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641.
Matthew W. Snyder LaVone E. Simmons Jacob O. Kitzman Donna A. Santillan Mark K. Santillan Hilary S. Gammill Jay Shendure 《黑龙江环境通报》2013,33(6):547-554
We recently demonstrated whole genome sequencing of a human fetus using only parental DNA samples and plasma from the pregnant mother. This proof-of-concept study demonstrated how samples obtained noninvasively in the first or second trimester can be analyzed to yield a highly accurate and substantially complete genetic profile of the fetus, including both inherited and de novo variation. Here, we revisit our original study from a clinical standpoint, provide an overview of the scientific approach, and describe opportunities and challenges along the path toward clinical adoption of noninvasive fetal whole genome sequencing. © 2013 John Wiley & Sons, Ltd. 相似文献
642.
Mark S. Wipfli John S. Richardson Robert J. Naiman 《Journal of the American Water Resources Association》2007,43(1):72-85
Abstract: Headwater streams make up a large proportion of the total length and watershed area of fluvial networks, and are partially characterized by the large volume of organic matter (large wood, detritus, and dissolved organic matter) and invertebrate inputs from the riparian forest, relative to stream size. Much of those inputs are exported to downstream reaches through time where they potentially subsidize river communities. The relative rates, timing, and conversion processes that carry inputs from small streams to downstream reaches are reasonably well quantified. For example, larger particles are converted to smaller particles, which are more easily exported. Also, dissolved organic matter and surface biofilms are converted to larger particles which can be more easily intercepted by consumers. However, the quality of these materials as it affects biological activity downstream is not well known, nor is the extent to which timing permits biological use of those particles. These ecological unknowns need to be resolved. Further, land uses may disrupt and diminish material transport to downstream reaches by removing sources (e.g., forest harvest), by affecting transport and decomposition processes (e.g., flow regulation, irrigation, changes in biotic communities), and by altering mechanisms of storage within headwaters (e.g., channelization). We present conceptual models of energy and nutrient fluxes that outline small stream processes and pathways important to downstream communities, and we identify informational gaps that, if filled, could significantly advance the understanding of linkages between headwater streams and larger rivers. The models, based on empirical evidence and best professional judgment, suggest that navigable waters are significantly influenced by headwater streams through hydrological and ecological connectivities, and land use can dramatically influence these natural connectivities, impacting downstream riverine ecosystems. 相似文献
643.
F. Richard Hauer Jack A. Stanford Mark S. Lorang 《Journal of the American Water Resources Association》2007,43(1):104-117
Abstract: The Crown of the Continent is one of the premiere ecosystems in North America containing Waterton‐Glacier International Peace Park, the Bob Marshall‐Great Bear‐Scapegoat Wilderness Complex in Montana, various Provincial Parks in British Columbia and Alberta, several national and state forest lands in the USA, and Crown Lands in Canada. The region is also the headwater source for three of the continent’s great rivers: Columbia, Missouri and Saskatchewan that flow to the Pacific, Atlantic and Arctic Oceans, respectively. Headwaters originate in high elevation alpine environs characterized by high snow accumulations in winter and rainstorms in summer. Most headwaters of the region contain high quality waters with few ions in solution and extremely low nutrient concentrations. Alpine streams have few species of aquatic organisms; however, they often possess rare species and have hydrogeomorphic features that make them vulnerable to climatic change. Subalpine and valley bottom streams of the Crown of the Continent Ecosystem (CCE) flow through well forested watersheds. Along the elevation gradient, the streams and rivers of the CCE flow through series of confining and nonconfining valleys resulting in distinct canyon and floodplain reaches. The alluvial floodplains are characterized by high species diversity and bioproduction maintained by the hydrologic linkages of habitats. The streams and rivers of the CCE have low nutrient concentrations, but may be significantly affected by wildfire, various resource extraction activities, such as logging or mining and exurban encroachment. Wildfire has been shown to increase nutrient loading in streams, both during a fire and then following the fire for as much as 5 years. Logging practices increase nutrient loading and the algal productivity of stream periphyton. Logging and associated roads are also known to increase sediment transport into Crown of the Continent streams directly affecting spawning success of native trout. The CCE is one of the fastest growing regions in the USA because of the many recreational amenities of the region. And, while the region has many remarkably pristine headwater streams and receiving rivers, there are many pending threats to water quality and quantity. One of the most urgent threats comes from the coal and gas fields in the northern part of the Crown of the Continent, where coal deposits are proposed for mountain‐top removal and open‐pit mining operations. This will have significant effects on the waters of the region, its native plants and animals and quality of life of the people. 相似文献
644.
Mark F. Colosimo Peter R. Wilcock 《Journal of the American Water Resources Association》2007,43(2):499-521
Abstract: Earlier measurements of stream channel geometry on 19 reaches were repeated to provide a longitudinal study of stream channel adjustment over 13 years (1987‐2000) in the urbanizing Gwynns Falls, Maryland watershed. We observed both enlargement and reduction in channel size, depending on the extent of upstream development, the timing and location of urbanization and upstream channel adjustment, and the presence of hydrologic constrictions and grade controls. Based on a relatively simple visual assessment of the composition, size, and extent of instream sediment storage, we categorized stream reaches into three phases: aggraded (7 sites), early erosion (7 sites), and late erosion (5 sites). Aggraded sites had point and lateral bars mantled with fine‐grained sediment and experienced some reduction in cross‐sectional area, primarily through the deposition of fine‐grained material on bars in the channel margins. Early erosion sites had smaller bars and increases in channel cross‐sectional area as a consequence of the evacuation of in‐channel fine‐grained sediment. Fine‐grained sediments were either entirely absent or found only at a few high bar elevations at late erosion sites. Sediment evacuation from late erosion sites has both enlarged and simplified channels, as demonstrated by an increase in cross‐sectional area and a strong decrease in channel width variation. Channel cross‐sectional area enlargement, reduced channel width variation, and channel incision were ubiquitous at erosion sites. As a result, overbank flows were less common in the erosion sites as determined by high water marks left by a 2‐year flood that occurred during the study period. Principal causes for channel changes appear to be increased high flow durations and reduced sediment supply. Spatial variation in channel conditions could not be tied simply to sub‐basin impervious cover or watershed area. In‐channel sediment storage is a useful indicator of channel form and adjustment. When combined with information on development and sedimentation conditions in the contributing drainage, instream sediment storage can be used to effectively assess future channel adjustments. 相似文献
645.
Key aspects of environmental management exist within a legislative framework. The Rivers and Foreshores Improvement Act 1948 (NSW) and several Regional Environmental Plans created under the Environmental Planning and Assessment Act 1979 (NSW) make reference to ‘the top of the bank’ for defining areas of protected land adjacent to rivers, within which development
consent may be required. It is an arbitrary term and its use within the Rivers and Foreshores Improvement Act 1948 (NSW) leads to confusion. This paper examines the range of definitions of ‘the top of the bank’ in respect of natural watercourses
and aims to provide a more lucid and effective definition that will clarify existing ambiguities in legal interpretation.
The paper examines the historical origins of the phrase ‘top of the bank’, finding that stereotyped Eurocentric views of what
a river ‘should look like’ have impaired the legal definition for Australian rivers, thereby influencing common law and the
development of statutory definitions. Judicial applications of the phrase ‘top of the bank’ are examined from a geomorphological
perspective, demonstrating the misconceptions of the term in a legal context. The paper identifies the existence of widespread
support for the need to protect land adjacent to rivers in the interests of environmental, economic and social sustainability.
It concludes by calling for legislative reform that is both tailored to the individual site and consistent with overarching
goals at the catchment scale. 相似文献
646.
/ Geographic information systems (GIS) allow users to explore possible spatial relations that may exist within their data. At the Missouri Department of Conservation (MDC), GIS data is being used to help make management decisions. Thirteen geographic data layers of the Meramec River Basin, Missouri, were used to help demonstrate the usefulness of GIS for making fisheries management decisions. The data were used to help identify potential acquisition areas within the Meramec River Basin. The basin was separated into 22 strata based on ecoregion boundaries, watershed boundaries, and stream order. Suitability for acquisition was determined for each stratum based on species richness, habitat characteristics, percent of public land, and number of human impacts, such as gravel and ore mining. Eleven strata scored high enough to be recommended as potential acquisition areas. After further evaluation of the 11 strata, three were chosen as areas where available land and willing sellers should be considered. Four strata needed more sampling before land within them should be considered for acquisition. The final four were considered low priority because there was already a considerable amount of public land present in the strata. The analysis was helpful in allowing managers to focus in on a smaller area for acquisition consideration; 91% of the area was eliminated from the analysis. Instead of having to survey every parcel of land that becomes available, parcels that don't fall within the recommended strata can be eliminated without further investigation. 相似文献
647.
PROBLEM: Safety belt use rates among front seat occupants of passenger vehicles are substantially lower at night than during the day despite the fact that night driving is more dangerous. METHOD: Recent advances in night vision equipment now make it possible to enforce belt use laws in darkness. Reading, Pennsylvania conducted a night belt use publicity and enforcement campaign during September 2004 using night vision equipment. RESULTS: Front seat occupant belt use at night increased significantly from 50% prior to the campaign to 56% just after the campaign. Daylight belt use also increased though to a lesser extent (56% to 59%). Survey data indicated that motorists had heard about the campaign in newspapers and on television. Belt use increases were not seen during the same time period in a comparison community. 相似文献
648.
Mark E Grismer 《Water environment research》2005,77(7):3047-3053
Although constructed wetland treatment systems have been used in a variety of applications, uncertainty in adequately determining flow conditions or hydraulic residence times ("hydraulic efficiencies") and degradation model parameters remains a problem with their design. Breakthrough or impulse-type tracer studies in constructed wetlands often result in residence-time distributions exhibiting long skewed "tails" suggesting multiple flow channels or perhaps unrealistically large dispersion factors. A fractional-flow analysis is developed here to quantify possible flow non-uniformity in a subsurface-flow constructed wetland and is then used to assess the effects of non-uniformity and degradation model parameter variability on constituent (for example, chemical oxygen demand) removal. A model application to tracer data developed previously demonstrates how flow non-uniformity alone can account for significant "tailing" and can be related to even moderate estimated dispersion numbers. From the analysis, it is evident that flow non-uniformity is of greater concern than decay parameter uncertainty, and that, from a constructed wetland design and operation perspective, every effort should be made to ensure relative flow uniformity across the constructed wetland. 相似文献
649.
Mark E. Hines 《Water, Air, & Soil Pollution: Focus》2006,6(5-6):523-536
Microorganisms are responsible for the bulk of transformations that occur in surficial sediments. They are most active at
redox boundaries where they can benefit from access to various oxidants and reductants generated during redox cycling events.
To illustrate the dynamics of microbially mediated processes, especially those involving sulfur and metal cycles, processes
were compared in habitats either bioturbated by a capitellid worm or inhabited by a salt marsh grass. The presence of macrofauna
and macroflora greatly altered the three-dimensional array of redox gradients in sediments, but the type and form of reductants
and oxidants provided varied greatly; clastic sedimentary infauna subducted solid phase organic material and iron oxides,
whereas plant roots released dissolved organic matter and oxygen. These differences resulted in a bioturbated system that
exhibited a rapid sulfur cycle (residence time of minutes), but a slower iron cycle (days), whereas vegetation caused a slow
sulfur cycle and rapid iron cycle. Alteration of sediments by higher life forms also greatly affected the composition and
relative abundances of sedimentary bacteria, even on short time scales. Although redox cycling at interfaces can be somewhat
predictable, variations in response to biological and physical perturbations demonstrated wide differences in the dynamics
of redox-mediated processes. 相似文献
650.