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   19079篇
  免费   1657篇
  国内免费   1篇
  20737篇
  2023年   78篇
  2021年   152篇
  2020年   113篇
  2019年   135篇
  2018年   360篇
  2017年   375篇
  2016年   405篇
  2015年   336篇
  2014年   448篇
  2013年   707篇
  2012年   1316篇
  2011年   1434篇
  2010年   753篇
  2009年   501篇
  2008年   1222篇
  2007年   1221篇
  2006年   1150篇
  2005年   1040篇
  2004年   992篇
  2003年   939篇
  2002年   923篇
  2001年   775篇
  2000年   891篇
  1999年   407篇
  1998年   191篇
  1997年   139篇
  1996年   177篇
  1995年   162篇
  1994年   140篇
  1993年   144篇
  1992年   135篇
  1991年   130篇
  1990年   126篇
  1989年   115篇
  1988年   129篇
  1987年   127篇
  1986年   113篇
  1985年   150篇
  1984年   146篇
  1983年   125篇
  1982年   162篇
  1981年   146篇
  1980年   112篇
  1979年   126篇
  1978年   97篇
  1977年   91篇
  1976年   82篇
  1975年   81篇
  1974年   81篇
  1973年   73篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
We have earlier demonstrated that a mixed population of immunologically specific killer cells, including cytotoxic T lymphocytes, non-T (“B”) lymphocytes and monocytes, infiltrate “sponge matrix” allografts at the peak of rejection on Day 8 after transplantation. We have now performed a sequential study covering both early and late stages of the rejection response. We demonstrate that the early infiltrating killer cells are sensitive to anti-Ø and anti-T cell serum plus complement treatment but the late killer cells are not. This finding indicates that the first cytotoxic host cells infiltrating the allograft are predominantly T lymphocytes, whereas as the rejection process proceeds also cytotoxic non-T (“B”) lymphocytes and monocytes are recruited to the site of inflammation.  相似文献   
13.
A familial mutation in SRY, the gene coding for the testis-determining factor TDF, was identified in an XY female with gonadal dysgenesis, her father, her two brothers and her uncle. The mutation consists of a T to C transition in the region of the SRY gene coding for a protein motif known as the high mobility group (HMG) box, a protein domain known to confer DNA-binding specificity on the SRY protein. This point mutation results in the substitution, at amino acid position 109, of a serine residue for phenylalanine, a conserved aromatic residue in almost all HMG box motifs known. This F109S mutation was not found in 176 male controls. When recombinant wildtype SRY and SRYF109S mutant protein were tested in vitro for binding to the target site AAC AAAG, no differences in DNA-binding activity were observed. These results imply that the F109S mutation either is a rare neutral sequence variant, or produces an SRY protein with slightly altered in vivo activity, the resulting sex phenotype depending on the genetic back-ground or environmental factors.This paper is dedicated by G. S. to Professor Ulrich Wolf on the occasion of his 60th birthday  相似文献   
14.
15.
A sensitive and reliable method to determine the stereochemical composition of 3-phosphoglyceric acid is presented. Results obtained with this method show that 3-phosphoglyceric acid formed in the ribulose-1,5-bisphosphate carboxylase reaction is a mixture of 10% L-3-PGA and 90% D-3-PGA.  相似文献   
16.
Pathogens causing bovine respiratory tract disease in Finland were investigated. Eighteen cattle herds with bovine respiratory disease were included. Five diseased calves from each farm were chosen for closer examination and tracheobronchial lavage. Blood samples were taken from the calves at the time of the investigation and from 86 calves 3–4 weeks later. In addition, 6–10 blood samples from animals of different ages were collected from each herd, resulting in 169 samples. Serum samples were tested for antibodies to bovine parainfluenza virus-3 (PIV-3), bovine respiratory syncytial virus (BRSV), bovine coronavirus (BCV), bovine adenovirus-3 (BAV-3) and bovine adenovirus-7 (BAV-7). About one third of the samples were also tested for antibodies to bovine virus diarrhoea virus (BVDV) with negative results. Bacteria were cultured from lavage fluid and in vitro susceptibility to selected antimicrobials was tested. According to serological findings, PIV-3, BAV-7, BAV-3, BCV and BRSV are common pathogens in Finnish cattle with respiratory problems. A titre rise especially for BAV-7 and BAV-3, the dual growth of Mycoplasma dispar and Pasteurella multocida, were typical findings in diseased calves. Pasteurella sp. strains showed no resistance to tested antimicrobials. Mycoplasma bovis and Mannheimia haemolytica were not found.  相似文献   
17.
Acetobacter acetii DSMZ3508 and related bacteria converted 2,2-dimethyl-1,3-propanediol into 3-hydroxypivalic acid (2,2-dimethyl-3-hydroxypropionic acid; 3HP) during submerged cultivation in mineral salt medium. The maximum yield of 3-hydroxypivalic acid was 24.4% of the fed substrate after 18 days. Cultivation parameters, as pH, cell density, optimal substrate concentration, and oxygen supply for the bioconversion process were determined.  相似文献   
18.
19.
Cerebellum Gangliosides in Postnatal Rats   总被引:1,自引:1,他引:0  
  相似文献   
20.
The importance of endemic species for plant communities in the Roumanian Carpathians Mts. has been studied and discussed. Associations of the classAsplenietea trichomanis endemic in the South Carpathians were surveyed; they were classified into some endemic alliances (Gypsophilion petraeae, Micromerion pulegii, andSilenion lerchenfeldianae). Their locus classicus, nomenclatoric type and present distribution were also given.  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