全文获取类型
收费全文 | 31396篇 |
免费 | 5671篇 |
国内免费 | 4332篇 |
专业分类
化学 | 22870篇 |
晶体学 | 473篇 |
力学 | 1762篇 |
综合类 | 260篇 |
数学 | 3061篇 |
物理学 | 12973篇 |
出版年
2024年 | 127篇 |
2023年 | 693篇 |
2022年 | 1214篇 |
2021年 | 1386篇 |
2020年 | 1433篇 |
2019年 | 1428篇 |
2018年 | 1241篇 |
2017年 | 1174篇 |
2016年 | 1638篇 |
2015年 | 1704篇 |
2014年 | 2036篇 |
2013年 | 2556篇 |
2012年 | 3006篇 |
2011年 | 2899篇 |
2010年 | 2069篇 |
2009年 | 1895篇 |
2008年 | 2131篇 |
2007年 | 1845篇 |
2006年 | 1667篇 |
2005年 | 1400篇 |
2004年 | 1057篇 |
2003年 | 830篇 |
2002年 | 769篇 |
2001年 | 613篇 |
2000年 | 545篇 |
1999年 | 596篇 |
1998年 | 469篇 |
1997年 | 424篇 |
1996年 | 429篇 |
1995年 | 344篇 |
1994年 | 298篇 |
1993年 | 262篇 |
1992年 | 206篇 |
1991年 | 184篇 |
1990年 | 187篇 |
1989年 | 142篇 |
1988年 | 94篇 |
1987年 | 68篇 |
1986年 | 86篇 |
1985年 | 77篇 |
1984年 | 34篇 |
1983年 | 34篇 |
1982年 | 34篇 |
1981年 | 21篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1957年 | 7篇 |
1930年 | 2篇 |
1916年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
X.P. Hu X. Wang Z. Yan H.X. Li J.L. He S.N. Zhu 《Applied physics. B, Lasers and optics》2007,86(2):265-268
High power red light was generated from a periodically-poled stoichiometric LiTaO3 (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of
2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and
with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method
to construct a reliable compact red laser.
PACS 42.70.Mp; 42.79.Nv; 42.55.Xi 相似文献
42.
43.
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
44.
本文采用文[1,2]中提出的平衡结构法研究子系统s≥3的非线性大系统在近平衡区内的稳定性;得到了判别这类大系统稳定性的两个一般性准则. 相似文献
45.
46.
K. C. Nicolaou Dionisios Vourloumis Tianhu Li Joaquin Pastor Nicolas Winssinger Yun He Sacha Ninkovic Francisco Sarabia Hans Vallberg Frank Roschangar N. Paul King M. Ray V. Finlay Pareskevi Giannakakou Pascal Verdier-Pinard Ernest Hamel 《Angewandte Chemie (International ed. in English)》1997,36(19):2097-2103
47.
In this paper a lattice Boltzmann (LB) model to simulate incompressible flow is developed. The main idea is to explicitly eliminate the terms of o(M 2), where M is the Mach number, due to the density fluctuation in the existing LB models. In the proposed incompressible LB model, the pressure p instead of the mass density ρ is the independent dynamic variable. The incompressible Navier–Stokes equations are derived from the incompressible LB model via Chapman–Enskog procedure. Numerical results of simulations of the plane Poiseuille flow driven either by pressure gradient or a fixed velocity profile at entrance as well as of the 2D Womersley flow are presented. The numerical results are found to be in excellent agreement with theory. 相似文献
48.
Indirect and direct boundary integral equations equivalent to the original boundary value problem of differential equation of plane elasticity are established rigorously. The unnecessity or deficiency of some customary boundary integral equations is indicated by examples and numerical comparison. 相似文献
49.
50.
YBa2Cu3O7-δ and Tl2Ba2CaCu2O8 thin films for microwave filters were synthesized by pulsed laser deposition and the two-step thalliation process. Substrate
quality requirements and the relation of thin film morphology, microstructure with microwave surface resistance were discussed. 相似文献