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   107778篇
  免费   5570篇
  国内免费   52篇
林业   4800篇
农学   3071篇
基础科学   733篇
  12151篇
综合类   20873篇
农作物   4362篇
水产渔业   4681篇
畜牧兽医   55303篇
园艺   1233篇
植物保护   6193篇
  2018年   1281篇
  2017年   1418篇
  2016年   1355篇
  2015年   1141篇
  2014年   1330篇
  2013年   4095篇
  2012年   2690篇
  2011年   3307篇
  2010年   2147篇
  2009年   2118篇
  2008年   3319篇
  2007年   3056篇
  2006年   2915篇
  2005年   2754篇
  2004年   2851篇
  2003年   2798篇
  2002年   2711篇
  2001年   3338篇
  2000年   3353篇
  1999年   2477篇
  1998年   1096篇
  1997年   1101篇
  1995年   1291篇
  1994年   1175篇
  1993年   1135篇
  1992年   2377篇
  1991年   2534篇
  1990年   2454篇
  1989年   2504篇
  1988年   2289篇
  1987年   2354篇
  1986年   2493篇
  1985年   2406篇
  1984年   1928篇
  1983年   1784篇
  1982年   1168篇
  1981年   1125篇
  1980年   1038篇
  1979年   1767篇
  1978年   1435篇
  1977年   1152篇
  1976年   1138篇
  1975年   1172篇
  1974年   1525篇
  1973年   1614篇
  1972年   1587篇
  1971年   1518篇
  1970年   1414篇
  1969年   1266篇
  1967年   1097篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
103.
104.
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   
105.
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   
106.
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   
107.
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   
108.
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