全文获取类型
收费全文 | 18022篇 |
免费 | 587篇 |
国内免费 | 360篇 |
专业分类
化学 | 9887篇 |
晶体学 | 108篇 |
力学 | 419篇 |
综合类 | 30篇 |
数学 | 2002篇 |
物理学 | 4056篇 |
无线电 | 2467篇 |
出版年
2022年 | 121篇 |
2021年 | 224篇 |
2020年 | 208篇 |
2019年 | 224篇 |
2018年 | 205篇 |
2017年 | 167篇 |
2016年 | 375篇 |
2015年 | 361篇 |
2014年 | 422篇 |
2013年 | 873篇 |
2012年 | 720篇 |
2011年 | 874篇 |
2010年 | 624篇 |
2009年 | 603篇 |
2008年 | 822篇 |
2007年 | 863篇 |
2006年 | 694篇 |
2005年 | 737篇 |
2004年 | 716篇 |
2003年 | 741篇 |
2002年 | 805篇 |
2001年 | 620篇 |
2000年 | 517篇 |
1999年 | 422篇 |
1998年 | 323篇 |
1997年 | 279篇 |
1996年 | 296篇 |
1995年 | 326篇 |
1994年 | 281篇 |
1993年 | 247篇 |
1992年 | 244篇 |
1991年 | 223篇 |
1990年 | 236篇 |
1989年 | 193篇 |
1988年 | 185篇 |
1987年 | 161篇 |
1986年 | 151篇 |
1985年 | 250篇 |
1984年 | 261篇 |
1983年 | 185篇 |
1982年 | 202篇 |
1981年 | 167篇 |
1980年 | 175篇 |
1979年 | 160篇 |
1978年 | 137篇 |
1977年 | 191篇 |
1976年 | 162篇 |
1975年 | 132篇 |
1974年 | 123篇 |
1973年 | 138篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
Carlos E. Alciaturi Thais Montero Carlos De La Cruz Marcos E. Escobar 《Analytica chimica acta》1997,340(1-3):233-240
Reduction of the representation of infrared spectra from coal samples by osculating polynomials of degree nine is discussed. The reduced representation contains polynomial coefficients of order zero to four. Mathematical models of the original spectra are obtained by linear combination of the coefficients. These compressed models are statistically correlated to coal properties, namely, volatile matter, fixed carbon, ash content, heating value, hydrogen, carbon, sulphur, nitrogen, and maximum vitrinite reflectance, and the results are compared with those previously obtained from second derivatives of the same spectra. The use of compressed data, while giving slightly better correlations for some of the properties, has the advantage of requiring less computational time. 相似文献
82.
A diagnostic study q (energy transfer processes in a He-N2 flowing discharge and afterglow has been performed in a radiofrequency-produced plasma cooled in a liquid nitrogen hath. Optical emission spectroscopy in the visible and infrared spectral range as well as Langrnuir probe diagnostics were used. The vibrational kinetics of CO injected in such an afterglow has been examined. It shows a slow cooling of the electrons in the afterglow regime. The electron kinetics responsible joy CO vibrahonal excitation is turned off when N2 is added to the He discharge, while that for vibrationally excited N2 molecules is turned on. The results are discussed on the basis of previous theorerical calculations and experiments on the He-N2 system. 相似文献
83.
84.
Quantum Monte Carlo techniques often suffer from the so-called minus-sign problem. This paper explores a possibility to circumvent this fundamental problem by combining the Projector Quantum Monte Carlo method with the variational principle. Results are presented for the two-dimensional Hubbard model. 相似文献
85.
Paolo De Lucia J. D. Maitland Wright 《Rendiconti del Circolo Matematico di Palermo》1991,40(3):442-452
Dopo aver dato una definizione di parte convessa di un gruppo topologico, si stabilisce una condizione affinchè il condominio
di una misura sia convesso. 相似文献
86.
A. Witvrouw K. Maex W. De Ceuninck G. Lekens J. D'Haen L. De Schepper 《Microelectronics Reliability》1998,38(6-8)
The degradation due to stress induced voiding of nitride passivated Al-1 wt.% Si and Ti/TN/ Al-1wt.% Si-0.5 wt. % Cu/Ti/TN interconnects with widths ranging between 0.4 and 1.2 μm was studied by in-situ conventional
high resolution resistance measurements (HRRM) during storage at temperatures between 168 and 240°C. The conventional measurements on Al-Si lines, which lasted more than one year, clearly showed that the interconnect lifetime decreases with decreasing line width. With HRRM the degradation due to stress induced voiding can be detected much sooner and with much more detail. From the HRRM it is clear that the resistance changes during storage often happen in jumps and that the degradation has a rather complex alloy, line width and temperature dependence. Both for 0.4 and 0.6 μm wide Al---Si lines more degradation occurred for storage at 175 °C compared to storage at 200 °C. For the Al---Si---Cu stacks the degradation of 0.4 μm wide lines was worse for storage at 240°C compared to storage at 200 °C, but the opposite was true for the 0.6 μm wide lines. 相似文献
87.
88.
Weikle R.M. II Kim M. Hacker J.B. De Lisio M.P. Popovic Z.B. Rutledge D.B. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1992,80(11):1800-1809
Although quasi-optical techniques are applicable to a large variety of solid-state devices, special attention is given to transistors, which are attractive because they can be used as either amplifiers or oscillators. Experimental results for MESFET bar-grid and planar grid oscillators are presented. A MESFET grid amplifier that receives only vertically polarized waves at the input and radiates horizontally polarized waves at the output is discussed. These planar grids can be scaled for operation at millimeter- and submillimeter-wave frequencies. By using modern IC fabrication technology, planar grid oscillators and amplifiers containing thousands of devices can be built, thereby realizing an efficient means for large-scale power combining 相似文献
89.
M. H. Gehlen M. Van der Auweraer F. C. De Schrwer 《Photochemistry and photobiology》1991,54(4):613-618
The luminescence decay of excited probes in micelles in the presence of a Poisson distribution of quenchers is considered under conditions where both probe and quencher within the lifetime of the excited probe may exchange between the micelles. Analytical and numerical results show that the luminescence decay can be expressed by a generalized self convolution product of a multiexponential decay function. 相似文献
90.
Balasa F. Catthoor F. Hugo De Man 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》1995,3(2):157-172
Memory cost is responsible for a large amount of the chip and/or board area of customized video and image processing system realizations. In this paper, we present a novel technique-founded on data-flow analysis which allows one to address the problem of background memory size evaluation for a given nonprocedural algorithm specification, operating on multidimensional signals with affine indexes. Most of the target applications are characterized by a huge number of signals, so a new polyhedral data-flow model operating on groups of scalar signals is proposed. These groups are obtained by a novel analytical partitioning technique, allowing to select a desired granularity, depending on the application complexity. The method incorporates a way to tradeoff memory size with computational and controller complexity 相似文献