全文获取类型
收费全文 | 5167篇 |
免费 | 595篇 |
国内免费 | 713篇 |
专业分类
安全科学 | 1052篇 |
废物处理 | 175篇 |
环保管理 | 611篇 |
综合类 | 2880篇 |
基础理论 | 392篇 |
环境理论 | 1篇 |
污染及防治 | 351篇 |
评价与监测 | 538篇 |
社会与环境 | 194篇 |
灾害及防治 | 281篇 |
出版年
2024年 | 14篇 |
2023年 | 78篇 |
2022年 | 165篇 |
2021年 | 224篇 |
2020年 | 182篇 |
2019年 | 147篇 |
2018年 | 152篇 |
2017年 | 199篇 |
2016年 | 234篇 |
2015年 | 251篇 |
2014年 | 289篇 |
2013年 | 322篇 |
2012年 | 450篇 |
2011年 | 445篇 |
2010年 | 304篇 |
2009年 | 298篇 |
2008年 | 220篇 |
2007年 | 354篇 |
2006年 | 324篇 |
2005年 | 283篇 |
2004年 | 214篇 |
2003年 | 220篇 |
2002年 | 158篇 |
2001年 | 147篇 |
2000年 | 128篇 |
1999年 | 115篇 |
1998年 | 103篇 |
1997年 | 113篇 |
1996年 | 63篇 |
1995年 | 50篇 |
1994年 | 41篇 |
1993年 | 42篇 |
1992年 | 25篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 19篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1975年 | 2篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有6475条查询结果,搜索用时 439 毫秒
111.
112.
113.
Compounds in the atmosphere contaminate samples of groundwater. An inexpensive and simple method for collecting groundwater samples is developed to prevent contamination when the background concentration of contaminants is high. This new design of groundwater sampling device involves a glass sampling bottle with a Teflon-lined valve at each end. A cleaned and dried sampling bottle was connected to a low flow-rate peristaltic pump with Teflon tubing and was filled with water. No headspace volume was remained in the sampling bottle. The sample bottle was then packed in a PVC bag to prevent the target component from infiltrating into the water sample through the valves. In this study, groundwater was sampled at six wells using both the conventional method and the improved method. The analysis of trichlorofluoromethane( CFC-11 ) concentrations at these six wells indicates that all the groundwater samples obtained by the conventional sampling method were contaminated by CFC-11 from the atmosphere. The improved sampling method greatly eliminated the problems of contamination, preservation and quantitative analysis of natural water. 相似文献
114.
欧拉观测的大气扩散参数计算方法探析及应用 总被引:2,自引:0,他引:2
根据湍流扩散统计理论,讨论了利用欧拉观测的风速资料求解正态扩散模式中大气扩散参数的计算方法及其实现,并以海南洋埔开关区各稳定度大气扩散参数的计算为实例作了分析。 相似文献
115.
116.
H. Cuckle N. Wald J. D. Stevenson H. M. May M. A. Ferguson-Smith A. Milford Ward H. M. Barbour K. M. Laurence B. Norgaard-Pedersen 《黑龙江环境通报》1990,10(2):71-77
Data on maternal serum alpha-fetoprotein (AFP) levels at 13–24 weeks' gestation in 46 twin pregnancies with open neural tube defects (22 with anencephaly, 24 with open spina bifida) and 169 unaffected twins were used to estimate the detection and false-positive rates associated with different cut-off levels. Using the conventional cut-off level of 2·5 multiples of the median (MoM) for unaffected singleton pregnancies of the same gestation and laboratory, the detection rate in twins was 99 per cent for anencephaly and 89 per cent for open spina bifida, with a false-positive rate of 30 per cent. Using a 5·0 MoM cut-off level to maintain a similar false-positive rate to that found among singleton pregnancies at 16–18 weeks' gestation (about 3 per cent), the detection rate was 83 per cent for anencephaly and 39 per cent for open spina bifida. Estimates are provided of the odds of having an affected twin pregnancy given a positive AFP result as well as the odds for individual women with a raised AFP level. 相似文献
117.
Iniencephaly is an uncommon, but not rare, lesion involving a fusion between the posterior occipital bone and the cervical spine. Many cases are associated with other cranio-cervical abnormalities and anencephaly, and most are associated with other structural abnormalities. The prognosis is thought to be dismal. We describe a male infant, one of twins, who was diagnosed prenatally as having iniencephaly. The child was born without complication and has grown and thrived. This is the fourth patient with long-term survival with iniencephaly. We recommend that non-directive counselling be applied when presenting the findings of iniencephaly to parents. 相似文献
118.
The outcome of the pregnancy following (a) a mid-trimester termination of pregnancy (TOP) for fetal neural tube defect (NTD) (77 women=group 1); (b) mid-trimester TOP for fetal Down's syndrome (13 women=group 2); (c) delivery of a baby with NTD (119 women=group 3) was studied. The prenatal fetal loss was relatively high in all groups. In group 1 it was similar to that found in other studies after first trimester TOP, in group 2 it was associated with advanced maternal age and the unexpected finding in group 3 was not attributable to advanced maternal age. It is suggested that a previous NTD per se might increase the risk of fetal loss in the next pregnancy. A previous mid-trimester TOP for NTD was not associated with an increase in premature labour, small for dates babies or congenital abnormality in the next pregnancy, but there was a slight increase in the number of babies weighing less than 2500 g. 相似文献
119.
J. G. Hooker M. Lucas B. A. Richards I. M. Shirley B. D. Thompson R. H. T. Ward 《黑龙江环境通报》1984,4(1):29-33
Estimation of maternal serum alpha-fetoprotein (AFP) was used as a screening method for the detection of neural tube defects (NTDs) in 6344 women over three years. Of 88 (1.4 per cent) who had one or more serum AFP levels equal to, or greater than, 2.5 multiples of the median (MoM) for the relevant gestational age, 43 (0.68 per cent) underwent amniocentesis. There were eight NTDs. Four of these were screened by serum AFP, and all cases of spina bifida had serum AFP levels greater than 3.0 MoM, including one small open defect which was not seen on ultrasound. The other four cases of NTD, which were not screened, were identified by ultrasound. Of 64 singleton pregnancies 32 (50 per cent) had serum AFP levels between 2.5 and 3.0 MoM, and low birthweight (⪕2500 g) occurred in 29 per cent. Because of improvements in ultrasound techniques and the apparent falling incidence of NTD, the role of serum AFP as the primary screening procedure should be regularly reviewed. Effective screening is dependent on mothers booking early. 相似文献
120.
Howard S. Cuckle 《黑龙江环境通报》1983,3(4):287-289
Data from 280 sibships in three published series were used to see if the increased risk of neural tube defect (NTD) associated with having had a miscarriage in the immediately preceding pregnancy was also found in women with a previous affected pregnancy. A statistically significant relative risk of 4.0 (2-tail P=0.0111, Fisher exact test) was found among such women, and this could not be accounted for by the effect of parity or of a history of miscarriage in general. The finding may be useful when counselling patients. 相似文献