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91.
Yuasa H Miyagawa N Nakatani M Izumi M Hashimoto H 《Organic & biomolecular chemistry》2004,2(24):3548-3556
Carbohydrates are among the potential materials for molecular devices, since they are abundant natural resources. However, their rigidity has restricted their use for movable devices. Hinge sugars, 2,4-diamino-2,4-dideoxy-xylopyranosides, shed light on the use of carbohydrates as movable components, as demonstrated by the motion by which all four equatorial substituents can change to an axial orientation in synchronization with a chelation-driven 4C1-1C4 ring flip. In this study, we synthesized a tong-like metal ion sensor, 1,3-di-O-pyrenylmethylated hinge sugar (1), and its model compound, methyl 2,4-di-O-pyrenecarbonyl-xylopyranoside (2), to extend the abilities of hinge sugars as molecular components. From observations of the solvent-dependent conformational and fluorescent behavior of 2, we found that the pyrene stacking assists the 1C4 formation of xylopyranoside by 1.7 kcal mol(-1). We also found that compound 1 produced excimer fluorescence by chelation to Pt2+, Zn2+, Cd2+, Mg2+ or Mn2+, and unexpectedly by addition of acids. 1H NMR measurements ascribed this behavior to the 4C1-1C4 ring flip of hinge sugar in response to chelation or protonation at N2, and revealed rapid and perfect 1C4 formation in the case of Zn2+. These findings will extend the scope of hinge sugars as movable components. 相似文献
92.
Nakatani S Yamamoto Y Hayashi M Komiyama K Ishibashi M 《Chemical & pharmaceutical bulletin》2004,52(3):368-370
Cycloanthranilylproline (1) and its derivatives (2--4) were isolated from field-collected fruit-bodies of a myxomycete Fuligo candida and their structures were elucidated by spectral data. Compound 4, which was contained in the water-soluble fraction of the extract of this myxomycete, was unstable and quite susceptible to decarboxylation to yield compound 2, which was a major constituent of the EtOAc-soluble fraction of this extract. 相似文献
93.
This paper presents a new method for robust and accurate fundamental frequency (F0) estimation in the presence of background noise and spectral distortion. Degree of dominance and dominance spectrum are defined based on instantaneous frequencies. The degree of dominance allows one to evaluate the magnitude of individual harmonic components of the speech signals relative to background noise while reducing the influence of spectral distortion. The fundamental frequency is more accurately estimated from reliable harmonic components which are easy to select given the dominance spectra. Experiments are performed using white and babble background noise with and without spectral distortion as produced by a SRAEN filter. The results show that the present method is better than previously reported methods in terms of both gross and fine F0 errors. 相似文献
94.
The temporal profile and phase of the fifth harmonic of a Ti:sapphire laser were fully characterized by two-photon ionization frequency-resolved optical gating technique for the first time. The fifth harmonic was found to have negative chirp and the pulse compression was demonstrated. The negative chirp is well explained by using a zero-range potential model. This technique is scalable to extreme ultraviolet (XUV) and soft x-ray regions by using currently available light sources, making it possible to measure the pulse duration and phase of vacuum ultraviolet, XUV, and soft x-ray pulses. 相似文献
95.
96.
K Nakatani S Sando H Kumasawa J Kikuchi I Saito 《Journal of the American Chemical Society》2001,123(50):12650-12657
Dimeric 2-amino-1,8-naphthyridine selectively binds to a G-G mismatch with high affinity (K(d) = 53 nM). We have investigated a binding mechanism of naphthyridine dimer 2 to a G-G mismatch by spectroscopic studies, thermodynamic analysis, and structure-activity studies for the thermal stabilization of the mismatch. 1H NMR spectra of a complex of 2 with 9-mer duplex d(CATCGGATG)2 containing a G-G mismatch showed that all hydrogens in two naphthyridine rings of 2 were observed upfield compared to those of 2 in a free state. The 2D-NOESY experiments showed that each naphthyridine of 2 binds to a guanine in the G-G mismatch within the pi-stack. In CD spectra, a large conformational change of the G-G mismatch-containing duplex was observed upon complex formation with 2. Isothermal calorimetry titration of 2 binding to the G-G mismatch showed that the stoichiometry for the binding is about 1:1 and that the binding is enthalpy-controlled. It is clarified by structure-activity studies that show (i) the linker connecting two naphthyridine rings was essential for the stabilization of the G-G mismatch, (ii) the binding efficiency was very sensitive to the linker structure, and (iii) the binding of two naphthyridines to each one of two Gs in the G-G mismatch is essential for a strong stabilization. These results strongly supported the intercalation of both naphthyridine rings of 2 into DNA base pairs and the formation of a hydrogen bonded complex with the G-G mismatch. 相似文献
97.
98.
Cover Picture: Theoretical and Experimental Study on Boron β‐Diketonate Complexes with Intense Two‐Photon‐Induced Fluorescence in Solution and in the Solid State (ChemPhysChem 14/2016) 下载免费PDF全文
99.
The shear orientation of viscoelastic clay-polymer solutions was investigated by means of rheology and flow birefringence
(Δn). The polymer chains are in dynamic adsorption/desorption equilibrium with the clay particles to form a “network”. The
elastic behavior of the network was characterized by constant stress, oscillatory shear, and stress relaxation experiments.
Constant stress experiments indicated a yield stress upon which shear flow started and no strain recovery could be observed.
Oscillatory shear experiments showed a broad elastic region followed by flow when a critical strain was reached. Stress relaxation
experiments showed several relaxation times when the same critical strain was reached. Experiments under steady flow characterized
the transient behavior of the network. With increasing steady shear rate a pronounced minimum in birefringence was observed
at a critical shear rate. The shear rate dependent viscosity showed near power law behavior and no corresponding critical
feature. While birefringence detects orientational effects on a microscopic length scale, rheology averages over macroscopic
changes in the sample. The same degree of orientation could be achieved under constant shear rate or constant stress conditions.
Received: 25 January 2001 Accepted: 22 May 2001 相似文献
100.
An analytical energy gradient formula for the density-matrix-based linear-scaling divide-and-conquer (DC) self-consistent field (SCF) method was proposed in a previous paper by Yang and Lee (YL) [J. Chem. Phys. 103, 5674 (1995)]. Since the formula by YL does not correspond to the exact gradient of the DC-SCF energy, we derive the exact formula by direct differentiation, which requires solving the coupled-perturbed equations while including the inter-subsystem coupling terms. Next, we present an alternative formula for approximately evaluating the DC-SCF energy gradient, assuming the variational condition for the subsystem density matrices. Numerical assessments confirmed that the DC-SCF energy gradient values obtained by the present formula are in reasonable agreement with the conventional SCF values when adopting a reliable buffer region. Furthermore, the performance of the present method was found to be better than that of the YL method. 相似文献