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   31433篇
  免费   1273篇
  国内免费   184篇
林业   1272篇
农学   1130篇
基础科学   265篇
  4493篇
综合类   4601篇
农作物   1204篇
水产渔业   1444篇
畜牧兽医   15962篇
园艺   379篇
植物保护   2140篇
  2021年   296篇
  2020年   335篇
  2019年   396篇
  2018年   631篇
  2017年   676篇
  2016年   611篇
  2015年   510篇
  2014年   644篇
  2013年   1467篇
  2012年   1062篇
  2011年   1230篇
  2010年   850篇
  2009年   857篇
  2008年   1198篇
  2007年   1073篇
  2006年   994篇
  2005年   864篇
  2004年   807篇
  2003年   826篇
  2002年   745篇
  2001年   1026篇
  2000年   987篇
  1999年   765篇
  1998年   308篇
  1997年   329篇
  1995年   305篇
  1994年   274篇
  1992年   531篇
  1991年   613篇
  1990年   551篇
  1989年   557篇
  1988年   532篇
  1987年   508篇
  1986年   539篇
  1985年   470篇
  1984年   375篇
  1983年   339篇
  1979年   449篇
  1978年   343篇
  1977年   276篇
  1976年   291篇
  1975年   315篇
  1974年   353篇
  1973年   392篇
  1972年   362篇
  1970年   304篇
  1969年   317篇
  1968年   295篇
  1967年   294篇
  1966年   274篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A cat with hindlimb ataxia which progressed to paraplegia was found to have bacterial discospondylitis and a paravertebral abscess at necropsy. The infection had penetrated the vertebral canal. It is postulated that the vertebral infection occurred following haematogenous spread from a pneumonic focus.  相似文献   
102.
The performance of three live attenuated feline parvovirus vaccines licensed for use in the dog was studied. At the end of the primary vaccination course 67 per cent of dogs had inadequate antibody levels (less than or equal to 32) as measured by a haemagglutination inhibition test. Interference by maternal antibody accounted for some of the failures but the fact that there was no significant difference in performance between dogs vaccinated at 12 weeks or 16 weeks of age indicated that maternal antibody was not the only factor.  相似文献   
103.
104.
105.
Summary It was established by weak ion exchange resin chromatography that 17 amino acids in proteins and 15 free amino acids account for almost all of the amino acids present in the leaves of evergreen oak (Quercus ilex L.) in four different stages of decomposition. No significant change in the amounts of these amino acids was observed in the course of decomposition. The amino acid content of evergreen oak leaves is comparable to that in pine needles and beech leaves.  相似文献   
106.
107.
A gilt subsequently found to have one ovary and one ovotestis exhibited two oestrous cycles with normal ovulations before lapsing into bahavioural anoestrus. The testicular tissue of the ovotestis was not developed at the time of oestrus and ovulation. After it developed cyclic behaviour was abolished.  相似文献   
108.
A 4-month-old colt with stage I flexural deformity of the distal interphalangeal joint was diagnosed as having a type IV nondisplaced fracture of the extensor process of the 3rd phalanx. An inferior check ligament desmotomy and internal fixation of the fracture were performed. Favorable long-term results for internal fixation of extensor process fractures are presented.  相似文献   
109.
Atmospheric Deposition in a Rural Area in India - Net and Potential Acidity   总被引:1,自引:0,他引:1  
Atmospheric deposition in India is generally described as alkaline and well buffered against an increase of acidifying components. Such conclusion has been based on measurements usually performed in urban or suburban areas. Our data on deposition in NE India (in the countryside N of Bhubaneswar) obtained with wet-only and bulk collectors show that: 1) the weighted mean concentrations (and wet deposition) of H+ and HCO3 ? are almost equal, with dustfall contributing a negligible amount of HCO3 ?, 2) the deposition of potential acidity, defined as the acidity that would give the same acidity contribution to the receiving surface as the actual deposition provided that all ammonium was converted to nitrate in the soil, could be as high as 40 mmol H+ m?2 a?1 corresponding to a pH of 4.3 in precipitation. The low buffer capacity against acidification and high potential acidity were discovered from long- term measurements in a vegetation covered rural area. Similar measurements in a nearby suburban area gave a much higher input of HCO3 ? both in wet deposition and dustfall. Further increase of the emission of acidifying components in the region will increase the acid deposition.  相似文献   
110.
Pluviographic data at 15 min interval from 6 stations in Pulau Penang of Peninsular Malaysia were used to compute rainfall erosivity factor (R) for the revised universal soil loss equation (RUSLE). Three different modelling procedures were applied for the estimation of monthly rainfall erosivity (EI30) values. While storm rainfall (P) and duration (D) data were used in the first approach, the second approach used monthly rainfall for days with rainfall ≥ 10 mm (rain10) and monthly number of days with rainfall ≥ 10 (days10). The third approach however used the Fournier index as the independent variable. Based on the root mean squared error (RMSE) and the percentage error (PE) criteria, models developed using the Fournier index approach was adjudged the best with an average PE value of 0.92 and an average RMSE value of 164.6. Further, this approach was extended to the development of a regional model. Using data from additional sixteen stations and the Fournier index based regional model, EI30 values were computed for each month. ArcView GIS was used to generate monthly maps of EI30 values and also annual rainfall erosivity (R). The rainfall erosivity factor (R) in the region was estimated to vary from 9000 to 14,000 MJ mm ha− 1 h− 1 year− 1.  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