全文获取类型
收费全文 | 8520篇 |
免费 | 1132篇 |
国内免费 | 350篇 |
专业分类
化学 | 4373篇 |
晶体学 | 54篇 |
力学 | 863篇 |
综合类 | 71篇 |
数学 | 949篇 |
物理学 | 3692篇 |
出版年
2024年 | 9篇 |
2023年 | 65篇 |
2022年 | 135篇 |
2021年 | 201篇 |
2020年 | 223篇 |
2019年 | 265篇 |
2018年 | 201篇 |
2017年 | 226篇 |
2016年 | 367篇 |
2015年 | 299篇 |
2014年 | 394篇 |
2013年 | 779篇 |
2012年 | 440篇 |
2011年 | 472篇 |
2010年 | 363篇 |
2009年 | 474篇 |
2008年 | 516篇 |
2007年 | 571篇 |
2006年 | 498篇 |
2005年 | 346篇 |
2004年 | 373篇 |
2003年 | 363篇 |
2002年 | 293篇 |
2001年 | 251篇 |
2000年 | 257篇 |
1999年 | 204篇 |
1998年 | 239篇 |
1997年 | 133篇 |
1996年 | 117篇 |
1995年 | 102篇 |
1994年 | 107篇 |
1993年 | 84篇 |
1992年 | 74篇 |
1991年 | 69篇 |
1990年 | 44篇 |
1989年 | 65篇 |
1988年 | 57篇 |
1987年 | 42篇 |
1986年 | 30篇 |
1985年 | 29篇 |
1984年 | 47篇 |
1983年 | 18篇 |
1982年 | 28篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 22篇 |
1978年 | 18篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
k 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):238
The modified k·p method (which includes both stress and polarization effects) has been used to investigate recombination phenomena in nitride quantum-well (QW) devices. Within their volumes, both spontaneous and piezoelectric polarization have been found to have an essential influence on carriers behaviour. In particular, as a result of the quantum-confined Stark effect, energy of radiation emitted within the AlGaN/GaN/AlGaN QW has been found to decrease rapidly with an increase in the AlN mole fraction of the barrier material, which means—with an increase in mechanical stresses at the GaN/AlGaN heterojunctions. It should also be stressed that screening of polarization effects induced by free carriers at least partly reduced the above stress influence. So both effects, polarization and its screening, are equally important in exact modelling of an operation of nitride QW devices. 相似文献
822.
Experimental evidence proving the unique stabilization of the 6s orbital in platinum and gold is presented. The conclusions are drawn from the chemical reactivities, of both elements, as well as from structural and spectroscopic features of selected compounds. In particular, the opening of a band gap in transparent CsAu and Cs2Pt, backed by band structure calculations, are regarded conclusive indications of Au− and Pt2− to exist as closed shell species in these compounds. 相似文献
823.
Substitution effects on the stereochemical outcome of bisspiroketalization on the C1-C17 carbon backbone of azaspiracid is presented. A possible explanation is offered to explain the observed stereochemical outcome. 相似文献
824.
Huan-You Wang Hui Xu Tie-Tie Huang Chao-Sheng Deng 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(1):39-43
The density function perturbation theory (DFPT) is employed to study
the linear thermal expansion and heat capacity at constant pressure
(with the quasiharmonic approximation) for wurtzite GaN. The
calculated results of linear thermal expansion coefficient and heat
capacity at constant pressure are compared with the available
experimental data in a wide temperature range. Generally these
properties calculated agree well with experimental data except at
high temperature, thus it suggests the thermal expansion and heat
capacity can be well calculated from this first-principle approach. 相似文献
825.
Wenjie Xie Siu-Chung Tam Hongru Yang Jianhui Gu Gang Zhao Yee-Loy Lam Chan-Hin Kam 《Optics & Laser Technology》1999,31(5):387
It is important for laser designers to study the characteristics of heat transfer from the laser crystal slab to the coolant in high-power DPSS laser operations. We have simulated and obtained the optimum heat transfer coefficient and coolant flow rate for our cavity design, in which the circulating coolant is maintained at a constant temperature. It has been determined that the coolant temperature and the convective heat transfer coefficient (h) are important parameters in the thermal analysis. The coefficient h is affected by the coolant flow rate, the physical properties of the laser slab and the coolant and the pumping cavity geometry. Using analytical heat transfer equation, for cooling water temperature of 300 K, the optimum flow rate for our cavity geometry is found to be 390 cm3/s, corresponding to h=5 W/cm2 K. 相似文献
826.
J. Kim A. Maciel E. D. O'Sullivan J. F. Ryan A. Schwarz A. Kaluza H. Hardtdegen Th. Schpers H. Lüth D. Meertens Ch. Dieker 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
We report the observation of strong Fermi-edge singularities in the photoluminescence spectrum of strongly-confined, modulation-doped GaAs v-groove quantum wires. The behaviour of the singularity has been investigated at high excitation intensity, and both lattice and electrical heating. The latter produces a strong reduction of the singularity due to Fermi surface smearing, whereas, increased photoexcitation produces complex electron–hole correlation effects. 相似文献
827.
The thermo-viscoplastic behavior of three metals is characterized in a large range of loading conditions by using a new phenomenological
constitutive model. The flow stress is decomposed into the sum of an effective stress with an internal stress depending upon
an internal parameter which describes the strain hardening effect. The evolution of the internal stress is sensitive to the
history of strain-rate and temperature. A systematic method is used for determining the model’s parameters. The model predictions
show a good correlation with experimental data. Temperature history effects are especially analyzed. 相似文献
828.
On the use of nickel foil strain gages at varying temperatures 总被引:1,自引:0,他引:1
When a strain gage made of nickel foil attached on the surface of a specimen is subjected to repeated loads, the elastic stress
is measured by observing slip-bands in the foil resulting from repeated strain. Calibration studies with rotating-bending
tests at various temperatures between room temperature and 350°C are performed on round steel bars with nickel foil. The relation
between the threshold stress for the first appearance of slip-bands and the number of stress cycles is examined at varying
temperatures, which provides the calibration values of the nickel foil tested at varying temperatures. Assuming that the first
appearance of slip-bands is based on the linear cumulative damage law, the calibration values at varying temperatures are
calculated from those established by the calibration tests at several constant temperatures. It is found that the calculated
calibration values agree well with the results obtained by the calibration tests at varying temperatures and that the calculation
applying the linear cumulative damage law is a useful method to presume the calibration values at varying temperatures without
performing the experiment. 相似文献
829.
In this paper, an algorithm for chemical non‐equilibrium hypersonic flow is developed based on the concept of energy relaxation method (ERM). The new system of equations obtained are studied using finite volume method with Harten–Lax–van Leer scheme for contact (HLLC). The original HLLC method is modified here to account for additional species and split energy equations. Higher order spatial accuracy is achieved using MUSCL reconstruction of the flow variables with van Albada limiter. The thermal equilibrium is considered for the analysis and the species data are generated using polynomial correlations. The single temperature model of Dunn and Kang is used for chemical relaxation. The computed results for a flow field over a hemispherical cylinder at Mach number of 16.34 obtained using the present solver are found to be promising and computationally (25%) more efficient. The present solver captures physically correct solution as the entropy conditions are satisfied automatically during the computations. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
830.