搜索用时 0 毫秒
21.
Effect of organophosphorus insecticide, phosphomidon (250 and 500 ppm) on human erythrocyte and plasma were studied in vitro to get insight into the cellular antioxidant defence mechanism and malondialdehyde formation. The antioxidant defence system of erythrocyte was altered as evident by depression of glutathione reductase, glucose 6 phosphate dehydrogenase, whereas the level of reduced glutathione, glutathione peroxidase, glutathione-S-transferase, superoxidedismutase and catalase were stimulated. In the case of plasma fraction, glutathione reductase, glutathione peroxidase, glutathione-s-transferase, glucose-6-phosphate dehydrogenase, superoxide dismutase and levels of reduced glutathione were significantly depressed and the malondialdehyde formation and catalase activity were elevated indicating the less adaptive response of plasma to protect it from oxidative damage.  相似文献   
22.
This report documents for the first time the in vitro autophosphorylation of purified 68 kDa hyaluronate binding protein in presence of [32P] ATP. The rate of phosphorylation is proportional to the concentration of protein and to the time of incubation up to 5 min. By both phosphoamino acid and western blot analysis with antiphosphotyrosine antibodies, we have confirmed that the phosphorylation occurs at tyrosine residues. Immunoprecipitation with anti HA binding protein antibody shows a 5 fold increase in the phosphorylation in macrophage histiocytoma compared to normal macrophage. Supplementing hyaluronate with hyaluronate binding protein in the medium is further shown to enhance total protein phosphorylation in rat histiocytoma.  相似文献   
23.
Reclassification of incompatibility group L (IncL) plasmids.   总被引:1,自引:0,他引:1  
H Richards  N Datta 《Plasmid》1979,2(2):293-295
Plasmids classified as IncL are shown to be incompatible with plasmids of IncM and we propose to reclassify them as IncM.  相似文献   
24.
The porphyrin photosensitizer, meso-Tetra (4-N-methylpyridyl) porphine tetraperchlorate binds to calf thymus DNA by intercalation and by external electrostatic association. This was concluded from the results of measruements involving Scatchard analysis, viscometry, thermal denaturation, and circular dichroism.  相似文献   
25.
Transformed cells from human lung carcinoma (Line A549), resembling type II pneumocytes, were cultured in monolayer at 37°C and incubated for five hours with 3H-choline and 14C-palmitate in the presence of various concentrations of prostaglandins (PGs) E2 and F. In the control (no PG) the level of % palmitate incorporation was 13.5 × as high as that of choline, after taking isotope dilution into account. Between the concentrations studied, 0.1 and 10 μM, both prostaglandins stimulated markedly the incorporation of both precursors, though choline up to 3 × better than palmitate. This was indicated by a change in the palmitate/choline incorporation ratio from 13.5 to as low as 4.2. At the lowest PG concentration, 0.1 μM, PGE2 was much more effective than PGF in stimulating the incorporation of both precursors.  相似文献   
26.
27.
International Journal of Peptide Research and Therapeutics - The growth of pathogens across the globe is developing at a very fast rate, thus turning into a worldwide health problem. Since, current...  相似文献   
28.
An aqueous extract of human placenta exhibits strong gelatinase/collagenase activity in zymography. 2-D gel electrophoresis of the extract with gelatin zymography in the second dimension displayed a single spot, identified as ubiquitin-like component upon MALDI/TOF MS/MS analysis. Immunoblot indicated presence of ubiquitin and absence of collagenase in the extract. Collagenase activity of the ubiquitin-like component was confirmed from the change in solubility of collagen in aqueous buffer, degradation of collagen by size-exclusion HPLC and atomic force microscopy. Quantification with DQ-gelatin showed that the extract contains 0.04 U/ml of collagenase activity that was inhibited up to 95% by ubiquitin antibody. Ubiquitin from bovine erythrocytes demonstrated mild collagenase activity. Bioinformatics studies suggest that placental ubiquitin and collagenase follow structurally divergent evolution. This thermostable intrinsic collagenase activity of placental extract might have wide physiological relevance in degrading and remodeling collagen as it is used as a drug for wound healing and pelvic inflammatory diseases.  相似文献   
29.
Sustainable rice production through selection of best suitable cultivar, water-efficient crop establishment method and optimum nitrogen (N) management practice is needed to feed the growing world population. Two polyhouse experiments were conducted to evaluate the response of rice to different rates and schedules of N application under different establishment methods subjected to alternate wetting and drying (AWD) irrigation. In the first experiment, the response of two rice cultivars (Pathumthani 1, RD57) under three establishment methods (transplanting [TP], wet direct seeding [WDS], dry direct seeding [DDS]) and five N rates (0 [N0], 30 [N30], 60 [N60], 90 [N90], 120 [N120] kg ha−1) was evaluated. The second experiment consisted of the same cultivars and establishment methods, but with four N application schedules (T1: 100% at basal; T2: 75% + 25% at basal and at active tillering, respectively; T3: 50% + 25% + 25% at basal, at active tillering and at panicle initiation, respectively; and T4: 25% + 25% + 25% + 25% each at basal, at active tillering, at panicle initiation and at early flowering or just before heading starts) applied at the rate of N60 kg ha−1. Plants were maintained under AWD irrigation (soil was saturated by applying water whenever soil water potential drops to −5 kPa during the implementation period) in both experiments. RD57 performed better than Pathumthani 1 having higher shoot dry matter, panicle number, grain yield, total N uptake and apparent N recovery efficiency. TP gave better response than WDS and DDS regardless of cultivars. Application of N120 resulted in better growth, yield and its components and total N uptake regardless of establishment methods and cultivars. Increasing N rate decreased N use efficiency (NUE). Scheduling the interval of N application to two or three times (T2 or T3) for RD57 and Pathumthani 1, respectively, provided overall better results, and could be recommended for the tested rice cultivars. An optimal N rate and selection of critical growth stages for N application would be very effective for maximising yield and NUE under the water-saving cultivation technique of AWD irrigation.  相似文献   
30.
Fusarium species causing wilt diseases in different plants were characterised by comparing nonpathogenic and different pathogenic species using rDNA RFLP analysis. The ITS (internal transcribed spacer) region of 12 isolates belonging to the section Elegans, Laseola, Mortiella, Discolor, Gibbosum, Lateritium and Sporotrichiella were amplified by universal ITS primers (ITS-1 and ITS-4) using polymerase chain reaction (PCR). Amplified products, which ranged from 522 to 565 bp were obtained from all 12 Fusarium isolates. The amplified products were digested with seven restriction enzymes, and restriction fragment length polymorphism (RFLP) patterns were analysed. A dendrogram derived from PCR-RFLP analysis of the rDNA region divided the Fusarium isolates into three major groups. Assessment of molecular variability based on rDNA RFLP clearly indicated that Fusarium species are heterogeneous and most of the forma speciales have close evolutionary relationships.  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