全文获取类型
收费全文 | 44418篇 |
免费 | 741篇 |
国内免费 | 4619篇 |
专业分类
安全科学 | 1520篇 |
废物处理 | 1941篇 |
环保管理 | 5155篇 |
综合类 | 14811篇 |
基础理论 | 9793篇 |
环境理论 | 14篇 |
污染及防治 | 11530篇 |
评价与监测 | 2139篇 |
社会与环境 | 2188篇 |
灾害及防治 | 687篇 |
出版年
2023年 | 300篇 |
2022年 | 727篇 |
2021年 | 621篇 |
2020年 | 459篇 |
2019年 | 515篇 |
2018年 | 1279篇 |
2017年 | 1320篇 |
2016年 | 1336篇 |
2015年 | 1070篇 |
2014年 | 1438篇 |
2013年 | 3221篇 |
2012年 | 1829篇 |
2011年 | 2704篇 |
2010年 | 1948篇 |
2009年 | 2099篇 |
2008年 | 2334篇 |
2007年 | 2431篇 |
2006年 | 1524篇 |
2005年 | 1294篇 |
2004年 | 1132篇 |
2003年 | 1277篇 |
2002年 | 1177篇 |
2001年 | 1279篇 |
2000年 | 1009篇 |
1999年 | 856篇 |
1998年 | 673篇 |
1997年 | 615篇 |
1996年 | 646篇 |
1995年 | 636篇 |
1994年 | 579篇 |
1993年 | 513篇 |
1992年 | 489篇 |
1991年 | 460篇 |
1990年 | 468篇 |
1989年 | 449篇 |
1988年 | 362篇 |
1987年 | 334篇 |
1986年 | 316篇 |
1985年 | 318篇 |
1984年 | 335篇 |
1983年 | 322篇 |
1982年 | 330篇 |
1981年 | 338篇 |
1980年 | 286篇 |
1979年 | 294篇 |
1978年 | 255篇 |
1976年 | 247篇 |
1974年 | 260篇 |
1973年 | 238篇 |
1967年 | 260篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
81.
H. T. Schreuder 《Environmental monitoring and assessment》1994,33(3):237-245
Simplicity and efficiency in design and estimation are all important in deciding on sampling strategies. A simple model is given and illustrated for four practical situations to show how a good sampling strategy should be selected.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
82.
This study examines 45 cases of trisomy 13 and 59 cases of trisomy 18 and reports an algorithm to identify pregnancies with a fetus affected by trisomy 13 or 18 by a combination of maternal age fetal nuchal translucency (NT) thickness, and maternal serum free β-hCG and PAPP-A at 11–14 weeks of gestation. In this mixed trisomy group the median MoM NT was increased at 2.819, whilst the median MoMs for free β-hCG and PAPP-A were reduced at 0.375 and 0.201 respectively. We predict that with the use of the combined trisomy 13 and 18 algorithm and a risk cut-off of 1 in 150 will for a 0.3% false positive rate allow 95% of these chromosomal defects to be identified at 11–14 weeks. Such algorithms will enhance existing first trimester screening algorithms for trisomy 21. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
83.
84.
Indices of abundance and reproduction rate are considered in some groups of aquatic and terrestrial vertebrates from the zones of technogenic disasters. Upon a critical population decline caused by external destructive factors, such as emissions of acute ecotoxicants, the ecophysiological and behavioral compensatory mechanisms are activated, which provide for restoration of the total population size to the optimum within a short period of time. Environmental pollution with substances disturbing the reproductive function has the gravest consequences for animals. In this case, population size may remain fairly high, and, therefore, the effect of enhanced reproduction as a response to population decline does not take place, which eventually leads to a gradual but irreversible destruction of the population. Pathologies of reproduction should be used as a criterion for assessing the state of animals in the zones of technogenic disasters.Translated from Ekologiya, No. 1, 2005, pp. 32–38.Original Russian Text Copyright © 2005 by Shilova, Shatunovskii. 相似文献
85.
New data on the composition of surface assemblages of plant macroremains from soil and swamp samples have been obtained in the study of geomorphologically different localities in the middle reaches of the Nizhnyaya Tunguska River. The results of paleocarpological analysis of forest soil sections supported by relevant palynological and geochronological data are presented. Natural changes of the forest cover over the past 2400 years and quantitative characteristics of the paleoclimate during each stage are described.Translated from Ekologiya, No. 1, 2005, pp. 3–10.Original Russian Text Copyright © 2005 by Koshkarova, Koshkarov. 相似文献
86.
87.
The amount of NO2 and NO produced by the machine smoking of cigarettes was determined for 15 commercial Canadian brands. Average yield of NO was 1.44 μmoles or about 13% of the average reported for American cigarettes. Levels of NO2 were less than 12% of NO and were probably due to the oxidation of NO. In order to assess the contribution of tobacco smoke to levels of NO in ambient air, 5 brands of cigarettes were smoked in 27 cubic meter controlled environment room. Ventilation conditions were either 2.5 or 5.0 air changes per hour (ACH) and each experiment was replicated 3 times for a total of 30 experiments. Ventilation rates of 0.3 and 1.5 ACH were also selected in a second series of experiments in which only one brand of cigarette was smoked. Least squares estimates for the effective ventilation rates were obtained in the usual manner after linearizing the decay portion of the NO time curve. In each of the experiments, the regression explained at least 95% of the variation in the levels of NO with time. Loss of NO due to factors other than ventilation appeared to be constant within experimental error and averaged 2.22 ACH. Equilibrium values for NO were grossly underestimated when results from currently accepted proecedures for smoke analysis were used in modeling the growth and decay of NO. Goodness-of-fit was improved when equilibrium values were estimated based on observed levels in ambient air. This approach may be more suitable for evaluating the potential contribution of cigarette smoke to levels of indoor air pollutants. 相似文献
88.
89.
Mamoru Morikawa Kazutoshi Cho Soromon Kataoka Emi H. Kato Takashi Yamada Hideto Yamada Hisanori Minakami 《黑龙江环境通报》2005,25(3):250-252
Two cases with a large cystic mass within the placenta are reported. By ultrasonography, it was found that both women had a subchorionic hypoechoic lesion (11.0 × 4.8 × 4.0 cm and 6.6 × 3.7 × 2.2 cm, respectively) at 24 and 35 weeks of gestation, respectively. In both cases, turbulent blood flow generated by a pulsatile jet flow (pulse rate; 40 to 60 beats per minute) into the cystic lesion seen on real-time imaging and lesions being low intensity on T1-weighted and isointensity on T2-weighted magnetic resonance image suggested that they contained fresh maternal blood. In both cases, the sonolucency of the lesions did not change until cesarean deliveries of females, both of whom were small-for-gestational-age infants (1940 g at 37 weeks and 2195 g at 37 weeks, respectively). Biochemical analysis of the fluid in the cystic lesion sampled during the cesarean section in the latter case confirmed that the fluid had originated from the maternal blood. These lesions histologically corresponded to large avillous areas surrounded by normal villi. Thus, a huge placental lake was diagnosed in both cases. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
90.
Lei Jun & Zhang Xiaolei Xinjiang Institute of Ecology Geography Chinese Academy of Sciences Urumqi China Institute of Geography Science Natural Resources Research Chinese Academy of Sciences Beijing .China 《中国人口.资源与环境(英文版)》2005,3(3)
As a special basic economic region in China, Xinjiang is situated in the arid area in the Northwest China. Oasis agriculture is the basis of the national economy. The development of oasis agriculture helps to accelerate the development of economy, social and environment. After 50 years of practice, from 1949 to 2002, oasis agriculture in Xinjiang enhanced rapidly the scale of agricultural industry and had great changes in its structure. The amount of cultivated area rose from 120.97*102 ha t… 相似文献