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   139933篇
  免费   8097篇
  国内免费   800篇
林业   5880篇
农学   4468篇
基础科学   1053篇
  16785篇
综合类   26165篇
农作物   5334篇
水产渔业   6518篇
畜牧兽医   71844篇
园艺   1832篇
植物保护   8951篇
  2019年   1385篇
  2018年   2040篇
  2017年   2324篇
  2016年   2094篇
  2015年   1944篇
  2014年   2266篇
  2013年   5110篇
  2012年   4249篇
  2011年   5124篇
  2010年   3443篇
  2009年   3338篇
  2008年   4827篇
  2007年   4626篇
  2006年   4200篇
  2005年   4015篇
  2004年   3688篇
  2003年   3862篇
  2002年   3603篇
  2001年   4112篇
  2000年   4133篇
  1999年   3232篇
  1998年   1380篇
  1997年   1356篇
  1995年   1447篇
  1994年   1284篇
  1993年   1266篇
  1992年   2657篇
  1991年   2970篇
  1990年   2886篇
  1989年   2839篇
  1988年   2666篇
  1987年   2672篇
  1986年   2772篇
  1985年   2535篇
  1984年   2214篇
  1983年   1880篇
  1982年   1324篇
  1979年   2005篇
  1978年   1565篇
  1977年   1401篇
  1976年   1383篇
  1975年   1437篇
  1974年   1854篇
  1973年   1859篇
  1972年   1789篇
  1971年   1669篇
  1970年   1634篇
  1969年   1553篇
  1968年   1274篇
  1967年   1412篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
821.
822.
The radiological changes observed in 100 dogs with confirmed intra-nasal disease are reviewed with particular reference to the differential features of neoplasia, destructive rhinitis and proliferative inflammatory conditions. The contribution of radiographic examination to the diagnosis, treatment and prognosis of these disorders is discussed.  相似文献   
823.
A RETROSPECTIVE STUDY OF OSTEOMYELITIS IN DOGS AND CATS   总被引:1,自引:0,他引:1  
Thirty-nine cases of osteomyelitis in dogs and cats were recorded at the Sydney University Veterinary Hospital and Clinic over a three and a half year period. In 36 cases osteomyelitis was established prior to admission. Three cases of osteomyelitis became established from a total of 502 orthopaedic surgery cases seen at the hospital in this period. In the dog the most common source of infection was open reduction of closed fractures, while in the cat, the most common source of infection was an extension from soft tissue infection. More males than females were affected. Ten cases of osteomyelitis were treated successfully, twelve cases required amputation, while euthanasia was performed on thirteen other cases. The problems and principles of treatment of active osteomyelitis as reflected in the treatment of this series of cases have been described.  相似文献   
824.
825.
Postnatal growth, steroid hormone profiles and response to steroid hormone treatment were studied in 18 freemartins and one normal female born co-twin with a bull. They were either treated postnatally with testosterone or estrone at one week of age, or left untreated until 50 weeks of age when they received silastic implants calculated to release either 12.9 microgram of estrone or 2.6 microgram of estradiol per day per kg of body weight. Later a dihydrotestosterone-treated group was added. Reproductive development was studied by palpation per rectum and by examination when animals were slaughtered at 79 weeks of age. Treated animals grew slightly faster than untreated animals. Testosterone in untreated freemartins averaged 76 and 87 pg/ml of blood plasma during weeks 1 to 48 and 52 to 56. Corresponding values for those animals with small testosterone implants (weeks 1 to 48) and with larger implants (weeks 52 to 56) were 130 and 272 pg/ml. Estrone and estradiol values appeared to fluctuate between 10 and 50 pg/ml but values are uncertain because they were below the sensitivity of the assay then available. Thus, circulating steroid hormone concentrations were similar to those reported for castrates. Testosterone stimulated clitoral development prenatally and postnatally. None of the treatments influenced vaginal depth, which averaged 4.0, 9.0 and 10.9 cm at 1, 24 and 52 weeks of age. Vaginal depth at birth was not a reliable indicator of freemartinism. Androgen may have inhibited udder development, whereas estrogen appeared to be stimulatory. The reproductive organs of the freemartin were characterized by differences in underdevelopment and the general presence of seminal vesicles. The latter structures, plus clitoral development at birth in 3 animals and postnatal response of the clitoris to testosterone is interpreted to indicate that the presence of androgens is one factor in abnormal development. Otherwise, gross morphology of the reproductive tract was not related to hormone treatment, postnatal gonadal histology, endocrinology or lymphocyte chromosomal karyotypes.  相似文献   
826.
827.
Up to now, prioritization of animals for conservation has been mainly based on pedigree information; however, genomic information may improve prioritization. In this study, we used two Holstein populations to investigate the consequences for genetic diversity when animals are prioritized with optimal contributions based on pedigree or genomic data and whether consequences are different at the chromosomal level. Selection with genomic kinships resulted in a higher conserved diversity, but differences were small. Largest differences were found when few animals were prioritized and when pedigree errors were present. We found more differences at the chromosomal level, where selection based on genomic kinships resulted in a higher conserved diversity for most chromosomes, but for some chromosomes, pedigree-based selection resulted in a higher conserved diversity. To optimize conservation strategies, genomic information can help to improve the selection of animals for conservation in those situations where pedigree information is unreliable or absent or when we want to conserve diversity at specific genome regions.  相似文献   
828.
829.
The effect of ciclosporin A (CsA) on glucose homeostasis was investigated in 16 dogs with atopic dermatitis by determining plasma glucose, serum fructosamine and insulin concentrations, and serial insulin and glucose concentrations following a glucagon stimulation test, before and 6 weeks after CsA therapy at 5 mg/kg once daily. All dogs completed the study. Following CsA treatment, the median serum fructosamine concentrations were significantly higher (pretreatment 227.5 μmol/L; post-treatment 246.5 μmol/L; P = 0.001; reference range 162-310 μmol/L). Based on analyses of the areas under concentration-time curves (AUC) pre- and post-CsA treatment, plasma glucose concentrations were significantly higher (AUC without baseline correction 31.0 mmol/L/min greater; P = 0.021) and serum insulin concentrations were significantly lower (AUC without baseline correction 217.1 μIU/mL/min lower; P = 0.044) following CsA treatment. Peak glucose concentrations after glucagon stimulation test were significantly higher following CsA treatment (10.75 versus 12.05 mmol/L; P = 0.021), but there was no significant difference in peak serum insulin (52.0 versus 35.0 μIU/mL; P = 0.052). There was a negative correlation between baseline uncorrected insulin AUC and trough serum log CsA concentrations (r = -0.70, P = 0.005). The administration of CsA to dogs with atopic dermatitis leads to disturbances in glucose homeostasis. The clinical significance of this is unclear, but it should be taken into account when considering CsA treatment in dogs that already have such impairments.  相似文献   
830.
We describe the movement of cattle throughout Argentina in 2005. Details of farm-to-farm and farm-to-slaughter movements of cattle were obtained from the Sanitary Management System database (Sistema de Gestión Sanitaria, SGS), maintained by the National Service for Agrifood Health and Quality (SENASA). Movements were described at the regional and district level in terms of frequency, the number of stock transported, the district of origin and destination and Euclidean distance traveled. Social network analysis was used to characterize the connections made between regions and districts as a result of cattle movement transactions, and to show how these characteristics might influence disease spread. Throughout 2005 a total of 1.3 million movement events involving 32 million head of cattle (equivalent to approximately 57% of the national herd) were recorded in the SGS database. The greatest number of farm-to-farm movements occurred from April to June whereas numbers of farm-to-slaughter movement events were relatively constant throughout the year. Throughout 2005 there was a 1.1-1.6-fold increase in the number of farm-to-farm movements of cattle during April-June, compared with other times of the year. District in-degree and out-degree scores varied by season, with higher maximum scores during the autumn and winter compared with summer and spring. Districts with high in-degree scores were concentrated in the Finishing region of the country whereas districts with high out-degree scores were concentrated not only in the Finishing region but also in Mesopotamia, eastern Border and southern Central regions. Although movements of cattle from the Border region tended not to be mediated via markets, the small number of districts in this area with relatively high out-degree scores is a cause for concern as they have the potential to distribute infectious disease widely, in the event of an incursion.  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