全文获取类型
收费全文 | 143717篇 |
免费 | 27469篇 |
国内免费 | 12895篇 |
专业分类
化学 | 112477篇 |
晶体学 | 1672篇 |
力学 | 7899篇 |
综合类 | 684篇 |
数学 | 15095篇 |
物理学 | 46254篇 |
出版年
2024年 | 259篇 |
2023年 | 2267篇 |
2022年 | 2790篇 |
2021年 | 4030篇 |
2020年 | 5508篇 |
2019年 | 6517篇 |
2018年 | 4602篇 |
2017年 | 4097篇 |
2016年 | 8312篇 |
2015年 | 8223篇 |
2014年 | 9325篇 |
2013年 | 11867篇 |
2012年 | 12694篇 |
2011年 | 12675篇 |
2010年 | 9661篇 |
2009年 | 9355篇 |
2008年 | 9337篇 |
2007年 | 8234篇 |
2006年 | 7326篇 |
2005年 | 6468篇 |
2004年 | 5067篇 |
2003年 | 4148篇 |
2002年 | 4587篇 |
2001年 | 3556篇 |
2000年 | 3240篇 |
1999年 | 2630篇 |
1998年 | 2075篇 |
1997年 | 1888篇 |
1996年 | 2050篇 |
1995年 | 1643篇 |
1994年 | 1610篇 |
1993年 | 1282篇 |
1992年 | 1184篇 |
1991年 | 1079篇 |
1990年 | 875篇 |
1989年 | 636篇 |
1988年 | 501篇 |
1987年 | 419篇 |
1986年 | 412篇 |
1985年 | 362篇 |
1984年 | 269篇 |
1983年 | 176篇 |
1982年 | 150篇 |
1981年 | 115篇 |
1980年 | 82篇 |
1979年 | 55篇 |
1978年 | 39篇 |
1976年 | 45篇 |
1975年 | 40篇 |
1974年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
951.
By using microlocal analysis, the propagation of weak singularities in Cauchy problems for quasilinear thermoelastic systems in three space variables are investigated. First, paradifferential operators are employed to decouple the quasilinear thermoelastic systems. Second, by investigating the decoupled hyperbolic-parabolic systems and using the classical bootstrap argument, the property of finite propagation speeds of singularities in Cauchy problems for the quasilinear thermoelastic systems is obtained. Finally, it is shown that the microlocal weak singularities for Cauchy problems of the thermoelastic systems are propagated along the null bicharacteristics of the hyperbolic operators. 相似文献
952.
LIANG Liang 《原子与分子物理学报》2003,20(4):575-578
By using the multichannel quantum defect theory(MQDT),we have evaluated the energy levels and lifetimes of 2sns ^3 S1,2snd ^3D(n=3-25)of BeI and 1 sns ^3s1,1snd ^3D(n=3-25)of BeⅢ,These energies and lifetimes that we have calculated not only agree with the recent measurements and theoretical calculation of Ref.4 and Ref.3, but also predict the lifetimes of 66 other highly excited states. 相似文献
953.
Hong-jun Liu Wei Zhao Guo-fu Chen Yi-shan Wang Lian-jun Yu Chi Ruan Xue-feng Li 《Optics & Laser Technology》2004,36(4):3482-314
Experimental investigations of a type-I noncollinear phase-matched optical parametric amplification based on lithium triborate, which was pumped by a 5-ns second-harmonic pulses from a Q-switched Nd:YAG, seeded by a cw Ti:sapphire laser at 800 nm, was presented. The experiments generated 2-ns signal output pulses at 800 nm, the maximum signal output pulse energy reached 19 μJ, the corresponding parametric gain was 44 dB. Furthermore, the experiments demonstrate that the 65 nm-FWHM parametric fluorescence gain spectrum could also be observed. A quantitative account of the ultrabroadband parametric fluorescence gain spectrum was given with our theory. The experimental measurements are in agreement with theoretical calculations. 相似文献
954.
Ying‐Ling Liu Chuan‐Shao Wu Yie‐Shun Chiu Wen‐Hsuan Ho 《Journal of polymer science. Part A, Polymer chemistry》2003,41(15):2354-2367
A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′‐diaminodiphenylmethane with the sol–gel reaction of a phosphorus‐containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with 3‐glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, 1H and 31P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass‐transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003 相似文献
955.
Xinghua Wang 《计算数学(英文版)》2003,(2)
The convergence problem of the family of Euler-Halley methods is considered under the Lipschitz condition with the L-average, and a united convergence theory with its applications is presented. 相似文献
956.
本文提出应用小参数法 ,探讨 Markov链中相邻两次更新时刻内稀疏事件的概率估计问题 .建立了三种最重要的具有更新时间的概率模型 .通过小参数的引入和对概率式的幂展开 ,进而推证出幂渐近展开系数的模型估算法 .论证了无偏估计的重要定理 ,给出了概率估计式和无偏估计精度 .亦将许多算法扩展到Markov链的任意状态空间 相似文献
957.
Ziqing Duan Xiaofeng Wang Danfeng Yang Xiaoming Pan Pingchu Wang 《Solid State Communications》2005,134(8):559-563
0.65Pb(In1/2Nb1/2)O3-0.35PbTiO3 (PINT65/35) (starting composition) single crystals were grown successfully through the solution Bridgman technique using PbO flux and PMNT67/33 seed crystals. Because of the composition variation, the final composition of achievable crystals is in a range of 0.32-0.34 with the corresponding Tc range of 265-269 °C. The (001) plates of as-grown PINT66/34 single crystals show high Curie temperature (Tc=269 °C) and rhombohedral-tetragonal phase transition temperature (Trt=134 °C). Besides, good electrical properties with high dielectric constant (ε>3000), low dielectric loss (tan δ∼1.2%), high piezoelectric constant (d33∼2000 pC/N) and large electromechanical coupling factor (kt≈59%) at room temperature have been obtained on the (001) plates. The sound velocity, acoustic impedance and other piezoelectric parameters were also measured on the (001) plates in this study, which provide us more detailed information about PINT66/34 single crystals. 相似文献
958.
The terminology ‘ID frequency’(w ID) is proposed after analyzing the 1D active photonic crystal based on the transfer matrix method. The relationship between wID and the structure parameters of the photonic crystal is investigated. 相似文献
959.
在相对碰撞平动能为 0 .0 5eV的分子束实验条件下 ,研究了亚稳态CO(a) +NO(X)的E E传能通道 .通过测量和分析交碰区的传能发射光谱 ,在 780和 860nm处观测到了NO(b -a)跃迁Ogawa带的△v =+ 4和△v =+ 3序的发射光谱 .从而首次在实验上直接证实了传能过程中第四通道的存在 (CO (a) +NO(X)→CO (X) +NO(b) ) .这一通道的发现解释了前人测量到的在CO(a)与NO(X)碰撞传能过程中CO(a)的猝灭速率远大于NO(A ,B)生成速率的实验结果 ,并进一步证实了这一“经典”E E传能体系为电子交换机理的传能观点 相似文献
960.
A series of 4,6-disubstituted pyrimidines were synthesized via Suzuki and Kumada coupling reaction of 4,6-dichloropyrimidine. 相似文献