首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   558篇
  免费   6篇
  国内免费   1篇
化学   328篇
晶体学   2篇
力学   7篇
数学   102篇
物理学   126篇
  2022年   6篇
  2020年   9篇
  2019年   6篇
  2017年   7篇
  2016年   8篇
  2015年   8篇
  2013年   23篇
  2012年   11篇
  2011年   9篇
  2010年   13篇
  2009年   10篇
  2008年   13篇
  2007年   20篇
  2006年   16篇
  2005年   11篇
  2004年   16篇
  2003年   12篇
  2002年   6篇
  2001年   6篇
  2000年   7篇
  1999年   7篇
  1996年   6篇
  1995年   7篇
  1994年   14篇
  1993年   11篇
  1992年   8篇
  1991年   7篇
  1990年   6篇
  1989年   11篇
  1987年   7篇
  1986年   7篇
  1984年   6篇
  1983年   5篇
  1982年   13篇
  1981年   7篇
  1980年   6篇
  1979年   11篇
  1978年   7篇
  1977年   8篇
  1976年   5篇
  1975年   7篇
  1974年   7篇
  1973年   6篇
  1963年   5篇
  1962年   5篇
  1958年   5篇
  1895年   5篇
  1890年   6篇
  1886年   10篇
  1882年   9篇
排序方式: 共有565条查询结果,搜索用时 0 毫秒
41.
Wetting of structured or imprinted surfaces which leads to a variety of different morphologies such as droplets, channels or thin films is studied theoretically using the general framework of surface or interface thermodynamics. The first variation of the interfacial free energy leads to the well-known Laplace equation and a generalized Young equation which involves spatially dependent interfacial tensions. Furthermore, we perform the second variation of the free energy for arbitrary surface patterns and arbitrary shape of the wetting morphology in order to derive a new and general stability criterion. The latter criterion is then applied to cylindrical segments or channels on homogeneous and structured surfaces. Received 4 August 1999  相似文献   
42.
The copolyester containing 40 mol % ethylene terephthalate (PET) and 60 mol % p-hydroxybenzoate (HB) units has been reported by several investigators to be biphasic in the solid and the liquid states. The reported thermal transitions in the two phases, however, are in part contradictory, perhaps partly due to different polymerization conditions. The present work is a study of the transitions in each of the two phases of this copolyester by polarized light microscopy and by light transmission measurements. By light transmission measurements, the two phases were found to have two different glass transition temperatures for the onset of segmental motion, consistent with two assignable temperatures (T.). Cold crystallization and melting in each of the two different phases was also detected. The results help clarify the nature of transitions and agree with the results of dynamic mechanical analysis on the same thermotropic liquid crystalline copolyester.  相似文献   
43.
The performance of the pulsed-laser atom probe can be limited by both instrument and specimen factors. The experiments described in this article were designed to identify these factors so as to provide direction for further instrument and specimen development. Good agreement between voltage-pulsed and laser-pulsed data is found when the effective pulse fraction is less than 0.2 for pulsed-laser mode. Under the conditions reported in this article, the thermal tails of the peaks in the mass spectra did not show any significant change when produced with either a 10-ps or a 120-fs pulsed-laser source. Mass resolving power generally improves as the laser spot size and laser wavelength are decreased and as the specimen tip radius, specimen taper angle, and thermal diffusivity of the specimen material are increased. However, it is shown that two of the materials used in this study, aluminum and stainless steel, depend on these factors differently. A one-dimensional heat flow model is explored to explain these differences. The model correctly predicts the behavior of the aluminum samples, but breaks down for the stainless steel samples when the tip radius is large. A more accurate three-dimensional model is needed to overcome these discrepancies.  相似文献   
44.
Semiflexible thermotropic aromatic polyesters with lateral groups were aligned magnetically and mechanically in monodomains after separation into high-molecular-weight (polymer) and low-molecular-weight (oligomer) fractions. Based on the x-ray intensity distributions recorded for a series of seven different substituents in the arylsulfonyl substituted group, a novel smectic structure was determined for H, F, Cl, OCH3, and CH3 in the para position while a normal nematic alignment prevailed when it contained Br or NO2.  相似文献   
45.
Thin films of PS-b-PEO block copolymers were utilized as structured reservoirs for localized nanoscale precipitation reactions. By consecutively immersing the film into solutions of thioacetamide and cadmium chloride, we were able to obtain a monolayer of cadmium sulfide nanostructures on top of the block copolymer film. AFM and grazing incidence small angle X-ray scattering revealed spherical nanostructures (d = 15 nm) corresponding to the dimensions given by the block copolymer film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1569–1573, 2010  相似文献   
46.
Let be graphs. The multicolor Ramsey number is the minimum integer r such that in every edge‐coloring of by k colors, there is a monochromatic copy of in color i for some . In this paper, we investigate the multicolor Ramsey number , determining the asymptotic behavior up to a polylogarithmic factor for almost all ranges of t and m. Several different constructions are used for the lower bounds, including the random graph and explicit graphs built from finite fields. A technique of Alon and Rödl using the probabilistic method and spectral arguments is employed to supply tight lower bounds. A sample result is for any t and m, where c1 and c2 are absolute constants.  相似文献   
47.
The cationic polymerization of p-chloro-α-methylstyrene was investigated for the effect of initiator and solvent on polymer tacticity, molecular weight, and molecular weight distribution. The products were generally crystalline polymers of 80–90% syndiotactic content with fairly high molecular weights and broad molecular weight distributions. Tacticities and molecular weight distributions followed similar patterns suggesting that the effect of reaction conditions on ionpair end-group structures was the dominant factor.  相似文献   
48.
We provide an ergodic theorem for certain Banach-space valued functions on structures over , which allow for existence of frequencies of finite patterns. As an application we obtain existence of the integrated density of states for associated discrete finite-range operators in the sense of convergence of the distributions with respect to the supremum norm. These results apply to various examples including periodic operators, percolation models and nearest-neighbour hopping on the set of visible points. Our method gives explicit bounds on the speed of convergence in terms of the speed of convergence of the underlying frequencies. It uses neither von Neumann algebras nor a framework of random operators on a probability space.   相似文献   
49.
The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei 9Be or 10Be, respectively. Molecular rotational bands up to high excitation energies are observed with 9Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with 10Be as the core. For 11Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2+, 5/2?, and 3/2?, respectively. Furthermore, we have studied particle-hole states of 16C using the 13C(12C, 9C)16C reaction and found 14 previously unknown states. Using the 12C(12C, 9C)15C reaction, five new states were observed for 15C.  相似文献   
50.
We carry out a careful study of operator algebras associated with Delone dynamical systems. A von Neumann algebra is defined using noncommutative integration theory. Features of these algebras and the operators they contain are discussed. We restrict our attention to a certain C *-subalgebra to discuss a Shubin trace formula.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号