全文获取类型
收费全文 | 27754篇 |
免费 | 298篇 |
国内免费 | 244篇 |
专业分类
安全科学 | 780篇 |
废物处理 | 922篇 |
环保管理 | 4030篇 |
综合类 | 5492篇 |
基础理论 | 7183篇 |
环境理论 | 10篇 |
污染及防治 | 7050篇 |
评价与监测 | 1505篇 |
社会与环境 | 1154篇 |
灾害及防治 | 170篇 |
出版年
2021年 | 191篇 |
2019年 | 214篇 |
2018年 | 341篇 |
2017年 | 332篇 |
2016年 | 525篇 |
2015年 | 386篇 |
2014年 | 553篇 |
2013年 | 2109篇 |
2012年 | 723篇 |
2011年 | 1032篇 |
2010年 | 816篇 |
2009年 | 892篇 |
2008年 | 1088篇 |
2007年 | 1135篇 |
2006年 | 1027篇 |
2005年 | 786篇 |
2004年 | 882篇 |
2003年 | 840篇 |
2002年 | 768篇 |
2001年 | 1049篇 |
2000年 | 720篇 |
1999年 | 476篇 |
1998年 | 375篇 |
1997年 | 341篇 |
1996年 | 381篇 |
1995年 | 398篇 |
1994年 | 440篇 |
1993年 | 373篇 |
1992年 | 401篇 |
1991年 | 375篇 |
1990年 | 418篇 |
1989年 | 404篇 |
1988年 | 318篇 |
1987年 | 316篇 |
1986年 | 279篇 |
1985年 | 305篇 |
1984年 | 317篇 |
1983年 | 309篇 |
1982年 | 310篇 |
1981年 | 313篇 |
1980年 | 259篇 |
1979年 | 270篇 |
1978年 | 245篇 |
1977年 | 229篇 |
1976年 | 200篇 |
1975年 | 213篇 |
1974年 | 242篇 |
1973年 | 216篇 |
1972年 | 235篇 |
1971年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Estimates of animal methane emissions 总被引:2,自引:0,他引:2
The enteric methane emissions into the atmospheric annually from domestic animals total about 77 Tg. Another 10 to 14 Tg are likely released from animal manure disposal systems. About 95% of global animal enteric methane is from ruminants, a consequence of their large populations, body size and appetites combined with the extensive degree of anaerobic microbial fermentation occurring in their gut. Accurate methane estimates are particularly sensitive to cattle and buffalo census numbers and estimated diet consumption. Since consumption is largely unknown and must be predicted, accuracy is limited often by the information required, i.e., distribution of animals by class, weight and productivity. Fraction of the diet lost as enteric methane mostly falls into the range of 5.5–6.5% of gross energy intake for the world's cattle, sheep and goats. Manure methane emissions are heavily influenced by fraction of disposal by anaerobic lagoon. Non-ruminants, i.e., swine, become major contributors to these emissions. 相似文献
62.
Carl W. Chen 《Journal of the American Water Resources Association》2003,39(6):1561-1562
63.
64.
David W. Mehlman 《Conservation biology》1994,8(4):1141-1145
65.
T. Antoniadi C. Yapijakis P. Kaminopetros C. Makatsoris V. Velissariou D. Vassilopoulos M. B. Petersen 《黑龙江环境通报》2002,22(5):425-429
The presence of maternal cells in fetal samples constitutes a serious potential source for prenatal misdiagnosis. Here we present our approach for detecting maternal cell contamination (MCC) at prenatal diagnosis for eight monogenic disorders (autosomal recessive: β-thalassaemia, sickle-cell anaemia, cystic fibrosis, prelingual deafness; autosomal dominant: achondroplasia, Huntington disease, myotonic dystrophy, neurofibromatosis type I; X-linked: spinobulbar muscular atrophy). Our aim was to apply a simple and low-cost approach, which would easily and accurately provide information on the fetal tissue MCC status. MCC testing was applied to cases of recessive inheritance where the primary mutation screening of the fetus revealed the presence of the maternal mutation, to cases concerning dominant inheritance and to cases of multiple gestation. The potential presence of maternal cells was determined by the amplification of the 3′-HVR/APO B, D1S80, THO1 and VNTRI of vWf polymorphic loci, which have previously demonstrated high heterozygosity in Caucasians. Among 135 prenatal diagnoses, 44 finally needed to be tested for MCC (32.6%). MCC was detected in four cases, where DNA was isolated directly from chorionic villi samples (CVS), and in one case with DNA isolated directly from amniotic fluid (AF). In almost 90% of cases a simple test of one polymorphic locus provided sufficient information about MCC. The choice of the appropriate locus is therefore essential, while the simultaneous screening of both parents provides the means for distinguishing non-informative sites about MCC. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
66.
67.
5p deletion syndrome commonly known as cri du chat is well described in affected neonates with catlike cry and hypotonia. Karyotyping will usually show a deletion of the short arm of one chromosome 5 with variable breakpoints. Only a few cases have been reported prenatally, and the fetal form of the syndrome has not been clearly individualised. We report a new case of 5p deletion syndrome diagnosed prenatally in association with Dandy–Walker syndrome and agenesis of the corpus callosum. Other brain anomalies have been reported previously, but this unusual association suggests the use of a specific probe in the investigation of these malformations. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
68.
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
69.
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
70.