全文获取类型
收费全文 | 22082篇 |
免费 | 3557篇 |
国内免费 | 3004篇 |
专业分类
化学 | 16775篇 |
晶体学 | 353篇 |
力学 | 1192篇 |
综合类 | 265篇 |
数学 | 2450篇 |
物理学 | 7608篇 |
出版年
2024年 | 50篇 |
2023年 | 407篇 |
2022年 | 599篇 |
2021年 | 690篇 |
2020年 | 840篇 |
2019年 | 887篇 |
2018年 | 704篇 |
2017年 | 679篇 |
2016年 | 1029篇 |
2015年 | 1018篇 |
2014年 | 1283篇 |
2013年 | 1712篇 |
2012年 | 1973篇 |
2011年 | 2191篇 |
2010年 | 1564篇 |
2009年 | 1480篇 |
2008年 | 1544篇 |
2007年 | 1524篇 |
2006年 | 1303篇 |
2005年 | 1046篇 |
2004年 | 943篇 |
2003年 | 710篇 |
2002年 | 703篇 |
2001年 | 572篇 |
2000年 | 484篇 |
1999年 | 383篇 |
1998年 | 312篇 |
1997年 | 256篇 |
1996年 | 264篇 |
1995年 | 197篇 |
1994年 | 199篇 |
1993年 | 168篇 |
1992年 | 155篇 |
1991年 | 125篇 |
1990年 | 122篇 |
1989年 | 97篇 |
1988年 | 59篇 |
1987年 | 56篇 |
1986年 | 56篇 |
1985年 | 54篇 |
1984年 | 36篇 |
1983年 | 29篇 |
1982年 | 13篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
Joseph M. Ling 《Discrete and Computational Geometry》2007,37(3):455-469
In this paper we prove four new (infinite) lists of quadratic inequalities, and four cubic inequalities, for the flag f-vectors
of 4-polytopes. These extend and supplement the only four currently known non-linear inequalities, which were proved by Bayer
in 1987. The new lists of inequalities for flag f-vectors yield new lists of inequalities for
f-vectors of 4-polytopes. Using the latter, we managed to improve an estimate discovered by Hoppner and Ziegler concerning
upper bounds of f1 in terms of f0 and f3. 相似文献
72.
将散射介质层在z轴方向划分成薄层,用薄层的一阶散射强度、Fourier变换和迭代方法求解散射介质整层的矢量辐射传输(VRT)方程的高阶散射解.该方法将一阶散射与高阶散射迭代结合起来,计算公式简明,可计算高阶迭代解,计算时间少.计算结果与一层均匀散射介质的VRT方程一阶Mueller矩阵解、半空间均匀散射介质二阶Mueller矩阵解、以及离散坐标-特征值特征矢量法的VRT热辐射的数值解作了全面的比较.提出并讨论了非均匀散射层主动与被动VRT方程的高阶解.本计算程序可以通用于非球形粒子多层结构及非均匀介质的散射和热辐射计算.
关键词:
VRT方程
分层
迭代解 相似文献
73.
等效电流偶极子(ECD)模型具有简要明确性,已经在心磁图(MCG)的逆问题中,如确定WPW综合症、心脏异常搏动根源、心律失常等方面,得到广泛应用.在多通道体表电势图(BSPM)的测量中也应用ECD.本文讨论用ECD的定位方法,临床研究仿真对ECD获得结果的描述,造影与动物研究和体导体模型的影响. 相似文献
74.
F. R. Ling B. Wang T. Geng S. Q. Fang W. Yuan D. D. Teng C. X. Guan 《Optics & Laser Technology》2004,36(7):541-544
In this paper experimental studies of nonvolatile photorefractive holographic recording in Ce:Cu:LiNbO3 crystals doped with Sc(0,1,2,3 mol%) were carried out. The Sc:Ce:Cu:LiNbO3 crystals were grown by the Czochralski method and oxidized in Nb2O5 powders. The nonvolatile holographic recording in Sc:Ce:Cu:LiNbO3 crystals was realized by the two-photon fixed method. We found that the recording time of Sc:Ce:Cu:LiNbO3 crystal became shorter with the increase of Sc doping concentration, especially doping with Sc(3 mol%), which exceeds the so-called threshold, and there was little loss of nonvolatile diffraction efficiencies between Sc(3 mol%):Ce:Cu:LiNbO3 and Ce:Cu:LiNbO3 crystals. 相似文献
75.
ChunXiaLI YingXiaLI LingBoYU HuaZHANG SiftDongCHU HuaShiGUAN 《中国化学快报》2003,14(8):776-778
A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained. 相似文献
76.
In this paper, we exhibit a unified treatment of the mixed initial boundary value problem for second order (in time) parabolic linear differential equations in Banach spaces, whose boundary conditions are of a dynamical nature. Results regarding existence, uniqueness, continuous dependence (on initial data) and regularity of classical and strict solutions are established. Moreover, several examples are given as samples for possible applications.
77.
§ 1. Introduction Anecessaryandsufficientconditionandasufficientconditiontoensurethataset valuedmappingandasingle valuedmappinginacompletemetricspaceandacompleteconvexmetricspacehavingacommonfixedpointarerespectivelygivenin [1 ] .Meanwhilethemainresultsin[2 ]— [5]areimprovedandextendedin [1 ] .Inthispaper ,theexistenceatcommonfixedpointsoftwoset valuedmappingandasing valuedmappingwerestudied ,andthecorrespond ingresultsin [1 ]— [5]wereextendedandimproved .Let(X ,d)beanon emptymetricspa… 相似文献
78.
采用显微Raman光谱方法对红外目标模拟器中重掺杂Si微电阻桥单元的热传导特性进行研究,根据Si桥的实际特性建立相应的Raman散射模型,通过测量Raman峰位的移动得到高功率激光辐照下测量点的温度.对Si桥桥面分别进行了沿某些特殊线段的逐点线扫描和覆盖全部桥面的面扫描,得到各点的温升及其分布.用基于有限元分析的软件结合Si桥结构参数对各测量点的温升进行了模拟计算,其结果在热导分布的基本趋势上与实验相一致.实验细致地揭示了热导分布的局域起伏,反映出实际器件的不均匀性,为改进器件设计、优化器件性能提供了实验依据.
关键词:
Raman光谱
Si桥
温度分布
热导 相似文献
79.
A new method based on anion exchange resin separation and graphite furnace atomic absorption spectrometry (GFAAS) detection
is proposed for the determination of inorganic tin species. The result showed that Sn(IV) was quantitatively retained on the
resin when [HCl] = 9.0 mol · L−1, but Sn(II) could not be adsorbed on the resin under the same condition. Thus, a separation of Sn(II) and Sn(IV) has been
realized. When the concentration of NaOH solution was between 2.0–7.0 mol · L−1, Sn(IV) that adsorbed on the resin could be eluated from the resin completely. Meanwhile, under the atmosphere and the nitrogen
states, the translation between Sn(II) and Sn(IV) was investigated. Under the optimal conditions, the detection limit of Sn(IV)
is 0.40 μg · L−1 with RSD of 2.3% (n = 5, c = 2.0 μg · L−1). The proposed method was applied to the speciation analysis of tin in different water samples and the recovery of total
Sn was in the range of 98.7–101.7%. In order to verify the accuracy of the method, a certified reference water sample was
analyzed and the results obtained were in good agreement with the certified value. 相似文献
80.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献