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851.
Ventilation system should blow large quantity of airflow particularly in case of toxic or explosive gasses emission from the wall rocks and face, especially in long tunnels. In these cases, multiple jet fans are usually required, so that they could be grouped together as serial, parallel or combined arrangements through ventilation system or equally spaced along the tunnel. There is a serious requirement to have some reserved jet fans along with the main once, so that the operation of the ventilation system could be reliable. Operation of a ventilation system is usually evaluated by experiences and engineering judgments which follow empirical methods.The aim of this paper is to introduce an approach to evaluate reliability of ventilation system in the long tunnels. The method is based upon using the failure rate time to determine the probability of the failure of an active jet fan and also the repair rate time to determine the probability of repairing the out of work ones .In this approach, the active and standby jet fans are modelled as a stochastic process. Therefore, the probability of replacing each failed jet fan with a standby jet fan is estimated using Markov Chains theory .From this point of view a more realistic decision-making for the number of standby jet fans and also reducing the risk as well as uncertainties can be based upon the analysis of such a results. 相似文献
852.
Dennis F. Naugle Terrence K. Pierson 《Journal of the Air & Waste Management Association (1995)》2013,63(10):1298-1307
Risk characterization is defined by both the U.S. National Academy of Sciences and the U.S. EPA as the estimation of human health risk due to harmful (i.e., toxic or carcinogenic) substances or organisms. Risk characterization studies are accomplished by integrating quantitative exposure estimates and dose-response relationships with the qualitative results of hazard identification. A Risk Characterization Framework has been developed to encourage a systematic approach for analysis and presentation of risk estimates. This methodology subdivides the four common components of the risk assessment process into ten elements. Each of these elements is based on a term in a predictive risk equation. The equation allows independent computations of exposure, dose, lifetime individual risk, and risk to affected populations. All key assumptions in the predictive risk equation can be explicitly shown. This is important to understand the basis and inherent uncertainties of the risk estimation process. The systematic treatment of each of the ten elements in this framework aids in the difficult job of comparing risk estimates by different researchers using different methodologies. The Risk Characterization Framework has been applied to various indoor and outdoor air pollutants of a carcinogenic nature. With further development, it also promises to be applicable to noncarcinogenic effects. 相似文献
853.
John S. Eckert Ralph F. Strigle Jr. 《Journal of the Air & Waste Management Association (1995)》2013,63(10):961-966
A general discussion of packed scrubbers for particle collection is presented. Data on liquid entrainment separation, ammonium chloride fume collection, and clay particle collection are given. 相似文献
854.
This paper provides a preliminary assessment of the suitability of Tertiary sedimentary basins in Northern, Western and Eastern Greece in order to identify geological structures close to major CO2 emission sources with the potential for long-term storage of CO2. The term “emissions” refers to point source emissions as defined by the International Energy Agency, including power generation, the cement sector and other industrial processes. The Prinos oil field and saline aquifer, along with the saline formations of the Thessaloniki Basin and the Mesohellenic Trough have been identified as prospective CO2 geological storage sites. In addition, a carbonate deep saline aquifer occurring at appropriate depths beneath the Neogene-Quaternary sediments of Ptolemais-Kozani graben (NW Greece) is considered. The proximity of this geological formation to Greece's largest lignite-fired power plants suggests that it would be worthwhile undertaking further site-specific studies to quantify its storage capacity and assess its structural integrity. 相似文献
855.
Abstract: The probability of persistence of many species of hibernating bats in the United States is greatly reduced by an emerging infectious disease, white‐nose syndrome (WNS). In the United States WNS is rapidly spreading and is associated with a psychrophilic fungus, Geomyces destructans. WNS has caused massive mortality of bats that hibernate. Efforts to control the disease have been ineffective. The culling of bats in hibernacula has been proposed as a way to break the transmission cycle or slow the spread of WNS. We formulated a disease model to examine the efficacy of culling to abate WNS in bat populations. We based the model dynamics on disease transmission in maternity roosts, swarms, and hibernacula, which are the arenas of contact among bats. Our simulations indicated culling will not control WNS in bats primarily because contact rates are high among colonial bats, contact occurs in multiple arenas, and periodic movement between arenas occurs. In general, culling is ineffective in the control of animal diseases in the wild. 相似文献
856.
Species differ widely with regard to parental investment strategies and mechanisms underlying those strategies. The passing of benefits to likely offspring can be instantiated with a number of different computational and behavioral systems. We report results from an agent-based model in which offspring maintain proximity with parents and parents transmit benefits to offspring without the capacity of either parent or offspring to 'recognize' one another. Instead, parents follow a simple rule to emit benefits after reproducing and offspring follow a simple rule of moving in the direction of positive benefit gradients. This model differs from previous models of spatial kin-based altruism in that individuals are modeled as having different behavioral rules at different life stages and benefits are transmitted unidirectionally from parents to offspring. High rates of correctly directed parental investment occur when mobility and sociality are low and parental investment occurs over a short period of time. We suggest that strategies based on recognition and bonding/attachment might serve to increase rates of correctly directed parental investment under parameters that are shown here to otherwise lead to high rates of misdirected and wasted parental investment. 相似文献
857.
E. Vignati M.C. Facchini M. Rinaldi C. Scannell D. Ceburnis J. Sciare M. Kanakidou S. Myriokefalitakis F. Dentener C.D. O'Dowd 《Atmospheric environment (Oxford, England : 1994)》2010,44(5):670-677
The chemical composition of marine aerosols as a function of their size is an important parameter for the evaluation of their impact on the global climate system. In this work we model fine particle organic matter emitted by sea spray processes and its influence on the aerosol chemical properties at the global scale using the off-line global Chemistry-Transport Model TM5. TM5 is coupled to a microphysical aerosol dynamics model providing size resolved information on particle masses and numbers. The mass of the emitted sea spray particles is partitioned between water insoluble organic matter (WIOM) and sea salt components in the accumulation mode using a function that relates the emitted organic fraction to the surface ocean chlorophyll-a concentrations. The global emission in the sub-micron size range of organic matter by sea spray process is 8.2 Tg yr?1, compared to 24 Tg fine yr?1 sea-salt emissions. When the marine sources are included, the concentrations of modelled primary particulate organic matter (POM) increase mainly over the oceans. The model predictions of WIOM and sea salt are evaluated against measurements carried out at Mace Head (Northern Hemisphere) and Amsterdam Island (Southern Hemisphere), showing that in clean marine conditions WIOM marine emissions contribute significantly to POM values. 相似文献
858.
859.
F. Ferrero M. Beckmann-Kluge U. Schmidtchen K. Holtappels 《Journal of Loss Prevention in the Process Industries》2010,23(5):654-661
In this paper two different approaches for predicting the heating-up of an acetylene cylinder involved in a fire and the afterward cooling with water are presented. In the simulations polynomial functions were used to describe the temperature dependency of the thermal properties of the cylinder interior, which is a complex system composed by a solid porous material, a solvent (typically acetone) and acetylene dissolved in it. Model equations covered heat conduction in the cylinder interior and at its walls. In the first approach the cylinder surroundings were simulated as a further domain constituted by CO2, during the fire exposure, and for water, during the cooling. In this domain the coupled heat transfer (convection and conduction) and the momentum equation (Navier–Stokes) were solved. In the second approach no further domain was considered but boundary conditions were set directly on the cylinder walls. Results of the calculations performed with both approaches are presented. This work could prove helpful in predicting to which extent the interior of an acetylene cylinder exposed to fire reaches temperatures capable of initiating the decomposition of acetylene and to determine how long a water cooling should be applied, so that the system is brought again under non-critical conditions. 相似文献
860.
Brazil is the largest worldwide producer of alcohol and sugar from sugar-cane and has an extensive alternative program for car fuel which is unique. The objective of this work is to offer one management option of a solid residue produced by this industrial segment. The pressed sugar-cane bagasse is burned to produce steam and electricity by cogeneration. The combustion yields both bottom and fly ashes which contain high amounts of silicon oxide as a major component. Fly ash which contains a high volume (>30% by weight) of charcoal was used in this work. The ash was sieved to separate the thick charcoal from inorganic materials which are concentrated in the thinner fraction. The briquettes were hand pressed using charcoal mixed with a binder (starch) obtained from cassava flour (a tropical root). The results (density, mechanical resistance) obtained with 8% by weight of starch binder are presented here. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to characterize the ashes and the briquettes. The results show that sugar-cane bagasse fly ash (SCBFA) can be used to produce briquettes with an average density of 1.12 g cm?3 and an average calorific value of 25,551 kJ/kg. 相似文献