全文获取类型
收费全文 | 3220篇 |
免费 | 98篇 |
国内免费 | 10篇 |
专业分类
化学 | 2256篇 |
晶体学 | 40篇 |
力学 | 29篇 |
数学 | 122篇 |
物理学 | 610篇 |
无线电 | 271篇 |
出版年
2023年 | 18篇 |
2022年 | 27篇 |
2021年 | 37篇 |
2020年 | 30篇 |
2019年 | 47篇 |
2018年 | 30篇 |
2017年 | 29篇 |
2016年 | 61篇 |
2015年 | 56篇 |
2014年 | 64篇 |
2013年 | 218篇 |
2012年 | 145篇 |
2011年 | 189篇 |
2010年 | 90篇 |
2009年 | 94篇 |
2008年 | 178篇 |
2007年 | 200篇 |
2006年 | 184篇 |
2005年 | 225篇 |
2004年 | 169篇 |
2003年 | 130篇 |
2002年 | 127篇 |
2001年 | 65篇 |
2000年 | 75篇 |
1999年 | 46篇 |
1998年 | 50篇 |
1997年 | 44篇 |
1996年 | 48篇 |
1995年 | 37篇 |
1994年 | 34篇 |
1993年 | 41篇 |
1992年 | 30篇 |
1991年 | 34篇 |
1990年 | 19篇 |
1989年 | 22篇 |
1988年 | 21篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 39篇 |
1984年 | 39篇 |
1983年 | 24篇 |
1982年 | 29篇 |
1981年 | 26篇 |
1980年 | 30篇 |
1979年 | 21篇 |
1978年 | 34篇 |
1977年 | 24篇 |
1976年 | 14篇 |
1975年 | 21篇 |
1974年 | 21篇 |
排序方式: 共有3328条查询结果,搜索用时 0 毫秒
991.
Hasegawa K. Ohara K. Oka A. Kamada T. Nagaoka Y. Yano K. Yamauchi E. Kashiro T. Nakagawa T. 《Solid-State Circuits, IEEE Journal of》1996,31(11):1780-1788
This paper describes the realization of a video encoder/decoder chip set for the consumer use digital video cassette recorder (VCR). The two chips with a 5 Mb external DRAM either encode the CCIR601 digital component video signal into the standard-definition digital VCR (DV) format or decode the DV format signal into a component video signal. The compression rate of the intraframe compression is about 1/6. The total power dissipation of the two LSI's is 142 mW at 2 V internal supply voltage, which is more than one order of magnitude smaller than the recently reported MPIEG2 (MP@ML) encoder systems. Low power was achieved primarily due to the compression scheme which is optimized for large-scale integration (LSI) implementation. The 0.5-μm 2-V CMOS standard cell library was also effective in reducing the power consumption. Each chip, fabricated in two-layer metal 0.5-μm CMOS technology, contains about 500 k transistors on 71 mm2 and 79 mm2 die, respectively 相似文献
992.
993.
Masatoshi Hasegawa Yoichi Shindo Tokuko Sugimura Shigeru Ohshima Kazuyuki Horie Masakatsu Kochi Rikio Yokota Itaru Mita 《Journal of Polymer Science.Polymer Physics》1993,31(11):1617-1625
Emission mechanism in an aromatic polyimide, PI(BPDA/PDA), derived from biphenyltetracarboxylic dianhydride and p-phenylene diamine were studied with ultraviolet visible absorption and fluorescence spectra of a series of the model compounds. The excitation spectrum of the intermolecular charge-transfer (CT) fluorescence peaking around 550 nm of PI(BPDA/PDA) thin film was completely consistent with the absorption spectrum, indicating that the intermolecular CT fluorescence emission of PI(BPDA/PDA) film is not caused by direct excitation of the CT absorption band, but by light absorption due to structural units in the polymer backbone. The UV-vis. absorption spectra of the model compounds corresponding to the structural units in PI(BPDA/PDA) showed that the longest wavelength absorption band is due to the biphenylbisimide moiety. The band was assigned as π, π* transition with the polarization spectrum of the model compound. The fluorescence spectra of the model compounds changed sensitively depending on the conformation around N-phenyl bond. The lifetime measurement for the model compounds suggested that intramolecular CT process occurs very rapidly. © 1993 John Wiley & Sons, Inc. 相似文献
994.
A new C14 Laves phase was synthesized by direct reaction of potassium and silver at high pressure in a diamond anvil cell. The structure was refined by Rietveld analysis on powder diffraction data in the space groupP63/mmcto anRF2value of 0.034. The lattice parameters area=5.589(5) andc=9.476(1). Formation of this phase under pressure is in agreement with predictions based on Miedema's rules. A novel double-sided laser heating system was developed for the synthesis of KAg2. 相似文献
995.
C. C. Hsu P. H. Geil Hideki Miyaji Kenjiro Asai 《Journal of Polymer Science.Polymer Physics》1986,24(10):2379-2401
Glassy isotactic propylene (PP) films of thickness up to 0.3 mm were obtained by an ultraquenching technique. The structure and properties of the as-quenched and subsequently crystallized samples were characterized by various techniques. Electron microscopy indicates the glass has no structure larger than 25 Å. X-ray diffraction shows PP crystallizes from the glass into a smectic structure at ca. ?20°C and then transforms to monoclinic microcrystals at ca. 40°C; a nodular structure (80 to 100 Å in diameter) was observed on the surface. The transformation temperature increases with the film thickness. Annealing above the α-relaxation temperature results in an increase in the nodule size. A correspondence was found between the diameter of the nodules observed on the surface and long spacings obtained by small-angle X-ray scattering from the bulk. Dynamic mechanical spectra show the presence of two relaxation-like peaks at ca. ?10°C and 10°C for the as-ultraquenched samples. X-ray scattering, differential scanning calorimetry (DSC), and torsion pendulum measurements show PP crystallizes from the glass at a temperature, depending on the rate of heating, that corresponds to the lower relaxation peak temperature. 相似文献
996.
997.
Hatakeyama A. Mochizuki H. Aikawa T. Takita M. Ishii Y. Tsuboi H. Fujioka S. Yamaguchi S. Koga M. Serizawa Y. Nishimura K. Kawabata K. Okajima Y. Kawano M. Kojima H. Mizutani K. Anezaki T. Hasegawa M. Taguchi M. 《Solid-State Circuits, IEEE Journal of》1997,32(11):1728-1734
This paper describes the key technologies used in a 256-Mb synchronous DRAM with a clock access time of 1 ns. This DRAM is stable against temperature, voltage, and process variation through the use of a register-controlled digital delay-locked loop (RDLL). The total timing error of the RDLL is about 0.4 ns, sufficient for high frequency operation at 150 to 200 MHz. Unlike most conventional high-density DRAMs, the bit lines are placed above the storage capacitors in this DRAM to relax the design rules of the core area. The noise issues were analyzed and resolved to help implement the technology for mass production of 0.28- to 0.24-μm 200-MHz DRAMs 相似文献
998.
Masaru Oda Atsushi Hasegawa Ken Nishiura Akira Nishiyama Toshiro Tani 《Journal of luminescence》2007,127(1):198-203
We report here the distinctive modifications of photoluminescence (PL) behaviors in single CdSe/ZnS/TOPO nanocrystals depending on their environments. Long-time traces of PL intensity from single nanocrystals have been obtained in both vacuum and a wet nitrogen atmosphere. While all of the nanocrystals in both environments exhibit PL blinking behaviors, i.e. on-off intermittency of PL intensity, as usual, some of the nanocrystals in the wet nitrogen atmosphere show significant increase in duration time of on-events. As for the duration time of blinking off-events, it is for the moment associated with the occasional events of carrier capturing at trap sites on or near the nanocrystal surfaces. We propose a model in which adsorbed water molecules at the trap sites on the nanocrystal surfaces transform them under light irradiation, which eventually decreases the occurrence of the trapping events due to their inactivation. It in turn increases the PL on-times. In addition to the drastic modification of the blinking profile, we also found that in the PL time traces some kinds of undulated behaviors, i.e. continuous and rather low frequency fluctuation of PL intensity, appear during each on-event in vacuum while they disappear totally in the wet nitrogen atmosphere. These results are also described on the basis of the inactivation model of the trap sites introduced above. 相似文献
999.
Katsuya Ikegami Masato Morifuji Hideki Momose Masahiko Kondow 《Physica E: Low-dimensional Systems and Nanostructures》2006,33(2):381-387
In order to investigate formation process of electronic quantum states in a confined system, we simulate motion of a wavepacket state and show how an eigenstate is formed due to coherence of electronic wave from the viewpoint that an eigenstate arises as a result of self-interference of a moving electron. Numerical results for a Hénon–Heiles potential in which chaotic motion can occur in the classical mechanics indicate that electronic eigenstates can arise even when motion of an electron is non-periodic. The results show that, in the quantum mechanics, periodicity is unnecessary for the formation of eigenstates. 相似文献
1000.
Hideki Miyachi 《Proceedings of the American Mathematical Society》2006,134(7):1917-1925
In this paper, we will establish that any invariant distance on asymptotic Teichmüller space is a complete distance.