全文获取类型
收费全文 | 5190篇 |
免费 | 555篇 |
国内免费 | 267篇 |
专业分类
化学 | 1157篇 |
晶体学 | 17篇 |
力学 | 744篇 |
综合类 | 104篇 |
数学 | 2492篇 |
物理学 | 1498篇 |
出版年
2024年 | 15篇 |
2023年 | 45篇 |
2022年 | 97篇 |
2021年 | 94篇 |
2020年 | 130篇 |
2019年 | 130篇 |
2018年 | 122篇 |
2017年 | 153篇 |
2016年 | 174篇 |
2015年 | 132篇 |
2014年 | 212篇 |
2013年 | 358篇 |
2012年 | 242篇 |
2011年 | 279篇 |
2010年 | 228篇 |
2009年 | 284篇 |
2008年 | 278篇 |
2007年 | 298篇 |
2006年 | 293篇 |
2005年 | 299篇 |
2004年 | 256篇 |
2003年 | 241篇 |
2002年 | 220篇 |
2001年 | 148篇 |
2000年 | 154篇 |
1999年 | 134篇 |
1998年 | 100篇 |
1997年 | 102篇 |
1996年 | 91篇 |
1995年 | 86篇 |
1994年 | 70篇 |
1993年 | 51篇 |
1992年 | 58篇 |
1991年 | 43篇 |
1990年 | 39篇 |
1989年 | 35篇 |
1988年 | 31篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 34篇 |
1983年 | 9篇 |
1982年 | 29篇 |
1981年 | 16篇 |
1980年 | 16篇 |
1979年 | 22篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1974年 | 12篇 |
排序方式: 共有6012条查询结果,搜索用时 15 毫秒
91.
L. Lukšan 《Journal of Optimization Theory and Applications》1994,83(1):27-47
Variable metric methods from the Broyden family are well known and commonly used for unconstrained minimization. These methods have good theoretical and practical convergence properties which depend on a selection of free parameters. We demonstrate, using extensive computational experiments, the influence of both the Biggs stabilization parameter and Oren scaling parameter on 12 individual variable metric updates, two of which are new. This paper focuses on a class of variable metric updates belonging to the so-called preconvex part of the Broyden family. These methods outperform the more familiar BFGS method. We also experimentally demonstrate the efficiency of the controlled scaling strategy for problems of sufficient size and sparsity. 相似文献
92.
ONTHEMIXEDPROBLEMSINANEIASTICPIANEWITHPER1ODICCRACKSZhengKe(郑可)(WuhanUniversity)ONTHEMIXEDPROBLEMSINANEIASTICPIANEWITHPER1ODI... 相似文献
93.
In this article,three-dimensional mixed convection flow over an exponentially stretching sheet is investigated.Energy equation is modelled in the presence of viscous dissipation and variable thermal conductivity.Temperature of the sheet is varying exponentially and is chosen in a form that facilitates the similarity transformations to obtain self-similar equations.Resulting nonlinear ordinary differential equations are solved numerically employing the Runge-Kutta shooting method.In order to check the accuracy of the method,these equations are also solved using bvp4c built-in routine in Matlab.Both solutions are in excellent agreement.The effects of physical parameters on the dimensionless velocity field and temperature are demonstrated through various graphs.The novelty of this analysis is the self-similar solution of the threedimensional boundary layer flow in the presence of mixed convection,viscous dissipation and variable thermal conductivity. 相似文献
94.
针对公共场所异常声的感知和识别问题,提出一种基于贝叶斯优化卷积神经网络的识别方法。提取声信号的Gammatone倒谱系数、倍频程功率谱、短时能量和谱质心,组合成声信号的特征图。构建卷积神经网络作为分类器,利用递增的卷积核设置和池化操作处理不同尺度的特征。基于贝叶斯优化算法优化卷积神经网络的模型参数,对包括火苗噼啪声、婴儿啼哭声、烟花燃放声、玻璃破碎声和警报声的5种公共场所异常声进行识别。该方法的识别结果与基于不同的特征提取和分类器方案得到的识别结果进行比较,结果表明该方法的识别效果优于其他特征提取和分类器方案的识别效果。最后分析了该方法在不同信噪比噪声干扰下的识别结果,验证了该方法的有效性。 相似文献
95.
QIAOYong-Fen LIRen-Jie MAYong-Sheng 《理论物理通讯》2004,42(6):801-804
Using the Lie Symmetry under infinitesimal transformations in which the time is not variable, the nonNoether conserved quantity of nonholonomic system having variable mass and unilateral constraints is studied. The differential equations of motion of the system are given. The determining equations of Lie symmetrical transformations of the system under infinitesimal transformations are constructed. The Hojman‘s conservation theorem of the system is established. Finally, we give an example to illustrate the application of the result. 相似文献
96.
Molar extinction coefficients of aqueous solutions of some organic compounds, viz. formamide (CH3NO),N-methylformamide (C2H5NO),NN-dimethylformamide (C3H7NO),NN-dimethylacetamide (C4H9NO), 1,4-dioxane (C4H8O24), succinimide (C4H5NO2) and solutions of acetamide (C2H5NO) and benzoic acid (C7H6O2) in 1,4-dioxane (C4H8O2) have been determined by narrow beam γ-ray transmission method at 81, 356, 511, 662, 1173 and 1332 keV. The experimental
values of mass attenuation coefficients of these compounds have been used to calculate effective atomic numbers and electron
densities. The additivity rule earlier used for aqueous solution has been extended to non-aqueous (1,4-dioxane) solutions. 相似文献
97.
T. M. Petrova A. M. Solodov A. A. Solodov V. M. Deichuli V. I. Starikov 《Molecular physics》2018,116(10):1409-1420
The water vapour line broadening and shifting for 97 lines in the ν1 + ν2 + ν3 band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm?1 and in a wide pressure range of H2. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν2, ν1, and ν3 vibrational bands are presented. 相似文献
98.
U. Turgut E. Büyükkasap O. ?im?ek M. Ertu?rul 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,92(2):143-151
The total mass attenuation coefficients for element Fe and compounds FeF3, Fe2O3, FeCl2·4H2O, FeCl32NH4Cl·H2O were measured at different energies between 4.508-17.443 keV range by using secondary excitation method. Ti, V, Cr, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo were chosen as secondary exciter. 59.5 keV gamma rays emitted from an 241Am annular source were used to excite secondary exciter and Kα(K-L3, L2) lines emitted of secondary exciter were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. It was observed that mixture rule method is not a suitable method for determination of the mass attenuation coefficients of compounds, especially at energy that is near the absorption edge. Obtained values were compared with theoretical values. 相似文献
99.
Ari Sihvola 《Optik》2006,117(7):317-320
A geometric visualization is presented for the Brewster angle for a plane wave reflecting from an interface. The surface is assumed to be isotropic but it is allowed to display both dielectric and magnetic susceptibility, and hence the Brewster (polarizing) angle can attain any value between 0 and 90°, and can exist for both parallel and perpendicular polarizations. The geometric construction (a tetrahedron) is spanned by the basic material parameters of the surface. The Brewster angle appears in one of the faces of the tetrahedron. 相似文献
100.
Optimal utilization of computational resources mandates spatio-temporal variation in resolution for computing complex engineering flows. Closure modeling in regions bridging between different resolutions is rendered difficult due to changing interactions between resolved and unresolved fields. We develop a closure model for the bridging region based on energy conservation principles. Then we proceed to provide a proof of concept in decaying isotropic turbulence with temporally varying resolution. The simplicity of the flow permits a thorough examination of various aspects of the proposed closure not feasible in more complex flows. The results demonstrate the potential promise of the approach, but more validation studies need to be performed.While the present development is in the context of partially averaged Navier–Stokes (PANS) method, the closure principle should apply for other variable-resolution (VR) approaches. 相似文献