全文获取类型
收费全文 | 1733篇 |
免费 | 118篇 |
国内免费 | 27篇 |
专业分类
化学 | 1200篇 |
晶体学 | 11篇 |
力学 | 70篇 |
综合类 | 2篇 |
数学 | 292篇 |
物理学 | 303篇 |
出版年
2023年 | 11篇 |
2022年 | 35篇 |
2021年 | 37篇 |
2020年 | 48篇 |
2019年 | 44篇 |
2018年 | 32篇 |
2017年 | 28篇 |
2016年 | 82篇 |
2015年 | 57篇 |
2014年 | 79篇 |
2013年 | 111篇 |
2012年 | 120篇 |
2011年 | 140篇 |
2010年 | 73篇 |
2009年 | 96篇 |
2008年 | 102篇 |
2007年 | 87篇 |
2006年 | 65篇 |
2005年 | 76篇 |
2004年 | 71篇 |
2003年 | 71篇 |
2002年 | 61篇 |
2001年 | 17篇 |
2000年 | 32篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 16篇 |
1996年 | 19篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 4篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1984年 | 20篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 12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1878条查询结果,搜索用时 0 毫秒
991.
Dual optical sensor for oxygen and temperature based on the combination of time domain and frequency domain techniques 总被引:1,自引:0,他引:1
In measuring specific conditions in the real world, there are many situations where both the oxygen concentration and the temperature have to be determined simultaneously. Here we describe a dual optical sensor for oxygen and temperature that can be adapted for different applications. The measurement principle of this sensor is based on the luminescence decay times of the oxygen-sensitive ruthenium complex tris-4,7-diphenyl-1,10-phenanthroline ruthenium(III) [Rudpp] and the temperature-sensitive europium complex tris(dibenzoylmethane) mono(5-amino-1,10-phenanthroline)europium(III) [Eudatp]. The excitation and emission spectra of the two luminophores overlap significantly and cannot be discriminated in the conventional way using band pass filters or other optical components. However, by applying both the frequency and time domain techniques, we can separate the signals from the individual decay time of the complexes. The europium complex is entrapped in a poly(methyl methacrylate) (PMMA) layer and the ruthenium complex is physically adsorbed on silica gel and incorporated in a silicone layer. The two layers are attached to each other by a double sided silicone based tape. The europium sensing film was found to be temperature-sensitive between 10 and 70 °C and the ruthenium oxygen-sensitive layer can reliably measure between 0 and 21% oxygen. 相似文献
992.
Wen-Liang Hung Miin-Shen Yang E. Stanley Lee 《Mathematical and Computer Modelling》2011,53(9-10):1776-1787
Cellular manufacturing is a useful way to improve overall manufacturing performance. Group technology is used to increase the productivity for manufacturing high quality products and improving the flexibility of manufacturing systems. Cell formation is an important step in group technology. It is used in designing good cellular manufacturing systems. The key step in designing any cellular manufacturing system is the identification of part families and machine groups for the creation of cells that uses the similarities between parts in relation to the machines in their manufacture. There are two basic procedures for cell formation in group technology. One is part-family formation and the other is machine–cell formation. In this paper, we apply a fuzzy relational data clustering algorithm to form part families and machine groups. A real data study shows that the proposed approach performs well based on the grouping efficiency proposed by Chandrasekharan and Rajagopalan. 相似文献
993.
Sunjong Oh Tran Quang Hung Migaku Takahashi CheolGi Kim 《Solid State Communications》2011,151(18):1248-1251
The AMR (anisotropic magnetoresistance) and PHR (planar Hall resistance) contribution was analyzed for fabricated ring type sensor junctions in single and multiring bridge sensors, and their field sensitivity was examined. The voltage profile, i.e. the sum of AMR and PHR effects, reveal anti-symmetric behavior with the magnetic field with small offsets due to the self-balancing of ring arm resistances, but the voltage variations for the external field are additive for all junction components. The field sensitivity of the resistance for a single ring sensor is , and its value monotonously increased to for 17 rings with an enhanced active area. 相似文献
994.
A heavy fourth generation with a mass of the order of 400 GeV or more could trigger dynamical electroweak symmetry breaking by forming condensates through the exchange of a fundamental Higgs scalar doublet. The dynamics leading to these condensates is studied within the framework of the Schwinger–Dyson equation. This scenario leads to the presence of three (two composite and one fundamental) Higgs doublets, with interesting phenomenological implications. In addition, this dynamical phenomenon occurs in the vicinity of the energy scale where the restoration of scale symmetry might happen. 相似文献
995.
Hung AM Konopliv NA Cha JN 《Langmuir : the ACS journal of surfaces and colloids》2011,27(20):12322-12328
We demonstrate a purely solvent-based approach to assembling CdSe nanorods into vertically aligned, hexagonally packed monolayers in solution. Nanorods were dispersed in a mixture of good solvent with high vapor pressure and bad solvent with low vapor pressure, and preferential evaporation of the good solvent led to ordered assembly under conditions of continuously decreasing solvent quality. No applied external bias, extensive control of drying conditions, exceptionally monodisperse nanoparticles, or high concentrations of additives were required. This clean and facile method yielded ordered nanorod sheets of up to 7.5 μm wide with potential use as active materials in unique applications. 相似文献
996.
Lou JL Shiu HW Chang LY Wu CP Soo YL Chen CH 《Langmuir : the ACS journal of surfaces and colloids》2011,27(7):3436-3441
We have grown 1-dodecandthiol (DDT) monolayer on a bare Si(111) surface through ultraviolet-assisted photochemical reaction. The resulting monolayer was investigated by means of water contact angle measurement, synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy, and polarization-dependent near-edge X-ray absorption fine structure spectroscopy. These combined probes for characterization reveal a hydrophobic ambient surface; the DDT was directly attached to Si through a Si-S bond, and the molecules formed an ordered monolayer with an average tilt angle of 57° of the alkyl chains relative to the substrate surface. 相似文献
997.
A liquid phase microextraction method using hollow fiber to support extraction solvent was developed for enrichment of trace level chloroanilines in environmental water samples. Target analytes, 2-chloroaniline, 3-chloroaniline, 2,3-dichloroaniline, 2,4-dichloroaniline, 3,4-dichloroaniline, and 3,5-dichloroaniline were determined using gas chromatography-flame ionization detector after extraction. Experimental conditions that affect extraction efficiency were investigated and optimized. The proposed method showed a wide linear range from lower ??g L?1 to 1,000 ??g L?1, low detection limits (??5.1 ??g L?1), and reasonable relative standard deviations (RSDs < 13%). Feasibility of the method was evaluated by analyzing river water samples collected from the Hudson River and the East River in New York City. 相似文献
998.
999.
1000.
Emmanuel A. Gonzalez John Y. Hung Lubomir Dorcak Jan Terpak Ivo Petras 《Central European Journal of Physics》2013,11(6):868-880
The number of studies on the control of fractional-order processes—processes having dynamics described by differential equations of arbitrary order—has been increasing in the past two decades and it is now ubiquitous. Various methods have emerged and have been proven to effectively control such processes—usually resulting in fractional-order controllers similar to their conventional integer-order counterparts, which include, but are not limited to fractional PID and fractional lead-lag controllers. However, such methods require a lot of computational effort and fractional-order controllers could be challenging when it comes to their synthesis and implementation. In this paper, we propose a simple yet effective delay-based controller with the use of the Posicast control methodology in controlling the overshoot of a fractional-order process of the class $\mathcal{P}:\left\{ {P\left( s \right) = {1 \mathord{\left/ {\vphantom {1 {\left( {as^\alpha + b} \right)}}} \right. \kern-0em} {\left( {as^\alpha + b} \right)}}} \right\}$ having orders 1 < α < 2. Such controllers have proven to be easy to implement because they only require delays and summers. In this paper, the Posicast control methodology introduced in the past few years is modified to minimize the overshoot of the processes step response to a level that is acceptable in control engineering and automation practices. Furthermore, proof of the existence of overshoot for such class of processes, as well as the determination of the peak-time of the open-loop response of a fractional-order process of the class P is presented. Validation through numerical simulations for a class of fractional-order processes are presented in this paper. 相似文献