全文获取类型
收费全文 | 15310篇 |
免费 | 2966篇 |
国内免费 | 2904篇 |
专业分类
化学 | 6570篇 |
晶体学 | 415篇 |
力学 | 628篇 |
综合类 | 209篇 |
数学 | 1159篇 |
物理学 | 4683篇 |
无线电 | 7516篇 |
出版年
2024年 | 87篇 |
2023年 | 301篇 |
2022年 | 584篇 |
2021年 | 644篇 |
2020年 | 585篇 |
2019年 | 520篇 |
2018年 | 517篇 |
2017年 | 673篇 |
2016年 | 628篇 |
2015年 | 846篇 |
2014年 | 1033篇 |
2013年 | 1131篇 |
2012年 | 1323篇 |
2011年 | 1340篇 |
2010年 | 1197篇 |
2009年 | 1277篇 |
2008年 | 1395篇 |
2007年 | 1195篇 |
2006年 | 1123篇 |
2005年 | 970篇 |
2004年 | 708篇 |
2003年 | 545篇 |
2002年 | 468篇 |
2001年 | 497篇 |
2000年 | 465篇 |
1999年 | 219篇 |
1998年 | 103篇 |
1997年 | 123篇 |
1996年 | 88篇 |
1995年 | 85篇 |
1994年 | 95篇 |
1993年 | 63篇 |
1992年 | 55篇 |
1991年 | 51篇 |
1990年 | 33篇 |
1989年 | 42篇 |
1988年 | 26篇 |
1987年 | 19篇 |
1986年 | 25篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1957年 | 2篇 |
1911年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
基于FPGA并行处理的实时图像相关速度计 总被引:3,自引:1,他引:2
研究制作了一种采用高速线阵CCD的实时相关速度计,其测量数据的输出速率可达每秒一万次。针对以往光学相关测速方法的问题进行了讨论,探讨了适合FPGA并行处理的算法,制作了高速线阵CCD摄像机及其处理装置。通过实验验证了系统的可行性和可实现性。 相似文献
32.
本文改进实验方法,在0.0001—1.23GPa流体静高压下测量了整片非晶锂离子导体B2O3-0.7Li2O-0.7LiCl-xAl2O3(x=0.05;0.15)及其粉末压片的离子电导率及激活体积。发现粉末压片电导率峰值是由非晶微粒间的接触电导及非晶微粒体电导两者叠加;对整片非晶电导率的压力效应用离子迁移通道的物理图象给出初步的微观解释。此外,还观测到氧化铝组分减少使电导率的压力转变点明显降低;测量出不同温度热处理以及300℃等温热处理4—20h后离子电导率-压力曲线的变化规律,仍可归因于非晶态相分离及两种非晶相的先后晶化。
关键词: 相似文献
33.
34.
在由低压直流电源供电的电路中,往往电路的某些部位需要使用高于电源所供的电压,将电源所供的低压转换为较高的电压,常用的方法有3种:自举升压、电感升压、逆变升压。结合实际应用电路对各种升压方法从器件选择、升压原理、升压结果等诸方面进行分析、探讨,解决了总体供电电压不变时,局部高压产生的关键性问题。它对电子电器电路的设计人员有一定的启发作用,对优化电路、遴选器件有较强的参考价值。 相似文献
35.
On effective offloading services for resource-constrained mobile devices running heavier mobile internet applications 总被引:1,自引:0,他引:1
Kun Yang Shumao Ou Hsiao-Hwa Chen 《Communications Magazine, IEEE》2008,46(1):56-63
Rapid advances in wireless mobile network technologies and mobile handsets (MHs) facilitate ubiquitous infrastructure that can support a range of mobile services and applications in addition to conventional mobile Internet access. One recent trend is to effectively run desktop PC-oriented heavier applications on MHs. However, due to their miniature, portable size, MHs are resource-constrained and therefore, running these applications directly on an MH is not satisfactory given a user's expectations. To cope with this problem, this article proposes a novel offloading service that can seamlessly offload some of the tasks of a mobile application from an MH to nearby, resource-rich PCs (called surrogates). The system architecture and key components of the proposed offloading service are presented, prototyped, and evaluated. The results of experiments and simulations have demonstrated the effectiveness and efficiency of this offloading service for mobile applications. 相似文献
36.
WANG Mingwei LI Bo FENG Kun RAO Jun KANG Zihua LI Xiujuan LILi WANG Minghong FAN Mingjie 《核工业西南物理研究院年报(英文版)》2004,(1):77-79
in order to study non-indutive plasma current production, the lower hybrid current drive(LHCD) experiment on the HL-2A tokamak is carried out. Simultaneously a microcomputer has been used to control the whole LHCD system. During the experiment this year, we can monitor and protect the LHCD system by use of the microcomputer control system, which will imediately switch off the microwave power to be launched into the tokamak if the plasma is disrupted. All this ensure that the microwave is injected into the equipment correctly. 相似文献
37.
38.
资源有限的加权总完工时间单机排序问题 总被引:1,自引:0,他引:1
本讨论资源有限的加权总工时间单机排序问题,对现在仍为OPEN问题1|pj=bj-ajuj,∑uj≤U|∑wjCj给出了一个有关最优解中最优资源分配的重要性质,并利用该性质分别给出了三种情况bj=b,wj=w,aj=a;bj=b,wj=w,uj=u;aj=a,wj=w,uj=u的最优算法。 相似文献
39.
A least‐squares meshfree method based on the first‐order velocity–pressure–vorticity formulation for two‐dimensional incompressible Navier–Stokes problem is presented. The convective term is linearized by successive substitution or Newton's method. The discretization of all governing equations is implemented by the least‐squares method. Equal‐order moving least‐squares approximation is employed with Gauss quadrature in the background cells. The boundary conditions are enforced by the penalty method. The matrix‐free element‐by‐element Jacobi preconditioned conjugate method is applied to solve the discretized linear systems. Cavity flow for steady Navier–Stokes problem and the flow over a square obstacle for time‐dependent Navier–Stokes problem are investigated for the presented least‐squares meshfree method. The effects of inaccurate integration on the accuracy of the solution are investigated. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
40.
Jem‐Kun Chen I‐Kuan Lin Fu‐Hsiang Ko Chih‐Feng Huang Kuo‐Shen Chen Chia‐Hao Chan Feng‐Chih Chang 《Journal of Polymer Science.Polymer Physics》2004,42(22):4063-4074
Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF4 plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004 相似文献