全文获取类型
收费全文 | 4546篇 |
免费 | 34篇 |
国内免费 | 13篇 |
专业分类
安全科学 | 63篇 |
废物处理 | 288篇 |
环保管理 | 266篇 |
综合类 | 737篇 |
基础理论 | 935篇 |
环境理论 | 4篇 |
污染及防治 | 1570篇 |
评价与监测 | 464篇 |
社会与环境 | 258篇 |
灾害及防治 | 8篇 |
出版年
2023年 | 47篇 |
2022年 | 143篇 |
2021年 | 138篇 |
2020年 | 53篇 |
2019年 | 65篇 |
2018年 | 169篇 |
2017年 | 127篇 |
2016年 | 230篇 |
2015年 | 120篇 |
2014年 | 262篇 |
2013年 | 461篇 |
2012年 | 277篇 |
2011年 | 277篇 |
2010年 | 215篇 |
2009年 | 166篇 |
2008年 | 239篇 |
2007年 | 250篇 |
2006年 | 226篇 |
2005年 | 153篇 |
2004年 | 124篇 |
2003年 | 110篇 |
2002年 | 95篇 |
2001年 | 59篇 |
2000年 | 48篇 |
1999年 | 35篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 26篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1987年 | 8篇 |
1982年 | 10篇 |
1970年 | 12篇 |
1967年 | 10篇 |
1966年 | 12篇 |
1965年 | 18篇 |
1964年 | 28篇 |
1963年 | 13篇 |
1962年 | 17篇 |
1961年 | 14篇 |
1960年 | 15篇 |
1959年 | 32篇 |
1958年 | 36篇 |
1957年 | 21篇 |
1956年 | 20篇 |
1955年 | 19篇 |
排序方式: 共有4593条查询结果,搜索用时 15 毫秒
971.
972.
M. J. Garcia-Muñoz J. Belloque B. Merinero C. Pérez-Cerdá P. Sanz M. Ugarte 《黑龙江环境通报》1989,9(7):473-476
We describe a prenatal diagnosis of a fetus at risk for non-ketotic hyperglycinaemia based on the glycine/serine ratio in amniotic fluid at 16 weeks of gestation. Although the glycine level and the glycine/serine ratio in amniotic fluid were within the normal range, the fetus was affected and therefore a false-negative prediction was made. The reliability of this method is questioned. 相似文献
973.
974.
975.
976.
One of the most useful diagnostic therian features is the division of the lateral surface of the scapula into two fossae separated by a scapular spine. A new model to describe this evolutionary innovation based on ontogenetic data is provided, consistent with information provided by recent fossil discoveries. The development of the scapula in three didelphid and one dasyurid marsupials using histological sections was studied. Only the ventral, acromial portion of the scapular spine, which originates from the anterior margin of the scapular blade, is preformed in cartilage. The major dorsal portion is formed at a later stage by appositional bone, which expands from the perichondral ossification of the scapula into an intermuscular aponeurosis between the supra-and infraspinatus muscles. This intermuscular aponeurosis inserts more or less in the middle of the lateral surface of the developing scapula. Thus, the floor of the supraspinous fossa is already present at the beginning of scapular development, simultaneous with the infraspinous fossa. The portion of the scapular spine that is situated dorsal to the acromial process is hypothesized to be a neomorphic structure of therians. The dorsal portion of the scapular spine evolved as additional attachment for powerful supraspinatus and infraspinatus muscles meeting near the middle of the lateral scapula. 相似文献
977.
978.
Insects are considered the most important predators of seed cones, the female reproductive structures of conifers, prior to seed dispersal. Slightly more than 100 genera of insects are known to parasitize conifer seed cones. The most diverse (i.e., number of species) of these genera is Megastigmus (Hymenoptera: Torymidae), which comprises many important seed pests of native and exotic conifers. Seed chalcids, Megastigmus spp., lay eggs inside the developing ovules of host conifers and, until recently, oviposition was believed to occur only in fertilized ovules. Ovule development begins just after pollination, but stops if cells are not fertilized. The morphological stage of cone development at the time of oviposition by seed chalcids has been established for many species; however, knowledge of ovule development at that time has been documented for only one species, M. spermotrophus. Megastigmus spermotrophus oviposits in Douglas-fir ovules after pollination but before fertilization. Unlike the unfertilized ovules, those containing a M. spermotrophus larva continue to develop, whether fertilized or not, stressing the need to broaden our understanding of the insect–plant interactions for this entire genus. To achieve this task, we reviewed the scientific literature and assembled information pertaining to the timing of oviposition and to the pollination and fertilization periods of their respective host(s). More specifically, we were searching for circumstantial evidence that other species of Megastigmus associated with conifers could behave (i.e., oviposit before ovule fertilization) and impact on female gametophyte (i.e., prevent abortion) like M. spermotrophus. The evidence from our compilation suggests that seed chalcids infesting Pinaceae may also oviposit before ovule fertilization, just like M. spermotrophus, whereas those infesting Cupressaceae seemingly oviposit after ovule fertilization. Based on this evidence, we hypothesize that all species of Megastigmus associated with Pinaceae can oviposit in unfertilized ovules, whereas those exploiting Cupressaceae cannot, and thus oviposit only in already fully developed fertilized seeds. Furthermore, we predict that the presence of a larva in unfertilized ovules of all Pinaceae will influence the development of the female gametophyte by preventing its abortion. This influence on the Pinaceae can be interpreted as an ability to parasitize any of the potential seeds present in a seed cone, and as such represents a much more efficient oviposition strategy than searching and locating only fertilized seeds. Concomitantly, this ability has likely led to an overestimation of the impact of the species of seed chalcid infesting Pinaceae on seed production. 相似文献
979.
980.
Oil spills caused by maritime transport of petroleum products are still an important source of ocean pollution, especially in main production areas and along major transport routes. We here provide a historical and geographic analysis of the major oil spills (>700 t) since 1960. Spills were recorded from several key marine ecosystems and marine biodiversity hotspots. The past four decades have been characterized by an overall decrease in the number of accidents and tonnes of oil spilled in the sea, but this trend was less distinct in the European Atlantic area. Recent black tides from the Erika and Prestige vessels provided new evidence for the high risk of accidents with serious ecological impact in this area, which according to our analysis is historically the most important oil spill hotspot worldwide. The English Channel and waters around Galicia in Spain were the areas with most accidents. Maritime transport in European Atlantic waters has been predicted to continue increasing. Together with our own results this suggests that, in addition to measures for increased traffic safety, deployment of emergency capacities in the spill hotspot areas may be crucial for a sustainable conservation of sea resources and ecosystems.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material. 相似文献