全文获取类型
收费全文 | 659篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
化学 | 445篇 |
晶体学 | 4篇 |
力学 | 11篇 |
数学 | 105篇 |
物理学 | 126篇 |
出版年
2023年 | 10篇 |
2022年 | 12篇 |
2021年 | 18篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 11篇 |
2017年 | 13篇 |
2016年 | 19篇 |
2015年 | 21篇 |
2014年 | 19篇 |
2013年 | 41篇 |
2012年 | 49篇 |
2011年 | 33篇 |
2010年 | 28篇 |
2009年 | 26篇 |
2008年 | 37篇 |
2007年 | 32篇 |
2006年 | 44篇 |
2005年 | 49篇 |
2004年 | 27篇 |
2003年 | 26篇 |
2002年 | 24篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 5篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1888年 | 1篇 |
1887年 | 1篇 |
排序方式: 共有691条查询结果,搜索用时 16 毫秒
1.
A mixed problem is considered for a system of partial differential equations modeling the process of adsorption dynamics. An existence and uniqueness theorem is proved for this problem, and the solution properties are investigated. The inverse problem is posed, involving the determination of the system coefficient given additional information about the solution. A uniqueness theorem is proved for the solution of the inverse problem.__________Translated from Prikladnaya Matematika i Informatika, No. 16, pp. 5 – 14, 2004. 相似文献
2.
K.B. Welter Q. Wu Y. You K. Abel D. McCreary S.M. Bajorek J.N. Reyes Jr 《International Journal of Multiphase Flow》2004,30(12):407-1484
This article describes a comprehensive literature review of liquid entrainment in horizontal pipes with vertical-up branches. Deficiencies in the available data and correlations were identified. The Air–water Test Loop for Advanced Thermal–hydraulic Studies (ATLATS) was constructed and entrainment onset and steady-state data were collected for a wide range of flow conditions. Using new insights gained from experimental testing, the authors developed a model for predicting the onset of entrainment and steady-state entrainment rate. Previously published correlations, along with the new model, are compared against all available data. The new model shows very good agreement with the onset data, but is not very good at predicting branch quality at high liquid flow rates. 相似文献
3.
On Covariant Phase Space and the Variational Bicomplex 总被引:1,自引:0,他引:1
Enrique G. Reyes 《International Journal of Theoretical Physics》2004,43(5):1267-1286
The notion of a phase space in classical mechanics is well known. The extension of this concept to field theory however, is a challenging endeavor, and over the years numerous proposals for such a generalization have appeared in the literature. In this paper We review a Hamiltonian formulation of Lagrangian field theory based on an extension to infinite dimensions of J.-M. Souriau's symplectic approach to mechanics. Following G. Zuckerman, we state our results in terms of the modern geometric theory of differential equations and the variational bicomplex. As an elementary example, we construct a phase space for the Monge–Ampere equation. 相似文献
4.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献
5.
Kar S Chanda N Mobin SM Urbanos FA Niemeyer M Puranik VG Jimenez-Aparicio R Lahiri GK 《Inorganic chemistry》2005,44(5):1571-1579
The reaction of cis-Ru(acac)2(CH3CN)2 (acac = acetylacetonate) with 2,2'-dipyridylamine (L) in ethanolic medium resulted in facile one-pot synthesis of stable [(acac)2RuIII(L)]ClO4 ([1]ClO4), trans-[(acac)2RuII(L)2] (2), trans-[(acac)2RuIII)L)2]ClO4 ([2]ClO4), and cis-[(acac)2RuII(L)2] (3). The bivalent congener 1 was generated via electrochemical reduction of [1]ClO4. Although in [1]+ the dipyridylamine ligand (L) is bonded to the metal ion in usual bidentate fashion, in 2/[2]+ and 3, the unusual monodentate binding mode of L has been preferentially stabilized. Moreover, in 2/[2]+ and 3, two such monodentate L's have been oriented in the trans- and cis-configurations, respectively. The binding mode of L and the isomeric geometries of the complexes were established by their single-crystal X-ray structures. The redox stability of the Ru(II) state follows the order 1 < 2 < 3. In contrast to the magnetic moment obtained for [1]ClO4, mu = 1.84 muB at 298 K, typical for low-spin Ru(III) species, the compound [2]ClO4 exhibited an anomalous magnetic moment of 2.71 muB at 300 K in the solid state. The variable-temperature magnetic measurements showed a pronounced decrease of the magnetic moment with the temperature, and that dropped to 1.59 muB at 3 K. The experimental data can be fitted satisfactorily using eq 2 that considered nonquenched spin-orbit coupling and Weiss constant in addition to the temperature-independent paramagnetism. [1]ClO4 and [2]ClO4 displayed rhombic and axial EPR spectra, respectively, in both the solid and the solution states at 77 K. 相似文献
6.
7.
M José Reyes 《Tetrahedron》2004,60(5):1093-1097
Differently substituted pyridinium N-heteroarylaminides have been prepared in one step with good yield from N-aminopyridinium iodide and the corresponding heteroaryl chloride. 相似文献
8.
Fernando Mendizabal Dana Reyes Claudio Olea‐Azar 《International journal of quantum chemistry》2006,106(4):906-912
Hydrogen bonding and metallophilic attractions are studied in the model systems: [(AuNH3Cl)2], [(AuNH(CH3)2Cl)2], [{Au2(μ‐SH)(PH2O)(PH2OH)}2], [(CuNH3Cl)2], and [{Cu(NH3)Cl}4] at the Hartree–Fock (HF) and second‐order Møller–Plesset (MP2) levels. The two interactions are found to be comparable and prevailing in the final structure. It is determined that the aurophilic contact has a same magnitude that the hydrogen bonding, and is stronger than the cuprophilic interaction. The presence of hydrogen bond directs the growth of the crystal. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
9.
Niyama E Brito HF Cremona M Teotonio EE Reyes R Brito GE Felinto MC 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(11-12):2643-2649
In this paper the synthesis, characterization and photoluminescent behavior of the [RE(DBM)3L2] complexes (RE=Gd and Eu) with a variety of sulfoxide ligands; L=benzyl sulfoxide (DBSO), methyl sulfoxide (DMSO), phenyl sulfoxide (DPSO) and p-tolyl sulfoxide (PTSO) have been investigated in solid state. The emission spectra of the Eu(3+)-beta-diketonate complexes show characteristics narrow bands arising from the 5D0-->7F(J) (J=0-4) transitions, which are split according to the selection rule for C(n), C(nv) or C(s) site symmetries. The experimental Judd-Ofelt intensity parameters (Omega2 and Omega4), radiative (A(rad)) and non-radiative (A(nrad)) decay rates, and R02 for the europium complexes have been determined and compared. The highest value of Omega2 (61.9x10(-20)cm2) was obtained to the complex with PTSO ligand, indicating that Eu3+ ion is in the highly polarizable chemical environment. The higher values of the experimental quantum yield (q) and emission quantum efficiency of the emitter 5D0 level (eta) for the Eu-complexes with DMSO, DBSO and PTSO sulfoxides suggest that these complexes are promising Light Conversion Molecular Devices (LCMDs). The lower value of quantum yield (q=1%), for the hydrated complex [Eu(DBM)3H2O], indicates that the luminescence quenching occurs via multiphonon relaxation by coupling with the OH-oscillators from water molecule coordinated to rare earth ion. The pure red emission of the Eu-complexes has been confirmed by (x, y) color coordinates. 相似文献
10.