全文获取类型
收费全文 | 7445篇 |
免费 | 1152篇 |
国内免费 | 725篇 |
专业分类
化学 | 3729篇 |
晶体学 | 58篇 |
力学 | 523篇 |
综合类 | 37篇 |
数学 | 326篇 |
物理学 | 4649篇 |
出版年
2024年 | 10篇 |
2023年 | 71篇 |
2022年 | 234篇 |
2021年 | 199篇 |
2020年 | 219篇 |
2019年 | 227篇 |
2018年 | 209篇 |
2017年 | 220篇 |
2016年 | 295篇 |
2015年 | 276篇 |
2014年 | 405篇 |
2013年 | 629篇 |
2012年 | 475篇 |
2011年 | 576篇 |
2010年 | 412篇 |
2009年 | 504篇 |
2008年 | 504篇 |
2007年 | 561篇 |
2006年 | 447篇 |
2005年 | 355篇 |
2004年 | 304篇 |
2003年 | 276篇 |
2002年 | 286篇 |
2001年 | 210篇 |
2000年 | 206篇 |
1999年 | 150篇 |
1998年 | 140篇 |
1997年 | 109篇 |
1996年 | 87篇 |
1995年 | 98篇 |
1994年 | 75篇 |
1993年 | 102篇 |
1992年 | 63篇 |
1991年 | 55篇 |
1990年 | 45篇 |
1989年 | 33篇 |
1988年 | 33篇 |
1987年 | 24篇 |
1986年 | 25篇 |
1985年 | 33篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1973年 | 5篇 |
排序方式: 共有9322条查询结果,搜索用时 62 毫秒
991.
周期激励浅拱1∶2内共振参数平面定常运动分布 总被引:1,自引:0,他引:1
本文研究了已具有静变形的受周期激励作用下浅拱在1:2内共振条件下的分岔特性,进而按系统的运动形式将整个参数平面分成不同的区域,得到了物理参数平面上浅拱的定常运动分布情况,结合数值分析方法详细分析了系统在各个区域内特别是Hopf分岔区域内系统的动力学特性,指出系统模态相互作用的规律及其通向混沌的过程· 相似文献
992.
Triplet state sublevel spectroscopy using optical detection of magnetic resonance (ODMR) in zero magnetic field can be successfully
employed to study (i) the environment of tryptophan (Trp) residues in a protein by observing the position and structure of
phosphorescence spectra, zero field ODMR transitions and triplet state sublevel kinetics, (ii) the energy transfer among Trp
residues, and (iii) whether any cysteine (Cys) residue is within van der Waals distance of any Trp residue by studying the
complex of the protein with methylmercury(II) iodide (CH3HgI) which binds to Cys residues. These studies are particularly important where crystal structure study is not possible.
Study of the S1 state often gives ambiguous results since fluorescence is always broad and shows multi-exponential decay. Our results on
bacteriophage lysozyme T4 which contains three Trp residues at positions 126, 138 and 158 are presented. Measurements were
facilitated by the use of a mutated enzyme containing one or two Trp-Tyr substitutions. The results indicate that (i) Trp
126 and 158 are solvent exposed, whereas Trp 138 is buried in a hydrophobic environment, (ii)S ↔S non-radiative energy transfer takes place predominantly from Trp 126 to Trp 158, and (iii) only Trp-158 undergoes a heavy
atom perturbation, which affects selectively the z-sublevel (z is an out-of-plane axis of the indole plane) as a result of
CH3HgI binding to nearby Cys 97. We suggest that the Hg atom is located on the z-axis of Trp 158 in the complex. This interpretation
is based on our investigations on the effect of orientation of heavy atom perturbers in some naphthalene-crown ether metal
ion complexes. 相似文献
993.
W. G. Hiller H. Schneider V. D. Fedotov 《Journal of Polymer Science.Polymer Physics》1992,30(9):931-942
A theoretical treatment of the nonexponential relaxation behavior of the different proton nuclear magnetic resonance (NMR) relaxation processes in polymer melts is presented. Formulas are derived for a three-component model given by two versions and a homogeneous distribution of correlation times. The theoretical results were tested with measurements of T1, T2e, and T2 as functions of frequency and molecular mass in linear fractionated polyethylene samples. While the T1 relaxation always yields exponential magnetization decays, the T2e and T2 measurements show biexponential relaxation behavior. From the calculations it was found that the correlation time of the local motion is independent of the molecular mass, whereas the correlation time of the slowest motional process increases with M2.8w for the three-component model and with M2.2w for the distribution of correlation times, respectively. © 1992 John Wiley & Sons, Inc. 相似文献
994.
In this paper some new eighth algebraic order symmetric eight-step methods are introduced. For these methods a direct formula for the computation of the phase-lag is given. Based on this formula, the calculation of free parameters is done in order the phase-lag to be minimal. The new methods have better stability properties than the classical one. Numerical illustrations on the radial Schrödinger equation indicate that the new method is more efficient than older ones. 相似文献
995.
Yu.B. Vasilyev C. Stellmach G. Nachtwei R.A. Suris S.D. Suchalkin B.Ya. Meltser S.V. Ivanov P.S. Kopev 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):308
In tilted magnetic fields a bilayer electron–hole system is found to generate a photocurrent under terahertz radiation as the system is tuned to electron cyclotron resonance conditions. The photoinduced current amplitude oscillates with the magnetic field in correlation with Shubnikov–de Haas oscillations for electrons. The phenomenon is accounted for by a photomagnetic effect in electron–hole systems in the quantum Hall regime and has potentialities for terahertz detection and spectroscopy. 相似文献
996.
R. M. Lazorenko-Manevich 《Russian Journal of Electrochemistry》2005,41(8):799-831
A contemporary review of research concerning the mechanism of surface enhanced Raman scattering (SERS) is presented and it is stated that this problem is yet to be solved. The necessity to yet once again analyze some of the familiar experimental observations and the deep-rooted beliefs and revise quantitative evaluations of SERS enhancement via major mechanisms (electromagnetic and chemical) with allowance made for most important experimental characteristics of SERS is substantiated. The characteristics are enumerated and the role they play in the above evaluations is sketched. Attention is focused mainly on electrochemical aspects of SERS problem, which to a large extent define the content and salient features of SERS and provide basic experimental justification for the so-called adatom hypothesis.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 899–935.Original Russian Text Copyright © 2005 by Lazorenko-Manevich.In memory of Vladislav Vladimirovich Marinyuk 相似文献
997.
本文报道国内建成的远红外激光磁共振 (FIRLMR)光谱仪的技术特点和工作原理。该谱仪采用CO2 激光横向泵浦远红外激光 ,样品吸收池置于远红外激光谐振腔内 ,由聚丙烯薄膜与远红外激光增益池隔开以获得很高的灵敏度 ,从而对寿命很短的自由基分子进行研究。利用该光谱仪在远红外波段测量得到了多个瞬态自由基分子CCH ,CF和CH2 的光谱 ,这些自由基分子由微波放电产生的氟原子与甲烷CH4 反应生成。 相似文献
998.
999.
Ultrafast time-resolved optical transmissions in purified and as-grown single-walled carbon nanotube films are measured at a temperature of 200K. The signal of the purified sample shows a crossover from photobleaching to photoabsorption. The former and the latter are interpreted as the state filling and the red shift of the π-plasmon, respectively. The signal of the as-grown sample can be perfectly fitted by a single-exponential with a time constant of 232fs. The disappearance of the negative component in the as-grown sample is attributed to the charge transfer between the semiconducting nanotubes and the impurities. 相似文献
1000.
A laser spectroscopic setup has been applied in the past to successfully investigate off-line the hyperfine structure splitting
of radionuclides. In the present paper, its modification is described which will enable the determination of nuclear magnetic
dipole and electric quadrupole moments with higher sensitivity and higher resolution. 相似文献