全文获取类型
收费全文 | 23222篇 |
免费 | 3738篇 |
国内免费 | 2681篇 |
专业分类
化学 | 12880篇 |
晶体学 | 184篇 |
力学 | 1046篇 |
综合类 | 105篇 |
数学 | 1821篇 |
物理学 | 7293篇 |
无线电 | 6312篇 |
出版年
2024年 | 120篇 |
2023年 | 619篇 |
2022年 | 759篇 |
2021年 | 962篇 |
2020年 | 969篇 |
2019年 | 900篇 |
2018年 | 795篇 |
2017年 | 748篇 |
2016年 | 1042篇 |
2015年 | 1107篇 |
2014年 | 1287篇 |
2013年 | 1603篇 |
2012年 | 1935篇 |
2011年 | 1840篇 |
2010年 | 1342篇 |
2009年 | 1276篇 |
2008年 | 1406篇 |
2007年 | 1301篇 |
2006年 | 1265篇 |
2005年 | 1136篇 |
2004年 | 776篇 |
2003年 | 700篇 |
2002年 | 703篇 |
2001年 | 553篇 |
2000年 | 486篇 |
1999年 | 587篇 |
1998年 | 467篇 |
1997年 | 450篇 |
1996年 | 428篇 |
1995年 | 379篇 |
1994年 | 307篇 |
1993年 | 269篇 |
1992年 | 211篇 |
1991年 | 180篇 |
1990年 | 181篇 |
1989年 | 122篇 |
1988年 | 91篇 |
1987年 | 62篇 |
1986年 | 60篇 |
1985年 | 64篇 |
1984年 | 33篇 |
1983年 | 33篇 |
1982年 | 31篇 |
1981年 | 20篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1942年 | 2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 15 毫秒
81.
He Ping LIU Xuan Yuan ZHENG 《数学学报(英文版)》2006,22(2):425-430
We consider the commutators of the HSrmander multiplier with CMO-functions on the Heisenberg group. The result of compactness on L^P spaces is proved. 相似文献
82.
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
83.
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
84.
85.
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
86.
采用紫外线、同平板梯度浓度亚硝基肌,纯铜蒸气激光诱变去甲基金霉素生产菌金霉素链霉菌的原生质体,结果表明原生质体对各种诱变剂的敏感性较高.正变幅度较大.原生质体经紫外线、同平板梯度浓度亚硝墓肌复合诱变后,筛选到一菌株,重新制备原生体,经激光诱变,选育出高产菌株S. A. HU02,去甲基金霉素效价从2831u/ml提高到4337u/ml,提高了53. 2,经多次传代产量性状非常稳定. 相似文献
87.
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
88.
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
89.
90.
He Ping 《电子科学学刊(英文版)》1994,11(4):296-302
The minimum squared Euclidean distance(MSED) of binary multi-h phase codes is presented. The signal segregation degree(SSD) has been put forward to determine MSED of multi-h phase codes. In order to maximize MSED, SSD should be as large as possible. The necessary and sufficient conditions of maximizing
SSD are derived. Finally, SSD and the exact formulae for MSED of binary 2-h phase codes are also presented. 相似文献