全文获取类型
收费全文 | 8944篇 |
免费 | 1648篇 |
国内免费 | 931篇 |
专业分类
化学 | 5956篇 |
晶体学 | 86篇 |
力学 | 730篇 |
综合类 | 65篇 |
数学 | 1128篇 |
物理学 | 3558篇 |
出版年
2024年 | 38篇 |
2023年 | 183篇 |
2022年 | 307篇 |
2021年 | 349篇 |
2020年 | 348篇 |
2019年 | 323篇 |
2018年 | 294篇 |
2017年 | 293篇 |
2016年 | 432篇 |
2015年 | 425篇 |
2014年 | 465篇 |
2013年 | 643篇 |
2012年 | 755篇 |
2011年 | 828篇 |
2010年 | 553篇 |
2009年 | 529篇 |
2008年 | 612篇 |
2007年 | 477篇 |
2006年 | 517篇 |
2005年 | 375篇 |
2004年 | 314篇 |
2003年 | 253篇 |
2002年 | 234篇 |
2001年 | 201篇 |
2000年 | 190篇 |
1999年 | 190篇 |
1998年 | 182篇 |
1997年 | 173篇 |
1996年 | 169篇 |
1995年 | 137篇 |
1994年 | 124篇 |
1993年 | 114篇 |
1992年 | 93篇 |
1991年 | 70篇 |
1990年 | 75篇 |
1989年 | 62篇 |
1988年 | 44篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 22篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
E2SiO5 thin films were fabricated on Si substrate by reactive magnetron sputtering method with subsequent annealing treatment. The morphology properties of as-deposited films have been studied by scanning electron microscope. The fraction of erbium is estimated to be 23.5 at% based on Rutherford backscattering measurement in as-deposited Er-Si-O film. X-ray diffraction measurement revealed that Er2SiO5 crystalline structure was formed as sample treated at 1100 °C for 1 h in O2 atmosphere. Through proper thermal treatment, the 1.53 μm Er3+-related emission intensity can be enhanced by a factor of 50 with respect to the sample annealed at 800 °C. Analysis of pump-power dependence of Er3+ PL intensity indicated that the upconversion phenomenon could be neglected even under a high photon flux of 1021(photons/cm2/sec). Temperature-dependent photoluminescence (PL) of Er2SiO5 was studied and showed a weak thermal quenching factor of 2. Highly efficienct photoluminescence of Er2SiO5 films has been demonstrated with Er3+ concentration of 1022/cm3, and it opens a promising way towards future Si-based light source for Si photonics. 相似文献
92.
We observed frequency splitting phenomenon of dual transverse modes (TEM00q and TEM01q) in a Nd:YAG microchip standing wave laser utilizing intracavity stress birefringence effects. Four resonance frequencies (ν00qe, ν00qo, ν01qe, and ν01qo, respectively) were produced and tuned by changing the diametral compression force applied on the laser crystal. The transverse mode frequency spacing for the same longitudinal mode number (Δνtrans) was 1.16 GHz, and the magnitude of frequency splitting (Δν) ranged from 0 MHz to 1.16 GHz. Based on this phenomenon, a four-mode differential standing wave laser, whose signal characteristics were a little like those of a four-mode differential travelling wave laser gyro however with a much larger frequency splitting range, was produced. The theoretical analysis is in good agreement with the experimental results. This phenomenon not only can be used to make lasers with two or more frequency differences, but also can be used to make high-resolution self-sensing laser sensors (e.g. laser force sensors and laser accelerometers). 相似文献
93.
Yuanhong Tao Weiwei Ding Chang’e Li 《International Journal of Theoretical Physics》2013,52(6):1970-1978
We first present the Hamel base of the density operator space for multipartite quantum system, and thus establish a representation of density matrix. Moreover, according to the structure of the density matrix for multipartite quantum system, we present two necessary criteria for separability of multipartite quantum system of arbitrary dimensions. 相似文献
94.
Ping Ding Xinhua Pan Zhizhen Ye Haiping He Honghai Zhang Wei Chen Chongyu Zhu Jingyun Huang 《Applied Physics A: Materials Science & Processing》2013,112(4):1051-1055
High-quality ZnO thin films were grown on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy. X-ray diffraction and transmission electron microscopy reveal that the ZnO films have high structural quality and an atomically sharp ZnO/Al2O3 interface. The full width at half maximum values of the 0002 and $30\bar{3}2$ ZnO ω-rocking curves are 467.8 and 813.5 arc sec for a 600 nm thick ZnO film. A screw dislocation density of 4.35×108 cm?2 and an edge dislocation density of 3.38×109 cm?2 are estimated by X-ray diffraction. The surface of the ZnO epilayers contains hexagonal pits, which can be observed in the Zn-polar ZnO. The films have a resistivity of 0.119 Ω?cm, an electron concentration of 6.85×1017 cm?3, and a mobility of 76.5 cm2?V?1?s?1 at room temperature. Low temperature photoluminescence measurements show good optical properties comparable to ZnO single crystals. 相似文献
95.
艾纳香中黄酮化合物的研究 总被引:6,自引:1,他引:6
从中药艾纳香(Blumea balsamifera DC)中分离得到两种新的黄酮化合物,应用NMR、MS、IR、UV等波谱数据,确定其化学结构为3,5,3'-三羟基-7,4'-二甲氧基黄酮(Ⅰ)和3,5,3',4'-四羟基-7-甲氧基黄酮(Ⅱ). 相似文献
96.
Drinfeld gave a current realization of the quantum affine algebras as a Hopf algebra with a simple comultiplication for the quantum current operators. In this Letter, we will present a generalization of such a realization of quantum Hopf algebras. As a special case, we will choose the structure functions for this algebra to be elliptic functions to derive certain elliptic quantum groups as a Hopf algebra, which degenerates into quantum affine algebras if we take certain degeneration of the structure functions. 相似文献
97.
LI Sheng YANG Huan FANG DeLong WANG ZhenYu TAO Jian DING XiaXin WEN HaiHu 《中国科学:物理学 力学 天文学(英文版)》2013,56(11):2019-2025
Electric transport and scanning tunneling spectrum(STS)have been investigated on polycrystalline samples of the new superconductor Bi4O4S3.A weak insulating behavior in the resistive curve has been induced in the normal state when the superconductivity is suppressed by applying a magnetic field.Interestingly,a kink appears on the temperature dependence of resistivity near 4 K at all high magnetic fields above 1 T when the bulk superconductivity is completely suppressed.This kink associated with the upper critical field as well as the wide range of excess conductance at low fields and high temperatures is explained as the possible evidence of strong superconducting fluctuation.From the tunneling spectra,a superconducting gap of about 3 meV is frequently observed yielding a ratio of 2Δ/kB TC~16.6.This value is much larger than the one predicted by the BCS theory in the weak coupling regime(2Δ/kB TC~3.53),which suggests the strong coupling superconductivity in the present system.Furthermore,the gapped feature persists on the spectra until 14 K in the STS measurement,which suggests a prominent fluctuation region of superconductivity.Such a superconducting fluctuation can survive at very high magnetic fields,which are far beyond the critical fields for bulk superconductivity as inferred both from electric transport and tunneling measurements. 相似文献
98.
一类广义非线性隐拟变分包含 总被引:5,自引:0,他引:5
引入和研究了一类新的涉及集值极大单调映象的广义非线性隐拟变分包含.对此类变分包含在没有紧性假设下证明了解的存在定理.为寻求此类变分包含的近似解,建议和分析了一个新的迭代算法.给出了由新算法产生的迭代序列的收敛性.作为特殊情形,也讨论了在此领域内的某些已知结果. 相似文献
99.
This paper presents a new parameter and state estimation algorithm for single-input single-output systems based on canonical state space models from the given input–output data. Difficulties of identification for state space models lie in that there exist unknown noise terms in the formation vector and unknown state variables. By means of the hierarchical identification principle, those noise terms in the information vector are replaced with the estimated residuals and a new least squares algorithm is proposed for parameter estimation and the system states are computed by using the estimated parameters. Finally, an example is provided. 相似文献
100.
It is proved that for any r.e. degreesv <u, there exists a properly d-r.e. degreec such thatc is a branching degree andv <c <u.
Project supported by the National Natural Science Foundation of China (Grant No. 19771045) and National 863 Hi-Tech R&D Programme. 相似文献