全文获取类型
收费全文 | 14350篇 |
免费 | 2410篇 |
国内免费 | 1662篇 |
专业分类
化学 | 7663篇 |
晶体学 | 249篇 |
力学 | 568篇 |
综合类 | 98篇 |
数学 | 803篇 |
物理学 | 9041篇 |
出版年
2024年 | 35篇 |
2023年 | 131篇 |
2022年 | 233篇 |
2021年 | 351篇 |
2020年 | 461篇 |
2019年 | 430篇 |
2018年 | 423篇 |
2017年 | 412篇 |
2016年 | 584篇 |
2015年 | 508篇 |
2014年 | 563篇 |
2013年 | 1510篇 |
2012年 | 752篇 |
2011年 | 902篇 |
2010年 | 705篇 |
2009年 | 915篇 |
2008年 | 917篇 |
2007年 | 918篇 |
2006年 | 877篇 |
2005年 | 764篇 |
2004年 | 693篇 |
2003年 | 718篇 |
2002年 | 631篇 |
2001年 | 470篇 |
2000年 | 559篇 |
1999年 | 416篇 |
1998年 | 341篇 |
1997年 | 275篇 |
1996年 | 247篇 |
1995年 | 194篇 |
1994年 | 208篇 |
1993年 | 170篇 |
1992年 | 154篇 |
1991年 | 126篇 |
1990年 | 107篇 |
1989年 | 95篇 |
1988年 | 76篇 |
1987年 | 58篇 |
1986年 | 76篇 |
1985年 | 66篇 |
1984年 | 68篇 |
1983年 | 17篇 |
1982年 | 34篇 |
1981年 | 41篇 |
1980年 | 32篇 |
1979年 | 26篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1976年 | 18篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
901.
To realize practical wide-area quantum communication,a satellite-to-ground network with partially entangled states is developed in this paper.For efficiency and security reasons,the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network.Based on this point,an efficient and secure quantum communication scheme with partially entangled states is presented.In our scheme,the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states.Thus,the security of quantum communication is guaranteed.The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices.Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high.In addition,the auxiliary quantum bit provides a heralded mechanism for successful communication.Based on the critical components that are presented in this article an efficient,secure,and practical wide-area quantum communication can be achieved. 相似文献
902.
《Comptes Rendus Physique》2015,16(2):143-152
Motivated by the potential applications of their intrinsic cross-coupling properties, the interest in multiferroic materials has constantly increased recently, leading to significant experimental and theoretical advances. From the theoretical point of view, recent progresses have allowed one to identify different mechanisms responsible for the appearance of ferroelectric polarization coexisting—and coupled—with magnetic properties. This chapter aims at reviewing the fundamental mechanisms devised so far, mainly in transition-metal oxides, which lie at the origin of multiferroicity. 相似文献
903.
《Current Applied Physics》2015,15(7):805-810
The acoustic and thermal properties of the liquid–glass transitions of propylene glycol and its oligomers, poly (propylene glycol)s, were studied by temperature modulated DSC and Brillouin scattering. The fragility indices were determined from Angell plots using the observed modulation frequency dependence of the complex heat capacity. The variation in the glass transition temperatures is discussed on the basis of the free volume theory. The relaxation time of the structural relaxation obeys the Vogel–Fulcher law, and its high frequency end is in good agreement with the result of the dielectric measurement in the literature. The correlation between the observed thermal expansion coefficients and the glass transition temperature is discussed based on the free volume theory. The sound velocity and attenuation were accurately determined as a function of the temperature by Brillouin scattering by combination with the refractive index measurement. The relaxation dynamics were discussed by considering the relaxation from segmental motions. All of these physical properties were discussed based on the third-order anharmonicity and the Grüneisen parameter. 相似文献
904.
905.
《Current Applied Physics》2015,15(10):1256-1261
P-type conductivity in MOCVD grown ZnO was obtained by directional thermal diffusion of arsenic from semi-insulating GaAs substrate. The films were single crystalline in nature and oriented along (002) direction. Ab initio calculations in the framework of density functional theory have been carried out with different chemical states of arsenic in ZnO. Present calculations suggested AsZn–2VZn defect is a shallow acceptor and results in ferromagnetism in ZnO. The magnetic measurements of the samples indeed showed ferromagnetic ordering at room temperature. X-ray photoelectron spectra confirmed the presence of AsZn and VZn. The core level chemical shift in binding energy of AsZn indicated the formation of AsZn–2VZn. Diffused arsenic substitutes zinc atom and creates additional zinc vacancies. The zinc vacancies, surrounding the oxygen atoms, result in unpaired O 2p electrons which in turn induce ferromagnetism in the samples. 相似文献
906.
采用密度泛函理论计算方法模拟了简单钴卟啉过氧中间体PCo-O2与环己烷C6H12的作用,分析了反应路径中各驻点能量和反应过渡态分子构型。研究结果表明,PCo-O2向底物环己烷夺氢的反应可以延正方向进行,二线态PCo-O2更具反应活性,反应过程中Co-O键得到加强,O-O键被削弱。依据理论计算结果,探讨了四苯基钴卟啉催化环己烷氧化生成环己醇和环己酮的反应机理,指出反应延Lyons高价金属氧代物机理生成环己醇,而反应循环中产生的烷基自由基可以延烷基过氧化过渡金属配合物反应机理进行生成环己酮。 相似文献
907.
Diana V. Aleksanyan Yulia V. Nelyubina Zinaida S. Klemenkova Vladimir A. Kozlov 《Phosphorus, sulfur, and silicon and the related elements》2014,189(7-8):1028-1042
AbstractNovel phosphorus-containing ligands have been synthesized by the condensation of 2-(thio)phosphorylated anilines with 2,6-dichloro- and 4-chloropyridine-2-carbonyl chlorides in the presence of Et3N and unsubstituted pyridine-2-carboxylic acid using P(OPh)3 as a coupling agent. The compounds derived readily form complexes with a range of transition metals (M=Re(I), Pd(II), and Cu(II)), serving as bi- or tridentate monoanionic ligands. The composition and structure of the resulting metallocycles depend both on the presence/amount of the Cl atoms in the pyridine ring and on the nature of the donor atom X in the P=X moiety. The novel compounds were characterized by multinuclear NMR and IR spectroscopy as well as X-ray crystallography. 相似文献
908.
Graded‐index plastic optical fibers, composed of doped polymers, have advantages over conventional glass optical fibers, but need to be developed further for practical application. Here, a variety of aromatic sulfide dopants were synthesized, and their effects on the refractive indexes and glass transition temperatures (Tg) of poly(methyl methacrylate) and methyl 2‐chloroacrylate/2,2,2‐trichloroethyl methacrylate copolymers were studied. While polymers containing large dopants exhibited relatively high refractive indices, their Tg values were low, making these materials unsuitable for graded‐index plastic optical fiber applications. Six dopants yielded polymers that exhibited higher Tg values than the conventionally used (diphenyl sulfide)‐doped polymer. The dopant dibenzothiophene, in particular, yielded polymers with the highest refractive indexes and Tg values, and polymers containing (phenylthio)benzene dopants also performed well. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
909.
910.
Dr. Kirill V. Kovtunov Dr. Milton L. Truong Danila A. Barskiy Prof. Igor V. Koptyug Dr. Aaron M. Coffey Prof. Kevin W. Waddell Prof. Eduard Y. Chekmenev 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14629-14632
Parahydrogen induced polarization was employed to prepare a relatively long‐lived correlated nuclear spin state between methylene and methyl protons in propane gas. Conventionally, such states are converted into a strong NMR signal enhancement by transferring the reaction product to a high magnetic field in an adiabatic longitudinal transport after dissociation engenders net alignment (ALTADENA) experiment. However, the relaxation time T1 of ~0.6 s of the resulting hyperpolarized propane is too short for potential biomedical applications. The presented alternative approach employs low‐field MRI to preserve the initial correlated state with a much longer decay time TLLSS=(4.7±0.5) s. While the direct detection at low‐magnetic fields (e.g. 0.0475 T) is challenging, we demonstrate here that spin‐lock induced crossing (SLIC) at this low magnetic field transforms the long‐lived correlated state into an observable nuclear magnetization suitable for MRI with sub‐millimeter and sub‐second spatial and temporal resolution, respectively. Propane is a non‐toxic gas, and therefore, these results potentially enable low‐cost high‐resolution high‐speed MRI of gases for functional imaging of lungs and other applications. 相似文献