全文获取类型
收费全文 | 7073篇 |
免费 | 183篇 |
国内免费 | 48篇 |
专业分类
化学 | 3975篇 |
晶体学 | 35篇 |
力学 | 222篇 |
数学 | 1380篇 |
物理学 | 1063篇 |
无线电 | 629篇 |
出版年
2022年 | 59篇 |
2021年 | 73篇 |
2020年 | 75篇 |
2019年 | 77篇 |
2018年 | 75篇 |
2017年 | 62篇 |
2016年 | 114篇 |
2015年 | 133篇 |
2014年 | 152篇 |
2013年 | 346篇 |
2012年 | 347篇 |
2011年 | 381篇 |
2010年 | 256篇 |
2009年 | 248篇 |
2008年 | 347篇 |
2007年 | 361篇 |
2006年 | 358篇 |
2005年 | 331篇 |
2004年 | 319篇 |
2003年 | 251篇 |
2002年 | 242篇 |
2001年 | 130篇 |
2000年 | 119篇 |
1999年 | 122篇 |
1998年 | 89篇 |
1997年 | 87篇 |
1996年 | 107篇 |
1995年 | 90篇 |
1994年 | 92篇 |
1993年 | 102篇 |
1992年 | 76篇 |
1991年 | 56篇 |
1990年 | 87篇 |
1989年 | 70篇 |
1988年 | 63篇 |
1987年 | 70篇 |
1986年 | 53篇 |
1985年 | 89篇 |
1984年 | 94篇 |
1983年 | 55篇 |
1982年 | 88篇 |
1981年 | 95篇 |
1980年 | 104篇 |
1979年 | 87篇 |
1978年 | 96篇 |
1977年 | 89篇 |
1976年 | 84篇 |
1975年 | 59篇 |
1974年 | 55篇 |
1973年 | 65篇 |
排序方式: 共有7304条查询结果,搜索用时 15 毫秒
1.
2.
Michel Hébert 《Archive for Mathematical Logic》1991,31(2):133-143
Summary We give a syntactic characterization of (finitary) theories whose categories of models are closed under the formation of connected limits (respectively the formation of pullbacks and substructures) in the category of all structures. They are also those theories whose consistent extensions by new atomic facts admit in each component an initial structure (respectively an initial term structure), and also thoseT for whichM(T) is locally finitely multi-presentable in a canonical way. We also show that these two properties of theories are nonuniform. 相似文献
3.
Constraint Programming and Operations Research: Comments from an Operations Researcher 总被引:4,自引:0,他引:4
Michel Gendreau 《Journal of Heuristics》2002,8(1):19-24
This paper relates the author's personal experience with constraint programming and gives a personal assessment of the relationships between constraint programming and operations research. 相似文献
4.
5.
Renaudier J. Brenot R. Dagens B. Lelarge F. Rousseau B. Poingt F. Legouezigou O. Pommereau F. Accard A. Gallion P. Duan G.-H. 《Electronics letters》2005,41(18):1007-1008
Self-pulsation at 45 GHz repetition frequency has been demonstrated in 1.5 /spl mu/m monolithic single-section quantum dot Fabry-Perot semiconductor lasers without saturable absorber. The mode-beating exhibits a narrow linewidth below 100 kHz, demonstrating high phase correlation between these modes. Such modelocked lasers open ways to low timing-jitter components for clock recovery or millimetre-wave generation in wireless transmission applications. 相似文献
6.
Franois Lavaud Michel Fontanille Yves Gnanou 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4964-4975
Studies on the anionic polymerization of methyl methacrylate in tetrahydrofuran and in the presence of sparteine have revealed a beneficial effect due to this additive, resulting in a decrease in the extent of termination. Better control of the definition of the polymers formed can thus be achieved in the presence of this additive. On the other hand, macromolecular engineering requires a range of active species concentrations lower than 10?3 mol L?1 and particularly the synthesis of polymers of high molar masses. For a better understanding of the mechanism of chain growth under such concentration conditions, the kinetics of polymerization have been investigated with a technique based on adiabatic calorimetry. Sparteine has been found to lack sufficient cation‐binding power to prevent the propagating enolate ion pairs from aggregating. The rate constant of propagation of nonaggregated species has been estimated, as well as the aggregation constant of equilibrium. For very low initiator concentrations, termination reactions have been shown to profoundly alter the control of the polymerization and to prevent a quantitative monomer conversion. Theoretical maximal conversions have been calculated from kinetic data and compare well with the experimental values. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4964–4975, 2004 相似文献
7.
Jean-Louis Iehl Rodolphe Grac Luc le Gratiet Véronique Bardinal Rainer Buhleier Elena Bedel-Pereira Chantal Fontaine Michel Pugnet Jacques-Henry Collet 《电信纪事》1997,52(11-12):627-637
We study the transient gratings photogenerated in the picosecond regime in three families of structures, namely : - structures of thickness in the order of one micron, including quantum wells (GaAs/GaAlAs, CdTe/ CdZnTe). A transmission modulation due to the electric field has been observed. We show that, in accordance with our calculations, this modulation is screened faster than 10 ps at a fluence of a few µJ/cm2. - A structure including GalnAs/GalnAsP MQWS in a cavity. This structure shows a top diffraction efficiency of 2.5 × 10-2 at 1.55 µm for an energy of excitation in the order of 100 µJ/cm2. The diffraction efficiency exhibits several oscillations due to Fabry-Pårot effects. By introducing cavity effects in our model, we show that the diffraction efficiency is amplified by more than a factor 2 with respect to the no-cavity case. Calculations show that the diffraction efficiency may reach 6 × 10-2 around 1.625 µm, for a front mirror reflectivity of 90 %. - Structures including bulk GaAs microcavities. The risetime is lower or in the order of 1 ps while the diffraction efficiency attains 1 %, with an average power of 4 mW (i.e. an energy of 2 µJ/cm2/pulse), compatible with a commutation of packets at 80 MHz. 相似文献
8.
Using the symbolic computation program MAPLE, we compute several terms of an asymptotic expansion for the distribution function of the logistic midrange. 相似文献
9.
Azuelos G. Benslama K. Costanzo D. Couture G. Garcia J.E. Hinchliffe I. Kanaya N. Lechowski M. Mehdiyev R. Polesello G. Ros E. Rousseau D. 《The European Physical Journal C - Particles and Fields》2004,39(2):13-24
The European Physical Journal C - We discuss possible searches for the new particles predicted by Little Higgs Models at the LHC. By using a simulation of the ATLAS detector, we demonstrate how the... 相似文献
10.
This article describes a professional development course intended to improve the content understanding of middle school mathematics teachers. The design of the course included three professional learning strategies: problem solving, examination of student thinking, and discussion of research. The concepts studied in the course included multi‐digit subtraction, multi‐digit multiplication, operations with fractions, and concepts of area and perimeter. Results from pre‐ and post‐tests administered to the nineteen participants indicate a significant increase in the mean score for each concept and document growth in the teachers' content understanding. In particular, their solutions moved from primarily procedural to more conceptual. Responses to an open‐ended survey indicate other important aspects of the professional development. Examples of teachers' work and comments are included. 相似文献