全文获取类型
收费全文 | 3401篇 |
免费 | 60篇 |
国内免费 | 10篇 |
专业分类
化学 | 1940篇 |
晶体学 | 41篇 |
力学 | 76篇 |
数学 | 297篇 |
物理学 | 1117篇 |
出版年
2021年 | 23篇 |
2020年 | 39篇 |
2019年 | 39篇 |
2016年 | 61篇 |
2015年 | 49篇 |
2014年 | 55篇 |
2013年 | 101篇 |
2012年 | 99篇 |
2011年 | 141篇 |
2010年 | 71篇 |
2009年 | 65篇 |
2008年 | 127篇 |
2007年 | 112篇 |
2006年 | 116篇 |
2005年 | 119篇 |
2004年 | 82篇 |
2003年 | 85篇 |
2002年 | 79篇 |
2001年 | 93篇 |
2000年 | 84篇 |
1999年 | 54篇 |
1998年 | 69篇 |
1997年 | 31篇 |
1996年 | 64篇 |
1995年 | 59篇 |
1994年 | 53篇 |
1993年 | 55篇 |
1992年 | 69篇 |
1991年 | 52篇 |
1990年 | 48篇 |
1989年 | 45篇 |
1988年 | 53篇 |
1987年 | 47篇 |
1986年 | 51篇 |
1985年 | 57篇 |
1984年 | 58篇 |
1983年 | 37篇 |
1982年 | 48篇 |
1981年 | 55篇 |
1980年 | 50篇 |
1979年 | 64篇 |
1978年 | 58篇 |
1977年 | 50篇 |
1976年 | 41篇 |
1975年 | 42篇 |
1974年 | 43篇 |
1973年 | 35篇 |
1971年 | 20篇 |
1970年 | 29篇 |
1969年 | 22篇 |
排序方式: 共有3471条查询结果,搜索用时 15 毫秒
81.
Zeus A. De los Santos Sean MacAvaney Katina Russell Christian Wolf 《Angewandte Chemie (International ed. in English)》2020,59(6):2440-2448
We have developed an optical method for accurate concentration, er, and dr analysis of amino alcohols based on a simple mix‐and‐measure workflow that is fully adaptable to multiwell plate technology and microscale analysis. The conversion of the four aminoindanol stereoisomers with salicylaldehyde to the corresponding Schiff base allows analysis of the dr based on a change in the UV maximum at 420 nm that is very different for the homo‐ and heterochiral diastereomers and of the concentration of the sample using a hypsochromic shift of another absorption band around 340 nm that is independent of the analyte stereochemistry. Subsequent in situ formation of CuII assemblies in the absence and presence of base enables quantification of the er values for each diastereomeric pair by CD analysis. Applying a linear programming method and a parameter sweep algorithm, we determined the concentration and relative amounts of each of the four stereoisomers in 20 samples of vastly different stereoisomeric compositions with an averaged absolute percent error of 1.7 %. 相似文献
82.
Michael P. Wolf 《Acta Analytica》2002,17(1):151-170
In this paper, I will outline some of the important points made by Kripke and Putnam on the meaning of natural kind terms. Their notion of the baptism of natural kinds- the process by which kind terms are initially introduced into the language — is of special concern here. I argue that their accounts leave some ambiguities that suggest a baptism of objects and kinds that is free of additional theoretical commitments. Both authors suggest that we name the stuff and then let the scientists tell us what properties it really has, and hence what the real meaning is. I contend that such a barren baptism, taken at face value, cannot succeed in the semantic roles it has been assigned and that softening the stance on baptism suggests a more subtle and complex relation between reference and theoretical commitment than has emerged thus far. 相似文献
83.
The stable adsorption sites for both Ga and N ions on the ideal and on the reconstructed LiNbO3 (0 0 0 1) surface are determined by means of first-principle total energy calculations. A single N layer is found to be more strongly bound to the substrate than a single Ga layer. The adsorption of a GaN monolayer on the polar substrate within different orientations is then modeled. On the basis of our results, we propose a microscopic model for the GaN/LiNbO3 interface. The GaN and LiNbO3 (0 0 0 1) planes are parallel, but rotated by 30° each other, with in-plane epitaxial relationship [1 0 0]GaN‖ [1 1 0]LiNbO3. In this way the (0 0 0 1) plane lattice mismatch between GaN and LiNbO3 is minimal and equal to 6.9% of the GaN lattice constant. The adsorbed GaN and the underlying LiNbO3 substrate have parallel c-axes. 相似文献
84.
Elke Wolf 《Numerical Functional Analysis & Optimization》2013,34(5-6):646-651
Let φ: 𝔻 → 𝔻 and ψ: 𝔻 → ? be analytic maps. They induce a weighted composition operator ψ C φ acting between weighted Bloch type spaces and weighted Banach spaces of holomorphic functions. Under some assumptions on the weights, we give a necessary as well as a sufficient condition when such an operator is bounded resp. compact. 相似文献
85.
Francis J. Vasko John A. McNamara Dennis D. Newhart Floyd E. Wolf 《The Journal of the Operational Research Society》1994,45(11):1285-1292
The optimum assignment of structural steel shapes to rail cars is an important logistical problem in the steel industry. In this paper, we discuss an application at Bethlehem Steel that not only involves weight and dimensional constraints, but also customer unloading constraints. The formulation is a generalized bin packing problem which is solved by modifying and extending the first fit decreasing algorithm. The solution algorithm, SOLID (for Structural Optimal Loading IDentification), has been used extensively for one of Bethlehem's high tonnage customers providing very good practical (implementable) results that achieve the desired goals. Bethlehem has enhanced this approach for use with other customers. 相似文献
86.
An alkali‐soluble polysaccharide, GM5‐1, from the mycelium of Ganoderma tsugae, was fractionated by the nonsolvent addition method. The weight‐average molecular mass (M w) and intrinsic viscosity ([η]) of fractions were studied by laser light scattering and viscometry with dimethylsulfoxide (DMSO) containing 0.25M LiCl (0.25M LiCl/DMSO) as the solvent at 30°C. The dependences of [η] and the radius of gyration (?S 2?z 1/2) on M w were found to be [η]=9.8×10?2 M w 0.57 (cm3g?1) and ?S 2?z 1/2=1.65×10?2 M w 0.58 (nm) in the M w range from 8.6×105 to 2.6×106. The analysis based on current theories for a wormlike chain showed that the chain conformational parameters of GM5‐1 were 4.2 nm for persistence length (q) and 833 nm?1 for linear mass density (ML) with an obvious excluded volume effect. The results suggested the alkali‐soluble polysaccharide behaves like a semiflexible chain in 0.25M LiCl/DMSO at 30°C. 相似文献
87.
Ladislav Hlavatý Stanly Steinberg Kurt Bernardo Wolf 《Journal of Mathematical Analysis and Applications》1984,104(1):246-263
Lie series and a special matrix notation for first-order differential operators are used to show that the Lie group properties of matrix Riccati equations arise in a natural way. The Lie series notation makes it evident that the solutions of a matrix Riccati equation are curves in a group of nonlinear transformations that is a generalization of the linear fractional transformations familiar from the classical complex analysis. It is easy to obtain a linear representation of the Lie algebra of the nonlinear group of transformations and then this linearization leads directly to the standard linearization of the matrix Riccati equations. We note that the matrix Riccati equations considered here are of the general rectangular type. 相似文献
88.
Grafting is a method of obtaining new projective structures from a hyperbolic structure, basically by gluing a flat cylinder into a surface along a closed geodesic in the hyperbolic structure, or by limits of that procedure. This induces a map of Teichmüller space to itself. We prove that this map is a homeomorphism by analyzing harmonic maps between pairs of grafted surfaces. As a corollary we obtain bending coordinates for the Bers embedding of Teichmüller space.
89.
F.?GebhardEmail author E.?Jeckelmann S.?Mahlert S.?Nishimoto R.?M.?Noack 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,36(4):491-509
We calculate the zero-temperature self-energy to fourth-order perturbation theory in the Hubbard interaction U for the half-filled Hubbard model in infinite dimensions. For the Bethe lattice with bare bandwidth W, we compare our perturbative results for the self-energy, the single-particle density of states, and the momentum distribution to those from approximate analytical and numerical studies of the model. Results for the density of states from perturbation theory at U/W = 0.4 agree very well with those from the Dynamical Mean-Field Theory treated with the Fixed-Energy Exact Diagonalization and with the Dynamical Density-Matrix Renormalization Group. In contrast, our results reveal the limited resolution of the Numerical Renormalization Group approach in treating the Hubbard bands. The momentum distributions from all approximate studies of the model are very similar in the regime where perturbation theory is applicable,
. Iterated Perturbation Theory overestimates the quasiparticle weight above such moderate interaction strengths.Received: 9 September 2003, Published online: 30 January 2004PACS:
71.10.Fd Lattice fermion models (Hubbard model, etc.) - 71.27. + a Strongly correlated electron systems; heavy fermions - 71.30. + h Metal-insulator transitions and other electronic transitions 相似文献
90.
Zhiqi Chen Joseph A. Wolf 《Abhandlungen aus dem Mathematischen Seminar der Universit?t Hamburg》2018,88(2):331-369
We develop the classification of weakly symmetric pseudo-Riemannian manifolds G / H where G is a semisimple Lie group and H is a reductive subgroup. We derive the classification from the cases where G is compact, and then we discuss the (isotropy) representation of H on the tangent space of G / H and the signature of the invariant pseudo-Riemannian metric. As a consequence we obtain the classification of semisimple weakly symmetric manifolds of Lorentz signature \((n-1,1)\) and trans-Lorentzian signature \((n-2,2)\). 相似文献