全文获取类型
收费全文 | 610篇 |
免费 | 57篇 |
国内免费 | 102篇 |
专业分类
化学 | 456篇 |
晶体学 | 16篇 |
力学 | 53篇 |
综合类 | 18篇 |
数学 | 69篇 |
物理学 | 157篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 18篇 |
2020年 | 44篇 |
2019年 | 26篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 34篇 |
2015年 | 22篇 |
2014年 | 37篇 |
2013年 | 39篇 |
2012年 | 57篇 |
2011年 | 51篇 |
2010年 | 40篇 |
2009年 | 34篇 |
2008年 | 24篇 |
2007年 | 23篇 |
2006年 | 28篇 |
2005年 | 17篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 15篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1997年 | 22篇 |
1996年 | 8篇 |
1995年 | 17篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有769条查询结果,搜索用时 218 毫秒
71.
The first air-stable mononuclear CuI complex (1) based on an unconjugated bisanthryl-tethered diimine ligand has been synthesized and characterized by elemental analysis, ESI-MS, UV-vis, FT-IR spectra and TGA analysis. X-ray diffraction analysis at room temperature reveals that complex 1 crystallizes in a monoclinic system, space group P21/c with a=15.611(3) ?, b=24.412 (5) ?, c=15.430 (6) ?, β=114.49 (3)°, V=5351.3 (19) ?3, ρ
calc=1.359 g cm−3, μ=0.472 mm−1 and Z=4. The crystal structure of 1 features a mononuclear tricoordinated complex with a distorted triagonal planar geometry. The CuI center is coordinated to three imine N atoms of two Schiff base ligands, while the remaining one imine N atom keeps uncoordinated. UV-vis absorption and emission spectra indicate that the complexation of metal ion has slight influence on the electronic structure of the ligand. TGA analysis confirms that complex 1 is stable up to 253°C.Supplementary materials Crystallographic data reported in this paper have been deposited with Cambridge Crystallographic Data center (CCDC no.282672). Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc. cam. ac.uk). 相似文献
72.
紫外线的应用、探测及其新发展 总被引:9,自引:0,他引:9
紫外辐射在电磁辐射波谱中的波长范围为400~10nm。随着波长的变化,紫外线具有各种不同的物理特性和效应。本文概述了各种紫外线效应及其应用,尤其指出了它在军事应用方面的新发展及其广阔前景,例如:紫外线制导,紫外线告警,紫外线通讯和干扰等。上述应用得到了广泛的重视和迅猛的发展。紫外技术的应用与探测技术有关。本文指出了紫外探测的三种方法:紫外荧光转换法,分光光度法和卫星遥感法。并着重指出了上述应用中需解决的有关探测技术方面的关键问题:紫外大气传输理论和散射模型及其仿真系统,新型高灵敏度低噪声紫外探测器,低噪声信息处理系统,高性能紫外光源和紫外光学系统。 相似文献
73.
74.
75.
提出了直接的二的补码阵列算法,基于混合二的补码表达方式,加法,减法和阵列乘法都能全并行地实现。直接算法克服了传统算法中存在的困难,即原理上对操作数的编码位数无限制,更有效地利用了空间带宽积,卷积后的序更直接加权求和即为两数的乘积,复数运算由包含四个区域的两层阵列完成,并进行了光学实验。 相似文献
76.
77.
Chen J Li S Zhang L Li YY Chen J Yang G Li Y 《The journal of physical chemistry. B》2006,110(9):4047-4053
A series of benzophenone (BP) and naphthalene (NA) labeled poly(aryl ether) dendrimers (BP-Gn-NA), generations 1-4, were synthesized, and their photophysical properties were examined. Flash photolysis demonstrates that the triplet energy in BP-Gn-NA can be transferred from the peripheral BP chromophores to the core NA group with the efficiencies of ca. 0.97, 0.96, 0.88, and 0.54 and with the rate constants of 1.4x10(8), 1.2x10(8), 9.5x10(7), and 1.3x10(7) s-1 at room temperature for generations 1-4, respectively. The transient absorption spectra of BP-Gn-NA show clearly the formation of the triplet NA absorption along with the decay of the triplet BP one with an isosbestic point at 475 nm, which gives direct evidence of the triplet energy transfer from the periphery BP chromphores to the core NA group. The phosphorescence of the NA group attached to the focal point was observed when the periphery BP chromophores were selectively irradiated in BP-G1-NA at 77 K. The triplet energy transfer occurs at 77 K with the efficiencies of 1.0, 0.16, 0.17, and 0.21 for generations 1-4, respectively. The intramolecular triplet energy transfer is proposed to proceed mainly via a through space mechanism. 相似文献
78.
Feng G Mareque-Rivas JC Williams NH 《Chemical communications (Cambridge, England)》2006,(17):1845-1847
Introducing ligand based hydrogen bond donors to increase the activity of a mononuclear Zn(II) complex for catalysing phosphate ester cleavage can be a more effective strategy than making the dinuclear analogue. 相似文献
79.
Yongbo Bian Jin Guo Changzheng Gao Chunguang Li Hong Li Jia Wang Bin Cui Xiaofeng He Chao Li Na Li Guoqiang Li Qiang Zhang Xueqiang Zhang Jibao Meng Yusheng He 《Physica C: Superconductivity and its Applications》2010,470(15-16):617-621
This paper presents a miniaturized high performance high temperature superconducting (HTS) microwave receiver front-end subsystem, which uses a mini stirling cryocooler to cool a high selective HTS filter and a low noise amplifier (LNA). The HTS filter was miniaturized by using specially designed compact resonators and fabricating with double-sided YBCO films on LAO substrate which has a relatively high permittivity. The LNA was specially designed to work at cryogenic temperature with noise figure of 0.27 dB at 71 K. The mini cryocooler, which is widely used in infrared detectors, has a smaller size (60 mm × 80 mm × 100 mm) and a lighter weight (340 g) than the stirling cryocoolers commonly used in other HTS filter subsystem. The whole front-end subsystem, including a HTS filter, a LNA, a cryocooler and the vacuum chamber, has a size of only φ120 mm × 175 mm and a weight of only 3.3 kg. The microwave devices inside the subsystem are working at 71.8 K with a consumed cooling power of 0.325 W. The center frequency of this subsystem is 925.2 MHz and the bandwidth is 2.7 MHz (which is a fractional bandwidth of 0.2%), with the gain of 19.75 dB at center frequency and the return loss better than ?18.11 dB in the pass band. The stop band rejection is more than 60 dB and the skirt slope is exceeding 120 dB MHz?1. The noise figure of this subsystem is less than 0.8 dB. This front-end subsystem can be used in radars and communication systems conveniently due to it’s compact size and light weight. 相似文献
80.
Guoqiang Zhao 《Algebras and Representation Theory》2018,21(1):163-179
For a class of modules \(\mathcal {X}\), we introduce the \(\mathcal {X}\)-transpose of a module with respect to a bimodule, which unifies some well-known transposes. Let \(\mathcal {V}\) be a subclass of \(\mathcal {X}\). The relations between \(\mathcal {X}\)-transposes and \(\mathcal {V}\)-transposes are investigated under the condition that \(\mathcal {V}\) is a generator or cogenerator of \(\mathcal {X}\). The dual aspects of \(\mathcal {X}\)-transposes are also discussed. Then we give some applications of these results. In particular, the dual counterparts of Gorenstein transposes are established. 相似文献