首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3745篇
  免费   38篇
  国内免费   198篇
安全科学   113篇
废物处理   218篇
环保管理   351篇
综合类   709篇
基础理论   837篇
环境理论   3篇
污染及防治   1274篇
评价与监测   260篇
社会与环境   199篇
灾害及防治   17篇
  2023年   21篇
  2022年   80篇
  2021年   60篇
  2020年   33篇
  2019年   44篇
  2018年   125篇
  2017年   63篇
  2016年   97篇
  2015年   96篇
  2014年   105篇
  2013年   317篇
  2012年   112篇
  2011年   178篇
  2010年   158篇
  2009年   166篇
  2008年   180篇
  2007年   203篇
  2006年   162篇
  2005年   130篇
  2004年   152篇
  2003年   153篇
  2002年   126篇
  2001年   248篇
  2000年   144篇
  1999年   77篇
  1998年   43篇
  1997年   51篇
  1996年   34篇
  1995年   45篇
  1994年   45篇
  1993年   44篇
  1992年   33篇
  1991年   39篇
  1990年   30篇
  1989年   34篇
  1988年   22篇
  1987年   17篇
  1986年   18篇
  1985年   18篇
  1984年   19篇
  1983年   24篇
  1982年   25篇
  1981年   21篇
  1980年   15篇
  1979年   13篇
  1978年   15篇
  1977年   9篇
  1975年   12篇
  1973年   9篇
  1972年   11篇
排序方式: 共有3981条查询结果,搜索用时 0 毫秒
921.
Polylactide (PLA)/polymethylmethacrylate (PMMA)/α-cellulose composites were fabricated using a twin-screw extruder. During fabrication, α-cellulose short fibres were incorporated for improving the toughness of the brittle PLA and a chain extender was used for reducing PLA hydrolysis. Highly transparent PLA and PMMA were blended to obtain miscible and transparent blends. For evaluating the performance of the PLA/PMMA/α-cellulose composites, a series of measurements, including tensile and Izod impact tests, light transmission and haze measurements, thermomechanical analysis, and determination of isothermal crystallisation behaviour, was conducted. Adding the chain extender considerably reduced the occurrence of hydrolytic degradation. Both the chain extender and α-cellulose short fibres increased the elongation at break and Izod impact strength of the composites. Compared with the neat PLA, including 1.0 wt% α-cellulose short fibres increased the elongation at break and Izod impact strength of the composite PLA by approximately 211 and 219 %, respectively. According to the observed mechanical performance, the optimal blending ratios for PLA and PMMA were between 90:10 and 80:20. The total light transmittance of the composites was as high as 91 %, indicating that the PLA/PMMA blend was highly miscible. The haze value of the PLA/PMMA/α-cellulose composites was lower than 32 %. Incorporating cellulose short fibres increased the number of crystallisation sites and crystallinity of the PLA/PMMA/α-cellulose composites while reducing the spherulite dimensions.  相似文献   
922.
923.
The nonferrous metal industry (NMI) of China consumes large amounts of energy and associated emissions of carbon dioxide (CO 2) are very high. Actions to reduce CO 2 emissions and energy consumption are warranted. This study aims to analyze current China NMI trends of CO 2 emissions and energy consumption including the underlying regional driver characteristics. We analyze the changes of CO 2 emissions in the NMI based on the Logarithmic Mean Divisia Index (LMDI) method from 2000 to 2011. Then, a classification system is used to study the regional differences in emission changes from the NMI. The results show that the emissions of the Chinese NMI increased rapidly at an average annual growth rate of 31 million metric tons. The economic scale and energy intensity are the main driving factors responsible for the change in the emissions, while carbon emission coefficients make only a small contribution toward decreasing the emissions, and the energy structure has a volatile effect. Emissions and energy intensity of 29 China provinces were divided into five categories. The change in the trend of each region is indicated in this paper. Hebei is one of the provinces that achieved the best performance, and Chongqing achieved the worst performance among all of the regions. The analysis suggests that the main emphasis of CO 2 emission mitigation should be focused on controlling the economic scale and improving the energy intensity. Developing the use of clean energy technologies and policies in both the NMI and power industries is important.  相似文献   
924.
This paper aims to develop quantitative insights based on measured deflagration parameters of hybrid mixtures of activated carbon (AC) dust and hydrogen (H2) gas in air. The generated experimental evidence is used to reject the claim of the null hypothesis (H0) that severity of deflagrations of H2/air mixtures always bound the severity of deflagrations of heterogenous combustible mixtures of AC dust/H2/air containing the same H2 concentrations as in the H2/air binaries. The core insights of this investigation show that the maximum deflagration pressure rise (ΔPMAX) and maximum rate of pressure rise ((dP/dt)MAX) of this hybrid mixture are greater than those corresponding to deflagrations of H2/air mixtures for all the dust and H2 concentrations being examined. The deflagration severity indices (KSt and ES) of the hybrid mixture containing 29 mol% H2 are found to be greater than those of the H2/air mixture containing 29 mol% H2. Also, the minimum explosible concentration (MEC) of the hybrid mixture is lower than that of the AC dust in air only. The insights gained should lead to better realization of the severity of a postulated safety-significant accident scenario associated with on-board cryoadsorption H2 storage systems for fuel-cell (FC) powered light-duty vehicles. The identified insights could also be relevant to other industrial processes where combustible dusts are generated in the vicinity of solvent vapors. Moreover, these insights should be useful for supporting quantitative risk assessment (QRA) of on-board H2 storage systems, designing improved safety measures for cryoadsorption H2 storage tanks, and guiding H2 safety standards and transportation regulations.  相似文献   
925.
The most important tool for testing seat-systems in rear impacts is a crash test dummy. However, investigators have noted limitations of the most commonly used dummy, the Hybrid III. The BioRID I is a step closer to a biofidelic crash test dummy, but it is not user-friendly and the straightening of the thoracic spine kyphosis is smaller than that 220of humans. To reduce these problems, a new BioRID prototype was developed, the P3. It has new neck muscle substitutes, a softer thoracic spine and a softer rubber torso than does the BioRID I.

The BioRID P3 was compared with volunteer test data in a rigid and a standard seal without head restraints. The dummy kinematic performance, pressure distribution between subject and seatback, neck loads and accelerations were compared with those of ten volunteers and a Hybrid III. The BioRID P3 provided repeatable test results and its response was very similar to that of the average volunteer in rear impacts at Δv = 9 km/h.  相似文献   
926.
Lake Baikal is the deepest and oldest freshwater lake in the world containing about 20% of the world's fresh water. The present state of its contamination with organic pollutants was studied during 1997–1998 by collecting samples of sediments, phytoplankton, Zooplankton, sponges, aquatic plants, algae, muscles of various fish species, eggs of various birds and blubber of seals. Samples were prepared and analysed using GC‐MS for semivolatile priority pollutants on the US EPA list, for the presence of organochlorine pesticides and for PCBs. The results showed that there was pronounced bioaccumulation of persistent organochlorine compounds along the trophic chain, leading to substantial residues of organochlorine compounds in seals (e.g. 0.87–25.3 ppm of p,p'‐DDT in blubber).  相似文献   
927.
Individual based model of slug population and spatial dynamics   总被引:1,自引:0,他引:1  
The slug, Deroceras reticulatum, is one of the most important pests of agricultural and horticultural crops in UK and Europe. In this paper, a spatially explicit individual based model (IbM) is developed to study the dynamics of a population of D. reticulatum. The IbM establishes a virtual field within which slug spatial dynamics and changes in abundance were simulated. The strong dependence of slug behaviour on environmental conditions is built into the model, which is based upon previous work on the environmental dependence of slug population dynamics. The simulation results show that the IbM described well changes in the slug population. The IbM proved capable of describing slug populations over 3.5 years, including the presence, magnitude and duration of D. reticulatum population crashes within this period. Moreover, the model was capable of reproducing slug population dynamics at two sites, with distinct weather and some 100 km apart, with minor changes in initialisation values but no change in model structure and parameter values. A study of field heterogeneity, which might simulate various field designs, indicated the importance of spatial structuring to slug population dynamics and the utility of the IbM for simulating a range of potential spatial management treatments for slug control to maximise crop yield. This IbM system performs well and is currently being used as part of an integrated approach to predict slug population dynamics and control in the UK.  相似文献   
928.
Phylogenetic relationships among vestimentiferans in the family Lamellibrachiidae collected from ten sites in the western Pacific were analyzed on the basis of the nucleotide sequence of part of a mitochondrial gene for cytochrome oxidase I. The 103 individuals analyzed were tentatively classified into five species: namely, Lamellibrachia satsuma, three tentative species inhabiting Japanese waters and one tentative species from the Manus Basin. Phylogenetic analysis of the four tentative species, L. satsuma, and two lamellibrachiids, whose sequences had been reported previously, namely L. columna from the Lau Basin and L. barhami from the Oregon Margin and the Middle Valley, revealed that the lamellibrachiids from Japanese waters were not monophyletic. While two tentative species from Japanese waters and L. columna formed a monophyletic group, the other tentative species from Japanese waters was closely related to the tentative species from the Manus Basin. L. satsuma was shown to be phylogenetically distinct from other lamellibrachiids of the western Pacific. A lamellibrachiid that had been collected from the Nikko Seamount was also demonstrated to be L. sastuma.  相似文献   
929.
Abstract

This study introduces the principles of KMG's (Kaoshiung Municipal Government) dealing with the non-poisonous urban and industrial waste through reclamation of shore land in reinforcing a sense of coastal protection and land development in Tai-Lin-Pu coastal area, southern Taiwan.

Through a series of experimental studies, we found that substitutes of coarse aggregate with a broad spectrum of integrating slag powder, fly ash, and cementitious material can be obtained with a benefit up to 80% saving of cement. the integrated aggregates from the non-poisonous industrial wastes were subsequently made into armour units and used in the field tests at Tai-Lin-Pu coastal area, where the shorelines are seriously eroded. After being subjected to several severe typhoon advents, the results showed that the waste-made units used as the protection breakwater, together with construction wastes and excavated soil as the filling material, prove to be an effective practice in utilizing recycled urban waste to reclaim erosive shore lands. Moreover, this study also demonstrates that through detailed analysis of the waste characteristics, scrap material could be turned into valuable construction aggregates, and highlights the value of non-poisonous urban and industrial waste as a alternative resource for the shore protection engineering.  相似文献   
930.
粤港澳地区大气中有机污染物初步研究   总被引:27,自引:5,他引:27  
用Tekmar多填层吸附管连接TMP-1500空气采样采集VOCs样,然后在Tekmar6032/3000吹扫捕集系统与GC/MSD联用仪上分析,用TH-1000L型大量采样器收集TSP气溶胶样,TSP滤膜经抽提分离后,烷径和芳烃进行GC/MSD分析,了广州,香港和澳门地区大气 有机物和气溶胶可溶有机物的与成因。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号