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481.
New information on the brooding reproduction of Amphiura carchara, and previous studies of several deep-sea congeners, contradict the prevailing notion that direct development is exceptional
among deep-sea echinoderms. Over 500 specimens of A. carchara from 2,850 to 4,100-m depths off the coast of California, USA, were studied. The species was found to be gonochoric, although
most brooding species of ophiuroids are hermaphroditic. Females each brooded up to 72 embryos at a time, with up to 10 in
a single bursa. The embryos of individual adults were often at different stages of development, but those brooded in a single
bursa tended to be at the same stage. Thus, the species has characteristics that breach the distinctions between sequential
and simultaneous brooding exhibited by shallow-water ophiuroids. The embryos developed from yolky eggs that are large for
an ophiuroid, with the mean largest oocytes 0.45 mm, and ranging to 1.28 mm in diameter. Almost all late-stage embryos were
positioned with their mouth and arms pressed against the wall of the bursa, possibly to facilitate the uptake of nutrients
from the parent. Thus, A. carchara may be matrotrophic. The largest embryos examined had a rudimentary disk skeleton, and arms with four joints and a terminal
plate. Emerging juveniles probably differ in disk diameter. The species appears to brood year round, although differences
in gonad size, the incidence of brooding, and the relative numbers of early developmental stages in summer and winter samples
indicated that there are seasonal trends in reproduction.
Received: 14 February 2000 / Accepted: 3 July 2000 相似文献
482.
The coastline near the southern tip of Africa is characterized by large mobile dunes that are driven along wide beaches by
strong winds throughout the year. This results in the blockage of the river mouths causing severe flooding of the low-lying
farmland of the Agulhas Plain during the rainy winter season. Large parts of the driftsands were stabilized with the European
dune pioneer species Marram grass (Ammophila arenaria), which has proved highly invasive along the North American west coast. In order to establish the potential invasiveness
ofA. arenaria in South African coastal dune systems and its role in the succession of a large stabilization area, studies were carried
out on De Mond Nature Reverve. Using aerial photos, maps and planting records, the vegetation of sites of various ages were
sampled. By means of this chronosequence of stands, there is clear evidence that succession takes place at De Mond. Four communities
are distinguished, varying from recent plantings ofA. arenaria to mature dune thicket or dune fynbos (heath) vegetation. These relate to four different stages of succession,A. arenaria occurring in reduced abundance in the older communities. After 50 years, formerA. arenaria areas are usually covered by dense dune scrub and in some places even in asteraceous dune fynbos. Succession is most rapid
in sheltered, moist dune slacks, butA. arenaria remains vigorous in conditions favourable for its growht, i.e. on exposed, steep dune slopes with strong sand movement.A. arenaria does not appear to spread unaidedly at De Mond and has been successfully used for temporary dune stabilization. 相似文献
483.
Elani UA 《Environmental monitoring and assessment》2007,124(1-3):235-241
The ultraviolet UV solar radiation flux is monitored over a fixed time interval to study the daily, monthly and annual variations
for a nearly one decade in Riyadh. Mathematical expressions will be presented based on a comparison between theoretical and
experimental values. It is believed that the present analysis of UV radiation suggest that the environmental effects led to
a better understanding of UV scattering, UV reflection, ozone and clouds layers in Riyadh and other selected areas in the
mid-east region. 相似文献
484.
Seasonal variation in physicochemical properties of coastal waters of Kalpakkam, east coast of India with special emphasis on nutrients 总被引:1,自引:0,他引:1
K. K. Satpathy A. K. Mohanty U. Natesan M. V. R. Prasad S. K. Sarkar 《Environmental monitoring and assessment》2010,164(1-4):153-171
A study pertaining to the seasonal variation in physicochemical properties of the coastal waters was carried out at Kalpakkam coast for a period of 1 year (February 2006 to January 2007). It revealed that the coastal water was significantly influenced by freshwater input during North East (NE) monsoon and post-monsoon periods. Concentration of all the nutrients and dissolved oxygen (DO) was relatively high during the NE monsoon, whereas, salinity and chlorophyll-a (chl-a) were at their minimum level during this period. Phytoplankton production peak was observed in summer during which a typical marine condition prevailed. The present observed values of nitrate, phosphate, silicate, and turbidity are significantly high (five to ten times) compared to that of the pre-Tsunami period from this coast. Relatively low DO and chl-a concentration was noticed during the post-Tsunami period. A notable feature of this study is that though nutrient concentration in the coastal waters during post-Tsunami period has increased significantly, turbidity, the most single dominating factor, was found to adversely affect the phytoplankton production during post-Tsunami period as reflected by relatively low chl-a concentration. Thus, the post-Tsunami period may result in a change in coastal biodiversity pattern concomitant with change in coastal water quality. 相似文献
485.
Pujari PR Padmakar C SuriNaidu L Vaijnath VU Kachawe B Gurunadha Rao VV Labhasetwar PK 《Environmental monitoring and assessment》2012,184(5):2921-2937
The Pithampur Industrial sectors I, II, and III, located approximately, 45 km from Indore in Central India have emerged as
one of the largest industrial clusters in the region. Various types of industries ranging from automobiles to chemicals and
pharmaceuticals have been set up in the region since 1990. Most of the industries have effluent treatment plants (ETP) for
treating wastewater before its disposal on land and/or in water body. The present study is an attempt to assess the groundwater
quality in the watersheds surrounding these industrial sectors to develop the baseline groundwater quality in order to enable
the policy makers to facilitate decisions on the development of industries in this region. The industries are located in two
sub-watersheds, namely, Gambhir river sub-watershed and Chambal river sub-watershed. Geologically, the study area is located
in the Deccan traps of Cretaceous to Paleocene age. The different basaltic flow units underlie clayey soils varying in thickness
from 2–3 m. The aquifer is mostly of unconfined nature. Samples have been collected from a network of observation wells set
up in the watersheds. The water quality analysis of the groundwater samples has been carried out six times during three hydrological
cycles of 2004, 2005, and 2006. The results indicate that a few observation wells in the vicinity of the industrial clusters
have very high TDS concentration and exceed the Bureau of Indian Standards (BIS) guideline for TDS concentration. The contamination
of groundwater has been more severe in the Gambhir watershed as compared to the Chambal watershed. The presence of the impermeable
clay layers has resulted in a slow migration of contaminants from the sources. The findings reveal that there is no significant
groundwater contamination in the Pithampur industrial sectors except in the vicinity of the industrial clusters, which indicates
that there is good environmental space available for the expansion of industrial units in the Pithampur industrial hub. 相似文献
486.
A. R. Ghumman I. Hassan Q. U. Z. Khan M. A. Kamal 《Environmental monitoring and assessment》2013,185(6):4897-4905
In this paper, variability in precipitation pattern of Pakistan due to environmental and climatic changes has been studied. Maps have been generated to depict global precipitation variation. Precipitation data of 25 stations of Pakistan have been used. These data were taken from Meteorological Department, Islamabad, Pakistan. The results of two global climate models, namely Australia’s Commonwealth Scientific and Industrial Research’s third generation general circulation model and National Center for Atmospheric Research’s first generation precipitation circulation model for A2 scenario have been applied to investigate the changes. It is observed that precipitation pattern will change significantly in the future. The occurrence of precipitation in all seasons for Pakistan is expected to increase with almost uniform distribution across a season. Average annual precipitation of the country will undergo an increase in the range of +57 to +71 % as compared to average of the base period. 相似文献
487.
R. B. Neveril J. U. Price K. L. Engdahl 《Journal of the Air & Waste Management Association (1995)》2013,63(11):1171-1174
Previous articles in this series discussed the equipment costs of control devices, gas conditioning equipment, hoods, ductwork, and dampers. In this article, the discussion will concern the fans and associated components required to convey the gas stream from the initial pollutant source to the control device. 相似文献
488.
This study investigated the removal of Reactive Black 5 (RB5) textile dye from aqueous solutions using cotton (Gossypium hirsutum) seed shell (CSS) as low cost adsorbents. The data were described according to the Freundlich and Langmuir isotherm models. Of these, the Langmuir model provided the best fit for the experimental data. The highest measured adsorption density was 12.19 mg/g at pH 2. An equilibrium adsorption rate of RB5 by CSS (q(e) = 11.879 mg/g) was observed at 30 minutes. In order to evaluate the adsorption kinetic mechanisms, pseudo first and second order rate kinetic models and an intraparticle diffusion model were applied, with the pseudo second order model providing an excellent fit for the data. 相似文献
489.
Aiming at the stimulation of intrinsic microbial activity, pulses of pure oxygen or pressurized air were recurrently injected into groundwater polluted with chlorobenzene. To achieve well-controlled conditions and intensive sampling, a large, vertical underground tank was filled with the local unconfined sandy aquifer material. In the course of two individual gas injections, one using pure oxygen and one using pressurized air, the mass transfer of individual gas species between trapped gas phase and groundwater was studied. Field data on the dissolved gas composition in the groundwater were combined with a kinetic model on gas dissolution and transport in porous media. Phase mass transfer of individual gas components caused a temporary enrichment of nitrogen, and to a lower degree of methane, in trapped gas leading to the formation of excess dissolved nitrogen levels downgradient from the dissolving gas phase. By applying a novel gas sampling method for dissolved gases in groundwater it was shown that dissolved nitrogen can be used as a partitioning tracer to indicate complete gas dissolution in porous media. 相似文献
490.
Raysoni AU Sarnat JA Sarnat SE Garcia JH Holguin F Luèvano SF Li WW 《Environmental pollution (Barking, Essex : 1987)》2011,159(10):2476-2486
Paired indoor and outdoor concentrations of fine and coarse particulate matter (PM), PM2.5 reflectance [black carbon(BC)], and nitrogen dioxide (NO2) were determined for sixteen weeks in 2008 at four elementary schools (two in high and two in low traffic density zones) in a U.S.-Mexico border community to aid a binational health effects study. Strong spatial heterogeneity was observed for all outdoor pollutant concentrations. Concentrations of all pollutants, except coarse PM, were higher in high traffic zones than in the respective low traffic zones. Black carbon and NO2 appear to be better traffic indicators than fine PM. Indoor air pollution was found to be well associated with outdoor air pollution, although differences existed due to uncontrollable factors involving student activities and building/ventilation configurations. Results of this study indicate substantial spatial variability of pollutants in the region, suggesting that children’s exposures to these pollutants vary based on the location of their school. 相似文献