全文获取类型
收费全文 | 15322篇 |
免费 | 515篇 |
国内免费 | 1969篇 |
专业分类
安全科学 | 564篇 |
废物处理 | 703篇 |
环保管理 | 1640篇 |
综合类 | 5201篇 |
基础理论 | 3793篇 |
环境理论 | 4篇 |
污染及防治 | 2995篇 |
评价与监测 | 1063篇 |
社会与环境 | 1639篇 |
灾害及防治 | 204篇 |
出版年
2024年 | 27篇 |
2023年 | 151篇 |
2022年 | 409篇 |
2021年 | 421篇 |
2020年 | 387篇 |
2019年 | 320篇 |
2018年 | 906篇 |
2017年 | 930篇 |
2016年 | 873篇 |
2015年 | 485篇 |
2014年 | 586篇 |
2013年 | 867篇 |
2012年 | 829篇 |
2011年 | 1398篇 |
2010年 | 924篇 |
2009年 | 992篇 |
2008年 | 1175篇 |
2007年 | 1304篇 |
2006年 | 465篇 |
2005年 | 416篇 |
2004年 | 325篇 |
2003年 | 434篇 |
2002年 | 443篇 |
2001年 | 302篇 |
2000年 | 270篇 |
1999年 | 173篇 |
1998年 | 163篇 |
1997年 | 121篇 |
1996年 | 96篇 |
1995年 | 103篇 |
1994年 | 84篇 |
1993年 | 82篇 |
1992年 | 75篇 |
1991年 | 57篇 |
1990年 | 67篇 |
1989年 | 52篇 |
1988年 | 41篇 |
1987年 | 31篇 |
1986年 | 31篇 |
1985年 | 32篇 |
1984年 | 42篇 |
1983年 | 43篇 |
1982年 | 34篇 |
1981年 | 43篇 |
1980年 | 30篇 |
1979年 | 31篇 |
1978年 | 28篇 |
1976年 | 28篇 |
1975年 | 26篇 |
1972年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
122.
123.
124.
The invertebrate neuromodulator octopamine is known to be involved in bees' associative learning, enhancing the responsiveness of a bee to a conditioned stimulus. In this study, we tested the effect of octopamine on the choice behavior of free-flying bumblebees using a two-phase experiment in an array of artificial flowers. During the first phase of the experiment, the bee was allowed to collect octopamine-laden sugar water from two types of equally rewarding flowers (yellow versus blue). In the second phase, one type of flower was set to be unrewarding. The behavior of the bee (proportion of visits to the unrewarding flowers) over the two phases was fitted to a sigmoid regression model. Our results show that octopamine had no significant effect on the bees' equilibrium choice or on the overall rate of the behavioral change in response to the change in reward. Rather, octopamine significantly affected the time interval between the change in reward status and the initiation of behavioral change in the bee. 相似文献
125.
126.
Climate change and temperature-dependent biogeography: oxygen limitation of thermal tolerance in animals 总被引:2,自引:0,他引:2
Pörtner HO 《Die Naturwissenschaften》2001,88(4):137-146
Recent years have shown a rise in mean global temperatures and a shift in the geographical distribution of ectothermic animals. For a cause and effect analysis the present paper discusses those physiological processes limiting thermal tolerance. The lower heat tolerance in metazoa compared with unicellular eukaryotes and bacteria suggests that a complex systemic rather than molecular process is limiting in metazoa. Whole-animal aerobic scope appears as the first process limited at low and high temperatures, linked to the progressively insufficient capacity of circulation and ventilation. Oxygen levels in body fluids may decrease, reflecting excessive oxygen demand at high temperatures or insufficient aerobic capacity of mitochondria at low temperatures. Aerobic scope falls at temperatures beyond the thermal optimum and vanishes at low or high critical temperatures when transition to an anaerobic mitochondrial metabolism occurs. The adjustment of mitochondrial densities on top of parallel molecular or membrane adjustments appears crucial for maintaining aerobic scope and for shifting thermal tolerance. In conclusion, the capacity of oxygen delivery matches full aerobic scope only within the thermal optimum. At temperatures outside this range, only time-limited survival is supported by residual aerobic scope, then anaerobic metabolism and finally molecular protection by heat shock proteins and antioxidative defence. In a cause and effect hierarchy, the progressive increase in oxygen limitation at extreme temperatures may even enhance oxidative and denaturation stress. As a corollary, capacity limitations at a complex level of organisation, the oxygen delivery system, define thermal tolerance limits before molecular functions become disturbed. 相似文献
127.
毛细管气相色谱法分析1,3—丁二烯中炔烃杂质含量 总被引:2,自引:0,他引:2
介绍了一种毛细管毛相谱法测定1,3-丁烯中炔烃质含量的新试验方法,该方法以氮气为载气,采用氢火焰离子化检测器,样品经分离后,采用外标法定量,操作简便,准确。该方法还可用于1,3-丁二烯纯度分析 。 相似文献
128.
129.
130.