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   92999篇
  免费   4362篇
  国内免费   36篇
林业   6838篇
农学   3720篇
基础科学   616篇
  11995篇
综合类   13538篇
农作物   5068篇
水产渔业   5573篇
畜牧兽医   41126篇
园艺   1929篇
植物保护   6994篇
  2018年   3657篇
  2017年   3702篇
  2016年   2232篇
  2015年   1008篇
  2014年   1181篇
  2013年   2931篇
  2012年   2932篇
  2011年   4620篇
  2010年   3711篇
  2009年   2865篇
  2008年   3834篇
  2007年   3990篇
  2006年   2290篇
  2005年   2297篇
  2004年   2175篇
  2003年   2376篇
  2002年   2068篇
  2001年   2297篇
  2000年   2285篇
  1999年   1803篇
  1998年   737篇
  1997年   793篇
  1996年   713篇
  1995年   881篇
  1994年   759篇
  1993年   760篇
  1992年   1519篇
  1991年   1667篇
  1990年   1630篇
  1989年   1637篇
  1988年   1523篇
  1987年   1485篇
  1986年   1561篇
  1985年   1479篇
  1984年   1285篇
  1983年   1080篇
  1982年   756篇
  1979年   1188篇
  1978年   896篇
  1977年   858篇
  1976年   812篇
  1975年   837篇
  1974年   1050篇
  1973年   1087篇
  1972年   1028篇
  1971年   964篇
  1970年   943篇
  1969年   910篇
  1968年   768篇
  1967年   849篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Feather abnormalities and skin lesions caused by a papovavirus infection in budgerigars are described. Diseased one to 15 day old birds displayed a lack of nestling down feathers and filoplumes on the head and neck. Survivors older than 15 days exhibited retarded growth and temporary absence of feathers variable from bird to bird. Several birds between 15 and 25 days of age had flight feathers with total absence or marked sparseness of the vanes. After 25 days, feathers began to grow, although the tail and/or some flight feathers of some of the birds remained underdeveloped or absent for several weeks. Several of these affected birds were unable to fly and are called “runners”

Microscopic lesions in the feather follicles of the affected birds less than 15 days of age, were characterized by focal, multifocal or diffuse ballooning degeneration in the lateral and axial plate cells of the barb ridges with the presence of large basophilic or amphophilic intranuclear inclusions in the same cells. Focal areas of ballooning degeneration with intranuclear inclusions were also found in the epidermis. Clinical observations made on these birds are compared with those reported in the literature for French molt.

  相似文献   
102.
  1. An enzymatic ‘reaction rate’ micro-method for the rapid routine estimation of D-B-hydroxybutyrate (D-B-HOB) in ruminant plasma, using an I.L. Multistat III centrifugal analyzer, is described.
  2. Reaction conditions were optimized to give a linear response for plasma D-B-HOB concentrations between 100 and 2500 μmoles per litre, at 30°C and pH 9.0.
  3. For the standardized method the within-run and between-run coefficients of variation for deproteinised ovine plasma were consistently less than 3.5%.
  4. There was good agreement between plasma concentrations obtained by the present method and both original U.V. end-point technique (r=0.927b=0.950) and a colorimetric end-point procedure (r=0.937. b=0.879).
  5. Utreated ovine and bovine plasma consistently exhibited high ‘blank’ activity and this was directly correlated with plasma lactate dehydrogenase (LDH) activity in both species (r=0.971; p<0.001 and r=0.949; p<0.001 respectively). The distribution of LDH activity in man was similar to sheep but, contrastingly, non-specific interference was extremely low in human plasma and unrelated to LDH. Horse, chicken and rat had negligible ‘blank” activity and comparatively low LDH levels. In both cattle and sheep non-specific interference was abolished by perchloric acid precipitation. In the sheep subtraction of ‘blank’ activity gave D-H-HOB concentrations for untreated plasma comparable to those in deproteinised samples. However, in the bovine, D-B-HOB levels remained significantly (t=6.44; p<0.001) higher even after ‘blank’ correlation. In contrast to man and other non-ruminants, perchloric acid precipitation is essential in ruminants to avoid false overestimation of plasma D-B-HOB levels.
  6. Plasma with EDTA as anticoagulant and serum gave concentrations of D-B-HOB approximately 60% lower, than samples containing heparin or oxalate/fluoride. However, heparin was associated with much higher (up to 50%) non-specific NAD rduction than oxalate/fluoride.
  7. High levels of acetoacetate (400–1000 μmoles per litre) reduced the recovery of D-B-HOB from ovine plasma by less than 10%. This effect was negated by the inclusion of hydrazine hydrates in the reaction mixture. Perchlorate ion concentrations above 25 μmoles per litre per test dramatically inhibited the assay in ovine plasma, and therefore precipitation conditions must be carefully controlled.
  8. Plasma with oxalate/fluoride as anticoagulant showed the greatest stability in storage; 24 hours at room temperature, one week at +4°C and at least one month at ?20°C.
  相似文献   
103.
Cysts found in the liver of a horse which had never been out of New Zealand were used to infect two dogs which were slaughtered 35 days after infection. Large numbers of Echinococcus granulosus were recovered. These cestodes were compared with mature dog-sheep cestodes, using light and scanning electron microscopy and identified as the dog-horse strain of E.granulosus.  相似文献   
104.
105.
106.
Infection with Fascioloides magna, the large American liver fluke, was diagnosed in two moose (Alces alces) and six wapiti (Cervus elaphus) from central Saskatchewan. This is believed to be the first record of the parasite in the province. Fecal samples collected from wild wapiti at five sites in the commercial forest zone in Saskatchewan contained eggs believed to be those of F. magna. Trematode eggs were not found in feces from five captive herds of wapiti in the province, nor in samples from wild wapiti in Moose Mountain Provincial Park. Operculate eggs were found in feces of wild wapiti from Cypress Hills, but these were believed to be from trematodes other than F. magna. The distribution and significance of F. magna in Canada, based partially on responses to a mail questionnaire, are reviewed.  相似文献   
107.
Two cases of noninfectious, nonerosive arthritis are presented. The diagnostic features, clinical course and treatment are reviewed. Potential etiologies are discussed in the light of relatively little current material on this subject in the veterinary literature.  相似文献   
108.
A developmental anomaly, resulting from partial segmental aplasia of the Mullerian ducts, was present in a Clydesdale mare. She had complete double cervices and a divided uterine body. In this mare, bilateral pregnancies were destroyed in sequence by squeezing them per rectum 25 and 29 days after insemination.  相似文献   
109.
Ten out of eleven subcutaneous abscesses in cats harboured anaerobic bacteria. Seven of the ten abscesses contained a mixture of obligate anaerobes and facultative anaerobes or microaerophilic bacteria. All of the anaerobic isolates were sensitive to the antibiotic metronidazole, but were resistant to streptomycin. Three isolates from one abscess were resistant to penicillin and ampicillin. Clinical resolution of subcutaneous abscesses was poor when procaine penicillin was used alone as treatment.  相似文献   
110.
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