全文获取类型
收费全文 | 14341篇 |
免费 | 1493篇 |
国内免费 | 1763篇 |
专业分类
安全科学 | 6337篇 |
废物处理 | 143篇 |
环保管理 | 1629篇 |
综合类 | 5339篇 |
基础理论 | 1501篇 |
环境理论 | 54篇 |
污染及防治 | 545篇 |
评价与监测 | 441篇 |
社会与环境 | 962篇 |
灾害及防治 | 646篇 |
出版年
2024年 | 65篇 |
2023年 | 272篇 |
2022年 | 497篇 |
2021年 | 626篇 |
2020年 | 655篇 |
2019年 | 642篇 |
2018年 | 442篇 |
2017年 | 788篇 |
2016年 | 692篇 |
2015年 | 879篇 |
2014年 | 551篇 |
2013年 | 790篇 |
2012年 | 1088篇 |
2011年 | 1169篇 |
2010年 | 925篇 |
2009年 | 966篇 |
2008年 | 637篇 |
2007年 | 886篇 |
2006年 | 952篇 |
2005年 | 682篇 |
2004年 | 519篇 |
2003年 | 500篇 |
2002年 | 429篇 |
2001年 | 311篇 |
2000年 | 303篇 |
1999年 | 213篇 |
1998年 | 186篇 |
1997年 | 155篇 |
1996年 | 132篇 |
1995年 | 121篇 |
1994年 | 96篇 |
1993年 | 88篇 |
1992年 | 63篇 |
1991年 | 44篇 |
1990年 | 31篇 |
1989年 | 30篇 |
1988年 | 25篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1982年 | 4篇 |
1981年 | 13篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1972年 | 4篇 |
1971年 | 11篇 |
1970年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
421.
422.
介绍了如何在国家级生态示范区的可持续发展评估中运用灰色系统理论构建定量评估系统模型,并给出了关系型指标表、量纲模型、多元灰色预测模型和发展系数模型以及应用实例.根据该评估系统模型所开发的灰色评估系统由数学模型、计算机软件和硬件组成,可自动完成量纲统一、指标预测、相关分析、综合评估和趋势图表的运算和输出. 相似文献
423.
利用GPS-RTK技术进行既有线曲线整正测量研究 总被引:1,自引:1,他引:1
既有线曲线整正测量是铁路既有线提速改造和工务部门大修设计的主要任务之一。需要改造的既有铁路一般均为繁忙干线,并行车密度较高。传统的测量方法是将测量仪器安置在线路上,这样不仅在作业过程中受行车干扰,作业效率也不够高,而曲线地段通视条件差,作业难度是相当大的。同时,作业人员的安全问题也变得十分突出。笔者提出采用先进的GPS-RTK技术,对既有线曲线整正进行测量。采用该技术不仅能克服气候条件的限制,而且能以较高的频率,较高的精度测定互不通视的各被测点的坐标,克服了传统的作业方法要求置镜点与被测点之间必须通视、作业受天气影响、存在误差累积、内业计算工作量大等缺陷。该法在保证作业人员安全的前提下大大提高作业效率。 相似文献
424.
The involvement of buses in accidents usually is assessed implicitly on the basis of the direct involvement of the bus in the collision or in injury production. This paper deals with the scope and forms of indirect involvement of buses (as a sight obstruction, for example). Accidents were selected by identifying the presence of the term ‘bus’ or synonyms in the text parts of complete police reports (testimonies, statements by the persons involved, etc.) available in electronic form, then analysed in detail. Direct or indirect involvement of a bus is found in 3.6% of traffic injury accidents reported by the police in the community studied (direct involvement: 1.4%; indirect involvement: 2.2%). The different forms of indirect involvement are then described, and some possibilities of preventive measures are discussed. 相似文献
425.
地下水水质评价的多元线性回归分析模型研究 总被引:4,自引:0,他引:4
运用回归分析理论和方法,建立了一个基于多元线性回归分析法的地下水水质评价模型,并将该模型用于遵义市海龙坝地下水水质评价.结果表明,建立的模型较符合本研究区的实际情况. 相似文献
426.
427.
在国民经济中占有主导地位的油气企业同时也是造成环境污染的主体之一。因此,建立油气企业环境会计制度有极其重要的现实意义。文章针对我国油气企业环境会计制度应用现状,运用环境会计基本理论,对企业环境会计核算方法及信息传播模式进行了探讨,以期为油气企业环境会计制度的实施提供一些理论依据和具体方法,推动油气企业环境会计制度的发展。 相似文献
428.
大气环境影响评价工作分级要求要点 总被引:1,自引:0,他引:1
根据大气环境影响评价工作的分级要求,提出了针对性的工作要点,以满足大气环境评价工作的需要. 相似文献
429.
Summary This paper is a comparative study of several antennas commonly used in cellular telephones. These include a monopole, a helix-monopole
and a patch antenna. Each one of these structures is modeled and numerically tested using finite-difference time-domain simulation
and human models based on magnetic-resonance images, which allow for inclusion of details of the human body in the simulation.
The testing procedure involves antenna simulation in the proximity of the human head. The behavior of each antenna is evaluated
for variable distances from the head geometry (0, 1, 2, 4, 8 and 16 mm). Continuous waveform, representative of the sources
used in mobile telephones, (250 mW, 1.8 GHz) is used as the form of the antenna excitation. The simulation outputs used as
measures for this comparative study include transmitting and receiving antenna characteristics and the specific absorption
rate (SAR). The SAR levels for the head tissues are calculated for and with accordance to the two currently accepted standards:
Federal Communications Commission (FCC) and International Commission on Non-Ionizing Radiation Protection (ICNIRP). The computed
SAR levels within each of the considered tissues vary for the three antennas under investigation and are within the determined
health safety standards. Results suggest that the patch antenna may be the structure of choice when considering safety standards,
as its radiation yields the lowest local SAR in the head tissues. 相似文献
430.
John V. Westra Julie K.H. Zimmerman Bruce Vondracek 《Journal of the American Water Resources Association》2005,41(2):309-322
ABSTRACT: Farmers can generate environmental benefits (improved water quality and fisheries and wildlife habitat), but they may not be able to quantify them. Furthermore, farmers may reduce their incomes from managing lands to produce these positive externalities but receive little monetary compensation in return. This study simulated the relationship between agricultural practices, water quality, fish responses to suspended sediment and farm income within two small watersheds, one of a cool water stream and one of a warm water stream. Using the Agricultural Drainage and Pesticide Transport (ADAPT) model, this study related best management practices (BMPs) to calculated instream suspended sediment concentrations by estimating sediment delivery, runoff, base flow, and streambank erosion to quantify the effects of suspended sediment exposure on fish communities. By implementing selected BMPs in each watershed, annual net farm income declined $18,000 to $28,000 (1 to 3 percent) from previous levels. “Lethal” fish events from suspended sediments in the cool water watershed decreased by 60 percent as conservation tillage and riparian buffers increased. Despite reducing suspended sediments by 25 percent, BMPs in the warm water watershed did not reduce the negative response of the fisheries. Differences in responses (physical and biological) between watersheds highlight potential gains in economic efficiency by targeting BMPs or by offering performance based “green payments.” 相似文献