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   395968篇
  免费   30738篇
  国内免费   1061篇
  2018年   16074篇
  2017年   15019篇
  2016年   11975篇
  2015年   5229篇
  2014年   5401篇
  2013年   8083篇
  2012年   13459篇
  2011年   23898篇
  2010年   20011篇
  2009年   15792篇
  2008年   19635篇
  2007年   21995篇
  2006年   7684篇
  2005年   8645篇
  2004年   8308篇
  2003年   8322篇
  2002年   7796篇
  2001年   12098篇
  2000年   12098篇
  1999年   9388篇
  1998年   3422篇
  1997年   3667篇
  1996年   3554篇
  1995年   3152篇
  1994年   3135篇
  1993年   3153篇
  1992年   7905篇
  1991年   7920篇
  1990年   7537篇
  1989年   7505篇
  1988年   6881篇
  1987年   6636篇
  1986年   6026篇
  1985年   6227篇
  1984年   5177篇
  1983年   4376篇
  1982年   3408篇
  1981年   3157篇
  1980年   2959篇
  1979年   4959篇
  1978年   3824篇
  1977年   3733篇
  1976年   3437篇
  1975年   3799篇
  1974年   4181篇
  1973年   4096篇
  1972年   4312篇
  1971年   4040篇
  1970年   3095篇
  1969年   2997篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
984.
By means of new plastic stereotactic ring and head fixers, stereotactic procedures can be combined with MRI, with stereotactic coordinates obtained from the MRI images. The method was rechecked against CT stereotaxy and shows a good correspondence of the target coordinates. With MRI stereotaxy, structures near bony regions will be more accessible than with CT stereotaxy. Moreover, the MRI procedure seems to have advantages for functional therapy without the necessity of contrast ventriculography.  相似文献   
985.

Background  

Meiotic prophase is a critical stage in sexual reproduction. Aberrant chromosome recombination during this stage is a leading cause of human miscarriages and birth defects. However, due to the experimental intractability of mammalian gonads, only a very limited number of meiotic genes have been characterized. Here we aim to identify novel meiotic genes important in human reproduction through computational mining of cross-species and cross-sex time-series expression data from budding yeast, mouse postnatal testis, mouse embryonic ovary, and human fetal ovary.  相似文献   
986.

Background  

Genome sequencing projects have expanded the gap between the amount of known protein sequences and structures. The limitations of current high resolution structure determination methods make it unlikely that this gap will disappear in the near future. Small angle X-ray scattering (SAXS) is an established low resolution method for routinely determining the structure of proteins in solution. The purpose of this study is to develop a method for the efficient calculation of accurate SAXS curves from coarse-grained protein models. Such a method can for example be used to construct a likelihood function, which is paramount for structure determination based on statistical inference.  相似文献   
987.
Ishida  Takuya  Uehara  Yoshitoshi  Ikeya  Tohru  Haraguchi  Takashi F.  Asano  Satoshi  Ogino  Yohei  Okuda  Noboru 《Limnology》2020,21(3):403-413
Limnology - Controlling phosphorous (P) loads from rice fields is important for the conservation of aquatic ecosystems, in part because P is relatively concentrated at its sources. Recently, winter...  相似文献   
988.
Seraspenide, a synthetic tetrapeptide, inhibits cell cycle entry of normal hematopoietic stem cells. In mice it protects hemopoiesis against the damage caused by cytarabine, cyclophosphamide and carboplatin. Seraspenide has been given to 53 cancer patients undergoing monochemotherapy with cytarabine and ifosfamide in a double-blind cross-over randomized study. A significant protection of peripheral blood cells has been observed. Seraspenide has been devoided of toxicity.  相似文献   
989.
990.
Pseudomonas sp. CBS3 was grown with 4-chlorobenzoate as sole source of carbon and energy. Freshly prepared cell-free extracts converted 4-chlorobenzoate to 4-hydroxybenzoate. After storage for 16 hours at 25 degrees C only about 50% of the initial activity was left. Treatment at 55 degrees C for 10 minutes, dialysis or desalting of the extracts by gel filtration caused a total loss of the activity of the 4-chlorobenzoate dehalogenase. The activity could be restored by the addition of ATP, coenzyme A and Mg2+. If one of these cofactors was missing, no dehalogenating activity was detectable. The amount of 4-hydroxybenzoate formed was proportional to the amount of ATP available in the test system whereas CoA served as a real coenzyme. A novel ATP/coenzyme A dependent reaction mechanism for the dehalogenation of 4-chlorobenzoate by 4-chlorobenzoate dehalogenase from Pseudomonas sp. CBS3 is proposed.  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