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   86043篇
  免费   5099篇
  国内免费   37篇
林业   4796篇
农学   3105篇
基础科学   551篇
  12568篇
综合类   12143篇
农作物   3275篇
水产渔业   4925篇
畜牧兽医   42355篇
园艺   1267篇
植物保护   6194篇
  2021年   733篇
  2020年   772篇
  2019年   845篇
  2018年   1746篇
  2017年   1878篇
  2016年   1759篇
  2015年   1421篇
  2014年   1754篇
  2013年   3588篇
  2012年   3241篇
  2011年   3532篇
  2010年   2323篇
  2009年   2235篇
  2008年   3507篇
  2007年   3234篇
  2006年   3019篇
  2005年   2837篇
  2004年   2836篇
  2003年   2767篇
  2002年   2532篇
  2001年   2688篇
  2000年   2663篇
  1999年   2181篇
  1998年   984篇
  1997年   894篇
  1996年   842篇
  1995年   917篇
  1994年   883篇
  1993年   799篇
  1992年   1611篇
  1991年   1621篇
  1990年   1727篇
  1989年   1586篇
  1988年   1510篇
  1987年   1401篇
  1986年   1456篇
  1985年   1414篇
  1984年   1179篇
  1983年   1080篇
  1979年   1058篇
  1978年   838篇
  1977年   751篇
  1976年   699篇
  1975年   737篇
  1974年   805篇
  1973年   883篇
  1972年   843篇
  1971年   793篇
  1970年   754篇
  1969年   772篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Twenty-one Bunaji (White Fulani, Zebu) and 21 Friesian X Bunaji cross-bred bull calves, approximately 6 months of age, were each divided after weaning into two groups and fed isocaloric rations containing 14.45% (high protein) and 8.51% (low protein) crude protein for 10 months. Serum samples were collected biweekly for 10 months and analysed for serum proteins. Age had no significant effect. The Bunaji had significantly (P less than 0.05) higher total protein, albumin, and alpha 1-globulin than Friesian X Bunaji. While there was no significant difference in body condition score between the two breeds, the Friesian X Bunaji had a significantly (P less than 0.05) higher growth rate. Animals on high protein diets had significantly (P less than 0.05) higher total protein, albumin, alpha 2-globulin, gamma-globulin and total globulin than those on low protein. However, alpha 1-globulin and beta-globulin were not significantly (P greater than 0.05) different for the two treatment groups.  相似文献   
92.
The Chilean Intermediate Depression to the north of Santiago has experienced a physiognomical transformation from a Prosopis chilensis woodland to an Acacia caven savanna. Today P. chilensis trees are scarce and belong mostly to the larger size classes. By contrast A. caven seems to reproduce frequently and its populations consist of individuals of all size classes. In this paper we document these changes and report the results of tests aimed at determining the causes of these physiognomical changes. We found that livestock, leporids, introduced Mediterranean forbs and agriculture account for differences in seed dispersal and survival of A. caven and P. chilensis, which can explain the documented changes in the Chilean landscape.  相似文献   
93.
Muscle biopsies were taken from the middle gluteal muscle of 28 Standardbred trotters, 3-4 years of age. The 13 horses in Group T were trained consistently from 18 months of age, whereas the 15 horses in Group UT were not exposed to any systematic training before 3 years of age. Group T horses had a lower percentage of Type IIB fibres (31%) than did Group UT horses (39%). Citrate synthase (CS) activity, representing oxidative capacity, was higher in Group T (72 mmol kg-1 min-1) than in Group UT (47 mmol kg-1 min-1). Biopsies were taken from 4 horses in each group when they were foals and then annually until 3-4 years of age. Results from this study indicate that regular training of Standardbreds from 18 months of age resulted in increased CS activity and a decrease in the percentage of Type IIB fibres. This study shows that training, not growth, is the main factor that induces a high oxidative capacity and a high Type IIA/IIB fibre ratio in muscle of Standardbred trotters.  相似文献   
94.
Lyophilised serum offers significant advantages over frozen serum when it comes to shipping such material over long distances. Babesia bigemina and B bovis were cultured in medium supplemented by either frozen-thawed or lyophilised-rehydrated serum. There were no significant differences between the two types of medium in the growth of parasites and percentage of infected cells during subcultivation for 18 days.  相似文献   
95.
The objective of these experiments was to examine methods of modifying the fatty acid composition of bovine tissues. In the first experiment, four steers were fitted with duodenal fistulas and were assigned to four diets in a Latin square design. The steers were fed a control diet or the same diet containing 10% high-oleate partially crushed sunflower seeds, serum-coated sunflower seeds, and heat-treated, serum-coated sunflower seeds for 5 d. Samples of digesta and feces were collected on d 5. The inclusion of sunflower seeds (plain or serum-coated) in the diet increased (P less than .05) the digesta concentration of stearate. The percentage of stearate in the digesta and feces was increased (P less than .05) from 51 to 67% and from 64 to 74%, respectively, when steers were fed the untreated sunflower seed. The fecal concentration of oleate was increased (P less than .05) by dietary sunflower seeds in steers that were fed the serum-coated, unheated sunflower seeds. In a second experiment, heifers (four per group) were fed a corn-based control diet or diets containing 10% of high-oleate sunflower oil encapsulated with calcium alginate, either plain, coated with blood meal, or with blood meal integrated into the pellet. After 50 d on treatment, samples of perianal adipose tissue were obtained by biopsy. The fatty acid composition of the adipose tissue was not modified by the inclusion of the encapsulated oleate in the diet. In summary, limited ruminal bypass of sunflower seed oleate was accomplished with sunflower seed but not with encapsulated oleate.  相似文献   
96.
97.
The relationship between the levels of CO and airborne Pb was evaluated against conditions of traffic flow, ambient air temperature and the ventilation rates in 3 underground car parks. During the study period significant variations were noted in the levels of the pollutants in each of the car parks which frequently exceeded the proposed Malaysian Air Quality Standard of 0.7 μg m?3Pb and 9 μg L?1 (8 hr average) CO for indoor environs. High correlation coefficient values were obtained between the levels of CO and traffic flow and Pb and traffic flow. High traffic flow also increased the mean air temperature inside the car parks. Reductions in the ventilation rates in the car parks caused an almost two-fold increase in the level of CO and vice versa. A simple mathematical model depicting the CO concentrations in relation to other parameters was formulated.  相似文献   
98.
A tumor of the third eyelid gland was diagnosed in a 13 year old female Chihuahua. Histopathology of the excised tissue revealed an apocrine adnexoma with squamous metaplasia. The literature regarding prolapse and tumors of the third eyelid gland was reviewed. No case with similar morphology to this tumor was described to our knowledge.  相似文献   
99.
The etiopathogenesis and diagnosis of discospondylitis are reviewed. Various therapy options are described. Also included is a discussion of the appropriate usage of specific antimicrobial agents.  相似文献   
100.
Antibody responses to a commercial avian encephalomyelitis virus (AEV) vaccine administered by different routes were measured by an enzyme-linked immunosorbent assay (ELISA). Responses to single doses of vaccine administered by the ocular route to 10% of a flock were comparable with those obtained when all birds received a single dose in the drinking water. However, ocular vaccination of 5% of the flock resulted in significantly lower responses than those obtained when 10% were vaccinated. Maternal antibody was shown by the ELISA to persist in chickens from vaccinated flocks for up to 21 days after hatching. Day-old chickens with serum absorbances of < 0.3 at 492 nm, as determined by the ELISA, were shown to be susceptible to intracerebral challenge with the neurotropic Van Roekel strain of AEV.  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