首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   774篇
  免费   15篇
  国内免费   3篇
化学   424篇
晶体学   9篇
力学   17篇
数学   72篇
物理学   270篇
  2023年   8篇
  2022年   4篇
  2021年   5篇
  2020年   4篇
  2018年   15篇
  2017年   11篇
  2016年   22篇
  2015年   16篇
  2014年   21篇
  2013年   55篇
  2012年   30篇
  2011年   53篇
  2010年   20篇
  2009年   28篇
  2008年   31篇
  2007年   35篇
  2006年   33篇
  2005年   34篇
  2004年   42篇
  2003年   26篇
  2002年   13篇
  2001年   11篇
  2000年   13篇
  1999年   12篇
  1998年   10篇
  1997年   12篇
  1996年   13篇
  1995年   19篇
  1994年   8篇
  1993年   14篇
  1992年   12篇
  1991年   15篇
  1990年   9篇
  1989年   11篇
  1988年   10篇
  1987年   7篇
  1986年   7篇
  1985年   9篇
  1984年   9篇
  1983年   8篇
  1982年   4篇
  1981年   5篇
  1980年   11篇
  1979年   6篇
  1978年   7篇
  1977年   7篇
  1976年   4篇
  1975年   5篇
  1973年   3篇
  1961年   4篇
排序方式: 共有792条查询结果,搜索用时 15 毫秒
171.
We recently reported the extension of CO laser operation to a variety of single-line transitions in the fundamental band (v=1 0). Now saturation stabilization of these lines could be achieved using an intracavity absorption cell with CO at low pressure. A 3f-detection technique allowed reliable frequency locking on transitions from P(8) to P(14). A frequency stability of better than 10kHz was indicated. The frequency of the P(14) transition was measured in a heterodyne experiment to be 62, 546, 358.324 (50) MHz.  相似文献   
172.
173.
On divergence-free wavelets   总被引:5,自引:0,他引:5  
This paper is concerned with the construction of compactly supported divergence-free vector wavelets. Our construction is based on a large class of refinable functions which generate multivariate multiresolution analyses which includes, in particular, the non tensor product case.For this purpose, we develop a certain relationship between partial derivatives of refinable functions and wavelets with modifications of the coefficients in their refinement equation. In addition, we demonstrate that the wavelets we construct form a Riesz-basis for the space of divergence-free vector fields.Work supported by the Deutsche Forschungsgemeinschaft in the Graduiertenkolleg Analyse und Konstruktion in der Mathematik at the RWTH Aachen.  相似文献   
174.
We propose a model to determine the influence of different cell properties, such as size, membrane capacitance and cytoplasm conductivity, on the impedance spectrum as measured in a microfabricated cytometer. A dielectric sphere of equivalent complex permittivity is used as a simplified model to describe a biological cell. The measurement takes place between a pair of facing microelectrodes in a microchannel filled with a saline solution. The model incorporates various cell parameters, such as dielectric properties, size and position in the channel. A 3D finite element model is used to evaluate the magnitude of the electric field in the channel and the resultant changes in charge densities at the measurement electrode boundaries as a cell flows past. The charge density is integrated on the electrode surface to determine the displacement current and the channel impedance for the computed frequency range. The complete impedance model combines the finite element model, the electrode-electrolyte interface impedance and stray impedance, which are measured from a real device. The modeled dielectric complex spectra for various cell parameters are discussed and a measurement strategy for cell discrimination with such a system is proposed. We finally discuss the amount of noise and measurement fluctuations of the sensor.  相似文献   
175.
Activation barriers of the title reactions are calculated using a DZ + P basis set with diffuse p functions on negative ions. In the correlation effects, which are large and negative, the importance of single and triple excitations is stressed. The barrier for the reaction of H? with CH3F is 12 kJ/mole, in good agreement with experiment, while the barrier for the reaction of F? with CH3F is predicted to be 14 kJ/mole.  相似文献   
176.
The partitioning of the free energy into additive contributions originating from different groups of atoms or force field terms has the potential to provide relationship between structure and biological activity of molecules. In this article, the theoretical foundation for the free energy decomposition in the free energy perturbation (FEP) methodology is formulated using Thiele cumulants, a powerful tool from the arsenal of probability theory and mathematical statistics. We establish that rigorous decomposition of the free energy into its components is precluded by the presence of mixed potential energy terms in Thiele cumulants of second and higher orders. However, we also show that the resultant nonadditivity error can be reduced to an arbitrary value by increasing the number of FEP steps. Consequently, the whole system can be in the limit of small perturbation steps adequately represented by the sum of its constituent parts.  相似文献   
177.
With the availability of resolution boosting and delocalization minimizing techniques, for example, spherical aberration correction and exit-plane wave function reconstruction, high-resolution transmission electron microscopy is drawing to a breakthrough with respect to the atomic-scale imaging of common semiconductor materials. In the present study, we apply a combination of these two state-of-the-art techniques to investigate lattice defects in GaAs-based heterostructures at atomic resolution. Focusing on the direct imaging of stacking faults as well as the core structure of edge and partial dislocations, the practical capabilities of both techniques are illustrated. For the first time, we apply the technique of bright-atom contrast imaging at negative spherical aberration together with an appropriate overfocus setting for the investigation of lattice defects in a semiconductor material. For these purposes, the elastic displacements associated with lattice defects in GaAs viewed along the 110 zone axis are measured from experimental images using reciprocal space strain map algorithms. Moreover, we demonstrate the benefits of the retrieval of the exit-plane wave function not only for the elimination of residual imaging artefacts but also for the proper on-line alignment of specimens during operation of the electron microscope--a basic prerequisite to obtain a fair agreement between simulated images and experimental micrographs.  相似文献   
178.
179.
We investigated the generation dependent shape and internal structure of star-burst dendrimers under good solvent conditions using small angle x-ray scattering and molecular modeling. Measurements have been performed on poly(amidoamine) dendrimers with generations ranging from g=0 up to g=8 at low concentrations in methanol. We described the static form factor P(q) by a model taking into account the compact, globular shape as well as the loose, polymeric character of dendrimers. Monomer distributions within dendrimers are of special interest for potential applications and have been characterized by the pair correlation function gamma(r), as well as by the monomer and end-group density profile, rho(r) and rho(e)(r), respectively. Monomer density profiles and gamma(r) can be derived from P(q) by modeling and via a model independent approach using the inverse Fourier transformation algorithm first introduced by Glatter. Experimental results are compared with computer simulations performed for single dendrimers of various generations using the cooperative motion algorithm. The simulation gives direct access to gamma(r) and rho(r), allows an independent determination of P(q), and yields in addition to the scattering experiment information about the distribution of the end groups. Excellent qualitative agreement between experiment and simulation has been found.  相似文献   
180.
[{Cp(CO)3Mo}4In4(PSiMe3)4], an Organometallic In4P4-Heterocubane [{Cp(CO)3Mo}InCl2] reacts with P(SiMe3)3 in THF as solvent to form [{Cp(CO)3Mo}4In4(PSiMe3)4] 1. 1 crystallizes in the space group P1 . The lattice constants (at 208 K) are: a = 1 770.1(6), b = 1 490.3(6), c = 1 317.5(6) pm, α = 76.59(4),β = 88.54(3), γ = 88.98(3)°. According to the crystal structure analysis, 1 contains a slightly distorted In4P4-core with an alternating arrangement of In and P atoms. The In atoms are coordinated roughly tetrahedrally by three PSiMe3 groups (In–P: 256.9(3)–262.3(3) pm) and a {Cp(CO)3Mo} substituent (In? Mo: 278.0(2)–279.5(3) pm).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号