全文获取类型
收费全文 | 1577574篇 |
免费 | 27685篇 |
国内免费 | 7855篇 |
专业分类
电工技术 | 35367篇 |
技术理论 | 1篇 |
综合类 | 7328篇 |
化学工业 | 276422篇 |
金属工艺 | 65912篇 |
机械仪表 | 45027篇 |
建筑科学 | 48358篇 |
矿业工程 | 11849篇 |
能源动力 | 50807篇 |
轻工业 | 121461篇 |
水利工程 | 16043篇 |
石油天然气 | 38354篇 |
武器工业 | 256篇 |
无线电 | 199388篇 |
一般工业技术 | 293918篇 |
冶金工业 | 194681篇 |
原子能技术 | 34361篇 |
自动化技术 | 173581篇 |
出版年
2021年 | 16537篇 |
2020年 | 12603篇 |
2019年 | 15171篇 |
2018年 | 17658篇 |
2017年 | 17084篇 |
2016年 | 22578篇 |
2015年 | 18221篇 |
2014年 | 29644篇 |
2013年 | 89010篇 |
2012年 | 38123篇 |
2011年 | 51768篇 |
2010年 | 44874篇 |
2009年 | 52708篇 |
2008年 | 47749篇 |
2007年 | 45016篇 |
2006年 | 46554篇 |
2005年 | 41399篇 |
2004年 | 43118篇 |
2003年 | 42790篇 |
2002年 | 41624篇 |
2001年 | 38760篇 |
2000年 | 36918篇 |
1999年 | 36561篇 |
1998年 | 55126篇 |
1997年 | 45380篇 |
1996年 | 39205篇 |
1995年 | 32974篇 |
1994年 | 30584篇 |
1993年 | 30526篇 |
1992年 | 26720篇 |
1991年 | 23799篇 |
1990年 | 24098篇 |
1989年 | 23177篇 |
1988年 | 21668篇 |
1987年 | 19933篇 |
1986年 | 19244篇 |
1985年 | 22562篇 |
1984年 | 22513篇 |
1983年 | 20465篇 |
1982年 | 19448篇 |
1981年 | 19623篇 |
1980年 | 18211篇 |
1979年 | 18625篇 |
1978年 | 17913篇 |
1977年 | 18091篇 |
1976年 | 19733篇 |
1975年 | 16077篇 |
1974年 | 15543篇 |
1973年 | 15659篇 |
1972年 | 13122篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
721.
The aim of this work was to establish the important parameters that control the hot compaction behaviour of woven oriented polypropylene. Five commercial woven cloths, based on four different polypropylene polymers, were selected so that the perceived important variables could be studied. These include the mechanical properties of the original oriented tapes or fibres, the geometry of the oriented reinforcement (fibres or tapes), the mechanical properties of the base polymer (which are crucially dependant on the molecular weight and morphology), and the weave style. The five cloths were chosen so as to explore the boundaries of these various parameters, i.e. low and high molecular weight: circular or rectangular reinforcement (fibres or tapes): low or high tape initial orientation: coarse or fine weave.A vital aspect of this study was the realisation that hot compacted polypropylene could be envisaged as a composite, comprising an oriented ‘reinforcement’ bound together by a matrix phase, formed by melting and recrystallisation of the original oriented material. We have established the crucial importance of the properties of the melted and recrystallised matrix phase, especially the level of ductility, in controlling the properties of the hot compacted composite. 相似文献
722.
723.
Previously unknown compounds AI
I(BUO5)2·nH2O (AI
I = Mg, Ca, Sr, Ba; n = 0-7) were synthesized. Their structure and thermal decomposition were studied by X-ray diffraction, IR spectroscopy, and thermal analysis. 相似文献
724.
Barch Deanna M.; Mitropoulou Vivian; Harvey Philip D.; New Antonia S.; Silverman Jeremy M.; Siever Larry J. 《Canadian Metallurgical Quarterly》2004,113(4):556
Research suggests that schizotypal personality disorder (SPD) is a part of the spectrum of schizophrenia-related illnesses. This article hypothesizes that a deficit in the representation and maintenance of context is a core cognitive disturbance in schizophrenia and that SPD individuals should demonstrate context-processing deficits. To test this hypothesis, the authors administered 3 versions of their AX-CPT task, designed to assess context processing, to 35 healthy controls and 26 individuals with DSM-IV SPD. They also administered working memory and selective attention tasks. SPD individuals displayed context representation deficits similar to those found in schizophrenia but did not show the same additional deficits in context maintenance. Context processing was strongly associated with working memory and selective attention performance in the SPD individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
725.
Stability analysis of the finite difference time domain scheme containing macromodels is presented. It is shown that for a stable macromodel, the stability of the combined scheme depends on the field interpolation at the macromodel boundary. The maximal allowable time step is shown to be much larger than for subgridding. 相似文献
726.
On the synergy between electrical and photonic switching 总被引:1,自引:0,他引:1
This article focuses on the values of electrical switching vs. photonic switching in the context of telecom transport networks. In particular, we show that the requirement of providing agility at the optical layer in the face of traffic forecast uncertainties is served better through photonic switching. On the other hand, some of the network-level functions, such as fast protection, subwavelength aggregation, and flexible client connectivity, require electrical switching. We further argue that additional values are achieved with hybrid photonic and electrical switching, which do not exist when either of these options is used in isolation. 相似文献
727.
A new method has been developed for compressing the matrices that occur in most integral-equation-based computer programs. This method is easy to interface with existing computer programs, and allows them to run significantly faster and with significantly less memory. This method applies not only to electromagnetic and acoustic computation, but also to most programs involving a Green's function or any integral equation with a kernel having some smoothness properties. Our numerical computations, running on a high-end personal computer, have achieved compression ratios of fifty times, and compressed inversion of the matrices fifty times faster than by previous methods. For larger problems, solved on high-performance computers, these ratios would improve to about one thousand to one for larger moment method problems. 相似文献
728.
E. A. Gurieva P. P. Konstantinov L. V. Prokof D. A. Pshenaĭ-Severin M. I. Fedorov Yu. I. Ravich 《Semiconductors》2006,40(7):763-767
The coefficients of thermopower and electrical and thermal conductivity in the PbTe0.8Se0.1 S 0.1 solid solution with electron concentration (4.6–54) × 1018 cm?3 are studied in the range of 85–300 K (and in some cases up to 700 K). The temperature dependences of electrical and thermal conductivity indicate that the low-temperature electron and phonon scattering initiated by the off-center impurity of sulfur exists. The temperature dependences of the electronic and lattice components of thermal conductivity are calculated in the approximation of a parabolic spectrum and electron scattering by acoustic phonons and neutral substitutional impurities. The lattice thermal conductivity is found to have a feature in the form of a shallow minimum in the range of 85–250 K. A similar feature, while not so clearly pronounced, is found to exist also in Pb1?x SnxTe1?x Sex alloys (x≥0.15) with an off-center tin impurity. An analysis of the possible origins of this effect suggests that, at low temperatures, the Lorentz numbers L of the materials under study are smaller than the L0 numbers employed which correspond to the above scattering mechanisms. The cause of the decrease in L is related to electron scattering at two-level systems, a mechanism whose effect grows with increasing electron energy. An analysis of experimental data obtained at high temperatures, as well as on undoped samples with the lowest possible carrier concentrations, yields the values of L for samples with different electron densities. The minimum value L/L0 = 0.75 is obtained for a lightly doped sample at ~130 K. 相似文献
729.
V. S. Butylkin G. A. Kraftmakher 《Journal of Communications Technology and Electronics》2006,51(5):484-497
A new composite medium based on waveguiding structures loaded with bianisotropic gratings of planar double split rings (PDSRs) and planar helices is considered. The microwave transmission spectra of this medium are studied experimentally. The effective parameters of the medium are determined theoretically, and its passbands are investigated. The characteristics of the medium are compared to those of infinite homogeneous bianisotropic media. A relationship between the spectral transmission characteristics and the type of resonance excitation is established. The transparency bands and overforbidden bands of the composite medium are revealed. The combinations of the medium’s effective parameters that correspond to these bands are determined. It is shown that the transparency bands where the medium is characterized simultaneously by negative permittivity and negative permeability can be identified. 相似文献
730.
The emerging software defined radio technologies will be an enabler for a new generation of dynamic wireless systems. It will also open up the possibility of allocating frequencies in a, more dynamic way than today. From an intersystem-interference point of view, this can cause unforeseen problems to occur due to the increased complexity in such applications. In such applications, a measure indicating whether or not a frequency band is possible to use from an electromagnetic interference point of view, must be found. A simple approach is to use the measured total average interference power within the receiver band. Since the interference impact on modern digital communication systems from an interference signal does not only depend on the power but also on the actual waveform of the interference signal, some kind of quality measure of the average-power approach would be convenient to use. In this paper, we introduce a simple quality measure of the average-power approach so that a rough adjustment for the interference-waveform properties can be done. 相似文献