全文获取类型
收费全文 | 3216篇 |
免费 | 256篇 |
国内免费 | 199篇 |
专业分类
化学 | 2018篇 |
晶体学 | 62篇 |
力学 | 109篇 |
综合类 | 26篇 |
数学 | 412篇 |
物理学 | 1044篇 |
出版年
2023年 | 50篇 |
2022年 | 71篇 |
2021年 | 76篇 |
2020年 | 83篇 |
2019年 | 85篇 |
2018年 | 82篇 |
2017年 | 93篇 |
2016年 | 119篇 |
2015年 | 93篇 |
2014年 | 126篇 |
2013年 | 194篇 |
2012年 | 212篇 |
2011年 | 208篇 |
2010年 | 144篇 |
2009年 | 153篇 |
2008年 | 170篇 |
2007年 | 154篇 |
2006年 | 128篇 |
2005年 | 124篇 |
2004年 | 101篇 |
2003年 | 98篇 |
2002年 | 89篇 |
2001年 | 52篇 |
2000年 | 34篇 |
1999年 | 42篇 |
1998年 | 30篇 |
1997年 | 24篇 |
1996年 | 33篇 |
1995年 | 41篇 |
1994年 | 34篇 |
1993年 | 37篇 |
1992年 | 46篇 |
1991年 | 28篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 23篇 |
1987年 | 28篇 |
1986年 | 28篇 |
1985年 | 40篇 |
1984年 | 37篇 |
1983年 | 26篇 |
1982年 | 23篇 |
1980年 | 18篇 |
1979年 | 25篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 20篇 |
1974年 | 22篇 |
1973年 | 25篇 |
1972年 | 15篇 |
排序方式: 共有3671条查询结果,搜索用时 46 毫秒
991.
N D Sen Gupta 《Pramana》1995,45(4):327-331
The object of the paper is to obtain the solution of the Dirac equation with the Pauli-term in an electromagnetic field depending
on the single variable (ct -nr) along the directionn. 相似文献
992.
N. D. Sen Gupta 《Pramana》2003,60(1):11-19
In this paper, we attempt to obtain the nature of the external field such that the Dirac equation with external electro-magnetic
field is invariant. The Poincaré group, which is the maximal symmetry group for field free case, is constrained by the presence
of the external field. Introducing infinitesimal transformation ofx and ψ, we apply Lie’s extended group method to obtain the class of external field which admit of the invariance of the equation.
It is important to note that the constraints for the existence of invariance are explicity on the electric and magnetic field,
though only potentials explicity appears in the equation.
Presented at the Sixth Chittagong Conference on Mathematical Physics, January 2001. 相似文献
993.
994.
Keith R. Burnett M.D. Edward J. Goldstein Ph.D. M.D. Gerald L. Wolf Ph.D. M.D. Swapan Sen B.S. R.T. R.D.M.S. Alex C. Mamourian M.D. 《Magnetic resonance imaging》1984,2(4):307-314
Mn+2 (as MnCl2) was administered to rabbits intravenously and orally (a route of administration which based upon our previous experiments in rats7 promises to give selective hepatobiliary enhancement with less systemic toxicity). Nuclear magnetic relaxation dispersion or T1 (NMRD) was performed on selected tissues (heart, liver, kidney, serum, and bile) in both animal groups to examine possible qualitative and semiquantitative differences in T1 relaxation at equivalent sacrifice times. One animal was given an oral dose of MnCl2 (620 micromoles/kg) and imaged sequentially (T1 weighted sequence, .12T) for 30 minutes. The NMRD curves for organ tissues show an increase in relaxation efficacy in the 10–20MHz range characteristic of Mn-macromolecular complexes and are similar irrespective of the route of administration. The lack of increased relaxation enhancement for bile in this frequency range reflects cleavage of this complex upon excretion. Decreased overall relaxation in the liver is observed when oral Mn+2 is compared to IV Mn+2 due to the small fraction of administered dose that is absorbed. However, the images document a significant increase in the intensity of liver signal after the oral dose. We suspect this dose may ultimately be adjusted downward to give selective hepatobiliary effects. 相似文献
995.
A compact cyclic shearing interferometer to be used with convergent light for testing lenses is described. It essentially consists of a combination of a prism pair and a plane mirror and is designed to eliminate the residual aberrations present in the oblique incidence interferometer. The interferometer is simple to adjust, occupies little space and is less prone to misalignment. 相似文献
996.
997.
Effect of porosity and pore size distribution on the low-frequency dielectric response, in the range 0.01–100 kHz, in sintered
ZrO2—8 mol% Y2O3 ceramic compacts have been investigated. Small-angle neutron scattering (SANS) technique has been employed to obtain the
pore characteristics like pore size distribution, specific surface area etc. It has been observed that the real and the imaginary
parts of the complex dielectric permittivity, for the specimens, depend not only on the porosity but also on the pore size
distribution and pore morphology significantly. Unlike normal Debye relaxation process, where the loss tangent vis-à-vis the
imaginary part of the dielectric constant shows a pronounced peak, in the present case the same increases at lower frequency
region and an anomalous non-Debye type relaxation process manifests. 相似文献
998.
借助抽运-探测技术研究了ZnTe晶体中光学整流产生的太赫兹(THz)辐射,利用ZnTe晶体的线性电光效应探测THz辐射场分布,观察到了较窄(约为0.2 ps)的THz场分布及相应较宽(响应超过4 THz,半峰宽约为2.4 THz)的THz频谱,并运用琼斯矩阵对实验结果进行了理论拟合. 研究了飞秒激光脉冲波长(750—850 nm)、脉冲宽度(56—225 fs)和晶体旋转与THz辐射产生的关系. 同时改变探测光偏振方向进行偏振调制,并从理论上分析了偏振调制对THz辐射探测的影响.
关键词:
THz辐射
光学整流
电光探测
ZnTe 相似文献
999.
We have carried out very accurate density measurements (with a precision of ±5 × 10-5g cm-3) near the smectic A-nematic transition in binary mixtures of 4-n-nonyl-4'-cyanobiphenyl (9CB) and 4-n-decyl-4'-cyanobiphenyl (10CB). The transition crosses over from second to first order as the temperature range of the nematic phase decreases. For mixtures with the shortest nematic range the data deviate noticeably from a single power law behaviour. Such a deviation is an indication of the first order nature of the transition. Very good fits to a single power law have been obtained for pure 9CB and the x = 0·04 mixture where x is the mole fraction of 10CB in 9CB. The critical exponent obtained from the power law fitting has enabled us to locate the tricritical point to be very close to x=0·04, which is in agreement with the results obtained previously by high resolution calorimetric [1] and X-ray scattering studies [2]. 相似文献
1000.