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排序方式: 共有278条查询结果,搜索用时 156 毫秒
51.
建立了双波长相移光纤光栅的理论模型,对双波长相移光纤光栅的透射谱特性进行了数值仿真,结果表明透射波长间隔会分别随相移量、折射率调制深度和光栅长度的变化而有规律地增减.借助光纤布拉格光栅的法布里-珀罗腔谐振相位条件计算了透射峰间隔的表达式,该表达式得到的透射峰间距曲线与数值仿真得到的曲线相符合,验证了数值仿真结果的正确性.最后,在光栅透射谱波长间隔变化规律的基础上提出一种传感方案,并对光栅的温度传感特性进行分析,理论推导得到灵敏度约为60pm/℃. 相似文献
52.
分子构象的聚类是搜索分子动力学模拟轨迹中代表构象的主要方法。 它是分析复杂构象改变或分子间相互作用机制的关键步骤. 作为一种基于密度的聚类算法,密度峰值搜索算法因其聚类的准确度而被应用于分子聚类过程中. 但随着模拟时长的增长,密度峰值搜索算法较低的计算效率限制了其应用的可能. 本文提出K-means密度峰值搜索算法的聚类算法,它是密度峰值搜索算法在计算效率方面的一个扩展版本,用于解决密度峰值搜索算法中巨大的资源消耗问题. 在K-means密度峰值搜索算法中,首先,通过高效的聚类算法(例如K-means)进行初始聚类,得到的聚类中心被定义为具有权重的典型点. 然后,对加权的典型点通过密度峰值搜索算法实现二次聚类,并细化点为核心点、边界点、加细光晕点. 在与密度峰值搜索算法具有相似的精度的同时,计算复杂度由O(n2)降至O(n). 通过二面角,二级结构,关联图描述的分子构象,将KFDP用于多个模拟轨迹的聚类过程中. 并通过与K-means聚类算法,DBSCAN聚类算法的比较结果,验证了K-means密度峰值搜索算法的优势. 相似文献
53.
Z.G. Koinov 《Annalen der Physik》2012,524(8):421-428
The t‐U‐V‐J model fits together three major parts of the superconductivity puzzle of the cuprite compounds: (i) it describes the opening of a d‐wave pairing gap, (ii) it is consistent with the fact that the basic pairing mechanism arises from the antiferromagnetic exchange correlations, and (iii) it takes into account the charge fluctuations associated with double occupancy of a site which play an essential role in doped systems. The strengths of the interactions U, V and J in YBa2Cu3O6.7 and La2‐xSrxCuO4 (x = 0.16) samples are obtained by requiring quantitative consistency between the angle‐resolved photoemission spectroscopy (ARPES) measurements, the sharp collective mode at the antiferromagnetic wave vector Q AF=(π,π), and the observed inelastic neutron scattering resonance (INSR) positions of the incommensurate peaks at wave vectors Q δ = ((1 ± δ)π,π) and Q δ = (π(1 ± δ)π). 相似文献
54.
Quantization of electromagnetic field in quadratic continuous nonlinear absorptive dielectrics 下载免费PDF全文
This paper reports that in the quantization of
electromagnetic field in the dielectrics, the wave equation with
regard to the Green function is analytically solved by a direct integral
method for a quadratic continuous nonlinear absorptive dielectric
medium. The quantization of the electromagnetic field in such a
nonlinear absorptive dielectric is carried out for which the
material dielectric function is assumed as a separable variable about
the frequency and the space coordinate. The vacuum field
fluctuations for different spatial continuous variations of
dielectric function are numerically calculated, which shows that the
present result is self-consistent. 相似文献
55.
Wavelet-Fourier self-deconvolution 总被引:5,自引:0,他引:5
Using a wavelet function as the filter function of Fourier self-deconvolution, a new method of resolving overlapped peaks, wavelet-Fourier self-deconvolution, is founded. The properties of different wavelet deconvolution functions are studied. In addition, a cutoff value coefficient method of eliminating artificial peaks and wavelet method of removing shoulder peaks using the ratio of maximum peak to minimum peak is established. As a result, some problems in classical Fourier self-deconvolution are solved, such as the bad result of denoising, complicated processing, as well as usual appearance of artificial and shoulder peaks. Wavelet-Fourier self-deconvolution is applied to determination of multi-components in oscillographic chronopotentiometry. Experimental results show that the method has characteristics of simpler process and better effect of processing. 相似文献
56.
The role of various mass spectrometric methods, including electron ionization, collisional activation, metastable peak shapes, analysis of neutrals from ionic unimolecular dissociations, field ionization kinetics, drift cell, and Fourier transform ion cyclotron resonance spectrometry, in ionic reaction mechanistic studies is described. This is illustrated by selected examples of research performed in the author’s group over the last three decades. They comprise inter alia intramolecular acid–base, anchimeric assistance, nucleophilic attack, isomerization, cycloaddition, SN2, and hydride ion transfer reactions. 相似文献
57.
Myung-Hwan Whangbo 《Theoretical chemistry accounts》2000,104(3-4):252-256
The size-consistent self-consistent matrix dressing method has been applied on an open-shell single-configuration reference
state. Once the reference state is converged, several low-lying roots can be obtained for the dressed configuration interaction
(CI) matrices of appropriate symmetry. The CI matrices were built with a complete-active-space singles and doubles CI method
in order to deal properly with multiconfiguration excited states. The vertical ionization and ionization–excitation transitions
are obtained from the difference to the closed shell ground-state energy of the neutral molecule. The method has been applied
to NH+
3 and N+
2 using atomic natural orbital basis sets and state-average adapted molecular orbitals. Two 2A1 states, very similar and showing great mixing of the (2a
l
−1) and (3a
l
−25a
l
1) determinants, can be assigned to the broad asymmetric band at 27.6 ± 2 eV in the photoelectron spectrum of NH3. The possible contribution of a 2Π
g
(3σ
g
−21π
g
1) state to the A shake-up peak of N2 at 24.6 eV is also discussed. Other states, doublets and quadruplets, are reported for both systems up to 30 eV for NH3 and 37 eV for N2.
Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000 相似文献
58.
二维小波变换与子窗口因子分析法结合用于含噪声HPLC-DAD数据的解析 总被引:1,自引:0,他引:1
将二维小波变换与子窗口因子分析法相结合,用于模拟的高噪声HPLC-DAD数据的解析.首先应用二维小波变换滤除噪声,然后采用子窗口因子分析法解析重叠峰.结果表明,信噪比为10的高噪声基本被滤除掉. 相似文献
59.
Cesar Hervs Pedro Antonio Gutierrez Manuel Silva Juan Manuel Serrano 《Journal of Chemometrics》2007,21(12):567-577
This is a study of the potential of neural networks built by using different transfer functions (sigmoidal, product and sigmoidal–product units) designed by an evolutionary algorithm to quantify highly overlapping electrophoretic peaks. To test this approach, two aminoglycoside antibiotics, amikacin and paramomycin, were quantified from samples containing either only one component or mixtures of them though capillary zone electrophoresis (CZE) with laser‐induced fluorescence (LIF) detection. The three models assayed used as input data the four‐parameter Weibull curve associated with the profile of the electrophoretic peak and in some cases the class label for each sample estimated by cluster analysis. The combination of classification and regression approaches allowed the establishment of straightforward network topologies enabling the analytes to be quantified with great accuracy and precision. The best models for mixture samples were provided by product unit neural networks (PUNNs), 4:4:1 (14 weights) for both analytes, after discrimination by cluster analysis, allowing the analytes to be quantified with great accuracy: 8.2% for amikacin and 5.6% for paromomycin within the standard error of prediction for the generalization test, SEPG. For comparison, partial least square regression was also used for the resolution of these mixtures; it provided a minor accuracy: SEPG 11.8 and 15.7% for amikacin and paramomycin, respectively. The reduced dimensions of the neural networks models selected enabled the derivation of simple quantification equations to transform the input variables into the output variable. These equations can be more easily interpreted from a chemical point of view than those provided by other ANN models. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
60.