全文获取类型
收费全文 | 22477篇 |
免费 | 3806篇 |
国内免费 | 1531篇 |
专业分类
化学 | 2751篇 |
晶体学 | 110篇 |
力学 | 2822篇 |
综合类 | 168篇 |
数学 | 2629篇 |
物理学 | 10638篇 |
综合类 | 8696篇 |
出版年
2024年 | 77篇 |
2023年 | 223篇 |
2022年 | 342篇 |
2021年 | 456篇 |
2020年 | 531篇 |
2019年 | 453篇 |
2018年 | 466篇 |
2017年 | 565篇 |
2016年 | 663篇 |
2015年 | 577篇 |
2014年 | 1046篇 |
2013年 | 1636篇 |
2012年 | 1225篇 |
2011年 | 1481篇 |
2010年 | 1158篇 |
2009年 | 1287篇 |
2008年 | 1342篇 |
2007年 | 1534篇 |
2006年 | 1382篇 |
2005年 | 1382篇 |
2004年 | 1198篇 |
2003年 | 1112篇 |
2002年 | 974篇 |
2001年 | 895篇 |
2000年 | 812篇 |
1999年 | 670篇 |
1998年 | 607篇 |
1997年 | 521篇 |
1996年 | 457篇 |
1995年 | 378篇 |
1994年 | 351篇 |
1993年 | 374篇 |
1992年 | 295篇 |
1991年 | 275篇 |
1990年 | 236篇 |
1989年 | 207篇 |
1988年 | 168篇 |
1987年 | 133篇 |
1986年 | 74篇 |
1985年 | 53篇 |
1984年 | 40篇 |
1983年 | 23篇 |
1982年 | 41篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1973年 | 8篇 |
1971年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
102.
The rotation-tunneling spectrum of the second most stable gGg′ conformer of ethylene glycol (1,2-ethanediol) in its ground vibrational state has been studied in selected regions between 77 and 579 GHz. Compared to the study of the more stable aGg′ conformer, a much larger frequency range was studied, resulting in a much extended frequency list covering similar quantum numbers, J?55 and Ka?19. While the input data were reproduced within experimental uncertainties up to moderately high values of J and Ka larger residuals remain at higher quantum numbers. The severe mixing of the states caused by the Coriolis interaction between the two tunneling substates is suggested to provide a considerable part of the explanation. In addition, a Coriolis interaction of the gGg′ ground vibrational state with an excited state of the aGg′ conformer may also contribute. Relative intensities of closely spaced lines have been investigated to determine the signs of the Coriolis constants between the two tunneling substates relative to the dipole moment components and to estimate the magnitudes of the dipole moment components and the energy difference between the gGg′ and the aGg′ conformers. Results of ab initio calculations on the total dipole moment and the vibrational spectrum were needed for these estimates. The current analysis is limited to transitions with quantum numbers J?40 and Ka?6 plus those having J?22 and Ka?17 which could be reproduced within experimental uncertainties. The results are aimed at aiding radioastronomers to search for gGg′ ethylene glycol in comets and in interstellar space. 相似文献
103.
A suitable derivative of Einstein's equations in the framework of the teleparallel equivalent of general relativity (TEGR) yields a continuity equation for the gravitational energy‐momentum. In particular, the time derivative of the total gravitational energy is given by the sum of the total fluxes of gravitational and matter fields energy. We carry out a detailed analysis of the continuity equation in the context of Bondi and Vaidya's metrics. In the former space‐time the flux of gravitational energy is given by the well known expression in terms of the square of the news function. It is known that the energy definition in the realm of the TEGR yields the ADM (Arnowitt‐Deser‐Misner) energy for appropriate boundary conditions. Here we show that the same energy definition also describes the Bondi energy. The analysis of the continuity equation in Vaidya's space‐time shows that the variation of the total gravitational energy is determined by the energy flux of matter only. 相似文献
104.
The modifying action of chloroform on photochemical reactions induced in the eye lenses of rats by UVB radiation is revealed. In anesthetic concentrations, halogenmethane increases the quantum yield of photodisintegration of protein tryptophanyls with formation of a new photochemical product that absorbs radiation in the UVA range and possesses the photosensitizing activity. 相似文献
105.
稀磁半导体Zn1-xMnxTe吸收光谱压力红移的理论研究 总被引:1,自引:1,他引:0
以自由Mn2+离子的径向波函数为基础,通过引入电子云延伸效应系数κ来修正这一径向波函数,得到了稀磁半导体Zn1-xMnxTe晶体中Mn2+离子的径向波函数.以此波函数为基础,研究了Zn1-xMnxTe晶体吸收光谱的高压谱移特性,并且得到了吸收谱中四条谱线随压力的红移规律. 相似文献
106.
利用相干渡越辐射(CTR)测量短和超短电子束团长度是国际上束测领域新发展的频域测量技术.文中理论分析和数值计算了北京自由电子激光装置的皮秒级的射频电子束团序列产生的CTR,当辐射波长在长于束长(4ps)时,渡越辐射发生相干增强效应;与非相干渡越辐射相比,当λ≥2πσz时,增强的倍数约等于束团中粒子的数目(108);CTR从亚毫米波到毫米波段呈宽带连续谱特性;渡越辐射能量主要集中在轴线附近,宏脉冲辐射能量高达几毫焦.设计采用偏振型束团长度测量系统,利用CTR自相关技术,实验测量该束团序列的纵向长度,并藉助傅里叶变换光谱法,推求束团电子分布. 相似文献
107.
周忆 《数学年刊B辑(英文版)》2003,24(3)
This paper considers the following Cauchy problem for semilinear wave equations in n spacedimensions□φ = F( φ),φ(0, x) = f(x), tφ(0, x) = g(x),The minimal value of s is determined such that the above Cauchy problem is locally well-posed in Hs. It turns out that for the general equation s must satisfyThis is due to Ponce and Sideris (when n = 3) and Tataru (when n ≥ 5). The purpose of thispaper is to supplement with a proof in the case n = 2, 4. 相似文献
108.
109.
类比方法与光的本性的探索 总被引:2,自引:0,他引:2
简要回顾了人类对光的本性的探索历程,介绍了物理学家在研究过程中对类比方法的运用。 相似文献
110.