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   247199篇
  免费   22668篇
  国内免费   251篇
  2018年   2681篇
  2017年   2629篇
  2016年   3514篇
  2015年   3785篇
  2014年   4729篇
  2013年   6744篇
  2012年   7455篇
  2011年   8143篇
  2010年   5519篇
  2009年   4890篇
  2008年   7053篇
  2007年   7227篇
  2006年   6846篇
  2005年   6544篇
  2004年   6428篇
  2003年   6243篇
  2002年   6086篇
  2001年   12020篇
  2000年   11972篇
  1999年   9162篇
  1998年   2691篇
  1997年   2758篇
  1996年   2699篇
  1995年   2489篇
  1994年   2431篇
  1993年   2326篇
  1992年   7177篇
  1991年   6986篇
  1990年   7062篇
  1989年   6845篇
  1988年   6367篇
  1987年   6009篇
  1986年   5354篇
  1985年   5664篇
  1984年   4467篇
  1983年   3863篇
  1982年   2677篇
  1981年   2498篇
  1980年   2304篇
  1979年   4110篇
  1978年   3140篇
  1977年   2884篇
  1976年   2832篇
  1975年   3274篇
  1974年   3499篇
  1973年   3530篇
  1972年   3061篇
  1971年   2844篇
  1970年   2533篇
  1969年   2301篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
973.
Summary A local isolate of Bacillus thuringiensis (B.t.81) produced crystal protein which was identified as a cry I gene of Class I. The synthesis and assembly of crystal complements were investigated at intervals throughout the growth cycle. Incubation temperature had a marked effect on toxin synthesis; production being the highest at 25°C and the lowest at 42°C. The mutants of B. t. 81, unable to synthesize crystal protein complements, have also been described.  相似文献   
974.
975.
976.

Objectives

The Levantine Middle Bronze Age (MBA, circa 2000–1500 BCE) marks a period of increased trade and regional interaction, spurred on by technological developments. In light of previous research exhibiting limited mobility in Sidon, further investigation was conducted using biodistance analysis to understand local population history and site development.

Materials and Methods

Dental nonmetric traits, a proxy for genetic information, were explored using ASUDAS on a sub-sample of primary inhumations (n = 35). The biodistance matrix was generated using Gower distance measures, and further tested using PERMDISP, PERMANOVA, Mantel test and hierarchical cluster analysis. The data was also contrasted to 87Sr/86Sr and δ18O as well as δ13C and δ15N values.

Results

There were no significant diachronic differences in isotopes values, and there was biological continuity (n = 35, Mantel test r = 0.11, p = 0.02, comparing local phases and biodistance). The analysis also suggested of a sub-group of individuals with biological proximity shared a more limited range of mobility and dietary habits.

Conclusions

The isotopes (87Sr/86Sr, δ18O, δ13C, δ15N) and biodistance analysis conducted on the Sidon College site skeletal assemblage exhibits stability and continuity of the people, despite the site's increasing role in the maritime network. This continuity may have been a key factor in Sidon's success, allowing it to accumulate wealth and resources for centuries to come.
  相似文献   
977.
978.
Short peptide domains target proteins to plant vacuoles.   总被引:18,自引:0,他引:18  
M J Chrispeels  N V Raikhel 《Cell》1992,68(4):613-616
  相似文献   
979.
Some differences were found in the ultrastructural, cultural and physiological-biochemical properties between the parent strainStreptomyces spectabilis 1000 and its natural selectantS. spectabilis 1011-10, producers of streptovaricin.  相似文献   
980.
The level of urine selenium in healthy adult population, 230 persons, was examined. Persons were selected regarding sex, ages, and smoking habits. No differences versus these observations have been found. For a total, group values are 16.96 Se nmol/creatinine mmol, SD=5.44. It is possible from a single-void specimen to express daily excretion of selenium.  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