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   232371篇
  免费   12751篇
  国内免费   149篇
林业   9417篇
农学   7470篇
基础科学   1538篇
  28699篇
综合类   38156篇
农作物   8806篇
水产渔业   11796篇
畜牧兽医   120313篇
园艺   3091篇
植物保护   15985篇
  2019年   2101篇
  2018年   3249篇
  2017年   3561篇
  2016年   3352篇
  2015年   2878篇
  2014年   3561篇
  2013年   9184篇
  2012年   6486篇
  2011年   8001篇
  2010年   5288篇
  2009年   5277篇
  2008年   7888篇
  2007年   7555篇
  2006年   7221篇
  2005年   6617篇
  2004年   6519篇
  2003年   6555篇
  2002年   6187篇
  2001年   7446篇
  2000年   7213篇
  1999年   5849篇
  1998年   2380篇
  1997年   2417篇
  1996年   2219篇
  1995年   2680篇
  1994年   2401篇
  1993年   2365篇
  1992年   4777篇
  1991年   5000篇
  1990年   5066篇
  1989年   5080篇
  1988年   4654篇
  1987年   4718篇
  1986年   4731篇
  1985年   4555篇
  1984年   3800篇
  1983年   3378篇
  1982年   2343篇
  1981年   2165篇
  1979年   3372篇
  1978年   2765篇
  1977年   2389篇
  1976年   2225篇
  1975年   2361篇
  1974年   2983篇
  1973年   3050篇
  1972年   2942篇
  1971年   2589篇
  1970年   2574篇
  1969年   2410篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Meat regulations also involve game inspection. This publication deals with the regulations concerning furred game intended for slaughter and furred game hunted for food.  相似文献   
122.
Abstract –  The interaction between brown trout ( Salmo trutta ; fork length (FL) range 255–390 mm) and inanga ( Galaxias maculatus ; FL range 55–115 mm) was tested during summer through autumn in an artificial stream consisting of a single run-riffle-pool sequence with a natural food supply. Each experimental trial lasted for 15 days, and consisted of two brown trout and 50 inanga collected fresh from a nearby stream, with each species given prior residence in four replicate tests, totalling eight trials in all. In addition, two control trials (each 10 days), with 50 inanga in each, were run. Brown trout almost exclusively occupied the pool, whereas inanga occupied all habitat types, although in different proportions, when tested with and without brown trout. The proportion of inanga in the pool was appreciably lower in the experimental trials with brown trout than in the control trials with no brown trout; prior residence had no significant effect on inanga habitat use. Mortality of inanga attributable to predation by brown trout ranged from 0 to 40% with a mean of 14.5 ± 4.7%. The results suggest that habitat use and survival of inanga populations in small streams can be adversely affected by brown trout.  相似文献   
123.
Monoclonal antibodies against hog cholera and bovine viral diarrhoea viruses were assayed on organ tissue sections of experimentally infected animals. The animals had been infected simultaneously with both viruses. The antibodies were tested using an indirect immunofluorescence test and an indirect enzyme immunoassay with a biotin/streptavidin/peroxidase detection system. A polyclonal hyperimmune serum was used as a control in direct immunofluorescence tests. Both techniques based on monoclonal antibodies were more sensitive and more specific than the conventional test, the enzyme immunoassay being more sensitive than the immunofluorescence test. Small amounts of BVD viral antigen were demonstrable with monoclonal antibodies in most organ tissues.  相似文献   
124.
125.
Diagnosis, evaluation, and management of the various grades of rectal tears is discussed. Surgical techniques, which include direct closure, diverting colostomies, and placement of temporary rectal liners, are detailed. Also, rectal prolapses and various methods of repair are outlined.  相似文献   
126.
The responses of some clinical and microbiological parameters of periodontal disease (PD) in sheep were examined subsequent to transferring animals between PD-affected and PD-free farms. Previously healthy animals showed transient deterioration in some clinical, but not microbiological parameters, which suggests either that a different microbiota to the one studied may be more important in the initiation of the disease, or that sampling did not intercept periods of destructive disease activity in the early lesions. In sheep with established disease, those parameters indicative of periodontitis which included pocket depth and bleeding on probing as well as the proportions of black-pigmented Bacteroides species were not significantly altered by environmental changes. This observation suggests that once the disease is established on PD-affected farms, the hand, some clinical signs of the disease including lengthening and mobility of incisor teeth increased in sheep on the PD-affected farm relative to the PD-free farm. This suggests that the disease may have a complex aetiology.  相似文献   
127.
Infectious diseases remain one of the most important limitations to the successful propagation of aquatic animals. Most of the losses caused by pathogens in aquaculture could be prevented by health inspection, adequate environment and sound management practices. Effective control measures, mainly based upon 1) avoidance of pathogens 2) modification of the environment 3) improvement of host resistance 4) vaccination and 5) chemoprophylaxis are described.  相似文献   
128.
129.
The structure and ultrastructure of the adenohypophyseal pars distalis in kids of the Murciano-granadiana breed (18 males and 12 females), aged 2-3 months and with an average carcass weight of 8 kg has been studied. Techniques of staining (Tetrachrome Herlant's, and Cleveland-Wolfe) and histochemistry (PAS, PAS-OG and BA-PAS-OG) contrasted with immunolabelling (PAP) have been used. In addition an ultrastructural study has been made and nucleus and cytoplasm, secretory granules, mitochondria and lysosomes have been measured with a semiautomatic image analyzer (IBAS-1). TSH cells are found in sagittal section in the anterior area and in an antero-caudodorsal band, and transversally in the ventral and medial region; they are 6% and their average size is 14.15 microns. Ultrastructurally they are a single cellular type with spherical granules whose size is 195 nm in males and 149 in females; these granules are characterized by a clear halo and a variable electronic density. The rough endoplasmic reticulum is found as slightly enlarged vesicles with a homogeneous and moderately electro-dense content or in concentric stratifications.  相似文献   
130.
Two 7 day feeding trials were conducted with channel catfish swim-up fry to evaluate growth, feed conversion ratio, and body composition of fish fed one of the following feeds: salmon starter, catfish starter, or trout starter. Fish fed the salmon or trout starter feeds gained 50–75% more weight, converted feed more efficiently, and had higher body fat stores than fish fed the catfish starter feed. This may be related to the higher protein and energy content of these two feeds. It may be advantageous to feed salmonid starter feeds to hatchery reared catfish fry; however, it is not known whether or not the improved performance observed in the hatchery continues once the fish are stocked into nursery and grow out ponds.  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