全文获取类型
收费全文 | 16588篇 |
免费 | 2895篇 |
国内免费 | 1944篇 |
专业分类
化学 | 11852篇 |
晶体学 | 174篇 |
力学 | 1181篇 |
综合类 | 69篇 |
数学 | 1724篇 |
物理学 | 6427篇 |
出版年
2024年 | 58篇 |
2023年 | 356篇 |
2022年 | 624篇 |
2021年 | 608篇 |
2020年 | 656篇 |
2019年 | 623篇 |
2018年 | 568篇 |
2017年 | 516篇 |
2016年 | 876篇 |
2015年 | 772篇 |
2014年 | 987篇 |
2013年 | 1185篇 |
2012年 | 1544篇 |
2011年 | 1502篇 |
2010年 | 1023篇 |
2009年 | 951篇 |
2008年 | 1096篇 |
2007年 | 978篇 |
2006年 | 885篇 |
2005年 | 788篇 |
2004年 | 552篇 |
2003年 | 448篇 |
2002年 | 435篇 |
2001年 | 361篇 |
2000年 | 318篇 |
1999年 | 352篇 |
1998年 | 277篇 |
1997年 | 248篇 |
1996年 | 293篇 |
1995年 | 278篇 |
1994年 | 195篇 |
1993年 | 162篇 |
1992年 | 159篇 |
1991年 | 151篇 |
1990年 | 133篇 |
1989年 | 105篇 |
1988年 | 91篇 |
1987年 | 73篇 |
1986年 | 52篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 27篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1978年 | 2篇 |
1972年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
X. -M. Xiu L. Dong Y. -J. Gao F. Chi 《Journal of Experimental and Theoretical Physics》2007,105(6):1132-1135
A theoretical scheme of a multiparty-controlled quantum secure direct communication is proposed. The supervisor prepares a
communication network with Einstein-Podolsky-Rosen pairs and auxiliary particles. After passing a security test of the communication
network, a supervisor tells the users the network is secure and they can communicate. If the controllers allow the communicators
to communicate, the controllers should perform measurements and inform the communicators of the outcomes. The communicators
then begin to communicate after they perform a security test of the quantum channel and verify that it is secure. The recipient
can decrypt the secret message in a classical message from the sender depending on the protocol. Any two users in the network
can communicate through the above processes under the control of the supervisor and the controllers.
The text was submitted by the authors in English. 相似文献
962.
分析了毕奥-萨伐尔定律的引入方式,提出了以围绕学生提出课题、参与定律发现过程、提炼物理思想和物理方法为中心的培养学生创新思维与探究能力的教学方案. 相似文献
963.
Size-dependence of optical properties and energy relaxation in CdSe/ZnS quantum dots (QDs) were investigated by two-colour femtosecond (fs) pump-probe (400/800 nm) and picosecond time-resolved photoluminescence (ps TRPL) experiments. Pump-probe measurement results show that there are two components for the excited carriers relaxation, the fast one with a time constant of several ps arises from the Auger-type recombination, which shows almost particle sizeindependence. The slow relaxation component with a time constant of several decades of ns can be clearly determined with ps TRPL spectroscopy in which the slow relaxation process shows strong particle size-dependence. The decay time constants increase from 21 to 34 ns with the decrease of particle size from 3.2 to 2.1 nm. The room-temperature decay lifetime is due to the thermal mixing of bright and dark excitons, and the size-dependence of slow relaxation process can be explained very well in terms of simple three-level model. 相似文献
964.
利用三阶混沌系统构造了一种新的微弱信号检测系统——类Liu系统, 对类Liu 系统进行了深度的理论分析. 类Liu系统中, 当输入待测信号幅值大于某临界值时, 系统可达到平衡点S0, S0中系统变量x平衡于摄动力信号, 系统变量y, z收敛于零态, 且S0 对应的Lyapunov指数小于零. 通过Matlab仿真、Multisim电路仿真以及实际电路证明了类Liu系统的周期态收敛性及广域检测性, 解决了传统Duffing系统进行微弱信号检测时周期态不收敛、只能进行窄域检测等问题, 同时谱级信噪比范围仍可达-46.57 dB. 类Liu系统采用了全新的设计理念, 具有较高的实用价值, 对未来海洋物联网中的水声通信有一定参考价值. 相似文献
965.
Controlling the gain shape of Er^3+—doped fluorozirconate fibre amplifier by a coherent field 下载免费PDF全文
We proposed a four-level system to explore the quantum interference effects on optical amplification.We found that the gain of the probe.including positions and values of gain peaks,can be adjusted by changing the coherent field and the incoherent pumping.At the same time,we can also modify the absorption profile of electromagnetically induced transparency by the incoherent pump.The results provide a method to flatten the gain of Erbium-doped fibre amplifiers. 相似文献
966.
In this paper, digital mask technique is presented, and a high-quality projecting reduction lithography system has been set up successfully. The core device of digital mask technique is digital micromirror device (DMD) which belongs to one of the electrically addressed spatial light modulators. The output image of DMD can be equivalent to a gray-scale mask of high precision, which can control the exposure precisely. If it is combined with a high-quality projecting reduction system, the fabrication of submicron diffractive optical elements can be realized successfully. The overall design of the system is described in detail, and some diffractive optical element masks are fabricated. Experimental results verify that the system is feasible. In the end, system characteristics and system error are summarized. 相似文献
967.
阐述了应用法拉第磁光旋转效应将磁通密度分布转换为亮度分布的图像,介绍了用微机采集和处理这种磁光图像,直接观测和研究磁通密度分布和运动,研究超导体的磁通动力学和磁性材料的磁性结构,叙述了目前应用磁光图像技术研究高温超导体性质和实用高温超导带材方面的最新进展. 相似文献
968.
Dr. Sheng‐Liang Zhong Dr. Yang Lu Dr. Min‐Rui Gao Dr. Shu‐Juan Liu Jun Peng Le‐Cheng Zhang Prof. Dr. Shu‐Hong Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5222-5231
A family of monodisperse YF3, YF3:Ce3+ and YF3:Ce3+/Ln3+ (Ln=Tb, Eu) mesocrystals with a morphology of a hollow spindle can be synthesized by a solvothermal process using yttrium nitrate and NH4F as precursors. The effects of reaction time, fluorine source, solvents, and reaction temperature on the synthesis of these mesocrystals have been studied in detail. The results demonstrate that the formation of a hollow spindle‐like YF3 can be ascribed to a nonclassical crystallization process by means of a particle‐based reaction route in ethanol. It has been shown that the fluorine sources selected have a remarkable effect on the morphologies and crystalline phases of the final products. Moreover, the luminescent properties of Ln3+‐doped and Ce3+/Ln3+‐co‐doped spindle‐like YF3 mesocrystals were also investigated. It turns out that Ce3+ is an efficient sensitizer for Ln3+ in the spindle‐like YF3 mesocrystals. Remarkable fluorescence enhancement was observed in Ce3+/Ln3+‐co‐doped YF3 mesocrystals. The mechanism of the energy transfer and electronic transition between Ce3+ and Ln3+ in the host material of YF3 mesocrystals was also explored. The cytotoxicity study revealed that these YF3‐based nanocrystals are biocompatible for applications, such as cellular imaging. 相似文献
969.
Lin JM Guan YF Wang DY Dong W Wang XT Gao S 《Dalton transactions (Cambridge, England : 2003)》2008,(44):6165-6169
Seven isomorphous 1D chain Ln3+ complexes Ln(BTA)(HCOO)(H2O)3 (Ln = Pr (1), Gd (2), Eu (3), Tb (4) Dy (5), Er (6) and Yb (7)), and two formate coordinating and bridging 3D Ln3+ complexes Ln(HCOO)3 (Ln = Pr (8) and Nd (9)) have been synthesized and characterized by single crystal X-ray diffraction analysis. Although the Ln3+ ions in 1-7 have different radius, the trivalent lanthanide ions in 1-7 show the same coordinated environment. The well-defined single crystal structures of 8 and 9 are first samples for formate-bridged Ln3+ metallic complexes. The luminescent properties of solid samples of 2-5 at room temperature and the magnetic property of 2 have been also reported and discussed in this paper. 相似文献
970.
Shi-Yu Wang Wen-Min Wang Ying-Ping Quan Hong-Ling Gao 《Journal of Coordination Chemistry》2016,69(4):594-603
Four lanthanide-nitronyl nitroxide radical complexes, [Ln(hfac)3(NIT-3Methien)2] (Ln = Pr (1), Tb (2), Dy (3), Ho (4); hfac = hexafluoroacetylacetonate; NIT-3Methien = 2-(3-methylthiophene)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), have been synthesized, and structurally and magnetically characterized. Single-crystal X-ray diffraction shows that 1–4 have similar mononuclear tri-spin structures in which central Ln(III) ions are eight coordinate by two NIT-3Methien radicals and three hfac coligands. The magnetic studies indicate that there are antiferromagnetic interactions between Ln(III) ions and radicals in 1, 2, and 4, while ferromagnetic interactions are present in 3. The luminescence properties of 2 and 3 were studied. 相似文献