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   87419篇
  免费   5190篇
  国内免费   42篇
林业   2982篇
农学   2713篇
基础科学   526篇
  9945篇
综合类   16234篇
农作物   3663篇
水产渔业   4302篇
畜牧兽医   45579篇
园艺   1083篇
植物保护   5624篇
  2019年   808篇
  2018年   1195篇
  2017年   1377篇
  2016年   1292篇
  2015年   1145篇
  2014年   1364篇
  2013年   3455篇
  2012年   2559篇
  2011年   3041篇
  2010年   1980篇
  2009年   1948篇
  2008年   2935篇
  2007年   2839篇
  2006年   2688篇
  2005年   2536篇
  2004年   2389篇
  2003年   2415篇
  2002年   2282篇
  2001年   2906篇
  2000年   2783篇
  1999年   2273篇
  1998年   977篇
  1997年   893篇
  1996年   790篇
  1995年   960篇
  1994年   864篇
  1993年   858篇
  1992年   1814篇
  1991年   1811篇
  1990年   1752篇
  1989年   1824篇
  1988年   1573篇
  1987年   1686篇
  1986年   1741篇
  1985年   1669篇
  1984年   1315篇
  1983年   1169篇
  1982年   843篇
  1981年   724篇
  1979年   1108篇
  1978年   900篇
  1977年   781篇
  1976年   736篇
  1975年   812篇
  1974年   1003篇
  1973年   1043篇
  1972年   996篇
  1971年   950篇
  1970年   890篇
  1969年   815篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
An unusual combination of blood cytopenias and monocytic proliferation was observed in a dog. Initial hematologic findings included severe thrombocytopenia, neutropenia, mild nonregenerative anemia and apparently normal bone marrow. Subsequently, a severe persistent monocytosis developed and the bone marrow became populated with monocytes and cytophagic macrophages. Splenomegaly was due to reticuloendothelial hyperplasia and extramedultary hematopoiesis. Treatment consisted of splenectomy and azathioprine but the response was poor and the dog was euthanized. Postmortem examination revealed a hypocellular bone marrow which contained moderate numbers of monocytes and plasma cells. Neoplastic proliferation was absent in visceral organs. No definite diagnosis was established; chronic blood cell consumption, perhaps immune-mediated, may have been responsible for the extensive reticuloendothelial hyperplasia and cytophagia.  相似文献   
182.
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   
183.
184.
185.
186.
Effects of pretreatment solutions containing varying concentrations of calcium, potassium, ammonium and nitrate were evaluated by measuring fluxes of the same ions during a subsequent 4-hour uptake by Douglas-fir seedlings. Maximal rate of ammonium uptake (11 microeq g(-1) root dry weight h(-1)) was about 5 times faster than that of nitrate (2 microeq g(-1) root dry weight h(-1)). Ammonium uptake was most rapid after pretreatment with low potassium levels and was unaffected by ammonium pretreatment. Nitrate uptake was most rapid after pretreatment with high levels of nitrate and low levels of potassium. Calcium uptake was greater when nitrate replaced ammonium as the N source. High calcium pretreatment levels depressed subsequent calcium uptake or resulted in calcium release in both ammonium and nitrate experiments. Potassium efflux occurred with both N sources, but the release was less during nitrate uptake than during ammonium uptake. Efflux of potassium is probably associated with the high potassium status of the seedlings and the exchange between potassium and other cations. High levels of potassium in the pretreatment solutions enhanced potassium efflux and caused a reduction in the subsequent rates of uptake of both ammonium and nitrate. Length of pretreatment and seedling size generally did not affect uptake rates.  相似文献   
187.
The validation of a liquid chromatographic procedure suitable for the determination of calcitriol and alfacalcidol in their respective formulations labeled to contain at least 0.25 micrograms drug per unit is described. The capsule content is diluted and chromatographed in 15-20 min on silica columns (5 micron) with a mobile phase of hexane-tetrahydrofuran-methylene dichloride-isopropanol (72 + 12 + 12 + 4, v/v) with detection at 254 nm. The calibration curve is linear. Recoveries of "spikes" averaged 101% with a standard deviation of 2%. Precision was better than 1.5%.  相似文献   
188.
189.
190.
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