全文获取类型
收费全文 | 850篇 |
免费 | 41篇 |
国内免费 | 95篇 |
专业分类
安全科学 | 38篇 |
废物处理 | 12篇 |
环保管理 | 128篇 |
综合类 | 402篇 |
基础理论 | 155篇 |
污染及防治 | 77篇 |
评价与监测 | 161篇 |
社会与环境 | 9篇 |
灾害及防治 | 4篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 8篇 |
2021年 | 19篇 |
2020年 | 22篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 20篇 |
2016年 | 33篇 |
2015年 | 28篇 |
2014年 | 32篇 |
2013年 | 52篇 |
2012年 | 34篇 |
2011年 | 46篇 |
2010年 | 34篇 |
2009年 | 36篇 |
2008年 | 34篇 |
2007年 | 34篇 |
2006年 | 46篇 |
2005年 | 25篇 |
2004年 | 27篇 |
2003年 | 38篇 |
2002年 | 20篇 |
2001年 | 21篇 |
2000年 | 26篇 |
1999年 | 25篇 |
1998年 | 23篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 22篇 |
1994年 | 33篇 |
1993年 | 19篇 |
1992年 | 20篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 24篇 |
1987年 | 18篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有986条查询结果,搜索用时 993 毫秒
431.
The dilemma of chromosomal mosaicism in chorionic villus sampling—‘direct’ versus long-term cultures
R. Nisani Dr J. Chemke R. Voss Z. Appelman B. Caspi A. Lewin H. Dar A. Reiter 《黑龙江环境通报》1989,9(4):223-226
Chromosomal mosaicism is one of several unanswered dilemmas in first-trimester prenatal diagnosis. We report the course of a pregnancy in which a normal karyotype was detected on direct CVS preparation and fetal blood, 100 per cent trisomy 21 in one long-term CVS culture, and low-rate trisomy 21 mosaicism in a second long-term CVS culture and amniocentesis. The phenotypically normal infant had a 6 per cent mosaicism of trisomy 21. It appears that a persistent low-rate mosaicism in different tissues may be indicative of the true status of the fetus. 相似文献
432.
S. Schwartz S. Ashai E. J. Meijboom M. F. Schwartz C. C.-J. Sun M. M. Cohen 《黑龙江环境通报》1989,9(8):549-554
Chromosomal mosaicism in amniotic fluid cells poses a serious dilemma in prenatal diagnosis since the observation may represent: (1) pseudomosaicism—an inconsequential tissue culture artefact; or (2) true mosaicism—occurring in approximately 0.0 per cent of amniocenteses with a significant impact on pregnancy outcome. Mosaicism for trisomy 9 was observed in an amniotic fluid specimen obtained for advanced maternal age with two cell lines [46,XX (46 per cent)/47,XX, + 9 (54 per cent)] present in each of four culture flasks. Since more than 75 per cent of newborns with trisomy 9 mosaicism have complex cardiac malformations, a fetal echocardiogram was obtained at 20 weeks' gestation and interpreted as normal. A fetal blood sample (22 weeks' gestation) disclosed only a single trisomy 9 cell among the 100 metaphases analysed. However, a second fetal echocardiogram performed at the time of blood sampling suggested a non-specific cardiac anomaly. Fetal autopsy following elective pregnancy termination revealed several malformations including severe micrognathia, persistence of the left superior vena cava, and skeletal anomalies. Cytogenetic studies of cell cultures derived from several fetal tissues demonstrated trisomy 9 ranging from 12 to 24 per cent. 相似文献
433.
石油开采、炼制及储存过程中含油污泥的综合处理 总被引:1,自引:0,他引:1
张显安 《石油化工环境保护》2006,29(4):38-40
主要介绍石油开采、炼制、储存过程中产生的石油油泥的处理和回收利用。油泥经化学水洗调质处理后,通过特殊的分离沉降罐与卧式离心机和碟式离心机分别配合使用达到降低分离难度,提高工艺适应性和获得良好的油、水、泥分离效果。 相似文献
434.
T. Dooley L. D. Fairbanks H. A. Simmonds C. H. Rodeck K. H. Nicolaides P. W. Soothill P. Stewart G. Morgan R. J. Levinsky 《黑龙江环境通报》1987,7(8):561-565
Adenosine deaminase deficiency has been detected in the first trimester by direct analysis of enzyme activity in chorionic villi in a pregnancy at risk. Data for purine nucleoside phosphorylase activity in chorionic villi from healthy controls in the first trimester are also presented and should allow equally rapid diagnosis of this disorder. 相似文献
435.
S. Christensen P. Ambus J.R.M. Arah H. Clayton B. Galle D.W.T. Griffith K.J. Hargreaves L. Klenzedtsson A.-M. Lind M. Maag A. Scott U. Skiba K.A. Smith M. Welling F.G. Wienhold 《Atmospheric environment (Oxford, England : 1994)》1996,30(24):4183-4190
The soil in a drained fjord area, reclaimed for arable farming, produced N2O mainly at 75–105 cm depth, just above the ground water level. Surface emissions of N2O were measured from discrete small areas by closed and open-flow chamber methods, using gas chromatographic analysis and over larger areas by integrative methods: flux gradient (analysis by FTIR), conditional sampling (analysis by TDLAS), and eddy covariance (analysis by TDLAS). The mean emission of N2O as determined by chamber procedures during a 9-day campaign was 162–202 μg N2ONm−2h−1 from a wheat stubble and 328–467 μg N2ONm−2 h−1 from a carrot field. The integrative approaches gave N2O emissions of 149–495 μg N2ONm−2 h−1, i.e. a range similar to those determined with the chamber methods. Wind direction affected the comparison of chamber and integrative methods because of patchiness of the N2O emission over the area. When a uniform area with a single type of vegetation had a dominant effect on the N2O gradient at the sampling mast, the temporal variation in N2O emission determined by the flux gradient/FTIR method and chamber methods was very similar, with differences of only 18% or less in mean N2O emission, well below the variation encountered with the chamber methods themselves. A detailed comparison of FTIR gradient and chamber data taking into account the precise emission footprint showed good agreement. It is concluded that there was no bias between the different approaches used to measure the N2O emission and that the precision of the measurements was determined by the spatial variability of the N2O emission at the site and the variability inherent in the individual techniques. These results confirm that measurements of N2O emissions from different ecosystems obtained by the different methods can be meaningfully compared. 相似文献
436.
Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in stack emission exist both as vapor and sorbed onto the surface of particles. The partition between the two phases is of a dynamic nature and changes rapidly with temperature. When monitoring stack emissions, a sampling method must be used that efficiently collects both phases as well as any condensation aerosol formed in the sampling train. In this study, the two sampling methods used in Sweden, the cooled probe polyurethane foam plug (PUFP) sampling train and the sampling train recommended by the Swedish Environmental Protection Board has been tested for particle collection ability. The results show that an aerosol filter has to be introduced after the condensor in order to collect particle bound PCDDs and PCDFs efficiently. 相似文献
437.
Optimal spatial sampling schemes for environmental surveys 总被引:4,自引:0,他引:4
Simone Di Zio Lara Fontanella Luigi Ippoliti 《Environmental and Ecological Statistics》2004,11(4):397-414
A practical problem in spatial statistics is that of constructing spatial sampling designs for environmental monitoring network. This paper presents a fractal-based criterion for the construction of coverage designs to optimize the location of sampling points. The algorithm does not depend on the covariance structure of the process and provides desirable results for situations in which a poor prior knowledge is available. The statistical characteristics of the method are explored by a simulation study while a design exercise concerning the Pescara area monitoring network is used to demonstrate potential designs under realistic assumptions. 相似文献
438.
MARTÍN H. FÉLIX-MEDINA 《Environmental and Ecological Statistics》2003,10(1):61-82
In this article we consider asymptotic properties of the Horvitz-Thompson and Hansen-Hurwitz types of estimators under the adaptive cluster sampling variants obtained by selecting the initial sample by simple random sampling without replacement and by unequal probability sampling with replacement. We develop an asymptotic framework, which basically assumes that the number of units in the initial sample, as well as the number of units and networks in the population tend to infinity, but that the network sizes are bounded. Using this framework we prove that under each of the two variants of adaptive sampling above mentioned, both the Horvitz-Thompson and Hansen-Hurwitz types of estimators are design-consistent and asymptotically normally distributed. In addition we show that the ordinary estimators of their variances are also design-consistent estimators. 相似文献
439.
Moment and maximum likelihood estimators for Weibull distributions under length- and area-biased sampling 总被引:1,自引:0,他引:1
Jeffrey H. Gove 《Environmental and Ecological Statistics》2003,10(4):455-467
Many of the most popular sampling schemes used in forestry are probability proportional to size methods. These methods are also referred to as size-biased because sampling is actually from a weighted form of the underlying population distribution. Length- and area-biased sampling are special cases of size-biased sampling where the probability weighting comes from a lineal or areal function of the random variable of interest, respectively. Often, interest is in estimating a parametric probability density of the data. In forestry, the Weibull function has been used extensively for such purposes. Estimating equations for method of moments and maximum likelihood for two- and three-parameter Weibull distributions are presented. Fitting is illustrated with an example from an area-biased angle-gauge sample of standing trees in a woodlot. Finally, some specific points concerning the form of the size-biased densities are reported. 相似文献
440.
Adaptive two-stage one-per-stratum sampling 总被引:1,自引:0,他引:1
Mary C. Christman 《Environmental and Ecological Statistics》2003,10(1):43-60
We briefly describe adaptive cluster sampling designs in which the initial sample is taken according to a Markov chain one-per-stratum design (Breidt, 1995) and one or more secondary samples are taken within strata if units in the initial sample satisfy a given condition C. An empirical study of the behavior of the estimation procedure is conducted for three small artificial populations for which adaptive sampling is appropriate. The specific sampling strategy used in the empirical study was a single random-start systematic sample with predefined systematic samples within strata when the initially sampled unit in that stratum satisfies C. The bias of the Horvitz-Thompson estimator for this design is usually very small when adaptive sampling is conducted in a population for which it is suited. In addition, we compare the behavior of several alternative estimators of the standard error of the Horvitz-Thompson estimator of the population total. The best estimator of the standard error is population-dependent but it is not unreasonable to use the Horvitz-Thompson estimator of the variance. Unfortunately, the distribution of the estimator is highly skewed hence the usual approach of constructing confidence intervals assuming normality cannot be used here. 相似文献