全文获取类型
收费全文 | 216篇 |
免费 | 0篇 |
专业分类
化学 | 185篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 10篇 |
物理学 | 16篇 |
出版年
2020年 | 1篇 |
2017年 | 3篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 11篇 |
2011年 | 8篇 |
2010年 | 4篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2005年 | 12篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1962年 | 1篇 |
1934年 | 1篇 |
1933年 | 2篇 |
排序方式: 共有216条查询结果,搜索用时 250 毫秒
171.
This paper presents an experimental technique for measuring internal strains of loaded artificial solids by means of single-strand, strain-gage wires. Specifically, in the present investigation, strain-gage wires were embedded lengthwise within rectangular prisms which were made of either pure-epoxy resin or silica crystals in an epoxy-resin matrix. Several prisms of both types were compressed longitudinally or loaded as simply supported beams. Experimentally measured unidirectional internal strains are compared with theoretically expected values, and agreement between experiment and theory is good. Thus, the validity of this new technique is demonstrated. 相似文献
172.
Direct detection and quantitation of He@C60 by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry 总被引:1,自引:0,他引:1
Cooper HJ Hendrickson CL Marshall AG Cross RJ Saunders M 《Journal of the American Society for Mass Spectrometry》2002,13(11):1349-1355
In this paper, we report negative ion microelectrospray Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry of C60 samples containing approximately 1% 3He@C60 or 4He@C60. Resolving He@C60- and 4He@C60- from C60 containing 3 or 4 13C instead of 12C atoms is technically challenging, because the target species are present in low relative abundance and are very close in mass. Nevertheless, we achieve baseline resolution of 3He@C60- from 13C3(12C57-) and 4He@C60- from 13C4(12C56-) in single-scan mass spectra obtained in broadband mode without preisolation of the ions of interest. The results constitute the first direct mass spectrometric observation of endohedral helium in a fullerene sample at this (low) level of incorporation. The results also demonstrate the feasibility of determining the extent of He incorporation from the FT-ICR mass spectral peak heights. The present measurements are in agreement with those obtained by the pyrolysis method [1-3]. Although limited in sensitivity, the mass spectral method is faster and easier than pyrolysis. 相似文献
173.
Freitas MA Hendrickson CL Marshall AG Rostom AA Robinson CV 《Journal of the American Society for Mass Spectrometry》2000,11(11):1023-1026
This communication demonstrates that gentle infrared laser heating can remove unwanted buffer adducts from a gas-phase protein complex without dissociating the complex itself. Specifically, noncovalent complexes of the oligopeptide-binding protein, OppA, bound to either (Ala)3 or LysTrpLys were electrosprayed from aqueous buffer solution into a 9.4 tesla Fourier transform ion cyclotron resonance mass spectrometer. In addition to the intact complexes, several additional buffer adduct species were produced under the conditions of the experiment. Irradiation of the trapped ion population with a continuous-wave infrared CO2 laser at relatively low power (2.5 W) for 1 s dissociated the buffer adducts but retained the intact protein:peptide complexes. Adduct-free complex(es) were then readily identified, and signal-to-noise ratio also increased by an order of magnitude because the same number of protein ions are distributed over fewer species. Higher IR power (5 W for 1 s) dissociated the adduct-free complex(es) without internal fragmentation. The present in-trap clean-up technique may prove especially useful for identifying and screening the combinatorial library ligands most strongly bound to a receptor in the gas phase. 相似文献
174.
175.
Lawrence J Yang EC Edwards R Olmstead MM Ramsey C Dalal NS Gantzel PK Hill S Hendrickson DN 《Inorganic chemistry》2008,47(6):1965-1974
High-frequency electron paramagnetic resonance (HFEPR) data are presented for four closely related tetranuclear Ni(II) complexes, [Ni(hmp)(MeOH)Cl]4.H2O (1a), [Ni(hmp)(MeOH)Br]4.H2O (1b), [Ni(hmp)(EtOH)Cl]4.H2O (2), and [Ni(hmp)(dmb)Cl]4 (3) (where hmp(-) is the anion of 2-hydroxymethylpyridine and dmb is 3,3'-dimethyl-1-butanol), which exhibit magnetic bistability (hysteresis) and fast magnetization tunneling at low temperatures, properties which suggest they are single-molecule magnets (SMMs). The HFEPR spectra confirm spin S = 4 ground states and dominant uniaxial anisotropy (DSz(2), D < 0) for all four complexes, which are the essential ingredients for a SMM. The individual fine structure peaks (due to zero-field splitting) for complexes 1a, 1b, and 2 are rather broad. They also exhibit further (significant) splitting, which can be explained by the fact that there exists two crystallographically distinct Ni 4 sites in the lattices for these complexes, with associated differences in metal-ligand bond lengths and different zero-field splitting (ZFS) parameters. The broad EPR lines, meanwhile, may be attributed to ligand and solvent disorder, which results in additional distributions of microenvironments. In the case of complex 3, there are no solvate molecules in the structure, and only one distinct Ni 4 molecule in the lattice. Consequently, the HFEPR data for complex 3 are extremely sharp. As the temperature of a crystal of complex 3 is decreased, the HFEPR spectrum splits abruptly at approximately 46 K into two patterns with very slightly different ZFS parameters. Heat capacity data suggest that this is caused by a structural transition at 46.6 K. A single-crystal X-ray structure at 12(2) K indicates large thermal parameters on the terminal methyl groups of the dmb (3,3-dimethyl-1-butanol) ligand. Most likely there exists dynamic disorder of parts of the dmb ligand above 46.6 K; an order-disorder structural phase transition at 46.6 K then removes some of the motion. A further decrease in temperature (<6 K) leads to further fine structure splittings for complex 3. This behavior is thought to be due to the onset of short-range magnetic correlations/coherences between molecules caused by weak intermolecular magnetic exchange interactions. 相似文献
176.
Sorai M Burriel R Westrum EF Hendrickson DN 《The journal of physical chemistry. B》2008,112(14):4344-4350
Magnetic and thermal properties of the iron(III) spin crossover complex [Fe(3MeO-salenEt)(2)]PF(6) are very sensitive to mechanochemical perturbations. Heat capacities for unperturbed and differently perturbed samples were precisely determined by adiabatic calorimetry at temperatures in the 10-300 K range. The unperturbed compound shows a cooperative spin crossover transition at 162.31 K, presenting a hysteresis of 2.8 K. The anomalous enthalpy and entropy contents of the transition were evaluated to be Delta(trs)H = 5.94 kJ mol(-1) and Delta(trs)S = 36.7 J K(-1) mol(-1), respectively. By mechanochemical treatments, (1) the phase transition temperature was lowered by 1.14 K, (2) the enthalpy and entropy gains at the phase transition due to the spin crossover phenomenon were diminished to Delta(trs)H = 4.94 kJ mol(-1) and Delta(trs)S = 31.1 J K(-1) mol(-1), and (3) the lattice heat capacities were larger than those of the unperturbed sample over the whole temperature range. In spite of different mechanical perturbations (grinding with a mortar and pestle and grinding in a ball-mill), two sets of heat capacity measurements provided basically the same results. The mechanochemical perturbation exerts its effect more strongly on the low-spin state than on the high-spin state. It shows a substantial increase of the number of iron(III) ions in the high-spin state below the transition temperature. The heat capacities of the diamagnetic cobalt(III) analogue [Co(3MeO-salenEt)(2)]PF(6) also were measured. The lattice heat capacity of the iron compounds has been estimated from either the measurements on the cobalt complex using a corresponding states law or the effective frequency distribution method. These estimations have been used for the evaluation of the transition anomaly. 相似文献
177.
178.
179.
Vladimirov G Hendrickson CL Blakney GT Marshall AG Heeren RM Nikolaev EN 《Journal of the American Society for Mass Spectrometry》2012,23(2):375-384
Particle-in-Cell (PIC) ion trajectory calculations provide the most realistic simulation of Fourier transform ion cyclotron
resonance (FT-ICR) experiments by efficient and accurate calculation of the forces acting on each ion in an ensemble (cloud),
including Coulomb interactions (space charge), the electric field of the ICR trap electrodes, image charges on the trap electrodes,
the magnetic field, and collisions with neutral gas molecules. It has been shown recently that ion cloud collective behavior
is required to generate an FT-ICR signal and that two main phenomena influence mass resolution and dynamic range. The first
is formation of an ellipsoidal ion cloud (termed “condensation”) at a critical ion number (density), which facilitates signal
generation in an FT-ICR cell of arbitrary geometry because the condensed cloud behaves as a quasi-ion. The second phenomenon
is peak coalescence. Ion resonances that are closely spaced in m/z coalesce into one resonance if the ion number (density) exceeds a threshold that depends on magnetic field strength, ion
cyclotron radius, ion masses and mass difference, and ion initial spatial distribution. These two phenomena decrease dynamic
range by rapid cloud dephasing at small ion density and by cloud coalescence at high ion density. Here, we use PIC simulations
to quantitate the dependence of coalescence on each critical parameter. Transitions between independent and coalesced motion
were observed in a series of the experiments that systematically varied ion number, magnetic field strength, ion radius, ion
m/z, ion m/z difference, and ion initial spatial distribution (the present simulations begin from elliptically-shaped ion clouds with
constant ion density distribution). Our simulations show that mass resolution is constant at a given magnetic field strength
with increasing ion number until a critical value (N) is reached. N dependence on magnetic field strength, cyclotron radius,
ion mass, and difference between ion masses was determined for two ion ensembles of different m/z, equal abundance, and equal cyclotron radius. We find that N and dynamic range depend quadratically on magnetic field strength
in the range 1–21 Tesla. Dependences on cyclotron radius and Δm/z are linear. N depends on m/z as (m/z)–2. Empirical expressions for mass resolution as a function of each of the experimental parameters are presented. Here, we provide
the first exposition of the origin and extent of trade-off between FT-ICR MS dynamic range and mass resolution (defined not
as line width, but as the separation between the most closely resolved masses). 相似文献
180.