全文获取类型
收费全文 | 45236篇 |
免费 | 4137篇 |
国内免费 | 3094篇 |
学科分类
工业技术 | 52467篇 |
出版年
2024年 | 153篇 |
2023年 | 677篇 |
2022年 | 881篇 |
2021年 | 1114篇 |
2020年 | 1316篇 |
2019年 | 1183篇 |
2018年 | 1256篇 |
2017年 | 1477篇 |
2016年 | 1497篇 |
2015年 | 1542篇 |
2014年 | 2401篇 |
2013年 | 3104篇 |
2012年 | 2742篇 |
2011年 | 3503篇 |
2010年 | 2670篇 |
2009年 | 2922篇 |
2008年 | 2914篇 |
2007年 | 2930篇 |
2006年 | 2604篇 |
2005年 | 2335篇 |
2004年 | 1970篇 |
2003年 | 1709篇 |
2002年 | 1485篇 |
2001年 | 1080篇 |
2000年 | 951篇 |
1999年 | 861篇 |
1998年 | 700篇 |
1997年 | 608篇 |
1996年 | 522篇 |
1995年 | 474篇 |
1994年 | 427篇 |
1993年 | 364篇 |
1992年 | 335篇 |
1991年 | 255篇 |
1990年 | 218篇 |
1989年 | 217篇 |
1988年 | 157篇 |
1987年 | 89篇 |
1986年 | 106篇 |
1985年 | 85篇 |
1984年 | 84篇 |
1983年 | 63篇 |
1982年 | 67篇 |
1981年 | 46篇 |
1980年 | 38篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1964年 | 26篇 |
1955年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Based on the current spin density functional theory, a theoretical model of three vertically aligned semiconductor quantum dots is proposed and numerically studied. This quantum dot molecule (QDM) model is treated with realistic hard-wall confinement potential and external magnetic field in three-dimensional setting. Using the effective-mass approximation with band nonparabolicity, the many-body Hamiltonian results in a cubic eigenvalue problem from a finite difference discretization. A self-consistent algorithm for solving the Schrödinger-Poisson system by using the Jacobi-Davidson method and GMRES is given to illustrate the Kohn-Sham orbitals and energies of six electrons in the molecule with some magnetic fields. It is shown that the six electrons residing in the central dot at zero magnetic field can be changed to such that each dot contains two electrons with some feasible magnetic field. The Förster-Dexter resonant energy transfer may therefore be generated by two individual QDMs. This may motivate a new paradigm of Fermionic qubits for quantum computing in solid-state systems. 相似文献
3.
4.
5.
基于模式理论光栅椭偏参数反演的数值模拟 总被引:5,自引:2,他引:3
将一种广泛用于求解系统优化问题的方法——正单纯形法,求解光栅的椭偏方程。首先,利用求解光栅的傅立叶模式理论对TE和TM波的复反射系数进行求解。然后计算出其相应的椭偏参数(△,Ψ),并在该值的基础上加入不同偏差的随机高斯噪声,将加入噪声后的值(△m,Ψm)作为模拟测量值。最后使用优化算法进行反演。通过对几种常用面形光栅椭偏参数的数值模拟,一方面表明傅立叶模式理论计算光栅的椭偏参数不仅精度高。而且速度快;另一方面表明利用正单纯形法得到的光栅参数值很接近于正演时假设的参数值,从而从理论上证明了利用椭偏法测量光栅各种光学参数的可行性。 相似文献
6.
An analysis is made of the characteristic features and problems of the optimal processing of the results of measurements in the case of a random observation function utilizing a nonlinear Kalman filter. A method is proposed for increasing the convergence domain of the filter with additional processing of measurements in the frequency domain. 相似文献
7.
Starting from a microscopic Hamiltonian defined on a semi-infinite cubic lattice, and employing a mean-field approximation, the surface parameters relevant for wetting in confined ternary mixtures are derived. These are found in terms of the microscopic coupling constants, and yield a physical interpretation of their origins. In comparison with the standard expression for the surface free-energy density, several new terms arising from the derivation are identified. The influence of the surface parameters on a predicted unbinding transition in a mixture of oil, water, and amphiphile demonstrate that existing results are robust to the addition of the extra surface terms. 相似文献
8.
J. Gegner 《Materialwissenschaft und Werkstofftechnik》2003,34(3):290-297
Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 2: Characterization of microstructure formation by means of high‐resolution transmission electron microscopy and selected area diffraction Liquid or solid silicone resins represent the economically most interesting class of organic precursors for the pyrolytic production of glass and ceramics materials on silicon basis. As dense, dimensionally stable components can be cost‐effectively achieved by admixing reactive filler powders, chemical composition and microstructure development of the polymer‐derived residues must be exactly known during thermal decomposition. Thus, in the present work, glasses and ceramics produced by pyrolysis of the model precursor polymethylsiloxane at temperatures from 525 to 1550 °C are investigated. In part 1, by means of analytical electron microscopy, the bonding state of silicon was determined on a nanometre scale and the phase separation of the metastable Si–C–O matrix into SiO2, C and SiC was proved. The in‐situ crystallization could be considerably accelerated by adding fine‐grained powder of inert fillers, such as Al2O3 or SiC, which permits effective process control. In part 2, the microstructure is characterized by high‐resolution transmission electron microscopy and selected area diffraction. Turbostratic carbon and cubic β‐SiC precipitate as crystallization products. Theses phases are embedded in an amorphous matrix. Inert fillers reduce the crystallization temperature by several hundred °C. In this case, the polymer‐derived Si–C–O material acts as a binding agent between the powder particles. Reaction layer formation does not occur. On the investigated pyrolysis conditions, no crystallization of SiO2 was observed. 相似文献
9.
10.