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   1072篇
  免费   83篇
林业   43篇
农学   33篇
基础科学   8篇
  103篇
综合类   196篇
农作物   32篇
水产渔业   53篇
畜牧兽医   633篇
园艺   20篇
植物保护   34篇
  2021年   10篇
  2020年   9篇
  2019年   16篇
  2018年   13篇
  2017年   18篇
  2015年   12篇
  2014年   25篇
  2013年   38篇
  2012年   39篇
  2011年   49篇
  2010年   22篇
  2009年   21篇
  2008年   51篇
  2007年   44篇
  2006年   43篇
  2005年   31篇
  2004年   43篇
  2003年   40篇
  2002年   22篇
  2001年   30篇
  2000年   33篇
  1999年   26篇
  1997年   10篇
  1996年   10篇
  1995年   13篇
  1994年   9篇
  1993年   11篇
  1992年   24篇
  1991年   30篇
  1990年   21篇
  1989年   18篇
  1988年   23篇
  1987年   12篇
  1986年   17篇
  1985年   23篇
  1984年   15篇
  1983年   11篇
  1981年   9篇
  1979年   19篇
  1978年   9篇
  1977年   15篇
  1974年   9篇
  1972年   23篇
  1971年   14篇
  1970年   11篇
  1969年   8篇
  1968年   8篇
  1967年   10篇
  1966年   11篇
  1965年   10篇
排序方式: 共有1155条查询结果,搜索用时 0 毫秒
31.
32.
33.
34.
In the past, it has been reported that neonatal diets made from unheated cow's milk were superior to those made from heated cow's milk. It was observed that piglets were equally protected from rotaviral diarrhea when they were fed diets made from either unheated milk that came from a cow immunized against porcine rotavirus or from a cow that was not immunized. Because of this observation, we examined four pools of "normal" cows' colostrum and 58 samples of "normal" cow's milk for the presence of antibody to rotavirus. All pools of colostrum, collected in four different years, had immunofluorescent antibody titers of 1:100 to rotavirus. Seventy-two percent of the samples of milk were also positive--titer no higher than 1:10. Antibodies to rotavirus were found in cow's milk at a creamery prior to but not after pasteurization. Rotaviral antibodies were detected in one out of eight brands of milk bought at the market--perhaps indicating inadequate pasteurization for this brand. These results support the proposition that, at least in part, unheated milk is superior to heated milk because unheated milk contains antibody to an ubiquitous enteropathogen like rotavirus.  相似文献   
35.
OBJECTIVES: To determine whether telomerase activity was present in lymph nodes, buffy coat, and serum samples from dogs with malignant lymphoma (ML) and in liver, lymph node, buffy coat, and serum samples from clinically normal dogs SAMPLE POPULATION: Tissue specimens and blood samples were obtained from 11 clinically normal adult dogs (age range, 1 to 4 years) and 14 client-owned dogs with ML. PROCEDURE: The telomere repeat amplification protocol assay was used to quantify telomerase activity in the tissues from clinically normal dogs and dogs with ML. RESULTS: Of 11 clinically normal dogs, 8 had lymph node samples, 5 had liver samples, and 1 had buffy coat samples with detectable telomerase activity. None of the serum samples from the clinically normal dogs had detectable telomerase activity. Of 14 dogs with ML, 9 had lymph node samples, 3 had buffy coat samples, and 1 had serum samples with measurable telomerase activity. CONCLUSIONS AND CLINICAL RELEVANCE: Telomerase activity was not specific to tumor cells and overlapped with that found in cells from clinically normal dogs. Telomerase activity in neoplastic lymph nodes was not substantially different from that found in lymph nodes from clinically normal dogs. The determination of telomerase activity cannot be used as a sole diagnostic test for cancer. Therapeutic modalities directed toward the telomerase enzyme may not be feasible in dogs, because somatic tissues from clinically normal dogs possess variable amounts of telomerase activity.  相似文献   
36.
Ultrasound has many industrial applications but it was first introduced as a medical diagnostic aid in the 1940s with its first veterinary application, the detection of ovine pregnancy, being reported in 1966. Since then, improvements in equipment quality combined with an increased awareness of the benefits of ultrasound as an imaging technique have led to its widespread use in the veterinary field. Recent advances in computer technology have significantly influenced equipment design and the miniaturization of transducers allows intra-operative and intra-vascular applications. Software advances have improved the ability to manipulate and process data, leading to an increased amount of information being obtained from each examination and the advent of 'remote diagnosis'. Ultrasound guided interventional techniques can now be used for diagnostic or therapeutic purposes. Many of these developments have been introduced by equipment manufacturers but have found specific applications in the veterinary field. Ultrasound is currently employed in a very diverse range of situations, not just as a diagnostic tool in the routine clinical workup of a range of species, but also for disease screening, conservation projects, commercial services, herd management and clinical research.  相似文献   
37.
A method for preparation of chromosomes from bovine zygotes and blastocysts   总被引:2,自引:0,他引:2  
A simple technique for making chromosome preparations from zygotes and early blastocysts is described. The morphological features of blastocysts and total number of cells greatly influence the quality of the preparation.  相似文献   
38.
1. The performance of six commercial stocks of laying hens fed on a diet composed of home‐produced foodstuffs, not usually used for human consumption, was compared with that of birds fed on a conventional diet.

2. The experimental diet was calculated to be low in energy and methionine and high in fibre by conventional standards. Birds ate up to 12% more of this diet, but the calculated intakes of energy and methionine were less than those of the corresponding controls.

3. White stocks fed on the experimental diet produced seven eggs less per bird than controls while the production of brown stocks was essentially unaffected.

4. The gross efficiency of energy utilisation for egg production was better with the experimental diet.  相似文献   

39.
40.
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