全文获取类型
收费全文 | 7349篇 |
免费 | 1122篇 |
国内免费 | 751篇 |
专业分类
化学 | 2335篇 |
晶体学 | 88篇 |
力学 | 1004篇 |
综合类 | 131篇 |
数学 | 1574篇 |
物理学 | 4090篇 |
出版年
2024年 | 17篇 |
2023年 | 72篇 |
2022年 | 150篇 |
2021年 | 184篇 |
2020年 | 169篇 |
2019年 | 158篇 |
2018年 | 147篇 |
2017年 | 232篇 |
2016年 | 319篇 |
2015年 | 217篇 |
2014年 | 422篇 |
2013年 | 541篇 |
2012年 | 443篇 |
2011年 | 528篇 |
2010年 | 457篇 |
2009年 | 463篇 |
2008年 | 507篇 |
2007年 | 526篇 |
2006年 | 437篇 |
2005年 | 418篇 |
2004年 | 337篇 |
2003年 | 313篇 |
2002年 | 289篇 |
2001年 | 227篇 |
2000年 | 212篇 |
1999年 | 181篇 |
1998年 | 159篇 |
1997年 | 146篇 |
1996年 | 124篇 |
1995年 | 118篇 |
1994年 | 112篇 |
1993年 | 92篇 |
1992年 | 72篇 |
1991年 | 68篇 |
1990年 | 47篇 |
1989年 | 50篇 |
1988年 | 47篇 |
1987年 | 25篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 31篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1973年 | 4篇 |
排序方式: 共有9222条查询结果,搜索用时 15 毫秒
41.
We apply a Bayesian approach to the problem of prediction in an unbalanced growth curve model using noninformative priors. Due to the complexity of the model, no analytic forms of the predictive densities are available. We propose both approximations and a prediction-oriented Metropolis-Hastings sampling algorithm for two types of prediction, namely the prediction of future observations for a new subject and the prediction of future values for a partially observed subject. They are illustrated and compared through real data and simulation studies. Two of the approximations compare favorably with the approximation in Fearn (1975, Biometrika, 62, 89–100) and are very comparable to the more accurate Rao-Blackwellization from Metropolis-Hastings sampling algorithm. 相似文献
42.
43.
用力敏传感器测量乙醇水溶液的表面张力系数与浓度的关系 总被引:6,自引:3,他引:3
用硅压阻式力敏传感器测量了纯水、乙醇的表面张力系数,并测量了不同浓度的乙醇水溶液的表面张力系数,得到了乙醇水溶液的表面张力系数随浓度的变化曲线. 相似文献
44.
《Surface and interface analysis : SIA》2004,36(9):1304-1313
For rough heterogeneous samples, the contrast observed in XPS images may result from both changes in elemental or chemical composition and sample topography. Background image acquisition and subtraction are frequently utilized to minimize topographical effects so that images represent concentration variations in the sample. This procedure may significantly increase the data acquisition time. Multivariate statistical methods can assist in resolving topographical and chemical information from multispectral XPS images. Principal component analysis (PCA) is one method for identification of the highest correlation/variation between the images. Topography, which is common to all of the images, will be resolved in the first most significant component. The score of this component contains spatial information about the topography of the surface, whereas the loading is a quantitative representation of the topography contribution to each elemental/chemical image. The simple‐to‐use self‐modelling mixture analysis (Simplisma) method is a pure variable method that searches for the source of most differences in the data and therefore has the potential to distinguish between chemical and topographical phases in images. The mathematical background correction scheme is developed and validated by comparing results to the experimental background correction for samples with differing degrees of topography. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
45.
46.
47.
激光水下扫描成像系统的图像修正机理 总被引:2,自引:0,他引:2
同步扫描系统可以克服后向散射,但同时也产生了两种非线性,一是扫描线速度的非线性,一是由于距离对光能衰减造成的非线性,两种非线性都需要修正,本文从原理上讨论水下激光成像时能量衰减的修正原理与修正方法,并给出仿真结果。 相似文献
48.
A.D. Bykov V.N. Saveliev C. Camy-Peyret A. Valentin 《Journal of Molecular Spectroscopy》2004,224(2):164-175
Forty-seven N2 broadened water vapor line-widths have been measured in the 1845-2140 cm−1 spectral range with a Fourier Transform spectrometer in the 258-330 K temperature range at a spectral resolution of 0.005 cm−1 for the lines with upper state rotational quantum number up to 16. The measured exponents of the temperature dependence of the width exhibit a large range of values from 1.60 to −0.86. Theoretical calculations were made using a semi-empirical technique based on the Anderson theory. The calculated broadening coefficients as well as the temperature exponents for the half-width agree satisfactory with measured values. 相似文献
49.
主要研究在高空核爆的双指数类型电磁脉冲平面波入射时,地面附近的电磁脉冲环境。计算给出了在不同入射波状态,不同地表介质电气特性和距地面不同高度等条件下的电磁脉冲环境参数,归纳了一些规律性认识。结果显示:地面附近的电场会随距地面高度的不同而发生显著的变化,对于水平场分量,其反射场总是试图抵消入射场,而对于垂直场分量,其反射场叠加在入射场上,使得地面附近的垂直场强幅值一般大于入射波场强幅值;当入射波仰角增大时,合成电场波形的脉冲宽度会变宽;地表介质的电气特性参数不同也会对地面附近电场的波形和幅值造成一定的影响。 相似文献
50.
Alan L. Andrew 《BIT Numerical Mathematics》2003,43(3):485-503
The asymptotic correction technique of Paine, de Hoog and Anderssen can dramatically improve the accuracy of finite difference or finite element eigenvalues at negligible extra cost if closed form expressions are available for the errors in a simpler related problem. This paper gives closed form expressions for the errors in the eigenvalues of certain Sturm–Liouville problems obtained by various methods, thereby increasing the range of problems for which asymptotic correction can achieve maximum efficiency. It also investigates implementation of the method for more general problems. 相似文献