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   141833篇
  免费   7392篇
  国内免费   83篇
林业   5680篇
农学   4346篇
基础科学   919篇
  16188篇
综合类   26671篇
农作物   5427篇
水产渔业   6742篇
畜牧兽医   73392篇
园艺   1633篇
植物保护   8310篇
  2018年   1769篇
  2017年   1953篇
  2016年   1846篇
  2015年   1547篇
  2014年   1828篇
  2013年   5268篇
  2012年   3549篇
  2011年   4403篇
  2010年   2999篇
  2009年   2884篇
  2008年   4447篇
  2007年   4128篇
  2006年   3895篇
  2005年   3668篇
  2004年   3761篇
  2003年   3712篇
  2002年   3509篇
  2001年   4685篇
  2000年   4711篇
  1999年   3539篇
  1998年   1503篇
  1997年   1457篇
  1995年   1688篇
  1994年   1554篇
  1993年   1473篇
  1992年   3169篇
  1991年   3365篇
  1990年   3296篇
  1989年   3283篇
  1988年   3037篇
  1987年   3088篇
  1986年   3184篇
  1985年   3035篇
  1984年   2482篇
  1983年   2254篇
  1982年   1460篇
  1981年   1397篇
  1980年   1301篇
  1979年   2219篇
  1978年   1791篇
  1977年   1484篇
  1976年   1429篇
  1975年   1522篇
  1974年   1925篇
  1973年   1980篇
  1972年   1968篇
  1971年   1834篇
  1970年   1710篇
  1969年   1596篇
  1967年   1370篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Samples of rapeseed from three Italian growing environments (Bologna, Perugia and Palermo) were analysed for glucose content and dry weight of 1000 seeds every three or four days starting from the end of flowering until complete ripening. In addition, the content of oil, soluble and total proteins, glucosinolates and myrosinase activity was determined in samples of mature seeds. The cultivars used were jet Neuf and Lingot (type 0) and Tandem, Jade and Santana (type 00). From the results it emerged that the point of intersection of the two branches of the linear regression plots for different glucose-consumption kinetics found during seed filling, in addition to being strongly affected by the climate of the test environment, is correlated with quantitative and qualitative production, independently of the genotype.  相似文献   
103.
104.
105.
106.
107.
108.
Four commercially available semiquantitative milk progesterone tests (Ovucheck-Praxistest: Cambridge Veterinary Science/Smith Kline), Progestassay-Milchprogesteron (Pitman-Moore/Janssen), Reprostrip-Progesteron-Schnelltest (Noctech/Albrecht), Enzygnost-Milchprogesteron (IQ, 'Bio' UK/Hoechst Veterin?r) were examined for their accuracy by using them for the determination of progesterone levels of 64 milk samples, i.e. 1556 single assays. Several test series were performed, using codified samples and changing sequences. Three or four test persons respectively, performed the tests independently and classified the samples semiquantitatively. These test results were then compared to the results acquired by measuring the progesterone levels of the same samples by means of an approved quantitative, labor-bound progesterone test (Hormonost: Biolab). These control tests were performed at a specialized routine labor, by different personnel and at a different location. Lastly, in 48 out of the 64 sampled animals the reproductive status could be evaluated clinically and was taken into account as well. Samples yielding high progesterone levels, i.e. greater than or equal to 9 ng/ml were classified correctly in 84.4 to 96.5% of the cases, whereas samples with low levels (less than or equal to 2.5 ng/ml) were classified correctly in 68.8 to 90.0% of the cases only. Samples ranging between this spectrum (greater than 2.5 less than 9 ng/ml) were classified correctly only in 42.1 to 52.6% of the cases. However, this range appears to be of the most interest for the veterinary practitioner since cows in proestrus or early interestrus tend to have mild progesterone levels within these values. On the other hand, clinical findings are often insufficient for a proper diagnosis just in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
109.
A review of investigations of the functional anatomy of the equine foot is presented. Emphasis is placed on the relationships of structures involved in the major diseases of the foot.  相似文献   
110.
Gold, bronze, and black (normal pigmentation) body colors in Tilapia mossambica are controlled by a single autosomal gene with incomplete dominant gene action: GG fish are black gg fish are gold; Gg fish are bronze. Because gold body color is produced by the recessive genotype, it is easy to produce and to maintain a truebreeding population of gold T. mossambica for commercial purposes. If all other colors are culled, the population will breed true, because gold × gold will always produce 100% gold offspring. The G gene will be a valuable genetic marker for many genetic studies, such as the production of gynogenetic T. mossambica .  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