收费全文 | 33631篇 |
免费 | 357篇 |
国内免费 | 240篇 |
安全科学 | 929篇 |
废物处理 | 1255篇 |
环保管理 | 4340篇 |
综合类 | 5326篇 |
基础理论 | 9501篇 |
环境理论 | 26篇 |
污染及防治 | 9100篇 |
评价与监测 | 2086篇 |
社会与环境 | 1461篇 |
灾害及防治 | 204篇 |
2022年 | 289篇 |
2021年 | 309篇 |
2020年 | 216篇 |
2019年 | 282篇 |
2018年 | 538篇 |
2017年 | 557篇 |
2016年 | 774篇 |
2015年 | 640篇 |
2014年 | 897篇 |
2013年 | 2468篇 |
2012年 | 1097篇 |
2011年 | 1513篇 |
2010年 | 1215篇 |
2009年 | 1191篇 |
2008年 | 1509篇 |
2007年 | 1567篇 |
2006年 | 1373篇 |
2005年 | 1152篇 |
2004年 | 1144篇 |
2003年 | 1056篇 |
2002年 | 1021篇 |
2001年 | 1289篇 |
2000年 | 883篇 |
1999年 | 584篇 |
1998年 | 440篇 |
1997年 | 448篇 |
1996年 | 452篇 |
1995年 | 507篇 |
1994年 | 460篇 |
1993年 | 403篇 |
1992年 | 428篇 |
1991年 | 381篇 |
1990年 | 388篇 |
1989年 | 420篇 |
1988年 | 358篇 |
1987年 | 307篇 |
1986年 | 290篇 |
1985年 | 310篇 |
1984年 | 295篇 |
1983年 | 330篇 |
1982年 | 333篇 |
1981年 | 279篇 |
1980年 | 251篇 |
1979年 | 272篇 |
1978年 | 235篇 |
1977年 | 197篇 |
1976年 | 203篇 |
1975年 | 197篇 |
1973年 | 174篇 |
1972年 | 206篇 |
Rock ptarmigan (Lagopus muta) and willow ptarmigan (L. lagopus) are Arctic birds with a circumpolar distribution but there is limited knowledge about their status and trends across their circumpolar distribution. Here, we compiled information from 90 ptarmigan study sites from 7 Arctic countries, where almost half of the sites are still monitored. Rock ptarmigan showed an overall negative trend on Iceland and Greenland, while Svalbard and Newfoundland had positive trends, and no significant trends in Alaska. For willow ptarmigan, there was a negative trend in mid-Sweden and eastern Russia, while northern Fennoscandia, North America and Newfoundland had no significant trends. Both species displayed some periods with population cycles (short 3–6 years and long 9–12 years), but cyclicity changed through time for both species. We propose that simple, cost-efficient systematic surveys that capture the main feature of ptarmigan population dynamics can form the basis for citizen science efforts in order to fill knowledge gaps for the many regions that lack systematic ptarmigan monitoring programs.
相似文献Although banned from production for decades, PCBs remain a significant risk to human health. A primary target of concern is the developing brain. Epidemiological studies link PCB exposures in utero or during infancy to increased risk of neuropsychiatric deficits in children. Nonclinical studies of legacy congeners found in PCB mixtures synthesized prior to the ban on PCB production suggest that non-dioxin-like (NDL) congeners are predominantly responsible for the developmental neurotoxicity associated with PCB exposures. Mechanistic studies suggest that NDL PCBs alter neurodevelopment via ryanodine receptor-dependent effects on dendritic arborization. Lightly chlorinated congeners, which were not present in the industrial mixtures synthesized prior to the ban on PCB production, have emerged as contemporary environmental contaminants, but there is a paucity of data regarding their potential developmental neurotoxicity. PCB 11, a prevalent contemporary congener, is found in the serum of children and their mothers, as well as in the serum of pregnant women at increased risk for having a child diagnosed with a neurodevelopmental disorder (NDD). Recent data demonstrates that PCB 11 modulates neuronal morphogenesis via mechanisms that are convergent with and divergent from those implicated in the developmental neurotoxicity of legacy NDL PCBs. This review summarizes these data and discusses their relevance to adverse neurodevelopmental outcomes in humans.
相似文献