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31.
Ayed Salman Andries P. Engelbrecht Mahamed G.H. Omran 《European Journal of Operational Research》2007
Differential evolution (DE) is generally considered as a reliable, accurate, robust and fast optimization technique. DE has been successfully applied to solve a wide range of numerical optimization problems. However, the user is required to set the values of the control parameters of DE for each problem. Such parameter tuning is a time consuming task. In this paper, a self-adaptive DE (SDE) algorithm which eliminates the need for manual tuning of control parameters is empirically analyzed. The performance of SDE is investigated and compared with other well-known approaches. The experiments conducted show that SDE generally outperform other DE algorithms in all the benchmark functions. Moreover, the performance of SDE using the ring neighborhood topology is investigated. 相似文献
32.
B. Buszewski M. Hummel E. Bayer J. Geiger K. Schierbaum W. G?pel 《Fresenius' Journal of Analytical Chemistry》1990,336(5):403-408
Summary Two different types of porous glass (PG) were submitted to a thermal treatment in a temperature range from 620°C–700°C for 2 to 100 h. The materials thereby obtained have been characterized by static Secondary Ion Mass Spectrometry (SIMS). Special attention was paid to the change of the boron surface concentration. In addition we studied the specific surface area (SBET) dependence on the thermal treatment parameters, such as heating time and heating temperature. Selected PG materials have been modified with organosilanes and characterized prior to their use as packings in RP-HPLC.Dedicated to B. B.'s parents on their 60th birthday 相似文献
33.
Lars Radke Christoph Giese Annika Lubitz Stephan Hinderlich Grit Sandig Michael Hummel Marcus Frohme 《Mikrochimica acta》2014,181(13-14):1733-1742
Quantitative real-time PCR (qPCR) is commonly used for gene expression analyses with defined documentation guidelines to compare published results. To minimize the impact of variances from qPCR performance, sample handling and processing reference genes are used. Their selection process cannot be completely aligned due to variations in experimental conditions. Furthermore, the named sources of error are also present when determining the stability of the reference genes themselves. Even software applications that are used to identify the best reference genes rarely coincide on their rankings and can be misleading under certain conditions. In previous experiments, peripheral blood mononuclear cells (PBMC) were analyzed to identify the most stable reference gene(s). Twelve of the 13 investigated genes showed sample type specific differences in the expression. Direct mRNA measurement was performed in the form of a NanoString analysis, a multiplexed absolute quantification method. The external validation showed a high concordance of the reference gene expression levels. However, it identified the same sample type specific expression pattern for only some of the tested reference genes. By comparing various combinations of reference genes with both methods we are able to suggest a set of well-performing reference genes. Figure
34.
In this survey recent results about q-analogues of some classical theorems in extremal set theory are collected. They are related to determining the chromatic number of the q-analogues of Kneser graphs. For the proof one needs results on the number of 0-secant subspaces of point sets, so in the second part of the paper recent results on the structure of point sets having few 0-secant subspaces are discussed. Our attention is focussed on the planar case, where various stability results are given. 相似文献
35.
The calibration performance of partial least squares for one response variable (PLS1) can be improved by elimination of uninformative variables. Many methods are based on so-called predictive variable properties, which are functions of various PLS-model parameters, and which may change during the variable reduction process. In these methods variable reduction is made on the variables ranked in descending order for a given variable property. The methods start with full spectrum modelling. Iteratively, until a specified number of remaining variables is reached, the variable with the smallest property value is eliminated; a new PLS model is calculated, followed by a renewed ranking of the variables. The Stepwise Variable Reduction methods using Predictive-Property-Ranked Variables are denoted as SVR-PPRV. In the existing SVR-PPRV methods the PLS model complexity is kept constant during the variable reduction process. In this study, three new SVR-PPRV methods are proposed, in which a possibility for decreasing the PLS model complexity during the variable reduction process is build in. Therefore we denote our methods as PPRVR-CAM methods (Predictive-Property-Ranked Variable Reduction with Complexity Adapted Models). The selective and predictive abilities of the new methods are investigated and tested, using the absolute PLS regression coefficients as predictive property. They were compared with two modifications of existing SVR-PPRV methods (with constant PLS model complexity) and with two reference methods: uninformative variable elimination followed by either a genetic algorithm for PLS (UVE-GA-PLS) or an interval PLS (UVE-iPLS). The performance of the methods is investigated in conjunction with two data sets from near-infrared sources (NIR) and one simulated set. The selective and predictive performances of the variable reduction methods are compared statistically using the Wilcoxon signed rank test. The three newly developed PPRVR-CAM methods were able to retain significantly smaller numbers of informative variables than the existing SVR-PPRV, UVE-GA-PLS and UVE-iPLS methods without loss of prediction ability. Contrary to UVE-GA-PLS and UVE-iPLS, there is no variability in the number of retained variables in each PPRV(R) method. Renewed variable ranking, after deletion of a variable, followed by remodelling, combined with the possibility to decrease the PLS model complexity, is beneficial. A preferred PPRVR-CAM method is proposed. 相似文献
36.
Let V
n
be the SL2-module of binary forms of degree n and let V = Vn1 ???Vnp V = {V_{{n_1}}} \oplus \cdots \oplus {V_{{n_p}}} . We consider the algebra
R = O(V)\textS\textL2 R = \mathcal{O}{(V)^{{\text{S}}{{\text{L}}_2}}} of polynomial functions on V invariant under the action of SL2. The measure of the intricacy of these algebras is the length of their chains of syzygies, called homological dimension hd R. Popov gave in 1983 a classification of the cases in which hd R ≤ 10 for a single binary form (p = 1) or hd R ≤ 3 for a system of two or more binary forms (p > 1). We extend Popov’s result and determine for p = 1 the cases with hd R ≤ 100, and for p > 1 those with hd R ≤ 15. In these cases we give a set of homogeneous parameters and a set of generators for the algebra R. 相似文献
37.
38.
E.Z. Kurmaev V.R. Galakhov S.N. Shamin V.I. Sokolov R.E. Hummel M.H. Ludwig 《Applied Physics A: Materials Science & Processing》1997,65(2):183-189
2,3 X-ray emission spectra of porous silicon (P-Si) and of spark-processed silicon (sp-Si). Both types of Si-structure display strong photoluminescence in the visible range of the spectrum. Porous
samples were prepared by anodization of n-- and p+-Si-wafers. Whereas for the P-Si processed from p+-Si the presence of some amorphous silicon is detected, the X-ray emission spectra of porous Si prepared from n--Si display a higher content of SiO2. For spark-processed Si the Si L2,3 X-ray emission spectra reveal a much stronger degree of oxidation which extends to depths larger than 10000 Å. Furthermore,
the chemical state of silicon atoms of sp-Si measured at the center of the processed area is close to that of silicon dioxide,
and it has an influence on the photoluminescence energy. Specifically, green photoluminescent sp-Si shows a higher degree
of oxidation than the blue luminescent specimen. However, the depth of oxidation consistently decreases in areas with weak
or no PL. Possible origins of the observed photoluminescence are discussed.
Accepted: 6 March 1997 相似文献
39.
Friedhelm C Hummel Bernhard Voller Pablo Celnik Agnes Floel Pascal Giraux Christian Gerloff Leonardo G Cohen 《BMC neuroscience》2006,7(1):73-10
Background
Previous studies showed that anodal transcranial DC stimulation (tDCS) applied to the primary motor cortex of the affected hemisphere (M1affected hemisphere) after subcortical stroke transiently improves performance of complex tasks that mimic activities of daily living (ADL). It is not known if relatively simpler motor tasks are similarly affected. Here we tested the effects of tDCS on pinch force (PF) and simple reaction time (RT) tasks in patients with chronic stroke in a double-blind cross-over Sham-controlled experimental design. 相似文献40.
We introduce a relaxation collision operator for a mixture of gases which satisfies several fundamental properties. Different BGK type collision operators for gas mixtures have been introduced earlier but none of them could satisfy all the basic physical properties: positivity, correct exchange coefficients, entropy inequality, indifferentiability principle. We show that all those properties are verified for our model, and we derive its Navier–Stokes limit by a Chapman–Enskog expansion. 相似文献