全文获取类型
收费全文 | 3353篇 |
免费 | 458篇 |
国内免费 | 1470篇 |
专业分类
安全科学 | 809篇 |
废物处理 | 105篇 |
环保管理 | 293篇 |
综合类 | 2610篇 |
基础理论 | 647篇 |
环境理论 | 1篇 |
污染及防治 | 487篇 |
评价与监测 | 183篇 |
社会与环境 | 78篇 |
灾害及防治 | 68篇 |
出版年
2024年 | 6篇 |
2023年 | 77篇 |
2022年 | 163篇 |
2021年 | 163篇 |
2020年 | 180篇 |
2019年 | 157篇 |
2018年 | 181篇 |
2017年 | 167篇 |
2016年 | 175篇 |
2015年 | 193篇 |
2014年 | 167篇 |
2013年 | 326篇 |
2012年 | 295篇 |
2011年 | 255篇 |
2010年 | 211篇 |
2009年 | 249篇 |
2008年 | 227篇 |
2007年 | 283篇 |
2006年 | 298篇 |
2005年 | 244篇 |
2004年 | 226篇 |
2003年 | 155篇 |
2002年 | 125篇 |
2001年 | 126篇 |
2000年 | 117篇 |
1999年 | 84篇 |
1998年 | 69篇 |
1997年 | 70篇 |
1996年 | 59篇 |
1995年 | 50篇 |
1994年 | 23篇 |
1993年 | 36篇 |
1992年 | 26篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 30篇 |
1970年 | 1篇 |
排序方式: 共有5281条查询结果,搜索用时 125 毫秒
991.
992.
993.
Cellulose degrading bacteria were isolated from the intestinal fluid of the silver cricket Lepisma Sp. and a culture was developed anoxigenically in the cellulose degrading medium following standard laboratory techniques. The cellulolytic activity of the microbe was examined in a broth culture using Whatman 42 filter paper as the source of insoluble cellulose. Activity was measured spectrophotometrically (620nm) following Anthrone reaction of the culture filtrate and the sugar produced was quantified as a factor of time. The pH optimum was found to be between 7 and 8. Temperature profile optimum was between 30–37°C.The microbes appeared as white colonies on a solid medium. Morphologically the bacterium is a gram-positive nonspore forming rod which was tentatively identified as a new strain of Cellulomonas sp. 相似文献
994.
Sylvie Pouteau 《Journal of Agricultural and Environmental Ethics》2000,13(3-4):273-291
The concept of substantial equivalence,introduced for the risk assessment of geneticallymodified (GM) food, is a reducing concept because itignores the context in which these products have beenproduced and brought to the consumer at the end of thefood chain. Food quality cannot be restricted to meresubstance and food acts on human beings not only atthe level of nutrition but also through theirrelationship to environment and society. To make thiscontext explicit, I will introduce an ``equivalencescale' for the evaluation of food chains (GM or notGM). By contrast with substantial equivalence, whichinvolves mainly quantitative, analytical methods ofevaluation, ``qualitative equivalence' refers to ``less'or non-substantial factors that require new methodsof evaluation based on qualitative principles.``Ethical equivalence' refers to factors that show themoral value contained in food products. To analyze thedifferent levels at which ethics is needed in foodchains, I will use the French principles: ``Liberty,Equality, Fraternity,' or freedom, equality,solidarity, and add a fourth principle:sustainability. Sustainability, solidarity, andfreedom can be applied to the evaluation ofenvironmental, socio-economic, and socio-culturalethical equivalence, respectively. Equality refers tojustice and should operate so as to guarantee thatsustainability, solidarity, and freedom are satisfied.I suggest that ethics can provide a basis for arenewal of the food chain concept. Besides QualityAssurance, it is now essential to develop an ``EthicalAssurance' and this equivalence scale could provide abasis to set up ``Ethical Assurance Standards' (EAS)for food chains. 相似文献
995.
Jason S. Lee Belinda L. Daniels David T. Eberiel Richard E. Farrell 《Journal of Polymers and the Environment》2000,8(2):81-89
Soil retrieval, processing and storage procedures can have a profound effect on soil microorganisms. In particular, changes in soil microbial populations may adversely affect the biological activity of a soil and drastically alter the soil's potential to mineralize added substrates. The effects of cold storage on the biodegradation of a series of test polymers was investigated using two soils—a synthetic soil mix (SM-L8) and a field soil (Bridgehampton silt loam) from Rhode Island (RI-1). Biodegradation tests were conducted using freshly prepared/collected soil and again following storage at 4°C for 3 to 8 months. Prior to each biodegradation test, the soils were incubated at 60% water-holding capacity (WHC) and 25°C to rejuvenate the microbial populations; the soils were incubated for periods of 48 h (freshly collected soil) or 25 days (soils stored at 4°C). Soil microbial populations were assessed by enumerating different segments of the population on agar plates containing different selective media. Mineralization of the test polymers (cellulose, poly-3-hydroxybutyrate, and starch acetate, d.s. 1.5) was monitored using standard respirometric techniques. Our results demonstrated that cold storage had a generally negative effect on the soil microbial populations themselves but that its effect on the capacity of the soil microorganisms to degrade the test polymers varied between soils and polymer type. Whereas cold storage resulted in dramatic shifts in the community structure of the soil microbial populations, substantial restoration of these populations was possible by first conditioning the soils at 60% WHC and ambient temperatures for 25 days. Likewise, although the effects of cold storage on polymer mineralization varied with the test polymer and soil, these effects could be largely offset by including an initial 25-day stabilization period in the test. 相似文献
996.
论述了岩体声发射技术的基本原理,介绍了其在采矿工程中的若干应用成果:地应力测量、高应力区圈定、冒顶预测预报、稳定性评价. 相似文献
997.
Ni2+改性的Cu-ZSM-5催化分解NO的性能 总被引:6,自引:1,他引:5
研究 Ni2+改性的 Cu- ZSM-5催化剂在无氧和有氧气氛下的 NO分解反应性能 ,考察 Ni2+的加入量及加入方式对 Cu-ZSM-5催化剂 NO分解活性的影响 .结果表明 ,先交换适量 Ni2+再交换 Cu2+的 Ni-Cu-ZSM-5催化剂较单组分 Cu-ZSM-5催化剂有较高的高温 (500℃~600℃) NO分解活性 .在含 5.5% O2 的反应气氛中 ,Ni-Cu-ZSM-5在 500℃下的 NO分解率较之 Cu-ZSM-5高出约 20% ,Ni2+的引入显著提高了催化剂的抗氧活性 .就 Ni2+对 Cu-ZSM-5催化剂的可能改性机制进行了讨论 . 相似文献
998.
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
999.
采用环境库兹涅茨曲线模型模拟江苏省1991年以来经济增长和工业污染之间的动态演进关系,应用分解分析法对2001~2004年间部分污染物排放变化的成因进行了定量分析.结果表明,江苏省工业污染排放量和人均GDP之间的关系类型有U型、倒U型、U型+倒U型以及N型4种,目前大部分污染物呈增长态势.将污染物排放变化的成因分为规模效应、结构效应和广义技术效应3类,结果显示,规模效应促进污染物排放量增加,结构效应和广义技术效应的作用方向不确定,但广义技术效应对污染物控制有决定性作用,强力的环境政策和管理措施能够有效地控制污染物排放. 相似文献
1000.
2004年9月~2005年9月对内蒙古锡林河流域4种草地类型的土壤呼吸速率及相关水热因子进行了野外测定,应用2种数学模型和不同温度指标对草地土壤呼吸的温度敏感性问题进行了探讨.结果表明,Van′tHoff模型对温度变化较为敏感,显示出冬季的Q10值明显大于夏季的特征,应用Arrhenius模型求算的不同季节的Q10值变化不大.在>5℃时,Q10值的变动范围,Van′tHoff模型为1.60~2.03,Arrhenius模型为1.48~1.67,略高于全球平均值;2种模型均对水分的变化比较敏感,表现为Q10值随土壤水分的降低而升高的趋势. 相似文献