全文获取类型
收费全文 | 544篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 280篇 |
力学 | 8篇 |
数学 | 61篇 |
物理学 | 203篇 |
出版年
2020年 | 4篇 |
2019年 | 8篇 |
2016年 | 7篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 13篇 |
2012年 | 17篇 |
2011年 | 14篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 26篇 |
2007年 | 40篇 |
2006年 | 24篇 |
2005年 | 20篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 16篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 18篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1971年 | 6篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1966年 | 3篇 |
1963年 | 3篇 |
1877年 | 6篇 |
排序方式: 共有552条查询结果,搜索用时 31 毫秒
71.
We show that, for fixed dimensionn, the approximation of inner and outerj-radii of polytopes in ℝ
n
, endowed with the Euclidean norm, is in ℙ. Our method is based on the standard polynomial time algorithms for solving a system
of polynomial inequalities over the reals in fixed dimension. 相似文献
72.
We develop the theory of information-based complexity from a parallel point of view. For a model of computation with p processors, each being capable of arithmetic operations and decisions, we analyze the complexity of function approximation, numerical integration, and solution of Fredholm integral equations. We obtain tight bounds on the complexity, considered as a function of three variables simultaneously: the number of processors, the required precision, and (in the case of approximation and integral equations) the number of points, in which the approximate solution is to be determined. 相似文献
73.
J. Brenneisen B. Erhardt F. Glatz Th. Kern R. Ott H. Röpke J. Schmälzlin P. Siedle B. H. Wildenthal 《Zeitschrift für Physik A Hadrons and Nuclei》1997,357(2):157-173
Assignments of I, π, T are made to 30 levels in 32S between 7.35 and 11.76 MeV excitation energy, making the spectroscopy of the T= 0 states rather complete up to 10 MeV and that of the T = 1 states up to 12 MeV. A reassessment of existing data in the light of the new results clarifies the spectrum of I π = 1+, T = 1 states up to 15 MeV excitation energy. High-spin states (I = 52 - 7) below 10 MeV excitation energy have been investigated by n t γ angular-correlation measurements with the 29Si(α, nγ) reaction at E α 14.4 MeV. Five g-wave resonances of the 31P(p, γ) reaction, leading to the formation of I π + 4+, 5+ states in 32S, have been identified between 10 and 12 MeV excitation energy. The spectrum of T = 1 states between 10.7 and 12 MeV, has been investigated by measurements of γ-ray angular distributions on resonances of the 31P(p, γ) reaction and by measurements of resonance strengths. Several 32S levels between 7.35 and 8.75 MeV excitation energy were studied as final states in resonance decays. Finally a search was performed for I π = 0+ resonances of the 28Si(α, γ) reaction. 相似文献
74.
J. Gerse J. Kern J. Imre L. Zsinka 《Journal of Radioanalytical and Nuclear Chemistry》1988,128(1):71-79
Three SUBLITECHR technetium generators were milked and generator products were tested for 5 d. Radionuclidic and radiochemical purity, pH of sodium pertechnetate solutions were -emitting impurities and pirogenity were not carried out. We can summarize that generators were running efficiently during our test period and in all cases the pertechnetate produced met the requirements of the European Pharmacopoeia. 相似文献
75.
Stephen R. Langhoff Michael L. Sink R.H. Pritchard C.William Kern 《Journal of Molecular Spectroscopy》1982,96(1):200-218
The spin-orbit coupling constant, A(r), as a function of internuclear distance (r) was computed for the X2Π state of OH, using the microscopic spin-orbit Hamiltonian, extended basis sets, and extensive configuration-interaction wavefunctions. Our best theoretical results are in excellent agreement with the “experimental” A(r) functions deduced from an inversion of the observed Av. Our calculated first-order contributions to Av, v ≤ 10, obtained by vibrationally averaging our theoretical A(r) function using the X2Π RKR potential, differ from experiment by less than 0.12%. A minimum occurs in the Av at v = 7 in agreement with experiment, reflecting the local minimum in A(r) near 2.8 bohr. The second-order contributions to Av are only about 0.1% for v ≤ 10. They arise mainly from the A2Σ+ state for the lower vibrational levels, but each of the A2Σ+, B2Σ+, (1)2Σ?, (1)4Σ?, and (1)2Δ states contributes significantly for higher vibrational levels. Spin-orbit centrifugal distortion parameters, ADv and aDv, are reported for v ≤ 6. The theoretical ADv are also in excellent agreement with experiment when the “experimental” A(r) function has the same slope at the equilibrium separation as that obtained from the effective spin-rotation constants of OH, OD, and OT. 相似文献
76.
A general linear programming model for an order-theoretic analysis of both Edmonds' greedy algorithm for matroids and the
NW-corner rule for transportation problems with Monge costs is introduced. This approach includes the model of Queyranne,
Spieksma and Tardella (1993) as a special case. We solve the problem by optimal greedy algorithms for rooted forests as underlying
structures. Other solvable cases are also discussed. 相似文献
77.
Dr.-Ing. J. Kern 《Heat and Mass Transfer》1976,9(4):267-272
Strictly speaking, the common two-fluid heat exchanger is a special version of a three-fluid exchanger because the environment also participates in the energy exchange. In a number of situations this effect is significant and leads to either reduced or increased area requirements, depending on the purpose of the exchange operation. With certain combinations of the system parameters it is even impossible to achieve an envisaged temperature change. For some typical flow arrangements these combinations are established in an analytic form so that one can rapidly assess the feasibility of a desired process without actually performing the rather tedious design calculations. 相似文献
78.
Ralf Kern 《manuscripta mathematica》1977,20(2):153-175
Multiply periodic real functions are rather pathological; continuous ones have to be constant and, as will be shown, measurable ones must be constant a.e. Beyond this, some other properties of these functions are discussed, and examples are given. Since the set of periods of a real function is a subgroup of (R,+), it is possible to apply algebraic methods to get a better survey. It will be shown that the homogeneous sets defined by Borel are just cosets of these subgroups; this leads to a transfer of theorems about homogeneous sets to results about period sets (and, at the same time, subgroups of (R,+)). 相似文献
79.
Uncollapsed polyethylene pyramids (200–1500 Å) in length are irradiated with the electron beam of a 100-kV transmission electron microscope. Their high stability is remarkable compared to the stability of 1–10 μm crystals collapsed on the substrate, usually taken as a reference. Therefore, the maximum magnifications (300,000–750,000 X) of the microscope can be used and high-resolution images can be obtained. No lattice defects can be detected in the images of PE pyramids. Irradiation with Dc > 800 C/m2 induces the orthorhombic → hexagonal transition, and slight lattice distortions appear in the high-resolution image of the hexagonal phase. For an irradiation dose Dc ≈ 2400 C/M2, the diffraction pattern disappears. Normal C36 orthorhombic and monoclinic paraffins have the same stability as orthorhombic PE and high-resolution patterns are obtained. These exceptional stabilities are discussed in detail. From the diffraction pattern of these uncollapsed pyramids, the fold surfaces of PE pyramids have been indexed as the {111} and paracrystalline distortions in the orthorhombic PE have been measured at low irradiation dose. Along the a and b axes g is ca. 5% and along the chain axis c it is ca. 17%; these values agree with the previous x-ray determinations of PE crystallized from the melt. The large difference between these two distortion factors may be interpreted in terms of packing. 相似文献
80.