全文获取类型
收费全文 | 32237篇 |
免费 | 337篇 |
国内免费 | 276篇 |
专业分类
安全科学 | 1055篇 |
废物处理 | 1579篇 |
环保管理 | 4193篇 |
综合类 | 4820篇 |
基础理论 | 8669篇 |
环境理论 | 8篇 |
污染及防治 | 7854篇 |
评价与监测 | 2295篇 |
社会与环境 | 2197篇 |
灾害及防治 | 180篇 |
出版年
2023年 | 132篇 |
2022年 | 263篇 |
2021年 | 324篇 |
2020年 | 196篇 |
2019年 | 245篇 |
2018年 | 536篇 |
2017年 | 565篇 |
2016年 | 883篇 |
2015年 | 578篇 |
2014年 | 866篇 |
2013年 | 2482篇 |
2012年 | 1382篇 |
2011年 | 1537篇 |
2010年 | 1121篇 |
2009年 | 1168篇 |
2008年 | 1451篇 |
2007年 | 1388篇 |
2006年 | 1264篇 |
2005年 | 1413篇 |
2004年 | 1502篇 |
2003年 | 1360篇 |
2002年 | 968篇 |
2001年 | 1121篇 |
2000年 | 786篇 |
1999年 | 508篇 |
1998年 | 367篇 |
1997年 | 391篇 |
1996年 | 399篇 |
1995年 | 471篇 |
1994年 | 398篇 |
1993年 | 345篇 |
1992年 | 379篇 |
1991年 | 361篇 |
1990年 | 329篇 |
1989年 | 326篇 |
1988年 | 295篇 |
1987年 | 241篇 |
1986年 | 247篇 |
1985年 | 247篇 |
1984年 | 267篇 |
1983年 | 254篇 |
1982年 | 268篇 |
1981年 | 221篇 |
1980年 | 165篇 |
1979年 | 181篇 |
1978年 | 162篇 |
1977年 | 133篇 |
1975年 | 138篇 |
1973年 | 168篇 |
1972年 | 143篇 |
排序方式: 共有10000条查询结果,搜索用时 875 毫秒
311.
312.
313.
314.
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
315.
316.
317.
Upper limb reduction was diagnosed by ultrasound scan at 17 weeks after chorion villus sampling at 9 weeks' gestation. Pregnancy was terminated and necropsy confirmed limb reduction in an otherwise normal fetus. The relationship of limb reduction to amniotic band syndrome is discussed. 相似文献
318.
M. Blunck W. -D. Busse G. Meister E. Möller A. Mullen L. A. A. van Rooijen 《Die Naturwissenschaften》1989,76(3):96-98
Online searching in publically available patent files opens up interesting possibilities to provide a rapid response to critical questions. A computerized analysis of all patents of leading German pharmaceutical companies over the last decade in important indication areas is described. Supported by subsequent manual processing of individual patents it is shown that duplicate experiments on animals practically never occur. 相似文献
319.
320.
Consensus on the evolutionary position of turtles within the amniote phylogeny has eluded evolutionary biologists for more than a century. This phylogenetic problem has remained unsolved partly because turtles have such a unique morphology that only few characters can be used to link them with any other group of amniotes. Among the many alternative hypotheses that have been postulated to explain the origin and phylogenetic relationships of turtles, a general agreement among paleontologists emerged in favoring the placement of turtles as the only living survivors of the anapsid reptiles (those that lack temporal fenestrae in the skull). However, recent morphological and molecular studies have radically changed our view of amniote phylogenetic relationships, and evidence is accumulating that supports the diapsid affinities of turtles. Molecular studies favor archosaurs (crocodiles and birds) as the living sister group of turtles, whereas morphological studies support lepidosaurs (tuatara, lizards, and snakes) as the closest living relatives of turtles. Accepting these hypotheses implies that turtles cannot be viewed any longer as primitive reptiles, and that they might have lost the temporal holes in the skull secondarily rather than never having had them. 相似文献