全文获取类型
收费全文 | 42621篇 |
免费 | 465篇 |
国内免费 | 388篇 |
专业分类
安全科学 | 1423篇 |
废物处理 | 1939篇 |
环保管理 | 5865篇 |
综合类 | 6152篇 |
基础理论 | 11210篇 |
环境理论 | 11篇 |
污染及防治 | 11047篇 |
评价与监测 | 2933篇 |
社会与环境 | 2609篇 |
灾害及防治 | 285篇 |
出版年
2022年 | 363篇 |
2021年 | 424篇 |
2020年 | 260篇 |
2019年 | 347篇 |
2018年 | 614篇 |
2017年 | 645篇 |
2016年 | 995篇 |
2015年 | 765篇 |
2014年 | 1179篇 |
2013年 | 3614篇 |
2012年 | 1419篇 |
2011年 | 1885篇 |
2010年 | 1521篇 |
2009年 | 1619篇 |
2008年 | 1953篇 |
2007年 | 1920篇 |
2006年 | 1759篇 |
2005年 | 1498篇 |
2004年 | 1487篇 |
2003年 | 1422篇 |
2002年 | 1353篇 |
2001年 | 1623篇 |
2000年 | 1178篇 |
1999年 | 706篇 |
1998年 | 546篇 |
1997年 | 530篇 |
1996年 | 586篇 |
1995年 | 645篇 |
1994年 | 580篇 |
1993年 | 518篇 |
1992年 | 507篇 |
1991年 | 495篇 |
1990年 | 472篇 |
1989年 | 465篇 |
1988年 | 421篇 |
1987年 | 361篇 |
1986年 | 363篇 |
1985年 | 357篇 |
1984年 | 397篇 |
1983年 | 390篇 |
1982年 | 403篇 |
1981年 | 364篇 |
1980年 | 276篇 |
1979年 | 310篇 |
1978年 | 253篇 |
1977年 | 211篇 |
1976年 | 194篇 |
1975年 | 212篇 |
1973年 | 244篇 |
1972年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 520 毫秒
641.
针对西北地区一综合炼油厂含硫污水管线的严重腐蚀问题,分析了腐蚀原因,确立了材料筛选方案,通过实验室静态挂片试验绘制了重量损失率变化曲线和现场挂片等试验手段,筛选推荐出了树脂玻璃钢耐蚀材料。工业生产应用结果表明,MFE-2型树脂玻璃钢是适用于该厂含硫污水系统的耐蚀材料,为类似装置的长周期运行提供了借鉴和经验。 相似文献
642.
Kurz Werner A. Beukema Sarah J. Apps Michael J. 《Mitigation and Adaptation Strategies for Global Change》1997,2(4):405-421
Land-use change from an unmanaged to a managed forested landscape in northern forests is associated with a reduction of the
area annually affected by natural disturbances (wildfires and forest insects) and the introduction of harvesting as a new
disturbance. This study examined the impacts of changes in the disturbance regime-the frequency and type of disturbance-on
landscape-level carbon (C) content and fluxes. The Carbon Budget Model of the Canadian Forest Sector was used to assess these
impacts in six representative landscapes (100,000 ha each) with a range of disturbance regimes that are characteristic of
conditions in coastal British Columbia, the interior of British Columbia, and the eastern boreal forest in Canada. The model
was used to simulate ecosystem C fluxes during a period of natural disturbances, a 50-year transition period during which
harvesting replaced natural disturbances, followed by 150 years of harvesting. The initial landscape-level biomass C content
under natural disturbance regimes in the six example landscapes was 22 to 75% of their potential maximum content which is
often used as the reference or baseline case. After 200 years of forest management, the C stored in the landscape plus the
C retained in forest products manufactured from harvested biomass was between 58 and 101% of the landscape C content prior
to the onset of harvesting. Landscape-level ecosystem C content was found to be affected by changes in the disturbance frequency,
the age-dependence of the disturbance probabilities, and the disturbance-specific impacts on ecosystem C content. The results
indicate that using the potential maximum C content of a landscape as the baseline always overestimates the actual C release
due to land use change. A more meaningful procedure would be to assess the actual differences in landscape-level C content
between the natural and the managed disturbance regime. 相似文献
643.
644.
645.
646.
This paper investigates the current treatment of environmental issues by two companies within the large made-to-order sector. Fifty questionnaires were issued to the design team of each company to assess current practice in the integration of environmental issues with design activities, awareness of environmental issues, awareness of existing environmental design tools and the preferred format for a potential clean design tool. 相似文献
647.
A. Kr?ner A. P. Willner E. Hegner A. Frischbutter J. Hofmann R. Bergner 《Geologische Rundschau》1995,84(3):437-456
Single zircons from two orthogneiss complexes, the Grey Gneiss and Red Gneiss, the lowermost tectonic units in the Erzgebirge, were dated. The grey Freiberg Gneiss is of igneous origin and has a 207Pb/206Pb emplacement age of 550±7 Ma. A quartz monzonite from Lauenstein contains idiomorphic zircons with a mean 207Pb/206Pb age of 555±7 Ma as well as xenocrysts ranging in age between 850 and 1910 Ma. Red gneisses from the central Erzgebirge contain complex zircon populations, including numerous xenocrysts up to 2464 Ma in age. The youngest, idiomorphic, zircons in all samples yielded uniform 207Pb/206Pb ages between 550±9 and 554±10 Ma. Nd isotopic data support the interpretation of crustal anatexis for the origin of both units. Nd(t) values for the grey gneisses are –7.5 and –6.0 respectively, (mean crustal residence ages of 1.7–1.8 Ga). The red gneisses have a wider range in Nd(t) values from –7.7 to –2.8 (T
DM ages of 1.4–1.8 Ga). The zircon ages document a distinct late Proterozoic phase of granitoid magmatism, similar in age to granitoids in the Lusatian block farther north-east. However, Palaeozoic deformation as well as medium pressure metamorphism ( 8 kbar/600–650° C) are identical in both gneiss units and distinguish these rocks from the Lusatian granitoids. The grey and red gneisses were overthrust by units with abundant high-pressure relicts and a contrasting P-T evolution. Zircon xenocryst and Nd model ages in the range 1000–1700 Ma are similar to those in granitoid rocks of Lusatia and the West-Sudetes, and document a pre-Cadomian basement in parts of east-central Europe that, chronologically, has similarities with the Sveconorwegian domain in the Baltic Shield. 相似文献
648.
Vanessa M. Barnabei MD PhD David A. Krantz James N. Macri John W. Larsen Jr 《黑龙江环境通报》1995,15(12):1131-1134
We have applied our multimarker approach of maternal serum alpha-fetoprotein (AFP) and free-beta human chorionic gonadotropin (hCG) for Down syndrome screening to multiple gestations to assess its efficacy for improved detection of twin and triplet pregnancies. This study matched 225 cases of twin pregnancy and 39 cases of triplet pregnancy each with ten singleton pregnancies based on gestational week, race, time to receive sample, time of year of sample, and geographical area. The ratios of the MOM for each group at the tenth, 50th, and 90th percentiles were compared by the Wilcoxon test. Risks for twins were calculated using Bayes' rule, the age-related incidence of twins, and the levels of AFP and free-beta hCG. The tenth, 50th, and 90th percentiles of free-beta hCG MOMs in twin and triplet cases were 0.85, 1.99, and 4.51, and 1.38, 2.78, and 4.07, respectively. For AFP, the MOMs at these percentiles were 1.26, 1.91, and 2.99, and 2.02, 2.68, and 5.30, respectively. The twin and triplet distributions for each marker were statistically significantly different from the singleton distributions (P<0.0001) and from each other (P=0.0012). At a twin risk cut-off of 1 in 50, 77.4 per cent of all twin gestations can be detected in a second-trimester AFP and free-beta hCG screening protocol with 5.1 per cent of singleton pregnancies falsely identified as at risk for twins. Our dual marker protocol for mid-trimester pregnancy screening combining AFP and free-beta hCG can identify over 77 per cent of twin pregnancies in women less than 35 years of age. This benefit may contribute to an improved outcome of pregnancy by early detection of multiple gestation. 相似文献
649.
650.
长江,嘉陵江重庆城区段二维水质对流扩散数学模型 总被引:6,自引:0,他引:6
对二水质对流扩散数学模型的有限差分解作了较详细的叙述,同时对距离步长,时间步长计算,网络内水深,流速,横向扩散系数的求取也作了简要介绍。 相似文献