全文获取类型
收费全文 | 34748篇 |
免费 | 446篇 |
国内免费 | 461篇 |
专业分类
安全科学 | 1089篇 |
废物处理 | 1495篇 |
环保管理 | 4751篇 |
综合类 | 5514篇 |
基础理论 | 9004篇 |
环境理论 | 17篇 |
污染及防治 | 9379篇 |
评价与监测 | 2202篇 |
社会与环境 | 1973篇 |
灾害及防治 | 231篇 |
出版年
2022年 | 370篇 |
2021年 | 422篇 |
2020年 | 324篇 |
2019年 | 332篇 |
2018年 | 611篇 |
2017年 | 595篇 |
2016年 | 893篇 |
2015年 | 633篇 |
2014年 | 937篇 |
2013年 | 2844篇 |
2012年 | 1224篇 |
2011年 | 1693篇 |
2010年 | 1292篇 |
2009年 | 1315篇 |
2008年 | 1585篇 |
2007年 | 1684篇 |
2006年 | 1426篇 |
2005年 | 1156篇 |
2004年 | 1178篇 |
2003年 | 1074篇 |
2002年 | 1028篇 |
2001年 | 1267篇 |
2000年 | 911篇 |
1999年 | 574篇 |
1998年 | 428篇 |
1997年 | 412篇 |
1996年 | 420篇 |
1995年 | 492篇 |
1994年 | 456篇 |
1993年 | 394篇 |
1992年 | 385篇 |
1991年 | 376篇 |
1990年 | 396篇 |
1989年 | 384篇 |
1988年 | 318篇 |
1987年 | 282篇 |
1986年 | 278篇 |
1985年 | 283篇 |
1984年 | 350篇 |
1983年 | 310篇 |
1982年 | 323篇 |
1981年 | 302篇 |
1980年 | 245篇 |
1979年 | 274篇 |
1978年 | 212篇 |
1977年 | 197篇 |
1975年 | 184篇 |
1974年 | 191篇 |
1973年 | 183篇 |
1972年 | 204篇 |
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
411.
Iigo Loureiro M. Concepcin Escorial Jos María García-Baudin M. Cristina Chueca 《Agriculture, ecosystems & environment》2007,120(2-4):384-390
Hybridization between Aegilops geniculata, A. biuncialis and bread wheat Triticum aestivum has been evaluated during two seasons under simulated field conditions to estimate the field hybridization rate under Central Spain conditions. The mean frequencies of hybridization between A. biuncialis and A. geniculata with wheat were 0.34% and 0.31%, respectively. Data from 10 hybrid plants for each combination showed that hybrids can be partially fertile by backcrossing with wheat parent, with percent averages of 3.17 grains/spikelets for A. biuncialis × wheat hybrids and 2.87 grains/spikelets for A. geniculata × wheat hybrids. Self-pollination, although at very low rates, was also possible in hybrids. The potential risks associated with natural hybridization in the context of transgenic wheat cultivation are discussed. 相似文献
412.
413.
414.
415.
416.
417.
418.
James A. Langley Earl O. Heady Kent D. Olson 《Agriculture, ecosystems & environment》1983,10(4):323-333
A national interregional linear programming model of U.S. agriculture is used to evaluate and compare two conventional and three organic production alternatives. The objective is to estimate the effects on production, supply prices, land use, farm income, and export potential, of a complete transformation of U.S. agriculture to organic practices. Crop yields and production costs are estimated for 150 producing regions for seven crops under both conventional and organic methods. Results indicate that compared with conventional methods, widespread organic farming leads to a decrease in total production, lower export potential, higher supply prices, higher value of production, lower costs of production, and higher net farm income. The United States domestic crop demand can be met with organic methods, but would be more expensive. Some interregional shifts in crop production would also occur. 相似文献
419.
Egyptian Blue, a multicomponent synthetic blue pigment has been recorded in ancient Egypt since the Fourth Dynasty of the Old Kingdom (2600–2480 B.C.). The pigment consisting of cuprorivaite (CaCuSi4O10) with variable amounts of wollastonite (CaSiO3), Cu-rich glass and cuprite (Cu3O) or tenorite (CuO) was prepared by melting the copper-rich ingredient with lime and desert sand. Low melting temperatures (below 742 °C) were achieved by addition of flux-like plant ashes. The high quality of the pigments collected from monuments of the Fifth Dynasty (2480–2320 B.C.) may indicate that the first manufacture was in early dynastic or perhaps predynastic eras. During the reign of Thutmosis III (18th Dynasty, 1490–1436 B.C.) probably bronze filings were first applied as starting material, thus indicating a technological innovation. This new method was employed till the Roman times. 相似文献
420.
The perception of pitch 总被引:1,自引:0,他引:1