全文获取类型
收费全文 | 362477篇 |
免费 | 12877篇 |
国内免费 | 7689篇 |
专业分类
化学 | 207318篇 |
晶体学 | 5052篇 |
力学 | 17229篇 |
综合类 | 525篇 |
数学 | 38381篇 |
物理学 | 114538篇 |
出版年
2022年 | 3686篇 |
2021年 | 4270篇 |
2020年 | 4621篇 |
2019年 | 4633篇 |
2018年 | 4800篇 |
2017年 | 4639篇 |
2016年 | 7493篇 |
2015年 | 6292篇 |
2014年 | 8096篇 |
2013年 | 17685篇 |
2012年 | 15867篇 |
2011年 | 18414篇 |
2010年 | 12269篇 |
2009年 | 12376篇 |
2008年 | 15909篇 |
2007年 | 15318篇 |
2006年 | 14685篇 |
2005年 | 13380篇 |
2004年 | 11733篇 |
2003年 | 10184篇 |
2002年 | 9835篇 |
2001年 | 11768篇 |
2000年 | 9077篇 |
1999年 | 7470篇 |
1998年 | 5650篇 |
1997年 | 5596篇 |
1996年 | 5502篇 |
1995年 | 4951篇 |
1994年 | 4770篇 |
1993年 | 4347篇 |
1992年 | 4970篇 |
1991年 | 4927篇 |
1990年 | 4461篇 |
1989年 | 4319篇 |
1988年 | 4195篇 |
1987年 | 4117篇 |
1986年 | 3824篇 |
1985年 | 5124篇 |
1984年 | 5017篇 |
1983年 | 4065篇 |
1982年 | 4196篇 |
1981年 | 3924篇 |
1980年 | 3821篇 |
1979年 | 4009篇 |
1978年 | 4164篇 |
1977年 | 4094篇 |
1976年 | 3941篇 |
1975年 | 3813篇 |
1974年 | 3706篇 |
1973年 | 3824篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
在氢化丁苯共聚物13C-NMR谱脂肪碳部分谱带归属的基础上,根据各谱带的主要来源,推导出六个二单元浓度的计算公式。计算出二单元、一单元的相对含量,各结构单元的数均序列长度、嵌段含量和其它结构参数。加氢前后的1H-和13C-NMR谱的组成计算结果基本一致。初步探讨了作为粘度指数改进剂的氢化丁苯共聚物微观结构与性能的关系,为合成提供了依据。 相似文献
12.
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
13.
14.
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
15.
16.
17.
18.
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
19.
S. A. Gurevich T. A. Zaraiskaya S. G. Konnikov V. M. Mikushkin S. Yu. Nikonov A. A. Sitnikova S. E. Sysoev V. V. Khorenko V. V. Shnitov Yu. S. Gordeev 《Physics of the Solid State》1997,39(10):1691-1695
The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material. 相似文献
20.
Ya. V. Fattakhov M. F. Galyautdinov T. N. L’vova I. B. Khaibullin 《Technical Physics》1997,42(12):1457-1459
The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface
upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures
is discussed.
Zh. Tekh. Fiz. 67, 97–99 (December 1997) 相似文献