全文获取类型
收费全文 | 109243篇 |
免费 | 29670篇 |
国内免费 | 29447篇 |
专业分类
化学 | 69851篇 |
晶体学 | 2706篇 |
力学 | 7631篇 |
综合类 | 1607篇 |
数学 | 15624篇 |
物理学 | 70941篇 |
出版年
2024年 | 542篇 |
2023年 | 974篇 |
2022年 | 2082篇 |
2021年 | 1902篇 |
2020年 | 2061篇 |
2019年 | 2530篇 |
2018年 | 2460篇 |
2017年 | 3730篇 |
2016年 | 3193篇 |
2015年 | 4077篇 |
2014年 | 4305篇 |
2013年 | 6409篇 |
2012年 | 6924篇 |
2011年 | 8820篇 |
2010年 | 12403篇 |
2009年 | 12748篇 |
2008年 | 7074篇 |
2007年 | 6103篇 |
2006年 | 5763篇 |
2005年 | 5581篇 |
2004年 | 5822篇 |
2003年 | 4391篇 |
2002年 | 4344篇 |
2001年 | 4625篇 |
2000年 | 4077篇 |
1999年 | 3413篇 |
1998年 | 2542篇 |
1997年 | 2231篇 |
1996年 | 2538篇 |
1995年 | 2980篇 |
1994年 | 2995篇 |
1993年 | 3080篇 |
1992年 | 2619篇 |
1991年 | 2261篇 |
1990年 | 1901篇 |
1989年 | 2000篇 |
1988年 | 1975篇 |
1987年 | 1254篇 |
1986年 | 1280篇 |
1985年 | 897篇 |
1984年 | 1043篇 |
1982年 | 928篇 |
1981年 | 769篇 |
1980年 | 805篇 |
1979年 | 568篇 |
1978年 | 543篇 |
1977年 | 639篇 |
1976年 | 1044篇 |
1972年 | 532篇 |
1971年 | 443篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
771.
772.
OSCILLATION OF A FORCED SECOND ORDER NONLINEAR EQUATION ¥KONGQINGKAI;ZHANGBINGGENAbstract:Thispapergivesseveralcriteriaontheo... 相似文献
773.
Analysis of the Coaxial Ridge-Loaded Helical Groove Waveguide 总被引:1,自引:0,他引:1
Yonghai Lan Wenxiang Wang Yubin Gong 《International Journal of Infrared and Millimeter Waves》2002,23(3):425-434
The coaxial ridge-loaded helical groove waveguide is proposed in this paper. As an all-metal slow-wave circuit, it has advantages of good heat dissipation and great size, and thus is suitable for use of millimeter TWT. By means of field theory, the expressions of the dispersion equation and the coupling impedance of the coaxial ridge-loaded helical groove waveguide are obtained. The influence of various circuit dimensions on the dispersion relation and the coupling impedance is investigated by the results of numerical computation. 相似文献
774.
PENG Zi-cheng LI Ping ZHOU Tai-xi LI Xue-ming Wept. of Earth Space Science Univ. of Science Tech. of China Hefei )HU Zhi-sheng 《高等学校化学研究》1992,(3)
When was the earliest glass produced in China? This has still been a question so far. Some archaeologists have thought that Yu Guo beads are real glass, the earliest glass(1100-771 B. C. ) in China. However, more details of scientific investigations in this paper show that Yu Guo beads are mainly made of clastic quartz (>95%) with a small amount of clay and sintered under the low temperature(500-600℃). It is not a glassy body, but a kind of polycrystal ornaments. 相似文献
775.
本文报道了一种测角单晶NMR探头。该探头采用单线圃双调谐电路,工作频率在90MHz-110 MHz连续可调,可进行交叉极化大功率去耦实验。文中提出了一种简单而有效的测角装置,可使单晶绕三个互相垂直轴转动实现单晶的NMR测量。作为典型的应用例子,本文利用该探头实现了单晶DGO(2NH2CH2COOH·H2C2O4)屏蔽张量的测量。 相似文献
776.
777.
I. N. Ivchenko S. K. Loyalka R. V. Tompson 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2002,25(6):58-72
The slip phenomena in gas mixtures are of fundamental significance in the specification of boundary conditions for flows in the slip regime. In a recent paper, new explicit results for the slip coefficients appropriate to binary gas mixtures were reported. The present work being reported extends the previous work to a higher level of accuracy by involving a higher order Chapman-Enskog expansion. In particular, new expressions for the slip coefficients are presented which are applicable for arbitrary models of the intermolecular interaction. Limiting expressions for the slip coefficients are given (for a simple gas) and the accuracy of the theory is discussed. Numerical calculations of the slip coefficients for different binary gas mixtures using the first and second order Chapman-Enskog approximations and the rigid sphere and Lennard-Jones (12-6) potential models have been carried out. The thermal creep and diffusion slip coefficients are found to be sensitive to the order of the approximation and to the potential model used. A comparison of the new higher order results with some of our previously obtained experimental data for the thermal transpiration effect has also been carried out and shows excellent agreement between the theory and the experiments which confirms the accuracy of the theory. 相似文献
778.
779.
Groove guide is widely recognized as one of the most promising millimeter wave transmission structures. In this paper, the mode-matching method is used to analyse the dispersion characteristics of single and asymmetrical double groove guides, and the unified formulae of Nth-order approximation dispersion equations are presented. Based on this analysis, a general program for calculating the dispersion characteristrics of single and asymmetrical double groove guides has been completed. Some comparisons between the results obtained by present method and published data show that very good agreement has been seen. The effectiveness and the reliability of the given formulae and program are thus verified. 相似文献
780.
本文研究了非晶锂离子导体P2O5-0.7Li2O-0.4LiCl-0.1Al2O3的60目、120目、200目粉末、粉末压片和整片非晶在60至380℃的离子电导率和激活能。发现颗粒度减小能使离子电导率提高四倍以上,但不影响激活能,它归因于同一非晶相的界面效应。各样品在380℃等温热处理76h内的离子电导率和X射线衍射研究表明:颗粒度越小,晶化就越容易。整片非晶比粉末压片不仅电导率提高两个数量级,激
关键词: 相似文献