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   89957篇
  免费   5073篇
  国内免费   321篇
林业   4352篇
农学   3278篇
基础科学   628篇
  12065篇
综合类   11747篇
农作物   3355篇
水产渔业   4632篇
畜牧兽医   48641篇
园艺   1115篇
植物保护   5538篇
  2020年   791篇
  2019年   907篇
  2018年   1579篇
  2017年   1684篇
  2016年   1578篇
  2015年   1360篇
  2014年   1642篇
  2013年   3821篇
  2012年   2834篇
  2011年   3401篇
  2010年   2278篇
  2009年   2264篇
  2008年   3189篇
  2007年   3078篇
  2006年   2927篇
  2005年   2608篇
  2004年   2486篇
  2003年   2484篇
  2002年   2295篇
  2001年   3238篇
  2000年   3126篇
  1999年   2418篇
  1998年   986篇
  1997年   951篇
  1996年   883篇
  1995年   992篇
  1994年   856篇
  1993年   803篇
  1992年   1778篇
  1991年   2007篇
  1990年   1990篇
  1989年   1913篇
  1988年   1768篇
  1987年   1739篇
  1986年   1707篇
  1985年   1573篇
  1984年   1310篇
  1983年   1068篇
  1979年   1262篇
  1978年   995篇
  1976年   844篇
  1975年   860篇
  1974年   1031篇
  1973年   1025篇
  1972年   1035篇
  1971年   901篇
  1970年   923篇
  1969年   896篇
  1968年   792篇
  1967年   818篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
93.
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   
94.
95.
2 groups of 20 cocks each were selected at random from non-dwarf White Leghorn (28 weeks post-hatch) and dwarf Krishna-J (38 weeks post-hatch) genotypes. The treated groups comprised 10 White Leghorn and 10 Krishna-J cocks. The remaining birds served as controls. 8 weeks prior to furazolidone treatment, semen was collected from both control groups at regular 4-day intervals, for 4 weeks. Cocks of the treated groups of both genotypes were administered furazolidone (0.14 g/bird/day) for 7 consecutive days. Semen was collected from all cocks at regular 4-day intervals for 4 weeks. Semen from the cocks of the same group was pooled. The pooled ejaculate volume and sperm density did not differ significantly in the 2 genotypes. The semen output as well as sperm density increased along with progressive attainment of sexual maturity. Furazolidone treatment caused significant reduction in semen volume as well as sperm concentration in either genotype.  相似文献   
96.
97.
Abstract. Experiments were started in 1967 to investigate the effects of soil mixing on fen peat soil. Peaty topsoil was mixed with mineral subsoil to a maximum depth of 80 cm at two sites, one with a clay subsoil, the other sand. Mixing was done on a commercial scale with a range of implements. After initial increases, yields of arable crops on both mixed soils were subsequently similar to those on unmixed soil. Residual herbicide activity was enhanced on mixed soils, and evidence of peat conservation was obtained at one site. The practice has not been taken up commercially because of the high capital cost of mixing and lack of serious problems which had been predicted following peat wastage.  相似文献   
98.
99.
100.
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