全文获取类型
收费全文 | 793篇 |
免费 | 55篇 |
专业分类
化学 | 654篇 |
晶体学 | 5篇 |
力学 | 17篇 |
数学 | 81篇 |
物理学 | 91篇 |
出版年
2023年 | 10篇 |
2022年 | 23篇 |
2021年 | 32篇 |
2020年 | 23篇 |
2019年 | 29篇 |
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 35篇 |
2015年 | 30篇 |
2014年 | 42篇 |
2013年 | 59篇 |
2012年 | 67篇 |
2011年 | 64篇 |
2010年 | 30篇 |
2009年 | 31篇 |
2008年 | 52篇 |
2007年 | 40篇 |
2006年 | 38篇 |
2005年 | 34篇 |
2004年 | 25篇 |
2003年 | 34篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1989年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1966年 | 2篇 |
1964年 | 1篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1958年 | 2篇 |
1955年 | 1篇 |
1954年 | 1篇 |
1922年 | 1篇 |
排序方式: 共有848条查询结果,搜索用时 15 毫秒
51.
Stationary phases for capillary electrochromatography with a longitudinal gradient of functionalities have been prepared via photoinitiated grafting of polymer chains onto the pore surface of a porous polymer monolith. In order to achieve the desired retention and electroosmotic flow, the hydrophobic poly(butyl methacrylate-co-ethylene dimethacrylate) monolith with optimized porous properties was grafted with a layer of ionizable polymer, poly(2-acrylamido-2-methyl-1-propanesulfonic acid). A moving shutter and a neutral density filter were used to control the dose of UV light received at different locations along the monolith in order to create the longitudinal gradient of functionalities. Formation of the desired gradients was confirmed using electron probe microanalysis of different locations along the column. The preparation technique significantly affects performance in the CEC mode as demonstrated on the separations of a model mixture using columns both with homogeneous distribution of grafts and with a gradient of functionality. Columns grafted with the gradient of functionalities were found superior to those functionalized uniformly. A comparison of the performance of the gradient column with another containing evenly distributed functionalities showed the performance benefits of the "gradient" column. 相似文献
52.
The behavior of the symmetrical ethane-bridged bis(Zn porphyrin) (1) has been investigated at the air-water interface. The molecular organization of floating films of pure 1 and its mixture with amphiphilic substances, such as arachidic acid and n-octadecylamine, was inspected by means of surface pressure-area isotherms, Brewster angle microscopy and reflection spectroscopy in the UV-Vis region. The overall results suggest the presence in all cases of mainly the anti conformer of 1 even when the dimer was spread on pure water, through the ligation of water molecules to the zinc atoms in the axial positions. It was also demonstrated for the first time that the syn-to-anti conformational transition of the porphyrin dimer can be accelerated by the ligation of suitable amphiphiles even at the liquid-air interface. In particular, it is noted that n-octadecylamine, and arachidic acid (to a lesser extent), added to the system as amphiphiles, drive the syn ? anti equilibrium of 1 towards the anti form through the axial ligation of the amino or carboxylate group to the zinc atoms. 相似文献
53.
B. Apicella A. Carpentieri R. Barbella P. Pucci 《Proceedings of the Combustion Institute》2007,31(1):547-553
Mass spectrometric analysis by laser desorption-time of flight-mass spectrometry (LDI-TOF-MS) was exploited to extend the detection of flame-formed polycyclic aromatic hydrocarbons (PAH) up to the mass limit of the first soot particles (>2000 Da) in the soot formation region of a premixed fuel-rich (C/O = 1) ethylene flame. The typical decreasing intensity of PAH ion peaks with increasing mass was found in the mass range m/z 500-1700 although a slight enrichment in the heavier part of PAH could be observed to occur along the flame axis. The separation by means of size exclusion chromatography (SEC) into two different classes of PAH followed by UV-visible spectroscopy corroborated the mass spectral identification of large mass PAH. Critical examination of mass spectral features and SEC separation was the starting point for speculation about the changes occurring in PAH growth from planar to concave structures which could be important for soot inception mechanisms. 相似文献
54.
Step-selective measurement by grating-based lateral shearing interferometry for segmented telescopes
We present an original step-selective mode which allows to measure only the steps and not the slowly varying aberrations of a wave front. This mode can be implemented when measuring segmented wave front by a diffraction-grating-based lateral shearing interferometer. This set-up rests on the different chromatic response of these interferometers depending on the rate of change of the impinging wave front: for smooth defects, the response is classically achromatic whereas it is chromatic for a step variation, which was to our knowledge overlooked. The interest of this mode for astronomical measurements is highlighted. First we present theoretical considerations to show how this mode of measure is possible; then a numerical simulation illustrates them. 相似文献
55.
Chengcheng Yang Valter Castelvetro Dominique Scalarone Sabrina Bianchi Yongming Zhang 《Journal of polymer science. Part A, Polymer chemistry》2011,49(21):4518-4530
Stable colloidal dispersions of nanostructured semifluorinated acrylic particles with an unfluorinated core and an outer layer consisting of copolymers of the highly hydrophobic and lipophobic heptadecafluorodecyl methacrylate (FMA) were successfully synthesized with the assistance of three different cyclodextrins as phase‐transfer catalysts: β‐cyclodextrin (β‐CD), hydroxypropyl β‐cyclodextrin (HpCD), and methyl β‐cyclodextrin (MeCD). While all the cyclodextrins form a stable inclusion complex (IC) with FMA, only the ICs with the more hydrophilic HpCD and MeCD are soluble in water. Nevertheless, incorporation of FMA in the particle shell copolymer could be achieved also when using β‐CD. On the other hand, the morphology of the nanostructured particles was characterized by a “patchy” fluorinated shell dependent on the cyclodextrin used, the best results being obtained with MeCD. A monomer‐starved semicontinuous emulsion polymerization procedure was essential to favor the CD‐mediated incorporation of FMA into the copolymer structure and to achieve a stable colloidal dispersion even in the presence of small amounts of mixed anionic–nonionic surfactants. The thermal and surface properties of the latex films showed a good correlation with the shell composition and patchy nanostructured morphology of the particles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
56.
57.
58.
59.
Sabrina Brait Stefano Deabate Selby A. R. Knox Enrico Sappa 《Journal of Cluster Science》2001,12(1):139-173
A survey of the synthetic pathways and of the reactivity and catalytic activity of transition metal carbonyl clusters substituted with benzyne (and, for comparison, benzene and diene) ligands is given. Cluster-surface analogies are helpful in gaining an understanding of the homogeneous and heterogeneous catalytic behaviour of the clusters. 相似文献
60.
Iolinda Aiello Mauro Ghedini Annarita Grisolia Daniela Pucci Oriano Francescangeli 《Liquid crystals》2005,32(6):763-769
New Ni(II) and UO2(II) metallomesogens obtained from mesomorphic N,N'-salicyliden(3,3'-diamine-N-methyldipropylamine) ligands containing a pentadentate N3O2 chelating cavity and bearing two or four lateral substituents, are isolated and fully characterized. Some of the synthesized nickel and dioxouranium complexes show a SmC mesophase. To the best of our knowledge, these species are the first pentacoordinated Ni(II) and heptacoordinated UO2(II) metallomesogens to be reported. 相似文献