全文获取类型
收费全文 | 145888篇 |
免费 | 4269篇 |
国内免费 | 2774篇 |
专业分类
化学 | 60563篇 |
晶体学 | 2095篇 |
力学 | 10050篇 |
综合类 | 274篇 |
数学 | 29858篇 |
物理学 | 50091篇 |
出版年
2023年 | 605篇 |
2022年 | 854篇 |
2021年 | 988篇 |
2020年 | 1173篇 |
2019年 | 1160篇 |
2018年 | 10667篇 |
2017年 | 11520篇 |
2016年 | 5822篇 |
2015年 | 2257篇 |
2014年 | 1820篇 |
2013年 | 2498篇 |
2012年 | 7801篇 |
2011年 | 16943篇 |
2010年 | 9991篇 |
2009年 | 10107篇 |
2008年 | 13891篇 |
2007年 | 17663篇 |
2006年 | 2169篇 |
2005年 | 9139篇 |
2004年 | 5080篇 |
2003年 | 4815篇 |
2002年 | 2534篇 |
2001年 | 1152篇 |
2000年 | 1246篇 |
1999年 | 922篇 |
1998年 | 795篇 |
1997年 | 742篇 |
1996年 | 997篇 |
1995年 | 730篇 |
1994年 | 674篇 |
1993年 | 554篇 |
1992年 | 532篇 |
1991年 | 495篇 |
1990年 | 415篇 |
1989年 | 357篇 |
1988年 | 308篇 |
1987年 | 265篇 |
1986年 | 241篇 |
1985年 | 258篇 |
1984年 | 237篇 |
1983年 | 182篇 |
1982年 | 169篇 |
1981年 | 164篇 |
1980年 | 140篇 |
1979年 | 152篇 |
1978年 | 168篇 |
1976年 | 109篇 |
1975年 | 103篇 |
1973年 | 120篇 |
1968年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
81.
Supposa that f(x) is a quasidifferentiable function, defined on S(?)R~n where S is an open set, with a -equivalent bounded quasidifferential subfam ily. Lenma I 相似文献
82.
M I Salema A P B Póvoa A Q Novais 《The Journal of the Operational Research Society》2006,57(6):615-629
In this paper, an MILP formulation is proposed for the design of a reverse logistics network based on a warehouse location–allocation model, which optimizes, simultaneously, the forward and reverse networks. A single product model with unlimited capacity is first defined. Subsequently, the model is extended to a multi-product capacitated recovery network model, where capacity limitations and a multi-product system can be considered. The proposed model is compared to published work in the field, where different model assumptions have been proposed. Two cases are described so as to gain a better insight into the model and allow a comparative analysis. 相似文献
83.
Jian Shen Huizhong Zeng Zhihong Wang Shengbo Lu Huidong Huang Jingsong Liu 《Applied Surface Science》2006,252(22):8018-8021
Polycrystalline Pb(Zr0.55Ti0.45)O3 thin film was deposited on Pt/Ti/SiO2/Si(1 0 0) by radio-frequency-magnetron sputtering method, and the writing of charge bits on the surface of PZT thin film was studied by Kelvin probe force microscopy. It is found that the surface potential of the negative charge bits are higher than those of the corresponding positive ones. When ferroelectric polarization switching occurs, the potential difference becomes even more remarkable. A qualitative model was proposed to explain the origin of the asymmetric charge writing. It is demonstrated that the internal field in the interface layer, which is near the ferroelectric/electrode interface in ferroelectric film, is likely to be the cause for the occurrence of this phenomenon. 相似文献
84.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak
estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum,
minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity
networks is considered.
Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002 相似文献
85.
86.
This paper reports that the growth of RuOx(110) thin layer growth on Ru(0001)
has been investigated by means of scanning tunnelling microscope (STM). The STM
images showed a domain structure with three rotational domains of RuOx(110)
rotated by an angle of 120℃.
The as-grown RuOx(110) thin layer is expanded from the bulk-truncated
RuOx(110) due to the large mismatch between RuOx(110) and the
Ru(0001) substrate. The results also indicate that growth of RuOx(110)
thin layer on the Ru(0001) substrate by oxidation tends first to formation
of the Ru-O (oxygen) chains in the [001] direction of RuOx(110). 相似文献
87.
L. Tong Y. Tian Q. Y. Wang Y. S. Ling 《International Journal of Infrared and Millimeter Waves》2006,27(9):1307-1314
The paper introduces a special system calibration technology in s-parameters measurement of microwave and millimeter wave
devices. The 8-term errors module is built by analyzing the signals flowing in the measurement system. Then the calibration
technology using non-standard kits is designed on the base. Finally, the experiment using the calibration technology is introduced. 相似文献
88.
V. Yu. Baranovskii L. L. Yasina M. V. Motyakin I. I. Aliev S. Shenkov M. Dimitrov N. Lambov A. M. Wasserman 《Polymer Science Series A》2006,48(12):1304-1309
Partially water-swellable polymer networks were synthesized on the basis of poly(acrylic acid) and various macrodiisocyanates. Hydrophilic and hydrophobic local regions were revealed in swollen networks (hydrogels) by means of the spin probe technique. The local mobility in hydrophobic regions depends on the macrodiisocyanate structure; however, it is substantially lower than that in hydrophilic regions for all gels. It was assumed that the presence of hydrophobic and hydrophilic regions and the difference in their local dynamics must have a substantial effect on the pharmacokinetics of release of drugs immobilized in these hydrogels. 相似文献
89.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame. 相似文献
90.
This study addresses the problem of the automatic flow regime identification in two-phase flows in pipes. A novel wavelet transform-based approach is proposed and validated using time series of differential pressure fluctuations. The experimental data on the differential pressure measured in a vertically installed Venturi meter for air-water flow were analyzed and found to be appropriate for flow regime identification. The wavelet spectrum of the measured signal is shown to characterize the flow patterns completely, and the vector of the wavelet variances is proposed as the characteristic vector for use in an on-line flow regime identification system. 相似文献