全文获取类型
收费全文 | 1865篇 |
免费 | 184篇 |
国内免费 | 109篇 |
专业分类
化学 | 572篇 |
晶体学 | 5篇 |
力学 | 388篇 |
综合类 | 26篇 |
数学 | 363篇 |
物理学 | 804篇 |
出版年
2024年 | 8篇 |
2023年 | 21篇 |
2022年 | 64篇 |
2021年 | 46篇 |
2020年 | 60篇 |
2019年 | 37篇 |
2018年 | 25篇 |
2017年 | 65篇 |
2016年 | 92篇 |
2015年 | 73篇 |
2014年 | 108篇 |
2013年 | 116篇 |
2012年 | 72篇 |
2011年 | 107篇 |
2010年 | 55篇 |
2009年 | 99篇 |
2008年 | 113篇 |
2007年 | 119篇 |
2006年 | 99篇 |
2005年 | 97篇 |
2004年 | 67篇 |
2003年 | 68篇 |
2002年 | 70篇 |
2001年 | 69篇 |
2000年 | 53篇 |
1999年 | 40篇 |
1998年 | 60篇 |
1997年 | 32篇 |
1996年 | 44篇 |
1995年 | 32篇 |
1994年 | 19篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有2158条查询结果,搜索用时 15 毫秒
181.
光纤白光干涉法与膜厚纳米测量新技术研究 总被引:6,自引:3,他引:3
运用薄膜光学干涉原理、光纤技术和干涉光谱分析技术,用光纤反射式干涉光谱仪(Reflectromic Interference Spectroscopy)直接测试宽带入射光在单晶硅表面超薄SiO2膜层前后界面反射形成的干涉光谱曲线,并用专业软件对被测光谱信号数据处理后,可直接用公式准确计算出SiO2氧化膜的厚度和光学折射率通过对单晶硅片表面超薄SiO2氧化膜的实测,并与成熟的椭圆偏振仪测试结果相比,测试误差≤2nm但该方法测试简单、快速,精度高,不需要制定仪器曲线和数表,可对薄膜任意位置的厚度在线测试经过对不同厚度聚苯乙烯薄膜的厚度测试表明,该方法适合0.5~20μm薄膜厚度的精确在线测量,测量误差小于7nm. 相似文献
182.
W. Jäger 《Accreditation and quality assurance》1997,2(4):199-202
The necessity for analytical quality assurance is primarily a feature of the analytical process itself. With the full establishment
of the EU domestic market, it is also becoming a legal necessity for an increasing number of analytical laboratories. The
requirements which laboratories will need to fulfil are stipulated in DIN EN 45 001. Accredited testing laboratories must
in fact provide evidence that they work solely in accordance with this standard. National and EU commissions, which are legislative
authorities, tend therefore to specify analytical methods, e.g. in the form of regulations or appendices thereto, intended
to ensure that results from different laboratories will be comparable and hence will stand up in a court of law. The analytical
quality assurance system (AQS), introduced by the Baden-Württemberg Ministry for the Environment in 1984, obliges laboratories
to regularly participate in collaborative studies and thereby demonstrate their ability to provide suitably accurate analyses.
This alone, however, does not sufficiently demonstrate the competence of a laboratory. Only personal appraisal of the laboratory
by an auditor, together with the successful analysis of a sample provided by the same and performed under his observation,
can provide proof of the competence of the laboratory. From an analytical point of view, the competence of a laboratory must
be regarded as the decisive factor. Competence can only be attained through analytical quality assurance, which thus must
be demanded of all laboratories.
Received: 4 October 1996 Accepted: 15 January 1997 相似文献
183.
Real-time visualisation of deformation fields using speckle interferometry and temporal phase unwrapping 总被引:1,自引:0,他引:1
A real-time system for analysing data from speckle interferometers, and speckle shearing interferometers, has been developed. Interferograms are continuously recorded by a digital camera at a rate of 60 frames s−1 with temporal phase shifting carried out at the same rate. The images are analysed using a pipeline image processor. With a standard 4-frame phase-shifting algorithm (phase steps of π/2), wrapped phase maps are calculated and displayed at 15 frames s−1. These are unwrapped using a temporal phase unwrapping algorithm to provide a real-time colour-coded display of the relevant displacement component. Each camera pixel (or cluster of pixels) behaves in effect as an independent displacement sensor. The reference speckle interferogram is updated automatically at regular user-defined intervals, allowing arbitrarily large deformations to be measured and errors due to speckle decorrelation to be minimised. The system has been applied to the problem of detecting sub-surface delamination cracks in carbon fibre composite panels. 相似文献
184.
ESPI solution for non-contacting MEMS-on-wafer testing 总被引:6,自引:0,他引:6
Petra Aswendt Claus-Dieter Schmidt Dirk Zielke Steffen Schubert 《Optics and Lasers in Engineering》2003,40(5-6):501-515
Rapid progress in the field of micro-electro-mechanical systems (MEMS) makes the development of appropriate measuring and testing means timely. Characterizing the mechanical properties of MEMS structures at a very early stage of manufacturing is a challenging task for quality assurance in this field. The paper describes a new solution that is based upon the vibration analysis of the microparts. The nanometer amplitudes are detected by advanced electronic speckle pattern interferometry (ESPI). A specific signal processing technique has been applied to make the solution robust. Comprehensive numerical simulations provide the theoretical base for the HNDT concept. A laboratory system for 4″ wafer has been built, and extensive tests show that such key properties as e.g. the thickness of springs or membranes can be determined exactly. Automated frequency scanning and corresponding digital image processing open the way to reliable and fast industrial systems for MEMS testing on wafer level. 相似文献
185.
热象无损检测技术应用 总被引:1,自引:1,他引:0
本文将热象无损检测技术应用于鉴定受测物结构和性质,并测出受测物中的缺陷,实验结果取得了较为满意的进展。 相似文献
186.
Zukang Zheng 《中国科学A辑(英文版)》1997,40(9):932-944
The stability of testing hypotheses is discussed. Differing from the usual tests measured by Neyman-Pearson lemma, the regret
and correction of the tests are considered. After the decision is made based on the observationsX
1,X
2, ⋅⋅⋅,X
n, one more piece of datumX
n+1 is picked and the test is done again in the same way but based onX
1,X
2, ⋅⋅⋅,X
n,X
n+l There are three situations: (i) The previous decision is right but the new decision is wrong; (ii) the previous decision
is wrong but the new decision is right; (iii) both of them are right or both of them are wrong. Of course, it is desired that
the probability of the occurrence of (i) is as small as possible and the probability of the occurrence of (ii) is as large
as possible. Since the sample size is sometimes not chosen very precisely after the type I error and the type II error are
determined in practice, it seems more urgent to consider the above problem. Some optimal plans are also given.
Project supported by the National Natural Science Foundation of China and the Doctoral Programme Foundation. 相似文献
187.
188.
189.
材料超声回波衰减是评价材料均匀一致性的常用方法, 针对具有复杂结构的航空发动机盘件难以进行材料底面超声回波衰减评价的问题, 本文提出了利用超声背散射波信号直接预测底面回波衰减的方法。采用10MHz聚焦探头进行超声背散射波数据的采集, 利用深度学习技术构建和训练模型,建立了基于深度学习的材料底面回波衰减预测方法, 同时讨论了采用不同信号形式的超声波信号分类识别模型的准确率差异。研究发现:基于深度学习技术可实现通过超声背散射波预测材料的底面回波衰减, 预测结果和实际底面回波衰减试验结果具有良好的一致性。 相似文献
190.
Operational modal analysis techniques allow us to extract the modal properties of structures based on their response to non-measured
stationary white noise, i.e., by considering only the system response to operational excitations. In this paper we outline
a procedure to deduce modal parameters from operational response measurements. In particular, we discuss a novel approach
to analyze operational responses due to unknown harmonic excitation in addition to noise. Structural eigenfrequencies and
modal damping are computed using a modified least-squares complex exponential method. Once the poles of the system are identified,
mode shapes are obtained by post-processing. The robustness and accuracy of the approach are illustrated by performing tests
on a plate structure. 相似文献