全文获取类型
收费全文 | 518篇 |
免费 | 21篇 |
国内免费 | 6篇 |
专业分类
化学 | 351篇 |
晶体学 | 1篇 |
力学 | 27篇 |
数学 | 82篇 |
物理学 | 84篇 |
出版年
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 20篇 |
2018年 | 22篇 |
2017年 | 18篇 |
2016年 | 37篇 |
2015年 | 13篇 |
2014年 | 31篇 |
2013年 | 49篇 |
2012年 | 37篇 |
2011年 | 26篇 |
2010年 | 26篇 |
2009年 | 30篇 |
2008年 | 20篇 |
2007年 | 26篇 |
2006年 | 16篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 16篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1959年 | 1篇 |
1956年 | 2篇 |
1943年 | 1篇 |
排序方式: 共有545条查询结果,搜索用时 15 毫秒
101.
Several sets of radially propagating null congruence generators are exploited in order to form 3-dimensional marginally trapped surfaces, referred to as black hole and cosmological apparent horizons in a Ho?ava universe. Based on this method, we deal with the characteristics of the 2-dimensional space-like spheres of symmetry and the peculiarities of having trapping horizons. Moreover, we apply this method in standard expanding and contracting FLRW cosmological models of a Ho?ava universe to investigate the conditions under which the extra parameters of the theory may lead to trapped/anti-trapped surfaces both in the future and in the past. We also include the cases of negative time, referred to as the finite past, and discuss the formation of anti-trapped surfaces inside the cosmological apparent horizons. 相似文献
102.
Mohamed Fathi El-Shahat Hisham Mohamed Kamal Reda Abd El-Gawad Ghazall Walid Mohamed Morsy 《无机化学学报》2016,32(8):1427-1433
利用三异辛胺(TOA)纯化Gattar小型试验工厂的高浓度铀溶液(洗脱液的铀浓度7 g·L-1),研究了脉冲萃取柱的性能。利用实验室级脉冲萃取柱进行了实验室规模的溶剂萃取实验和后续实验。结果表明,在室温、pH=1和有机相与水相的比例(VO/VA)约为1.8:1时,加入二(2-乙基己基)磷酸(D2EHPA)使其与TOA的比例(VD2EHPA/VTOA)为2:3,可使萃取克服Cl-的抑制效应,提高效率。将结论用于考察试验工厂级萃取柱的流体力学和传质性能,结果表明用脉冲萃取柱萃取铀可以达到97%的萃取效率,具有可行性。 相似文献
103.
104.
This paper obtains solitons and singular periodic solutions to the generalized resonant dispersive nonlinear Schrödinger’ equation with power law nonlinearity. There are several integration tools that are adopted to extract these solutions. They are simplest equation method, functional variable method, sine–cosine function method, tanh function method and the G′/G-expansion method. These integration techniques reveal bright and singular solitons as well as the corresponding singular periodic solutions to the nonlinear evolution equation. These solitons solutions are important in the nonlinear fiber optics community as well as in the study of rogue waves. 相似文献
105.
Magda F. Mohamed Mervat S. Mohamed Samia A. Shouman Mohamed M. Fathi Ismail Abdelshafy Abdelhamid 《Applied biochemistry and biotechnology》2012,168(5):1153-1162
A newly synthesized series of chalcone derivatives containing pyrazole rings were synthesized and evaluated for their cytotoxic activities in vitro against several human cancer cell lines. Most of the prepared compounds showed potential cytotoxicity against human breast cancer cell lines MCF-7, HEPG-2, and HCT-116. Also the compounds were evaluated as antimicrobial agents. The three compounds 3, 4, and 5 were proved to be better anticancer agents than the positive standard doxorubicin with IC50 values (4.7, 4.4, and 3.9???g/ml) against the same human cancer cell lines, whereas compounds 5 and 6 showed the most active antimicrobial compounds in comparison to the other chalcones. 相似文献
106.
Lombardo G Amoddeo A Hamdi R Ayeb H Barberi R 《The European physical journal. E, Soft matter》2012,35(5):32-6
Thermotropic nematic materials relax strong distortions by lowering the nematic order: the uniaxial symmetry is broken and is locally replaced by biaxial domains. We investigated the dynamics of the nematic order near a boundary surface of an asymmetric π-cell submitted to an external electric field, close to the electric order reconstruction threshold. An unexpected phenomenon is observed close, but below the threshold: the biaxial order spreads on the surface inducing a consequent bulk topological behaviour equivalent to the splay-bend fast transition allowed by order reconstruction at higher voltage. 相似文献
107.
Fathi Kallel Mondher Frikha Mohamed Ghorbel Ahmed Ben Hamida Christian Berger-Vachon 《Applied Acoustics》2012,73(1):12-20
In this paper, two speech enhancement algorithms (SEAs) based on spectral subtraction (SS) principle have been evaluated for bilateral cochlear implant (BCI) users. Specifically, dual-channel noise power spectral estimation algorithm using power spectral densities (PSD) and cross power spectral density (CPSD) of the observed signals was studied. The enhanced speech signals were obtained using either Dual Channel Non Linear Spectral Subtraction ‘DC-NLSS’ or Dual-Channel Multi-Band Spectral Subtraction ‘DC-MBSS’ algorithms. For performance evaluation, some objective speech assessment tests relying on Perceptual Evaluation of Speech Quality (PESQ) score and speech Itakura-Saito (IS) distortion measurement were performed to fix the optimal number of frequency band needed in DC-MBSS algorithm. In order to evaluate the speech intelligibility, subjective listening tests were assessed with 50 normal hearing listeners using a specific BCI simulator and with three deafened BCI patients. Experimental results, obtained using French Lafon database corrupted by an additive babble noise at different Signal-to-Noise Ratios (SNR), showed that DC-MBSS algorithm improves speech understanding better than DC-NLSS algorithm for single and multiple interfering noise sources. 相似文献
108.
Kambale Mondo Senda Agrebi Fathi Hamdi Fatma Lakhal Amsini Sadiki Mouldi Chrigui 《Entropy (Basel, Switzerland)》2022,24(5)
Even though there is a pressing interest in clean energy sources, compression ignition (CI) engines, also called diesel engines, will remain of great importance for transportation sectors as well as for power generation in stationary applications in the foreseeable future. In order to promote applications dealing with complex diesel alternative fuels by facilitating their integration in numerical simulation, this paper targets three objectives. First, generate novel diesel fuel surrogates with more than one component. Here, five surrogates are generated using an advanced chemistry solver and are compared against three mechanisms from the literature. Second, validate the suggested reaction mechanisms (RMs) with experimental data. For this purpose, an engine configuration, which features a reacting spray flow evolving in a direct-injection (DI), single-cylinder, and four-stroke motor, is used. The RNG k-Epsilon coupled to power-law combustion models is applied to describe the complex in-cylinder turbulent reacting flow, while the hybrid Eulerian-Lagrangian Kelvin Helmholtz-Rayleigh Taylor (KH-RT) spray model is employed to capture the spray breakup. Third, highlight the impact of these surrogate fuels on the combustion properties along with the exergy of the engine. The results include distribution of temperature, pressure, heat release rate (HRR), vapor penetration length, and exergy efficiency. The effect of the surrogates on pollutant formation (, , ) is also highlighted. The fifth surrogate showed 47% exergy efficiency. The fourth surrogate agreed well with the maximum experimental pressure, which equaled 85 Mpa. The first, second, and third surrogates registered 400, 316, and 276 g/kg fuel, respectively, of the total CO mass fraction at the outlet. These quantities were relatively higher compared to the fourth and fifth RMs. 相似文献
109.
Fathi Morteza Ganji Davood Domiri Jahanian Omid 《Journal of Thermal Analysis and Calorimetry》2020,139(4):2447-2454
Journal of Thermal Analysis and Calorimetry - The low-temperature combustion (LTC) concept presents solutions for simultaneous reduction in pollution and fuel consumption of internal combustion... 相似文献
110.
Albert Fathi 《Communications in Mathematical Physics》1989,126(2):249-262
We show that there exists a simple upper bound on the dimension of a hyperbolic compact set of a dynamical system in terms of topological entropy and a uniform contraction rate on the stable and unstable manifolds. This allows us to give proofs of several apparently unrelated theorems. 相似文献