全文获取类型
收费全文 | 4628篇 |
免费 | 257篇 |
国内免费 | 27篇 |
专业分类
化学 | 3228篇 |
晶体学 | 20篇 |
力学 | 99篇 |
数学 | 648篇 |
物理学 | 917篇 |
出版年
2024年 | 6篇 |
2023年 | 48篇 |
2022年 | 65篇 |
2021年 | 97篇 |
2020年 | 137篇 |
2019年 | 133篇 |
2018年 | 90篇 |
2017年 | 73篇 |
2016年 | 217篇 |
2015年 | 158篇 |
2014年 | 188篇 |
2013年 | 258篇 |
2012年 | 392篇 |
2011年 | 489篇 |
2010年 | 227篇 |
2009年 | 143篇 |
2008年 | 312篇 |
2007年 | 323篇 |
2006年 | 290篇 |
2005年 | 273篇 |
2004年 | 193篇 |
2003年 | 125篇 |
2002年 | 110篇 |
2001年 | 46篇 |
2000年 | 34篇 |
1999年 | 31篇 |
1998年 | 24篇 |
1997年 | 23篇 |
1996年 | 41篇 |
1995年 | 36篇 |
1994年 | 32篇 |
1993年 | 34篇 |
1992年 | 28篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 17篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1974年 | 8篇 |
1973年 | 34篇 |
排序方式: 共有4912条查询结果,搜索用时 10 毫秒
71.
Ceramides are important intracellular second messengers that play a role in the regulation of cell growth, differentiation and programmed cell death. Qualitative and quantitative analysis of these second messengers requires sensitive and specific analytical methods to detect endogenous levels of individual ceramide species and to differentiate between them. Nine synthetic ceramides were separated by liquid chromatography coupled to tandem mass spectrometry on a C18 bonded silica column. The lipids were eluted in gradient elution mode using a mixture of water, acetonitrile and 2-propanol as mobile phase. They were detected by reaction monitoring performed on positive ion electrospray generated ions. Collision-induced fragmentations conducted on ceramides produced a well characteristic product ion at m/z 264, making multiple reaction monitoring (MRM) well suited for various ceramides quantitative measurements. After optimization of the extraction step, the proposed methodology was able to identify and quantify different ceramide species issued from human cancer cells. The method could be validated for C16, C18 and C20 ceramides, quantified at the nanogram level. The validation exhibits good results with respect to linearity, accuracy and precision. 相似文献
72.
73.
Ortmans I Elias B Kelly JM Moucheron C Kirsch-DeMesmaeker A 《Dalton transactions (Cambridge, England : 2003)》2004,(4):668-676
The lowest excited state of [Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene, dppz = dipyrido[3,2-a:2',3'-c]phenazine) 1 is strongly luminescent, even in water, and very oxidizing. Therefore it is able to oxidise not only guanosine-5'-monophosphate (GMP), as demonstrated by laser flash photolysis, but also guanine-containing polynucleotides such as calf thymus DNA and [poly(dG-dC)]2. The luminescence quenching was found to be faster in H2O than in D2O, as is the back reaction, indicating that both processes probably proceed by proton-coupled electron transfer. These properties, that are controlled by the triplet MLCT state in which the charge has been transferred from the Ru to a TAP ligand, contrast with those of the well known [Ru(phen)2(dppz)]2+ 2. 相似文献
74.
75.
O'Driscoll BM Ruggles JL Gentle IR 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6246-6251
Langmuir and Langmuir-Blodgett (LB) films of a cationic amphiphilic porphyrin mixed with n-alkanes octadecane and hexatriacontane were prepared and characterized, to examine the influence of the alkanes on film structure and stability. While the structure present in these films was controlled primarily by the porphyrin, the addition of the alkanes resulted in significant changes to both the phase behavior of the Langmuir films and the molecular arrangement of the LB films. These changes, as well as the observed chain length effects, are explained in terms of the intermolecular interactions present in the films. 相似文献
76.
77.
Shape-controlled synthesis of metal nanostructures: the case of silver 总被引:19,自引:0,他引:19
The concept of shape-controlled synthesis is discussed by investigating the growth mechanisms for silver nanocubes, nanowires, and nanospheres produced through a polymer-mediated polyol process. Experimental parameters, such as the concentration of AgNO(3) (the precursor to silver), the molar ratio between poly(vinylpyrrolidone) (PVP, the capping agent) and AgNO(3), and the strength of chemical interaction between PVP and various crystallographic planes of silver, were found to determine the crystallinity of seeds (e.g., single crystal versus decahedral multiply twinned particles). In turn, the crystallinity of a seed and the extent of the PVP coverage on the seed were both instrumental in controlling the morphology of final product. The ability to generate silver nanostructures with well-defined morphologies provides a great opportunity to experimentally and systematically study the relationship between their properties and geometric shapes. 相似文献
78.
Benjamin Scharf 《Chemical physics letters》1983,96(1):89-92
Prominent progressions of non-totally symmetric modes may ensue in non-linear molecules in electronic transitions involving degenerate states in the absence of Jahn-Teller distortions. In the presence of Jahn-Teller interactions prominent non-Jahn-Teller progressions may result. 相似文献
79.
Population balance equations (PBEs) for reversible aggregation-fragmentation processes are important to particle agglomeration and dissolution, polymerization and degradation, liquid droplet coalescence and breakup, and floc coagulation and disintegration. Moment solutions provide convenient solutions to the PBEs, including steady state and similarity solutions, but may not be feasible for complex forms of size-dependent rate coefficients and stoichiometric kernels. Numeric solutions are thus necessary not only for applications, but also for the study of the mathematics of PBEs. Here we propose a numerical method to solve PBEs and compare the results to moment solutions. The numeric results are consistent with known steady state and asymptotic long-time similarity solutions and show how processes can be approximated by self-similar formulations. 相似文献
80.
Photosensitized oxidation through stearate monomolecular films 总被引:1,自引:0,他引:1
Abstract— The photosensitized oxidations of rubrene by methylene blue and of diphenylan-thracene by eosin have been studied where the sensitizer and the oxidizable substrate are separated by oxygen permeable layers of barium or cadmium stearate monomolecular films. The rate of the photosensitized oxidation reaction was followed by measurements of the hydrocarbon fluorescence, as a function of the stearate layer thickness. It has been found that the sensitized reaction is observable for thickness up to 500 Å and depends only on the deactivation process of the excited species (singlet oxygen) diffusing through the layers. It has been found also that half of the excited oxygen molecules are deactivated after a diffusion path of 115 A. The starting hydrocarbon can be regenerated by heating the sample after the photoreaction to approximately 120°C showing the transannular peroxide nature of the oxidation product. 相似文献