全文获取类型
收费全文 | 428644篇 |
免费 | 6010篇 |
国内免费 | 1681篇 |
专业分类
化学 | 233542篇 |
晶体学 | 6073篇 |
力学 | 18411篇 |
综合类 | 14篇 |
数学 | 50479篇 |
物理学 | 127816篇 |
出版年
2020年 | 2833篇 |
2019年 | 2815篇 |
2018年 | 2825篇 |
2017年 | 2752篇 |
2016年 | 5595篇 |
2015年 | 4659篇 |
2014年 | 6233篇 |
2013年 | 19460篇 |
2012年 | 15008篇 |
2011年 | 18757篇 |
2010年 | 11671篇 |
2009年 | 11764篇 |
2008年 | 17242篇 |
2007年 | 17571篇 |
2006年 | 16931篇 |
2005年 | 15477篇 |
2004年 | 13912篇 |
2003年 | 12237篇 |
2002年 | 11982篇 |
2001年 | 13667篇 |
2000年 | 10557篇 |
1999年 | 8275篇 |
1998年 | 6596篇 |
1997年 | 6444篇 |
1996年 | 6465篇 |
1995年 | 5910篇 |
1994年 | 5540篇 |
1993年 | 5278篇 |
1992年 | 5912篇 |
1991年 | 5772篇 |
1990年 | 5311篇 |
1989年 | 5176篇 |
1988年 | 5463篇 |
1987年 | 5067篇 |
1986年 | 4899篇 |
1985年 | 7142篇 |
1984年 | 7172篇 |
1983年 | 5845篇 |
1982年 | 6299篇 |
1981年 | 6246篇 |
1980年 | 6030篇 |
1979年 | 6099篇 |
1978年 | 6157篇 |
1977年 | 6106篇 |
1976年 | 6005篇 |
1975年 | 5890篇 |
1974年 | 5685篇 |
1973年 | 5913篇 |
1972年 | 3455篇 |
1971年 | 2470篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as
hydroxyl (OH−) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as
provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place.
In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested
hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development
of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
102.
C. Fallnich B. Ruffing Th. Herrmann A. Nebel R. Beigang R. Wallenstein 《Applied physics. B, Lasers and optics》1995,60(5):427-436
We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency. 相似文献
103.
104.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields. 相似文献
105.
In this paper we consider a wavelet algorithm for the piecewise constant collocation method applied to the boundary element solution of a first kind integral equation arising in acoustic scattering. The conventional stiffness matrix is transformed into the corresponding matrix with respect to wavelet bases, and it is approximated by a compressed matrix. Finally, the stiffness matrix is multiplied by diagonal preconditioners such that the resulting matrix of the system of linear equations is well conditioned and sparse. Using this matrix, the boundary integral equation can be solved effectively. 相似文献
106.
107.
108.
109.
A. J. Parsons S. D. J. Inglethorpe D. J. Morgan A. C. Dunham 《Journal of Thermal Analysis and Calorimetry》1997,48(1):49-62
Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday 相似文献
110.