全文获取类型
收费全文 | 26867篇 |
免费 | 1762篇 |
国内免费 | 62篇 |
专业分类
电工技术 | 398篇 |
综合类 | 33篇 |
化学工业 | 6289篇 |
金属工艺 | 1098篇 |
机械仪表 | 1673篇 |
建筑科学 | 488篇 |
矿业工程 | 8篇 |
能源动力 | 1090篇 |
轻工业 | 2137篇 |
水利工程 | 101篇 |
石油天然气 | 17篇 |
无线电 | 4549篇 |
一般工业技术 | 5888篇 |
冶金工业 | 1776篇 |
原子能技术 | 367篇 |
自动化技术 | 2779篇 |
出版年
2024年 | 24篇 |
2023年 | 332篇 |
2022年 | 477篇 |
2021年 | 808篇 |
2020年 | 587篇 |
2019年 | 659篇 |
2018年 | 851篇 |
2017年 | 849篇 |
2016年 | 970篇 |
2015年 | 790篇 |
2014年 | 1215篇 |
2013年 | 1730篇 |
2012年 | 1846篇 |
2011年 | 2208篇 |
2010年 | 1577篇 |
2009年 | 1639篇 |
2008年 | 1487篇 |
2007年 | 1149篇 |
2006年 | 1000篇 |
2005年 | 859篇 |
2004年 | 800篇 |
2003年 | 755篇 |
2002年 | 729篇 |
2001年 | 620篇 |
2000年 | 536篇 |
1999年 | 539篇 |
1998年 | 813篇 |
1997年 | 502篇 |
1996年 | 457篇 |
1995年 | 299篇 |
1994年 | 220篇 |
1993年 | 199篇 |
1992年 | 151篇 |
1991年 | 136篇 |
1990年 | 97篇 |
1989年 | 100篇 |
1988年 | 92篇 |
1987年 | 73篇 |
1986年 | 64篇 |
1985年 | 72篇 |
1984年 | 50篇 |
1983年 | 35篇 |
1982年 | 36篇 |
1981年 | 34篇 |
1980年 | 43篇 |
1979年 | 23篇 |
1977年 | 27篇 |
1976年 | 41篇 |
1975年 | 23篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We have examined the applicability of this simple and effective test to polymer systems widely used in the medical industry. First, it was found that not every polymer examined exhibited a distinct onset of autocatalytic oxidation detectable by DSC. However, for cases where distinct onsets are found, powerful insights can be obtained. These included activation energy of the degradation, thermal oxidative shelf life prediction, and correlation, with product performances. Actual examples are presented to illustrate the utility of the test. 相似文献
92.
K.-H. Zum Gahr R. Telle B. Zimmerlin S.-H. Park 《Materialwissenschaft und Werkstofftechnik》1992,23(9):329-338
Influence of grain size on mechanical properties and dry oscillating sliding wear of Al2O3-ceramics Specimens with average grain sizes varying between about 0.8 μm and 12 μm were produced by cold isostatic pressing of high purity Al2O3-powder followed by sintering between 1300°C and 1700°C. Hardness, Young's modulus, bending strength and fracture toughness were measured as a function of average grain sizes. Tribological tests were carried out on the different microstructures at normal laboratory air and room temperature by using a ring-on-block tribometer. Experimental results showed the dependence of mechanical properties on grain size, hardness and bending strength obeying a Hall-Petch type relation, approximately. Coefficient of friction was relatively independent of grain size under the test conditions used. However, wear intensity increased substantially if a critical grain size was surpassed. This was due to a change in mechanisms of material removal which was confirmed by scanning electron microscopical studies of the worn surfaces. 相似文献
93.
94.
Park Y.C. Lee K.Y. Youn D.H. Kim N.H. Kim W.K. Park S.H. 《IEEE transactions on bio-medical engineering》1992,39(8):868-871
An efficient algorithm detecting the presence of a fetal QRS complex is presented. The proposed fetal QRS detection method computes the averaged magnitude of the difference between the fetal ECG signal and the reference signal to detect the fetal QRS event. The detected fetal QRS complexes are exponentially averaged to generate the template signal which can track the slowly varying shape of the fetal ECG signal. As an effort to obtain improved detection performances, two approaches of normalizing the fetal ECG signal and the template are considered. 相似文献
95.
Disagreement exists in the literature concerting the activity of NiO in (Ni,Mg)O solid solutions. Ideal behavior, as well as strong positive deviations and strong negative deviations from ideality, has been reported. In the present study, the activity of NiO was determined by electromotive force measurements using the solid-state cell Pt/Ni-NiO/0.92ZrO2 -0.08Y2 O3 /Ni-(Ni,Mg)O/Pt. The compositions studied had NiO mole fractions of 0.1,0.3,0.5,0.7, and 0.9. In agreement with theoretical expectations, the solid solutions exhibited ideal behavior at 882° and 982°C. Possible reasons for the conflicting results in the literature arc presented. 相似文献
96.
The humidity response characteristics of La doped BaTiO3 with different sintered densities and room temperature electrical conductivities were investigated using complex impedance measurement. The samples with low density and high resistivity showed the large and nearly linear sensitivity to the change of humidity. The impedance spectra of samples, when exposed to high humidity, can exhibit microstructure-related features, even though they do not give rise to a noticeable characteristic change when exposed to low humidity. The observed impedance patterns were dependent upon the density, and hence the oxidation kinetics of BaTiO3. 相似文献
97.
Experimental studies on the aerodynamic coupling effect on natural frequencies and flutter instability of rotating disks
are investigated in this paper. The experiments performed using a vacuum chamber and optical disks give two main results.
One is that the aerodynamic effect by surrounding air reduces the natural frequencies and critical speeds of the vibration
modes in pre-flutter regions. The other is that the natural frequency of the disk rotating at ambient atmospheric pressure
is equal to that in vacuum at the flutter onset speed where the disk experiences aero-induced flutter. In post-flutter regions,
the aerodynamic coupling between the disk and surrounding air increases the natural frequencies of the disk.
Received: 17 June 2002/Accepted: 7 October 2002
The work was supported by Grant No. R11-1997-042-090001-0 of the Center for Information Storage Devices designated by the
Korea Science & Engineering Foundation.
Paper presented at the 13th Annual Symposium on Information Storage and Processing Systems, Santa Clara, CA, USA, 17–18 June,
2002 相似文献
98.
The Error-in-Variables Model (EVM) applies to a large class of problems in parameter estimation in which there is error in all the variables. This property makes it of more general applicability than the widely used technique of ordinary Least Squares. While there is a voluminous literature on EVM there is nothing on a general method for designing experiments when EVM applies. In this paper we present an extension of the concept of D-optimality to provide such a general method. It is illustrated by applying it to the estimation of copolymer reactivity ratios and to fitting an ellipse. 相似文献
99.
Optical measurements of thermal diffusivity of a material 总被引:2,自引:0,他引:2
The measurement of thermal diffusivity of a material (in particular, a thin film) is important for various reasons, e.g., to predict the heat transfer in the solid subjected to a thermal process, to monitor surface composition or morphology, or to detect invisible subsurface defects like delaminations. This measurement can be done in a noncontact manner using various photothermal methods. Such methods typically involve pulsed heating of the surface by small amounts using a laser source; the decay of the surface temperature after this pulsed photothermal heating is then probed to provide the thermal diffusivity. Various probing methods have been developed in the literature, including the probing of reflection, refraction, and diffraction from the pulsed heated area, infrared thermal radiometry, and surface deformation. This paper provides an overview of such techniques and some examples of their applications. 相似文献
100.