全文获取类型
收费全文 | 23634篇 |
免费 | 729篇 |
国内免费 | 125篇 |
专业分类
化学 | 15612篇 |
晶体学 | 243篇 |
力学 | 695篇 |
数学 | 2182篇 |
物理学 | 5756篇 |
出版年
2023年 | 149篇 |
2022年 | 416篇 |
2021年 | 576篇 |
2020年 | 428篇 |
2019年 | 433篇 |
2018年 | 383篇 |
2017年 | 361篇 |
2016年 | 675篇 |
2015年 | 578篇 |
2014年 | 815篇 |
2013年 | 1393篇 |
2012年 | 1699篇 |
2011年 | 1905篇 |
2010年 | 1206篇 |
2009年 | 1047篇 |
2008年 | 1605篇 |
2007年 | 1387篇 |
2006年 | 1431篇 |
2005年 | 1207篇 |
2004年 | 1071篇 |
2003年 | 898篇 |
2002年 | 848篇 |
2001年 | 527篇 |
2000年 | 473篇 |
1999年 | 329篇 |
1998年 | 210篇 |
1997年 | 205篇 |
1996年 | 270篇 |
1995年 | 184篇 |
1994年 | 197篇 |
1993年 | 202篇 |
1992年 | 151篇 |
1991年 | 123篇 |
1990年 | 125篇 |
1989年 | 97篇 |
1988年 | 68篇 |
1987年 | 72篇 |
1986年 | 50篇 |
1985年 | 74篇 |
1984年 | 50篇 |
1983年 | 42篇 |
1982年 | 63篇 |
1981年 | 62篇 |
1979年 | 46篇 |
1978年 | 45篇 |
1977年 | 34篇 |
1976年 | 41篇 |
1975年 | 37篇 |
1974年 | 36篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
231.
232.
In this paper, a fast method is proposed to estimate the sonar cross section of acoustically large and complex underwater targets such as submarines and torpedoes. The proposed method is based on a deterministic scattering center model which constructs scattering center database by using a combining method of physical optics and geometric optics and then reconstructs sonar cross section patterns from that database with a polynomial interpolation with respect to the incident angle. The parametric studies to find appropriate intervals of the reference incident angle are systematically carried out for simple targets such as a flat square plate and an orthogonal dihedral. Moreover, to validate the proposed method, sonar cross sections of real-like targets such as a pressure hull and an idealized submarine are calculated. The comparisons show that the results by the proposed method are in good agreement with those by the direct calculation. 相似文献
233.
Interlayer-free phosphorescent white organic light-emitting diodes (PHWOLEDs) with a mixed-host emitting structure in red emitting layer were developed and device performances were investigated according to the host composition in the red emitting layer. Device performances could be effectively managed by a simple change of host materials in the red emitting layer. A high quantum efficiency was obtained in PHWOLEDs with electron transport-type host in the red emitting layer and red emission was strong in PHWOLEDs with mixed-host in the red emitting layer. In addition, stable color performances were obtained in electron transport-type host rich devices. 相似文献
234.
Dual mode near-field scanning optical microscopy for near-field imaging of surface plasmon polariton
In this paper, we theoretically and experimentally demonstrate that metal coated apertured probes are efficient near-field probes on surfaces with high reflectivity for the scattering as well as for the collection mode near-field scanning optical microscopy (NSOM). We show that a blunt apertured metal coated tip is very effective in suppressing image dipoles which affect strongly the signals scattered from frequently used sharp metal tips or gold nanoparticle attached probes. By using a simultaneous collection and scattering mode (dual mode) NSOM we measure the near-field images of surface plasmon polariton (SPP) launched from a slit. The collection mode measures propagating SPP along lateral distance in a long scan range with high signal-to-noise ratio, and the scattering mode measures the polarization resolved near-field of SPP. Comparisons of the measured data obtained in the dual mode enable to easily characterize SPP and to separate the measured near-field into the propagating SPP and the directly transmitted light. 相似文献
235.
We present a first-principles study of the geometrical and electronic structures of a hexagonal single-walled silicon nanotube with a monovacancy or a substitutional defect. The B, C, N, Al and P atoms are chosen as substitutional impurities. It is found that the defect such as a monovacancy or a substitutional impurity results in deformation of the hexagonal single-walled silicon nanotube. In both cases, a relatively localized unoccupied state near the Fermi level occurs due to this local deformation. The differences in geometrical and electronic properties of different substitutional impurities are discussed. 相似文献
236.
Temperature-dependent photoluminescence (PL) measurements were carried out ZnSe/ZnS quantum dots (QDs) grown with post-growth interruption under a dimethylzinc (DMZn) flow. The PL spectra showed sigmoidal peak shifts and V-shaped full width at half maximum (FWHM) variations with increasing temperature, which strongly suggest that the QD structure of ZnSe/ZnS is quite similar to that of other material systems grown in the Stranski–Krastanov mode. Apparent differences are revealed as a consequence of DMZn treatment: (i) the PL spectra of ZnSe/ZnS QDs showed peaks at higher energies and persisted up to 300 K, and(ii) the minimum points of the V-shaped FWHM appear at a higher temperature compared to H2-purged ZnSe/ZnS QDs. Experimental results demonstrate the enhancement of localization energy. 相似文献
237.
Ki Young Kim 《中国光学快报(英文版)》2009,7(10):904-908
The cutoff characteristics of dielectric-filled circular holes embedded in a dispersive plasmonic medium are investigated. Since two distinctive operating modes, surface plasmon polariton and circular waveguide modes, can exist in the slow and fast wave regions, respectively, the cutoff characteristics for each are separately investigated for linear and radial polarizations of the guided fields. As a result, the cutoff wavelengths for the linear and radial polarizations with very small subwavelength hole radii are found to be limited by the plasma resonance wavelength and plasma wavelength, which in turn are dependent and independent, respectively, of the dielectric constant of the dielectric filler material. 相似文献
238.
C.H. Kim H.B. Moon S.S. Min Y.H. Jang J.H. Cho 《Solid State Communications》2009,149(39-40):1611-1615
We have studied the nanoscale electrical properties of NiO thin films by using conducting atomic force microscopy (CAFM) to understand the mechanism of resistance change of the NiO thin films as we changed the applied voltage. We observed that inhomogeneous conducting filaments were generated by external voltage bias; in addition, some of the inhomogeneous conducting filaments were durable while some of them were not, and they disappeared. We deduced that the resistance change of the NiO thin films was related to inhomogeneous filamentary conducting paths generated by both Ni ions in thermodynamically unstable NiO and the existence of conducting filament segments generated by high voltage bias. 相似文献
239.
Phan Van Cuong Joonghoe Dho Hyo Yeol Park Do-Hyung Kim 《Applied Physics A: Materials Science & Processing》2009,95(2):567-571
This paper reports on the sonochemical-assisted synthesis of La0.7Sr0.3MnO3 (LSMO) nanoparticles (NPs) which have a single-crystalline perovskite structure. The average particle size of LSMO NPs was
controlled from about 40 to 120 nm by changing the annealing temperatures from 750 to 1050°C. The particle size, electrical
resistivity, and ferromagnetic transition temperature of LSMO NPs were strongly dependent on the annealing temperature. A
substantial decrease in resistivity and an enhancement in the insulator–metal transition temperature were found on increasing
the annealing temperature. Furthermore, the enhancement in magnetization and paramagnetic–ferromagnetic (PM–FM) transition
temperatures was observed as the annealing temperature increases. 相似文献
240.
We theoretically and numerically investigate the modulation efficiencies of integrated electro-optic (EO) modulators based on ferroelectric crystals with the point symmetry of orthorhombic mm2. An analytical expression describing the index-ellipsoid under the EO effect is derived, where all 5 non-zero linear EO coefficients of mm2-crystals are considered. As practical candidates for integrated EO platform, three mm2-crystals (KNbO3, KTiOPO4, and Ba2NaNb5O15) that are well-established and commercially available are chosen for numerical simulations. The refractive-index (RI) changes caused by an external electric field applied to each crystal with an arbitrary direction are analyzed in detail for the given optical polarization states of input light wave. For each crystal, the modulation efficiency is evaluated in terms of the half-wave voltage required for a π-phase shift of input wave, which is compared with the established counterpart based on LiNbO3. The results indicate that higher modulation efficiencies are achievable in the two schemes using KNbO3 and Ba2NaNb5O15 than those for other cases, meaning that either lower power-consuming or larger beam-window integrated EO devices are feasible. 相似文献