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   65531篇
  免费   3818篇
  国内免费   78篇
林业   2715篇
农学   2212篇
基础科学   348篇
  7432篇
综合类   10777篇
农作物   2321篇
水产渔业   3111篇
畜牧兽医   35453篇
园艺   782篇
植物保护   4276篇
  2018年   1053篇
  2017年   1084篇
  2016年   950篇
  2015年   935篇
  2014年   997篇
  2013年   2849篇
  2012年   1886篇
  2011年   2277篇
  2010年   1471篇
  2009年   1419篇
  2008年   2121篇
  2007年   2050篇
  2006年   1908篇
  2005年   1741篇
  2004年   1656篇
  2003年   1703篇
  2002年   1579篇
  2001年   2007篇
  2000年   1928篇
  1999年   1604篇
  1998年   680篇
  1997年   671篇
  1996年   593篇
  1995年   696篇
  1994年   629篇
  1993年   618篇
  1992年   1299篇
  1991年   1454篇
  1990年   1337篇
  1989年   1345篇
  1988年   1232篇
  1987年   1200篇
  1986年   1254篇
  1985年   1246篇
  1984年   1016篇
  1983年   940篇
  1982年   615篇
  1979年   955篇
  1978年   746篇
  1977年   738篇
  1976年   759篇
  1975年   757篇
  1974年   922篇
  1973年   904篇
  1972年   854篇
  1971年   771篇
  1970年   801篇
  1969年   769篇
  1968年   682篇
  1967年   689篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Caprine β-mannosidosis, a fatal inherited deficiency of the lysosomal enzyme β-mannosidase, was diagnosed in neonatal female Nubian crossbred twin kids from a small herd near Guelph, Ontario. The kids had been tetraplegic since birth, with whole body tremors, abnormal nystagmus and an intention tremor of the head.  相似文献   
92.
A one month old Quarterhorse colt was presented after a week history of bilateral nasal discharge and respiratory difficulty. The cervical esophagus was greatly dilated, tortuous and filled with diluted milk. A nasogastric tube could not be passed beyond the base of the heart. An aspiration pneumonia was found at postmortem examination and the esophageal segment from the pharynx to the base of the heart was dilated, thin-walled, had degenerative muscular changes, and a reduction in size and number of ganglion cells of the myenteric plexus. Muscular hypertrophy of the terminal esophagus had reduced its lumen size. Some similarities and disparities of this condition to achalasia of man and megaesophagus of dogs are discussed.  相似文献   
93.
Serum alkaline phosphatase activity was found to be increased in 32.6% of equine samples analyzed at the Ontario Veterinary College over an 18 month period. An attempt was made using sensitivity to L-phenylalanine and heat to identify the origin of increased serum alkaline phosphatase isoenzymes present in 44 clinical cases. No difference in sensitivity to either procedure was observed for serum alkaline phosphatase from groups of foals and horses representing different clinical problems. Alkaline phosphatase of osseous tissue origin appeared to be the major source of activity for each group of animals reported.  相似文献   
94.
95.
Kinematics of the equine thoracolumbar spine   总被引:2,自引:0,他引:2  
At least three types of movement take place in the joint complexes of the equine thoracolumbar spine: dorsoventral flexion and extension, axial rotation and lateral bending. Using the standard right-handed Cartesian coordinate system, these movements may be defined as rotation about the x, y and z axes respectively. Except in cases of intervertebral fusion, all three types of movement occur in each joint complex of the equine back. The greatest amount of dorsoventral movement takes place at the lumbosacral and the first thoracic intervertebral joints. The greatest amount of axial rotation and lateral bending was measured in the mid-thoracolumbar spine at the level of the 11th or 12th thoracic intervertebral joints. The caudal thoracic and the lumbar spine is the least mobile region of the equine back. In the mid-thoracic spine, lateral bending was always accompanied by a "coupled" axial rotation. The presence of the rib cage stabilised the cranial thoracic vertebrae against axial rotation.  相似文献   
96.
A damaging virus isolated in the Netherlands from lettuce was studied and compared with a virus isolated from dandelion orginating from Czechoslovakia. It was found to biologically resemble dandelion yellow mosaic virus incompletely described from dandelion and lettuce in Great Britain (Kassanis, 1944, 1947) and from dandelion in Germany (Hein, 1963). Mechanical transmission was greatly improved by buffer solution and transmission byMyzus persicae seemed to be in the non-persistent manner. Longevity in vitro of the virus hardly exceeded one day. Thermal inactivation was between 60 and 65 °C and the dilution end-point was between 10 000 and 100 000. It was still infectious in leaf material dried and stored over CaCl2 at 4 °C for 6 1/2 years. The virus was isolated and purified with difficulty and was found to consist of one type of spherical particle of ca 30 nm diameter, with a sedimentation coefficient of 159 S, a buoyant density of 1.42 g.cm?3 and an A260/A280 ratio of 1.67. An antiserum was prepared with a titre of 256 in the agar double-diffusion test. The virus could be identified in crude extracts from lettuce andChenopodium amaranticolor by enzyme-linked immunosorbent assay (ELISA), but not by agar double diffusion. It could only be visualized in crude sap in the electron microscope after trapping of virus particles on antiserum-coated grids. The virus cannot yet be assigned to any known virus group. It is of potential economic importance to lettuce because of its occurrence in widely differing regions in Europe, its aggressiveness and virulence on 22 out of 23 lettuce cultivars tested (and on endive) and its pathogenicity toLactuca genotypes which are resistant to lettuce mosaic virus and other important pathogens of lettuce. ‘Laibacher Eis’ was the only cultivar showing some tolerance.  相似文献   
97.
98.
99.
Summary. When paraquat was added to four different soils, nitrification was not appreciably affected but ammonification of soil organic-matter nitrogen was slightly retarded. Carbon dioxide evolution as well as oxygen consumption was used as an index of metabolic activity of soil micro-organisms and paraquat had a stimulatory effect at higher concentrations. Oxidation of added sulphur was slightly depressed. Paraquat decreased both the total mould and bacterial populations in Chehalis silt loam. After 30 days incubation the percentages of Streptomyces and Penicillia were markedly increased by most treatments but were little affected in Chehalis silt clay and Woodburn soils. Except for the temporary suppression of nitrification, paraquat had no significant influence on general microbial activities of importance to soil fertility. Some bimodal effects or toxicity inversions were observed with intermediate concentrations. Effet du paraquat sur les activités microbiennes dans les sols  相似文献   
100.
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