全文获取类型
收费全文 | 1534篇 |
免费 | 77篇 |
国内免费 | 7篇 |
专业分类
化学 | 1249篇 |
晶体学 | 14篇 |
力学 | 13篇 |
数学 | 82篇 |
物理学 | 260篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 26篇 |
2019年 | 47篇 |
2018年 | 20篇 |
2017年 | 17篇 |
2016年 | 44篇 |
2015年 | 37篇 |
2014年 | 48篇 |
2013年 | 78篇 |
2012年 | 101篇 |
2011年 | 100篇 |
2010年 | 78篇 |
2009年 | 70篇 |
2008年 | 102篇 |
2007年 | 106篇 |
2006年 | 81篇 |
2005年 | 69篇 |
2004年 | 86篇 |
2003年 | 64篇 |
2002年 | 47篇 |
2001年 | 26篇 |
2000年 | 26篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 17篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1976年 | 14篇 |
1975年 | 18篇 |
1974年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有1618条查询结果,搜索用时 640 毫秒
1.
Recently, we developed a convenient microfluidic droplet generation device based on vacuum‐driven fluid manipulation with a piezoelectric diaphragm micropump. In the present study built on our previous work, we investigate the influence of settings applied to the piezoelectric pump, such as peak‐to‐peak drive voltage (Vp‐p) and wave frequency, on droplet generation characteristics. Stepwise adjustments to the drive voltage in ±10‐Vp‐p increments over the range of 200?250 Vp‐p during droplet creation revealed that the droplet generation rate could be reproducibly controlled at a specific drive voltage. The droplet generation rate switched within <0.5 s after the input of a new voltage. Although the droplet generation rate depended on the drive voltage, this setting had almost no influence on droplet size. The frequency over the selected range (50?60 Hz) did not markedly influence the droplet generation rate or droplet size. We show that the current fluid manipulation system can be conveniently used for both droplet generation and for rapid droplet reading, which is required in many microfluidic‐based applications. 相似文献
2.
3.
4.
Resonance-enhanced multiphoton ionization mass spectrometry using a two-color laser beam generated by stimulated Raman scattering. 总被引:2,自引:0,他引:2
Two-color (1+1') resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (REMPI/TOF-MS) combined with supersonic jet (SSJ) spectrometry has been demonstrated. The methodology uses a two-color laser beam consisting of a Stokes beam generated by stimulated Raman scattering (SRS) and a fundamental beam for the excitation and subsequent ionization of p-dichlorobenzene. The MPI signal was found to be substantially increased when a two-color laser beam was employed. This approach greatly simplifies the analytical system and reduces the cost of the instrumentation required for two-color ionization. The potential advantage of applying this method for the analysis of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) emitted from an incinerator is discussed. 相似文献
5.
6.
Kohji Masaki Shin-ichi Ohkawara Tomohiro Hirano Makiko Seno Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4437-4447
The crosslinking reaction of 1,2-polybutadiene (1,2-PB) with dicumyl peroxide (DCPO) in dioxane was kinetically studied by means of Fourier transform near-infrared spectroscopy (FTNIR). The crosslinking reaction was followed in situ by the monitoring of the disappearance of the pendant vinyl group of 1,2-PB with FTNIR. The initial disappearance rate (R0) of the vinyl group was expressed by R0 = k[DCPO]0.8[vinyl group]−0.2 (120 °C). The overall activation energy of the reaction was estimated to be 38.3 kcal/mol. The unusual rate equation was explained in terms of the polymerization of the pendant vinyl group as an allyl monomer involving degradative chain transfer to the monomer. The reaction mixture involved electron spin resonance (ESR)-observable polymer radicals, of which the concentration rapidly increased with time owing to a progress of crosslinking after an induction period of 200 min. The crosslinking reaction of 1,2-PB with DCPO was also examined in the presence of vinyl acetate (VAc), which was regarded as a copolymerization of the vinyl group with VAc. The vinyl group of 1,2-PB was found to show a reactivity much higher than 1-octene and 3-methyl-1-hexene as model compounds in the copolymerization with VAc. This unexpectedly high reactivity of the vinyl group suggested that an intramolecular polymerization process proceeds between the pendant vinyl groups located on the same polymer chain, possibly leading to the formation of block-like polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4437–4447, 2004 相似文献
7.
Studies on ternary phase diagrams of the Na-Fe-O system have been carried out from the thermodynamic point of view. Thermodynamic data of main ternary Na-Fe oxides Na4FeO3(s), Na3FeO3(s), Na5FeO4(s) and Na8Fe2O7(s) have been assessed. A user database has been created by reviewing literature data together with recent DSC and vapor pressure measurements by the present authors. New ternary phase diagrams of the Na-Fe-O system have been constructed from room temperature to 1000 K. Stable conditions of the ternary oxides at 800 K were presented in predominance diagram as functions of oxygen pressure and sodium pressure. 相似文献
8.
9.
In this paper, we study Schrödinger type operator on a Riemannian manifold. Under some assumptions on a potential function, we characterize the domain of the square root of the Schrödinger type operator on L p space. In the proof, the defective intertwining properties and the Littlewood-Paley inequalities play important roles. 相似文献