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   149078篇
  免费   7993篇
  国内免费   82篇
林业   6222篇
农学   4368篇
基础科学   936篇
  16682篇
综合类   28428篇
农作物   5717篇
水产渔业   6767篇
畜牧兽医   77322篇
园艺   1773篇
植物保护   8938篇
  2018年   1863篇
  2017年   1993篇
  2016年   1867篇
  2015年   1675篇
  2014年   1897篇
  2013年   5652篇
  2012年   3766篇
  2011年   4642篇
  2010年   3023篇
  2009年   2972篇
  2008年   4562篇
  2007年   4287篇
  2006年   4027篇
  2005年   3799篇
  2004年   3840篇
  2003年   3820篇
  2002年   3710篇
  2001年   4514篇
  2000年   4534篇
  1999年   3494篇
  1998年   1506篇
  1997年   1517篇
  1995年   1722篇
  1994年   1589篇
  1993年   1538篇
  1992年   3170篇
  1991年   3444篇
  1990年   3333篇
  1989年   3389篇
  1988年   3087篇
  1987年   3086篇
  1986年   3284篇
  1985年   3196篇
  1984年   2603篇
  1983年   2424篇
  1982年   1574篇
  1981年   1502篇
  1979年   2375篇
  1978年   1945篇
  1977年   1656篇
  1976年   1645篇
  1975年   1690篇
  1974年   2163篇
  1973年   2193篇
  1972年   2148篇
  1971年   2026篇
  1970年   1950篇
  1969年   1794篇
  1968年   1501篇
  1967年   1570篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Mid-storage hydration-dehydration treatments with medium-vigour lettuce seed very effectively reduced physiological deterioration in storage and ultimately showed better field emergence and final yield. Soaking-drying treatment of high-vigour lettuce seed was not effective. Pre-sowing treatment of medium-vigour lettuce seed, though less effective than mid-storage treatment, gave better field performance, but high-vigour seed did not benefit from the treatment. For carrot, both mid-storage and pre-sowing seed treatments proved beneficial, with the former showing better performance than the latter. Unlike lettuce, well-preserved carrot seed responded positively to the pre-sowing treatment.  相似文献   
72.
Images with high resolution and exceptionally broad gray scale can be obtained by the application of video contrast enhancement to an optimized procedure for imaging transparent objects with oblique rays of illumination. This technique is simple to set up. A conventional microscope with a light source whose position can be adjusted and a video camera with controls for gain and black level are the only essential components. Features such as high resolution, optical sectioning, control of contrast, and operation under low light intensity make this technique preferable, in several instances, to currently used video microscopy techniques.  相似文献   
73.
Washed and unwashed red blood cells (RBC) from young calves, adult cattle, hamsters and humans were incubated with Leptospira interrogans serovars pomona and ballum. Washed cells suspended in saline were always haemolysed while unwashed cells and those which were washed and resuspended in plasma were never haemolysed, despite the presence of large numbers of organisms within the culture supernatant. Pomona produced greater haemolysis of cattle and human RBC than did ballum, but with hamster RBC ballum produced greater haemolysis than did pomona. A group of 6- to 9-month-old cattle infected with pomona showed no signs of clinical disease and RBC taken from them before infection and during the development of antibodies to pomona were haemolysed by pomona only after the cells were washed. Plasma therefore appears to have a protective function. This in vitro protective function of plasma even extended to plasma from young seronegative calves.  相似文献   
74.
In addition to the well-defined phenolic estrogens in human pregnancy urine there appears to be another estrogenic substance which is a neutral non-ketonic compound.  相似文献   
75.
76.
77.
78.
79.
80.
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