全文获取类型
收费全文 | 9399篇 |
免费 | 618篇 |
国内免费 | 667篇 |
专业分类
化学 | 1704篇 |
晶体学 | 149篇 |
力学 | 641篇 |
综合类 | 58篇 |
数学 | 920篇 |
物理学 | 2009篇 |
综合类 | 5203篇 |
出版年
2024年 | 15篇 |
2023年 | 46篇 |
2022年 | 89篇 |
2021年 | 103篇 |
2020年 | 116篇 |
2019年 | 107篇 |
2018年 | 94篇 |
2017年 | 132篇 |
2016年 | 168篇 |
2015年 | 164篇 |
2014年 | 309篇 |
2013年 | 401篇 |
2012年 | 417篇 |
2011年 | 461篇 |
2010年 | 409篇 |
2009年 | 548篇 |
2008年 | 598篇 |
2007年 | 703篇 |
2006年 | 727篇 |
2005年 | 760篇 |
2004年 | 671篇 |
2003年 | 538篇 |
2002年 | 454篇 |
2001年 | 344篇 |
2000年 | 300篇 |
1999年 | 302篇 |
1998年 | 239篇 |
1997年 | 214篇 |
1996年 | 172篇 |
1995年 | 174篇 |
1994年 | 151篇 |
1993年 | 128篇 |
1992年 | 123篇 |
1991年 | 88篇 |
1990年 | 73篇 |
1989年 | 86篇 |
1988年 | 58篇 |
1987年 | 47篇 |
1986年 | 36篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 4篇 |
1979年 | 20篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
931.
为研究翻堆和补水工艺对绿化废弃物堆肥腐熟度的影响,以园林绿化废弃物为研究对象,采用好氧条垛式堆肥方法,设计2因素3水平正交试验,研究不同补水和翻堆工艺对堆肥进程中碳氮比(C/N)、p H、电导率(EC)等指标的影响规律;同时选取T值、高温持续时间、发芽指数(GI)、吸光度比值(E4/E6)等指标,利用模糊数学法进行腐熟度评价。结果表明,堆肥过程中各处理的碳氮比逐渐降低,p H逐渐上升,温度、EC值和E4/E6随堆肥进行均先升后降,发芽指数相反;除高温好氧堆肥处理外,其他处理均达到腐熟;其中T4处理腐熟度最好;最优水平组合为每4 d翻堆、每8 d补水;影响腐熟程度的主因素是补水频率,其次是翻堆频率。 相似文献
932.
J. B. Gosk 《Crystal Research and Technology》2010,45(5):465-478
To investigate the one‐dimensionally disordered structures (ODDS) in the close packed (cp) crystals, the Monte Carlo computer simulation technique has been applied. Calculations of the diffraction intensity distributions along the 10.L reciprocal lattice row from the 6H(33) structure with the four different kinds of the stacking faults (SFs): growth, deformation, layer displacement and extrinsic fault are presented. In particular, using the simple frequency functions of the fault to fault distances, both random and non‐random distributions of the SFs are considered. Distinctive features of the diffraction patterns corresponding to the chosen examples of the transformations from the parent 6H(33) structure into another small‐period polytypes are discussed in detail. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
933.
934.
Sm3+ doped CdS nanoparticles have been prepared by sol-gel method. The effect of annealing temperatures and doping concentrations of CdS on the photoluminescence spectra of Sm3+ were studied. From the measurement of its optical absorption, three phenomenological Judd-Ofelt intensity parameters (Ω2, Ω4, and Ω6) have been computed and used to parameterize the radiative properties. The influences of CdS on Sm3+ ions were studied by fluorescence spectroscopy. The fluorescence spectra revealed that the emission intensity of samarium increased considerably in the presence of CdS nanoparticles. The evaluation of radiative properties of Sm3+ containing CdS showed that the 4G5/2→6H7/2 transition in silica matrix had the potential to be a laser transition. 相似文献
935.
Vladimir Schmidt Roman Schuh 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(11):1705-1710
Different preconditioning techniques for the iterative method MinRes as solver for the Discrete Sources Method (DSM) are presented. This semi-analytical method is used for light scattering computations by particles in the Mie scattering regime. Its numerical schema includes a linear least-squares problem commonly solved using the QR decomposition method. This could be the subject of numerical difficulties and instabilities for very large particles or particles with extreme geometry. In these cases, we showed that iterative methods with preconditioning techniques can provide a satisfying solution.In our previous paper, we studied four different iterative solvers (RGMRES, BiCGStab, BiCGStab(l), and MinRes) considering the performance and the accuracy of a solution. Here, we study several preconditioning techniques for the MinRes method for a variety of oblate and prolate spheroidal particles of different size and geometrical aspect ratio. Using preconditioning techniques we highly accelerated the iterative process especially for particles with a higher aspect ratio. 相似文献
936.
We report on the structural and optical characterization of waveguides formed in YbVO4 crystals by Cu2+-ion implantation with an energy of 3.0 MeV and doses of 3.0×1014-1.0×1015 ions/cm2. The damage properties are determined by RBS/Channeling measurements with the help of simulation code RUMP. The m-line method is used to characterize the dark-mode spectroscopy in the planar waveguides. According to the reconstructed refractive index profile of the waveguide cross section, a numerical simulation is carried out to investigate the confinement of the light in the waveguides based on the beam propagation method. 相似文献
937.
We report on third order optical nonlinear experimental characterization using Z-scan method through focal shift measurements of a converging lens. The sample is fixed in front of a lens and is illuminated by a collimated beam. The shift of the geometrical focus in the nonlinear regime using input Gaussian beams is related to the nonlinear induced dephasing owing to a simple linear relation. Numerical calculations based on the Helmholtz wave equation are performed. Good agreement is obtained between experimental and theoretical results. 相似文献
938.
In this paper we have measured second order nonlinear refractive index of Ag and Au nano-particles using the moiré deflectometry with a CW He-Ne laser at wavelength of 632.8 nm. The main advantages of this technique are its extreme experimental simplicity and low sensitivity to external distribution in comparison with other interfrometric methods that need very stable experimental set-up. Because of self-focusing (or self-defocusing) that is due to intensity dependent refractive index, presence of sample in the moiré deflectometry set-up lead to rotation of moiré fringes. By moving the sample in set-up we have measured these rotation angles in different displacements from focus point of lens used in this set-up and then we have calculated the nonlinear refractive index of Ag and Au nano-particles using their values. Also we have obtained the sign of n2 regard to the direction of rotations. Consequently by using the Mathematica software we have exhibited the suitable fitness of theoretical curve with experimental results. 相似文献
939.
Nadine Werth Mathias S. Müller Johann Meier Alexander W. Koch 《Optics Communications》2011,284(9):2317-2322
Using Laser-based Speckle-Interferometers, the shape of optically rough surfaces can be measured precisely and contactlessly from variable measuring distances even in regions of difficult access. This work is concerned with the integration of a micromirror array (MMA) into an electronic Speckle-Pattern-Interferometer. With the adaptive optics, it is intended to adapt the phasefront of a reference wave to critical surface areas of the measurement object. Yet, due to the topography of the MMA, diffraction effects occur which affect the phase and intensity of the generated wavefront. We demonstrate how these diffraction effects can be efficiently modelled by a Fraunhofer diffraction method. We compare the results of this model to theoretical data obtained by a numerical Fresnel diffraction model and to measurement data obtained from a measurement setup incorporating a multi mirror array. 相似文献
940.
We propose a new two-mode squeezed coherent state representation |z1, z2〉g which is characteristic of the correlation between the squeezing and the displacement. Based on it and using the technique of integration within an ordered product of operators we obtain a generalized two-mode Fresnel operator (GTFO), which is an image of the mapping from (z1, z2) to in |z1, z2〉g representation. The matrix element of GTFO in the coordinate representation leads to a generalized two-dimensional Collins formula (Huygens-Fresnel integration transformation describing optical diffraction) in entangled form. 相似文献