全文获取类型
收费全文 | 16309篇 |
免费 | 2652篇 |
国内免费 | 1294篇 |
专业分类
化学 | 3161篇 |
晶体学 | 228篇 |
力学 | 3144篇 |
综合类 | 254篇 |
数学 | 6681篇 |
物理学 | 6787篇 |
出版年
2024年 | 24篇 |
2023年 | 146篇 |
2022年 | 226篇 |
2021年 | 311篇 |
2020年 | 384篇 |
2019年 | 344篇 |
2018年 | 313篇 |
2017年 | 493篇 |
2016年 | 589篇 |
2015年 | 414篇 |
2014年 | 727篇 |
2013年 | 1165篇 |
2012年 | 851篇 |
2011年 | 928篇 |
2010年 | 840篇 |
2009年 | 913篇 |
2008年 | 975篇 |
2007年 | 1130篇 |
2006年 | 995篇 |
2005年 | 1018篇 |
2004年 | 831篇 |
2003年 | 868篇 |
2002年 | 767篇 |
2001年 | 639篇 |
2000年 | 616篇 |
1999年 | 551篇 |
1998年 | 436篇 |
1997年 | 417篇 |
1996年 | 276篇 |
1995年 | 266篇 |
1994年 | 228篇 |
1993年 | 236篇 |
1992年 | 170篇 |
1991年 | 157篇 |
1990年 | 124篇 |
1989年 | 81篇 |
1988年 | 88篇 |
1987年 | 70篇 |
1986年 | 66篇 |
1985年 | 93篇 |
1984年 | 74篇 |
1983年 | 34篇 |
1982年 | 63篇 |
1981年 | 59篇 |
1980年 | 45篇 |
1979年 | 41篇 |
1978年 | 51篇 |
1977年 | 37篇 |
1976年 | 31篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
101.
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
102.
R. Centore P. Riccio S. Fusco A. Carella A. Quatela S. Schutzmann F. Stella F. De Matteis 《Journal of polymer science. Part A, Polymer chemistry》2007,45(13):2719-2725
We have prepared new polyesters containing quadratic, nonlinear optical (NLO) active chromophores covalently incorporated into the main chain. In these polymers, the sequence of the chromophore units along the main chain is rigorously head to tail. All the polyesters are processable, both in the melt and in solution. For one polyester, a full second‐order NLO characterization has been performed. An out‐of‐resonance d33 coefficient of 21 pm/V at 1368 nm has been measured. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2719–2725, 2007 相似文献
103.
We have presented an investigation of the induced focusing in Kerr media of two laser beams, the pump beam and the probe beam,
which could be either Gaussian or elliptic Gaussian or a combination of the two. We have used variational formalism to derive
relevant beam-width equations. Among several important findings, the finding that a very week probe beam can be guided and
focused when power of both beams are well below their individual threshold for self-focusing, is a noteworthy one. It has
been found that induced focusing is not possible for laser beams of any wavelength and beam radius. In case both beams are
elliptic Gaussian, we have shown that when power of both beams is above a certain threshold value then the effective radius
of both beams collapses and collapse distance depends on power. Moreover, it has been found that induced focusing can be employed
to convert a circular Gaussian beam into an elliptic Gaussian beam. 相似文献
104.
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
105.
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
106.
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
107.
基于正弦灰度变换的X光图像增强 总被引:11,自引:0,他引:11
介绍了灰度变换法的几种形式 ,提出了一种正弦非线性变换法 ,对三幅数字X光医学图像进行了处理 ,获得了令人满意的对比度增强效果 ,证明该方法有效而实用 相似文献
108.
Dirichlet boundary value problems for perturbed second-order differential equations on a half line are investigated in this paper. The methods mainly depend on the calculus of variations to the classical functionals. Sufficient conditions are obtained for the existence of the solutions. 相似文献
109.
110.
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