全文获取类型
收费全文 | 1902篇 |
免费 | 127篇 |
国内免费 | 826篇 |
专业分类
安全科学 | 89篇 |
废物处理 | 146篇 |
环保管理 | 122篇 |
综合类 | 1170篇 |
基础理论 | 366篇 |
环境理论 | 2篇 |
污染及防治 | 658篇 |
评价与监测 | 124篇 |
社会与环境 | 55篇 |
灾害及防治 | 123篇 |
出版年
2023年 | 28篇 |
2022年 | 111篇 |
2021年 | 101篇 |
2020年 | 88篇 |
2019年 | 64篇 |
2018年 | 70篇 |
2017年 | 87篇 |
2016年 | 96篇 |
2015年 | 122篇 |
2014年 | 158篇 |
2013年 | 174篇 |
2012年 | 155篇 |
2011年 | 183篇 |
2010年 | 157篇 |
2009年 | 135篇 |
2008年 | 131篇 |
2007年 | 92篇 |
2006年 | 109篇 |
2005年 | 59篇 |
2004年 | 72篇 |
2003年 | 59篇 |
2002年 | 62篇 |
2001年 | 53篇 |
2000年 | 59篇 |
1999年 | 59篇 |
1998年 | 58篇 |
1997年 | 66篇 |
1996年 | 48篇 |
1995年 | 45篇 |
1994年 | 29篇 |
1993年 | 38篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1930年 | 1篇 |
排序方式: 共有2855条查询结果,搜索用时 140 毫秒
991.
Second-trimester serum inhibin-A is increasingly used as a fourth marker in addition to the triple test to screen for Down syndrome. We investigated whether fetal gender had an effect on serum inhibin-A concentration. A retrospective analysis was done on 316 normal pregnancies and 48 Down syndrome pregnancies in which maternal serum inhibin-A assays were performed between 15 and 20 weeks of gestation and in which the fetal sex was known. The median inhibin-A MoM (95% CI) for normal pregnancies in the presence of a male fetus was 0.93 (range 0.88–1.03). This was significantly lower than that in the presence of a female fetus (median MoM=1.04). The gender difference was not observed in the Down syndrome pregnancies. The increased inhibin-A concentration would lead to a 2.3-fold higher false-positive rate in the presence of a female fetus (10.6% vs 4.6%; p<0.05, Chi-square test). Because of the small number of cases studied, the results need to be substantiated by a larger series. If the gender effect is confirmed, adjustment for fetal sex may be necessary when inhibin-A is used as a screening marker. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
992.
993.
S. Hallsworth A.J. Dore W.J. Bealey U. Dragosits M. Vieno S. Hellsten Y.S. Tang M.A. Sutton 《Environmental Science & Policy》2010,13(8):671-687
New ‘critical levels’ (CLE) for assessing the effects of atmospheric ammonia on sensitive ecosystems have recently been adopted by the United Nations Economic Commission for Europe (UNECE) of 1 and 3 [2–4] μg NH3 m?3 of ambient air (including water vapour), for different species sensitivities and their associated habitats. Based on these values, we examined how indicator choice affects estimates of stock-at-risk in the European ‘Natura 2000’ network.We applied an atmospheric model, FRAME, to estimate surface air concentrations of ammonia at 5 km and 1 km resolution for the UK network of Natura sites, optionally including calibration with the National Ammonia Monitoring Network. As a base indicator, we estimated the overall percentage area of the UK Natura network that exceeded critical level thresholds (‘Area Weighted Indicator’, AWI). We compared this with an alternative approach, estimating the percentage number of Natura sites where the critical level was exceeded (‘Designation Weighted Indicator’, DWI), which we consider more relevant under the terms of the Habitats Directive.Using the AWI (with 1 km calibrated ammonia), we estimate that 11.2%, 1.3% and 0.2% area of the UK Natura network exceeds the critical level values of 1, 2 and 3 μg NH3 m?3, respectively. By contrast, using the DWI, the equivalent exceedances are 59.1%, 23.6% and 9.8%. The highest regional exceedance (DWI, critical level 1 μg NH3 m?3) was calculated for England (91.9% exceeded), and the lowest for Scotland (24.0% exceeded). High resolution maps show that the larger threat estimated by the DWI approach is explained by (i) an anti-correlation between NH3 concentration and Natura site area and (ii) the fact that exceedance over part of a Natura site is considered to represent a threat to the integrity of the whole site. 相似文献
994.
The response of the antioxidant defense system of an intertidal macroalgae Corallina officinalis L. to different dosages of UV-B irradiation was investigated. Results showed that superoxide dimutase (SOD) and peroxidase (POX) increased and then maintained at a relatively stable level when subjected to UV-B irradiation. Catalase (CAT) activity under medium dosage of UV-B irradiation (Muv) and high dosage of UV-B irradiation (Huv) treatments were significantly decreased. Ascorbate peroxidase (APX) activity first remained unaltered and then increased in Huv treatment. In addition, the assay on isozymes was carried out using non-denaturing polyacrylamide gel electrophoresis (PAGE). The activities of some SOD isoforms were altered by UV-B. Two new bands (POX V and POX Ⅶ) appeared upon exposure to all three UV-B dosages. CAT Ⅲ activity was increased by low dosage of UV-B irradiation (Luv),whereas CAT Ⅲ and CAT Ⅳ disappeared when the alga was exposed to Muv and Huv. Two bands of APX (APX Ⅵ and APX Ⅶ)were increased and a new band (APX X) was observed under Huv exposure. H2O2 and thiobarbituric acid reacting substance (TBARS)increased under Muv and Huv treatments. Overall, UV-B protection mechanisms are partly inducible and to a certain extent sufficient to prevent the accumulation of damage in C officinalis. 相似文献
995.
996.
997.
莱州湾地区土壤及底泥中多溴联苯醚水平及其分布 总被引:9,自引:1,他引:8
对莱州湾地区十溴联苯醚生产厂家附近土壤及底泥中的多溴联苯醚的含量进行了检测.所采集土壤和河流底泥样品中Σ8 PBDEs(BDE-28、-47、-100、-99、-154、-153、-183、-209) 的含量在58.2~7190.7 ng·g-1(干重)之间, 所有样品中,BDE-209 相对含量最高,其对Σ8PBDEs 的贡献为74.81% ~99.01 %.在8种PBDEs同族体的相关性研究中发现BDE-209与BDE-183、-154、-153、-100、-99呈现显著负相关,相关系数r为-0.842~-0.996(α=0.01).BDE-183、-154、-153、-100、-99之间呈显著正相关,相关系数r为0.805~0.994(α=0.01).产品十溴联苯醚在环境中的降解可能是测定样品中BDE-99、-100、-153、-154、-183的来源之一. 相似文献
998.
999.
1000.
矿业废弃地对环境的扰动及其有效化解的对策选择 总被引:1,自引:0,他引:1
作为矿产资源开发活动的直接结果之一,矿业废弃地对环境的压力与污染在相当程度上与矿产资源开发利用的方式及环境直接相关。依据矿业废弃地污染环境的性质与特点,具体治理过程中,将基于生态恢复与生物技术利用以及正式与非正式的制度约束方面的对策措施结合起来,具有相当的必要性与合理性。 相似文献