全文获取类型
收费全文 | 21159篇 |
免费 | 238篇 |
国内免费 | 166篇 |
专业分类
安全科学 | 655篇 |
废物处理 | 796篇 |
环保管理 | 2708篇 |
综合类 | 5770篇 |
基础理论 | 4556篇 |
环境理论 | 5篇 |
污染及防治 | 5017篇 |
评价与监测 | 1167篇 |
社会与环境 | 784篇 |
灾害及防治 | 105篇 |
出版年
2022年 | 159篇 |
2019年 | 163篇 |
2018年 | 284篇 |
2017年 | 309篇 |
2016年 | 425篇 |
2015年 | 325篇 |
2014年 | 449篇 |
2013年 | 1504篇 |
2012年 | 546篇 |
2011年 | 750篇 |
2010年 | 671篇 |
2009年 | 737篇 |
2008年 | 781篇 |
2007年 | 801篇 |
2006年 | 711篇 |
2005年 | 631篇 |
2004年 | 650篇 |
2003年 | 583篇 |
2002年 | 559篇 |
2001年 | 713篇 |
2000年 | 479篇 |
1999年 | 348篇 |
1998年 | 252篇 |
1997年 | 253篇 |
1996年 | 243篇 |
1995年 | 281篇 |
1994年 | 305篇 |
1993年 | 251篇 |
1992年 | 263篇 |
1991年 | 259篇 |
1990年 | 285篇 |
1989年 | 257篇 |
1988年 | 206篇 |
1987年 | 196篇 |
1986年 | 197篇 |
1985年 | 201篇 |
1984年 | 215篇 |
1983年 | 214篇 |
1982年 | 216篇 |
1981年 | 240篇 |
1980年 | 189篇 |
1979年 | 198篇 |
1978年 | 161篇 |
1974年 | 149篇 |
1973年 | 148篇 |
1968年 | 160篇 |
1967年 | 185篇 |
1966年 | 157篇 |
1965年 | 149篇 |
1964年 | 151篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
871.
Benefits of Bt cotton counterbalanced by secondary pests? Perceptions of ecological change in China 总被引:1,自引:0,他引:1
Jennifer H. Zhao Peter Ho Hossein Azadi 《Environmental monitoring and assessment》2011,173(1-4):985-994
In the past, scientific research has predicted a decrease in the effectiveness of Bt cotton due to the rise of secondary and other sucking pests. It is suspected that once the primary pest is brought under control, secondary pests have a chance to emerge due to the lower pesticide applications in Bt cotton cultivars. Studies on this phenomenon are scarce. This article furnishes empirical evidence that farmers in China perceive a substantial increase in secondary pests after the introduction of Bt cotton. The research is based on a survey of 1,000 randomly selected farm households in five provinces in China. We found that the reduction in pesticide use in Bt cotton cultivars is significantly lower than that reported in research elsewhere. This is consistent with the hypothesis suggested by recent studies that more pesticide sprayings are needed over time to control emerging secondary pests, such as aphids, spider mites, and lygus bugs. Apart from farmers?? perceptions of secondary pests, we also assessed their basic knowledge of Bt cotton and their perceptions of Bt cotton in terms of its strengths and shortcomings (e.g., effectiveness, productivity, price, and pesticide use) in comparison with non-transgenic cotton. 相似文献
872.
Heather M. Renner Joel H. Reynolds Michelle Sims Martin Renner 《Environmental monitoring and assessment》2011,174(1-4):665-679
This study assessed metals in water and different tissues of Labeo rohita and the impact of these metals on DNA and proteins as biomarkers of gills and muscles of these fish from three different polluted sites (reference or low = KW, medium = CH and high = SK) of the Indus River, Pakistan. The Mn, Pb, Cu, Zn, Hg, and Cr levels in water, gills, liver, muscles, and skin of these fish were compared with the international permissible levels. All metals except Pb and Hg in water were within the acceptable limits of drinking water. In contrast, the Mn, Hg, and Cr levels in the fish tissues were higher than their permissible limits for fish as a human food. Here, the gills contained higher metals than the other tissues. Different patterns of biomarkers were found in fish from these sites. While the gills did not show four protein bands (55, 30, 18.4, and 16.4 kDa), the muscles showed four new protein bands (100, 85, 45, and 20 kDa) for fish from the medium and high polluted sites as compared to the reference or low polluted site. The fish from the CH and SK sites of the Indus River contained low molecular weight DNA in their gills but high molecular weight DNA in their muscles when compared with the KW site. This study suggests that the proteins and DNA profiles of L. rohita could be used as biomarkers to assess the impact of potential environmental stressors such as metals on the freshwater systems. 相似文献
873.
Polycyclic aromatic hydrocarbons in effluents from wastewater treatment plants and receiving streams in Tianjin, China 总被引:1,自引:0,他引:1
Weixiao Qi Huijuan Liu Jiuhui Qu Chengzhi Hu Huachun Lan Michael Berg Huimin Ren Wei Xu 《Environmental monitoring and assessment》2011,177(1-4):467-480
Surface water, suspended particulate matter, pore water, and sediment samples were collected and analyzed for polycyclic aromatic hydrocarbons (PAHs) in Yongding New River, South Drainage Canal and North Drainage Canal, which receive most of wastewater from industrial city of Tianjin. PAH concentrations in effluent samples of wastewater treatment plants (WTP) discharging into the South Drainage Canal and North Drainage Canal were quantified for the first time. The results showed that the discharge of the WTPs recently only contributed to the PAH contamination in the canals near the outlets of the WTPs. PAH levels in sediments of the streams were greatly higher than those in soils by riverbank probably due to receiving large amounts of untreated wastewater. Unusually high benz[a] anthracene concentration strongly influenced the seasonal and spatial variation of total PAH concentrations in South Drainage Canal. Paired samples t test of ??Nap, Fl, Phe, Fluo and ??Nap, Phe, Fluo, Chry concentrations, which were dominant components in the air samples from non-heating and heating season, respectively, in the suspended particulate matters from the streams showed that PAH source from air deposition was more important for Yongding New River than that for South Drainage Canal and North Drainage Canal. Source apportionment based on PAH profiles indicated that coal combustion was the major PAH contamination source, and coke oven sources and wood combustion also contributed to the PAH contamination of the streams. This was further indicated by organic petrography analysis. 相似文献
874.
This paper sub-samples four 35 year water quality time series to consider the potential influence of short-term hydrological variability on process inference derived from short-term monitoring data. The data comprise two time series for nitrate (NO(3)-N) and two for DOC (using water colour as a surrogate). The four catchments were selected not only because of their long records, but also because the four catchments are very different: upland and lowland, agricultural and non-agricultural. Multiple linear regression is used to identify the trend and effects of rainfall and hydrological 'memory effects' over the full 35 years, and then a moving-window technique is used to subsample the series, using window widths of between 6 and 20 years. The results suggest that analyses of periods between six and eleven years are more influenced by local hydrological variability and therefore provide misleading results about long-term trends, whereas periods of longer than twelve years tend to be more representative of underlying system behaviour. This is significant: if such methods for analysing monitoring data were used to validate changes in catchment management, a monitoring period of less than 12 years might be insufficient to demonstrate change in the underlying system. 相似文献
875.
876.
The Australian buprestid beetle Merimna atrata (Coleoptera: Buprestidae) approaches forest fires because its larvae develop in freshly burnt wood. So far nothing is known
about possible sensory systems enabling the beetles to detect fires and to cope with the thermal environment close to the
flames. We found that M. atrata has two pairs of infrared (IR) organs on the ventrolateral sides of the abdomen. Each IR organ consists of a specialized
IR-absorbing area which is innervated by one thermosensitive multipolar neuron. The primary dendritic branches ramify into
more than 800 closely packed terminal endings which contain a large number of mitochondria. We called the special morphology
of the dendritic region a terminal dendritic mass. The type of IR receptor found in M. atrata is unique in insects and can best be compared with the IR organs of boid snakes.
Received: 14 August 2000 / Accepted in revised form: 18 October 2000 相似文献
877.
Self-diffusion coefficients were studied for the highly polar liquid N-methylformamide at pressures up to 200 MPa between the melting pressure curves and 420 K by the spin-echo method. N-Methylformamide exists as a mixture of two conformers in the neat liquid. These conformers have large differences at lower
temperatures in their dynamic and structural properties. The self-diffusion coefficient of the cis-conformer being 17% lower than that of the trans-conformer at the same T and p. This is the first observation of such an effect. The experimental study is supported by Monte Carlo (MC) calculations which
show that the first neighbors around a cis conformer are arranged differently than in an all trans liquid. The difference leads in the simulations to a much lower dielectric constant for the trans-cis mixture and might also explain the retardation of diffusion for the cis conformer.
Received: 15 November 1999 / Accepted in revised form: 28 February 2000 相似文献
878.
The GPS recorder consists of a GPS receiver board, a logging facility, an antenna, a power supply, a DC-DC converter and
a casing. Currently, it has a weight of 33 g. The recorder works reliably with a sampling rate of 1/s and with an operation
time of about 3 h, providing time-indexed data on geographic positions and ground speed. The data are downloaded when the
animal is recaptured. Prototypes were tested on homing pigeons. The records of complete flight paths with surprising details
illustrate the potential of this new method that can be used on a variety of medium-sized and large vertebrates.
Received: 2 February 2000 / Accepted in revised form: 17 April 2000 相似文献
879.
High-performance permanent magnets 总被引:2,自引:0,他引:2
High-performance permanent magnets (pms) are based on compounds with outstanding intrinsic magnetic properties as well as
on optimized microstructures and alloy compositions. The most powerful pm materials at present are RE–TM intermetallic alloys
which derive their exceptional magnetic properties from the favourable combination of rare earth metals (RE=Nd, Pr, Sm) with
transition metals (TM=Fe, Co), in particular magnets based on (Nd,Pr)2Fe14B and Sm2(Co,Cu,Fe,Zr)17. Their development during the last 20 years has involved a dramatic improvement in their performance by a factor of >15 compared
with conventional ferrite pms therefore contributing positively to the ever-increasing demand for pms in many (including new)
application fields, to the extent that RE–TM pms now account for nearly half of the worldwide market. This review article
first gives a brief introduction to the basics of ferromagnetism to confer an insight into the variety of (permanent) magnets,
their manufacture and application fields. We then examine the rather complex relationship between the microstructure and the
magnetic properties for the two highest-performance and most promising pm materials mentioned. By using numerical micromagnetic
simulations on the basis of the Finite Element technique the correlation can be quantitatively predicted, thus providing a
powerful tool for the further development of optimized high-performance pms. 相似文献
880.
针对目前国内外垃圾渗沥液处理中存在的问题,采用电化学氧化与上流式厌氧污泥床(UASB)相结合,研究建立了对香港垃圾渗沥液的二步法处理工艺.本文着重探讨了电化学间接氧化去除渗沥液中氨氮的反应机制及主要影响因素,并通过实验找出了最佳的操作条件:入水初始 pH值为9.0;流速为0.01-0.10cm/s;CI加入量2000mg/L;电流密度 32.3mA/cm2.在此条件下,经过 6h电解后,UASB反应器出水中NH-N和COD的去除率分别达到100%和87%.对该电化学氧化过程的运行成本进行了评估. 相似文献