全文获取类型
收费全文 | 148607篇 |
免费 | 1625篇 |
国内免费 | 502篇 |
专业分类
化学 | 70281篇 |
晶体学 | 2061篇 |
力学 | 5014篇 |
综合类 | 5篇 |
数学 | 12514篇 |
物理学 | 40063篇 |
无线电 | 20796篇 |
出版年
2016年 | 1466篇 |
2015年 | 1119篇 |
2014年 | 1547篇 |
2013年 | 5184篇 |
2012年 | 3731篇 |
2011年 | 4744篇 |
2010年 | 3092篇 |
2009年 | 3116篇 |
2008年 | 4662篇 |
2007年 | 4970篇 |
2006年 | 4943篇 |
2005年 | 4874篇 |
2004年 | 4337篇 |
2003年 | 3950篇 |
2002年 | 3890篇 |
2001年 | 4396篇 |
2000年 | 3516篇 |
1999年 | 2923篇 |
1998年 | 2628篇 |
1997年 | 2594篇 |
1996年 | 2512篇 |
1995年 | 2463篇 |
1994年 | 2278篇 |
1993年 | 2289篇 |
1992年 | 2512篇 |
1991年 | 2469篇 |
1990年 | 2342篇 |
1989年 | 2299篇 |
1988年 | 2226篇 |
1987年 | 1994篇 |
1986年 | 1860篇 |
1985年 | 2455篇 |
1984年 | 2535篇 |
1983年 | 2173篇 |
1982年 | 2459篇 |
1981年 | 2233篇 |
1980年 | 2300篇 |
1979年 | 2275篇 |
1978年 | 2370篇 |
1977年 | 2291篇 |
1976年 | 2310篇 |
1975年 | 2236篇 |
1974年 | 2085篇 |
1973年 | 2339篇 |
1972年 | 1427篇 |
1971年 | 1115篇 |
1970年 | 1046篇 |
1969年 | 999篇 |
1968年 | 1149篇 |
1967年 | 1188篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
W. Boltz 《e & i Elektrotechnik und Informationstechnik》2003,120(10):309-311
Ohne Zusammenfassung
Kurzfassung eines Vortrags der 41. Fachtagung der ?sterreichischen Gesellschaft für Energietechnik (OGE) im OVE, die am 5.
und 6. November 2003 in Salzburg stattfindet. 相似文献
102.
103.
It is shown that the dephasing which suppresses the weak localization correction to the conductivity has the same physical origin than pair-breaking in superconductors and thus-following de Gennes-may be expressed in terms of the correlation function of the operator for time reversal. 相似文献
104.
Many cognitive tasks that are easy for humans to perform are proving difficult to emulate in computer systems. Combining the disciplines of psychology and engineering may offer a solution to some of these problems. A connectionist or neural network model of face recognition by humans which incorporates aspects of a model proposed by cognitive psychologists is presented. A comparative set of experiments has been performed using this simulation and human subjects for familiar face recognition. By employing the same stimuli for both humans and the computer model, it is possible to advance not only our understanding of human cognition but also to develop improved automated systems for face recognition 相似文献
105.
G. Weber 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):639-642
Summary For accurate speciation analyses it is important to know the stability of the respective species, especially in the case of metal complexes. Factors affecting the chromatographic stability of such metal species are investigated. By using thermodynamic models for complex formation and chromatographic retention equilibria the influence of species concentration, stoichiometry and excess of ligand is calculated and compared with experimental results for iron complexes (lactate, gluconate and citrate species). Iron citrate is the only species, that is chromatographed as 1:2 complex (metal: ligand), while iron lactate and gluconate are transformed to 1:1 species. Problems resulting from the coelution of different species are discussed.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
106.
In this paper we deal with the numerical solution of movingboundary problems of two-phase Stefan type. Based on an implicitdiscretization in time and the use of continuous, piecewiselinear finite elements in the space variables with respect tothe weak formulation of the problem, a globally convergent multi-gridalgorithm is developed. That algorithm strongly relies on thevariational characterization of the fully discretized problemas the unconstrained minimization of a subdifferentiable convexobjective functional. Numerical results indicate a significantimprovement in efficiency compared with previous multi-gridapproaches. 相似文献
107.
We propose a new image multiresolution transform that is suited for both lossless (reversible) and lossy compression. The new transformation is similar to the subband decomposition, but can be computed with only integer addition and bit-shift operations. During its calculation, the number of bits required to represent the transformed image is kept small through careful scaling and truncations. Numerical results show that the entropy obtained with the new transform is smaller than that obtained with predictive coding of similar complexity. In addition, we propose entropy-coding methods that exploit the multiresolution structure, and can efficiently compress the transformed image for progressive transmission (up to exact recovery). The lossless compression ratios are among the best in the literature, and simultaneously the rate versus distortion performance is comparable to those of the most efficient lossy compression methods. 相似文献
108.
The device degradation under ac and dc stress have been discussed and a relationship between the two has been established,. We have shown that the commonly used lifetime criteria of 10% linear current degradation for 10 years for a transistor under dc stress is overly conservative for representing the circuit operating lifetime. Using experimental and simulated data for inverter chains, we proposed that a meaningful equivalent lifetime based on 10% Idl degradation under dc stress is 1 year lifetime (for a 10 year circuit lifetime based on 54b degradation in ring oscillator frequency). We also compared this criteria to actual circuit degradation for microprocessors and a DRAM. For DSP microprocessors with 0.8 μm LDD transistors, the projected lifetime was more than 200 years at 5.5 V, with a corresponding 10% I dr lifetime of 20 years. For 1 Mb DRAMs with 1 pm LDD transistors, the 5% speed degradation lifetime at 5.5 V was more than 100 years, whereas the individual transistors had 10% Idl lifetime of 4 years. These circuit results support the 10% Idl transistor lifetime. We believe these criterion should be very safe and reasonable for digital IC chips currently in the field, as well as those in future design and development 相似文献
109.
The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy
(CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a
cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The
products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH2 and C4H9 radicals. These undergo subsequent reactions to form the stable products C4H8, PH3 and H2, with smaller amounts of P and P2 being produced. The production of the sub-hydride PH2 using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing
the amount of carbon incorporated into the growing epitaxial layer. 相似文献
110.