全文获取类型
收费全文 | 280504篇 |
免费 | 2141篇 |
国内免费 | 775篇 |
专业分类
化学 | 131647篇 |
晶体学 | 4069篇 |
力学 | 14737篇 |
综合类 | 7篇 |
数学 | 43049篇 |
物理学 | 89911篇 |
出版年
2021年 | 1028篇 |
2020年 | 1168篇 |
2019年 | 1199篇 |
2018年 | 10466篇 |
2017年 | 11435篇 |
2016年 | 6611篇 |
2015年 | 2923篇 |
2014年 | 2723篇 |
2013年 | 8163篇 |
2012年 | 11013篇 |
2011年 | 21123篇 |
2010年 | 12581篇 |
2009年 | 12751篇 |
2008年 | 18541篇 |
2007年 | 22194篇 |
2006年 | 7509篇 |
2005年 | 14158篇 |
2004年 | 9798篇 |
2003年 | 8791篇 |
2002年 | 6621篇 |
2001年 | 6325篇 |
2000年 | 5035篇 |
1999年 | 3596篇 |
1998年 | 2747篇 |
1997年 | 2709篇 |
1996年 | 2859篇 |
1995年 | 2464篇 |
1994年 | 2390篇 |
1993年 | 2261篇 |
1992年 | 2540篇 |
1991年 | 2478篇 |
1990年 | 2189篇 |
1989年 | 2184篇 |
1988年 | 2192篇 |
1987年 | 2130篇 |
1986年 | 2032篇 |
1985年 | 2999篇 |
1984年 | 2978篇 |
1983年 | 2370篇 |
1982年 | 2562篇 |
1981年 | 2452篇 |
1980年 | 2419篇 |
1979年 | 2379篇 |
1978年 | 2458篇 |
1977年 | 2316篇 |
1976年 | 2301篇 |
1975年 | 2256篇 |
1974年 | 2169篇 |
1973年 | 2298篇 |
1972年 | 1275篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame. 相似文献
32.
33.
C. Kimberling 《Aequationes Mathematicae》2002,63(1-2):158-167
34.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
35.
In the following we find all of the three-dimensional flat spacetimes which are static and rotationally symmetric. 相似文献
36.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
37.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps. 相似文献
38.
Graham Smith 《The Journal of the Operational Research Society》1989,40(9):761-770
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation. 相似文献
39.
A two-dimensional, nonlinear, compressible, diabatic, nonhydrostatic photochemical-dynamical gravity wave model has been advanced. The model includes diabetic process produced by photochemistry and the effect of gravity wave on atmospheric chemical species. In the horizontal direction, the pseudospectral method is used. The finite difference approximations are used in vertical direction z and time t. The FICE method is used to solve the model. The model results on small amplitude fluctuation are very close to those of linear theory, which demonstrates the correctness of the model.
相似文献40.
Using Wagner's polarization technique and EMF method the joinic and silver ionic transport number measurements of various
compositions of the mixed system CdI2-Ag2O-CrO3 have been made. The presence of AgI in these materials has been inferred from the typical β → α phase transition of AgI,
which is characterized by an endothermic peak at around 420 K in the DSC traces of these specimens. While the structural analysis
performed by means of powder X-ray diffraction has revealed the formation of ionic phases involving polycrystalline compounds,
the Fourier transform infrared (FTIR) spectroscopic results have indicated the presence of ionic species thus confirming the
ionic nature of the products. The complex impedance studies carried out in the frequency range 20 Hz - 1 MHz and over the
temperature range 294 – 442 K have revealed that the best conducting composition, namely 55%(CdI2) – 45%(Ag2O·CrO3), would exhibit a silver ionic conductivity of 1.3×10−5Scm−1 at 294 K. 相似文献