全文获取类型
收费全文 | 6752篇 |
免费 | 1031篇 |
国内免费 | 483篇 |
专业分类
化学 | 950篇 |
晶体学 | 19篇 |
力学 | 1144篇 |
综合类 | 79篇 |
数学 | 802篇 |
物理学 | 5272篇 |
出版年
2024年 | 6篇 |
2023年 | 45篇 |
2022年 | 122篇 |
2021年 | 125篇 |
2020年 | 138篇 |
2019年 | 102篇 |
2018年 | 109篇 |
2017年 | 257篇 |
2016年 | 282篇 |
2015年 | 258篇 |
2014年 | 415篇 |
2013年 | 416篇 |
2012年 | 390篇 |
2011年 | 450篇 |
2010年 | 330篇 |
2009年 | 401篇 |
2008年 | 460篇 |
2007年 | 477篇 |
2006年 | 400篇 |
2005年 | 351篇 |
2004年 | 332篇 |
2003年 | 306篇 |
2002年 | 267篇 |
2001年 | 281篇 |
2000年 | 236篇 |
1999年 | 189篇 |
1998年 | 165篇 |
1997年 | 174篇 |
1996年 | 143篇 |
1995年 | 121篇 |
1994年 | 73篇 |
1993年 | 77篇 |
1992年 | 56篇 |
1991年 | 48篇 |
1990年 | 42篇 |
1989年 | 33篇 |
1988年 | 35篇 |
1987年 | 30篇 |
1986年 | 12篇 |
1985年 | 30篇 |
1984年 | 23篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有8266条查询结果,搜索用时 15 毫秒
11.
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
12.
Software failures have become the major factor that brings the system down or causes a degradation in the quality of service. For many applications, estimating the software failure rate from a user's perspective helps the development team evaluate the reliability of the software and determine the release time properly. Traditionally, software reliability growth models are applied to system test data with the hope of estimating the software failure rate in the field. Given the aggressive nature by which the software is exercised during system test, as well as unavoidable differences between the test environment and the field environment, the resulting estimate of the failure rate will not typically reflect the user‐perceived failure rate in the field. The goal of this work is to quantify the mismatch between the system test environment and the field environment. A calibration factor is proposed to map the failure rate estimated from the system test data to the failure rate that will be observed in the field. Non‐homogeneous Poisson process models are utilized to estimate the software failure rate in both the system test phase and the field. For projects that have only system test data, use of the calibration factor provides an estimate of the field failure rate that would otherwise be unavailable. For projects that have both system test data and previous field data, the calibration factor can be explicitly evaluated and used to estimate the field failure rate of future releases as their system test data becomes available. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
13.
Fiber-optic reflex sensor for in-line production measurement 总被引:1,自引:0,他引:1
The paper describes experiments concerning distance measurement with fiber-optic sensor and improvement of the measurement principle. The sensor probe was well-designed with a small structure and multi-function. The novel optical fiber probe arrangement as well as the possibilities of use for complex measurement problems are explained using the measurement of an internal screw thread as an example. The experimental results show that the measurement uncertainty of the thread minor diameter can reach ±10 μm, and the stability of the measurement system is better than 0.07%. 相似文献
14.
15.
Assisted Cloning and Orthogonal Complementing of an Arbitrary Unknown Two-Qubit Entangled State 总被引:1,自引:0,他引:1
Based on A.K. Pati‘s original idea [Phys. Rev. A 61 (2000) 022308] on single-qubit-state-assisted clone, very recently Zhan has proposed two assisted quantum cloning protocols of a special class of unknown two-qubit entangled states [Phys. Lett. A 336 (2005) 317]. In this paper we further generalize Zhan‘s protocols such that an arbitrary unknown two-qubit entangled state can be treated. 相似文献
16.
17.
Relying on reliability growth testing to improve system designis neither usually effective nor efficient. Instead it is importantto design in reliability. This requires models to estimate reliabilitygrowth in the design that can be used to assess whether goalreliability will be achieved within the target timescale forthe design process. Many models have been developed for analysisof reliability growth on test, but there has been much lessattention given to reliability growth in design. This paperdescribes and compares two models: one motivated by the practicalengineering process; the other by extending the reasoning ofstatistical reliability growth modelling. Both models are referencedin the recently revised edition of international standard IEC61164. However, there has been no reported evaluation of theirproperties. Therefore, this paper explores the commonalitiesand differences between these models through an assessment oftheir logic and their application to an industrial example.Recommendations are given for the use of reliability growthmodels to aid management of the design process and to informproduct development. 相似文献
18.
Noboru Nakatani 《Optical Review》2003,10(4):206-210
This paper describes a compulsorily phase locked differential interferometer using an orthogonally polarized light source of a modulated LD with high extinction ratio to reduce non-linearity of the interferometer caused by polarization cross-talk. The current modulated LD is used as a light source to make the interferometer compact and for the scanning phase of the interferometer. The interferometer is operated compulsorily at the maximum inclination point of the fringe intensity curve by fringe scanning and an electric system. A Wollaston prism of high extinction ratio (50 dB) is used to combine the polarizing beams and to make the polarization cross-talk very small. In one light source the polarized output beams are on the same propagation axis; in the other they have a small crossing angle (2.5 mrad ∼ 10 mrad) to completely exclude non-linearity of the interferometer causded by polarization cross-talk. Using jets of a gas mixture of nitrogen and ethylene, this interferometer was demonstrated to be useful in detecting the photothermal effect of a photothermal velocimeter under phase fluctuation in a turbulent flow. 相似文献
19.
Summary Excessive breakdown of elastin, a structural protein, may be related to aortic disease and emphysema. Since L-valyl-L-proline occurs in high concentrations in elastin, a rapid and sensitive method using HPLC with post-column on-line derivatization was used to measure the dipeptide from swine aortic tissue, and the amount of elastin present was determined. Elastin was extracted by alkaline hydrolysis. After neutralization and filtration, the sample was injected onto a ODS-2 gel column, and the dipeptide was eluted by a linear gradient of 0 to 10% of 1-propanol in 50 mM heptafluorobutyrate, pH 3, at a flow rate of 1 ml/min. The eluent was reacted with fluorescamine at pH 8.6, and fluorescence was detected at an excitation wavelength of 395 nm and a 455 nm cutoff emission filter.Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria. 相似文献
20.
FJZ-250型高速分幅相机时间测量不确定度分析 总被引:2,自引:1,他引:1
FJZ-250型高速转镜分幅相机因转镜速度的不可重复性,光机结构的构造原理和控制系统各路高压触发时间的漂移,导致了时间测量的不确定度。为此,须对相机测量数据进行校正。阐述了校正方法、提供了逐幅校正位置误差的修正系数。若以预置转速对应的名义周期值去处理测量结果,则相机的时间测量合成小确定度将达1%,对名义周期值和名义幅间间隔时间值进行修正后,则可降至0.3%。 相似文献