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   68238篇
  免费   3088篇
  国内免费   43篇
林业   2940篇
农学   1773篇
基础科学   476篇
  7108篇
综合类   15794篇
农作物   2764篇
水产渔业   2724篇
畜牧兽医   33090篇
园艺   859篇
植物保护   3841篇
  2018年   634篇
  2017年   648篇
  2016年   652篇
  2014年   684篇
  2013年   2112篇
  2012年   1499篇
  2011年   1788篇
  2010年   1103篇
  2009年   1033篇
  2008年   1805篇
  2007年   1733篇
  2006年   1730篇
  2005年   1742篇
  2004年   1681篇
  2003年   1761篇
  2002年   1680篇
  2001年   1584篇
  2000年   1534篇
  1999年   1270篇
  1996年   580篇
  1995年   635篇
  1994年   617篇
  1993年   607篇
  1992年   1356篇
  1991年   1432篇
  1990年   1502篇
  1989年   1529篇
  1988年   1432篇
  1987年   1395篇
  1986年   1427篇
  1985年   1413篇
  1984年   1188篇
  1983年   1041篇
  1982年   744篇
  1981年   711篇
  1980年   663篇
  1979年   1146篇
  1978年   938篇
  1977年   846篇
  1976年   789篇
  1975年   880篇
  1974年   1150篇
  1973年   1080篇
  1972年   1137篇
  1971年   1090篇
  1970年   1029篇
  1969年   880篇
  1968年   717篇
  1967年   852篇
  1966年   698篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A study was designed to evaluate the representativeness and accuracy of data collected on swine birth defects by mailed questionnaire. The study was conducted in the three contiguous counties of Johnson, Lafayette and Pettis in west central Missouri. A personal interview survey and an examination of malformed pigs were used to validate mailed questionnaire data which estimated the frequency and distribution of malformations observed in pigs over a six month period. This period between April and September 1970 was defined as the study period. The results were compared to a previous six month period (April-September 1969), or baseline period, when only the mailed questionnaire was used. The frequency and distribution of the reported malformations by type did not differ significantly (at the p=0.05 level) between the study period (70.4% response) and the baseline period (31.3% response). Evaluation of this and additional data collected during the study suggested that the mailed questionnaire can be used effectively to estimate the frequency and distribution of swine malformations within a defined geographic area.  相似文献   
992.
993.
Thirty‐three light hybrids aged 11 months were caged individually and fed for S weeks according to three regimes, viz. A, a conventional mash ad libitum; B, a mixture of whole wheat, barley and kibbled maize ad libitum in the morning, with concentrate pellets ad libitum in the afternoon; or C, ad libitum the same grain mixture together with concentrate pellets and oystershell grit in the ratio 70 : 23 : 7 so that the nutritive value of the complete diet was similar to that of the conventional mash. The concentrate pellets used in the two regimes differed. Those used in regime B contained ground limestone while those used in regime C did not.

Egg production was similar on the three regimes (74.8, 74.7 and 74.5% respectively) . Food intake was lowest on regime C and highest on regime B, although the intakes of metabolisable energy were very similar on the three regimes. Compared with the results obtained with the conventional mash diet (regime A), the conversions of food and dietary protein to eggs were lower on regime B but higher on regime C.  相似文献   

994.
Nine cases of granulomatous dermatitis in carnivores (eight dogs, one cat) are described. In three cases, in which there were no fungi in hair shafts, nor any other evidence of mycotic infection initially, fungal elements were demonstrated in the granulomas with the aid of special stains (PAS and Grocott). Granulomatous dermatitis in case of dermatophyte infections is thought to be an hypersensitivity reaction and has been reported to occur in a variety of mammals. It is suggested that pyogranulomatous skin reactions and trichogranulomas could be associated with dermatophytes and it is recommended to carry out further laboratory studies in order to detect fungi in such cases.  相似文献   
995.
996.
The amounts of copper, iron, magnesium, manganese, potassium, sodium and zinc in the embryo and in the rest of the egg were determined daily from the 5th to 18th days of incubation.

For all minerals the relationships between the amounts present in the embryo and the embryo dry weight were allometric over this period.

There were significant, positive, within‐day correlations between the amounts of copper, manganese, sodium and potassium and between iron, magnesium and zinc present in the embryo.

Only in the cases of iron and sodium was there evidence to suggest that the total amount of the element present in the egg was correlated with the amount transferred to the embryo.  相似文献   

997.
998.
999.
1000.
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