全文获取类型
收费全文 | 104932篇 |
免费 | 15582篇 |
国内免费 | 6652篇 |
专业分类
化学 | 70935篇 |
晶体学 | 1767篇 |
力学 | 11267篇 |
综合类 | 710篇 |
数学 | 23427篇 |
物理学 | 19060篇 |
出版年
2024年 | 114篇 |
2023年 | 508篇 |
2022年 | 951篇 |
2021年 | 1223篇 |
2020年 | 1868篇 |
2019年 | 3417篇 |
2018年 | 3356篇 |
2017年 | 4198篇 |
2016年 | 4671篇 |
2015年 | 6597篇 |
2014年 | 7170篇 |
2013年 | 9982篇 |
2012年 | 8036篇 |
2011年 | 8103篇 |
2010年 | 6745篇 |
2009年 | 6823篇 |
2008年 | 7104篇 |
2007年 | 6410篇 |
2006年 | 5953篇 |
2005年 | 5628篇 |
2004年 | 4698篇 |
2003年 | 4227篇 |
2002年 | 4703篇 |
2001年 | 2899篇 |
2000年 | 2705篇 |
1999年 | 1749篇 |
1998年 | 1138篇 |
1997年 | 979篇 |
1996年 | 787篇 |
1995年 | 694篇 |
1994年 | 601篇 |
1993年 | 513篇 |
1992年 | 503篇 |
1991年 | 380篇 |
1990年 | 320篇 |
1989年 | 241篇 |
1988年 | 198篇 |
1987年 | 144篇 |
1986年 | 108篇 |
1985年 | 129篇 |
1984年 | 125篇 |
1983年 | 62篇 |
1982年 | 86篇 |
1981年 | 54篇 |
1980年 | 35篇 |
1979年 | 51篇 |
1978年 | 41篇 |
1977年 | 47篇 |
1976年 | 17篇 |
1957年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this paper, the nonlinear Boussinesq equations with the conformable time-fractional derivative are solved analytically using the well-established modified Kudryashov method. As a consequence, a number of new exact solutions for this type of equations are formally derived. It is believed that the method is one of the most effective techniques for extracting new exact solutions of nonlinear fractional differential equations. 相似文献
992.
Pseudogap in the Eliashberg approach based on electron‐phonon and electron‐electron‐phonon interaction 下载免费PDF全文
The properties of the superconducting and the anomalous normal state were described by using the Eliashberg method. The pairing mechanism was reproduced with the help of the Hamiltonian, which models the electron‐phonon and the electron‐electron‐phonon interaction (EEPh). The set of the Eliashberg equations, which determines the order parameter function (φ), the wave function renormalization factor (Z), and the energy shift function (χ), was derived. It was proven that for the sufficiently large values of the EEPh potential, the doping dependence of the order parameter () has the analogous course to that observed experimentally in cuprates. The energy gap in the electron density of states is induced by Z and χ ‐ the contribution from φ is negligible. The electron density of states possesses the characteristic asymmetric form and the pseudogap is observed above the critical temperature.
993.
Barbara Drossel 《Annalen der Physik》2017,529(3)
By considering (non‐relativistic) quantum mechanics as it is done in practice in particular in condensed‐matter physics, it is argued that a deterministic, unitary time evolution within a chosen Hilbert space always has a limited scope, leaving a lot of room for embedding the quantum‐classical transition into our current theories without recurring to difficult‐to‐accept interpretations of quantum mechanics. Nonunitary projections to initial and final states, the breaking of time‐reversal symmetry, a change of Hilbert space, and the introduction of classical concepts such as external potentials or localized atomic nuclei are widespread in quantum mechanical calculations. Furthermore, quantum systems require classical environments that enable the symmetry breaking that is necessary for creating the atomic configurations of molecules and crystals. This paper argues that such classical environments are provided by finite‐temperature macroscopic systems in which the range of quantum correlations and entanglement is limited. This leads to classical behavior on larger scales, and to collapse‐like events in all dynamical processes that become coupled to the thermalized degrees of freedom.
994.
Simultaneous two‐state lasing is a unique property of semiconductor quantum‐dot (QD) lasers. This not only changes steady‐state characteristics of the laser device but also its dynamic response to perturbations. In this paper we investigate the dynamic stability of QD lasers in an external optical injection setup. Compared to conventional single‐state laser devices, we find a strong suppression of dynamical instabilities in two‐state lasers. Furthermore, depending on the frequency and intensity of the injected light, pronounced areas of bistability between both lasing frequencies appear, which can be employed for fast optical switching in all‐optical photonic computing applications. These results emphasize the suitability of QD semiconductor lasers in future integrated optoelectronic systems where a high level of stability is required. 相似文献
995.
Chung‐Lun Wu Cheng‐Hsuan Hsieh Gong‐Ru Lin Wen‐Chun Chi Yi‐Jen Chiu Yuan‐Yao Lin Yung‐Jr Hung Min‐Hsiung Shih Ann‐Kuo Chu Chao‐Kuei Lee 《Annalen der Physik》2017,529(3)
A tantalum pentoxide‐based (Ta2O5‐based) micro‐ring all‐optical modulator was fabricated. The refractive index inside the micro‐ring cavity was modified using the Kerr effect by injecting a pumped pulse. The transmittance of the ring resonator was controlled to achieve all‐optical modulation at the wavelength of the injected probe. When 12 GHz pulses with a peak power of 1.2 W were coupled in the ring cavity, the transmission spectrum of the Ta2O5 resonator was red‐shifted by 0.04 nm because of the Kerr effect. The relationship between the modulation depth and gap of the Ta2O5 directional coupler is discussed. An optimized gap of 1100 nm was obtained, and a maximum buildup factor of 11.7 with 84% modulation depth was achieved. The nonlinear refractive index of Ta2O5 at 1.55 μm was estimated as 3.4 × 10?14 cm2/W based on the Kerr effect, which is almost an order of magnitude higher than that of Si3N4. All results indicate that Ta2O5 has potential for use in nonlinear waveguide applications with modulation speeds as high as tens of GHz.
996.
Quantum Kinetic Theory of a Massless Scalar Model in the Presence of a Schwarzschild Black Hole 下载免费PDF全文
Slava Emelyanov 《Annalen der Physik》2017,529(10)
We employ quantum kinetic theory to investigate local quantum physics in the background of spherically symmetric and neutral black holes formed through the gravitational collapse. For this purpose in mind, we derive and study the covariant Wigner distribution function near to and far away from the black‐hole horizon. We find that the local density of the particle number is negative in the near‐horizon region, while the entropy density is imaginary. These pose a question whether kinetic theory is applicable in the near‐horizon region. We elaborate on that and propose a possible interpretation of how this result might nevertheless be self‐consistently understood. 相似文献
997.
998.
999.
Theoretical studies on structure and performance of [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine‐based derivatives 下载免费PDF全文
Ke Wang Yuanjie Shu Ning Liu Weipeng Lai Tao Yu Xiaoyong Ding Zongkai Wu 《Journal of Physical Organic Chemistry》2017,30(1)
Based on energetic compound [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine, a series of functionalized derivatives were designed and first reported. Afterwards, the relationship between their structure and performance was systematically explored by density functional theory at B3LYP/6‐311 g (d, p) level. Results show that the bond dissociation energies of the weakest bond (N–O bond) vary from 157.530 to 189.411 kJ · mol?1. The bond dissociation energies of these compounds are superior to that of HMX (N–NO2, 154.905 kJ · mol?1). In addition, H1, H2, H4, I2, I3, C1, C2, and D1 possess high density (1.818–1.997 g · cm?3) and good detonation performance (detonation velocities, 8.29–9.46 km · s?1; detonation pressures, 30.87–42.12 GPa), which may be potential explosives compared with RDX (8.81 km · s?1, 34.47 GPa ) and HMX (9.19 km · s?1, 38.45 GPa). Finally, allowing for the explosive performance and molecular stability, three compounds may be suggested as good potential candidates for high‐energy density materials. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
1000.
Nondoped blue fluorescent OLED based on cyanophenanthrimidazole‐styryl‐triphenylamine/carbazole materials 下载免费PDF全文
Thanikachalam Venugopal Jeeva Palanivel Jayabharathi Jayaraman 《Journal of Physical Organic Chemistry》2017,30(12)
New 2‐(4′‐9H‐carbazole‐9‐yl)‐styryl‐1H‐phenathro[9,10‐d]imidazole‐1‐yl)benzonitrile (SPICN‐Cz) and 4‐(2‐(4‐(diphenylamino)phenyl‐styryl‐1H‐phenathro[9,10‐d]imidazole‐1‐yl)benzonitrile (SPICN‐TPA) have been synthesised, and their photophysical, electrochemical, and electroluminescent properties were analysed in comparison with their cyano‐free parent compounds, SPI‐Cz, and SPI‐TPA. Solvatochromic effects show the transformation of an excited state character from locally excited (LE) state to charge transfer (CT) state. Using time‐dependent density functional theory calculation, the excited state properties of these donor‐acceptor blue emissive materials have been analysed. Their excited state properties have been tuned by replacing the strong donor triphenylamine to weak donor carbazole to achieve the combination of high photoluminance efficiency locally excited (LE) component and high exciton‐utilizing CT component in one excited state. Hybridization processes between LE and CT components of SPICN‐Cz and SPICN‐TPA in the emissive state have been discussed. The nondoped organic light emitting diode device based on SPICN‐Cz exhibit better electroluminescent performances than those of SPICN‐TPA–based device: high external quantum efficiency of 2.58 %, current efficiency of 2.90 cd A‐1, and power efficiency of 2.26 lm W‐1 with Commission Internationale de l'Éclairage (CIE) coordinates of (0.15, 0.12). The excited state modulation and the composition of LE and CT states in the donor‐acceptor system could be useful to design low‐cost, high‐efficiency fluorescent organic light emitting diode materials. 相似文献