全文获取类型
收费全文 | 2070篇 |
免费 | 43篇 |
国内免费 | 24篇 |
专业分类
安全科学 | 74篇 |
废物处理 | 64篇 |
环保管理 | 382篇 |
综合类 | 877篇 |
基础理论 | 349篇 |
环境理论 | 4篇 |
污染及防治 | 247篇 |
评价与监测 | 80篇 |
社会与环境 | 48篇 |
灾害及防治 | 12篇 |
出版年
2023年 | 14篇 |
2022年 | 16篇 |
2021年 | 18篇 |
2020年 | 24篇 |
2019年 | 16篇 |
2018年 | 43篇 |
2017年 | 45篇 |
2016年 | 67篇 |
2015年 | 47篇 |
2014年 | 46篇 |
2013年 | 122篇 |
2012年 | 65篇 |
2011年 | 88篇 |
2010年 | 57篇 |
2009年 | 61篇 |
2008年 | 63篇 |
2007年 | 67篇 |
2006年 | 49篇 |
2005年 | 34篇 |
2004年 | 47篇 |
2003年 | 46篇 |
2002年 | 38篇 |
2001年 | 15篇 |
2000年 | 18篇 |
1999年 | 18篇 |
1998年 | 29篇 |
1997年 | 23篇 |
1996年 | 15篇 |
1995年 | 64篇 |
1994年 | 53篇 |
1993年 | 50篇 |
1992年 | 41篇 |
1991年 | 34篇 |
1990年 | 34篇 |
1989年 | 27篇 |
1988年 | 38篇 |
1987年 | 37篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1973年 | 10篇 |
1919年 | 47篇 |
1918年 | 44篇 |
1917年 | 36篇 |
1916年 | 53篇 |
1915年 | 37篇 |
1914年 | 71篇 |
1913年 | 106篇 |
排序方式: 共有2137条查询结果,搜索用时 31 毫秒
181.
182.
183.
Francesca Porri Gerardo I. Zardi Christopher D. McQuaid Sarah Radloff 《Marine Biology》2007,152(3):631-637
Settlement is a major determinant of intertidal populations. However, the energy costs of lost larvae are very high. Accordingly,
arrival and attachment on suitable substrata are essential requirements for species’ survival. On the intertidal, the presence
of cues left by adult or juvenile conspecifics could be vital for the successful establishment of larvae arriving on the shore.
Two mussel species, the indigenous Perna perna and the invasive Mytilus galloprovincialis, co-occur on the lower eulittoral zone on the south coast of South Africa. P.
perna dominates the low and M. galloprovincialis the high mussel zones, with co-existence in the mid mussel zone. This study tested the hypothesis of settlement selectivity
for conspecifics in these two mussel species, to understand whether the final adult distribution of mussels on the shores
is determined by active behavioural and chemical mechanisms. Preferential selection by larvae for conspecifics was tested
in the field during the peak settlement period in 2004 in natural mussel beds across zones and through manipulative experiments
in the mid-zone where the species co-exist. On natural beds, settlement was determined by counts of settlers attached over
48 h onto artificial collectors. Collectors were placed on beds of P. perna and M. galloprovincialis present at both high- and low-adult densities, as well as in mixed beds. On such natural beds, settlers of both species consistently
favored low-zone P. perna beds. Settlement patterns over 24 h onto experimentally created mussel patches consisting of P.
perna, M. galloprovincialis or the two species combined beds, set in the mixed zone, did not conform with the results of the natural beds study: settlers
of both species settled with no discrimination among different patches. The results indicate that mussels, which are sedentary,
lack attraction to conspecifics at settlement. This highlights the importance of tidal height in setting settlement rates,
and of post-settlement events in shaping populations of these broadcast spawners. 相似文献
184.
Christopher R. Smith 《Behavioral ecology and sociobiology》2007,61(9):1479-1487
Limitation of a necessary resource can affect an organism’s investment into growth and reproduction. Pogonomyrmex harvester ants store vast quantities of seeds in their nests that are thought to buffer the ants when external resources
are not available. This research uses externally controlled food availability to examine how resource shortage affects colony
investment, resource use, and resource distribution within the nest. Colonies were either starved or supplemented with resources
for 2 months, beginning at the onset of reproductive investment and ending immediately before nuptial flights. Fed colonies
invested more in overall production, proportionally more in reproduction relative to growth and in female reproductives relative
to males. Stored seeds in starved colonies did not buffer production in this study. However, worker fat reserves were depleted
in starved colonies, indicating that fat reserves fuel the spring bout of production. In starved colonies, worker fat reserves
were depleted evenly throughout the nest, distributing the burden of starvation on all workers regardless of caste and age.
A reallocation of diploid eggs into female workers rather than reproductives best explains the observed change in sex ratio
investment between treatments. The redistribution of resources into growth relative to reproduction in starved colonies is
consistent with life history theory for long-lived organisms, switching from current to future reproduction when resources
are scarce. 相似文献
185.
186.
Alireza A. Shamshirsaz Kelsey A. Stewart Hadi Erfani Ahmed A. Nassr Nathan C. Sundgren Amy R. Mehollin-Ray Shaine A. Morris Jimmy Espinoza Magdalena Sanz Cortes Christopher Cassady Timothy C. Lee Eumenia C. Castro Olutoyin A. Olutoye Deepak K. Mehta Darrell Cass Oluyinka O. Olutoye Michael A. Belfort 《黑龙江环境通报》2019,39(4):287-292
187.
Jonathan A. Villines Carmen T. Agouridis Richard C. Warner Christopher D. Barton 《Journal of the American Water Resources Association》2015,51(6):1667-1687
Headwater streams have a significant nexus or physical, chemical, and/or biological connection to downstream reaches. Generally, defined as 1st‐3rd order with ephemeral, intermittent, or perennial flow regimes, these streams account for a substantial portion of the total stream network particularly in mountainous terrain. Due to their often remote locations, small size, and large numbers, conducting field inventories of headwater streams is challenging. A means of estimating headwater stream location and extent according to flow regime type using publicly available spatial data is needed to simplify this complex process. Using field‐collected headwater point of origin data from three control watersheds, streams were characterized according to a set of spatial parameters related to topography, geology, and soils. These parameters were (1) compared to field‐collected point of origin data listed in three nearby Jurisdictional Determinations, (2) used to develop a geographic information system (GIS)‐based stream network for identifying ephemeral, intermittent, and perennial streams, and (3) applied to a larger watershed and compared to values obtained using the high‐resolution National Hydrography Dataset (NHD). The parameters drainage area and local valley slope were the most reliable predictors of flow regime type. Results showed the high‐resolution NHD identified no ephemeral streams and 9 and 65% fewer intermittent and perennial streams, respectively, than the GIS model. 相似文献
188.
189.
190.
In the past decade Australia has experienced a series of large‐scale, severe natural disasters including catastrophic bushfires, widespread and repeated flooding, and intense storms and cyclones. There appears to be a prima facie case for rebuilding damaged infrastructure to a more disaster resilient (that is, to ‘betterment’) standard. The purpose of this paper is to develop and illustrate a consistent and readily applied method for advancing proposals for the betterment of essential public assets, which can be used by governments at all levels to determine the net benefits of such proposals. Case study results demonstrate that betterment investments have the potential to deliver a positive economic return across a range of asset types and regions. Results, however, are highly sensitive to underlying assumptions; in particular the probability of the natural disaster affecting the infrastructure in the absence of betterment. 相似文献