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   4412篇
  免费   207篇
  国内免费   1777篇
安全科学   309篇
废物处理   283篇
环保管理   342篇
综合类   2481篇
基础理论   747篇
污染及防治   1705篇
评价与监测   163篇
社会与环境   154篇
灾害及防治   212篇
  2024年   10篇
  2023年   73篇
  2022年   236篇
  2021年   182篇
  2020年   130篇
  2019年   147篇
  2018年   153篇
  2017年   238篇
  2016年   286篇
  2015年   296篇
  2014年   319篇
  2013年   485篇
  2012年   364篇
  2011年   433篇
  2010年   278篇
  2009年   269篇
  2008年   351篇
  2007年   273篇
  2006年   258篇
  2005年   165篇
  2004年   123篇
  2003年   171篇
  2002年   135篇
  2001年   104篇
  2000年   129篇
  1999年   114篇
  1998年   104篇
  1997年   115篇
  1996年   82篇
  1995年   86篇
  1994年   61篇
  1993年   61篇
  1992年   56篇
  1991年   44篇
  1990年   27篇
  1989年   9篇
  1988年   6篇
  1987年   6篇
  1986年   5篇
  1985年   2篇
  1984年   3篇
  1983年   3篇
  1982年   3篇
  1981年   1篇
排序方式: 共有6396条查询结果,搜索用时 15 毫秒
31.
采用膜过滤-气相色谱法测定涂料中的苯系物、环己酮和甲苯二异氰酸酯(TD I)。用7种规格的石英毛细管色谱柱对混合标准溶液和涂料试样进行了分析实验,实验结果表明,不同属性的涂料试样添加固定量的正十四烷作内标物,经膜过滤净化后,苯系物、环己酮和TD I可采用DB-1-3或DB-1-2色谱柱同时分离并测定。测试数据经多级校准曲线处理后涂料试样中苯系物、环己酮和TD I的加标回收率为98.6%~101.8%,各组分分析结果的变异系数均小于2.0%,检出限均小于1.50×10^-5g。  相似文献   
32.
33.
Determined the contribution of root derived CO2 efflux to total CO2 efflux (including root and non-root derived CO2 efflux) is import to grope the mechanism of CO2 efflux, however, becaused of ‘rhizoshere priming effect’ (RPE), it is difficult to achieve in practice. In this study, we attempted to estimate the RPE via comparing basal soil respiration (Rb) achieved by two different methods namely, y-intercept regression and direct bare plot approach in an arid cotton field, central Asia. On the basis of the y-intercept of linear regressions between below-ground respiration (BGR) and root biomass, Rb was indirectly calculated. Comparing with the first approach, the second approach involved direct measurements of soil respiration from bare plots. Rb estimated by y-intercept method contained the component of RPE whereas direct bare plot did not. We found that RPE showed a phenological trend with highest value in flowering stage at 0.145 g CO2 m–2 h–1 and lowest at budding stage (0.007 g CO2 m–2 s–1), even after the data had been corrected for the influence of soil temperature. We concluded that RPE needed to be considered when Rb was estimated by y-intercept approach.  相似文献   
34.
The only joint effort area of provincial and municipal governments resides in Guangdong Province and Shenzhen City in China’s carbon emission trading system (ETS) pilots, which characterize the national carbon ETS plots. The present study on the operating experience from this area has important reference value for the national carbon ETS. Analysis and comparison of the key elements show many differences in coverage, total allowance, allowance allocation, and MRV mechanism between Guangdong and Shenzhen carbon ETS. The present study provides the following explanation: (1) the design characteristics of carbon ETS (e.g. coverage, total quotas, the allocation, and MRV mechanism) depend on the local geographical conditions and policy goals. The differences of economic structure in Guangdong Province and Shenzhen City result in different coverage, which then result in differences in other management elements. (2) The operating state of the carbon market is affected by overall design of carbon ETS: in the case of tighter total allowance, lower proportion of China Certified Emission Reductions, and harsher punishment, the carbon market is relatively active, which intends to produce carbon financial market. Based on deep analysis of operation characteristics of carbon ETS in Guangdong and Shenzhen, the present study suggests that (1) the allowance should be allocated freely at the beginning stage and then gradually transited to the voluntary paid auction; (2) the allowances assigned to companies shall be linked up with their energy-saving objectives; (3) the output fluctuations and economic influence on the allowance allocation should be properly handled to maintain the fairness and consistence of allowance allocation standards; (4) stable public expectation is one of the key elements to maintain the regular operation of carbon ETS; (5) constrained carbon emission behavior outside ETS can contribute to social justice; and (6) the improvement of professional skills of relevant personnel in the enterprise and independent third party can enhance carbon emissions data reliability.  相似文献   
35.
采用电称冲击低压系统(ELPI)将无烟室和吸烟室内的空气颗粒物(0.03~10.00 μm)分成12级,对其粒子数和质量浓度进行测定.结果表明,吸烟室PM0.03~10.00的日平均粒子数和质量浓度分别是无烟室的1.50、1.13倍.烟草烟雾对室内颗粒物粒子数的影响集中在0.03~1.00 μm粒径段;对室内颗粒物质量浓度的影响表现为双模态结构,峰值分别在0.20~0.70、5.00~8.20 μm粒径段.烟草烟雾颗粒物的粒子数和质量浓度随烟雾消散时间的增加而减少,粒径越小,减小的越明显;烟草烟雾颗粒物在室内消散缓慢,会在长时间内造成影响,应引起足够关注.  相似文献   
36.
双水相气浮浮选光度法处理环境水样中痕量土霉素残留物   总被引:1,自引:0,他引:1  
建立了一种新型分离方法--双水相气浮浮选光度法,使其处理环境水样中痕量土霉紊(OTC)残留物,研究了其工作原理,并用高效液相色谱法对该方法的可靠性进行了验证.利用自制的双水相气浮浮选装置,选择四氢呋喃作亲水有机溶剂、质量分数为10%的NaCl溶液作分相剂,NaOH溶液调节pH,将Cu2+与OTC形成的疏水配合物浮选至有机相,实现OTC与水样分离.浮选完毕后,经紫外-可见分光光度法分析,线性回归方程为A=1.532×105c+0.1230(其中:A为有机相的吸光度;c为水样的OTC摩尔浓度,mol/L),相关系数为0.9998,该方法的线性范围为4.8×10-7~7.3×10-5 mol/L,OTC加标回收率为99.5%~100.1%.  相似文献   
37.
毛细屏障作为核废物处置库顶盖的工程屏障之一,已经在国内外得到了广泛应用.采用箱体实验方法,研究了非饱和稳定流条件下粗石英砂层厚度和倾角对毛细屏障效应的影响.结果表明,随着粗石英砂层厚度的增大,水分的相对绕流量增大,毛细屏障效应增强;随着粗石英砂层倾角的增大,其表面积水减少,水的横向流动能力增强,毛细屏障效应增强.  相似文献   
38.
Following the intent of the National Environmental Policy Act of 1969, many states have adopted policies and procedures directing state agencies and local government units to evaluate the potential environmental impacts of development projects prior to their undertaking. In contrast to a rich literature on federal requirements, current understanding of state environmental review is narrowly focused and outdated. This paper seeks to provide information on the landscape of state environmental review policy frameworks. The paper identifies 37 states with formal environmental review requirements through a document review of state statutes, administrative rules and agency-prepared materials, and confirms this finding through a survey of state administrators. A two-tier classification is used to distinguish states based on the approach taken to address environmental review needs and the scope and depth of relevant policies and procedures implemented. This paper also provides a discussion of policy and programme attributes that may contribute to effective practice, and of the potential for adopting relevant legislation in states where environmental review is currently lacking.  相似文献   
39.
光合细菌强化二级流化床工艺处理焦化废水的研究   总被引:1,自引:0,他引:1  
采用厌氧酸化加二级流化床组合工艺处理焦化废水。一级反应器内光合细菌与兼性厌氧菌处于共生状态,二级反应器内光合细菌与亚硝酸细菌处于共生状态。一级反应器内光合细菌有充分的小分子有机酸可降解并形成二次酸化,在二级反应器内完成进一步降解。结合反应条件:温度,pH,DO和基质浓度等,将二级反应器内硝化反应控制在亚硝化阶段,有效地保证了废水中碳源的利用。稳定运行了60 d,结果显示,出水COD和NH3-N浓度分别为105~135 mg/L和14~20 mg/L,去除率分别稳定在90.3%~92.5%和92%~95%。TN去除率稳定在83%~86%。酚、氰化物和BOD5的去除率均在95%以上。  相似文献   
40.
微生物絮凝剂改善城市污水厂浓缩污泥脱水性能的研究   总被引:7,自引:2,他引:5  
采用酱油曲霉(Aspergillus sojae)产生的微生物絮凝剂(MBF)作为污泥絮凝脱水剂,对城市污水处理厂浓缩污泥进行调理,确定该絮凝剂对浓缩污泥脱水的处理工艺参数为:微生物絮凝液最佳投加体积为6%~8%(体积比),发挥絮凝作用的最适污泥温度为28~32℃,最适pH为6~7。经微生物絮凝剂调理的污泥在3 000 r/min离心9 min,污泥脱水率高达82.7%,滤饼含水率降低至77.3%,污泥脱水后体积减至原来的1/5左右。  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