全文获取类型
收费全文 | 2655篇 |
免费 | 82篇 |
国内免费 | 9篇 |
专业分类
化学 | 1755篇 |
晶体学 | 26篇 |
力学 | 60篇 |
数学 | 335篇 |
物理学 | 570篇 |
出版年
2023年 | 18篇 |
2022年 | 84篇 |
2021年 | 82篇 |
2020年 | 57篇 |
2019年 | 58篇 |
2018年 | 56篇 |
2017年 | 41篇 |
2016年 | 79篇 |
2015年 | 88篇 |
2014年 | 85篇 |
2013年 | 156篇 |
2012年 | 169篇 |
2011年 | 180篇 |
2010年 | 113篇 |
2009年 | 109篇 |
2008年 | 156篇 |
2007年 | 124篇 |
2006年 | 111篇 |
2005年 | 111篇 |
2004年 | 92篇 |
2003年 | 56篇 |
2002年 | 74篇 |
2001年 | 45篇 |
2000年 | 44篇 |
1999年 | 40篇 |
1998年 | 36篇 |
1997年 | 34篇 |
1996年 | 29篇 |
1995年 | 31篇 |
1994年 | 33篇 |
1993年 | 27篇 |
1992年 | 33篇 |
1991年 | 24篇 |
1990年 | 19篇 |
1989年 | 11篇 |
1988年 | 22篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 28篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 16篇 |
1976年 | 9篇 |
1974年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有2746条查询结果,搜索用时 390 毫秒
991.
992.
Blois Lucca Neto Albano N. Carneiro Longo Ricardo L. Costa Israel F. Paolini Tiago B. Brito Hermi F. Malta Oscar L. 《Optics and Spectroscopy》2022,130(1):10-17
Optics and Spectroscopy - Eu3+ complexes and specially β-diketonate compounds are well known and studied in several areas due to their luminescence properties, such as sensors and lightning... 相似文献
993.
Costa E Lloyd MM Chopko C Aguiar-Ricardo A Hammond PT 《Langmuir : the ACS journal of surfaces and colloids》2012,28(26):10082-10090
The layer-by-layer (LbL) assembly of polyelectrolyte pairs on temperature and pH-sensitive cross-linked poly(N-isopropylacrylamide)-co-(methacrylic acid), poly(NIPAAm-co-MAA), microgels enabled a fine-tuning of the gel swelling and responsive behavior according to the mobility of the assembled polyelectrolyte (PE) pair and the composition of the outermost layer. Microbeads with well-defined morphology were initially prepared by synthesis in supercritical carbon dioxide. Upon LbL assembly of polyelectrolytes, interactions between the multilayers and the soft porous microgel led to differences in swelling and thermoresponsive behavior. For the weak PE pairs, namely poly(L-lysine)/poly(L-glutamic acid) and poly(allylamine hydrochloride)/poly(acrylic acid), polycation-terminated microgels were less swollen and more thermoresponsive than native microgel, whereas polyanion-terminated microgels were more swollen and not significantly responsive to temperature, in a quasi-reversible process with consecutive PE assembly. For the strong PE pair, poly(diallyldimethylammonium chloride)/poly(sodium styrene sulfonate), the differences among polycation and polyanion-terminated microgels are not sustained after the first PE bilayer due to extensive ionic cross-linking between the polyelectrolytes. The tendencies across the explored systems became less noteworthy in solutions with larger ionic strength due to overall charge shielding of the polyelectrolytes and microgel. ATR FT-IR studies correlated the swelling and responsive behavior after LbL assembly on the microgels with the extent of H-bonding and alternating charge distribution within the gel. Thus, the proposed LbL strategy may be a simple and flexible way to engineer smart microgels in terms of size, surface chemistry, overall charge and permeability. 相似文献
994.
M. Znini J. Paolini L. Majidi J.-M. Desjobert J. Costa N. Lahhit A. Bouyanzer 《Research on Chemical Intermediates》2012,38(2):669-683
The essential oil of the aerial parts of Lavandula multifida L., collected in Errachidia region (three samples) in southeast Morocco, was extracted by hydrodistillation and analyzed by GC and GC-MS. The oil was predominated by carvacrol (57.9–59.0%). L. multifida oil was tested as corrosion inhibitor of C38 steel in 0.5 M H2SO4 using weight loss measurements, electrochemical polarization, and EIS methods. The results obtained by measurements of weight loss showed that inhibition efficiency increases with inhibitor concentration to attain 72.2% at 2 g/l of oil at 298 K. Polarization curves revealed that L. multifida oil acts as mixed type inhibitor. The temperature effect on the corrosion behavior of steel in 0.5 M H2SO4 without and with the inhibitor at 2 g/l was studied in the temperature range from 303 and 343 K. The adsorption of inhibitor on the C38 steel surface was found to be a spontaneous process and to obey Langmuir’s adsorption isotherm. The associated activation energy has been determined. 相似文献
995.
Priebe JP Souza FD Silva M Tondo DW Priebe JM Micke GA Costa AC Bunton CA Quina FH Fiedler HD Nome F 《Langmuir : the ACS journal of surfaces and colloids》2012,28(3):1758-1764
Addition of salts, especially perchlorates, to zwitterionic micelles of SB3-14, C(14)H(29)NMe(2)(+)(CH(2))(3)SO(3)(-), induces anionic character and uptake of H(3)O(+) by SB3-14 micelles. Thus, the addition of alkali metal perchlorates accelerates the acid hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane, HPD, in the presence of SB3-14 micelles, which depends on the local proton concentration at the micelle surface. The addition of metal chlorides to solutions of such perchlorate-modified SB3-14 micelles decreases both the negative zeta potential of the micelles and the observed rate constant for acid hydrolysis of HPD. The effect of the monovalent cations Li(+), Na(+), and K(+) is smaller than that of the divalent cations Be(2+), Mg(2+), and Ca(2+), and much smaller than that of the trivalent cations Al(3+), La(3+), and Er(3+). The major factor responsible for this cation valence dependence of these effects is shown to be electrostatic in nature, reflecting the strong dependence of the micellar surface potential on the cation valence. The fact that the salt effects are not identical after correction for the electrostatic effects indicates that additional secondary nonelectrostatic effects may contribute as well. 相似文献
996.
J. Nunes‐Pereira A. C. Lopes C. M. Costa R. Leones M. M. Silva S. Lanceros‐Méndez 《Electroanalysis》2012,24(11):2147-2156
Porous membranes of poly(vinylidene fluoride‐trifluoroethylene) with different contents of montmorillonite (MMT) particles were prepared. The filler content does not affect the porous morphology but leads to an increase in the average pore size, porosity and electrolyte uptake up to 16 μm, 85 % and 325 %, respectively, for a membrane with 16 wt% of MMT particles. The mechanical properties, ionic conductivity and its temperature stability are improved by the presence of clays. The electrochemical stability reveals a stable operation window up to 5 V. The overall characteristics of the membranes for battery separators are optimized for the 4 wt% MMT filler content. 相似文献
997.
A. Gonçalves C. Costa S. Pereira N. Correia M. M. Silva P. C. Barbosa L. C. Rodrigues I. Henriques R. Martins E. Fortunato 《先进技术聚合物》2012,23(4):791-795
This paper reports the application of a polymethacrylate hydroxyethylene resin based electrolyte in electrochromic (EC) devices. The electrolyte is characterized by electrochemical impedance spectroscopy, visible spectroscopy, TGA, DSC, and DRX and tested as an ionic conductor in an EC device with the following configuration: Substrate/IZO/WO3/Polymer Electrolyte/(CeO2)TiO2/IZO/Substrate. The electrolyte presents an ionic conductivity of 10?7 S/cm at room temperature and TGA analysis show that electrolyte is thermally degraded at 200°C. The EC device based on this polymethacrylate hydroxyethylene resin electrolyte system shows memory effect and exhibits an excellent optical density. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
998.
Over the past years, the development of capillary electrophoresis (CE) and microchip electrophoresis (ME) systems has grown due to instrumental simplicity and wide application. In both CE and ME, the application of a high voltage (HV) is a crucial step in the electrokinetic (EK) injection and separation processes. Particularly on ME devices, EK injection is often performed with three different modes: gated, pinched, and unpinched. In all these cases, different potential values may be applied to one or multiple channels to control the injection of small sample volumes as well as the separation process. For this reason, the construction of reliable HV power supplies (HVPS) is required. This review covers the advances of the development of commercial and laboratory-built HVPS for CE and ME. Moreover, it intends to be a guide for new developers of electrophoresis instrumentation. 相似文献
999.
Synthesis of nanostructured magnetic photocatalyst by colloidal approach and spray-drying technique 总被引:1,自引:0,他引:1
A.L. Costa B. Ballarin A. SpegniF. Casoli D. Gardini 《Journal of colloid and interface science》2012,388(1):31-39
Nanostructured particles with a magnetic core and a photocatalytic shell are very interesting systems for their properties to be magnetically separable (and so reusable) in photocatalytic water depuration implant. Here, a robust, low time-consuming, easily scale up method to produce Fe3O4/SiO2/TiO2 hierarchical nanostructures starting from commercial precursors (i.e. Fe3O4, SiO2) by employing a colloidal approach (i.e. heterocoagulation) coupled with the spray-drying technique is presented. In particular, a self-assembled layer-by-layer methodology based on the coagulation of dissimilar colloidal particles was applied. First, a passive layer of silica (SiO2, amorphous) was created on magnetite in order to avoid detrimental phenomena arising from the direct contact between magnetite and titania, then the deposition of titania onto silica-coated-magnetite was promoted. TiO2, SiO2 and Fe3O4 nanosols were characterized in terms of zeta potential, optimized and a self-assembled layer-by-layer approach was followed in order to promote the heterocoagulation of silica onto magnetite surface and of titania onto silica coated magnetite. Once optimized the colloidal route, the mixture was then spray-dried to obtain a granulated powder with nano-scale reactivity, easier to handle and re-disperse in comparison to starting nanopowders with the same surface properties. The nanostructured particles have been characterized by different techniques such as SEM, TEM, XDR and their magnetic properties have been investigated. Moreover, preliminary photocatalytic texts have been performed. 相似文献
1000.
R. Carlini G. Zanicchi G. Borzone N. Parodi G. A. Costa 《Journal of Thermal Analysis and Calorimetry》2012,108(2):793-797
The results recently obtained by our group to get new thermoelectric materials belonging to the M–Pn–Ch ternary systems (M=Co,
Fe, Ni; Pn=P, As, Sb, Ch=S, Se, Te) are here reported. We have considered the Ni–Sb–S ternary system, and some homogeneous
samples of composition near to 1:1:1 were prepared employing a new and simple synthetic route, starting from pure elements.
Scanning electronic microscopy, electron-probe microanalysis and X-ray powder diffraction were used to investigate the microstructure.
The NiSbS lattice parameters were determined and the crystal structure was refined by Rietveld method. The crystal cell of
NiSbS belongs to the P213 space group with a = 0.5931 nm. The thermal stability of the ternary compounds Ni–Sb–S was investigated by DSC technique. Electrical resistivity
and thermoelectric power measurements at room temperature and at 77 K were performed on platelets obtained by cleavage of
the bulk. 相似文献