全文获取类型
收费全文 | 32709篇 |
免费 | 353篇 |
国内免费 | 231篇 |
专业分类
安全科学 | 825篇 |
废物处理 | 1401篇 |
环保管理 | 4210篇 |
综合类 | 5406篇 |
基础理论 | 9110篇 |
环境理论 | 14篇 |
污染及防治 | 8388篇 |
评价与监测 | 2087篇 |
社会与环境 | 1638篇 |
灾害及防治 | 214篇 |
出版年
2022年 | 234篇 |
2021年 | 222篇 |
2019年 | 208篇 |
2018年 | 396篇 |
2017年 | 448篇 |
2016年 | 660篇 |
2015年 | 511篇 |
2014年 | 820篇 |
2013年 | 2547篇 |
2012年 | 962篇 |
2011年 | 1363篇 |
2010年 | 1145篇 |
2009年 | 1119篇 |
2008年 | 1356篇 |
2007年 | 1423篇 |
2006年 | 1229篇 |
2005年 | 1049篇 |
2004年 | 1054篇 |
2003年 | 1016篇 |
2002年 | 989篇 |
2001年 | 1257篇 |
2000年 | 937篇 |
1999年 | 523篇 |
1998年 | 383篇 |
1997年 | 438篇 |
1996年 | 439篇 |
1995年 | 508篇 |
1994年 | 478篇 |
1993年 | 412篇 |
1992年 | 428篇 |
1991年 | 408篇 |
1990年 | 444篇 |
1989年 | 416篇 |
1988年 | 357篇 |
1987年 | 369篇 |
1986年 | 337篇 |
1985年 | 319篇 |
1984年 | 369篇 |
1983年 | 328篇 |
1982年 | 363篇 |
1981年 | 312篇 |
1980年 | 279篇 |
1979年 | 293篇 |
1978年 | 257篇 |
1977年 | 241篇 |
1976年 | 198篇 |
1975年 | 205篇 |
1974年 | 226篇 |
1973年 | 234篇 |
1972年 | 215篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
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
53.
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
54.
55.
56.
57.
58.
59.
60.