全文获取类型
收费全文 | 29847篇 |
免费 | 340篇 |
国内免费 | 246篇 |
专业分类
安全科学 | 1000篇 |
废物处理 | 1454篇 |
环保管理 | 3997篇 |
综合类 | 4482篇 |
基础理论 | 7792篇 |
环境理论 | 8篇 |
污染及防治 | 7349篇 |
评价与监测 | 2127篇 |
社会与环境 | 2043篇 |
灾害及防治 | 181篇 |
出版年
2023年 | 163篇 |
2022年 | 272篇 |
2021年 | 345篇 |
2020年 | 220篇 |
2019年 | 243篇 |
2018年 | 435篇 |
2017年 | 460篇 |
2016年 | 719篇 |
2015年 | 531篇 |
2014年 | 854篇 |
2013年 | 2464篇 |
2012年 | 1018篇 |
2011年 | 1349篇 |
2010年 | 1102篇 |
2009年 | 1145篇 |
2008年 | 1410篇 |
2007年 | 1329篇 |
2006年 | 1207篇 |
2005年 | 1079篇 |
2004年 | 1037篇 |
2003年 | 990篇 |
2002年 | 933篇 |
2001年 | 1091篇 |
2000年 | 768篇 |
1999年 | 482篇 |
1998年 | 363篇 |
1997年 | 383篇 |
1996年 | 397篇 |
1995年 | 465篇 |
1994年 | 394篇 |
1993年 | 343篇 |
1992年 | 376篇 |
1991年 | 355篇 |
1990年 | 326篇 |
1989年 | 322篇 |
1988年 | 295篇 |
1987年 | 241篇 |
1986年 | 247篇 |
1985年 | 247篇 |
1984年 | 267篇 |
1983年 | 254篇 |
1982年 | 268篇 |
1981年 | 221篇 |
1980年 | 165篇 |
1979年 | 181篇 |
1978年 | 162篇 |
1977年 | 133篇 |
1975年 | 137篇 |
1973年 | 167篇 |
1972年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Watershed analysis and watershed management are developing as tools of integrated ecological and economic study. They also assist decision-making at the regional scale. The new technology and thinking offered by the advent of the Internet and the World Wide Web is highly complementary to some of the goals of watershed analysis. Services delivered by the Web are open, interactive, fast, spatially distributed, hierarchical and flexible. The Web offers the ability to display information creatively, to interact with that information and to change and modify it remotely. In this way the Internet provides a much-needed opportunity to deliver scientific findings and information to stakeholders and to link stakeholders together providing for collective decision-making. The benefits fall into two major categories: methodological and educational. Methodologically the approach furthers the watershed management concept, offering an avenue for practical implementation of watershed management principles. For educational purposes the Web is a source of data and insight serving a variety of needs at all levels. We use the Patuxent River case study to illustrate the web-based approach to watershed management. A watershed scale simulation model is built for the Patuxent area and it serves as a core for watershed management design based on web applications. It integrates the knowledge available for the Patuxent area in a comprehensive and systematic format, and provides a conceptual basis for understanding the performance of the watershed as a system. Moreover, the extensive data collection and conceptualisation required within the framework of the modeling effort stimulates close contact with the environmental management community. This is further enhanced by offering access to the modeling results and the data sets over the Web. Additional web applications and links are provided to increase awareness and involvement of stakeholders in the watershed management process. We argue that it is not the amount and quality of information that is crucial for the success of watershed management, but how well the information is disseminated, shared and used by the stakeholders. In this respect the Web offers a wealth of opportunities for the decision-making process, but still to be answered are the questions at what scale and how widely will the Web be accepted as a management tool, and how can watershed management benefit from web applications. 相似文献
142.
Saif Ud din R.P. Oskui Maurice B. Dusseault A.N. Al Ghadban 《Journal of environmental management》2009,91(1):186-194
Waste generation and accumulating quantities of oil field waste are a matter of environmental concern. This study proposes the Slurry Fracture Injection (SFI) technique as an alternative waste disposal method. The slurried solids injection waste disposal method is environmentally secure and permanent, leaving no future liabilities that must be risk-evaluated or priced. An entire waste stream comprising ground solids and waste water can be injected into deep and hydraulically secure target strata with no contamination of potable water-bearing formations or formations outside the target zone that may contain resources (gas and oil). The slurry injection method can be used to clean and reclaim landfills, oil pits and granular waste dumps. This article proposes a two-tier screening method for evaluating the feasibility of this technique and the identification of suitable target zones. A stringent environmental and process control monitoring program should complement the planning and operational period to ensure environmental protection, waste containment, and regulatory HSE compliance. 相似文献
143.
144.
Cattle (Bos taurus) producers can replace a part of the traditional diet of barley (Hordeum vulgare L.) grain/silage with sunflower (Helianthus annus L.) seeds or canola meal (Brassica napus L.)/oil to enhance conjugated linoleic acids (CLA) content in milk and meat for its positive health benefits. The objective of this study is to investigate the effects of feeding sunflower or canola to finishing steers on cattle manure chemical properties and volatile fatty acid (VFA) content. The control diet contained 84% rolled barley and 15% barley silage, which provided only 2.6% lipid. The other six treatments had 6.6 to 8.6% lipid delivered from sources such as hay, sunflower seed (SS), canola meal/oil, and SS forage pellets. Manure samples (a mixture of cattle urine, feces, and woodchip bedding materials) were collected and analyzed after cattle had been on these diets for 113 d. The dietary source and level of lipid had no effect on organic N and nitrate N content in manure, but significantly affected ammonia N and VFA. Inclusion of SS forage pellets, hay, or canola meal/oil in cattle diets had no significant impact on manure characteristics, but SS significantly reduced the pH and increased propionic, isobutyric, and isovaleric content. In addition, N loss after excretion (mainly from urine N) increases with the pH and N levels in both feed and manure. The combination of SS with barley silage resulted in a lower VFA and NH3 content in manure and should be a more attractive option. To better manage N nutrient cycles and reduce NH3 related odor problems, feed and manure pH should be one of the factors to consider when determining feed mix rations. 相似文献
145.
Substantial amounts of NO3 from agricultural crop production systems on poorly drained soils can be transported to surface water via subsurface drainage. A field study was conducted from the fall of 1993 through 2000 on a tile-drained Canisteo clay loam soil (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) to determine the influence of fall vs. spring application of N and nitrapyrin [NP; 2-chloro-6-(trichloromethyl) pyridine] on NO3 losses from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Four anhydrous ammonia treatments (fall N, fall N + NP, spring preplant N, and spring N + NP) were replicated four times and applied at 135 kg N ha(-1) for corn on individual drainage plots. Drainage occurred in all seven years. Seventy-one percent of the annual drainage and 75% of the annual NO3 loss occurred in April, May, and June. Fifty-four percent of the NO3 lost in the drainage occurred during the corn phase and 46% during the soybean phase. Annual flow-weighted NO3-N concentrations for the fall, fall + NP, spring, and spring + NP treatments averaged 14.3, 11.5, 10.7, and 11.3 mg L(-1) during the corn phase but annual NO3-N concentrations were still > or =10 mg L(-1) in three of six years for the spring preplant treatment. Averaged across the six rotation cycles, flow-normalized NO3-N losses ranked in the order: fall N > spring N + NP > fall N + NP > spring N. Under these conditions, NO3 losses in subsurface drainage from a corn-soybean rotation can be reduced 14% by spring N and 10% by late fall N + NP compared with fall-applied N. Nitrate losses were not appreciably reduced by adding NP to spring preplant N. 相似文献
146.
Lee Benda Marwan A. Hassan Michael Church Christine L. May 《Journal of the American Water Resources Association》2005,41(4):835-851
Headwater streams comprise 60 to 80 percent of the cumulative length of river networks. In hilly to mountainous terrain, they reflect a mix of hillslope and channel processes because of their close proximity to sediment source areas. Their morphology is an assemblage of residual soils, landslide deposits, wood, boulders, thin patches of poorly sorted alluvium, and stretches of bedrock. Longitudinal profiles of these channels are strongly influenced by steps created by sediment deposits, large wood, and boulders. Due to the combination of small drainage area, stepped shallow gradient, large roughness elements, and cohesive sediments, headwater streams typically transport little sediment or coarse wood debris by fluvial processes. Consequently, headwaters act as sediment reservoirs for periods spanning decades to centuries. The accumulated sediment and wood may be episodically evacuated by debris flows, debris floods, or gully erosion and transported to larger channels. In mountain environments, these processes deliver significant amounts of materials that form riverine habitats in larger channels. In managed steepland forests, accelerated rates of landslides and debris flows resulting from the harvest of headwater forests have the potential to seriously impact the morphology of headwater streams and downstream resources. 相似文献
147.
Jennifer E. Kay Stephanie K. Kampf Rebecca N. Handcock Keith A. Cherkauer Alan R. Gillespie Stephen J. Burges 《Journal of the American Water Resources Association》2005,41(5):1161-1175
Emitted thermal infrared radiation (TIR, λ= 8 to 14 μm) can be used to measure surface water temperatures (top approximately 100 μm). This study evaluates the accuracy of stream (50 to 500 m wide) and lake (300 to 5,000 m wide) radiant temperatures (15 to 22°C) derived from airborne (MASTER, 5 to 15 m) and satellite (ASTER 90 m, Landsat ETM+ 60 m) TIR images. Applied atmospheric compensations changed water temperatures by ?0.2 to +2.0°C. Atmospheric compensation depended primarily on atmospheric water vapor and temperature, sensor viewing geometry, and water temperature. Agreement between multiple TIR bands (MASTER ‐ 10 bands, ASTER ‐ 5 bands) provided an independent check on recovered temperatures. Compensations improved agreement between image and in situ surface temperatures (from 2.0 to 1.1°C average deviation); however, compensations did not improve agreement between river image temperatures and loggers installed at the stream bed (from 0.6 to 1.6°C average deviation). Analysis of field temperatures suggests that vertical thermal stratification may have caused a systematic difference between instream gage temperatures and corrected image temperatures. As a result, agreement between image temperatures and instream temperatures did not imply that accurate TIR temperatures were recovered. Based on these analyses, practical accuracies for corrected TIR lake and stream surface temperatures are around 1°C. 相似文献
148.
Jeris A. Danielson A. Raziq Qazi 《Journal of the American Water Resources Association》1972,8(2):359-366
The agricultural production from the Lower South Platte Basin in Colorado represents a significant portion of the state economy. Until the early 1950's the production had developed almost exclusively by use of river water. Drought conditions combined with improved well technology resulted in an inordinate amount of well development in the valley during the period 1952-56. These wells were used for supplemental supply in many cases, but the application of sprinkler irrigation brought many acres of here-to-fore dry land into irrigated production. As a result of the vast amounts of groundwater withdrawal by the newly developed wells, senior surface appropriators found a decreasing amount of water available for use in the streams. The legislature, observing the doctrine of prior appropriation, ruled that all surface and ground water in a tributary would be treated and administered as one resource. This, of course, spelled doom for the well-oriented segment of the economy. Analysis of a segment of the river on an inflow-outflow basis was made with careful determination of all inflow-outflow in the study reach to include correlations required to determine ungaged side-channel in-flow and unmetered irrigation wells. Results indicate that wells have intercepted normal return flows to the river resulting in a decreased amount of surface water during the irrigation season. Stream depletion appears to equal the expected consumptive use of well water which ranged between 40% to 50% of the groundwater extraction. 相似文献
149.
Judith A. Pickering Richard A. Andrews 《Journal of the American Water Resources Association》1979,15(4):1039-1049
ABSTRACT: The objective of the study was to evaluate alternative land developments around New Hampshire lakes. Alternative development patterns, evaluated by their impacts on the lake area environment and area economy, included residential patterns, commercial patterns, and combinations of these two types. Phosphorus loading of the lake water was used as a proxy variable for changes in the lake water quality. Commercial developments yielded the highest revenues to the town and the local area. It also attracted the most lake users to the area as well as contributing the largest phosphorus loading in the lake waters. Residential developments, although contributing high revenues to the businessmen in the area, yielded less net income to the town. Phosphorus loading levels from residential developments were much lower than lake phosphorus loading by commercial developments. 相似文献
150.
David R. Hargis Charles A. McCauley 《Journal of the American Water Resources Association》1981,17(3):494-497
Two wellfields have been developed to provide water for a coal fired electric generating station in Arizona. Wellfield No. 1 penetrates the unconfined Coconino Sandstone aquifer, and wellfield No. 2 penetrates the composite Kaibab Limestone-Coconino Sandstone aquifer where ground water occurs under confined conditions. A well in each wellfield was pumped and water level drawdown data were collected before and after acidizing. The drawdown data at the various pumping rates were analyzed to determine the potential benefits of acidizing production water wells in both wellfields. After acidizing, the specific capacity of the well in wellfield No. 1 was improved about 50 percent at water production rates ranging from about 200 to 500 gallons per minute (gpm) (13 to 32 liters per second (lps)). After acidizing, the specific capacity of the well completed in wellfield No. 2 was improved about 100 percent at pumping rates ranging from about 1,250 to 2,200 gpm (79 to 139 lps). An annual saving of approximately 11 percent in pumping costs can be realized in wellfield No. 2, and savings are approximately four percent in wellfield No. 1. Acidization is beneficial for wells that can produce more than 500 gpm (32 lps), and is of marginal value for those that produce less than that amount. 相似文献