全文获取类型
收费全文 | 58865篇 |
免费 | 9625篇 |
国内免费 | 6658篇 |
专业分类
化学 | 41673篇 |
晶体学 | 809篇 |
力学 | 3455篇 |
综合类 | 392篇 |
数学 | 6644篇 |
物理学 | 22175篇 |
出版年
2024年 | 204篇 |
2023年 | 1289篇 |
2022年 | 2389篇 |
2021年 | 2451篇 |
2020年 | 2594篇 |
2019年 | 2449篇 |
2018年 | 2093篇 |
2017年 | 2010篇 |
2016年 | 2899篇 |
2015年 | 2982篇 |
2014年 | 3454篇 |
2013年 | 4390篇 |
2012年 | 5365篇 |
2011年 | 5265篇 |
2010年 | 3654篇 |
2009年 | 3450篇 |
2008年 | 3727篇 |
2007年 | 3301篇 |
2006年 | 2942篇 |
2005年 | 2537篇 |
2004年 | 1914篇 |
2003年 | 1560篇 |
2002年 | 1447篇 |
2001年 | 1172篇 |
2000年 | 1034篇 |
1999年 | 1155篇 |
1998年 | 934篇 |
1997年 | 871篇 |
1996年 | 871篇 |
1995年 | 782篇 |
1994年 | 661篇 |
1993年 | 564篇 |
1992年 | 466篇 |
1991年 | 418篇 |
1990年 | 360篇 |
1989年 | 256篇 |
1988年 | 191篇 |
1987年 | 175篇 |
1986年 | 171篇 |
1985年 | 149篇 |
1984年 | 96篇 |
1983年 | 106篇 |
1982年 | 60篇 |
1981年 | 41篇 |
1980年 | 30篇 |
1979年 | 22篇 |
1976年 | 21篇 |
1975年 | 21篇 |
1972年 | 19篇 |
1957年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
本文利用85年5—6月间对乌鲁木齐市主要商业区及部分中、小商业区的实地调查资料,对乌市商业中心等级系统进行了定性和定量的分级分类,将全市商业中心划分为五个等级,八组商业中心,对已形成的商业中心分布现状进行了初步探讨,并对今后商业网点的合理布局提出了建议。 相似文献
103.
提出了一种基于增强现实的室内漫游系统,在这个系统中用户通过HMD观察增强的视景。在这个视景中不但包含真实布景的图像,还包含有计算机生成的虚拟物体的图像。为了实现虚实场景之间的注册,在HMD上安装有两个摄像机:场景摄像机与跟踪摄像机。并且在用户所在房间的顶部安装了一系列的红外标志点,这些标志点的图像由跟踪摄像机获取,并通过位置估计算法计算用户头部的位置和姿态。另外,通过一对安装有ARtoolKit标志点的手套,实现用户与虚拟环境之间的交互。最后,一套海底漫系统被开发出来,以验证整个漫游系统的可用性 相似文献
104.
We consider the M(t)/M(t)/m/m queue, where the arrival rate λ(t) and service rate μ(t) are arbitrary (smooth) functions of time. Letting pn(t) be the probability that n servers are occupied at time t (0≤ n≤ m, t > 0), we study this distribution asymptotically, for m→∞ with a comparably large arrival rate λ(t) = O(m) (with μ(t) = O(1)). We use singular perturbation techniques to solve the forward equation for pn(t) asymptotically. Particular attention is paid to computing the mean number of occupied servers and the blocking probability
pm(t). The analysis involves several different space-time ranges, as well as different initial conditions (we assume that at t = 0 exactly n0 servers are occupied, 0≤ n0≤ m). Numerical studies back up the asymptotic analysis.
AMS subject classification: 60K25,34E10
Supported in part by NSF grants DMS-99-71656 and DMS-02-02815 相似文献
105.
The contrast of interference pattern formed by two circularly polarized waves and by a linearly polarized wave and a circularly polarized one is discussed. The results are compared with that by two linear beams. It shows that the use of circular light in holographic fabrication of three-dimensional periodic microstructures may remove the necessity of beam ratio and polarization optimization needed in the interference of three linear noncoplanar beams and improve the uniform contrast of resultant pattern simultaneously. 相似文献
106.
107.
Zhao Yang YIN 《数学学报(英文版)》2006,22(3):819-826
Sufficient conditions for the existence of positive solutions to a class of quasilinear elliptic equations in two-dimensional exterior domains are given. 相似文献
108.
109.
Calcium lanthanide oxyborate doped with rare-earth ions LnCa4O(BO3)3:RE3+ (LnCOB:RE, Ln=Y, La, Gd, RE=Eu, Tb, Dy, Ce) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos’ and Jφrgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. Jφrgensen, Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln,A) and charge transfer band Ect were calculated and compared with their excitation spectra.Eu3+ and Tb3+ ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce3+ ions do not show efficient luminescence and quench the luminescence of Tb3+ ions when Tb3+ and Ce3+ ions are co-doped into LnCOB. GdCOB doped with Dy3+ shows yellowish white light under irradiation of 254 nm light for the reason that Gd3+ ions transfer the energy from itself to Dy3+. Because of the existence of Gd3+, the samples of GdCOB:RE3+ show higher excitation efficiency than LaCOB:RE3+ and YCOB:RE3+, around 188 nm, which indicates that the Gd3+ ions have an effect on the host absorption and can transfer the excitation energy to the luminescent center such as Tb3+, Dy3+ and Eu3+. 相似文献
110.
Hui-Ling Li De-Jiang Qi Qing-Quan Jiang Shu-Zheng Yang 《International Journal of Theoretical Physics》2006,45(12):2428-2436
An extension of the Parikh-Wilczek's semi-classical quantum tunneling method, the tunneling radiation of the charged particle from a torus-like black hole is investigated. Difference from the uncharged mass-less particle, the geodesics of the charged massive particle tunneling from the black hole is not light-like, but determined by the phase velocity. The derived result shows that the tunneling rate depends on the emitted particle's energy and electric charge, and takes the same functional form as uncharged particle. It proves also that the exact emission spectrum is not strictly pure thermal, but is consistent with the underlying unitary theory.
PACS Numbers: 04.70.Dy, 97.60.Lf, 05.30.Ch. 相似文献