全文获取类型
收费全文 | 891篇 |
免费 | 47篇 |
国内免费 | 8篇 |
专业分类
化学 | 682篇 |
晶体学 | 6篇 |
力学 | 21篇 |
数学 | 104篇 |
物理学 | 83篇 |
无线电 | 50篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 28篇 |
2021年 | 38篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 23篇 |
2017年 | 16篇 |
2016年 | 50篇 |
2015年 | 34篇 |
2014年 | 41篇 |
2013年 | 69篇 |
2012年 | 70篇 |
2011年 | 82篇 |
2010年 | 37篇 |
2009年 | 30篇 |
2008年 | 65篇 |
2007年 | 44篇 |
2006年 | 51篇 |
2005年 | 48篇 |
2004年 | 32篇 |
2003年 | 23篇 |
2002年 | 26篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有946条查询结果,搜索用时 642 毫秒
61.
Michele Lo Giudice Giuseppe Varone Cosimo Ieracitano Nadia Mammone Giovanbattista Gaspare Tripodi Edoardo Ferlazzo Sara Gasparini Umberto Aguglia Francesco Carlo Morabito 《Entropy (Basel, Switzerland)》2022,24(1)
The differential diagnosis of epileptic seizures (ES) and psychogenic non-epileptic seizures (PNES) may be difficult, due to the lack of distinctive clinical features. The interictal electroencephalographic (EEG) signal may also be normal in patients with ES. Innovative diagnostic tools that exploit non-linear EEG analysis and deep learning (DL) could provide important support to physicians for clinical diagnosis. In this work, 18 patients with new-onset ES (12 males, 6 females) and 18 patients with video-recorded PNES (2 males, 16 females) with normal interictal EEG at visual inspection were enrolled. None of them was taking psychotropic drugs. A convolutional neural network (CNN) scheme using DL classification was designed to classify the two categories of subjects (ES vs. PNES). The proposed architecture performs an EEG time-frequency transformation and a classification step with a CNN. The CNN was able to classify the EEG recordings of subjects with ES vs. subjects with PNES with 94.4% accuracy. CNN provided high performance in the assigned binary classification when compared to standard learning algorithms (multi-layer perceptron, support vector machine, linear discriminant analysis and quadratic discriminant analysis). In order to interpret how the CNN achieved this performance, information theoretical analysis was carried out. Specifically, the permutation entropy (PE) of the feature maps was evaluated and compared in the two classes. The achieved results, although preliminary, encourage the use of these innovative techniques to support neurologists in early diagnoses. 相似文献
62.
Magdi M. Naoum Nadia H. Metwally Manal M. Abd eltawab Hoda A. Ahmed 《Liquid crystals》2013,40(10):1351-1369
Eight homologous series of 2- (or 3-) substituted phenyl 4?-(4?-alkoxy phenylazo) benzoates (Ina–h) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 6, 8, 10 and 12 carbons, while the other substituent, X, is a laterally attached polar group that alternatively changed from CH3, H, F, Br and CN. Compounds prepared were characterised by infrared and 1H-NMR spectroscopy, and their mesophase behaviour investigated by differential scanning calorimetry and identified by polarised light microscopy. The results were discussed in terms of polarity and steric effects. The stability of the mesophase was correlated once with the dipolar anisotropy of the whole molecule and another with the dipolar anisotropy of the substituent, X. A comparative study was made between the investigated compounds and their previously prepared linear 4-substituted isomers, namely 4-substituted phenyl 4?-(4?-alkoxy phenylazo) benzoates (Ini–k). 相似文献
63.
64.
JPC – Journal of Planar Chromatography – Modern TLC - A simple, rapid, and selective densitometric thin-layer chromatographic (TLC) method has been established and validated for... 相似文献
65.
A family of Hecke C*-algebras can be realised as crossed productsby semigroups of endomorphisms. It is shown by dilating representationsof the semigroup crossed product that the category of representationsof the Hecke algebra is equivalent to the category of continuousunitary representations of a totally disconnected locally compactgroup. 相似文献
66.
Most K Köpke S Dall'Antonia F Mösch-Zanetti NC 《Chemical communications (Cambridge, England)》2002,(16):1676-1677
Molybdenum dioxo compounds [MoO2Cl(eta 2-pz)] and [MoO2(eta 2-pz)2] with pz = eta (2)-3,5-di-tert-butylpyrazolate have been synthesized; crystallographic data, catalytic activity, and oxo transfer properties are described. 相似文献
67.
Kenneth Bryan Pádraig Cunningham Nadia Bolshakova 《IEEE transactions on information technology in biomedicine》2006,10(3):519-525
In a gene expression data matrix, a bicluster is a submatrix of genes and conditions that exhibits a high correlation of expression activity across both rows and columns. The problem of locating the most significant bicluster has been shown to be NP-complete. Heuristic approaches such as Cheng and Church's greedy node deletion algorithm have been previously employed. It is to be expected that stochastic search techniques such as evolutionary algorithms or simulated annealing might improve upon such greedy techniques. In this paper we show that an approach based on simulated annealing is well suited to this problem, and we present a comparative evaluation of simulated annealing and node deletion on a variety of datasets. We show that simulated annealing discovers more significant biclusters in many cases. Furthermore, we also test the ability of our technique to locate biologically verifiable biclusters within an annotated set of genes. 相似文献
68.
Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) was covered with an hydrophobic layer from plasma polymerization of tetradecafluorohexane, octadecafluorooctane, 3,3,4,4,5,5,6,6,6-nonafluoro-hex-1-ene and 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-oct-1-ene. The water contact angle increased from 74° for untreated films to 98° for the treated films and the surface energy decreased from 40.9 to 18.8 mJ m−2. XPS analysis showed the introduction of 54% fluorine and 3-7% oxygen, the binding energies were assigned to chemically differently bonded carbon atoms. CF2/CF3 molar ratio in plasma layers was lower than that in the monomers due to molecular fragmentation, however the extent of monomer structure retention in PFH, PFO saturated chains is higher than in NFH, TDFO unsaturated chains. Biodegradation tests under aerobic conditions showed that the fluorinated plasma layer inhibited the biodegradation of the PHBV film underneath. 相似文献
69.
The Internet is a set of interconnected domains in which different QoS technologies can be deployed. The dynamic provision of end-to-end QoS over heterogeneousip networks assumes the negotiation of mutually acceptablesla. This paper presents the concept of intra-, inter- and multiple-domain service level negotiation using thecops-sls protocol. The negotiation process gives different parties in the negotiation the ability to agree upon the service level that a data stream can obtain, along with the permissible pricing of the service. 相似文献
70.
Scalora M Syrchin MS Akozbek N Poliakov EY D'Aguanno G Mattiucci N Bloemer MJ Zheltikov AM 《Physical review letters》2005,95(1):013902
A new generalized nonlinear Schr?dinger equation describing the propagation of ultrashort pulses in bulk media exhibiting frequency dependent dielectric susceptibility and magnetic permeability is derived and used to characterize wave propagation in a negative index material. The equation has new features that are distinct from ordinary materials (mu=1): the linear and nonlinear coefficients can be tailored through the linear properties of the medium to attain any combination of signs unachievable in ordinary matter, with significant potential to realize a wide class of solitary waves. 相似文献