全文获取类型
收费全文 | 4611篇 |
免费 | 262篇 |
国内免费 | 265篇 |
专业分类
化学 | 2311篇 |
晶体学 | 26篇 |
力学 | 219篇 |
综合类 | 33篇 |
数学 | 1398篇 |
物理学 | 1151篇 |
出版年
2024年 | 15篇 |
2023年 | 179篇 |
2022年 | 51篇 |
2021年 | 87篇 |
2020年 | 98篇 |
2019年 | 160篇 |
2018年 | 100篇 |
2017年 | 123篇 |
2016年 | 100篇 |
2015年 | 101篇 |
2014年 | 174篇 |
2013年 | 297篇 |
2012年 | 177篇 |
2011年 | 223篇 |
2010年 | 167篇 |
2009年 | 250篇 |
2008年 | 281篇 |
2007年 | 297篇 |
2006年 | 279篇 |
2005年 | 201篇 |
2004年 | 179篇 |
2003年 | 163篇 |
2002年 | 142篇 |
2001年 | 145篇 |
2000年 | 123篇 |
1999年 | 121篇 |
1998年 | 121篇 |
1997年 | 83篇 |
1996年 | 64篇 |
1995年 | 56篇 |
1994年 | 53篇 |
1993年 | 47篇 |
1992年 | 43篇 |
1991年 | 38篇 |
1990年 | 21篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 31篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 30篇 |
1980年 | 30篇 |
1979年 | 29篇 |
1978年 | 13篇 |
1977年 | 19篇 |
1975年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有5138条查询结果,搜索用时 15 毫秒
921.
Summary The purpose of this work is the numerical simulation of the ISO-LWS spectrometer output with a computer code aiming at obtaining
data similar as far as possible to those to be gained during the mission. With such data the processing and analysis programmes
will be tested in order to assess the instrument capabilities and limits. As an example we have simulated the realization
of a spectral and spatial map of the sky region with the outflow of L1551-IRS5.
Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992. 相似文献
922.
923.
We consider random iterated function systems which consist of strictly increasing and (not necessarily strictly) convex functions
on a compact interval or on a half line. We assume that the system is contracting on average in a sense which is wide enough
to permit the existence of a common fixpoint at which some functions of the system are expanding and perhaps none of them
are contracting (see Fig. 1). We prove that the Hausdorff dimension of any of the possibly uncountably many invariant measures
is smaller than or equal to the accumulated entropy divided by the Liapunov exponent.
Mathematics Subject Classification. Primary 42A85 Secondary 11R06; 26A46; 26A30; 26A78; 28A80 相似文献
924.
L. G. Samsonova N. S. Eremina V. A. Svetlichnyi T. N. Kopylova G. V. Maier N. S. Kobotaeva E. E. Sirotkina 《Journal of Applied Spectroscopy》2006,73(2):194-199
We have studied the spectral and lasing properties of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM)
in polyepoxypropylcarbazole (PEPK), polybutylcarbazole (PBK), and polyvinylcarbazole (PVK) films when excited by emission
from a XeCl laser (λ = 308 nm) and the second harmonic of a YAGNd laser (λ = 532 nm). Stimulated emission was excited without
an external cavity in the traveling wave mode in films of thickness 0.5–0.8 μm, obtained by the centrifuging method.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 177–181, March–April, 2006. 相似文献
925.
This paper investigates finite-stretching corrections
to the classical Milner-Witten-Cates theory for semi-dilute
polymer brushes in a good solvent. The dominant correction to the
free energy originates from an entropic repulsion caused by the
impenetrability of the grafting surface, which produces a
depletion of segments extending a distance μ∝L-1
from the substrate, where L is the classical brush height. The
next most important correction is associated with the
translational entropy of the chain ends, which creates the
well-known tail where a small population of chains extend beyond
the classical brush height by a distance ξ∝L-1/3.
The validity of these corrections is confirmed by quantitative
comparison with numerical self-consistent field theory. 相似文献
926.
在常重力下模拟微重力燃烧对载人航天器的火灾安全具有重要意义.窄通道就是这样一种可以有效限制自然对流的模拟设施.但是,不同重力下火焰传播的相似性仍然是有待研究的问题.本文用实验和数值模拟的方法,比较了不同重力下有限空间内热薄材料表面的逆风传播火焰.不同重力下火焰形状和火焰传播速度的比较表明,1cm高的水平窄通道可以有效地限制自然对流,在常重力下用这种通道能够模拟微重力下相同几何尺寸的通道中的火焰传播.因此,在地面上首先利用水平窄通道,模拟相同环境中的微重力火焰传播,然后考虑通道尺寸变化对火焰传播的影响,有可能成为地面模拟其他尺寸的空间中的微重力燃烧的方法. 相似文献
927.
L. Ward 《Optics & Laser Technology》2002,34(7):3280
Contour graphs of 2 vs 4 for different film thicknesses and a range of angles of incidence have been plotted for the ellipsometric functions Δ and Ψ in both the reflection and transmission modes. In the case of reflection ellipsometry, when the plots for ΔR and ΨR are superimposed, the two sets of contours cross nearly at right angles over a large part of the field, this being indicative of the high accuracy obtainable in using this technique to determine 4 and 2 and hence the optical constants, n and k, for the film material. The reflection ellipsometric technique is accurate over angles of incidence between 30° and 75° and for a range of film thicknesses between λ/30 and 5λ. Transmission ellipsometry is less useful, due to anomalies in both Xs and Xp where sudden phase changes of ±π occur in regions of interest. There is also the possibility of multiple solutions, although the use of a multiangle technique would enable the “correct” values to be more easily determined. 相似文献
928.
《Discrete Mathematics》2023,346(6):113349
The problem of reconstructing the characteristic polynomial of a graph of order at least 3 from the collection of characteristic polynomials of its vertex-deleted subgraphs was posed by Cvetkovi? in 1973 as a spectral counter part to the well-known Ulam's reconstruction conjecture. Over the last 50 years, this problem has received notable attention, many positive results have been obtained, but in the general case the problem is still unresolved. In particular, no counter example is found in literature. In this expository paper we survey classical and some more recent results concerning the polynomial reconstruction problem, discuss some related problems, variations and generalizations. 相似文献
929.
In two-phase materials, each phase having a non-local response in time, it has been found that for some driving fields the response somehow untangles at specific times, and allows one to directly infer useful information about the geometry of the material, such as the volume fractions of the phases. Motivated by this, and to obtain an algorithm for designing appropriate driving fields, we find approximate, measure independent, linear relations between the values that Markov functions take at a given set of possibly complex points, not belonging to the interval [-1,1] where the measure is supported. The problem is reduced to simply one of polynomial approximation of a given function on the interval [-1,1] and, to simplify the analysis, Chebyshev approximation is used. This allows one to obtain explicit estimates of the error of the approximation, in terms of the number of points and the minimum distance of the points to the interval [-1,1]. Assuming this minimum distance is bounded below by a number greater than 1/2, the error converges exponentially to zero as the number of points is increased. Approximate linear relations are also obtained that incorporate a set of moments of the measure. In the context of the motivating problem, the analysis also yields bounds on the response at any particular time for any driving field, and allows one to estimate the response at a given frequency using an appropriately designed driving field that effectively is turned on only for a fixed interval of time. The approximation extends directly to Markov-type functions with a positive semidefinite operator valued measure, and this has applications to determining the shape of an inclusion in a body from boundary flux measurements at a specific time, when the time-dependent boundary potentials are suitably tailored. © 2022 Wiley Periodicals, Inc. 相似文献
930.