全文获取类型
收费全文 | 209篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 171篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 17篇 |
物理学 | 22篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 8篇 |
2014年 | 4篇 |
2013年 | 9篇 |
2012年 | 14篇 |
2011年 | 14篇 |
2010年 | 12篇 |
2009年 | 4篇 |
2008年 | 22篇 |
2007年 | 15篇 |
2006年 | 24篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1980年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有214条查询结果,搜索用时 640 毫秒
131.
DJ Smith KW Ledingham RP Singhal T McCanny P Graham HS Kilic P Tzallas C Kosmidis AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1366-1373
With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
132.
Jae Ho Yang Woong Kil Choo Chang Hee Lee 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):i86-i88
The room‐temperature structure of the B‐site‐ordered complex perovskite dicalcium magnesium tungstate, Ca2MgWO6, has been determined by simultaneous Rietveld refinement of neutron and X‐ray powder diffraction patterns. Ca2MgWO6 is characterized by B‐site ordering and an a−a−c+‐type BO6 octahedral tilt mechanism. 相似文献
133.
Viktor Sándor Balázs Viktor Berkics Anikó Kilár Béla Kocsis Ferenc Kilár Ágnes Dörnyei 《Electrophoresis》2020,41(13-14):1178-1188
Lipid A represents a heterogeneous group of bacterial outer membrane phosphoglycolipids, which play a major role in the pathogenesis of Gram-negative sepsis. The number and position of phosphoryl and acyl groups in lipid A molecules are key structural determinants in their bioactivities. In this study, a NACE–ESI-MS/MS method was developed for the simultaneous analysis of lipid A isomers possessing a different degree of phosphorylation and acylation. Various C4’- and C1-monophosphorylated lipid A isobars, as well as acylation isomers, were baseline separated within 43 min in a separation medium of methanol/dichloromethane/triethylamine/acetic acid 60:40:1.08:0.36 (v/v/v/v). Both normal and reverse CE polarities could be applied for proper detection of the analytes owing to the combination of a suction effect caused by the nebulizer gas at the outlet end of the capillary and external pressure applied on the inlet vial. The separated lipid A species could be identified unequivocally by their characteristic fragmentation patterns through CID performed in both negative- and positive-ionization modes. The uniqueness of the NACE–ESI-MS/MS method lies in its simplicity and reliability for proving the phosphorylation isomerism (C1 or C4’) and acylation pattern of native lipid A species or those designed for therapeutic applications. 相似文献
134.
V. V. Nikonorov R. V. Ivanov N. R. Kil’deeva L. N. Bulatnikova V. I. Lozinskii 《Polymer Science Series A》2010,52(8):828-834
The mechanism of cryotropic gelation in moderately frozen solutions of chitosan crosslinked by glutaric aldehyde is studied.
Chitosan cryogels with large pores are synthesized at a low content of crosslinking agent in the reaction mixture or under
conditions that do not lead to gelation at temperatures above 0°C. The dependences of the yield of gel fractions, the degree
of swelling of the polymer phase of cryogels, and the hydrodynamic characteristics of cryogels on the temperature of synthesis
are shown to be extremal. This result may be explained by the competition between the cryoconcentration of reagents in the
nonfrozen liquid microphase, which assists the development of a crosslinked polymer network, and such factors as an increase
in the viscosity of the reaction mixture and a reduced reagent mobility, which prevent gelation. The morphology of chitosan
cryogels is studied, and the character of the macroporous structure of the samples prepared at different temperatures is shown
to exert a stronger effect on the hydrodynamic characteristics of a cryogel than the degree of swelling of crosslinked polymers
in the walls of its macropores. 相似文献
135.
Ibolya Kiss Ivett Bacskay Ferenc Kilár Attila Felinger 《Analytical and bioanalytical chemistry》2010,397(3):1307-1314
The characterization of mass-transfer processes in a chromatographic column during a separation process is essential, since
the influence of the mass-transfer kinetics on the shape of the chromatographic band profiles and on the efficiency of the
separation is crucial. Several sources of mass transfer in a chromatographic bed have been identified and studied: the axial
dispersion in the stream of mobile phase, the external mass-transfer resistance, intraparticle diffusion, and the kinetics
of adsorption–desorption. We measured and compared the characteristics and performance of a new brand of shell particles and
those of a conventional brand of totally porous silica particles. The shell stationary phase was made of 2.7-μm superficially
porous particles (a 1.7-μm solid core is covered with a 0.5-μm-thick shell of porous silica). The other material consisted
of totally porous particles of conventional 3.5-μm commercial silica. We measured the first and second central moments of
the peaks of human insulin over a wide range of mobile phase velocities (from 0.02 to 1.3 mL/min) at 20°C. The plate height
equations were constructed and the axial dispersion, external mass transfer, as well as the intraparticle diffusion coefficients
were calculated for the two stationary phases. 相似文献
136.
Kamada T Aratani N Ikeda T Shibata N Higuchi Y Wakamiya A Yamaguchi S Kim KS Yoon ZS Kim D Osuka A 《Journal of the American Chemical Society》2006,128(23):7670-7678
In noncoordinating solvents, meso-cinchomeronimide appended Zn(II) porphyrin 2 forms a cyclic trimer, while diporphyrins 7 exhibit high-fidelity self-sorting assembling to form discrete cyclic trimer, tetramer, and pentamer with large association constants from 7(in-in), 7(in)(-)(out), and 7(out-out), respectively, through almost perfect discrimination of enantiomeric and conformational differences of the meso-cinchomeronimide substituents. In the latter self-sorting processes, the dihedral angles dictated by the two pyridyl nitrogen atoms control the size of the aggregates; the trimer from 7(in-in), the tetarmer from 7(in)(-)(out), and the pentamer from 7(out-out). Cyclic structures of (2)(3) and (R-7(out-out))(5) have been determined by single-crystal X-ray diffraction analysis. 相似文献
137.
Ahn TK Kim KS Kim DY Noh SB Aratani N Ikeda C Osuka A Kim D 《Journal of the American Chemical Society》2006,128(5):1700-1704
Recently, covalently linked or self-assembled porphyrin array systems have attracted much attention for their enhanced two-photon absorption (TPA) behaviors. In this study, we have investigated the TPA properties of various dihedral angle controlled, directly linked porphyrin dimers and arrays to elucidate the relationship between the pi-conjugation pathway and TPA properties. We have demonstrated a strong correlation between pi-conjugation (aromaticity) and TPA properties in porphyrin assemblies. 相似文献
138.
We study the large-time dynamics of Cucker-Smale (C-S) flocking particles interacting with non-Newtonian incompressible fluids. Dynamics of particles and fluids were modeled using the kinetic Cucker-Smale equation for particles and non-Newtonian Navier-Stokes system for fluids, respectively and these two systems are coupled via the drag force, which is the main flocking (alignment) mechanism between particles and fluids. We present a global existence theory for weak solutions to the coupled Cucker-Smale-Navier-Stokes system with shear thickening. We also use a Lyapunov functional approach to show that sufficiently regular solutions approach flocking states exponentially fast in time. 相似文献
139.
The reaction of (NBu4)3[V(III)(ox)3] (1, ox = oxalate) and M(II) (M = Fe, Co, Ni, Cu) ions in MeCN, leads to the isolation of V-based coordination polymers of [N(n-Bu)4][Fe(II)V(II)I(ox)3].0.30[[N(n-Bu)4](BF4)] (2), [N(n-Bu)4][Co(II)V(III)(ox)3].0.75[[N(n-Bu)4](BF4)] (3), [N(n-Bu)4][Ni(II)V(III)(ox)3].0.20[[N(n-Bu)4](BF4)].0.20MeCN (4), and [N(n-Bu)4][Cu(II)V(III)(ox)2](BF4)2 (5) composition. Due to the lability of [V(III)(ox)3]3- to dissociate ox2-, these compounds cannot be prepared from aqueous media. 5 is best described as [N(n-Bu)4][V(III)Cu(II)(ox)2](BF4)2, and 2, 3, 4, and 5 are proposed to have a layered (2-D) motif for the MM(ox)x (x = 2, 3) extended framework. The [V(III)Cu(II)(ox)2] composition of 5 is reported for the first time for a bimetallic oxalate. 2 shows a weak antiferromagnetic interaction between Fe(II), S = 2 and V(III), S = 1 ions (theta = -9.4 K) within the 2-D layers. 3 and 5 do not magnetically order above 2 K. 4 magnetically order as ferromagnets below 2.55 K [taken as the onset of magnetization in chi'(T)], and has a glass transition temperature (chi'(max) at 1000 Hz) at 2.26 K. 相似文献
140.
The introductions of the continuous beds, now often called monoliths [S. Hjertén, J.-L. Liao, R. Zhang, J. Chromatogr. 473 (1989), 273-275] and the artificial, highly selective gel antibodies against antigens as large as proteins, viruses and cells [J.-L. Liao, Y. Wang, S. Hjertén, Chromatographia 42 (1996), 259-262] were breakthroughs in the design of chromatographic beds. This paper deals with a combination of these two methods, i.e., the artificial gel antibodies have been synthesized in the monolithic mode. As antigen we have used human hemoglobin. A comparison of the ion-exchange chromatograms of the eluates from the monolithic columns shows that the monolith prepared in the presence of hemoglobin adsorbed this protein, but not the other proteins in the sample (ribonuclease A and cytochrome c), i.e., this monolith was selective for hemoglobin, whereas the blank column (prepared in the absence of hemoglobin) had no selective properties, since none of the applied proteins were adsorbed. The diameter of the column was 6mm, but the same approach to synthesize a monolithic selective bed can very likely also be used for capillaries and microchips. 相似文献