全文获取类型
收费全文 | 95682篇 |
免费 | 1461篇 |
国内免费 | 1176篇 |
专业分类
化学 | 28627篇 |
晶体学 | 816篇 |
力学 | 7065篇 |
综合类 | 35篇 |
数学 | 32631篇 |
物理学 | 17318篇 |
无线电 | 11827篇 |
出版年
2023年 | 236篇 |
2022年 | 249篇 |
2021年 | 383篇 |
2020年 | 352篇 |
2019年 | 308篇 |
2018年 | 12016篇 |
2017年 | 11626篇 |
2016年 | 7249篇 |
2015年 | 1237篇 |
2014年 | 798篇 |
2013年 | 889篇 |
2012年 | 4862篇 |
2011年 | 12305篇 |
2010年 | 7286篇 |
2009年 | 7187篇 |
2008年 | 7669篇 |
2007年 | 10049篇 |
2006年 | 697篇 |
2005年 | 1933篇 |
2004年 | 1998篇 |
2003年 | 2421篇 |
2002年 | 1252篇 |
2001年 | 471篇 |
2000年 | 486篇 |
1999年 | 362篇 |
1998年 | 351篇 |
1997年 | 285篇 |
1996年 | 371篇 |
1995年 | 287篇 |
1994年 | 183篇 |
1993年 | 187篇 |
1992年 | 143篇 |
1991年 | 144篇 |
1990年 | 150篇 |
1989年 | 130篇 |
1988年 | 107篇 |
1987年 | 98篇 |
1986年 | 90篇 |
1985年 | 69篇 |
1984年 | 59篇 |
1983年 | 59篇 |
1982年 | 61篇 |
1981年 | 51篇 |
1980年 | 54篇 |
1979年 | 69篇 |
1978年 | 56篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Anindya Datta 《Pramana》2003,60(2):363-368
We propose a novel method for the search of supersymmetry, especially for the electroweak gauginos at the large hadron collider
(LHC). Gauge boson fusion technique was shown to be useful for heavy and intermediate mass Higgs bosons. In this article,
we have shown that this method can also be applied to find the signals of EW gauginos in supersymmetric theories where the
canonical search strategies for these particles fail. 相似文献
72.
A group of machines for processing a set of jobs in a manufacturing system is often located in a serial line. An efficient strategy for locating these machines such that the total travel distance or the cost of transporting the jobs is minimized is desired. In this research, the assumption of a linear line with equally spaced machine location is relaxed. This research addressed problems of locating unique machines. It is found that the machine distances possess unique properties in this type of a problem. Utilizing these properties, heuristic strategies are proposed to obtain efficient solution where optimal methods are expected to be computationally prohibitive. A lower bound for the optimum solution is also proposed. Results are encouraging. 相似文献
73.
关于方程(1)的极限环唯多性问题,不少人作了研究,[1]引进“n重互相包含”曲线类,,经[2]的改进获得较好的结果,但这类曲线要求的条件较多。本文不从[1]的观点出发,不包含[1]的全部条件,独立地用①11。’,LtnnoB变换折叠相平面,据轨线与折叠线交点的位置,对(1)的等价方程按线性方程积分,将积分的正负项作成比值进行比较,得出一组充分条件。 相似文献
74.
Dasgupta U. Wooi Gan Yeoh Chun Geik Tan Sheng Jau Wong Mori H. Singh R. Itoh M. 《Microwave Theory and Techniques》2002,50(11):2443-2452
An implementation of the IF section of WCDMA mobile transceivers with a set of two chips fabricated in an inexpensive 0.35-/spl mu/m two-poly three-metal CMOS process is presented. The transmit/receive chip set integrates quadrature modulators and demodulators, wide dynamic range automatic gain control (AGC) amplifiers, with linear-in-decibel gain control, and associated circuitry. This paper describes the problems encountered and the solutions envisaged to meet stringent specifications, with process and temperature variations, thus overcoming the limitations of CMOS devices, while operating at frequencies in the range of 100 MHz-1 GHz. Detailed measurement results corroborating successful application of the new techniques are reported. A receive AGC dynamic range of 73 dB with linearity error of less than /spl plusmn/2 dB and spread of less than 5 dB for a temperature range of -30/spl deg/C to +85/spl deg/C in the gain control characteristic has been measured. The modulator measurement shows a carrier suppression of 35 dB and sideband/third harmonic suppression of over 46 dB. The core die area of each chip is 1.5 mm/sup 2/. 相似文献
75.
Cornelis Van de Panne 《The Journal of the Operational Research Society》1992,43(12):1159-1171
The paper deals with the appropriate form of interaction between two refineries with different demand patterns. This problem can be formulated as finding a decentralized solution of linear programming problems linked by buying and selling activities. The complete problem is first solved for central values of product demands and costs and revenues. The structure of the basis then determines the organization of the interaction in terms of which unit sets quantities and which prices, or whether centralized decisions should be made. If, for expected values of product demand and costs, the structure of the basis is the same then the related organization of trading can be used for day-to-day transactions. For a well-known oil refinery model it is found that, for fairly large demand variations, decentralized interaction is effective, but that the structure of the basis changes easily with crude price variations, and that simulations did not converge for these variations. 相似文献
76.
77.
78.
James Tanton 《Mathematical Intelligencer》2007,29(3):55-59
This column is a place for those bits of contagious mathematics that travel from person to person in the community, because
they are so elegant, suprising, or appealing that one has an urge to pass them on.
Contributions are most welcome. 相似文献
79.
In this paper, we present a technique for using an additional parallel neural network to provide adaptive enhancements to a basic fixed neural network-based nonlinear control system. This proposed parallel adaptive neural network control system is applicable to nonlinear dynamical systems of the type commonly encountered in many practical position control servomechanisms. Properties of the controller are discussed, and it is shown that if Gaussian radial basis function networks are used for the additional parallel neural network, uniformly stable adaptation is assured and the approximation error converges to zero asymptotically. In the paper, the effectiveness of the proposed parallel adaptive neural network control system is demonstrated in real-time implementation experiments for position control in a servomechanism with asymmetrical loading and changes in the load 相似文献
80.
Shye Lin Wu Chung Len Lee Tan Fu Lei Chen C.F. Chen L.J. Ho K.Z. Ling Y.C. 《Electron Device Letters, IEEE》1994,15(4):120-122
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device 相似文献