全文获取类型
收费全文 | 3426篇 |
免费 | 334篇 |
国内免费 | 485篇 |
专业分类
化学 | 1929篇 |
晶体学 | 12篇 |
力学 | 64篇 |
综合类 | 36篇 |
数学 | 81篇 |
物理学 | 851篇 |
无线电 | 1272篇 |
出版年
2024年 | 16篇 |
2023年 | 74篇 |
2022年 | 151篇 |
2021年 | 193篇 |
2020年 | 187篇 |
2019年 | 104篇 |
2018年 | 87篇 |
2017年 | 140篇 |
2016年 | 166篇 |
2015年 | 183篇 |
2014年 | 203篇 |
2013年 | 279篇 |
2012年 | 233篇 |
2011年 | 242篇 |
2010年 | 154篇 |
2009年 | 177篇 |
2008年 | 206篇 |
2007年 | 202篇 |
2006年 | 190篇 |
2005年 | 180篇 |
2004年 | 128篇 |
2003年 | 131篇 |
2002年 | 101篇 |
2001年 | 79篇 |
2000年 | 78篇 |
1999年 | 58篇 |
1998年 | 39篇 |
1997年 | 33篇 |
1996年 | 27篇 |
1995年 | 41篇 |
1994年 | 34篇 |
1993年 | 17篇 |
1992年 | 24篇 |
1991年 | 8篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 16篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
排序方式: 共有4245条查询结果,搜索用时 15 毫秒
81.
A robust system for backlit keyboard inspection is revealed. The backlit keyboard not only has changeable diverse colors but also has the laser marking keys. The keys on the keyboard can be divided into regions of function keys, normal keys, and number keys. However, there might have some types of defects:incorrect illuminating area, non-uniform illumination of specified inspection region (IR), and incorrect luminance and intensity of individual key. Since the illumination features of backlit keyboard are too complex to inspect for human inspector in the production line, an auto-mated inspection system for the backlit keyboard is proposed in this paper. The system was designed into the operation module and inspection module. A set of image processing methods were developed for these defects inspection. Some experimental results demonstrate the robustness and effectiveness of the proposed system. 相似文献
82.
机器人的视觉相当于机器人的眼睛,机器人视觉系统是当下研究热点。本文主要研究基于视觉信息的机器人系统,通过对获得的图像信息的处理来实现对机器人的控制。详细讨论了摄像机标定、图像处理等方面的设计,实现了对机器人控制系统的设计。 相似文献
83.
84.
为了实现玻璃中气泡尺寸的在线测量,基于激光视觉原理,采用线结构激光器、线阵CCD相机和运动控制系统在实验室搭建玻璃气泡的动态测量系统。投射到玻璃表面的线结构激光光斑经变焦镜头成像在相机的光敏阵列上,相机的横向扫描与运动平台的纵向扫描配合,利用Sapera CamExpert图像采集软件获得玻璃气泡的灰度图像;理论上讨论了图像的纵向和横向精度,给出了气泡图像失真的判断依据及工作像素时钟频率与玻璃板纵向运动速率之间的匹配关系;采集了不同纵向运动速率下气泡的灰度图像,利用Sapera Architect软件测量气泡图像的横向和纵向像素数,通过理论计算得出气泡的横向和纵向尺寸,并与直尺测量结果比较,发现纵向尺寸相对误差为0.18,横向尺寸相对误差为0.05。结果表明,在相机工作距离、焦距和像元尺寸确定的情况下在误差允许的范围内该系统可以用来测量气泡的横向尺寸。 相似文献
85.
Multifunctional Silver‐Exchanged Zeolite Micromotors for Catalytic Detoxification of Chemical and Biological Threats 下载免费PDF全文
Virendra V. Singh Beatriz Jurado‐Sánchez Sirilak Sattayasamitsathit Jahir Orozco Jinxing Li Michael Galarnyk Yuri Fedorak Joseph Wang 《Advanced functional materials》2015,25(14):2147-2155
Multifunctional reactive‐zeolite‐based micromotors have been developed and characterized toward effective and rapid elimination of chemical and biological threats. The incorporation of silver ions (Ag+) into aluminosilicate zeolite framework imparts several attractive functions, including strong binding to chemical warfare agents (CWA) followed by effective degradation, and enhanced antibacterial activity. The new zeolite‐micromotors protocol thus combines the remarkable adsorption capacity of zeolites and the efficient catalytic properties of the reactive Ag+ ions with the autonomous movement of the zeolite micromotors for an accelerated detoxification of CWA. Furthermore, the high antibacterial activity of Ag+ along with the rapid micromotor movement enhances the contact between bacteria and reactive Ag+, leading to a powerful “on‐the‐fly” bacteria killing capacity. These attractive adsorptive/catalytic features of the self‐propelled zeolite micromotors eliminate secondary environmental contamination compared to adsorptive micromotors. The distinct cubic geometry of the zeolite micromotors leads to enhanced bubble generation and faster movement, in unique movement trajectories, which increases the fluid convection and highly efficient detoxification of CWA and killing of bacteria. The attractive capabilities of these zeolite micromotors will pave the way for their diverse applications in defense, environmental and biomedical applications in more economical and sustainable manner. 相似文献
86.
The title compound, neogeodin hydrate (C17H14C1208, CAS: 94540-50-8), was derived from marine fungus Aspergilhts terreus CRIM301. It was unequivocally characterized by IR, NMR spectroscopies, and single-crystal X-ray crystallography and tested for various biological activities. Neogeodin hydrate crystallizes in the triclinic space group P1 with a = 8.1159(5) A, b = 8.2472(4) A, c= 14.1278(7) A, a = 81.448(2)°, β = 84.860(2)°, γ= 70.400(2)°, V = 880.13(8) A3; Z = 2. It comprises a diphenyl ether, asterric acid skeleton and dichloro substituents. The methoxyphenoxy rings of the inversely related molecules form a ribbon-like structure that is stabilized by O-H...O hydrogen bonds through the doubly disordered carboxyl groups and by C-H...O interactions, generating the same R22(8) ring motif. The chlorinated methylbenzoate rings, making mostly a right angle, link the parallel upper and lower ribbons via bifurcated O-H...O and C-H...O hydrogen bonds, yielding endless channels. The channels formed are further sustained by C-H...O and π...π interactions Neogeodin hydrate exhibits inhibition against superoxide anion radical formation in the xanthine/xanthine oxidase (XXO) assay, but has no aromatase inhibitory activity. 相似文献
87.
夜视战场环境视觉传感信息的实时获取是跟踪夜视战场图像处理分析的前提,针对夜视战场环境的复杂特征,设计了夜视战场环境视觉传感信息采集系统,分析了系统的总体结构,系统硬件主要包括视觉传感器、传感器控制卡和扩展卡、图像采集与存储以及信号调理电路,给出了系统采集节点的程序设计流程以及传感信息采集的具体程序代码实现过程。实验结果说明,所设计系统可有效采集到夜间军事战场中的传感信息,并且具有较高的采集精度。 相似文献
88.
Kucerka N Pencer J Nieh MP Katsaras J 《The European physical journal. E, Soft matter》2007,23(3):247-254
The influence of cholesterol on the structure of unilamellar-vesicle (ULV) phospholipid bilayers is studied using small-angle
neutron scattering. ULVs made up of short-, mid- and long-chain monounsaturated phospholipids (diCn :1PC, n = 14 , 18, 22, respectively) are examined over a range (0-45mol %) of cholesterol concentrations. Cholesterol's effect on
bilayer structure is characterized through changes to the lipid's transmembrane thickness, lateral area and headgroup hydration.
For all three lipids, analysis of the experimental data shows that the addition of cholesterol results in a monotonic increase
of these parameters. In the case of the short- and mid-chain lipids, this is an expected result, however, such a finding was
unexpected for the long-chain lipid. This implies that cholesterol has a pronounced effect on the lipid's hydrocarbon chain
organization. 相似文献
89.
This paper investigates finite-stretching corrections
to the classical Milner-Witten-Cates theory for semi-dilute
polymer brushes in a good solvent. The dominant correction to the
free energy originates from an entropic repulsion caused by the
impenetrability of the grafting surface, which produces a
depletion of segments extending a distance μ∝L-1
from the substrate, where L is the classical brush height. The
next most important correction is associated with the
translational entropy of the chain ends, which creates the
well-known tail where a small population of chains extend beyond
the classical brush height by a distance ξ∝L-1/3.
The validity of these corrections is confirmed by quantitative
comparison with numerical self-consistent field theory. 相似文献
90.