全文获取类型
收费全文 | 265637篇 |
免费 | 2579篇 |
国内免费 | 890篇 |
专业分类
化学 | 116666篇 |
晶体学 | 3996篇 |
力学 | 10757篇 |
综合类 | 1篇 |
数学 | 25503篇 |
物理学 | 78708篇 |
无线电 | 33475篇 |
出版年
2020年 | 2038篇 |
2019年 | 2285篇 |
2018年 | 3027篇 |
2017年 | 2922篇 |
2016年 | 4302篇 |
2015年 | 2527篇 |
2014年 | 4359篇 |
2013年 | 10736篇 |
2012年 | 7975篇 |
2011年 | 9901篇 |
2010年 | 7231篇 |
2009年 | 7571篇 |
2008年 | 9901篇 |
2007年 | 10264篇 |
2006年 | 9731篇 |
2005年 | 8927篇 |
2004年 | 8343篇 |
2003年 | 7402篇 |
2002年 | 7298篇 |
2001年 | 8386篇 |
2000年 | 6677篇 |
1999年 | 5418篇 |
1998年 | 4729篇 |
1997年 | 4580篇 |
1996年 | 4280篇 |
1995年 | 3991篇 |
1994年 | 3891篇 |
1993年 | 3975篇 |
1992年 | 3995篇 |
1991年 | 4173篇 |
1990年 | 3911篇 |
1989年 | 3752篇 |
1988年 | 3713篇 |
1987年 | 3307篇 |
1986年 | 3183篇 |
1985年 | 4158篇 |
1984年 | 4377篇 |
1983年 | 3532篇 |
1982年 | 3656篇 |
1981年 | 3602篇 |
1980年 | 3480篇 |
1979年 | 3520篇 |
1978年 | 3614篇 |
1977年 | 3554篇 |
1976年 | 3625篇 |
1975年 | 3320篇 |
1974年 | 3313篇 |
1973年 | 3369篇 |
1972年 | 2373篇 |
1971年 | 1966篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
901.
QRS feature extraction using linear prediction 总被引:10,自引:0,他引:10
This communication proposes a method called linear prediction (a high performant technique in digital speech processing) for analyzing digital ECG signals. There are several significant properties indicating that ECG signals have an important feature in the residual error signal obtained after processing by Durbin's linear prediction algorithm. This communication also indicates that the prediction order need not be more than two for fast arrhythmia detection. The ECG signal classification puts an emphasis on the residual error signal. For each ECG's QRS complex, the feature for recognition is obtained from a nonlinear transformation which transforms every residual error signal to a set of three states pulse-code train relative to the original ECG signal. The pulse-code train has the advantage of easy implementation in digital hardware circuits to achieve automated ECG diagnosis. The algorithm performs very well in feature extraction in arrhythmia detection. Using this method, our studies indicate that the PVC (premature ventricular contraction) detection has at least a 92 percent sensitivity for MIT/BIH arrhythmia database. 相似文献
902.
Correlation between the particles from the proton-nucleus interactions in emulsion at 70 GeV/c is presented through the study of the rapidity gap analysis and compared with the two-particle rapidity correlations. It is observed that the strength of correlation decreases as the size of cluster increases. Asymmetry between the forward and backward components were also studied.Authors are thankful to Prof. K. D. Tolstov, JINR, Dubna, USSR for sending the exposed emulsion plates. Thanks are also due to UGC for financial assistance. We sincerely acknowledge the encouragement from Prof. T. Roy. 相似文献
903.
A. G. Zhdanov A. K. Zvezdin A. P. Pyatakov T. B. Kosykh D. Viehland 《Physics of the Solid State》2006,48(1):88-95
The specific features of the “incommensurate-commensurate” phase transitions induced by a magnetic field in multiferroics
(materials with coexisting magnetic and electric ordering) are considered. These materials are ferroelectromagnets, for example,
bismuth ferrite BiFeO3 and BiFeO3-based compounds, which have spatially modulated spin structures. It is shown that the interaction between the electric and
magnetic subsystems of the multiferroic material can lead to an electric-field-induced shift of the critical magnetic field
corresponding to the transition from a spatially modulated state to a homogeneous antiferromagnetic state. According to the
theoretical estimates obtained for material parameters characteristic of the bismuth ferrite, this shift is of the order of
0.5 T in an electric field of 50 kV/cm. The phase diagrams are constructed in the “electric field-magnetic field” coordinates.
The results of calculations performed in the harmonic incommensurate structure approximation are compared with the exact soliton
solution. 相似文献
904.
A. P. Suponina L. G. Kolzunova M. A. Karpenko 《Russian Journal of Applied Chemistry》2006,79(6):924-929
The effect of coatings based on a copolymer of acrylamide, N,N′-methylenebisaxcrylamide and formaldehyde deposited by electrochemical polymerization on the corrosion resistance of 08Kh18N10T stainless steel (field studies at sea) and low-carbon steel (laboratory experiments) was examined. 相似文献
905.
T. Yu. Gumerov A. F. Dobrynina R. A. Yusupov V. P. Barabanov 《Russian Journal of Applied Chemistry》2006,79(12):1935-1939
The behavior of real disperse systems with organic impurities was examined under conditions of destabilization by inorganic coagulants. A number of physicochemical methods of analysis and a simulation method were used to identify the character and type of the complexes formed and to calculate their stability constants. 相似文献
906.
907.
H. Kim R.C.Y. Auyeung M. Ollinger G.P. Kushto Z.H. Kafafi A. Piqué 《Applied Physics A: Materials Science & Processing》2006,83(1):73-76
Low-temperature laser sintering has been successfully demonstrated to improve the overall conversion efficiency of dye-sensitized solar cells. Mesoporous TiO2 electrodes were prepared from a colloidal solution of TiO2 nanopowders by a laser direct-write technique and then sintered by a quasi-continuous-wave UV laser (λ=355 nm) for the fabrication of dye-sensitized solar cells. The overall conversion efficiency of the cells based on the laser-sintered TiO2 electrodes was double that of the devices with non-laser-treated TiO2 electrodes. This enhancement is attributed to both the removal of organic additives and the improved inter-nanoparticle electrical contacts induced by the laser-sintering process, which led to an increase in porosity and dye-absorption sites in the TiO2 electrodes. PACS 61.80.Ba; 61.46.+w; 73.22.-f; 84.60.Jt 相似文献
908.
G. Hanna T. Glatzel S. Sadewasser N. Ott H.P. Strunk U. Rau J.H. Werner 《Applied Physics A: Materials Science & Processing》2006,82(1):1-7
The influence of different film textures on the electronic properties of polycrystalline Cu(In,Ga)Se2 absorbers is studied by measuring the laterally resolved optoelectronic properties of differently textured Cu(In,Ga)Se2 films with Kelvin probe force microscopy and cathodoluminescence. The grain boundaries in (112)- and (220/204)-textured films behave differently. The work-function profile measured with the Kelvin probe across a grain boundary in (112)-textured films shows a dip indicating positive charges at the grain boundaries. In panchromatic cathodoluminescence mappings in a transmission electron microscope, such grain boundaries appear dark, i.e. the strongly reduced luminescence indicates that the grain boundaries represent strong non-radiative recombination centers. In contrast, grain boundaries in (220/204)-textured films give rise to a dip or a step in the work function indicating slightly negative charge or neutrality. Cathodoluminescence is reduced at such grain boundaries, but less dramatically than in the (112)-textured case. However, when Na is present in the (220/204)-textured films, the grain boundaries are almost invisible in cathodoluminescence mappings. This strong passivating action of Na occurs only in the (220/204)-textured films, due to a particular grain-boundary population. In (112)-textured films and films without pronounced texture, this passivation effect is much less noticeable. PACS 73.50.Gr; 73.61.Ga; 78.60.Hk; 87.64.Dt 相似文献
909.
910.
Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic
energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping
to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties
in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been
evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic
domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural
and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm
in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron
scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films. 相似文献