全文获取类型
收费全文 | 626篇 |
免费 | 13篇 |
国内免费 | 6篇 |
专业分类
化学 | 326篇 |
晶体学 | 2篇 |
力学 | 19篇 |
数学 | 84篇 |
物理学 | 214篇 |
出版年
2023年 | 8篇 |
2022年 | 11篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 18篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 30篇 |
2012年 | 32篇 |
2011年 | 30篇 |
2010年 | 23篇 |
2009年 | 21篇 |
2008年 | 33篇 |
2007年 | 28篇 |
2006年 | 27篇 |
2005年 | 24篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 6篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1971年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有645条查询结果,搜索用时 15 毫秒
101.
102.
The extensivity property of entropy is clarified in the light of a critical examination of the entropy formula based on quantum
statistics and the relevant thermodynamic requirement. The modern form of the Gibbs paradox, related to the discontinuous
jump in entropy due to identity or non-identity of particles, is critically investigated. Qualitative framework of a new resolution
of this paradox, which analyses the general effect of distinction mark on the Hamiltonian of a system of identical particles,
is outlined. 相似文献
103.
Unified study of the different properties of metals clearly reveals the inadequacy of the empty-core Ashcroft pseudopotential
even in the case of simple metals. In the present paper we propose a modification of the one-parameter Ashcroft pseudopotential
by assuming the parameterr
c to be wave vector-dependent. This introduces a simple modification of the electron-ion pseudopotential in the reciprocal
space. The corresponding potential in the configuration space shows that the abrupt change in the Coulomb potential atr=r
c is replaced by a continuous change spread over a small region near the core boundary. The present model has been used to
make a unified study of Al and is found to be a significant improvement over the simple Ashcroft model. The agreement between
the calculated and experimental values is found to be quite satisfactory. 相似文献
104.
With a view to exploring the possibility of wider implication of Bell's theorem, we argue that Bell's inequality is derivable as a general consequence of non-contextual hidden-variable theories. We formulate a new type of gedanken example indicating incompatibility of Bell's inequality with quantum mechanical predictions concerning simultaneous measurement of commuting observables associated with a system having no spatially separated components, where the locality condition is not at issue. Significance of this example is pointed out. 相似文献
105.
Manoj K. Rajpoot Tapan K. Sengupta Pravir K. Dutt 《Journal of computational physics》2010,229(10):3623-3651
In this paper we examine the constrained optimization of explicit Runge–Kutta (RK) schemes coupled with central spatial discretization schemes to solve the one-dimensional convection equation. The constraints are defined with respect to the correct error propagation equation which goes beyond the traditional von Neumann analysis developed in Sengupta et al. [T.K. Sengupta, A. Dipankar, P. Sagaut, Error dynamics: beyond von Neumann analysis, J. Comput. Phys. 226 (2007) 1211–1218]. The efficiency of these optimal schemes is demonstrated for the one-dimensional convection problem and also by solving the Navier–Stokes equations for a two-dimensional lid-driven cavity (LDC) problem. For the LDC problem, results for Re=1000 are compared with results using spectral methods in Botella and Peyret [O. Botella, R. Peyret, Benchmark spectral results on the lid-driven cavity flow, Comput. Fluids 27 (1998) 421–433] to calibrate the method in solving the steady state problem. We also report the results of the same flow at Re=10,000 and compare them with some recent results to establish the correctness and accuracy of the scheme for solving unsteady flow problems. Finally, we also compare our results for a wave-packet propagation problem with another method developed for computational aeroacoustics. 相似文献
106.
Ukrainian Mathematical Journal - Following the line of investigation in [Linear Algebra Appl., 487, 22–42 (2015)], for y ∈ ? and a sequence... 相似文献
107.
We show that the defect density n, for a slow nonlinear power-law quench with a rate tau(-1) and an exponent alpha>0, which takes the system through a critical point characterized by correlation length and dynamical critical exponents nu and z, scales as n approximately tau(-alphanud/(alphaznu+1)) [n approximately (alphag((alpha-1)/alpha)/tau)(nud/(znu+1))] if the quench takes the system across the critical point at time t=0 [t=t(0) not = 0], where g is a nonuniversal constant and d is the system dimension. These scaling laws constitute the first theoretical results for defect production in nonlinear quenches across quantum critical points and reproduce their well-known counterpart for a linear quench (alpha=1) as a special case. We supplement our results with numerical studies of well-known models and suggest experiments to test our theory. 相似文献
108.
Segmented conjugated macromolecules containing silicon and boron: ADMET synthesis and luminescent properties 下载免费PDF全文
Arijit Sengupta Ami Doshi Frieder Jäkle Ralf M. Peetz 《Journal of polymer science. Part A, Polymer chemistry》2015,53(14):1707-1718
Boron‐ and silicon‐containing conjugated homo‐ and copolymers could be synthesized using acyclic diene metathesis (ADMET) condensation of bis‐styryl monomers. Both, tri‐and tetra‐coordinated boron monomers were successfully polymerized forming homopolymers, or random copolymers (if polymerized together with a silicon containing co‐monomer). Polymer molecular weights Mn were measured at ~6000 to 15,000 g/mol (NMR end group analysis) with molecular weight distributions Mw/Mn ~1.8 to 2.2. The polymers absorbed at λmax ~317 to 406 nm and emitted at λmax ~370 to 494 nm with fluorescent quantum efficiencies ~24 to 48%. The copolymer with tri‐coordinate boron showed highly efficient fluorescence quenching in the presence of fluoride ions at ratios boron/fluoride ~5/1, demonstrating its potential as anion sensor. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1707–1718 相似文献
109.
2-Isopropylbenzimidazole and 2-methylbenzimidazole have been found to be effective bulky proton sources for stereoselective protonation of chiral enolate anions. 2-Isopropylbenzimidazole worked in the stereoselective protonation of the Birch reduction of chiral α,β-unsaturated imides. On the other hand, 2-methylbenzimidazole was found to be the best protonation reagent in the isomerization reaction of α,β-unsaturated imide into β,γ-unsaturated imide. The Birch reduction using 2-isopropylbenzimidazole realized a concise and stereoselective synthesis of δ-lactone 14, a sex pheromone of Macrocentrus grandii, while the isomerization reaction using 2-methylbenzimidazole was employed in the highly stereoselective synthesis of the γ-lactone intermediate in the synthesis of depsipeptide antibiotics. These bulky proton sources would be powerful tools to achieve a concise synthesis of natural products. 相似文献
110.
Journal of Solid State Electrochemistry - In dye-sensitized solar cell (DSSC) application, the particulate morphologies of photo-anode facilitate efficient dye loading and thus lead to better... 相似文献