全文获取类型
收费全文 | 364篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 174篇 |
晶体学 | 2篇 |
力学 | 26篇 |
数学 | 62篇 |
物理学 | 108篇 |
出版年
2022年 | 25篇 |
2021年 | 21篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 30篇 |
2012年 | 28篇 |
2011年 | 15篇 |
2010年 | 20篇 |
2009年 | 6篇 |
2008年 | 7篇 |
2007年 | 10篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 3篇 |
2003年 | 7篇 |
2002年 | 18篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有372条查询结果,搜索用时 15 毫秒
331.
Mohamed Abd Elaziz Abdelghani Dahou Naser A. Alsaleh Ammar H. Elsheikh Amal I. Saba Mahmoud Ahmadein 《Entropy (Basel, Switzerland)》2021,23(11)
Currently, the world is still facing a COVID-19 (coronavirus disease 2019) classified as a highly infectious disease due to its rapid spreading. The shortage of X-ray machines may lead to critical situations and delay the diagnosis results, increasing the number of deaths. Therefore, the exploitation of deep learning (DL) and optimization algorithms can be advantageous in early diagnosis and COVID-19 detection. In this paper, we propose a framework for COVID-19 images classification using hybridization of DL and swarm-based algorithms. The MobileNetV3 is used as a backbone feature extraction to learn and extract relevant image representations as a DL model. As a swarm-based algorithm, the Aquila Optimizer (Aqu) is used as a feature selector to reduce the dimensionality of the image representations and improve the classification accuracy using only the most essential selected features. To validate the proposed framework, two datasets with X-ray and CT COVID-19 images are used. The obtained results from the experiments show a good performance of the proposed framework in terms of classification accuracy and dimensionality reduction during the feature extraction and selection phases. The Aqu feature selection algorithm achieves accuracy better than other methods in terms of performance metrics. 相似文献
332.
V. I. Kelarev M. Bellul' R. A. Karakhanov Dibi Ammar A. F. Lunin 《Chemistry of Heterocyclic Compounds》1987,23(3):298-304
The reaction of 2-amino- and 2,4-diamino-sym-triazines with nitrourea and phenyl isocyanate was studied; it gives N-mono- and N,N-disubstituted ureas that contain sym-triazine segments. General features were established for the decomposition of carbamide derivatives of sym-triazine under electron impact.For communication 4, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 356–362, March, 1987. 相似文献
333.
This paper explores the relations between the matrix Riccati equation and the standard matrix eigenvalue methods. It is demonstrated that the mathematics of the analysis of the two objects is essentially the same; consisting of the analysis of flows on the homogeneous spaces of various Lie groups.Supported in part by DOE Contract DE-ACOL-80RA-5256.Supported in part by DOE Contract DE-ACOL-80RA-5256 and by NASA Grant DAG2-82. 相似文献
334.
A. S. A. Ammar Ali M. Okaz M. El-Osairy N. S. Mahmoud 《Journal of Thermal Analysis and Calorimetry》1990,36(2):433-439
The ferro-paramagnetic phase transition in dilute Cr-Ni base alloys is investigated through a qualitative study of their thermal conductivity as a function of temperature in the near vicinity of the transition. A single apparatus was used to measure the thermal and electrical conductivities and the specific heat of three thin rod samples having Cr concentrations of 0.12, 0.51 and 1.13 at.%.A voltage-temperature (V-) realign was applied to measure the ratio between the thermal and electrical conductivities. The thermal conductivity data were then evaluated by using the electrical resistivity results obtained from the measured current-voltage (I–V) characteristic curves. A model describing the effect of Cr concentration on the I–V curve is proposed and tested. The effect of Cr concentration on specific heat is also presented.
Zusammenfassung Der ferro-paramagnetische Phasenübergang von gestreckten Cr-Ni Ausgangslegierungen wurde mittels einer quantitativen Untersuchung ihrer Wärmeleitfähigkeit als eine Funktion der Temperatur in nächster Nähe des Phasenüberganges untersucht. Mit Hilfe einer einzigen Apparatur wurden Wärme- und elektrische Leitfähigkeit sowie die spezifische Wärme von drei Probenstäben mit einem Cr-Gehalt von 0.12, 0.51 bzw. 1.13% bestimmt.Für die Ermittlung des Verhältnisses zwischen Wärme- und elektrischer Leitfähigkeit wurde eine Spannungs-Temperatur (V-) Beziehung angewendet. Aus dem elektrischen Widerstand, erhalten aus den gemessenen Strom-Spannungskurven (I-V), kann dann die Wärmeleitfähigkeit ermittelt werden. Es wurde ein Modell entwickelt und getestet, um den Einfluß der Cr-Konzentration auf die (I-V)- Kurven wiederzugeben. Die Wirkung der CrKonzentration auf die spezifische Wärme wird ebenfalls beschrieben.相似文献
335.
Ammar R Baringer P Bean A Besson D Coppage D Copty N Davis R Hancock N Kelly M Kotov S Kravchenko I Kwak N Lam H Kubota Y Lattery M Momayezi M Nelson JK Patton S Poling R Savinov V Schrenk S Wang R Alam MS Kim IJ Ling Z Mahmood AH O'Neill JJ Severini H Sun CR Wappler F Crawford G Daubenmier CM Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Sung M White C Wolf A Zoeller MM Butler F Fu X Nemati B Ross WR Skubic P Wood M Bishai M Fast J Gerndt E Hinson JW McIlwain RL Miao T Miller DH 《Physical review letters》1995,74(18):3534-3537
336.
Yu. Batusov S. Bunyatov O. Kuznetsov V. Lyukov V. Tretyak O. Egorov P. Goritchev E. Kolganova I. Makhlyueva E. Pozharova V. Shamanov V. Smirnitsky V. Ammosov V. Baranov V. Gapienko V. Klukhin V. Koreshev P. Pitukhin V. Sirotenko A. Jurak A. Olszewski B. Wilczynska H. Wilczynski W. Wolter B. Wosiek H. Tchernev M. Ivanova W. Smart L. Voyvodic H. Rubin R. Ammar D. Coppage R. Davis J. Grees N. Kwak R. Riemer R. Stump T. Burnett S. Krzywdzinski J. Lord R. Rosenbladt R. Wilkes A. Bakich L. Peak FERMILAB E- Collaboration 《Zeitschrift fur Physik C Particles and Fields》1990,45(4):557-565
Cryogenically sensitive nuclear emulsion was placed inside the 15-foot bubble chamber of FNAL and exposed to a wide-band energy (up to 200 GeV) neutrino beam. 194 charged-current neutrino interactions and 13 decays of charmed particles were registered. Using the nuclear emulsion as a vertex detector with the good spectrometric properties of the 15-foot bubble chamber has allowed the decays of charmed particles to be effectively analysed. Attentions is focussed on the new physical results. Λ c + baryon andD s + meson decay channels, production of charmed ∑ c baryons and Λ c + via ∑ c . For the first time an event interpreted as production of the excited (c \(\overline s\) )-state with mass ~2790 MeV/c2 has been registered. 相似文献
337.
Avery P Besson D Garren L Yelton J Kinoshita K Pipkin FM Procario M Wilson R Wolinski J Xiao D Zhu Y Ammar R Baringer P Coppage D Haas P Kwak N Lam H Ro S Kubota Y Nelson JK Perticone D Poling R Fulton R Jensen T Johnson DR Kagan H Kass R Morrow F Whitmore J Wilson P Bortoletto D Dominick J McIlwain RL Miller DH Ng CR Schaffner SF Shibata EI Shipsey IP Yao W Sparks K Thorndike EH Wang C Alam MS Kim IJ Li WC Lou XC Romero V Sun CR Wang P Zoeller MM Goldberg M Haupt T Horwitz N Jain V Mestayer MD 《Physical review D: Particles and fields》1991,43(11):3599-3610
338.
Multivalent interactions in which multiple ligands on one object bind to multiple receptors on another are commonly found in natural biological systems. In addition, these interactions can lead to increased strength and selectivity when compared to the corresponding monovalent interaction. These attributes have also guided the design of synthetic multivalent ligands to control biological interactions. This review will highlight the recent literature describing the use of multivalent ligand display in the design of vaccines, immunomodulators, cell signaling effectors, and vehicles for targeted drug delivery. 相似文献
339.
This work presents an estimation of the neutron dose distribution for common bladder cancer cases treated with high-energy photons of 15 MV therapy accelerators. Neutron doses were measured in an Alderson phantom, using TLD 700 and 600 thermoluminescence dosimeters, resembling bladder cancer cases treated with high-energy photons from 15 MV LINAC and having a treatment plan using the four-field pelvic box technique. Thermal neutron dose distribution in the target area and the surrounding tissue was estimated. The sensitivity of all detectors for both gamma and neutrons was estimated and used for correction of the TL reading. TLD detectors were irradiated with a Co60 gamma standard source and thermal neutrons at the irradiation facility of the National Institute for Standards (NIS). The TL to dose conversion factor was estimated in terms of both Co60 neutron equivalent dose and thermal neutron dose. The dose distribution of photo-neutrons throughout each target was estimated and presented in three-dimensional charts and isodose curves. The distribution was found to be non-isotropic through the target. It varied from a minimum of 0.23 mSv/h to a maximum of 2.07 mSv/h at 6 cm off-axis. The mean neutron dose equivalent was found to be 0.63 mSv/h, which agrees with other published literature. The estimated average neutron equivalent to the bladder per administered therapeutic dose was found to be 0.39 mSv Gy?1, which is also in good agreement with published literature. As a consequence of a complete therapeutic treatment of 50 Gy high-energy photons at 15 MV, the total thermal neutron equivalent dose to the abdomen was found to be about 0.012 Sv. 相似文献
340.
Mohamed Aziz Nasri Camille Robert Amine Ammar Saber El Arem Franck Morel 《Comptes Rendus Mecanique》2018,346(2):132-151
The numerical modelling of the behaviour of materials at the microstructural scale has been greatly developed over the last two decades. Unfortunately, conventional resolution methods cannot simulate polycrystalline aggregates beyond tens of loading cycles, and they do not remain quantitative due to the plasticity behaviour. This work presents the development of a numerical solver for the resolution of the Finite Element modelling of polycrystalline aggregates subjected to cyclic mechanical loading. The method is based on two concepts. The first one consists in maintaining a constant stiffness matrix. The second uses a time/space model reduction method. In order to analyse the applicability and the performance of the use of a space–time separated representation, the simulations are carried out on a three-dimensional polycrystalline aggregate under cyclic loading. Different numbers of elements per grain and two time increments per cycle are investigated. The results show a significant CPU time saving while maintaining good precision. Moreover, increasing the number of elements and the number of time increments per cycle, the model reduction method is faster than the standard solver. 相似文献