全文获取类型
收费全文 | 1868篇 |
免费 | 42篇 |
国内免费 | 255篇 |
专业分类
化学 | 1125篇 |
力学 | 55篇 |
综合类 | 19篇 |
数学 | 331篇 |
物理学 | 635篇 |
出版年
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 3篇 |
2013年 | 24篇 |
2012年 | 40篇 |
2011年 | 387篇 |
2010年 | 184篇 |
2009年 | 256篇 |
2008年 | 35篇 |
2007年 | 30篇 |
2006年 | 69篇 |
2005年 | 136篇 |
2004年 | 337篇 |
2003年 | 193篇 |
2002年 | 109篇 |
2001年 | 109篇 |
2000年 | 21篇 |
1999年 | 25篇 |
1998年 | 23篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 36篇 |
1992年 | 30篇 |
1991年 | 10篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1986年 | 5篇 |
1982年 | 1篇 |
排序方式: 共有2165条查询结果,搜索用时 156 毫秒
91.
XU ShangJin WU ZhengFei & DENG YunPing College of Mathematics Information Science Guangxi University Nanning 《中国科学A辑(英文版)》2009,(2)
A graph is said to be s-arc-regular if its full automorphism group acts regularly on the set of its s-arcs. In this paper, we investigate connected cubic s-arc-regular Cayley graphs of finite nonabelian simple groups. Two suffcient and necessary conditions for such graphs to be 1- or 2-arc-regular are given and based on the conditions, several infinite families of 1-or 2-arc-regular cubic Cayley graphs of alternating groups are constructed. 相似文献
92.
Jinxia Gua b Zhipeng Baib Weifang Lib Liping Wua Aixia Liuc Haiyan Dongd Yiyang Xiec a Tianjin Institute of Urban Construction Tianjin China b State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention Control College of Environmental Science Engineering Nankai University Tianjin China c Tianjin Institute of Meteorological Instruments Tianjin China d Tianjin Environmental Monitoring Central Station Tianjin China 《中国颗粒学报》2011,(3)
PM2.5 samples for 24 h were collected during winter in Tianjin,China. The ambient mass concentration and chemical composition of the PM2.5 were determined. Ionic species were analyzed by ion chromatog-raphy,while carbonaceous species were determined with the IMPROVE thermal optical reectance(TOR) method,and inorganic elements were measured by inductively coupled plasma-atomic emission spec-trometer. The daily PM2.5 mass concentrations ranged from 48.2 to 319.2 g/m3 with an arithmetic average of 144.6 g/m3. ... 相似文献
93.
Zheng Wang Wei Zhang Feng Tao Kai Ge Meng Long Yi Xi Ying Li Qing Jiang 《中国化学快报》2011,22(8):1001-1004
Two novel copolymers based on squaraine and fluorine units have been synthesized through palladium catalyzed Suzuki coupling reaction and Sonogashira coupling reaction,respectively.The structures and properties of the two copolymers were characterized by FT-IR.NMR,UV-vis absorbance(Abs),gel permeation chromatography(GPC),thermal gravimetric analysis (TGA),differential scanning calorimetry(DSC) and cyclic voltammetry(CV).The solution absorption spectrums of P1 and P2 show two distinct absorption bands,one locates at 300-500 nm and the other at 600-800 nm.The absorption spectrums of P1 and P2 in films are broadened obviously and the spectral responses are extended up to 900 nm.Thermal gravimetric analysis demonstrates that the polymers are stable.Cyclic voltammetry experiment shows that the band gaps of the copolymers are 1.65 eV and 1.67 eV. respectively,suggesting their potential for applications as solar cells materials. 相似文献
94.
A novel approach to the synthesis of 4-phenylethynylphthalic anhydride has been described.The target compound was synthesized by Pd/Cu catalyzed Sonogashira coupling reaction between phenylacetylene and 4-bromophthalic acid which was for the first time employed as start material,followed by dehydration of 4-phenylethynylphthalic acid.Compared with traditional synthetic routes,this method provides several advantages such as readily available raw materials,convenient manipulation and high yield.The product... 相似文献
95.
LI ShuXia SUN PuNan & XIAO DeHang College of Physical Science Technology Heilongjiang University Harbin China 《中国科学:物理学 力学 天文学(英文版)》2011,(5)
We examine two-pion Bose-Einstein correlations for partially coherent particle-emitting sources within quantum statistical formalism, where the sources are treated as classical currents with chaotic and coherent components. The two-pion correlation functions of the partially coherent sources contain a phase which is sensitive to the asymmetry of the source emission function. We investigate the influence of source opacity and expansion in high energy heavy ion collisions on the phase by Monte Carlo calculati... 相似文献
96.
System calibration, which usually involves complicated and time-consuming procedures, is crucial for any three-dimensional (3D) shape measurement system based on vision. A novel improved method is proposed for accurate calibration of such a measurement system. The system accuracy is improved with considering the nonlinear measurement error created by the difference between the system model and real measurement environment. We use Levenberg-Marquardt optimization algorithm to compensate the error and get a good result. The improved method has a 50% improvement of re-projection accuracy compared with our previous method. The measurement accuracy is maintained well within 1.5% of the overall measurement depth range. 相似文献
97.
<正>SnO_2 nanorods were deposited on the Si substrates in an aqueous solution containing both SnCl_4 and CO(NH_2)_2.It is found that different self-assembled patterns of SnO_2 nanorods can be obtained by changing the deposition conditions such as the molar ratio of CO(NH_2)_2 to SnCl_4 and the pretreatment of the substrate.Scattered SnO_2 nanorods,for example,can be changed into flower-like patterns when the molar ratio of CO(NH_2)_2 to SnCl_4 is raised,and well-aligned nanorod arrays can be formed when the pretreatment of the substrate is changed.In addition,some interesting patterns,e.g.tree-like patterns,can also be observed. 相似文献
98.
研究了桂枝和桂皮醛对环丙沙星在小鼠体内分布的影响,并基于此探讨了桂枝作为引药使用的作用机制.实验中将小鼠分为三组,分别灌胃生理盐水、桂枝(50gkg-1)和桂皮醛(0.25mLkg-1),然后对三组小鼠尾静脉注射环丙沙星(20mgkg-1),并以荧光法测定不同时间点小鼠体内各组织中环丙沙星的浓度.结果显示桂枝、桂皮醛均促进了环丙沙星在四肢的分布,桂枝与桂皮醛组相对于生理盐水组可将环丙沙星在四肢的含量提高约40%~200%,证实了桂枝引药到达肢节的作用.桂枝与桂皮醛组对环丙沙星分布情况的影响没有显著性差异,说明桂皮醛很可能是发挥桂枝引药作用的主要物质. 相似文献
99.
ZHANG ZhaoXiang ZHANG XiaoWei & LI Feng Key Laboratory of Eco-Chemical Engineering Ministry of Education College of Chemistry Molecular Engineering Qingdao University of Science Technology Qingdao China School of Science Qingdao Technological University Qingdao China 《中国科学:化学》2010,(5)
A novel method has been developed by integration of multi-concentration and two-dimensional(2D) capillary electrophoresis(CE) for simultaneous enhancement of detection sensitivity and separation power in complex samples.Capillary zone electrophoresis(CZE) was used as the first dimension separation according to mobilities,from which the effluent fractions were further analyzed by micellar electrokinetic capillary chromatography(MEKC) acting as the second dimension.Cation-selective exhaustive injection(CSEI) ... 相似文献
100.
Wei Shuo FANG* Qi Cheng FANG Xiao Tian LIANG Institute of Materia Medica Chinese Academy of Medical Sciences Peking Union Medical College Xian Nong Tan Street Beijing 《中国化学快报》2001,(8)
Numerous efforts towards synthesis of anticancer drug paclitaxel (Taxol(r), 1a) with improved activities led to the modification at 13-phenylisoserine side chain and different positions of its core structure-baccatin III 1c1. At the same time, the activities of searching new taxoids for starting materials of new semi-synthetic paclitaxel analogs from Taxus spp. plant have not ever been stopped. Among these taxoids, 14?-hydroxy-10-deacetylbaccatin III 22 and 13-acetyl-9-dihydrobaccatin III … 相似文献