全文获取类型
收费全文 | 6944篇 |
免费 | 68篇 |
国内免费 | 995篇 |
专业分类
安全科学 | 218篇 |
废物处理 | 203篇 |
环保管理 | 505篇 |
综合类 | 3738篇 |
基础理论 | 573篇 |
污染及防治 | 1880篇 |
评价与监测 | 479篇 |
社会与环境 | 302篇 |
灾害及防治 | 109篇 |
出版年
2023年 | 36篇 |
2022年 | 50篇 |
2021年 | 35篇 |
2020年 | 63篇 |
2019年 | 49篇 |
2018年 | 48篇 |
2017年 | 67篇 |
2016年 | 49篇 |
2015年 | 102篇 |
2014年 | 76篇 |
2013年 | 55篇 |
2012年 | 411篇 |
2011年 | 520篇 |
2010年 | 114篇 |
2009年 | 144篇 |
2008年 | 462篇 |
2007年 | 515篇 |
2006年 | 396篇 |
2005年 | 398篇 |
2004年 | 344篇 |
2003年 | 350篇 |
2002年 | 313篇 |
2001年 | 237篇 |
2000年 | 172篇 |
1999年 | 103篇 |
1998年 | 46篇 |
1997年 | 48篇 |
1996年 | 51篇 |
1995年 | 82篇 |
1994年 | 66篇 |
1993年 | 106篇 |
1992年 | 92篇 |
1991年 | 117篇 |
1990年 | 136篇 |
1989年 | 101篇 |
1988年 | 197篇 |
1987年 | 238篇 |
1986年 | 123篇 |
1985年 | 238篇 |
1984年 | 216篇 |
1983年 | 196篇 |
1982年 | 163篇 |
1981年 | 146篇 |
1980年 | 128篇 |
1979年 | 78篇 |
1978年 | 77篇 |
1977年 | 34篇 |
1976年 | 62篇 |
1975年 | 47篇 |
1974年 | 69篇 |
排序方式: 共有8007条查询结果,搜索用时 15 毫秒
291.
Predation is often considered as one of the most important biotic factor determining the success of exotic species. The freshwater amphipod Gammarus roeseli has widely colonized Western Europe, where it is frequently found in sympatry with the native species (Gammarus pulex). Previous laboratory experiments revealed that G. roeseli may have an advantage over G. pulex through differential predation by native fish (brown trout). Morphological anti-predator defences (spines) were found responsible for lower rates of predation on the invasive G. roeseli. Here, using both field surveys and laboratory experiments, we tested if a differential of predation exists with other fish predators naturally encountered by gammarids. The main predators present in our field site were nocturnal benthic feeders (mainly bullheads, Cottus gobio). Fish diet analysis showed that, compared to its global availability in the river, G. roeseli was less consumed than G. pulex. In the field, however, G. roeseli was found mainly in the aquatic vegetation whereas G. pulex was found in all habitat types. Laboratory experiments in microcosms revealed that G. roeseli was less prone to predation by C. gobio only when vegetation was present. Depending on the type of predator, the differential of predation could therefore be mediated by antipredator behaviour, and a better usage of refuges, rather than by morphological defences. 相似文献
292.
293.
Ryan L. Fimmen Tamara D. Trouts Daniel D. Richter Jr. Dharni Vasudevan 《环境科学学报(英文版)》2008,20(10):1273-1280
The objective of this study was to improve primary-amine nitrogen (1°-N) quantification in dissolved organic matter (DOM) originating from natural waters where inorganic forms of N, which may cause analytical interference, are commonly encountered. Efforts were targeted at elucidating organic-N structural criteria influencing the response of organic amines to known colorimetric and fluorescent reagents and exploring the use of divalent metal-assisted amide hydrolysis in combination with fluorescence analyse... 相似文献
294.
Sperm number is often a good predictor of success in sperm competition; however, it has become increasingly clear that, for
some species, variation in probability of paternity cannot be explained by sperm number alone. Intraspecific variation in
ejaculate characteristics, such as the number of viable sperm and sperm longevity, may play an equally important role in determining
fertilization success. Here, we assess variation among ejaculates in three factors that may contribute to fertilization success
(number of sperm per ejaculate, viability, and longevity), in a population of Peron’s tree frog (Litoria peronii). We detected large variation among males in the number of sperm per ejaculate and the proportion of viable sperm within
ejaculates, which could not be explained by variation in either male size or body condition. However, the proportion of viable
sperm released by males increased over the season. Finally, we assessed sperm longevity (proportion viable sperm determined
using a dual-fluorochrome vital dye) at two different temperatures. At 23°C, on average, 75% of sperm remained viable after
2 h, but there were significant differences amongst males with the percentage of viable sperm ranging from 43% to 95%. For
sperm incubated at 4°C, ejaculates varied fivefold in sperm longevity with some males having 50% viable sperm after 5 days.
Our data suggest that ejaculate characteristics (sperm number, viability, and longevity) vary widely in Peron’s tree frog
and may therefore play an important role in determining siring success both in the presence and absence of sperm competition.
We discuss the results in relation to selection on ejaculate traits via natural and sexual selection in this and other amphibians. 相似文献
295.
A 13.4 L biofilter treating an off-gas stream supplemented with methanol under two different situations was studied in terms of MeOH removal efficiency, microbial ecology and odor removal. During Period 1 (P1) the reactor was packed with wood bark chips with no pH control, treating an off-gas resulting from the aerobic chamber of a membrane biological reactor treating sewage and located outdoor, whereas during Period 2 (P2) a compressed air stream fed with MeOH was treated using PVC rings and maintaining pH at neutral values. Both systems operated at 96 g MeOH m−3 h−1 achieving removal efficiencies of around 90% during P1 and 99.9% during P2. The relative activity of biomass developed in both systems was assessed using respirometric analysis with samples obtained from both biofilms. Higher biomass activity was obtained during P2 (0.25-0.35 kg MeOH kg−1 VSS d−1) whereas 1.1 kg MeOH kg−1 VSS d−1 was obtained in the case of P1. The application of molecular and microscopic techniques showed that the eukaryotes were predominant during P1, being the yeast Candida boidinii the most abundant microorganism. A specific Fluorescence in situ hybridization probe was designed for C. boidinii and tested successfully. As a result of the neutral pH, a clear predominance of prokaryotes was detected during P2. Interestingly, some anaerobic bacteria were detected such as Desulfovibrio, Desulfobacteraceae species and also some archaea such as Methanosarcina. 相似文献
296.
Pentachlorobenzene (PeCB) in simulated flue gas was destructed by a commercial V2O5-WO3/TiO2 catalyst in this study. The effects of reaction temperature, oxygen concentration, space velocity and some co-existing pollutants on PeCB conversion were investigated. Furthermore, a possible mechanism for the oxidation of PeCB over the vanadium oxide on the catalysts was proposed. Results show that the increase of gas hourly space velocity (GHSV) and the decrease of operating temperature both resulted in the decrease of PeCB removal over the catalyst, while the effect of the oxygen content in the range of 5-20% (v/v) on PeCB conversion was negligible. PeCB decomposition could be obviously affected by the denitration reactions under the conditions because of the positive effect of NO but negative effect of NH3. The introduction of SO2 caused the catalyst poisoning, probably due to the sulfur-containing species formed and deposited on the catalyst surface. The PeCB molecules were first adsorbed on the catalyst surface, and then oxidized into the non-aromatic acyclic intermediates, low chlorinated aromatics and maleic anhydride. 相似文献
297.
298.
中国西部本底大气中CO的连续测量 总被引:14,自引:2,他引:14
在中国西北部的瓦里关全球基准站(36°17'N,100°54'E,3810m asl)建立了气相色谱-汞置换法大气CO连续测量系统.组装调试和运行标定表明,色谱方法的基线稳定,分离度高,检测方法可靠,系统具有高自动化的操作性能和严格的质量控制,其设计完全符合世界气象组织(WMO)全球大气本底测量的要求.根据采样现场大气CO浓度的变化,采用经国际比对的CO标准气系列,用峰高外标法设定可调整的标准工作曲线计算环境CO浓度,系统对CO的检测限低至1×10-9(V/V),检测精度小于0.1%,准确度在±0.05%以内,可提供我国本底地区近地层大气CO连续而精确的现场测量结果. 相似文献
299.
种植密度和降水对冬小麦田N2O排放的影响 总被引:4,自引:2,他引:4
为研究种植密度对农田N2O排放的影响和探讨N2O排放季节性波动的原因,于1999~2000年小麦生长季在南京市郊江宁县进行了不同播种量(0、90、180和270kg/hm2)的大田试验.观测分析结果表明:在相同的气象条件和田间管理下,播种~越冬阶段的N2O排放不受播种量的影响,返青~成熟阶段的N2O排放通量与播种量成正比.裸地条件下的N2O排放与播量为90kg/hm2下的排放无明显差异.造成该生长季内N2O排放季节性波动的主要原因是降水,返青~成熟阶段的N2O排放通量随观测日前6d的加权平均降水量呈指数增加. 相似文献
300.
The perceived position of a moving object can be misleading because the object has advanced while its previous retinal image has been transmitted through the visual stream, leading to a mismatch between actual location and its neural representation. It has been suggested that the human visual system compensates for neural processing delays to retrieve instantaneous position. However, such a mechanism would require a precise measure of the actual delay in order to provide a reliable position estimate. A novel illusory deformation of moving contours demonstrates that humans misjudge the spatial relationship between parts of coherently moving targets, and therefore do not perfectly account for neural delays. The size of this deformation increases with growing speed. In some subjects this illusion can be reversed by varying the luminance of individual dots; a manipulation that affects the neural delays. Our experiments agree with other evidence that the capacity of the visual system to compensate for processing delays is limited. 相似文献