全文获取类型
收费全文 | 3486篇 |
免费 | 91篇 |
国内免费 | 12篇 |
专业分类
化学 | 2061篇 |
晶体学 | 26篇 |
力学 | 121篇 |
数学 | 613篇 |
物理学 | 578篇 |
无线电 | 190篇 |
出版年
2023年 | 19篇 |
2022年 | 58篇 |
2021年 | 75篇 |
2020年 | 63篇 |
2019年 | 52篇 |
2018年 | 43篇 |
2017年 | 39篇 |
2016年 | 118篇 |
2015年 | 60篇 |
2014年 | 76篇 |
2013年 | 187篇 |
2012年 | 185篇 |
2011年 | 210篇 |
2010年 | 118篇 |
2009年 | 120篇 |
2008年 | 195篇 |
2007年 | 196篇 |
2006年 | 166篇 |
2005年 | 149篇 |
2004年 | 135篇 |
2003年 | 122篇 |
2002年 | 100篇 |
2001年 | 57篇 |
2000年 | 42篇 |
1999年 | 44篇 |
1998年 | 38篇 |
1997年 | 44篇 |
1996年 | 69篇 |
1995年 | 33篇 |
1994年 | 47篇 |
1993年 | 35篇 |
1992年 | 37篇 |
1991年 | 33篇 |
1990年 | 29篇 |
1989年 | 32篇 |
1988年 | 29篇 |
1987年 | 27篇 |
1986年 | 26篇 |
1985年 | 26篇 |
1984年 | 34篇 |
1983年 | 31篇 |
1982年 | 38篇 |
1981年 | 30篇 |
1980年 | 27篇 |
1979年 | 24篇 |
1978年 | 18篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1973年 | 15篇 |
排序方式: 共有3589条查询结果,搜索用时 17 毫秒
991.
992.
D. Alderighi M. Zamfirescu M. Gurioli A. Vinattieri M. Colocci S. Sanguinetti R. Ntzel M. Povolotskyi J. Gleize A. Di Carlo 《Physica E: Low-dimensional Systems and Nanostructures》2004,23(3-4):449
We present a study of the optical properties and carrier dynamics in strained InGaAs sidewall quantum wires (QWR) on patterned GaAs (3 1 1)A substrates by means of picosecond time-resolved photoluminescence (PL). A pronounced dynamical red shift of the QWR-PL band when increasing the delay time after the pulse excitation is observed. In addition, time-resolved data show a significant shortening of the PL decay time from the wire at short delay and when high excitation power is used. The data are compared with theoretical predictions. The results, i.e. the dynamical red shift observed in the wire emission and the shortening of the PL decay with increasing the excitation density, are interpreted in terms of a dynamical screening effect of the piezoelectric field. 相似文献
993.
994.
Moro G Bonati L Bruschi M Cosentino U De Gioia L Fantucci PC Pandini A Papaleo E Pitea D Saracino GA Zampella G 《Theoretical chemistry accounts》2007,117(5-6):723-741
Computational approaches based on Molecular Dynamics simulations, Quantum Mechanical methods and 3D Quantitative Structure-Activity
Relationships were employed by computational chemistry groups at the University of Milano-Bicocca to study biological processes
at the molecular level. The paper reports the methodologies adopted and the results obtained on Aryl hydrocarbon Receptor
and homologous PAS proteins mechanisms, the properties of prion protein peptides, the reaction pathway of hydrogenase and
peroxidase enzymes and the defibrillogenic activity of tetracyclines. 相似文献
995.
Alessandro Casoni Giuseppe Celentano Francesca Clerici Alessandro Contini Maria Luisa Gelmi Giuseppe Mazzeo Sara Pellegrino Carlo Rosini 《Tetrahedron: Asymmetry》2009,20(19):2247-2256
Herein we report a mild and efficient method to synthesize chiral 3-aminosubstituted isothiazole sulfoxides taking advantage of (+)- and (?)-((8,8-dichlorocamphoryl)sulfonyl)oxaziridine under microwave irradiation. The determination of the absolute configuration of the chiral sulfoxide was achieved by theoretical calculation of the CD spectra. The reason for the observed stereoselectivity was enlightened by means of analysis of our data using DFT calculations. 相似文献
996.
Liberata Guadagno Carlo Naddeo Vittoria Vittoria 《Journal of Polymer Science.Polymer Physics》2008,46(6):599-606
Syndiotactic polypropylene (sPP), obtained at 0 °C in the trans‐planar mesophase, was drawn at room temperature up to λ = 6, and left at room temperature for 1 year with fixed or relaxed ends. Data analysis allowed the clarification of the structure of the crystalline phases and their transformations during the aging. In both oriented samples similar structural changes were observed, although they were due to different aging mechanisms. The physical aging led to the crystallization in both samples of an oriented helical form, due to a partial transformation of the mesophase and of the amorphous phase. In the oriented sample aged with fixed ends, a small fraction of the crystalline trans‐planar form III became stable even by releasing the tension after 1 year. This last sample did not undergo the large shrinkage, always observed by unloaded sPP after drawing, and therefore was no more elastic. Also, the sample aged with free ends for 1 year showed a reduced elasticity in terms of both dissipated energy and permanent set. However, after a new deformation up to λ = 6, the fiber recovered its previous elasticity. Indeed a mechano‐reversibility was apparent for the oriented elastic sample of sPP aged at room temperature with free ends, leading to a renewed elasticity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 599–606, 2008 相似文献
997.
Cutting stock problems deal with the generation of a set of cutting patterns that minimizes waste. Sometimes it is also important to find the processing sequence of this set of patterns to minimize the maximum queue of partially cut orders. In such instances a cutting sequencing problem has to be solved. This paper presents a new mathematical model and a three-phase approach for the cutting sequencing problem. In the first phase, a greedy algorithm produces a good starting solution that is improved in the second phase by a tabu search, or a generalized local search procedure, while, in the last phase, the problem is optimally solved by an implicit enumeration procedure that uses the best solution previously found as an upper bound. Computing experience, based on 300 randomly generated problems, shows the good performance of the heuristic methods presented. 相似文献
998.
999.
1000.
Programmable built-in self-testing of embedded RAM clusters in system-on-chip architectures 总被引:1,自引:0,他引:1
Benso A. Di Carlo S. Di Natale G. Prinetto P. Bodoni M.L. 《Communications Magazine, IEEE》2003,41(9):90-97
Multiport memories are widely used as embedded cores in all communication system-on-chip devices. Due to their high complexity and very low accessibility, built-in self-test (BIST) is the most common solution implemented to test the different memories embedded in the system. This article presents a programmable BIST architecture based on a single microprogrammable BIST processor and a set of memory wrappers designed to simplify the test of a system containing a large number of distributed multiport memories of different sizes (number of bits, number of words), access protocols (asynchronous, synchronous), and timing. 相似文献