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121.
菲涅耳波带板直接成像,应用到激光等离子体或惯性约束聚变靶的X射线成像诊断,可实现μm甚至亚μm的空间分辨能力。在对成像进行数值模拟时,考虑到光源的光谱带宽和几何尺度对成像的影响,要进行菲涅耳-基尔霍夫衍射积分与卷积等数值计算,需占用大量计算机内存并且耗费运行机时。改进了数值计算方法,采用了蒙特卡罗积分法和新的卷积算法。模拟了菲涅耳波带板对大尺度多色X射线源的二维成像,新算法与以往算法相比,可显著减少运算机时,在台式机上实现模拟成像的快速计算。结果表明随着光源尺度增大、光谱带宽增加,像的背景增强,导致反衬度与成像质量下降。 相似文献
122.
Solar broadband heating directly drives the atmospheric and ocean circulations, and is largely determined by cloud spatial 3-diminesional (3D) structures. To study the cloud 3D effects on radiation, a 3D broadband Monte-Carlo radiative transfer model, along with an Independent Pixel/Column Approximation (IPA) method, is used to simulate radiation and heating rate of three typical cloud fields generated by cloud resolving models (CRM). A quantitative and statistical estimation of cloud 3D effects has been developed to investigate the impact of cloud 3D structures on both heating rate strength, STD_Bias, and vertical distribution, CorrCoef. The cloud 3D structures affect some clouds more in heating rate strength and others more in vertical distribution. It is crucial to use the combination of CorrCoef and STD_Bias for better quantitative evaluation of the 3D effects. Furthermore, there is no simple way to define a critical resolution (or average radius), within which the IPA heating rate profiles closely represent the true 3D heating rate profiles. The critical radius (or resolution) strongly depends on solar incident angle as well as cloud vertical distribution. Also, the critical radii for clear-sky columns are larger than for cloudy columns, although the corresponding STD_Bias for clear-sky columns are smaller than for cloudy columns. Analysis based on two different statistical average methods illustrates that the cloud 3D effects due to the dimensionality difference between the 3D clouds (circle average) and 2D clouds (line average) significantly impact on the heating rate profiles. 相似文献
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为了将氘化液闪探测器(BC537)测量的反冲电子谱转换为射线能谱, 利用标准点源对BC537探测器的响应进行了测量并运用基于蒙特卡罗方法的Geant4程序计算了BC537探测器探测射线的响应函数。讨论了探测器建模中有无铝壳和入射射线束流半径对探测效率和响应函数的影响。对比模拟和实验测量的反冲电子谱, 两者符合较好。利用模拟的响应函数和实验测量标准源Cs-137和Co-60以及Am-Be源在BC537探测器中的反冲电子谱, 经迭代法解谱得到了对应的标准射线能谱, 验证了模拟参数的合理性以及该响应函数的实用性。 相似文献
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惯性约束聚变靶材料面密度及其均匀性分布可以通过β射线束透射法进行测量,要完成这一测量,需首先用一系列面密度已知、组成成分与待测材料相同的标准材料对测量装置进行刻度。针对惯性约束聚变靶材料一类还处于研制阶段的新材料的密度测量,提出了用成分相近的材料作为替代标准进行刻度的方法,并用蒙特卡罗方法模拟计算了不同能量电子穿过不同材料的透射率,得到了这种刻度方法对测量结果带来的误差大小,用纸作标准测量CH泡沫靶材料的误差只有百分之几,这一误差在实际测量中可以由蒙特卡罗模拟方法得到修正。该刻度方法解决了惯性约束聚变靶材料一类新材料面密度用β透射法测量中的定标问题。 相似文献
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128.
Ching-Cher Sanders Yan 《Applied Surface Science》2005,252(3):784-792
Monte-Carlo technique was applied to simulate the nonisothermal oxide formation/removal model for kinetic oscillation of carbon monoxide oxidation over nano-scaled catalysts. The nonisothermal oxide model interprets kinetic oscillation more properly with shorter oscillatory period and lower maximum CO coverage. Two channels transferring the system back and forth between low and high rate states are necessary to achieve kinetic oscillation. Oxide formation switches the state from high to low rate and found no changes in nonisothermal condition. Oxide removal reverses the process and it is accelerated in nonisothermal simulations cutting low rate period. The role of CO diffusion was found important for the kinetic oscillation. Without CO diffusion, oxide formation rate is increased keeping oxide coverage constant. Thus, the nondiffusive system is always in low reactive state. 相似文献
129.
Alexander Barvinok 《Mathematical Programming》1997,79(1-3):33-53
We discuss some consequences of the measure concentration phenomenon for optimization and computational problems. Topics include
average case analysis in optimization, efficient approximate counting, computation of mixed discriminants and permanents,
and semidefinite relaxation in quadratic programming. 相似文献
130.
A. Gustavo Gonzalez M. Angeles Herrador Agustín G. Asuero 《Accreditation and quality assurance》2005,10(4):149-154
The first Supplemental Guide to the current edition of the Guide to the expression of uncertainty measurement (GUM) deals with the propagation of distributions, and emphasizes the use of Monte-Carlo Simulation (MCS) for estimating the uncertainty of measurands. In order to carry out MCS we need computer programs for generating pseudo-random numbers and for solving numerically the integral equations arising when simulating the values of the specification variables with a given probability density function (PDF). Crystal-Ball commercial software is very suitable for performing MCS and to estimate the expanded uncertainty for the measurand. The use of Crystal-Ball is illustrated with two working examples dealing with specification models of non-linear features and with correlated variables (such as the slope and intercept of calibration straight lines), respectively.An erratum to this article can be found at 相似文献