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   254篇
  免费   9篇
林业   33篇
农学   4篇
  42篇
综合类   68篇
农作物   12篇
水产渔业   7篇
畜牧兽医   73篇
园艺   3篇
植物保护   21篇
  2020年   4篇
  2019年   6篇
  2018年   4篇
  2017年   4篇
  2015年   3篇
  2014年   2篇
  2013年   9篇
  2012年   15篇
  2011年   15篇
  2010年   11篇
  2009年   12篇
  2008年   12篇
  2007年   4篇
  2006年   14篇
  2005年   11篇
  2004年   6篇
  2003年   10篇
  2002年   12篇
  2001年   2篇
  2000年   8篇
  1999年   7篇
  1998年   2篇
  1996年   4篇
  1995年   6篇
  1994年   6篇
  1993年   3篇
  1992年   5篇
  1991年   8篇
  1990年   2篇
  1988年   2篇
  1987年   4篇
  1986年   2篇
  1984年   2篇
  1979年   2篇
  1974年   2篇
  1970年   4篇
  1967年   2篇
  1943年   1篇
  1942年   1篇
  1941年   1篇
  1935年   1篇
  1934年   1篇
  1933年   1篇
  1932年   1篇
  1931年   1篇
  1930年   2篇
  1927年   1篇
  1925年   1篇
  1924年   1篇
  1921年   2篇
排序方式: 共有263条查询结果,搜索用时 0 毫秒
261.
The physical basis of life and learning   总被引:1,自引:0,他引:1  
  相似文献   
262.
Much of what needs to be changed in U.S. industry involves close ties to manufacturing, design for manufacturability, a rapid design cycle, and up-to-date technical knowledge on the part of the engineers themselves. Being up-to-date requires conscious company effort. Traveling to meetings, reading the technical literature, and being a part of the engineering community are necessities if we are to compete with others who make these efforts and are thus better able to incorporate technical change rapidly into their own products. Outside the product improvement cycle, a research (as opposed to development) organization in industry must have close ties to development and manufacturing in order to succeed. With these close ties, researchers can understand the progress of the cycle and can introduce new steps at the appropriate time and in an acceptable form. A research organization that surmounts the internal barriers and becomes an accepted contributor to the development and manufacturing process can, because of its greater technical depth, its scientific knowledge, and its close ties with the university world, become a forceful initiator of progress. It is more difficult, in our opinion, to make these contributions from a university base and from government laboratories as they are now constituted. Much has been said by industry and government leaders about reforming the educational system and strengthening the national science base-things that help build a strong foundation. A strong science base supplies a vast storehouse of new ideas, and a good educational system provides engineers and manufacturing workers with knowledge; but strength here cannot make up for inadequacies in the functioning of the development and manufacturing cycle. The United States must learn to succeed, not only in the ladder type of innovation in which a wholly new idea from science creates a wholly new product (the science-dominated process at which we have succeeded in the past), but also in the rapid, cyclical, engineer-dominated process of incremental product improvement. Neither process is a substitute for the other; we need both.  相似文献   
263.
The hydroalcoholic extract of Maytenus krukovii bark was investigated for its in vitro mutageno-protective activities by means of the Ames Salmonella/microsome assay. The extract showed an inhibitory effect in both T98 and T100 strains against the mutagenic activity of promutagen 2-aminoanthracene but was not protective against directly acting mutagens sodium azide and 2-nitrofluorene. When tested as a radical scavenger and antioxidant it produced a dose-dependent inhibition. The extract did not show significant antibacterial properties, and was weakly active against dermatophyte and phytopathogenic fungi, but inhibited the growth of phytopathogen Pithyum ultimum.  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