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1.
大气压非平衡等离子体甲烷干法重整零维数值模拟   总被引:1,自引:0,他引:1       下载免费PDF全文
大气压非平衡等离子体由于其独特的非平衡特性,可为甲烷和二氧化碳稳定温室气体分子活化和重整提供非热平衡和活化环境.本文采用了零维等离子体化学反应动力学模型,考虑了详细的CH4/CO2等离子体化学反应集,重点研究了反应气体CH4/CO2摩尔分数(5%—95%)对大气压非平衡等离子体甲烷干法重整制合成气和重要含氧化合物的影响.首先,给出了进料气体不同体积比时电子密度和温度随时间的演化规律,结果表明初始甲烷摩尔分数的提高有利于获得较高的电子密度和电子温度.随后,讨论了主要自由基和离子数密度在不同的甲烷摩尔分数下随着时间的变化规律,并给出了反应气体的转化率、合成气体和重要含氧化合物的选择性.此外,还明确了合成气和含氧化合物主要生成和损耗的化学反应路径,发现甲基和羟基是合成含氧化合物的关键中间体.最后,归纳总结给出了主要等离子体粒子之间的总体等离子体化学反应流程图.  相似文献   
2.
The behavior and mechanism of background signals during depth profiling of atmospheric elements using dual-beam time-of-flight secondary ion mass spectrometry (TOF-SIMS) have been experimentally investigated for silicon wafers. The background signals of atmospheric elements were found to be inversely proportional to the sputtering rate. Most of the background signals are largely attributable to the accumulation of components through adsorption and ion bombardment in the pre-equilibrium state. On the other hand, the contribution of real-time adsorption during the instant after the last sputtering in the equilibrium state is negligible under the present experimental conditions. H2O is dominant in the background formation process of hydrogen and oxygen, which is supported by the higher adsorption coefficients. The background levels of carbon and nitrogen are lower than those of hydrogen and oxygen. Furthermore, the background signal of carbon with respect to the sputtering rate shows a different trend than the other elements. This could be attributed to accumulation in the pre-equilibrium state. These results indicate that the background levels can be lowered close to those of dynamic-SIMS by using an extremely high sputtering rate in dual-beam TOF-SIMS.  相似文献   
3.
为了探究钢筋混凝土桥梁抗力退化对桥梁可靠性能的影响,综合考虑一般大气环境下混凝土强度、钢筋强度、混凝土与钢筋黏结性能的降低,建立普通钢筋混凝土桥梁的抗力退化时变模型,分析规范车辆荷载作用的桥梁时变可靠度。研究结果表明,(1)一般大气环境下,桥梁抗力随着服役时间的增加而减小,其中钢筋强度退化对桥梁抗力的影响最大,其次是钢筋与混凝土黏结性能降低,而混凝土强度退化对桥梁抗力的影响相对较小; (2)桥梁可靠指标随着服役时间的增加而减小,密集行车占比越大,桥梁承载能力失效的概率就越大;非平稳车载作用下的桥梁可靠指标小于平稳车载,桥梁需要维修补强的时间比平稳车载提前; (3)多梁式简支梁桥在建造时应该提高边梁的安全储备,在管养时可以采取限载措施进行干预。  相似文献   
4.
旷金鑫  张春涛  郝志明  李洪祥 《爆炸与冲击》2021,41(2):023303-1-023303-11
为研究大气腐蚀对Q420钢管构件服役期内耐撞性的影响,提出了计及腐蚀损伤的材料模型。引入损伤因子(ω)修正Voce模型,推导随腐蚀程度变化的低合金钢材本构方程,并通过加速腐蚀试验结果回归相应参数。利用ABAQUS软件定义构件材料特性,建立起受腐蚀的Q420钢管仿真模型,采用显式动力算法分析多种初始状态下,撞击体与不同腐蚀程度钢管的冲击响应规律。开展预腐蚀Q420钢管的落锤试验,将试验结果与数值计算结果进行对比,验证所建模型的合理性。结果表明:大气腐蚀导致材料名义强度降低,对Q420钢管抗撞击能力影响显著;随着腐蚀程度增加,冲击力峰值减小,撞击时间和深度增加;Q420钢管受腐蚀后抗冲击刚度减小,构件整体变形耗能增加,表明大气腐蚀使其抗冲击性能下降;同等动能增量下,增大撞击体初速度比增加初始质量获得的冲击力峰值增幅更大,而所得到的接触时间增幅更小。  相似文献   
5.
大气中Pb、Cd、Cr、Mn、Ni、Tl等重金属污染物是目前国内外城市大气污染的主要因子之一,研究大气降尘中重金属元素含量具有重大意义。本文采用盐酸-硝酸混合酸为消解体系,在105℃条件下用电热板消解回流大气降尘样品2小时后定容测定,通过电感耦合等离子发射光谱法仪(ICP-AES)和电感耦合等离子体质谱仪(ICP-MS)测定大气降尘中铅、镉、铬、锌、锰、镍、铜和铊等8种重金属元素。测定结果表明: ICP-AES(铅、镉、铬、锌、锰、镍、铜)和ICP-MS(铊)两种方法的曲线线性好,准确度高,测定范围宽,检出限在0.024mg/kg-0.548mg/kg之间,精密度在0.15%-2.38%之间,能准确测定大气降尘中的重金属元素含量。  相似文献   
6.
Faced with the contradictory results of two recent experimental studies [Jara‐Toro et al., Angew. Chem. Int. Ed. 2017 , 56, 2166 and Chao et al., Angew. Chem. Int. Ed. 2019 , 58, 5013] of the possible catalytic effect of water vapor on CH3OH + OH reaction, we report calculations that corroborate the conclusion made by Chao et al. and extend the rate constant evaluation down to 200 K. The rate constants of the CH3OH + OH reaction catalyzed by a water molecule are computed as functions of temperature and relative humidity using high‐level electronic structure and kinetics calculations. The Wuhan–Minnesota Scaling (WMS) method is used to provide accurate energetics to benchmark a density functional for direct dynamics. Both high‐frequency and low‐frequency anharmonicities are included. Variational and tunneling effects are treated by canonical variational transition state theory with multidimensional small‐curvature tunneling. And, most significantly, we include multistructural effects in the rate constant calculations. Our calculations show that the catalytic effect of water vapor is not observable at 200–400 K.  相似文献   
7.
The hydrolysis of sulfonylamine (HNSO2) results in the formation of sulfuric acid along with ammonia, and is of significant interest due to their negative impact on environment and life on Earth. The formation of H2SO4 through the reaction of HNSO2 with (H2O)2-4 has been studied using high level electronic structure calculations. This hydrolysis reaction is a step-wise process, in the first step a H-atom from H2O is transferred to the N-atom of HNSO2 which results in the formation of NH2, and in the next step, H2SO4, NH3 and water molecule(s) are formed. The results show that the energy barrier associated with the formation of intermediates and product complexes is reduced by 7 to 10 kcal/mol when the number of water molecules is increased from 2 to 4. The rate constant was calculated using canonical variational transition state theory with small curvature tunneling correction over the temperature range of 200 to 1000 K. At 298 K, the calculated rate constant for the formation of intermediate in the first step is 2.24 × 10−16, 1.03 × 10−12, and 2.10 × 10−11 cm3 mol−1 s−1, respectively, for the reaction with water dimer, trimer and tetramer. The calculated enthalpy and free energy show that the reaction corresponding to the formation of H2SO4 is highly exothermic and exoergic in nature.  相似文献   
8.
The urgency to address global climate change induced by greenhouse gas emissions is increasing. In particular, the rise in atmospheric CO2 levels is generating alarm. Technologies to remove CO2 from ambient air, or “direct air capture” (DAC), have recently demonstrated that they can contribute to “negative carbon emission.” Recent advances in surface chemistry and material synthesis have resulted in new generations of CO2 sorbents, which may drive the future of DAC and its large‐scale deployment. This Review describes major types of sorbents designed to capture CO2 from ambient air and they are categorized by the sorption mechanism: physisorption, chemisorption, and moisture‐swing sorption.  相似文献   
9.
王海潮  唐明金  谭照峰  彭超  陆克定 《化学进展》2020,32(10):1535-1546
硝酰氯(nitryl chloride,ClNO2)是大气中一种重要的气态污染物,对大气氧化性、一次污染物的降解和二次污染物的生成具有重要影响,并在全球氮循环和氯循环中扮演着不可忽视的角色。本文归纳了ClNO2的基本物理化学性质及其在大气中的生成和去除机制,并介绍了实验室研究和外场观测中ClNO2的主要测量方法。在此基础上,本文总结了过去十几年报道的ClNO2在实际大气中的时空分布特征,通过分析实验室模拟和外场观测的研究结果系统讨论了ClNO2非均相生成的机制、产率及其影响因素,探讨了ClNO2对氯自由基、大气氧化性以及臭氧和硝酸盐形成的影响。我们指出,ClNO2既耦合了气相化学和非均相化学,又耦合了夜间大气化学和日间光化学,在我国大气复合污染中可能起着非常重要的作用。最后,本文提出了ClNO2大气化学研究中尚待解决的关键科学问题,并简要讨论了该领域的未来发展方向。  相似文献   
10.
Enols are important species in atmospheric and combustion chemistry. However, their implications in these environments are not well established due to a lack of accurate rate constants and mechanisms to determine their fate. In this work, we investigate the formic acid catalyzed keto-enol tautomerizations converting vinyl alcohol, propen-2-ol and 1-propenol into acetaldehyde, acetone and propanal, respectively. High-level ab initio and multistructural torsional variational transition state theory calculations are performed with small-curvature tunneling corrections to obtain rate constants in the temperature range 200 K-3000 K. Tunneling is shown to be pronounced as a consequence of very narrow adiabatic potential energy curves, and indicates a need to revisit previous calculations. We show the implications of the studied reactions on the fate of enols under combustion relevant conditions by detailed kinetic modeling simulations. The yield of vinyl alcohol predicted by our calculated rate constants may be useful to lessen the underestimation of organic acids concentrations in current atmospheric models.  相似文献   
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