全文获取类型
收费全文 | 1815篇 |
免费 | 120篇 |
国内免费 | 27篇 |
专业分类
化学 | 1245篇 |
晶体学 | 11篇 |
力学 | 72篇 |
综合类 | 2篇 |
数学 | 316篇 |
物理学 | 316篇 |
出版年
2023年 | 13篇 |
2022年 | 38篇 |
2021年 | 40篇 |
2020年 | 50篇 |
2019年 | 46篇 |
2018年 | 37篇 |
2017年 | 32篇 |
2016年 | 85篇 |
2015年 | 62篇 |
2014年 | 83篇 |
2013年 | 117篇 |
2012年 | 124篇 |
2011年 | 147篇 |
2010年 | 78篇 |
2009年 | 98篇 |
2008年 | 104篇 |
2007年 | 90篇 |
2006年 | 67篇 |
2005年 | 76篇 |
2004年 | 71篇 |
2003年 | 72篇 |
2002年 | 61篇 |
2001年 | 18篇 |
2000年 | 32篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 20篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 4篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1984年 | 20篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 15篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有1962条查询结果,搜索用时 15 毫秒
961.
962.
C.Y. Hung 《Optics Communications》2006,259(2):670-675
A new configuration of L-band erbium-doped fiber amplifiers (EDFAs) is presented here. The system contains a double-pass L-band EDFA and an optical preamplifier. Different from conventional preamplified double-pass L-band EDFA systems in which only the forward ASE of the preamplifier is re-used as an auxiliary pump, the new system recycles the backward ASE of the preamplifier as well. Two kinds of main L-band EDFAs are studied, both of which include a section of un-pumped erbium-doped fiber placed in a loop reflector. An improvement of up to 110% in pump conversion efficiency is demonstrated with the proposed recycling of the backward ASE, with respect to the system without recycling. 相似文献
963.
Hong Fang ZHANG Jian Bin ZHENG Hong Gang NI Hung KAO 《中国化学快报》2005,16(9):1249-1251
Oscillographic chronopotentiometry is a type of current-controlled electroanalytical technique founded by J.Heyrovsky in19411and developed by Hung Kao after19632-5.In this technique,a constant-amplitude of alternating current j=j0sin(ωt)as well as a less direct current,passed through the electrolytic cell and the change of potential of the polarizable electrode exhibited on the oscillograph directly as a function of time during a continuous potential scan from zero to–2V.Generally,quantita… 相似文献
964.
A characteristic of data envelopment analysis (DEA) is to allow individual decision-making units (DMUs) to select the factor weights that are the most advantageous for them in calculating their efficiency scores. This flexibility in selecting the weights, on the other hand, deters the comparison among DMUs on a common base. In order to rank all the DMUs on the same scale, this paper proposes a compromise solution approach for generating common weights under the DEA framework. The efficiency scores calculated from the standard DEA model are regarded as the ideal solution for the DMUs to achieve. A common set of weights which produces the vector of efficiency scores for the DMUs closest to the ideal solution is sought. Based on the generalized measure of distance, a family of efficiency scores called ‘compromise solutions’ can be derived. The compromise solutions have the properties of unique solution and Pareto optimality not enjoyed by the solutions derived from the existing methods of common weights. An example of forest management illustrates that the compromise solution approach is able to generate a common set of weights, which not only differentiates efficient DMUs but also detects abnormal efficiency scores on a common base. 相似文献
965.
966.
Hsuan‐Ming Huang I‐Chun Liu Ching‐Yu Chang Hung‐Chieh Tsai Chuan‐Hsiao Hsu Raymond Chien‐Chao Tsiang 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5802-5810
A new method was developed for preparing polystyrene‐functionalized multiple‐walled carbon nanotubes (MWNTs) through the termination of anionically synthesized living polystyryllithium with the acyl chloride functionalities on the MWNTs. The acyl chloride functionalities on the MWNTs were in turn obtained by the formation of carboxyls via chemical oxidation and their conversion into acyl chlorides. The polystyrene‐functionalized MWNTs had good dispersion in common organic solvents, and this indicated good compatibility for the preparation of styrenic nanocomposite materials. The synthesis results and characterization data for the functionalized MWNTs, collected via Fourier transform infrared, thermogravimetric analysis, solid‐state NMR, and electron microscopy, are presented and discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5802–5810, 2004 相似文献
967.
Chun-Min Hung Yueh-Min Huang Ming-Shi Chang 《Nonlinear Analysis: Theory, Methods & Applications》2006
A hybrid evolutionary model is used to propose a hierarchical homology of protein sequences to identify protein functions systematically. The proposed model offers considerable potentials, considering the inconsistency of existing methods for predicting novel proteins. Because some novel proteins might align without meaningful conserved domains, maximizing the score of sequence alignment is not the best criterion for predicting protein functions. This work presents a decision model that can minimize the cost of making a decision for predicting protein functions using the hierarchical homologies. Particularly, the model has three characteristics: (i) it is a hybrid evolutionary model with multiple fitness functions that uses genetic programming to predict protein functions on a distantly related protein family, (ii) it incorporates modified robust point matching to accurately compare all feature points using the moment invariant and thin-plate spline theorems, and (iii) the hierarchical homologies holding up a novel protein sequence in the form of a causal tree can effectively demonstrate the relationship between proteins. This work describes the comparisons of nucleocapsid proteins from the putative polyprotein SARS virus and other coronaviruses in other hosts using the model. 相似文献
968.
Chien-Lun Hung Yi Sheng Yeh 《International Journal of Infrared and Millimeter Waves》2005,26(1):29-39
Overmoded coaxial waveguides have been used in coaxial gyrotrons as a key interaction structure. To achieve the required mode selectivity, the resistivity of the center conductor is properly chosen to damp unwanted modes. Considering attenuation due to conductor loss, this study employs the perturbational method to determine the propagation constants of higher-order modes in the coaxial waveguide. The validity of the theoretical model is confirmed by comparison with results obtained using the high-frequency structure simulator (HFSS). Moreover, the method proposed herein is applied to analyze the ohmic mode selection of the coaxial waveguide. 相似文献
969.
Hybrid microspheres of poly(methyl acrylate‐co‐divinylbenzene) (PMADVB) with a thin and porous nickel–phosphorus (Ni–P) alloy layer were prepared via suspension polymerization and electroless nickel plating. The characterization of pristine and nickel‐coated microspheres was carried out with a differential scanning calorimeter and a scanning electron spectroscope equipped with an energy‐dispersive system. The glass‐transition range of Ni–P‐coated PMADVB was broadened and extended in the higher temperature direction. This effect allowed the PMADVB network to embrace more diversified energy states of the segment motion, this being a desired feature for damping sound waves. The low‐frequency (100–1000‐Hz) sound absorption behavior of the microspheres was tested with a sound attenuation kit. Besides the testing of their low‐frequency damping performance, an investigation into the ultrasonic‐wave (~35 kHz) absorption feature of the microspheres was conducted through chemical means; that is, the attenuation to the ultrasonic wave with respect to the unprotective situation was assessed through the chemisorption extent of copper ions on a biomass adsorbent. The Ni–P deposition layer was found to augment the damping capacity of the polymer network. The alloy layer was determined to cause an expansion of the glass‐transition range of PMADVB and its wave‐scattering capability because this layer was made up of submicrometer metallic grains. In this work, the particulars of the metal–polymer interactions were associated with a core–shell structure. The metal outer layer was thought to create a spherical temperature field inside the PMADVB network, and concerted motions of the polymer segments resulted. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2710–2723, 2004 相似文献
970.
The mitigating effect of a water wall on the generation and propagation of blast waves of a nearby explosive has been investigated
using a numerical approach. A multimaterial Eulerian finite element technique is used to study the influence of the design
parameters, such as the water-to-explosive weight ratio, the water wall thickness, the air-gap and the cover area ratio of
water on the effectiveness of the water mitigation concept. In the computational model, the detonation gases are modelled
with the standard Jones–Wilkins–Lee (JWL) equation of state. Water, on the other hand, is treated as a compressible fluid
with the Mie–Gruneisen equation of state model. The validity of the computational model is checked against a limited amount
of available experimental data, and the influence of mesh sizes on the convergence of results is also discussed. From the
results of the extensive numerical experiments, it is deduced that firstly, the presence of an air-gap reduces the effectiveness
of the water mitigator. Secondly, the higher the water-to-explosive weight ratio, the more significant is the reduction in
peak pressure of the explosion. Typically, water-to-explosive weight ratios in the range of 1–3 are found to be most practical.
PACS 47.40.-x; 47.40.Nm; 02.60.Cb
This paper was based on work that was presented at the 19th Interna-tional Colloquium on the Dynamics of Explosions and Reactive
Sys-tems, Hakone, Japan, July 27 - August 1, 2003 相似文献