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   4128篇
  免费   388篇
  国内免费   4篇
林业   64篇
农学   28篇
基础科学   5篇
  201篇
综合类   165篇
农作物   43篇
水产渔业   51篇
畜牧兽医   3894篇
园艺   14篇
植物保护   55篇
  2023年   57篇
  2022年   8篇
  2021年   26篇
  2020年   138篇
  2019年   23篇
  2018年   117篇
  2017年   118篇
  2016年   72篇
  2015年   128篇
  2014年   187篇
  2013年   197篇
  2012年   188篇
  2011年   181篇
  2010年   162篇
  2009年   221篇
  2008年   137篇
  2007年   116篇
  2006年   110篇
  2005年   94篇
  2004年   130篇
  2003年   98篇
  2002年   144篇
  2001年   131篇
  2000年   91篇
  1999年   108篇
  1998年   115篇
  1997年   86篇
  1996年   87篇
  1995年   99篇
  1994年   71篇
  1993年   115篇
  1992年   126篇
  1991年   119篇
  1990年   121篇
  1989年   84篇
  1988年   96篇
  1987年   86篇
  1986年   75篇
  1985年   62篇
  1984年   49篇
  1983年   45篇
  1982年   24篇
  1981年   11篇
  1980年   5篇
  1978年   4篇
  1977年   5篇
  1976年   7篇
  1974年   6篇
  1973年   6篇
  1972年   4篇
排序方式: 共有4520条查询结果,搜索用时 31 毫秒
81.
82.
Increasing pressures from agriculture and urbanization have resulted in drainage of many floodplains along the eastern Australian coastline, which are underlain by sulphidic sediments, to lower water tables and reduce soil salinity. This leads to oxidation of the sediments with a rapid decline in pH and an increase in salinity. Accurately mapping soil salinity and pH in coastal acid sulphate soil (CASS) landscapes is therefore important. One required map is the extent of highly acidic (i.e. pH < 4.5) areas, so that the application of alkaline amendments (e.g. lime) to neutralize the acid produced can be specifically targeted to the variation in pH. One approach is to use digital soil mapping (DSM) using ancillary information, such as an EM38, digital elevation models (DEM – elevation) and trend surface parameters (east and north). We used an EM38 in the horizontal (EM38h) and vertical (EM38v) modes together with elevation data to develop multiple linear regressions (MLR) for predicting EC1:5 and pH. For pH, best results were achieved when the EM38 ECa data were log‐transformed. By comparing MLR models using REML analysis, we found that using all ancillary data was optimal for mapping EC1:5, whereas the best predictors for pH were north, log‐EM38v and elevation. Using residual maximum likelihood (REML), the final EC1:5 and pH maps produced were consistent with previously defined soil landscape units, particularly CASS. The DSM approach used is amenable for mapping saline soils and identifying areas requiring the application of lime to manage acidic soil conditions in CASS landscape.  相似文献   
83.
The present study reports data on the skull bone morphometry of barking and sambar deer. The skulls of adult barking deer (n = 6) and sambar deer (n = 6) of either sex (n = 3 males and n = 3 females) were collected from the Aizawl Zoological Park, Aizawl, Mizoram, India, with official permission from the Government of Mizoram. Anatomically, barking and sambar deer's skulls were elongated, pyramid-like, dolichocephalic and consisted of thirty-two cranial and facial bones. The cranial bones were eleven (three single and four paired), comprising of occipital, sphenoid, ethmoid, frontal, interparietal, parietal and temporal. The facial bones were twenty-one (one single and ten were paired), consisting of the maxilla, premaxilla (incisive), palatine, pterygoid, nasal, lacrimal, zygomatic (malar), vomer, turbinates, mandible and hyoid. In the present study, altogether 41 different measurements were taken morphologically and 6 different indices were applied. The obtained morphometrical parameters were significantly (p < .01, p < .05) higher in males than females of both species. Species wise, all obtained parameters were higher in sambar deer than barking deer. The obtained 41 different skull parameters and 6 indices showed statistically significant differences (p < .01 and p < .05) between both sexes of barking and sambar deer; however, practically these differences were meagre. The present morphometrical study on the skull of both species can help the wildlife professionals and zoo veterinarians determine the sex of these animals and differentiate it from other domestic and wild small ruminants for solving veterolegal cases. This study's findings will also motivate and assist other comparative studies with various domestic and wild small ruminants.  相似文献   
84.
A 4-mo-old northern red-shouldered macaw (Diopsittaca nobilis) was admitted to the veterinary hospital of the Arruda Câmara Zoo, in the State of Paraiba, Brazil, for investigation of an orbital mass. Given rapid progression and lack of response to treatment, the bird was euthanized, and an autopsy was performed. Histologically, the mass consisted of a retrobulbar invasive tumor characterized by tubular and rosette-like structures, with interspersed heteroplastic tissues, such as aggregates of neuroglial cells and islands of hyaline cartilage. The tumor was immunopositive for pancytokeratin, GFAP, NSE, and S100. These findings were compatible with an ocular teratoid medulloepithelioma, a neoplasm best described in humans but also reported rarely in young cockatiels and African Grey parrots.  相似文献   
85.
86.
87.
88.
89.
90.
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