全文获取类型
收费全文 | 2133篇 |
免费 | 636篇 |
国内免费 | 287篇 |
专业分类
化学 | 1058篇 |
晶体学 | 22篇 |
力学 | 77篇 |
综合类 | 31篇 |
数学 | 278篇 |
物理学 | 1590篇 |
出版年
2024年 | 6篇 |
2023年 | 27篇 |
2022年 | 61篇 |
2021年 | 48篇 |
2020年 | 59篇 |
2019年 | 56篇 |
2018年 | 76篇 |
2017年 | 99篇 |
2016年 | 91篇 |
2015年 | 103篇 |
2014年 | 187篇 |
2013年 | 149篇 |
2012年 | 185篇 |
2011年 | 216篇 |
2010年 | 174篇 |
2009年 | 161篇 |
2008年 | 172篇 |
2007年 | 175篇 |
2006年 | 141篇 |
2005年 | 147篇 |
2004年 | 106篇 |
2003年 | 106篇 |
2002年 | 63篇 |
2001年 | 62篇 |
2000年 | 46篇 |
1999年 | 39篇 |
1998年 | 40篇 |
1997年 | 44篇 |
1996年 | 35篇 |
1995年 | 40篇 |
1994年 | 26篇 |
1993年 | 15篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
排序方式: 共有3056条查询结果,搜索用时 125 毫秒
921.
K.H. Lee 《Solid State Communications》2011,151(12):900-903
We have studied the vortex dynamics in a ratchet array of Josephson junctions in the presence of magnetic field of 1/5 flux quantum per plaquette. The ratchet potential consists of both alternate critical currents for all the vertical junctions and alternate shunt capacitances for all the horizontal junctions. The vortices driven by an ac current in some parameters are found to show the directional motion as well as the asymmetric current-voltage characteristics. We use the time-dependent vorticity and the time-dependent vorticity-vorticity correlation function to analyze the motion of vortices on a few fractional Shapiro steps. We have found that vortices on a fractional Shapiro n/5-step move coherently through n plaquettes during a single ac cycle. The asymmetric features of the ratchet array gradually disappear as finite temperature increases. 相似文献
922.
In this work the moving ultrasound linear array technique has been used to perform 3D echographic images of different human hands, in order to evaluate this technique to biometric recognition purposes. An automated set up, based on a commercial echographic machine provided with a high frequency (12 MHz) linear array, has been built up. The probe is moved in the direction orthogonal to the array and at each step a B-scan is performed and stored to form a 3D matrix representing the under skin hand volume.B-scan and C-scan images of the hand of different users were analysed and compared. The results have shown that, in the analysed region (about 10 mm under the palm skin), there are several anatomic elements (including hand bones, bending tendons, muscle tissue, blood vessels) that can be exploited for measurements of biometric parameters.The characteristics of the proposed technique are compared with those of the 2D optical hand geometry, which is a well established biometric technique, and its possible advantages are underlined and discussed. 相似文献
923.
This paper presents a parametric study on the efficiency of ultrasound focusing in an attenuative medium, using phased arrays. Specifically, an analytical model of ultrasound wave focusing in a homogeneous, isotropic and attenuative fluid with point sources is presented. Calculations based on the model have shown that in an attenuative medium, an optimum frequency exists for the best focusing performance for a particular size of aperture and focal distance. The effect of different f numbers on the focusing performance in the attenuative medium is further investigated. The information obtained from the analytical model provides insights into the design and installation of a phased transducer array for energy efficient wave focusing. 相似文献
924.
Xiang FengXiang Qi Jun LiLiwen Yang Mengchun QiuJinjie Yin Fang LuJianxin Zhong 《Applied Surface Science》2011,257(13):5571-5575
Bi2SiO5 modified Si nanowire array films were fabricated as photo-catalysts via dip-coating Bi(NO3)3 on silver-assisted electroless wet chemical etching Si nanowires and subsequently annealing. The structures and morphologies of as-prepared samples are characterized by X-ray diffraction, Fourier transform infrared spectrum, scanning electron microscopy and transmission electron microscopy. The results of photocatalytic experiments indicated that the Bi2SiO5 modified Si nanowire arrays benefit the improvement for efficient electron-hole separation and photo-catalytic stability, thereby possessing superior photo-degradation performance. These hybrid nanowire arrays will be promising materials for photo-catalysts and degradation agents. 相似文献
925.
Hui ZhaoWuyou Fu Haibin YangYang Xu Wenyan ZhaoYanyan Zhang Hui ChenQiang Jing Xuefeng QiJing Cao Xiaoming ZhouYixing Li 《Applied Surface Science》2011,257(21):8778-8783
TiO2/Fe2O3 core-shell nanocomposition film has been fabricated via two-step method. TiO2 nanorod arrays are synthesized by a facile hydrothermal method, and followed by Fe2O3 nanoparticles deposited on TiO2 nanorod arrays through an ordinary chemical bath deposition. The phase structures, morphologies, particle size, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer. The results confirm that Fe2O3 nanoparticles of mean size ca. 10 nm coated on the surface of TiO2 NRs. After depositing Fe2O3, UV-vis absorption property is induces the shift to the visible-light range, the annealing temperature of 600 °C is the best condition for UV-vis absorption property of TiO2/Fe2O3 nanocomposite film, and increasing Fe content, optical activity are enhanced one by one. The photoelectrochemical (PEC) performances of the as-prepared composite nanorods are determined by measuring the photo-generated currents under illumination of UV-vis light. The TiO2 NRs modified by Fe2O3 show the photocurrent value of 1.36 mA/cm2 at 0 V vs Ag/AgCl, which is higher than those of unmodified TiO2 NRs. 相似文献
926.
927.
基于面阵CCD的时间延时积分模式的空间相机自动对焦 总被引:1,自引:0,他引:1
空间面阵相机在轨运动会产生运动模糊,影响自动对焦准确率。为解决该问题,提出行间转移面阵CCD的时间延时积分(TDI)模式实现去运动模糊。选取行间转移面阵CCD KAI-1003作为成像器件,利用可编程逻辑器件(PLD)控制时序信号,匹配CCD的行转移速度与目标运动速度,实现去运动模糊。实验表明该成像系统不仅能去运动模糊而且还大幅提高图像信噪比。去运动模糊后,根据较短时间间隔内空间相机拍摄的图像有重叠区域的特点提出一种空间相机自动对焦方法。通过配准算法找出序列图像间的重叠区域,并计算重叠区域的清晰度评价值,然后根据传递特性将评价值映射到同一个评价体系中,最后找到最佳对焦位置。实验表明该成像系统对高速运动的目标能够实现自动对焦。 相似文献
928.
A Glycan Array‐Based Assay for the Identification and Characterization of Plant Glycosyltransferases
Colin Ruprecht Max P. Bartetzko Deborah Senf Anna Lakhina Peter J. Smith Maria J. Soto Hyunil Oh Jeong‐Yeh Yang Digantkumar Chapla Daniel Varon Silva Mads H. Clausen Michael G. Hahn Kelley W. Moremen Breeanna R. Urbanowicz Fabian Pfrengle 《Angewandte Chemie (International ed. in English)》2020,59(30):12493-12498
Growing plants with modified cell wall compositions is a promising strategy to improve resistance to pathogens, increase biomass digestibility, and tune other important properties. In order to alter biomass architecture, a detailed knowledge of cell wall structure and biosynthesis is a prerequisite. We report here a glycan array‐based assay for the high‐throughput identification and characterization of plant cell wall biosynthetic glycosyltransferases (GTs). We demonstrate that different heterologously expressed galactosyl‐, fucosyl‐, and xylosyltransferases can transfer azido‐functionalized sugar nucleotide donors to selected synthetic plant cell wall oligosaccharides on the array and that the transferred monosaccharides can be visualized “on chip” by a 1,3‐dipolar cycloaddition reaction with an alkynyl‐modified dye. The opportunity to simultaneously screen thousands of combinations of putative GTs, nucleotide sugar donors, and oligosaccharide acceptors will dramatically accelerate plant cell wall biosynthesis research. 相似文献
929.
A Palladium‐Nanoparticle and Silicon‐Nanowire‐Array Hybrid: A Platform for Catalytic Heterogeneous Reactions 下载免费PDF全文
Dr. Yoichi M. A. Yamada Yoshinari Yuyama Dr. Takuma Sato Dr. Shigenori Fujikawa Dr. Yasuhiro Uozumi 《Angewandte Chemie (International ed. in English)》2014,53(1):127-131
We report the development of a silicon nanowire array‐stabilized palladium nanoparticle catalyst, SiNA‐Pd. Its use in the palladium‐catalyzed Mizoroki‐Heck reaction, the hydrogenation of an alkene, the hydrogenolysis of nitrobenzene, the hydrosilylation of an α,β‐unsaturated ketone, and the C‐H bond functionalization reactions of thiophenes and indoles achieved a quantitative production with high reusability. The catalytic activity reached several hundred‐mol ppb of palladium, reaching a TON of 2 000 000. 相似文献
930.
A LecA Ligand Identified from a Galactoside‐Conjugate Array Inhibits Host Cell Invasion by Pseudomonas aeruginosa 下载免费PDF全文
Dr. Alexandre Novoa Dr. Thorsten Eierhoff Dr. Jérémie Topin Dr. Annabelle Varrot Dr. Sofia Barluenga Dr. Anne Imberty Prof. Winfried Römer Prof. Nicolas Winssinger 《Angewandte Chemie (International ed. in English)》2014,53(34):8885-8889
Lectin LecA is a virulence factor of Pseudomonas aeruginosa involved in lung injury, mortality, and cellular invasion. Ligands competing with human glycoconjugates for LecA binding are thus promising candidates to counteract P. aeruginosa infections. We have identified a novel divalent ligand from a focused galactoside(Gal)‐conjugate array which binds to LecA with very high affinity (Kd=82 nM ). Crystal structures of LecA complexed with the ligand together with modeling studies confirmed its ability to chelate two binding sites of LecA. The ligand lowers cellular invasiveness of P. aeruginosa up to 90 % when applied in the range of 0.05–5 μM . Hence, this ligand might lead to the development of drugs against P. aeruginosa infection. 相似文献