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   2221篇
  免费   150篇
  国内免费   739篇
安全科学   183篇
废物处理   142篇
环保管理   167篇
综合类   1247篇
基础理论   359篇
污染及防治   747篇
评价与监测   97篇
社会与环境   96篇
灾害及防治   72篇
  2024年   4篇
  2023年   52篇
  2022年   137篇
  2021年   134篇
  2020年   81篇
  2019年   83篇
  2018年   101篇
  2017年   111篇
  2016年   105篇
  2015年   121篇
  2014年   183篇
  2013年   207篇
  2012年   164篇
  2011年   193篇
  2010年   146篇
  2009年   166篇
  2008年   138篇
  2007年   131篇
  2006年   100篇
  2005年   88篇
  2004年   76篇
  2003年   74篇
  2002年   54篇
  2001年   64篇
  2000年   65篇
  1999年   50篇
  1998年   38篇
  1997年   31篇
  1996年   33篇
  1995年   28篇
  1994年   24篇
  1993年   23篇
  1992年   17篇
  1991年   21篇
  1990年   19篇
  1989年   9篇
  1988年   12篇
  1987年   4篇
  1986年   4篇
  1985年   3篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
  1978年   3篇
  1975年   1篇
  1972年   1篇
  1970年   1篇
  1968年   1篇
排序方式: 共有3110条查询结果,搜索用时 375 毫秒
891.
892.
“教学做一体化”课程有利于理论教学与实践教学相结合,有利于高职学校长期健康的发展。“教学做一体化”教学模式是基于实际工作过程导向,以工作中典型项目任务引领,激发学生兴趣,以满足培养高等技能型人才的迫切需要。一体化课程的构建应通过项目设立、建立小组、实施、反馈等环节完成。  相似文献   
893.
本文是电驱动道路车辆动力锂离子电池的试验和要求标题下的电池组和电池系统性能试验部分。结合国标转化过程和实验室能力验证经历,在能量、容量、功率、内阻、能效和损耗等性能试验方法和要求作了具体的描述和解释。供实验室和相关产品的供需方双参考。  相似文献   
894.
Three-dimensional, coupled variably saturated flow and biogeochemical reactive transport modeling of a 2008 in situ uranium bioremediation field experiment is used to better understand the interplay of transport and biogeochemical reactions controlling uranium behavior under pulsed acetate amendment, seasonal water table variation, spatially variable physical (hydraulic conductivity, porosity) and geochemical (reactive surface area) material properties. While the simulation of the 2008 Big Rusty acetate biostimulation field experiment in Rifle, Colorado was generally consistent with behaviors identified in previous field experiments at the Rifle IFRC site, the additional process and property detail provided several new insights. A principal conclusion from this work is that uranium bioreduction is most effective when acetate, in excess of the sulfate-reducing bacteria demand, is available to the metal-reducing bacteria. The inclusion of an initially small population of slow growing sulfate-reducing bacteria identified in proteomic analyses led to an additional source of Fe(II) from the dissolution of Fe(III) minerals promoted by biogenic sulfide. The falling water table during the experiment significantly reduced the saturated thickness of the aquifer and resulted in reactants and products, as well as unmitigated uranium, in the newly unsaturated vadose zone. High permeability sandy gravel structures resulted in locally high flow rates in the vicinity of injection wells that increased acetate dilution. In downgradient locations, these structures created preferential flow paths for acetate delivery that enhanced local zones of TEAP reactivity and subsidiary reactions. Conversely, smaller transport rates associated with the lower permeability lithofacies (e.g., fine) and vadose zone were shown to limit acetate access and reaction. Once accessed by acetate, however, these same zones limited subsequent acetate dilution and provided longer residence times that resulted in higher concentrations of TEAP reaction products when terminal electron donors and acceptors were not limiting. Finally, facies-based porosity and reactive surface area variations were shown to affect aqueous uranium concentration distributions with localized effects of the fine lithofacies having the largest impact on U(VI) surface complexation. The ability to model the comprehensive biogeochemical reaction network, and spatially and temporally variable processes, properties, and conditions controlling uranium behavior during engineered bioremediation in the naturally complex Rifle IFRC subsurface system required a subsurface simulator that could use the large memory and computational performance of a massively parallel computer. In this case, the eSTOMP simulator, operating on 128 processor cores for 12h, was used to simulate the 110-day field experiment and 50 days of post-biostimulation behavior.  相似文献   
895.

Purpose  

The performance of nature reserves depends on the degree to which they represent a region's full biodiversity. Here, we conducted a study on Hainan Island, China, to assess how well Hainan's biodiversity features were captured by existing nature reserves. We also explored the driving forces behind the current protection pattern so as to provide guidelines for improving the island's conservation system.  相似文献   
896.
A study of carbonaceous aerosol was initiated in Nanchang, a city in eastern China, for the first time. Daily and diurnal (daytime and nighttime) PM2.5 (particulate matter with aerodynamic diameter < or =2.5 microm) samples were collected at an outdoor site and in three different indoor environments (common office, special printing and copying office, and student dormitory) in a campus of Nanchang University during summer 2009 (5-20 June). Daily PM10 (particulate matter with aerodynamic diameter < or =10 microm) samples were collected only at the outdoor site, whereas PM2.5 samples were collected at both indoor and outdoor sites. Loaded PM2.5 and PM10 samples were analyzed for organic and elemental carbon (OC, EC) by thermal/optical reflectance following the Interagency Monitoring of Protected Visual Environments-Advanced (IMPROVE-A) protocol. Ambient mass concentrations of PM10 and PM2.5 in Nanchang were compared with the air quality standards in China and the United States, and revealed high air pollution levels in Nanchang. PM2.5 accounted for about 70% of PM10, but the ratio of OC and EC in PM2.5 to that in PM10 was higher than 80%, which indicated that OC and EC were mainly distributed in the fine particles. The variations of carbonaceous aerosol between daytime and nighttime indicated that OC was released and formed more rapidly in daytime than in nighttime. OC/EC ratios were used to quantify secondary organic carbon (SOC). The differences in SOC and SOC/OC between daytime and nighttime were useful in interpreting the secondary formation mechanism. The results of (1) OC and EC contributions to PM2.5 at indoor sites and the outdoor site; (2) indoor-outdoor correlation of OC and EC; (3) OC-EC correlation; and (4) relative contributions of indoor and outdoor sources to indoor carbonaceous aerosol indicated that OC indoor sources existed in indoor sites, with the highest OC emissions in I2 (the special printing and copying office), and that indoor EC originated from outdoor sources. The distributions of eight carbon fractions in emissions from the printer and copier showed obviously high OC1 (>20%) and OC2 (approximately 30%), and obviously low EC1-OP (a pyrolyzed carbon fraction) (<10%), when compared with other sources.  相似文献   
897.
在两点进水的条件下采用A2/O工艺处理化工园区废水厌氧水解出水,分析配水比对A2/O工艺处理效果的影响,以及在最优配水条件下,各类A2/O工艺处理废水的实际效果。结果表明,在厌氧段-缺氧段的配水比为30%~70%时,A2/O工艺的处理效果最好。在两点进水条件下的各类A2/O工艺中,倒置A2/O和改良A2/O比常规A2/O工艺具有更好的废水处理效果。  相似文献   
898.
研究沸石、胶质芽孢杆菌(Bacillus mucilaginosus)、黑曲霉(Aspergillus Niger)、胶质芽孢杆菌与沸石联合以及黑曲霉与沸石联合对模拟废水中Fe3+的吸附等温曲线,分析它们对Fe3+模拟废水的吸附及絮凝作用。结果表明:沸石对Fe3+吸附作用符合Freundlich方程;胶质芽孢杆菌分泌含有—OH和COO-的胞外多糖,对Fe3+具有较好的吸附效果;沸石与胶质芽孢杆菌联合对模拟废水中Fe3+的处理,低浓度以沸石对Fe3+的吸附为主,加入胶质芽孢杆菌絮凝剂使吸附了Fe3+的沸石进行絮凝沉降,吸附等温曲线符合Langmuir吸附等温方程,高浓度两者共同作用使吸附量增加;黑曲霉对Fe3+的吸附符合BET吸附等温方程;沸石与黑曲霉两者共同作用对Fe3+模拟废水吸附等温曲线为直线。通过去除效果对比分析可知:胶质芽孢杆菌既有吸附又有絮凝功能;胶质芽孢杆菌絮凝剂无论是对Fe3+的吸附还是对吸附Fe3+沸石的絮凝都比黑曲霉对Fe3+处理效果好;胶质芽孢杆菌和一些非金属矿物复合处理污染废水是一种无毒、低成本环保的处理方法,本研究将为它们在工程中的应用提供实践依据。  相似文献   
899.
分点进水A/O工艺处理低碳源生活污水的脱氮性能研究   总被引:2,自引:1,他引:1  
针对低C/N比污水脱氮的难点问题,在缺氧段不同点设置进水口,采用分点进水A/O工艺处理校园生活污水.考察了在污泥回流比为100%,硝化液回流比为200%,分流比为1∶1,缺氧池水力停留时间(HRT)分别为2、2.4和3 h情况下,分点进水A/O工艺的反硝化性能,并与传统的A/O工艺进行比较.结果表明,当缺氧池的水力停留...  相似文献   
900.
以钛酸四丁酯为钛源,硫脲为掺硫前驱物,采用聚乙二醇辛基苯基醚(Triton X-100)/正己醇/环己烷/氨水的微乳液体系合成了掺硫的纳米TiO2粉体;对其结构进行了表征,以甲基橙为目标降解物考察了其光催化性能.烧结温度通过影响TiO2的晶型转变和颗粒尺寸来影响其光催化性能,随着烧结温度的升高,TiO2的光催化性能先是...  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