首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   396篇
  免费   51篇
  国内免费   81篇
安全科学   150篇
废物处理   13篇
环保管理   41篇
综合类   194篇
基础理论   34篇
污染及防治   41篇
评价与监测   13篇
社会与环境   5篇
灾害及防治   37篇
  2024年   1篇
  2023年   4篇
  2022年   7篇
  2021年   28篇
  2020年   12篇
  2019年   7篇
  2018年   12篇
  2017年   19篇
  2016年   20篇
  2015年   31篇
  2014年   16篇
  2013年   19篇
  2012年   39篇
  2011年   25篇
  2010年   30篇
  2009年   28篇
  2008年   18篇
  2007年   33篇
  2006年   24篇
  2005年   30篇
  2004年   27篇
  2003年   18篇
  2002年   6篇
  2001年   9篇
  2000年   16篇
  1999年   10篇
  1998年   5篇
  1997年   6篇
  1996年   3篇
  1995年   5篇
  1994年   3篇
  1993年   4篇
  1992年   2篇
  1991年   1篇
  1989年   1篇
  1984年   3篇
  1983年   1篇
  1979年   1篇
  1977年   1篇
  1973年   1篇
  1971年   2篇
排序方式: 共有528条查询结果,搜索用时 46 毫秒
51.
A methodology to determine the laminar burning velocity from closed vessel gas explosions is explored. Unlike other methods which have been used to measure burning velocities from closed vessel explosions, this approach belongs to the category which does not involve observation of a rapidly moving flame front. Only the pressure–time curve is required as experimental input. To verify the methodology, initially quiescent methane–air mixtures were ignited in a 20-l explosion sphere and the equivalence ratio was varied from 0.67 to 1.36. The behavior of the pressure in the vessel was measured as a function of time and two integral balance models, namely, the thin-flame and the three-zone model, were fitted to determine the laminar burning velocity. Data on the laminar burning velocity as a function of equivalence ratio, pressure and temperature, measured by a variety of other methods have been collected from the literature to enable a comparison. Empirical correlations for the effect of pressure and temperature on the laminar burning velocity have been reviewed and two were selected to be used in conjunction with the thin-flame model. For the three-zone model, a set of coupled correlations has been derived to describe the effect of pressure and temperature on the laminar burning velocity and the laminar flame thickness. Our laminar burning velocities are seen to fall within the band of data from the period 1953–2003. A comparison with recent data from the period 1994–2003 shows that our results are 5–10% higher than the laminar burning velocities which are currently believed to be the correct ones for methane–air mixtures. Based on this observation it is concluded that the methodology described in this work should only be used under circumstances where more accurate methods can not be applied.  相似文献   
52.
以某隧道爆破开挖为实例,利用BP神经网络解决复杂非线性函数逼近问题的能力,以最大段药量、爆心距、爆破分段数、泊松比、岩石基本质量指标作为影响爆破振动速度的主要因素,选取不同维数的输入变量建立BP神经网络模型来预测爆破振动速度。对比分析各组预测值与实测值之间的相对误差,选取合理维数的输入变量建立了爆破振动危害预测的BP神经网络模型。  相似文献   
53.
Large TNT equivalent explosions usually arise from accidents occurring during the transportation, storage, and manufacturing of chemicals relevant to process industries. The blast wave generated by the explosion will spread and interact with the surrounding factories and storehouses, damaging the building structures within several kilometers and causing significant casualties and property losses. This study aims to develop an efficient numerical simulation method to predict blast loads to estimate the consequences of accidents involving far-field free air bursts or surface burst explosions. Before its interaction with the interested target, a blast wave is generated in the numerical model by specifying the initial and boundary conditions of the disturbed air. Based on empirical data of incident overpressure, an explicit formula to calculate the air particle velocity is derived from the governing equations of a perfect inviscid gas. A simplified path line method is proposed to calculate the air density. The proposed method is applied to the LS-DYNA CESE solver to simulate the blast loads on building structures in the far field. Validations against empirical data and experiments indicate that the proposed method is sufficiently accurate for engineering applications and, through a case study, presents a more efficient performance than the LOAD_BLAST_ENHANCED (LBE) and mapping methods.  相似文献   
54.
The roughness length at the air-sea interface during free convection (z0fc) is mainly related to the convective velocity (w*) rather than the friction velocity (u*). The parameterization of z0fc with w * 2 /g as proposed by Abdella and DAlessio in 2003 is evaluated. It is shown that their proposed formula is consistent with field measurements. In order to avoid self-correlation by using u*, a new parameterization of w* with wind speed (Uz) at height z and stability parameter (z/L, where L is the buoyancy length) is proposed. This new formula for w* is in agreement with an independent field result.  相似文献   
55.
大气污染源监测采样技术   总被引:3,自引:0,他引:3  
依据气态污染源共同的排放特性及平均排放浓度,排放速率的概念,导出气态污染源监测中常用的三种采样方法:积分法、分部积分法、有限加合近似法。根据分析化学的要求,提出样品采集时间的设计方法。由此得出不同类型排放源的监测时间和采样频率确定方法。  相似文献   
56.
The evaluation of dispersant effectiveness used for oil spills is commonly done using tests conducted in laboratory flasks. We used a Hot Wire Anemometer (HWA) to characterize mixing dynamics in the Swirling Flask (SF) and the Baffled Flask (BF), the latter is being considered by the EPA to replace the prior to test dispersant effectiveness in the laboratory. Five rotation speeds of the orbital shaker carrying the flasks were considered, Ω = 50, 100, 150, 175 and 200 rpm. The radial and azimuthal water speeds were measured for each Ω. It was found that the flow in the SF is, in general, two-dimensional changing from horizontal at low Ω to axi-symmetric at high Ω. The flow in the BF appeared to be three-dimensional at all rotation speeds. This indicates that the BF is more suitable for representing the (inherently) 3-D flow at sea. In the SF, the speeds and energy dissipation rates ɛ increased gradually as the rotation speed increased. Those in the BF increased sharply at rotation speeds greater than 150 rpm. At 200 rpm, the Kolmogorov scale (i.e., size of smallest eddies) was about 250 and 50 μm in the SF and BF, respectively. Noting that the observed droplet sizes of dispersed oils range from 50 to 400 μm (hence most of it is less than 250 μm), one concludes that the mixing in the SF (even at 200 rpm) is not representative of the vigorous mixing occurring at sea.  相似文献   
57.
切断位置对赤子爱胜蚓再生速度的影响   总被引:4,自引:0,他引:4  
将赤子爱胜蚓从脑、生殖环部位和总体节的 1/ 2和 3/ 4的位置切断 ,得到有头无尾、无头无尾、无头有尾 3种类型 16个处理体段 ,在 (2 0± 1)℃人工气候箱中培养 ,测定其再生速度 .结果表明 ,赤子爱胜蚓切断的位置不同 ,其再生速度不同 .其中 ,脑部的存在与否 ,对再生速度没有显著的影响 .但是生殖环存在的处理比切除生殖环的处理再生速度快 ,且存活率高 .无头无尾体段再生前部和再生后部的比较表明 ,再生前部比再生后部慢 .体节的损失越少 ,再生的速度越快 .图 6表 3参 11  相似文献   
58.
Sperm competition models on the evolution of sperm size assume associations with another sperm quality trait, sperm longevity. Sperm length can also provide an indication of possible mechanisms affecting motility and thus fertilization success. Despite their importance, however, detailed mechanisms of sperm competition at the gamete level are poorly understood. In simultaneously hermaphroditic land snails, sperm traits and cryptic female choice are assumed to be crucial in determining fertilization success. We examined the variation in sperm length and number among individuals from four natural populations of the land snail Arianta arbustorum, a species with multiple mating and long-term sperm storage. We also assessed variation in velocity, motility and longevity of sperm in snails from two of the four populations. Independent of shell size, sperm length differed among populations and, to a minor extent, even among individuals within populations. Mean sperm length of a snail was not correlated with the number of sperm delivered in a spermatophore. The mean sperm velocity (=VCL) did not differ between snails from two populations. However, VCL varied among snails. Percentage motility and longevity of sperm differed between snails from the two populations. No correlations were found between length, velocity, percentage motility and longevity of sperm. To conclude, individual snails differed in sperm quality, and this variation may partly explain the differential fertilization success between A. arbustorum snails. Moreover, our findings did not support the positive association between sperm length and longevity assumed by sperm competition models for internally fertilizing species.  相似文献   
59.
This article demonstrates the applicability of vector autoregression (VAR) modeling in probing the causality relationships among wildfire, El Niño/Southern Oscillation (ENSO), timber harvest, and urban sprawl in the U.S. The VAR approach allows for the multi-directional, multi-faceted interactions among the variables concerned and enables us to portray the temporal impacts of ENSO, the volume of timber harvested, and urban sprawl on wildfire. The empirical analysis, though intended mainly for illustration, reveals that an individual factor may not affect wildfire activity (number of fires and area burned) when acting alone, but can significantly influence fire activity when coupled with other factors, and that wildfire activity has feedback effects on other variables. The impact of a change in ENSO, the volume of timber harvested, and urban population density on wildfire activity could last two decades with the most noticeable impact occurring in the initial 5–10 years. Though ENSO, timber harvest, and urban sprawl all Granger-cause wildfire activity, the impulse response functions show that wildfire activity is more responsive to urban population density than to the volume of timber harvested or ENSO. Thus, controlling urban sprawl represents another option for wildfire mitigation; and integrative wildfire management is essential.  相似文献   
60.
论述了将小型链条炉排工业锅炉的炉拱设计成在运行中可以全量调节的结构,以适应燃用多种煤种的需要,并减少与固定拱操作有关的意外伤亡事故。这项技术有创新性,适用性和推广价值  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号