全文获取类型
收费全文 | 10709篇 |
免费 | 1629篇 |
国内免费 | 1227篇 |
专业分类
化学 | 2825篇 |
晶体学 | 139篇 |
力学 | 1164篇 |
综合类 | 232篇 |
数学 | 5110篇 |
物理学 | 4095篇 |
出版年
2024年 | 25篇 |
2023年 | 102篇 |
2022年 | 163篇 |
2021年 | 218篇 |
2020年 | 260篇 |
2019年 | 255篇 |
2018年 | 226篇 |
2017年 | 334篇 |
2016年 | 428篇 |
2015年 | 302篇 |
2014年 | 534篇 |
2013年 | 853篇 |
2012年 | 600篇 |
2011年 | 736篇 |
2010年 | 667篇 |
2009年 | 672篇 |
2008年 | 713篇 |
2007年 | 821篇 |
2006年 | 673篇 |
2005年 | 637篇 |
2004年 | 516篇 |
2003年 | 502篇 |
2002年 | 459篇 |
2001年 | 380篇 |
2000年 | 360篇 |
1999年 | 293篇 |
1998年 | 237篇 |
1997年 | 249篇 |
1996年 | 176篇 |
1995年 | 160篇 |
1994年 | 149篇 |
1993年 | 112篇 |
1992年 | 97篇 |
1991年 | 94篇 |
1990年 | 68篇 |
1989年 | 50篇 |
1988年 | 59篇 |
1987年 | 37篇 |
1986年 | 32篇 |
1985年 | 50篇 |
1984年 | 35篇 |
1983年 | 19篇 |
1982年 | 54篇 |
1981年 | 30篇 |
1980年 | 30篇 |
1979年 | 21篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
D.L. Skuratov Yu.L. Ratis I.A. Selezneva J. Pérez P. Fernández de Córdoba J.F. Urchueguía 《Applied Mathematical Modelling》2007
This paper deals with modelling the workpiece temperature field produced during the grinding process. The proposed model is given in terms of a two-dimensional boundary-value problem where the interdependence among the grinding wheel, the workpiece and the coolant is described by two variable functions in the boundary condition. An explicit integral form solution is constructed using the Laplace and Fourier transforms and the Green’s function method. 相似文献
52.
一个改进的Hardy-Hilbert不等式 总被引:1,自引:1,他引:0
通过建立权系数的不等式,得到一个改进的Hardy-Hilbert不等式. 相似文献
53.
I. A. Anoshko V. S. Ermachenko L. E. Sandrigailo 《Journal of Applied Spectroscopy》2007,74(1):102-106
We present the results of a spectroscopic study of a nonequilibrium plasma in a Hall accelerator, in particular for such an
important parameter as the electron temperature. For the studied conditions, we used the semicoronal equilibrium model, which
relates the intensity ratios for two successive ionization steps for the same element.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 93–96, January–February, 2007. 相似文献
54.
一个推广的Hardy-Hilbert型不等式及其逆式 总被引:1,自引:0,他引:1
本文引入单参数λ及应用Beta函数,给一个Hardy-Hilbert型不等式以具有最佳常数因子的推广,作为应用,给出了它的逆向形式. 相似文献
55.
Poisson回归模型广泛应用于分析计数型数据 ,Dean&Lawless(1989)和Dean(1992 )讨论了非重复测量得到的计数型数据的偏大离差存在性的检验问题 .本文分别利用随机系数模型和对数非线性模型讨论了基于重复测量得到的计数型数据的偏大离差的检验问题 ,得到了检验的score统计量 . 相似文献
56.
Liang-gen Hu 《应用数学学报(英文版)》2007,23(2):281-288
In this paper,we will establish several strong convergence theorems for the approximation ofcommon fixed points of r-strictly asymptotically pseudocontractive mappings in uniformly convex Banachspaces using the modiied implicit iteration sequence with errors,and prove the necessary and sufficient conditionsfor the convergence of the sequence.Our results generalize,extend and improve the recent work,in thistopic. 相似文献
57.
58.
This paper investigates mutual influence of duct and room acoustics in the whole fan-duct-plenum-room integrations. Applying the parametric design language of finite element software ANSYS (APDL), dimensional and positional influence on system acoustics has been studied. Models with different room dimensions, duct lengths, duct cross-sections, duct locations, duct discharges and duct elbow were constructed, and their characteristics were compared qualitatively. Results show that small rooms, short ducts, large duct cross-sections and bell mouth duct discharges help to increase room sound pressure levels (SPLs); SPLs in ducts and plenums are sensitive to duct dimensions and duct discharge types but insensitive to duct locations and room dimensions; duct elbows have relatively indistinct acoustic influence in each component. Based on the calculation results, a semi-experimental method was proposed for simply and approximately evaluating indoor acoustic spectra of fan-duct-plenum-room integrations, then an example was used to demonstrate the prediction process. Finally, by adopting several ideal models, sound field constitutions, duct and room wall admittances and duct end reflection were explored quantitatively. This study may give a detailed understanding of fan-duct-plenum-room acoustics for researchers, also it might provide a new, simple and approximate prediction method for professionals to evaluate and improve fan-ducted acoustics. 相似文献
59.
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
60.
研究了基于级联二阶非线性的铌酸锂波导全光波长变换器的特性.首先从耦合模方程出发,比较了数值分析结果与小信号近似分析的结果.其次在数值分析基础上,分析了铌酸锂晶体的温度变化导致相应基频光波波长与极化反转光栅周期的变化关系.最后分析了在不同相互作用长度下,转换的光波功率与有效基频光波波长带宽、温度调谐带宽、极化反转光栅周期带宽等关系,以对全光波长变换器件进行优化设计
关键词:
级联二阶非线性
波长变换
准位相匹配
铌酸锂光波导 相似文献