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   5923篇
  免费   281篇
  国内免费   14篇
  6218篇
  2023年   61篇
  2022年   151篇
  2021年   324篇
  2020年   137篇
  2019年   179篇
  2018年   212篇
  2017年   178篇
  2016年   238篇
  2015年   290篇
  2014年   330篇
  2013年   458篇
  2012年   421篇
  2011年   441篇
  2010年   256篇
  2009年   205篇
  2008年   242篇
  2007年   234篇
  2006年   230篇
  2005年   178篇
  2004年   145篇
  2003年   117篇
  2002年   115篇
  2001年   67篇
  2000年   77篇
  1999年   57篇
  1998年   33篇
  1997年   18篇
  1996年   21篇
  1995年   21篇
  1993年   17篇
  1992年   44篇
  1991年   58篇
  1990年   48篇
  1989年   44篇
  1988年   38篇
  1987年   53篇
  1986年   42篇
  1985年   43篇
  1984年   38篇
  1983年   25篇
  1982年   21篇
  1981年   16篇
  1980年   17篇
  1979年   28篇
  1978年   26篇
  1977年   16篇
  1975年   18篇
  1974年   17篇
  1973年   25篇
  1971年   17篇
排序方式: 共有6218条查询结果,搜索用时 0 毫秒
101.
102.
103.
104.
105.
NADPH-cytochrome-c-reductase from guts of gypsy moth, Porthetria dispar, oxidized NADPH at the following rates: 11·6, 41·9, and 57·6 nmol/30 min per 0·6 mg protein, in the third, fourth and fifth instar, respectively. The increase in specific activity may be due to a natural induction process controlled by materials in the food. This could also explain the observed decreases just prior to ecdysis at which time the larvae have ceased feeding.  相似文献   
106.
Summary Four genes, deoA, deoB, deoC, and deoD, involved in the synthesis of nucleoside and deoxynucleoside catabolic enzymes, are located contiguously in the order C-A-B-D on the linkage map of E. coli. They constitute two overlapping operons, one transcribing all the four genes and the other deoB and deoD. To the left of deoC are located two promoter-operator regions in the order deoPO-cytPO. They are involved in controlling the expression of the tetracistronic mRNA. For efficient binding of RNA polymerase at the cytPO site the cAMP+CRP complex is required, whereas binding of RNA polymerase at the deoPO site is independent of this complex. Evidence is available for the existence of yet another controlling site, PO-3, located between deoA and deoB; this controls the expression of deoB and deoD. Both the operons are transcribed in a clockwise direction. An operator constitutive (O c) type mutant affecting the synthesis of all four deo enzymes has been analysed. Because of this mutation the strain has become insensitive to catabolite repression. The results confirm the order of the gene in the controlling region to be deoPO-cytPO and the mutation, previously analysed as a deletion, appears to have deleted cytPO deoC region of the chromosome.  相似文献   
107.
A pentose-rich acidic glycoprotein was isolated from protease digested bovine vitreous humor by fractionation on an AG1-X2 column using NaCl solution gradient.The material eluted at 0.35 M NaCl (glycoprotein) was electrophoretically heterogeneous at pH 8.6 after partial purification on Sephadex G-25. Gel filtration on G-100 resolved the glycoprotein into two fractions. These fractions differ in molecular weight; mol. wt approx. 95 000 material consisted of two components on electrophoresis and mol. wt approx. 28 000 material showed only a single component on electrophoresis. The lower molecular weight component was re-chromatographed on Sephadex G-100 yielding a single orcinol positive component which gave a homogeneous band on gel electrophoresis.Quantitative analysis of this material gave 30% protein, 7.0% pentose, 18.7% glucosamine, 9.2% galactosamine, 10.9% hexuronic acid and 16.1% hexose.Treatment with 0.5 M NaOH at 20°C for 24 h resulted in a 50% decrease in the threonine content suggesting the possible involvement of this amino acid in the protein-carbohydrate linkage group.Paper chromatography of the fraction hydrolysate demonstrated the presence of glucurone, xylose, arabinose, glucose and galactose.  相似文献   
108.
In this study, the diversity of Plasmodium vivax populations circulating in Pakistan and Iran has been investigated by using circumsporozoite protein (csp) and merozoite surface proteins 1 and 3α (msp-1 and msp-3α) genes as genetic markers. Infected P. vivax blood samples were collected from Pakistan (n = 187) and Iran (n = 150) during April to October 2008, and were analyzed using nested-PCR/RFLP and sequencing methods. Genotyping pvmsp-1 (variable block 5) revealed the presence of type 1, type 2 and recombinant type 3 allelic variants, with type 1 predominant, in both study areas. The sequence analysis of 33 P. vivax isolates from Pakistan and 30 from Iran identified 16 distinct alleles each, with one allele (R-8) from Iran which was not reported previously. Genotyping pvcsp gene also showed that VK210 type is predominant in both countries. Moreover, based on the size of amplified fragment of pvmsp-3α, three major types: type A (1800 bp), type B (1500 bp) and type C (1200 bp), were distinguished among the examined isolates that type A was predominant among Pakistani (72.7%) and Iranian (77.3%) parasites. PCR/RFLP products of pvmsp-3α with HhaI and AluI have detected 40 and 39 distinct variants among Pakistani and Iranian examined isolates, respectively. Based on these three studied genes, the rate of combined multiple genotypes were 30% and 24.6% for Pakistani and Iranian P. vivax isolates, respectively. These results indicate an extensive diversity in the P. vivax populations in both studies.  相似文献   
109.
International Journal of Peptide Research and Therapeutics - Piwi interacting RNA (piRNA) molecules belong to a largest class of small non coding RNA molecules which are originally discovered in...  相似文献   
110.
Consumers’ demand is increasing for safe foods without impairing the phytochemical and sensory quality. In turn, it has increased research interest in the exploration of innovative food processing technologies. Cold plasma technology is getting popularity now days owing to its high efficacy in decontamination of microbes in fruit and fruit-based products. As a on-thermal approach, plasma processing maintains the quality of fruits and minimizes the thermal effects on nutritional properties. Cold plasma is also exploited for inactivating enzymes and degrading pesticides as both are directly related with quality loss and presently are most important concerns in fresh produce industry. The present review covers the influence of cold plasma technology on reducing microbial risks and enhancing the quality attributes in fruits.  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