全文获取类型
收费全文 | 116561篇 |
免费 | 18589篇 |
国内免费 | 12417篇 |
专业分类
化学 | 61590篇 |
晶体学 | 915篇 |
力学 | 5746篇 |
综合类 | 512篇 |
数学 | 10088篇 |
物理学 | 37256篇 |
无线电 | 31460篇 |
出版年
2024年 | 503篇 |
2023年 | 3058篇 |
2022年 | 3681篇 |
2021年 | 4786篇 |
2020年 | 4759篇 |
2019年 | 4178篇 |
2018年 | 3758篇 |
2017年 | 3590篇 |
2016年 | 5217篇 |
2015年 | 5472篇 |
2014年 | 6521篇 |
2013年 | 8295篇 |
2012年 | 9939篇 |
2011年 | 10014篇 |
2010年 | 7011篇 |
2009年 | 7031篇 |
2008年 | 7554篇 |
2007年 | 6668篇 |
2006年 | 6400篇 |
2005年 | 5337篇 |
2004年 | 3757篇 |
2003年 | 3124篇 |
2002年 | 2867篇 |
2001年 | 2464篇 |
2000年 | 2312篇 |
1999年 | 2648篇 |
1998年 | 2298篇 |
1997年 | 2125篇 |
1996年 | 2076篇 |
1995年 | 1763篇 |
1994年 | 1563篇 |
1993年 | 1293篇 |
1992年 | 1165篇 |
1991年 | 976篇 |
1990年 | 756篇 |
1989年 | 570篇 |
1988年 | 447篇 |
1987年 | 352篇 |
1986年 | 354篇 |
1985年 | 291篇 |
1984年 | 181篇 |
1983年 | 130篇 |
1982年 | 112篇 |
1981年 | 66篇 |
1980年 | 49篇 |
1979年 | 21篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
991.
分别从系统像的信息量和信息自由度的角度分析了大气湍流对相干和不相干照明光学系统成像质量和分辨率的影响。理论上,处于一定大气湍流条件下的相干照明系统存在着超出经典衍射极限的超分辨率。 相似文献
992.
本设计为一种便携式条形码阅读译码器(简称阅读器),它采用INTEL8031CPU微处理器为主芯片,辅以其它大规模集成电路芯片,构成一智能化系统,阅读及识别采用Code39码编制的条形码,并能完成条形码信息的存储、数目统计及与微机进行串行通信功能。 相似文献
993.
Xiufang Zhang 《Hyperfine Interactions》1994,91(1):917-921
Several applications of Mössbauer spectroscopy (MS) as an analytical tool in research on biomedical physics are reviewed: (1) The evaluation of treatments for some diseases such as thalassemia, iron-overload disease, high altitude polycythemia. (2) Medical research on the effects of environmental factors on the human body, for example, the effects of electromagnetic radiation on human red blood cells (RBCs). Some advantages and weaknesses of MS, a new application of the Mössbauer effect, cancer therapy, and some possible applications such as monitoring the RBCs of the patients before, during, and after surgical operation, are discussed. 相似文献
994.
995.
Zhang Peixuan 《分析论及其应用》1992,8(4):66-78
In this paper, we discuss the “conjugate” Quasi-Fourier-Legendre (Q.F.L.) series and the corresponding conjugate function.
Moreover we give some equiconvergence theorems and applications. 相似文献
996.
This paper is mainly concerned with the existence and uniqueness of mild solutions for fractional impulsive neutral functional infinite delay integrodifferential systems with nonlocal initial conditions. The results are obtained by the fixed point theorem combined with a strongly continuous operator semigroup. 相似文献
997.
Shunhua Zhang 《Journal of Algebra》2010,323(9):2538-2546
998.
The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and
spin reorientation of a series of polycrystalline Tb0.3Dy0.7(Fe1−x
Alx)1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found
that the primary phase of Tb0.3Dy0.7(Fe1−x
Alx)1.95 is the MgCu2-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb0.3Dy0.7(Fe1−x
Alx)1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction λ inceases slightly in a low magnetic field (H ⩽ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy.
It was also found that the spontaneous magnetostriction λ
111 decreases greatly with x increasing. The analysis of the M?ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates
slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small
amount of non-magnetic phase exists for x = 0.15 in Tb0.3Dy0.7(Fe1−x
Alx)1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperature, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing. 相似文献
999.
Based on our study on field emission from multi-walled carbon nanotubes (MWNTs), we experimentally manufactured field emission display (FED) triode with a MWNTs cold cathode, and demonstrated an excellent performance of MWNTs as field emitters. The measured luminance of the phosphor screens was 1.8 × 103 cd/m2 for green light. The emission is stable with a fluctuation of only 1.5% at an average current of 260 μA. 相似文献
1000.
A cross-linked azopolymer with high optical and thermal stability was prepared. A pure polarization grating without surface topology was fabricated from cross-linked azopolymer by polarization holography by use of orthogonal linearly polarized beams from a He-Cd laser with a power density of 60 mW/cm(-2). The surface relief structure was investigated by atomic-force microscopy, and the polarization grating was observed by polarization optical microscopy. The grating spacing is 1.5 microm. The grating is stable at room temperature and can endure repeated writing-erasing. 相似文献