全文获取类型
收费全文 | 1342篇 |
免费 | 261篇 |
国内免费 | 507篇 |
专业分类
化学 | 1223篇 |
晶体学 | 142篇 |
力学 | 120篇 |
综合类 | 13篇 |
数学 | 12篇 |
物理学 | 600篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 33篇 |
2021年 | 29篇 |
2020年 | 25篇 |
2019年 | 21篇 |
2018年 | 21篇 |
2017年 | 51篇 |
2016年 | 54篇 |
2015年 | 36篇 |
2014年 | 66篇 |
2013年 | 148篇 |
2012年 | 121篇 |
2011年 | 135篇 |
2010年 | 103篇 |
2009年 | 119篇 |
2008年 | 103篇 |
2007年 | 133篇 |
2006年 | 108篇 |
2005年 | 120篇 |
2004年 | 99篇 |
2003年 | 101篇 |
2002年 | 67篇 |
2001年 | 75篇 |
2000年 | 65篇 |
1999年 | 41篇 |
1998年 | 32篇 |
1997年 | 52篇 |
1996年 | 26篇 |
1995年 | 29篇 |
1994年 | 27篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有2110条查询结果,搜索用时 0 毫秒
141.
The RTP electro-optical Q-switched ceramic laser at the wavelength of 678 nm with narrow pulse width is studied. We used the laser diode arrays side-pumped Nd:YAG ceramic crystal with 1.1 at% Nd doping and dimensions of Φ3 mm × 50 mm, designed folding cavity parameters, and discussed the variation of the beam radius in the ceramic crystal and frequency doubling crystal with the thermal focal length of ceramic crystal or KTP crystal. By using double RTP crystals as electro-optic Q-switch and KTP crystal type II phase matching for intracavity frequency-doubling, a narrow pulse width electro-optical Q-switched Nd:YAG ceramic laser was obtained. The output energy of 0.9 mJ and the pulse width of 41.6 ns at 678 nm are obtained at the repetition rate of 1000 Hz and pumped power of 144 W. The results formed the basis for the further development of the high power and high efficiency ceramic red laser. 相似文献
142.
143.
The significance of kinetics on the development of microstructures in connection with sintering of ceramics is well recognized. In practice, however, it still remains a challenge to prepare designed microstructures via engineering the sintering kinetics because of an insufficient understanding of the different operative mechanisms that are in many cases overlapping. In this article the kinetic issues involved in sintering are described and discussed with respect to their potential for prototyping microstructures that yield desired properties. By exploiting and mastering the differences present in the kinetics of grain sliding, densification, chemical reactions, and grain growth, respectively, we have established processing principles for producing bulk ceramics with microstructures consisting of nano-sized grains, aligned grains, and/or non-equilibrium-phase constitutions, and for achieving radically improved superplasticity in brittle ceramics. Although the studies quoted in this article were mainly carried out by spark plasma sintering, more general implications of them are expected, including efficient particle sliding, deformation-induced dynamic ripening, superplastic deformation-induced dynamic ripening, and non-equilibrium integration. 相似文献
144.
We have investigated the IR reflection spectra of ferroelectric ceramics based on solid solutions of lead zirconate-titanate with a rhombohedral structure obtained by high-pressure cold precompaction. In the 55–65-cm–1 frequency range, we have revealed by experiment that the soft ferroelectric-active mode for the ceramics compacted by a higher pressure under the conditions of cold compaction is shifted into the region of lower frequencies. For the ceramics precompacted at various pressures, we have determined the frequencies of longitudinal and transverse phonons and calculated the frequency dependences of the imaginary and real parts of the dielectric constant. 相似文献
145.
This paper reports the formation and properties of nano-composite pyroelectric thin films. They consist of pyroelectric triglycine sulfate (TGS) single-crystal nano-rods grown inside a highly dense array of alumina pores (about 65 nm diameter and density of 1011 cm−2). The nucleation and growth of the TGS single crystals are obtained by precipitation from a supersaturated aqueous solution. Nucleation is preferred only at the bottom of the pores due to a tight control of temperature, composition and pore diameter. Growth of single crystals with preferred crystallographic orientation is obtained with the aid of an applied electric field. Various crystallographic orientations (1 0 0) (−1 1 0) (−1 2 0) are obtained separately as a single preferred orientation by changing the amplitude of the electric field during crystal growth. The films exhibit ferroelectric behavior. 相似文献
146.
研究了纳米SiO2对可水合氧化铝水化行为的影响以及纳米SiO2与可水合氧化铝混合料浆的流变性.利用XRD和SEM,研究了水化产物的物相组成和形貌特征,并利用Zeta电位仪与流变仪,测试了纳米SiO2-可水合氧化铝料浆的表面电位与流变行为.结果表明:纳米SiO2的添加减缓了可水合氧化铝的水化速度,其原因是纳米SiO2在可水合氧化铝颗粒表面形成包覆层阻碍了其与水的直接接触,从而降低了可水合氧化铝的水化速率;在碱性条件下,纳米SiO2的添加使可水合氧化铝料浆具有良好的分散性,降低了料浆的触变性,使料浆呈现剪切变稀行为. 相似文献
147.
Lü Qing WANG ShuFang LI LongJiang WANG JiangLong DAI ShouYu YU Wei FU GuangSheng 《中国科学:物理学 力学 天文学(英文版)》2014,57(9):1644-1648
High temperature electrical and thermal transport properties, that is, electrical conductivity, Seebeck coefficient and thermal conductivity, of CdO ceramics have been investigated. Because of the good electrical properties and low thermal conductivity, the dimensionless figure-of-merit ZT of the CdO ceramics reaches 0.34 at 1023 K. This value is comparable to the best reported ZT for the n-type oxide ceramic thermoelectric materials and remains as potential to be further improved by porosity controlling or nanostructuring. 相似文献
148.
149.
Thermostimulated luminescence (TSL) of PbWO4, Bi2WO6, and Y2WO6 ceramics on x-ray excitation is investigated. The spectral luminosity of the thermostimulated luminescence is analyzed. The thermal activation energies conforming to the corresponding thermostimulated luminescence peaks are determined. It is established that on emptying trapping centers radiative recombination occurs at the intrinsic-luminescence centers associated with tungsten-oxygen complexes WO4
2–. 相似文献
150.
富氧条件下Ag/Al2O3和Cu/Al2O3组合催化剂催化C3H6选择性还原Nox的性能 总被引:4,自引:0,他引:4
在全自动催化剂活性评价装置上,考察了富氧条件下Ag/Al2O3和Cu/Al2O3两种催化剂上催化丙烯还原NOx的活性. 在实验温度范围(200~650 ℃)内,Ag/Al2O3具有
优异的催化丙烯选择性还原NOx的活性,但同时有大量副产物CO形成. Cu/Al2O3选择性催化丙烯还原NOx的活性不高,却能有效促进CO的氧化. 在无水条件,Ag/Al2O3-Cu/Al2O3组合体系具有与Ag/Al2O3相似的脱除NOx活性,同时使CO在300 ℃以后几乎完全转化. 在10%水蒸气存在的情况下,Ag/Al2O3-Cu/Al2O3组合催化剂脱除NOx的活性下降,但水蒸气对CO转化率的影响不大. 相似文献