全文获取类型
收费全文 | 81689篇 |
免费 | 6566篇 |
国内免费 | 5189篇 |
专业分类
化学 | 24700篇 |
晶体学 | 1835篇 |
力学 | 3659篇 |
综合类 | 331篇 |
数学 | 18843篇 |
物理学 | 44076篇 |
出版年
2022年 | 350篇 |
2021年 | 388篇 |
2020年 | 668篇 |
2019年 | 969篇 |
2018年 | 918篇 |
2017年 | 649篇 |
2016年 | 473篇 |
2015年 | 462篇 |
2014年 | 1105篇 |
2013年 | 1780篇 |
2012年 | 1206篇 |
2011年 | 1798篇 |
2010年 | 2369篇 |
2009年 | 6912篇 |
2008年 | 7996篇 |
2007年 | 6505篇 |
2006年 | 5912篇 |
2005年 | 4046篇 |
2004年 | 3856篇 |
2003年 | 4070篇 |
2002年 | 5303篇 |
2001年 | 3802篇 |
2000年 | 3565篇 |
1999年 | 3418篇 |
1998年 | 2826篇 |
1997年 | 1978篇 |
1996年 | 1753篇 |
1995年 | 2222篇 |
1994年 | 2151篇 |
1993年 | 1606篇 |
1992年 | 1125篇 |
1991年 | 842篇 |
1990年 | 684篇 |
1989年 | 612篇 |
1988年 | 571篇 |
1987年 | 408篇 |
1986年 | 194篇 |
1985年 | 945篇 |
1984年 | 622篇 |
1983年 | 487篇 |
1982年 | 643篇 |
1981年 | 794篇 |
1980年 | 721篇 |
1979年 | 559篇 |
1978年 | 583篇 |
1977年 | 538篇 |
1976年 | 541篇 |
1975年 | 319篇 |
1974年 | 356篇 |
1973年 | 463篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
A Garcia-Quiroz David L AzevedoE.C da Silva 《Journal of Physics and Chemistry of Solids》2002,63(10):1863-1866
Properties of oxygenated carbon nitride films have attracted the attention of physics researchers due to their magnetic and physical properties, as well as for their usefulness in the industry. The free radicals were investigated using electron paramagnetic resonance applied in the study of spin concentration due to the different mechanism of preparation of carbon nitride films by RF-discharge with different kinds of plasma. Unpaired spin concentrations, in the order of 1020 per cm3, were measured and their time recombination dependency was important in those films. The films were grown by plasma enhanced chemical vapor deposition using mixtures of hydrocarbons, N2 and O2 in different proportions. 相似文献
72.
A.R. Phani M. PassacantandoS. Santucci 《Journal of Physics and Chemistry of Solids》2002,63(3):383-392
Crack free, dense and transparent CdTiO3 thin films have been prepared by sol-gel technique using titanium butoxide and cadmium acetate. The formation of the CdTiO3 phase started from 500°C annealing temperature onwards. The complete orthorhombic structure of CdTiO3 was formed on Silicon (100) substrate at an annealing temperature of 600°C for 5 h. As the annealing temperature increased from 600 to 700°C, we have observed the cadmium silicate phase at the interface of Si and CdTiO3 phase. Structural, morphological and elemental evolution of these CdTiO3 thin films produced by sol-gel synthesis were characterised by grazing incidence X-ray diffraction (GIXRD), tapping mode atomic force microscopy (TMAFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) respectively. 相似文献
73.
K. Batra V. Prasad M. Mohan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):191-198
The scattering of heavy ion with a multilevel Rydberg atom in the presence of an electromagnetic field is studied. The interaction
of Rydberg atom and the e.m field is explored using non-perturbative quasi-energy technique. Although the results are presented
for selected excitations but in actual calculations we have included many levels of the atom. The effect of various parameters
are shown on collisional excitation process. As an illustration detailed calculations are performed for the inelastic proton-Na
Rydberg atom collision accompanied by the transfer of photons and the effects of dressing due to the field are considered.
The emphasis of the present work is on collision induced transitions especially the case that involves change of orbital as
well as principal quantum number.
Received 26 December 2001 / Received in final form 8 April 2002 Published online 19 July 2002 相似文献
74.
F. Iachello S. Oss 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):307-314
We present a brief review of algebraic techniques developed and applied in molecular spectroscopy in the last five years.
We also outline perspectives for new applications of the Lie algebraic method in the first decade of the new century.
Received 21 November 2001 相似文献
75.
利用红外特征峰波数偏移值与单体含量间的非线性定量关系,BP人工神经网络-FTIR法在较宽的含量范围(10%-90%之间)之内,准确测定了苯乙烯-丙烯酸丁酯共聚物中丙烯酸丁酯单体含量,回收率在97.3%-101.8%之间. 相似文献
76.
Ludmila C. Fidale Sarah Köhler Martin H.G. Prechtl Thomas Heinze Omar A. El Seoud 《Cellulose (London, England)》2006,13(5):581-592
The concentrations of water, W, and electrolytes present in solutions of LiCl in N,N-dimethylacetamide, LiCl/DMAc, and of tetrabutylammonium fluoride. x-hydrate in DMSO, TBAF.xW/DMSO can be accurately and expediently determined by three independent methods, UV–vis, FTIR and EMF measurement. The first relies on the use of solvatochromic probes whose spectra are sensitive to solution composition. It is applicable to W/LiCl/DMAc solutions but not to TBAF.xW/DMSO, because the charge-transfer complex bands of the probes are suppressed by strong interactions with the latter electrolyte. Integration of νOH band of water may be employed in order to determine [W], hence [electrolyte] by weight difference. EMF measurement uses ion-selective electrodes in order to determine [electrolyte], hence [W] by weight difference. Results of the latter method were in excellent agreement with those of FTIR. The reason for the failure of Karl Fischer titration is addressed, and the relevance of the results obtained to functionalization of cellulose under homogenous solution conditions is briefly commented on. 相似文献
77.
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states. 相似文献
78.
We have applied Engel-Vosko exchange energy within density functional theory, to calculate the electronic structure and the optical properties of BaX (X = Te, Se, and S) compounds via full potential linearized augmented plane wave method. We have found that this improves the band gap results comparing to our previous work in which we had made use of Perdew et al. exchange energy functional. We have also calculated the dielectric constant of these compounds, using both Perdew et al. and Engel-Vosko schemes. It is shown that Engel-Vosko exchange energy functional leads to a better result. We have also reported the effect of spin-orbit coupling on the results. 相似文献
79.
考虑约束最优化问题:minx∈Ωf(x)其中:f:R^n→R是连续可微函数,Ω是一闭凸集。本文研究了解决此问题的梯度投影方法,在步长的选取时采用了一种新的策略,在较弱的条件下,证明了梯度投影响方法的全局收敛性。 相似文献
80.
We construct the complex simple Lie algebras using elementary algebraic geometry. We use our construction to obtain a new
proof of the classification of complex simple Lie algebras that does not appeal to the classification of root systems. 相似文献