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   1043篇
  免费   44篇
林业   168篇
农学   68篇
基础科学   4篇
  165篇
综合类   130篇
农作物   23篇
水产渔业   38篇
畜牧兽医   426篇
园艺   22篇
植物保护   43篇
  2021年   11篇
  2020年   9篇
  2019年   14篇
  2018年   18篇
  2017年   20篇
  2016年   16篇
  2015年   18篇
  2014年   24篇
  2013年   35篇
  2012年   48篇
  2011年   50篇
  2010年   18篇
  2009年   30篇
  2008年   46篇
  2007年   45篇
  2006年   34篇
  2005年   38篇
  2004年   45篇
  2003年   44篇
  2002年   33篇
  2001年   31篇
  2000年   31篇
  1999年   12篇
  1998年   11篇
  1997年   9篇
  1996年   11篇
  1994年   12篇
  1993年   9篇
  1992年   14篇
  1991年   15篇
  1990年   14篇
  1989年   21篇
  1988年   19篇
  1987年   12篇
  1985年   10篇
  1984年   9篇
  1983年   12篇
  1979年   9篇
  1978年   13篇
  1977年   14篇
  1975年   9篇
  1974年   10篇
  1973年   6篇
  1972年   10篇
  1971年   10篇
  1969年   9篇
  1967年   8篇
  1966年   16篇
  1933年   6篇
  1921年   9篇
排序方式: 共有1087条查询结果,搜索用时 15 毫秒
1.
The significance of sheep and goats in this country in connection with the zoonoses rabies, tick-borne encephalitis, contagious ecthyma, Q-fever, chlamydiosis, brucellosis, campylobacteriosis, echinococcosis and toxoplasmosis is discussed.  相似文献   
2.
This article reviews the capabilities of transrectal ultrasonography for determining the distribution of fluid and tissue within stallion accessory sex glands. Emphasis is placed on describing the normal ultrasonographic appearance of the accessory sex glands, excurrent ducts, and pelvic urethra of stallions during rest, after teasing, and after ejaculation and using this information to detect glandular abnormalities.  相似文献   
3.
The effectiveness of the morantel sustained release trilaminate (MSRT) in controlling gastrointestinal nematodes through a grazing season was evaluated using 60 yearling beef stocker calves randomly divided into 2 groups of 30 animals each. In April 1985, the calves comprising the treatment group each received an MSRT designed to release morantel tartrate continuously for 90 days while those of the control group remained unmedicated. All animals were weighed and samples of rectal feces were taken at 14-day intervals, beginning on Day 0, until trial termination (Day 168). At trial termination, 10 control and 10 treated calves were necropsied for recovery of gastrointestinal nematodes. Three sets of parasite-na?ve tracer calves were utilized to evaluate the initial, interim and final levels of pasture contamination by nematode larvae. Overall, the use of the MSRT resulted in a 75.5% reduction (P less than 0.001) in output of nematode eggs from the principals, an 81.8% reduction (P less than 0.001) in numbers of gastrointestinal nematodes in principals (at trial termination), and a 96.9% reduction (P less than 0.05) of pasture larval nematode contamination (as indirectly indicated by parasite burdens in tracer calves). The mean weight advantage of treated calves was 16.6 kg per head (P less than 0.001).  相似文献   
4.
5.
6.
7.
8.
In a university beef herd of 304 cattle in which six died of lymphosarcoma between 1980 and 1984, 77% of the Angus and 26% of the Charolais cattle were determined to be infected with bovine leukemia virus (BLV). Changes in iatrogenic procedures were initiated as early control measures. In vitro viral expression (VE) was used as a criterion to identify cattle for subsequent segregation or culling. This involved determinations of percentages of BLV-associated lymphocyte profiles among thin-sectioned Ficoll-Paque-isolated blood lymphocytes that were processed into plastic after culture for 48 h. Cattle retained until completion of nutritional studies or as breeding stock were separated into two groups. The BLV-seronegative cattle, BLV-seropositive cattle with 0% VE, and BLV-seropositive cattle with 1% to 4% VE were placed in group 1. Seropositive cattle with greater than or equal to 5% VE were placed in group 2. In 1985, evaluation of in vitro VE in 108 mature BLV-seropositive cattle retained for breeding revealed 36 (33%) had no observable VE. In 1986, 58 of 108 cattle were available to be reexamined, and 21 (36%) had 0% VE in both years. The VE expression values for individual cattle were generally comparable over the 2-year period. Of 48 initial seronegative breeding stock housed in group 1 with BLV-seropositive cattle with low or no VE, 21 (44%) seroconverted during 1985 to 1986. A positive correlation of 0.585 was found between VE and age-related absolute lymphocyte number.  相似文献   
9.
We analyzed urine samples from 191 cats for bacteriuria with an automated urine sediment analyzer (Idexx SediVue Dx), combined with image review by an observer, and compared to bacteriologic culture results. Sixty-nine samples were unambiguously assigned to be free of bacteria by the instrument and the observer, and no bacterial growth was detected. Twenty-seven samples were unambiguously assigned to have bacteriuria; 24 of these 27 samples were culture-positive. For these samples, bacteriuria was predicted with a sensitivity of 100% and a specificity of 96%. A clear assignment was not possible for 95 samples, 81 of which were culture-negative. Specificity dropped to 45% when all samples were considered. Using the automated leukocyte count to predict bacteriuria, sensitivity was 82% and specificity was 75%. Automated sediment analysis is faster and less observer-dependent than sediment analysis under a microscope, but accurate detection of bacteriuria remains difficult in a large proportion of samples. Bacteriuria was significantly associated with leukocyte count; the leukocyte count was >5/high power field in 82% of culture-positive samples.  相似文献   
10.
The objectives of the experiment were (1) to determine whether MAC-T cells would accurately mimic the previously observed proliferative responses of primary mammary epithelial cells (MEC) to mammary tissue extracts from high and low-fed heifers and (2) to determine whether mammary tissue extracts from ovariectomized (OVX) heifers would have lower mitogenic activity than intact controls. Addition of mammary tissue extracts to cell culture media of MAC-T cells plated on plastic or collagen-coated plastic to a range of concentrations between 1 and 8% resulted in dose-dependent increases in cell proliferation. Furthermore, mammary tissue extracts from low-fed prepubertal heifers aged 9 months, stimulated significantly more proliferation of MAC-T cells, as measured by 3H-thymidine incorporation into DNA than mammary tissue extracts from high-fed heifers (40.6 cpm x 10(3) per well versus 21.9+/-1.8 cpm x 10(3) per well). These observations suggested that MAC-T cells would be a suitable alternative to primary MECs for measuring the mitogenic activity of mammary tissue extracts. Conversely, no difference was observed in the mitogenic activity of mammary tissue extracts from OVX or control heifers. Possibly, MAC-T cells provide a good model for nutrition- but not ovarian-induced changes in mammary growth. Alternatively, that reduction of in vivo mammary development following OVX did not result in reduced mitogenic activity of the mammary tissue extracts emphasizes that heifer mammary development is the result of complex interactions between local growth factors and systemic hormones.  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