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   148221篇
  免费   8230篇
  国内免费   139篇
林业   6526篇
农学   4362篇
基础科学   955篇
  17465篇
综合类   27310篇
农作物   5795篇
水产渔业   7114篇
畜牧兽医   75991篇
园艺   1827篇
植物保护   9245篇
  2018年   2034篇
  2017年   2238篇
  2016年   2062篇
  2015年   1761篇
  2014年   2238篇
  2013年   5440篇
  2012年   4162篇
  2011年   4998篇
  2010年   3208篇
  2009年   3305篇
  2008年   5030篇
  2007年   4741篇
  2006年   4464篇
  2005年   4203篇
  2004年   4100篇
  2003年   4230篇
  2002年   3844篇
  2001年   4252篇
  2000年   4266篇
  1999年   3339篇
  1998年   1393篇
  1997年   1436篇
  1996年   1361篇
  1995年   1579篇
  1994年   1367篇
  1993年   1416篇
  1992年   2835篇
  1991年   3120篇
  1990年   2979篇
  1989年   2997篇
  1988年   2761篇
  1987年   2772篇
  1986年   2898篇
  1985年   2817篇
  1984年   2298篇
  1983年   2049篇
  1982年   1410篇
  1979年   2194篇
  1978年   1710篇
  1977年   1515篇
  1976年   1372篇
  1975年   1509篇
  1974年   1920篇
  1973年   1948篇
  1972年   1935篇
  1971年   1812篇
  1970年   1788篇
  1969年   1662篇
  1968年   1473篇
  1967年   1547篇
排序方式: 共有10000条查询结果,搜索用时 906 毫秒
871.
A developmental anomaly, resulting from partial segmental aplasia of the Mullerian ducts, was present in a Clydesdale mare. She had complete double cervices and a divided uterine body. In this mare, bilateral pregnancies were destroyed in sequence by squeezing them per rectum 25 and 29 days after insemination.  相似文献   
872.
Ten out of eleven subcutaneous abscesses in cats harboured anaerobic bacteria. Seven of the ten abscesses contained a mixture of obligate anaerobes and facultative anaerobes or microaerophilic bacteria. All of the anaerobic isolates were sensitive to the antibiotic metronidazole, but were resistant to streptomycin. Three isolates from one abscess were resistant to penicillin and ampicillin. Clinical resolution of subcutaneous abscesses was poor when procaine penicillin was used alone as treatment.  相似文献   
873.
874.
An endoscopic survey was performed to assess arytenoid cartilage movement during quiet respiration in 48 Clydesdale horses. Physical characteristics which could influence the length of the recurrent laryngeal nerves were also recorded from these horses and the relationship of these characteristics to the presence of abnormal left arytenoid cartilage movements was assessed statistically. Some degree of abnormal arytenoid movement was observed in 50% of the animals over one year of age. No significant correlation between sex, age, estimated weight, height, or neck length could be found although affected animals were, on average, slightly taller, lighter and longer necked.  相似文献   
875.
In this review, "productive efficiency" in dairy cows is defined as the yield of milk obtained in ratio to the nutritional costs associated with maintenance, milk synthesis and loss of body condition during lactation. Improvements in efficiency could occur as a result of changes in digestion and nutrient absorption, maintenance requirement, utilization of metabolizable energy for production or nutrient partitioning. Digestibility can be greatly enhanced by appropriate dietary manipulation. Likewise, it may be possible to reduce maintenance requirements and improve the efficiency with which metabolizable energy is used for milk synthesis by manipulation of the pattern of nutrients presented to tissues. However, these factors apparently do not respond to selection for increased milk yield, and little variation is observed among cows. In contrast, individual cows differ substantially in feed intake and in the partitioning of nutrients among body tissues. Techniques associated with genetic engineering and the early prediction of genetic merit have the potential to improve productive efficiency by manipulation of these processes. However, changes in nutrient partitioning and feed intake during lactation are coordinated by a complex network of controls that accommodate the nutrient requirements of each tissue while maintaining homeostatic balance. Future improvements in productive efficiency will therefore depend on our ability to understand the manner in which these controls operate.  相似文献   
876.
1. Automatic weighing equipment was tested on a flock of 752 roaster chickens reared on litter to 10 weeks of age.

2. Mean body weights obtained automatically were lower than those obtained manually, mainly because of birds perching on the automatic weighing perch with part of their body in contact with the floor.

3. Birds observed on the weighing perch on one day of the week were 3–5 times more likely to use the perch again on the following 2 d than expected on the basis of random perch use by flock members. These birds were also more likely to be seen in the area immediately surrounding the perch than in similar areas elsewhere in the pen.  相似文献   

877.
878.
879.
Advances in immunoparasitology   总被引:1,自引:0,他引:1  
A selective review of the advances in immunoparasitology is presented. It is selective simply because it is not feasible to embrace the whole field of parasitology within the compass of a single review paper, for if it were attempted, it would suffer undue abbreviation. Emphasis is placed on the advances in helminthology and especially the gastro-intestinal parasites of ruminants, an obvious selection because of the interests of the author. Reviews are always somewhat retrospective in outlook; to write a review at the present time is especially foolhardy since developments in biology are such that totally new concepts can arise almost overnight, as it were. This is a particularly healthy state, and the discipline of parasitology is caught up in the application and interpretation of molecular biological considerations. "Parasitism" is a field of increasing importance and challenge.  相似文献   
880.
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