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231.
K. W. Kwok R. C. W. Tsang H. L. W. Chan C. L. Choy 《Journal of Sol-Gel Science and Technology》2008,47(2):148-153
Niobium (Nb)-doped lead zirconate titanate (PZT) films have been prepared on platinized silicon substrates using a sol–gel
method. The Zr/Ti ratios of the films are 53/47 and 40/60, and the Nb doping level ranges from 0 mol% to 3 mol%. Similar to
the cases in bulk ceramics, after the doping with Nb, the remanent polarization Pr, effective transverse piezoelectric coefficients e31,c and pyroelectric coefficient p of the PZT films increase; but the longitudinal effective piezoelectric coefficient d33,c remains roughly unchanged. At the optimum Nb doping levels, the observed Pr, −e31,c and p reach a maximum value of 30 μC/cm2, 18 C/m2 and 350 μC/m2 K, respectively, for the PZT (53/47) films, and 37 μC/cm2, 7.9 c/m2 and 370 μC/m2 K for the PZT (40/60) films. Our results also reveal that there exist linear relations between p, e31,c/εr and Pr. 相似文献
232.
Resonant perturbations are effective for harnessing nonlinear oscillators for various applications such as controlling chaos and inducing chaos. Of physical interest is the effect of small frequency mismatch on the attractors of the underlying dynamical systems. By utilizing a prototype of nonlinear oscillators, the periodically forced Duffing oscillator and its variant, we find a phenomenon: resonant-frequency mismatch can result in attractors that are nonchaotic but are apparently strange in the sense that they possess a negative Lyapunov exponent but its information dimension measured using finite numerics assumes a fractional value. We call such attractors pseudo-strange. The transition to pesudo-strange attractors as a system parameter changes can be understood analytically by regarding the system as nonstationary and using the Melnikov function. Our results imply that pseudo-strange attractors are common in nonstationary dynamical systems. 相似文献
233.
Choy J Ling W Jerschow A 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,180(1):105-109
Given the correlation between the concentrations of ordered (23)Na and the onset of tissue disorders, the ability to select the signal from ordered (23)Na over that of free (23)Na is of particular importance and can greatly enhance the potential of (23)Na-MRI as a diagnostic tool. Here, we describe a simple method that selectively detects the central transition of ordered sodium while minimizing the signal from free sodium. Our method relies upon the influence of the quadrupolar interaction on nutation frequencies and may also benefit solid-state imaging experiments. Both a liquid crystalline environment and a cartilage sample are used to demonstrate a clean separation between anisotropic and isotropic regions in the experiments. 相似文献
234.
Zinc oxide-layered titanate nanohybrids with a 1 ratio 1 ordered heterostructure have been successfully synthesized by reassembling exfoliated titanate nanosheets in the sol solution of zinc acetate under hydrothermal conditions. 相似文献
235.
Let J be an abelian surface with a generic ample line bundle . For n≥1, the moduli space MJ(2,0,2n) of (1)-semistable sheaves F of rank 2 with Chern classes c1(F)=0, c2(F)=2n is a singular projective variety, endowed with a holomorphic symplectic structure on the smooth locus. In this paper, we
show that there does not exist a crepant resolution of MJ(2,0,2n) for n≥2. This certainly implies that there is no symplectic desingularization of MJ(2,0,2n) for n≥2.
Jaeyoo Choy was partially supported by KRF 2003-070-C00001
Young-Hoon Kiem was partially supported by a KOSEF grant R01-2003-000-11634-0. 相似文献
236.
Chin Chye Teo Swee Ngin Tan Jean Wan Hong Yong Choy Sin Hew Eng Shi Ong 《Journal of separation science》2009,32(4):613-622
An approach that combined green‐solvent methods of extraction with chromatographic chemical fingerprint and pattern recognition tools such as principal component analysis (PCA) was used to evaluate the quality of medicinal plants. Pressurized hot water extraction (PHWE) and microwave‐assisted extraction (MAE) were used and their extraction efficiencies to extract two bioactive compounds, namely stevioside (SV) and rebaudioside A (RA), from Stevia rebaudiana Bertoni (SB) under different cultivation conditions were compared. The proposed methods showed that SV and RA could be extracted from SB using pure water under optimized conditions. The extraction efficiency of the methods was observed to be higher or comparable to heating under reflux with water. The method precision (RSD, n = 6) was found to vary from 1.91 to 2.86% for the two different methods on different days. Compared to PHWE, MAE has higher extraction efficiency with shorter extraction time. MAE was also found to extract more chemical constituents and provide distinctive chemical fingerprints for quality control purposes. Thus, a combination of MAE with chromatographic chemical fingerprints and PCA provided a simple and rapid approach for the comparison and classification of medicinal plants from different growth conditions. Hence, the current work highlighted the importance of extraction method in chemical fingerprinting for the classification of medicinal plants from different cultivation conditions with the aid of pattern recognition tools used. 相似文献
237.
In this paper, the networks with optimal synchronizability are obtained using the local structure information. In scale-free networks, a node will be coupled by its neighbors with maximal degree among the neighbors if and only if the maximal degree is larger than its own degree. If the obtained coupled networks are connected, they are synchronization optimal networks. The connection probability of coupled networks is greatly affected by the average degree which usually increases with the average degree. This method could be further generalized by taking into account the degree of next-nearest neighbors, which will sharply increase the connection probability. Compared to the other proposed methods that obtain synchronization optimal networks, our method uses only local structure information and can hold the structure properties of the original scale-free networks to some extent. Our method may present a useful way to manipulate the synchronizability of real-world scale-free networks. 相似文献