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   93211篇
  免费   5706篇
  国内免费   59篇
林业   3968篇
农学   3594篇
基础科学   662篇
  11962篇
综合类   14051篇
农作物   3577篇
水产渔业   5271篇
畜牧兽医   48709篇
园艺   1287篇
植物保护   5895篇
  2020年   814篇
  2019年   1036篇
  2018年   1660篇
  2017年   1919篇
  2016年   1743篇
  2015年   1466篇
  2014年   1802篇
  2013年   3875篇
  2012年   3134篇
  2011年   3823篇
  2010年   2488篇
  2009年   2453篇
  2008年   3667篇
  2007年   3430篇
  2006年   3329篇
  2005年   2854篇
  2004年   2765篇
  2003年   2777篇
  2002年   2539篇
  2001年   3434篇
  2000年   3345篇
  1999年   2600篇
  1998年   1017篇
  1997年   1079篇
  1996年   917篇
  1995年   1049篇
  1994年   923篇
  1993年   935篇
  1992年   1868篇
  1991年   1949篇
  1990年   1875篇
  1989年   1892篇
  1988年   1632篇
  1987年   1612篇
  1986年   1647篇
  1985年   1545篇
  1984年   1246篇
  1983年   1050篇
  1982年   724篇
  1979年   1068篇
  1978年   825篇
  1975年   829篇
  1974年   913篇
  1973年   880篇
  1972年   810篇
  1971年   800篇
  1970年   804篇
  1969年   782篇
  1968年   710篇
  1967年   738篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
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   
105.
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   
106.
107.
Described in this paper are 2 methodological variants for photometric recording of sperm aggregation. Heparin was used to induce aggregation. One of the working principles was related to aggregation-associated alteration of turbidity in an agitated cell suspension, measured by the KZM-1 coagulation-time meter, in analogy to measurement of thrombocyte aggregation. The 2nd variant was based on variation of cloudiness due to sedimentation of aggregates in a non-agitated suspension. Both methods provided equally valid information. They characterised both intensity of aggregation as a combined effect of the number and size of aggregates as well as the rate of aggregation. Photometric recording has proved to be an objectivated method for quantitative assessment of aggregation. Its use is proposed for studies into capacitation or immunological response of spermatozoa.  相似文献   
108.
In this study, the effects of nitrogen (N) rate (60, 120, 180 and 240 kg N ha?1 applied in three equal dressings at seeding and after the first and second cuttings) and stubble height (7, 14 and 21 cm) on the dry matter (DM) yield, crude protein (CP) content, and CP yield of a sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench × Sorghum sudanense (Piper) Stapf., cv. Pioneer 988] in the three‐cut system was investigated. The N rate had no significant effect in the first and third cuttings, but in the second cutting DM yields increased significantly with increase in N rate. The highest yield of 9.1 t ha?1 was obtained with 80 kg N ha?1 for the average of 2 years at the second cutting, but no significant difference was found among the 40, 60 and 80 kg N ha?1 rates. CP content and yield were not significantly affected by N rate at the first and third cuttings, but CP content and yield were significantly affected by application of N at the second cutting. Stubble height had a significant effect on CP content at the third cutting. However, it had no significant effect on CP content at the first and second cuttings. Stubble height had a significant effect on the CP yield at the first cutting, but no significant effect on CP yield at the second and third cuttings.  相似文献   
109.
110.
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