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   2177篇
  免费   126篇
  国内免费   1篇
  2022年   8篇
  2021年   10篇
  2020年   11篇
  2019年   18篇
  2018年   32篇
  2017年   15篇
  2016年   33篇
  2015年   53篇
  2014年   64篇
  2013年   176篇
  2012年   119篇
  2011年   139篇
  2010年   64篇
  2009年   81篇
  2008年   147篇
  2007年   152篇
  2006年   140篇
  2005年   139篇
  2004年   145篇
  2003年   145篇
  2002年   140篇
  2001年   44篇
  2000年   32篇
  1999年   39篇
  1998年   42篇
  1997年   34篇
  1996年   21篇
  1995年   17篇
  1994年   24篇
  1993年   10篇
  1992年   23篇
  1991年   14篇
  1990年   24篇
  1989年   12篇
  1988年   7篇
  1987年   11篇
  1986年   8篇
  1985年   9篇
  1984年   10篇
  1983年   9篇
  1982年   14篇
  1981年   14篇
  1980年   12篇
  1979年   5篇
  1978年   4篇
  1976年   3篇
  1975年   3篇
  1973年   4篇
  1970年   5篇
  1968年   4篇
排序方式: 共有2304条查询结果,搜索用时 31 毫秒
21.
Epidemiological typing, based on restriction fragment length polymorphism (RFLP) by pulsed-field gel electrophoresis (PFGE), was attempted for the 38 clinical isolates of Moraxella catarrhalis obtained at Shinshu University Hospital during the years 1987 and 1993. Digestion with SmaI or NotI generated well separable, 12 to 5 genomic DNA fragments ranging from 1,000 kb to 30 kb and the strains could be classified into 14 or 13 types, respectively. The electrophoretic profile differed with the strain in most of them and was hence useful to distinguish the each strain. Investigation for their RFLP have, however, suggested that majority of them, including the type strain ATCC25238, may have derived from a common ancestor.  相似文献   
22.
Hepatocellular carcinoma associated with chronic Schistosoma mansoni infection in a chimpanzee, estimated to be a 12-year-old and born in West Africa, is reported. The hepatic tumor appeared as a solitary firm nodule, and histological examination revealed well-differentiated hepatocellular carcinoma with a trabecular pattern. Hepatitis B virus and hepatitis C virus infections were excluded by serological testing in that animal. This is the first report of hepatocellular carcinoma in the chimpanzee with schistosomiasis.  相似文献   
23.
Summary We prepared various TNF- derivatives by protein engineering techniques. Mutant 471, in which 7 N-terminal amino acids were deleted and Pro8Ser9Asp10 was replaced by ArgLysArg, had a 8-fold higher antitumor activity against mouse L929 cells than wild-type TNF-. The additional substitution of Ala156 or Leu157 by more hydrophobic amino acids enhanced the activity of mutant 471. These results suggested that the combinational mutations in the N- and C-terminal regions of TNF- are effective for the improvement of antitumor activity.  相似文献   
24.
Summary -Fructofuranosidase, which produces fructo-oligosaccharides (1-kestose and nystose) from sucrose, was purified fromAureobasidium and immobilized on DEAE-cellulose at especially high efficiency (95%). The enzymatic profiles of the immobilized enzyme were almost identical to those of the native form except that the stability was slightly improved. The immobilized enzyme was stable during long-term continuous reaction for up to 360 h.  相似文献   
25.
26.
This study aimed to describe the change in the number of successful nests of the white-tailed eagle, Haliaeetus albicilla, for 25 years (1997–2021) along the Teshio River (100 km), Japan, which is a new habitat for this endangered species and identify factors driving the number of nests. The number of nests grew from two to nine. The logistic function fitted in well with the growth, and the capacity of the study area sustaining the successful nests was estimated at 6.5. The precipitation in January and April explained the deviation of the observed values from the model prediction. In particular, heavy rain in April was associated with low numbers. Forty-six nest remains were collected from 17 nest locations. Twelve genera of birds, six genera of mammals, and four genera of fishes were identified. Fish and bird items occupied 93.6% of prey individuals. The fish proportion was similar between high-performance years when the observed number of successful nests was higher than the model prediction and low-performance years with a lower number than the prediction (55.2% and 51.0%). However, it was higher in the nests with two fledglings (63.0%) than those with a single fledgling (41.5%). The nearest neighbor distance (NND) of the successful nests declined with the increase in the number of nests. Based on territory size (the mean NND = 7.8 km), the study area can hold 13 nests. The process and mechanism of the dynamics of the number of nests were discussed, focusing on territoriality and weather effects.  相似文献   
27.
We have developed ODS (Overlapping Oligonucleotide Databasefor Signal Sequence Search)—the first relational databasethat integrates information on biological features into thesearch for signal sequences. In existing biological sequencedatabases, even relational ones, retrieving nucleotide sequencesbased on their biological features involves much labour andtime or even the development of a new program. GenBank sequencedata, including FEATURES records, are organized into three relationaltables in ODS. Nucleotide sequences are transformed into overlappingoligonucleotides in order to facilitate the signal sequencesearch rapidly without the need for specific alignment programs.This transformation leads to a one-to-one correspondence betweenthe nucleotide sequence and its biological feature. The signalsequence search by ODS is done in SQL queries and ODS obviatesthe need for molecular biologists to write computer programs.The application of ODS to searches of promoter regions revealedputative cis-acting elements and basic statistical analysesof occurrences of oligonucleotides showed interesting findingsconcerning the ‘cg’ dinucleotide.  相似文献   
28.
29.
30.
The primary reaction product of chloroplast ascorbate peroxidaseactivity was shown to be monodehydroascorbate radical (MDA).MDA reductase (EC 1.6.5.4 [EC] ) was localized in spinach chloroplaststroma. The MDA reductase activity of spinach chloroplasts,using NAD(P)H as electron donor, could account for the regenerationof ascorbate from MDA produced by ascorbate peroxidase activity.In the absence of MDA reductase, MDA disproportionated to ascorbate(AsA) and dehydroascorbate (DHA). The DHA was reduced to AsAby DHA reductase (EC 1.8.5.1 [EC] ) in chloroplasts. Both NADH andNADPH served as the electron donor of partially purified MDAreductase from spinach leaves. (Received September 24, 1983; Accepted January 23, 1984)  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