全文获取类型
收费全文 | 8921篇 |
免费 | 681篇 |
国内免费 | 755篇 |
专业分类
化学 | 2967篇 |
晶体学 | 114篇 |
力学 | 524篇 |
综合类 | 60篇 |
数学 | 2695篇 |
物理学 | 3997篇 |
出版年
2024年 | 7篇 |
2023年 | 45篇 |
2022年 | 163篇 |
2021年 | 193篇 |
2020年 | 145篇 |
2019年 | 154篇 |
2018年 | 151篇 |
2017年 | 218篇 |
2016年 | 250篇 |
2015年 | 177篇 |
2014年 | 229篇 |
2013年 | 617篇 |
2012年 | 356篇 |
2011年 | 552篇 |
2010年 | 455篇 |
2009年 | 828篇 |
2008年 | 826篇 |
2007年 | 707篇 |
2006年 | 738篇 |
2005年 | 518篇 |
2004年 | 326篇 |
2003年 | 305篇 |
2002年 | 413篇 |
2001年 | 308篇 |
2000年 | 301篇 |
1999年 | 229篇 |
1998年 | 223篇 |
1997年 | 122篇 |
1996年 | 145篇 |
1995年 | 113篇 |
1994年 | 97篇 |
1993年 | 53篇 |
1992年 | 48篇 |
1991年 | 39篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 25篇 |
1987年 | 20篇 |
1986年 | 14篇 |
1985年 | 30篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1979年 | 22篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Yu E. Karpeshina 《Proceedings Mathematical Sciences》2002,112(1):117-130
We consider a matrix operatorH = (-Δ)l +V inR
n, wheren ≥ 2,l ≥ 1, 4l > n + 1, andV is the operator of multiplication by a periodic inx matrixV(x). We study spectral properties ofH in the high energy region. Asymptotic formulae for Bloch eigenvalues and the corresponding spectral projections are constructed.
The Bethe-Sommerfeld conjecture, stating that the spectrum ofH can have only a finite number of gaps, is proved. 相似文献
992.
Martin Kon Thomas M. Moy Martin E. Rogers Allan R. Shultz Thomas C. Ward James E. Mcgrath 《Journal of Polymer Science.Polymer Physics》1995,33(10):1429-1439
Soluble, fully cyclized m-amino phenyl acetylene terminated polyimides based on several anhydride/diamine monomers were prepared in N-methylpyrrolidine (NMP) and cyclized by solution imidization to controlled molecular weight. The polyimides and a polyamic acid precursor were successfully analyzed by size exclusion chromatography (SEC) utilizing online parallel coupled refractive index and differential viscometer detectors. The calculated M nvalues were varied from 3,000 to 20,000 daltons. N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and chloroform served as mobile phases for the cross-linked polystyrene gel packings. Normal retention behavior of the polyimides was observed in chloroform, THF, and NMP containing LiBr, or in NMP stirred over P2O5 before use. Values of Mark-Houwink-Sakurada exponents for narrow distribution linear polystyrene indicate that pure NMP and NMP with 0.06 M LiBr are good solvents for polystyrene standards at 60°C. In contrast, SEC behavior of polyimides in pure NMP leads to splitting of the peaks with the major portion observed to pass through the columns at the exclusion limit. In contrast to strong polymeric chain expansion of the polyamic acid in dilute solution, presumably due to a polyelectrolyte effect, no increase of intrinsic viscosity of polyimide samples in pure NMP was observed. This exclusion effect of polyimides analyzed in NMP is discussed in terms of possible ion-exclusion from pores of the stationary phase. Differences in polystyrene calibration in NMP with or without additives and the temperature dependence of calibration curves in these mobile phases is discussed as well. ©1995 John Wiley & Sons, Inc. 相似文献
993.
994.
R. Leturcq R. Bianchetti G. Gtz T. Ihn K. Ensslin D.C. Driscoll A.C. Gossard 《Physica E: Low-dimensional Systems and Nanostructures》2006,35(2):327
While equilibrium properties of mesoscopic systems are well understood, many questions are still debated concerning the non-equilibrium properties, which govern nonlinear transport. Nonlinear transport measurements have been performed on two-terminal semiconductor quantum rings in the open regime, where the rings are used as electron interferometers and show the Aharonov–Bohm effect. We observe a magnetic field asymmetry of the nonlinear conductance, compatible with the non-validity of the Onsager–Casimir relations out-of-equilibrium. In particular, the voltage-antisymmetric part of the nonlinear conductance of these two-terminal devices is not phase rigid, as it is the case for the linear conductance. We show that this asymmetry is directly related to the electronic phase accumulated by the electrons along the arms of the ring and can be tuned using an electrostatic gate. 相似文献
995.
Satyawati S. Joshi Prajakta R. Patil Madhav S. Nimase P.P. Bakare 《Journal of nanoparticle research》2006,8(5):635-643
The electrochemical synthesis of alpha Fe2O3 nanoparticles was performed using quaternary ammonium salts viz. TPAB, TBAB and TOAB in an organic medium by optimizing current density and molar concentration of the ligand. The role of ligands in the formation of α phase, structure and magnetic properties was investigated in details. The effect of increasing chain length on the particle size confirmed that as the chain length increases from propyl to octyl, the particle size decreases. X-ray diffraction spectra of as prepared samples and TEM analysis confirmed the amorphous nature of iron oxide. TEM showed beads of iron oxide joined together with a size distribution in the range of 6–30 nm. The Mossbauer studies also support this observation that for the lowest particle size, the line width is broader which successively reduces with increase in particle size. Iron oxide capped with TOAB indicated superparamagnetic nature at room temperature. The resultant internal magnetic field of 506 mm/s due to hyperfine splitting clearly established the formation of α-Fe2O3 The infrared spectroscopy and pH measurements revealed the binding of tetra alkyl ligand with iron oxide. The IR spectra and the increase in basicity of as prepared samples confirmed the formation of hydrated iron oxide. Above 800°C the spectra indicated only iron oxide. Surface area obtained by BET method was 205 m2/g. 相似文献
996.
997.
We present how enlarging the size of a telescope from the current 10 meter telescope to the future 100 meter Extremely Large Telescopes increases the complexity of a classical or multiconjugate adaptive optics instrument. We point out elements or parameters of the system for which it is critical to propose new ideas as solutions and we study the effect of the increase of the diameter on the point spread function of an MCAO and a Ground Layer AO system. To cite this article: R. Ragazzoni et al., C. R. Physique 6 (2005). 相似文献
998.
系统地研究了晶粒尺寸对CoSb3化合物热电性能的影响规律,结果表明晶粒尺寸对CoSb3化合物的晶格热导率κp、电导率σ、能隙宽度Eg和Seebeck系数α有显著影响.当晶粒尺寸由微米尺度减小到纳米尺度时,晶格热导率κp显著降低,Seebeck系数α有较大幅度的增加,能隙宽度Eg变宽,电导率σ有一定程度的下降.平均晶粒尺寸为200nm的CoSb3化合物在温度为700K时,ZT值达到0.43,比平均晶粒尺寸为5000nm的试样增加了4倍. 相似文献
999.
Dong-Wook Kim 《Solid State Communications》2006,137(10):545-548
A pulsed laser deposition technique was used to grow ferromagnetic La0.7Sr0.3MnO3 (LSMO) films on antiferromagnetic La0.33Ca0.67MnO3 (LCMO) and Pr0.7Ca0.3MnO3 (PCMO) films in bilayer forms. The LSMO film on the PCMO layer had a more elongated out-of-plane lattice than that on the LCMO layer. The former had a lower ferromagnetic transition temperature (320 K) than the latter (350 K). The enhanced low-temperature magnetoresistance of the LSMO/PCMO bilayer suggests that the spin frustration is stronger at this bilayer than in the LSMO/LCMO bilayer. These differences indicate that strain state and defect concentration play important roles in governing interfacial spin interactions. 相似文献
1000.
Hong Chen J.A. Peters Yue Pan J.J. Heremans N. Goel S.J. Chung M.B. Santos W. Van Roy G. Borghs 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):374
Spin–orbit interaction in two-dimensional electron systems can lead to a spin-dependent reflection of carriers off a lithographic barrier. Scattering of a spin-unpolarized beam from the barrier leads to the creation of two fully spin-polarized side beams in addition to an unpolarized specularly reflected beam. We experimentally demonstrate a method to create spin-polarized beams of ballistic electrons in mesoscopic samples fabricated on InSb/InAlSb and InAs/AlGaSb heterostructures. We describe two geometries, one open and one closed, in which the spin-dependent reflection and spin-dependent semiclassical trajectories were observed. 相似文献