全文获取类型
收费全文 | 9266篇 |
免费 | 1025篇 |
国内免费 | 741篇 |
专业分类
化学 | 4772篇 |
晶体学 | 86篇 |
力学 | 565篇 |
综合类 | 167篇 |
数学 | 1873篇 |
物理学 | 3569篇 |
出版年
2023年 | 95篇 |
2022年 | 216篇 |
2021年 | 229篇 |
2020年 | 279篇 |
2019年 | 256篇 |
2018年 | 213篇 |
2017年 | 273篇 |
2016年 | 272篇 |
2015年 | 228篇 |
2014年 | 369篇 |
2013年 | 479篇 |
2012年 | 359篇 |
2011年 | 524篇 |
2010年 | 464篇 |
2009年 | 605篇 |
2008年 | 550篇 |
2007年 | 495篇 |
2006年 | 440篇 |
2005年 | 336篇 |
2004年 | 266篇 |
2003年 | 279篇 |
2002年 | 252篇 |
2001年 | 195篇 |
2000年 | 224篇 |
1999年 | 158篇 |
1998年 | 143篇 |
1997年 | 116篇 |
1996年 | 103篇 |
1995年 | 87篇 |
1994年 | 69篇 |
1993年 | 47篇 |
1992年 | 58篇 |
1991年 | 40篇 |
1990年 | 37篇 |
1989年 | 32篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1985年 | 421篇 |
1984年 | 293篇 |
1983年 | 236篇 |
1982年 | 210篇 |
1981年 | 154篇 |
1980年 | 117篇 |
1979年 | 136篇 |
1978年 | 75篇 |
1977年 | 88篇 |
1976年 | 88篇 |
1975年 | 88篇 |
1974年 | 117篇 |
1973年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
M. Sakai S. Ishiuchi M. Fujii 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):399-402
The picosecond time-resolved IR spectrum of the 7-azaindole dimer has been measured by picosecond time-resolved nonresonant
ionization detected IR spectroscopy. This new time-resolved technique was developed by combining nonresonant ionization detected
IR (NID-IR) spectroscopy with tunable picosecond IR and UV lasers. The time-resolved NID-IR spectrum from 2 600 cm-1 to 3 800 cm-1 shows a drastic change from 1.5 ps to 11 ps time evolution. A mode-specific vibrational redistribution has been suggested.
Received 14 May 2002 / Received in final form 11 June 2002 Published online 13 September 2002 相似文献
992.
993.
Er3+:Yb3+共掺杂氟氧混合物玻璃的上转换发光研究 总被引:3,自引:1,他引:2
制备了化学配方为 (5 0 -x)GeO2 ·PbF2 ·WO3·(6 +x)CdF2 ·1 4Yb2 O3·0 6Er2 O3(x =10 ,2 0 ,30 )氟氧混合物玻璃。研究了 930nm发光二极管激发下Er3+ :Yb3+ 共掺杂情形下的Er3+ 离子的上转换发光特性 ,观测到了Er3+ 离子中心波长位于 5 4 3,5 5 0和 6 5 5nm处的三个强荧光发射带。通过对样品的反斯托克斯喇曼光谱的测量 ,确定了基质的最大声子能量 ,在此基础上分析了上转换荧光的产生机制。利用基质的平均电负性差和平均阳离子场强这两个参数 ,讨论了基质材料中GeO2 和CdF2 含量的调整对上转换发光的影响。 相似文献
994.
Effect of conversion process ([I]-P→ΛΛ) on[I]--hypernucleus is studied for [I]12-Be. It is found that theconversion process has a certain extent effect on properties of low-lying states of the[I]--hypernuclei. 相似文献
995.
M. J. Cánovas M. A. López J. Parra F. J. Toledo 《Journal of Optimization Theory and Applications》2006,130(2):173-183
We consider the parameter space of all the linear inequality systems, in the n-dimensional Euclidean space and with a fixed index set, endowed with the topology of the uniform convergence of the coefficient vectors. A system is ill-posed with respect to the consistency when arbitrarily small perturbations yield both consistent and inconsistent systems. In this paper, we establish a formula for measuring the distance from the nominal system to the set of ill-posed systems. To this aim, we use the Fenchel-Legendre conjugation theory and prove a refinement of the formula in Ref. 1 for the distance from any point to the boundary of a convex set.This research has been partially supported by grants BFM2002–04114-C02 (01–02) from MEC (Spain) and FEDER (EU) and by grants GV04B-648 and GRUPOS04/79 from Generalitat Valenciana (Spain). 相似文献
996.
Two random-walk related problems which have been studied independently in the past, the expected maximum of a random walker
in one dimension and the flux to a spherical trap of particles undergoing discrete jumps in three dimensions, are shown to
be closely related to each other and are studied using a unified approach as a solution to a Wiener-Hopf problem. For the
flux problem, this work shows that a constant c = 0.29795219 which appeared in the context of the boundary extrapolation length, and was previously found only numerically,
can be derived analytically. The same constant enters in higher-order corrections to the expected-maximum asymptotics. As
a byproduct, we also prove a new universal result in the context of the flux problem which is an analogue of the Sparre Andersen
theorem proved in the context of the random walker's maximum. 相似文献
997.
文章简要介绍了“数字信号处理”与“数字信号处理器(DSP)”的发展历史.在数字信号处理的应用中,实时实现是非常重要的,而DSP在实时处理中,扮演了一个重要的角色.文章中还介绍了DSP在实际应用中的一些关键技术,例如DSP的种类和选型,DSP的开发工具,实时软件的开发过程等.最后,还介绍了一些DSP的应用实例,如语音编码器,视频电话和视频会议系统,用于雷达和声纳的DSP并行处理系统 相似文献
998.
Teik-Cheng Lim 《Journal of mathematical chemistry》2002,31(4):421-428
A set of mathematical relationship between torsion potential functions such as trigonometric and Fourier series is presented herein. A harmonic approximation form is also introduced, and its stiffness constant is related to the parameters of trigonometric and Fourier series. Mathematical relationships between various force field parameters are presented in the form of conversion matrices. 相似文献
999.
B. H. Lavenda 《Foundations of Physics Letters》1990,3(3):285-290
A probabilistic derivation of van der Waals' equation is given where the non-ideal contributions to the entropy coincide with the log-likelihood ratios, at their maxima, of the binomial distribution and the upper or lower bounds on the hypergeometric and Pólya distributions. The hypergeometric distribution accounts for the repulsive interactions of a hard sphere gas while the Pólya distribution accounts for the attractive interactions.1. Work supported in part by contributions from the Ministry of Public Education (M.P.I.) and the National Science Council (C.N.R.). 相似文献
1000.
Derivation of two point spread functions PSFs suitable for infrared thermograms analysis is illustrated, based on two unique approaches, one based on depth decaying limit and one on diffusion limit. Experimental work using PMMA sample with back drilled holes and pulsed thermographic routine is utilized to show the effectiveness of deconvoluting pixel temperature transient history with suggested PSF’s. Synthetic second time derivative thermograms are utilized for comparison and the signal to noise ratio is used as a figure of merit for quantification. 相似文献