全文获取类型
收费全文 | 3401篇 |
免费 | 86篇 |
国内免费 | 27篇 |
专业分类
安全科学 | 178篇 |
废物处理 | 149篇 |
环保管理 | 938篇 |
综合类 | 321篇 |
基础理论 | 853篇 |
环境理论 | 2篇 |
污染及防治 | 715篇 |
评价与监测 | 217篇 |
社会与环境 | 102篇 |
灾害及防治 | 39篇 |
出版年
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 31篇 |
2020年 | 22篇 |
2019年 | 37篇 |
2018年 | 58篇 |
2017年 | 55篇 |
2016年 | 77篇 |
2015年 | 65篇 |
2014年 | 71篇 |
2013年 | 362篇 |
2012年 | 129篇 |
2011年 | 180篇 |
2010年 | 139篇 |
2009年 | 144篇 |
2008年 | 182篇 |
2007年 | 173篇 |
2006年 | 170篇 |
2005年 | 116篇 |
2004年 | 94篇 |
2003年 | 123篇 |
2002年 | 119篇 |
2001年 | 78篇 |
2000年 | 71篇 |
1999年 | 36篇 |
1998年 | 58篇 |
1997年 | 39篇 |
1996年 | 49篇 |
1995年 | 59篇 |
1994年 | 40篇 |
1993年 | 53篇 |
1992年 | 45篇 |
1991年 | 24篇 |
1990年 | 33篇 |
1989年 | 24篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 28篇 |
1985年 | 34篇 |
1984年 | 34篇 |
1983年 | 28篇 |
1982年 | 42篇 |
1981年 | 39篇 |
1980年 | 39篇 |
1979年 | 26篇 |
1978年 | 30篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1974年 | 12篇 |
1972年 | 10篇 |
排序方式: 共有3514条查询结果,搜索用时 250 毫秒
991.
Richard Rodakowski 《Journal of the American Water Resources Association》1978,14(6):1295-1303
ABSTRACT: Traditional procedures for evaluating flood damages to residential dwellings do not reflect intrinsic values when applied to historic homes. Such structures are worth more than that determined by using depth-damage curves provided by insurance companies who assess damage values based upon current labor and material costs. The evaluation of the worth of a historic home and subsequent damages due to inundation can be regarded as a problem of externalities. An assessment technique reflecting historic amenities or what has been termed replication cost is proposed in this paper. Replication costs would have widespread use not only in solving flood dammage problems, but also in any study where historic entities are subject to damages from catastrophies such as hurricanes, soil and beach erosion, and increasing urbanization. If adopted as a technique, it would enhance and preserve the ever-decreasing enclaves of historic homes and neighborhoods. 相似文献
992.
Gregory E. Kamedulski Richard H. McCuen 《Journal of the American Water Resources Association》1979,15(4):1146-1152
ABSTRACT: Storm water detention is an effective and popular method for controlling the effects of increased urbanization and development. Detention basins are used to control both increases in flow rates and sedimentation. While numerous storm water management policies have been proposed, they most often fail to give adequate consideration to maintenance of the basin. Sediment accumulation with time and the growth of grass and weeds in the emergency spillway are two maintenance problems. A model that was calibrated with data from a storm water detention basin in Montgomery County, Maryland, is used to evaluate the effect of maintenance on the efficiency of the detention basin. Sediment accumulation in the basin caused the peak reduction factor to decrease while it increased as vegetation growth in the emergency spillway increased. Thus, the detention basin will not function as intended in the design when the basin is not properly maintained. Thus, maintenance of detention basins should be one component of a comprehensive storm water management policy. 相似文献
993.
Robert R. Lansford Shaul Ben-David Fred Roach Bobby J. Creel Thomas H. Stevens Raymond J. Supalla Lynn Gelhar William D. Gorman Richard W. Mead Donald B. Wilson 《Journal of the American Water Resources Association》1979,15(6):1589-1601
ABSTRACT: The economic feasibility of a large scale dual purpose (desalting water and power production) facility were evaluated. Although a site in the Tularosa basin of southern New Mexico was chosen as a case study for this analysis, it is believed that the approach and consequential results would be applicable to alternative sites in the Southwest. The basic project evaluated included: a) a ground water well field; b) a dual purpose, nuclear, desalination plant; c) a mineral recovery plant; and d) a reservoir for recreation and irrigation storage. Principle project outputs included electrical power, minerals, recreation, and water for either irrigated agricultural production or export to an adjoining river basin. Two alternative project designs were developed for detailed analysis. The first alternative encompassed all major project components. The results, in discounted net values used to assess the feasibility of the project, were essentially negative; that is, values were less than zero for full scale development. The net benefits ranged from $-986.57 million at a 5 percent discount rate, to $-1,137.528 million at a discount rate of 10 percent. In the second alternative, exportation of the desalted water from the Tularosa basin to two adjacent rivers was analyzed with somewhat better net benefits, ranging from $-382,527 million to $-478,612 million at the 5 and 10 percent discount rates. 相似文献
994.
Mean temperature is employed universally as an index to the energy status of the environment, and to indicate probable reaction rates of physical and biological processes in nature. A versatile chemical method of temperature integration, based on the temperature dependence of sucrose hydrolysis, has been tested in central Pennsylvania. The chemical technique (after Pallmann) permits economical mass sampling of air, water, and soil temperatures in situations where conventional methods are too expensive or otherwise unsatisfactory. Short-wave radiation effects are negligible since the sensing elements are transparent. Repeatability is excellent: in field tests duplicate sensors yield the same mean temperature ± 0.02°C. Non-linearity of sensor response has been resolved, and the data can be related directly to measurements obtained in standard climatological networks. The technique can be used to good advantage in a variety of hydrological investigations, including evaporation, consumptive-use, and them pollution studies. 相似文献
995.
Roy A. Williams Robert Y. Lai Gabor M. Karadi 《Journal of the American Water Resources Association》1972,8(2):294-303
Confined flow toward a single well of finite radius in an extensive aquifer of uniform transmissibility is studied under the assumption of time-dependent drawdown. Three particular cases are considered: (a) linear drawdown (including constant drawdown); (b) exponential drawdown; (c) periodic (sinusoidal) drawdown. The differential equation governing unsteady axial symmetric flow toward a single well in a confined aquifer is solved for the three different situations by the use of the Laplace transform method. The resulting expressions are integrated by adapting a modified Gemant scheme. General computer programs have been developed and operated for several combinations of characteristics. The results are plotted to show the effect of time dependent drawdown on the variation of the well discharge and the piezometric head distribution. 相似文献
996.
Richard H. Hawkins John H. Judd 《Journal of the American Water Resources Association》1972,8(6):1246-1252
The use of salt to melt ice and snow on streets and roads has become prevalent throughout the Northeast. Several states apply as much as 20 tons per lane-mile. Salt runoff may be sorted in various locations within the hydrologic system. Eventually the salt reaches streams and lakes. In Meadowbrook, it was observed that the chloride content reached a high of 11,000 ppm in December 1969. The runoff from the watershed was emitted in several surges. Chloride concentrations declined with the onset of summer, but still remained high, suggesting that some of the salt applied during the past winter appeared in the summer stream flow. Salt runoff entering a small lake, flowed directly to the lake bottom. The buildup of high density saline water in the lower portion of the lake prevented complete mixing in the spring. Incomplete mixing led to anoxic conditions in the lower lake strata. The population of bent hic fauna of the lake was changed by the flow of salt water into the lake. From a total of 10 species of dipteran larva and oligochaetes, only 4 species of the latter remained. 相似文献
997.
Richard A. Andrews 《Journal of the American Water Resources Association》1971,7(5):905-912
ABSTRACT. This study investigates economies associated with size of New England water utilities. Regression analysis techniques were applied to annual water cost and production data reported in the American Directory of Water Utilities (1968-1969). Modest economies of size in the production of water were found. Because in large communities more water is used per person, total cost increases at a slightly faster rate than population increases, but per unit costs of producing water decline. Substantial economies occurred when the number of customers was held constant and volume of water per customer increased. This study indicates possible economies when two or more of the many very small utilities combine activities to form a larger unit and by encouraging present customers to use more water. 相似文献
998.
ABSTRACT. We present a new approach to the nonlinear equations for the phreatic surface of groundwater flow from or into a reservoir. The differential equation is converted into an equivalent integral equation, which is then solved by a method of iteration. We obtain exact results for both drawdown and infiltration, including the special case of groundwater penetration into dry soil. 相似文献
999.
Richard A. Stephenson 《Journal of the American Water Resources Association》1971,7(6):1172-1179
Stream tributaries in the Des Moines River basin have been classified according to the glacial terrain through which they flow. Three stream types were categorized as follows: (1) streams that flow entirely on Wisconsin drift, (2) streams that flow entirely on Kansan drift, and (3) streams that have their headwaters located on new drift but have their lower reaches flowing on older drift. Selected channel and valley characteristics were measured and used to verify the stream type classification. Five variables were chosen for use in a multiple linear discriminatory analysis, which is a statistical technique developed for the purpose of classifying observations into one of several categories which have been predetermined. The streams in each group were verified with the exception of three anomalies based on the probability associated with the largest linear discriminant function. The rationale for the three anomalous streams is not easily determined. But, they are considered to be associated with pre-glacial drainage or at least pre-Wisconsin age drainage. Otherwise, the analysis shows that the major channels and valleys in the Des Moines River basin tend to reflect the glaciated upland surface. 相似文献
1000.
Abdul Rahim Hj. Nik Richard Lee J. D. Helvey 《Journal of the American Water Resources Association》1983,19(1):47-50
ABSTRACT: This study tests the hypothesis that climatic data can be used to develop a watershed model so that stream flow changes following forest harvest can be determined. Measured independent variables were precipitation, daily maximum and minimum temperature, and concurrent relative humidity. Computed variables were humidity deficit, saturated vapor pressure, and ambient vapor pressure. These climatic variables were combined to compute a monthly evaporation index. Finally, the evaporation index and monthly precipitation were regressed with measured monthly stream flow and the monthly estimates of stream flow were combined for the hydrologic year. A regression of predicted versus measured annual stream flow had a standard error of 1.5 inches (within 6.1 percent of the measured value). When 10, 15, and 20 years of data were used to develop the regression equations, predicted minus measured stream flow for the last 7 years of record (1972–1978) were within 16.8, 11.5, and 9.7 percent of the measured mean, respectively. Although single watershed calibration can be used in special conditions, the paired watershed approach is expected to remain the preferred method for determining the effects of forest management on the water resource. 相似文献