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排序方式: 共有347条查询结果,搜索用时 15 毫秒
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Summary Three extensions of the basic PCA and PLS methodologies are described. These extensions are hierarchical, non-linear and batch-based
in nature. The objectives of these methods are to assist in problem understanding and problem solving in very complex (QSAR)
problem formulations. The method extensions are illustrated using two example QSAR data sets containing many X- and Y-variables. 相似文献
56.
Lennart Ljung Lei Guo 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(1):27-42
Model Validation is at the heart of the System Identification process. Recently, much renewed interest has been expressed in so called "identification for control". This means that the design variables associated with the identification process are tailored to achieve models that are well suited for control design purposes. A separate, but closely related issue is to devise validation tests that give information about the model's quality and suitability for control design. This paper shows and discusses how a basic and classical residual test gives such information. 相似文献
57.
Pandur Venkatesan Balaji Lennart Brewitz Naoya Kumagai Masakatsu Shibasaki 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(9):2670-2674
Thioureas have emerged as effective hydrogen‐bonding catalysts over the last two decades, and they are broadly utilized in asymmetric catalysis. We report that achiral trisubstituted thioureas function as beneficial secondary ligands to CuI catalysts, thereby enabling highly diastereo‐ and enantioselective addition of α‐fluoronitriles to imines. The structure of the thiourea significantly affects the reaction outcome, and kinetic experiments indicate that the thioureas enhance the stereocontrol by binding to the CuI complex. The reaction products can be readily transformed into valuable β‐amino acid derivatives bearing a fluorinated tetrasubstituted stereogenic center. 相似文献
58.
Thirty-eight saponins in two chromatographic fractions (QH-B and QH-C) from Quillaja saponaria Molina have been separated by a two-step high-performance liquid chromatography (HPLC) procedure and investigated by electrospray ionisation ion trap multiple-stage mass spectrometry (ESI-ITMS(n)) in positive ion mode. MS(2) and MS(3) spectra of the compounds were investigated by principal component analysis (PCA) and could be classified by partial least squares - discriminant analysis (PLS-DA) according to the structures of the oligosaccharides at C-3 and C-28 of the saponins. Four minor components with novel structures were found in a previously non-investigated fraction of QH-C. The structures of two of these components, J1 and J1a, were predicted by PLS-DA whereas the structures of the two others, J2 and J3, were only partly predicted. The structures of J1 and J1a were composed of structural elements found in the 34 known saponins whereas a new acyl substituent, not included in the training set used for calibration of the PLS-DA models, was found in J2 and J3, making these two components outliers. The complete structures of the four components were confirmed by monosaccharide analysis, MS(n) data and (1)H NMR spectroscopy. 相似文献
59.
Johan?Cedervall Lennart?H?ggstr?mEmail authorView authors OrcID profile Tore?Ericsson Martin?Sahlberg 《Hyperfine Interactions》2016,237(1):47
Mössbauer spectroscopy in the ferromagnetic AlFe2 B 2 reveals Tc=299 K and shows good agreement with magnetic measurements. The crystals are plate-shaped. The flakes are found from X-ray diffraction to be in the crystallographic ac-plane in the orthorhombic system. The axes of the principle electric field gradient tensor are, by symmetry, colinear with the crystal a-, b- and c-axes. By using information about the quadrupole splitting and line asymmetry in the paramagnetic regime together with the quadrupole shift of the resonance lines in the ferromagnetic regime the magnetic hyperfine field direction is found to be in the ab-plane having an angle =40° to the b-axis. 相似文献
60.
Isaksson M Norlin N Westlund PO Johansson LB 《Physical chemistry chemical physics : PCCP》2007,9(16):1941-1951
An extended F?rster theory (EFT) on electronic energy transfer is presented for the quantitative analysis of time-resolved fluorescence lifetime and depolarisation experiments. The EFT, which was derived from the stochastic Liouville equation, yields microscopic information concerning the reorientation correlation times, the order parameters, as well as inter chromophoric distances. Weakly interacting donor and acceptor groups, which reorient and interact in a pair wise fashion, are considered, under isotropic and anisotropic conditions. For the analysis of experiments it is shown that not only do we need to consider the orientational distributions of the transition dipoles, but the internal reorienting molecular dynamics within the pair which is of even greater importance. The latter determines the shape as well as the rate of the observed donor fluorescence and depolarisation decays, which are most often not mono-exponential functions. It is shown that the commonly used F?rster theory is a special case of the EFT. Strategies are presented for applying the EFT, which makes use of Brownian dynamics simulation. 相似文献