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   106604篇
  免费   5723篇
  国内免费   64篇
林业   3843篇
农学   2998篇
基础科学   699篇
  12887篇
综合类   18042篇
农作物   4044篇
水产渔业   4838篇
畜牧兽医   57399篇
园艺   1149篇
植物保护   6492篇
  2018年   1485篇
  2017年   1685篇
  2016年   1517篇
  2015年   1218篇
  2014年   1620篇
  2013年   4234篇
  2012年   2800篇
  2011年   3576篇
  2010年   2302篇
  2009年   2373篇
  2008年   3442篇
  2007年   3240篇
  2006年   3124篇
  2005年   2679篇
  2004年   2628篇
  2003年   2598篇
  2002年   2419篇
  2001年   3222篇
  2000年   3352篇
  1999年   2548篇
  1998年   1019篇
  1997年   999篇
  1995年   1219篇
  1994年   1054篇
  1993年   1018篇
  1992年   2247篇
  1991年   2386篇
  1990年   2251篇
  1989年   2267篇
  1988年   2106篇
  1987年   2204篇
  1986年   2247篇
  1985年   2128篇
  1984年   1729篇
  1983年   1535篇
  1982年   1017篇
  1979年   1727篇
  1978年   1381篇
  1977年   1221篇
  1976年   1256篇
  1975年   1310篇
  1974年   1619篇
  1973年   1626篇
  1972年   1540篇
  1971年   1396篇
  1970年   1360篇
  1969年   1299篇
  1968年   1174篇
  1967年   1204篇
  1966年   1102篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Amado RD 《Science (New York, N.Y.)》1980,210(4475):1241-1242
  相似文献   
993.
Geology of the athabasca oil sands   总被引:1,自引:0,他引:1  
In-place bitumen resources in the Alberta oil sands are estimated at 1350 billion barrels. Open-pit mining and hot water extraction methods, which involve the handling of huge tonnages of earth materials, are being employed in the two commercial plants now operating. In situ recovery methods will be required to tap the 90 percent of reserves that are too deeply buried to be surface mined. Development of in situ technologies will be painstaking and expensive, and success will hinge on their compatibility with extremely complex geological conditions in the subsurface.  相似文献   
994.
995.
Sergin VY 《Science (New York, N.Y.)》1980,209(4464):1477-1482
Numerical experiments with a simplified thermodynamic model of the glacier-ocean-atmosphere global system have been performed. Characteristic regimes of the system are auto-oscillations with periods varying between 20,000 and 80,000 years. The longer climatic waves are generated by the influence of variations of the earth's orbital parameters. Computed changes of glacial area, temperature, sea level, and other climate characteristics have values within expected ranges. The transition from a relatively warm epoch (when continental ice sheets are absent) to conditions characteristic of the Pleistocene is modeled. The calculated curves show how weak temperature fluctuations have been followed by large-scale oscillations.  相似文献   
996.
A solid electrolyte fuel cell operating on ammonia fuel has been constructed and tested. The yield of nitric oxide can exceed 60 percent with simultaneous electric energy production. Two dimensionless numbers have been identified which govern the product selectivity and power output of this fuel cell. The cell appears to be a promising candidate for nitric acid and electric energy cogeneration.  相似文献   
997.
Shur BD 《Science (New York, N.Y.)》1980,209(4460):1010-1011
  相似文献   
998.
It is proposed that human comfort could be provided in otherwise chilly surroundings by filling the occupied space with electromagnetic energy of centimeter wavelength. Very considerable reductions in the consumption of energy required for the heating of buildings should result from the lowering of interior temperatures thereby permitted.  相似文献   
999.
Innovation     
  相似文献   
1000.
1. Dry rabbit excreta were found to contain 188.1 g crude protein, 6.6 g non‐protein nitrogen, 0.3 g ammonia, 89.8 g moisture, 8.0 g ether extractives, 135.2 g crude fibre, 266.9 g ash and 19.18 MJ gross energy/kg. Methionine and lysine contents were 3.95 and 4.29 g/100 g protein, respectively.

2. In one experiment, 0, 50, 100 or 200 g rabbit excreta/kg were substituted for maize in a broiler diet. Chickens receiving the diet containing 200 g rabbit excreta/kg gained significantly less weight to 8 weeks of age than those receiving other diets.

3. In a second experiment, 0, 100, 150 or 200 g rabbit excreta/kg were substituted primarily for maize in a broiler diet to provide equal energy and protein contents. Weight gains to 8 weeks of birds receiving these diets did not differ significantly. The uncorrected metabolisable energy content of the excreta was 9.15 MJ/kg.

4. There were no gross pathological changes in the birds fed on the experimental diets.  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