全文获取类型
收费全文 | 439篇 |
免费 | 31篇 |
国内免费 | 19篇 |
专业分类
化学 | 88篇 |
力学 | 38篇 |
综合类 | 10篇 |
数学 | 167篇 |
物理学 | 186篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 30篇 |
2012年 | 25篇 |
2011年 | 29篇 |
2010年 | 30篇 |
2009年 | 43篇 |
2008年 | 31篇 |
2007年 | 29篇 |
2006年 | 27篇 |
2005年 | 18篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 14篇 |
1998年 | 13篇 |
1997年 | 16篇 |
1996年 | 1篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有489条查询结果,搜索用时 312 毫秒
101.
In this paper, we study a rational function which plays an important role in several problems of interest (eigenvalue problems,
linear control theory, ... ). Our main interest is to determine zero-free regions. We also derive upper and lower bounds for
this function.
Communicated by T.L. Freeman 相似文献
102.
103.
拟合及预测饱和增长趋势的广义逻辑(Logistic)曲线模型 总被引:6,自引:0,他引:6
本文讨论了逻辑(Logistic)曲线与龚柏兹(Gompertz)曲线模型结构上的缺点。针对这些缺点,文中提出利用广义逻辑曲线模型拟合及预测饱和增长趋势,解释了该模型包含的实际经济意义,并给出了相应的参数估计算法,以实例说明了该模型具有高于逻辑曲线和龚柏兹曲线的预测精度。 相似文献
104.
L.M. Ruan H. Qi L.H. Liu H.P. Tan 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,86(4):343-352
In this paper the radiative transfer in one-dimensional and two-dimensional cylindrical medium is simulated by the Monte-Carlo (M-C) method. Our results agree with the previous ones very well. It indicates that our cylindrical M-C model is creditable. In this paper, the partition allocation method of radiative heat transfer in participating cylindrical media is presented, in which every sub-domain is isolated by imaginary black wall at certain equivalent temperature and overlaps each other. The stitched results of all sub-domains can predict the results of a whole zone accurately. The partitioned treatment by overlap regions can achieve reasonable result, save memory efficiently, and compute parallel. 相似文献
105.
106.
Paul G. Mezey 《Theoretical chemistry accounts》1981,58(4):309-330
The space of internal coordinates of a molecular system is partitioned into catchment regions of various critical points of the energy hypersurface. The partitioning is based on an ordering of steepest descent paths into equivalence classes. The properties of these catchment regions and their boundaries are analyzed and the concepts of chemical structure, reaction path and reaction mechanism are discussed within the framework of the Born-Oppenheimer and energy hypersurface approximations. Relations between catchment regions and the chemically important reactive domains of energy hypersurfaces, as well as models for branching of reaction mechanisms, caused by instability domainsD
, 1, are investigated. 相似文献
107.
Sonal Singhal 《Journal of solid state chemistry》2007,180(1):296-300
Cation distribution have been investigated using X-ray diffraction, magnetic and Mössbauer spectral studies in chromium-substituted nickel ferrites prepared by aerosol route. Cation distribution indicates that the chromium atom occupy octahedral site upto x=0.8, and then also enters into tetrahedral site. The saturation magnetization decreases linearly with the increase of chromium concentration due to the diamagnetic nature of the Cr3+. However, interesting behaviour is observed in the coercivity. Initially it increases slowly with the chromium concentration but when x>0.8 a very large increase has been observed. This was attributed to the specific cation distribution of Cr3+ which results an unquenched orbital angular momentum and a large anisotropy. Room temperature Mössbauer spectra of as obtained samples exhibited a broad doublet resolved into two doublets corresponding to the surface and internal region atoms. The samples annealed at 1200 °C show broad sextets, which were fitted with different sextets, indicating different local environment of both tetrahedral and octahedral coordinated iron cation. 相似文献
108.
We study the motion of isentropic gas in nozzles. This is a major subject in fluid dynamics. In fact, the nozzle is utilized to increase the thrust of rocket engines. Moreover, the nozzle flow is closely related to astrophysics. These phenomena are governed by the compressible Euler equations, which are one of crucial equations in inhomogeneous conservation laws.In this paper, we consider its unsteady flow and devote to proving the global existence and stability of solutions to the Cauchy problem for the general nozzle. The theorem has been proved in Tsuge (2013). However, this result is limited to small data. Our aim in the present paper is to remove this restriction, that is, we consider large data. Although the subject is important in Mathematics, Physics and engineering, it remained open for a long time. The problem seems to rely on a bounded estimate of approximate solutions, because we have only method to investigate the behavior with respect to the time variable. To solve this, we first introduce a generalized invariant region. Compared with the existing ones, its upper and lower bounds are extended constants to functions of the space variable. However, we cannot apply the new invariant region to the traditional difference method. Therefore, we invent the modified Godunov scheme. The approximate solutions consist of some functions corresponding to the upper and lower bounds of the invariant regions. These methods enable us to investigate the behavior of approximate solutions with respect to the space variable. The ideas are also applicable to other nonlinear problems involving similar difficulties. 相似文献
109.
The transition of a separated shear layer over a flat plate, in the presence of periodic wakes and elevated free-stream turbulence (FST), is numerically investigated using Large Eddy Simulation (LES). The upper wall of the test section is inviscid and specifically contoured to impose a streamwise pressure distribution over the flat plate to simulate the suction surface of a low-pressure turbine (LPT) blade. Two different distributions representative of a ‘high-lift’ and an ‘ultra high-lift’ turbine blade are examined. Results obtained from the current LES compare favourably with the extensive experimental data previously obtained for these configurations. The LES results are then used to further investigate the flow physics involved in the transition process.In line with experimental experience, the benefit of wakes and FST obtained by suppressing the separation bubble, is more pronounced in ‘ultra high-lift’ design when compared to the ‘high-lift’ design. Stronger ‘Klebanoff streaks’ are formed in the presence of wakes when compared to the streaks due to FST alone. These streaks promoted much early transition. The weak Klebanoff streaks due to FST continued to trigger transition in between the wake passing cycles.The experimental inference regarding the origin of Klebanoff streaks at the leading edge has been confirmed by the current simulations. While the wake convects at local free-stream velocity, its impression in the boundary layer in the form of streaks convects much slowly. The ‘part-span’ Kelvin–Helmholtz structures, which were observed in the experiments when the wake passes over the separation bubble, are also captured. The non-phase averaged space-time plots manifest that reattachment is a localized process across the span unlike the impression of global reattachment portrayed by phase averaging. 相似文献
110.
《Discrete Mathematics》2022,345(8):112921
For a graph F, we say that another graph G is F-saturated, if G is F-free and adding any edge to G would create a copy of F. We study for a given graph F and integer n whether there exists a regular n-vertex F-saturated graph, and if it does, what is the smallest number of edges of such a graph. We mainly focus on the case when F is a complete graph and prove for example that there exists a -saturated regular graph on n vertices for every large enough n.We also study two relaxed versions of the problem: when we only require that no regular F-free supergraph of G should exist or when we drop the F-free condition and only require that any newly added edge should create a new copy of F. 相似文献