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   144974篇
  免费   7701篇
  国内免费   102篇
林业   6116篇
农学   4223篇
基础科学   884篇
  15852篇
综合类   27920篇
农作物   5563篇
水产渔业   6617篇
畜牧兽医   75146篇
园艺   1652篇
植物保护   8804篇
  2018年   1724篇
  2017年   1888篇
  2016年   1762篇
  2015年   1575篇
  2014年   1910篇
  2013年   5161篇
  2012年   3390篇
  2011年   4311篇
  2010年   2755篇
  2009年   2774篇
  2008年   4182篇
  2007年   4052篇
  2006年   3907篇
  2005年   3570篇
  2004年   3448篇
  2003年   3495篇
  2002年   3313篇
  2001年   4394篇
  2000年   4510篇
  1999年   3571篇
  1998年   1366篇
  1997年   1395篇
  1995年   1651篇
  1994年   1410篇
  1993年   1382篇
  1992年   3064篇
  1991年   3235篇
  1990年   3201篇
  1989年   3212篇
  1988年   3000篇
  1987年   3042篇
  1986年   3105篇
  1985年   3021篇
  1984年   2451篇
  1983年   2181篇
  1982年   1484篇
  1979年   2359篇
  1978年   1884篇
  1977年   1656篇
  1976年   1586篇
  1975年   1727篇
  1974年   2228篇
  1973年   2295篇
  1972年   2244篇
  1971年   2093篇
  1970年   1996篇
  1969年   1786篇
  1968年   1546篇
  1967年   1609篇
  1966年   1441篇
排序方式: 共有10000条查询结果,搜索用时 921 毫秒
951.
952.
The pathology of carcinoma of the small intestine in six adult cattle is described. The lesions were similar to those of carcinoma of the small intestine of sheep although a slightly less fibrous stroma and a greater tendency to metastasise was observed. Initial findings suggest the disease resembles small-intestinal carcinoma of sheep and cola-rectal carcinomas of man in having a higher prevalence in New Zealand than most other countries. This highlights the need to investigate common environmental factors which may be responsible for the induction and promotion of these tumours in both grazing ruminants and man.  相似文献   
953.
A study was made of various aspects of 53 naturally occurring cases of foot abscess in sheep in New Zealand. Radiographic techniques were used to follow the progress of the lesion and from this it was concluded that foot abscess could be defined as an infection of the distal interphalangeal joint. The term foot abscess was considered preferable to the term "infective bulbar necrosis". The attack rate of foot abscess was reported to be higher for rams than for ewes and the condition was less prevalent during summer. Once infection was established in the distal interphalangeal joint a relatively uniform and thus predictable series of events took place that inevitably resulted in some permanent damage and deformity to the digit. If rupture of the axial collateral ligaments occurred, the joint became unstable and the degree of permanent deformity was greater. Treatment with antibiotics did not appear to markedly affect the progress of the lesion or the outcome, once infection had become established in the joint. Although the prognosis for complete recovery was poor, in most cases the foot healed sufficiently after a period of about two months to allow the animal to walk normally.  相似文献   
954.
955.
Antiserum directed against equine intestinal Alkaline Phosphatase (ALP) was produced in rabbits and used to develop a sensitive and quantitative assay for the detection of intestinal ALP in equine serum. This assay was then used to measure the half-life of intravenously injected intestinal ALP and to determine if the intestinal ALP was present in normal horse sera, sera from horses presented for lesions not involving the gastrointestinal tract and sera from horses presented with lesions involving the gastrointestinal tract. The results suggest that intestinal ALP is not likely to appear in equine serum even when gastrointestinal disease is present and, therefore, appears to be of no diagnostic value.  相似文献   
956.
Equine herpesvirus abortion in Australia 1977 to 1982   总被引:1,自引:0,他引:1  
Until 1977 no case of abortion caused by equine herpesvirus 1 (EHV1) had been recorded in Australia although the virus, called equine rhinopneumonitis virus, had been known to have been present at least since 1962. Outbreaks of EHV1 abortion occurred in New South Wales in 1977 and in 1981. Sporadic cases of EHV1 abortion had been confirmed in some parts of Australia each year since 1975. It was concluded that an abortigenic subtype of EHV1 had been introduced to Australia in 1977 and that the previously endemic respiratory subtype occasionally caused abortion. Virus isolation in a variety of cell cultures and histopathological examination of tissue were shown to be satisfactory methods of diagnosis of EHV1 abortion. Lung proved to be the specimen of choice. Slight serological differences between "abortigenic" and "respiratory" subtypes of EHV1 were found in cross neutralisation tests. A serological survey of 219 Sydney horses of various ages revealed that most yearlings had already acquired neutralising antibody to both subtypes.  相似文献   
957.
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   
958.
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   
959.
960.
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