全文获取类型
收费全文 | 33352篇 |
免费 | 388篇 |
国内免费 | 235篇 |
专业分类
安全科学 | 907篇 |
废物处理 | 1356篇 |
环保管理 | 4577篇 |
综合类 | 5898篇 |
基础理论 | 9004篇 |
环境理论 | 18篇 |
污染及防治 | 8270篇 |
评价与监测 | 2053篇 |
社会与环境 | 1650篇 |
灾害及防治 | 242篇 |
出版年
2022年 | 233篇 |
2021年 | 238篇 |
2019年 | 243篇 |
2018年 | 396篇 |
2017年 | 439篇 |
2016年 | 678篇 |
2015年 | 536篇 |
2014年 | 765篇 |
2013年 | 2688篇 |
2012年 | 972篇 |
2011年 | 1333篇 |
2010年 | 1093篇 |
2009年 | 1138篇 |
2008年 | 1308篇 |
2007年 | 1398篇 |
2006年 | 1287篇 |
2005年 | 1062篇 |
2004年 | 1022篇 |
2003年 | 1021篇 |
2002年 | 947篇 |
2001年 | 1169篇 |
2000年 | 899篇 |
1999年 | 534篇 |
1998年 | 418篇 |
1997年 | 433篇 |
1996年 | 441篇 |
1995年 | 493篇 |
1994年 | 465篇 |
1993年 | 447篇 |
1992年 | 444篇 |
1991年 | 433篇 |
1990年 | 441篇 |
1989年 | 408篇 |
1988年 | 372篇 |
1987年 | 348篇 |
1986年 | 346篇 |
1985年 | 330篇 |
1984年 | 369篇 |
1983年 | 354篇 |
1982年 | 380篇 |
1981年 | 348篇 |
1980年 | 305篇 |
1979年 | 321篇 |
1978年 | 267篇 |
1977年 | 251篇 |
1975年 | 199篇 |
1974年 | 244篇 |
1973年 | 230篇 |
1972年 | 232篇 |
1971年 | 215篇 |
排序方式: 共有10000条查询结果,搜索用时 739 毫秒
811.
Barry D. Keim Gregory E. Faiers 《Journal of the American Water Resources Association》1996,32(1):117-124
ABSTRACT: In most studies, quantile estimates of extreme 24-hour rainfall are given in annual probabilities. The probability of experiencing an excessive storm event, however, differs throughout the year. As a result, this paper explored the differences between heavy rainfall distributions by season in Louisiana. It was concluded by using the Kruskal-Wallis and Mann-Whitney tests that the distribution of heavy rainfall events differs significantly between particular seasons at the sites near the Gulf Coast. Furthermore, seasonal frequency curves varied dramatically at the four sites examined. Mixed distributions within these data were not found to be problematic, but the mechanisms that produced the events were found to change seasonally. Extreme heavy rainfall events in winter and spring were primarily generated by frontal weather systems, while summer and fall events had high proportions of events produced by tropical disturbances and airmass (free-convective) conditions. 相似文献
812.
William R. Krug 《Journal of the American Water Resources Association》1996,32(4):745-752
ABSTRACT: Streamflow for 67 years was simulated for Coon Creek at Coon Valley, Wisconsin, for three conditions in the drainage basin: (1) conditions in the 1930s; (2) conditions in the 1970s, excluding flood-detention reservoirs; and (3) conditions in the 1970s, including flood-detention reservoirs. These simulations showed that the changes in agricultural practices over 40 years (1940–80) reduced the 100-year flood by 53 percent (from 38,900 to 18,300 cubic feet per second). The flood-detention reservoirs reduced the 100-year flood by an additional 17 percent (to 15,100 cubic feet per second). The simulation was accomplished by calibrating a precipitation-runoff model to observed rainfall and runoff during two separate periods (1934–40 and 1978–81). Comparisons of model simulations showed that differences between the model calibrations for the two periods were statistically significant at the 95 percent confidence level. 相似文献
813.
L. Jeffrey Lefkoff Donald R. Kendall 《Journal of the American Water Resources Association》1996,32(3):451-463
ABSTRACT: A non-linear optimization model is applied to the California State Water Project (SWP) and portions of the Central Valley Project (CVP). The model accounts for the major hydrologic, regulatory, and operational features of both projects. The model maximizes long-term SWP yields over a 70-year period, using a quarterly time step. The potential for increased yield associated with a proposed facility improvement is evaluated with the model. The proposed facility is an extension of the Folsom-South Canal, which would allow water to be conveyed from the American River below Folsom Reservoir into New Melones Reservoir on the Stanislaus River or into the California Aqueduct. Model results indicate that extension of the Folsom-South Canal has the potential to increase SWP yields by 13 percent. 相似文献
814.
D. E. Barb J. F. Cruise X. Mo 《Journal of the American Water Resources Association》1996,32(3):511-519
ABSTRACT: A model for urban stormwater quality was developed in this study. The basis for the model is the process by which pollutants build up on the watershed surface. For the wet climate of the study site, it was assumed that there exists an interval of time over which the pollutant buildup equals the pollutant washoff (no accumulation of pollutant). The buildup model was represented by a linear function of the antecedent dry time. The buildup function was then linked with a pollutant washoff model represented by a power function of the storm runoff volume. Various time intervals for no net accumulation were tested to calibrate the model. The model was calibrated to observed data for two small urban basins in Baton Rouge, Louisiana, and model results were used to analyze the behavior of phosphorus concentrations in storm runoff from these basins over a long period of time. 相似文献
815.
Thermal and mechanical properties of poly(lactic Acid) and poly(ethylene/butylene Succinate) blends 总被引:2,自引:0,他引:2
In this study, blends of poly (lactic acid) (PLA) with poly(ethylene/butylene succinate) (Bionolle) have been investigated
for their thermal and mechanical properties as a function of the concentration of Bionolle. Differential scanning calorimetry
(DSC), dynamic mechanical analysis (DMA), and tensile tests were used to characterize the blends. From the results of the
DMA and DSC, it was found that this blend system was not miscible within the compositions studied. DSC results showed that
adding Bionolle aids in crystallization of PLA. It was observed that increasing the Bionolle concentration led to a slight
increase in the strain-at-break of the blends but a decrease in the Young’s modulus and ultimate tensile strength. Biaxially
oriented films showed an increase in tensile strength, modulus, and strain-at-break. 相似文献
816.
There are numerous technologies currently being tested by EPA, universities throughout the world, and private research organizations. A few of the more promising innovative technologies as well as fully tested and proven remedies for treating contaminated groundwater are presented in this article. Although several of those technologies have been in existence for only four to five years, the results of full-scale testing are being produced. The method for each of these promising technologies is described, results from recent field-scale studies are summarized, and a discussion of cost is presented. 相似文献
817.
Werner E. G. Müller 《Die Naturwissenschaften》1998,85(1):11-25
Geodia cydonium , which code for proteins. The analyses of their deduced amino acid sequences allowed a molecular biological approach to solve
the problem of monophyly of Metazoa. Molecules of the extracellular matrix/basal lamina, with the integrin receptor, fibronectin,
and galectin as prominent examples, cell-surface receptors (tyrosine kinase receptor), elements of sensory systems (crystallin,
metabotropic glutamate receptor), and homologs/modules of an immune system (immunoglobulin like molecules, scavenger receptor
cysteine-rich, and short consensus repeats, rhesus system) classify the Porifera as true Metazoa. As living fossils, provided
with simple, primordial molecules allowing cell-cell and cell-matrix adhesion as well as processes of signal transduction
as known in a more complex manner from higher Metazoa, they also show peculiarities not known in other metazoan phyla. Tissues
of sponges are rich in telomerase activity, suggesting a high plasticity in the determination of cell lineages. It is concluded
that molecular biological studies with sponges as model will not only help to understand the evolution of Protoctista to Metazoa
but also the complex, hierarchial regulatory network of cells in higher Metazoa. 相似文献
818.
819.
820.