全文获取类型
收费全文 | 146415篇 |
免费 | 14635篇 |
国内免费 | 9500篇 |
专业分类
化学 | 49339篇 |
晶体学 | 2290篇 |
力学 | 11425篇 |
综合类 | 1705篇 |
数学 | 40023篇 |
物理学 | 65768篇 |
出版年
2023年 | 719篇 |
2022年 | 1654篇 |
2021年 | 2676篇 |
2020年 | 2435篇 |
2019年 | 2568篇 |
2018年 | 2327篇 |
2017年 | 2550篇 |
2016年 | 2808篇 |
2015年 | 2393篇 |
2014年 | 4157篇 |
2013年 | 6625篇 |
2012年 | 4569篇 |
2011年 | 5617篇 |
2010年 | 5814篇 |
2009年 | 10852篇 |
2008年 | 11806篇 |
2007年 | 10411篇 |
2006年 | 9051篇 |
2005年 | 6796篇 |
2004年 | 6375篇 |
2003年 | 6297篇 |
2002年 | 9156篇 |
2001年 | 5647篇 |
2000年 | 5134篇 |
1999年 | 4778篇 |
1998年 | 4054篇 |
1997年 | 3050篇 |
1996年 | 2755篇 |
1995年 | 3142篇 |
1994年 | 2965篇 |
1993年 | 2461篇 |
1992年 | 1922篇 |
1991年 | 1412篇 |
1990年 | 1202篇 |
1989年 | 1020篇 |
1988年 | 1006篇 |
1987年 | 757篇 |
1986年 | 536篇 |
1985年 | 1420篇 |
1984年 | 1013篇 |
1983年 | 719篇 |
1982年 | 1018篇 |
1981年 | 1147篇 |
1980年 | 995篇 |
1979年 | 903篇 |
1978年 | 812篇 |
1977年 | 691篇 |
1976年 | 653篇 |
1974年 | 388篇 |
1973年 | 540篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
71.
XU Jun YAN Ai-Zhen XU Qin-Hua Department of Chemistry Nanjing University Nanjing Jiangsu China 《中国化学》1995,(2)
The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework. 相似文献
72.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献
73.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well. 相似文献
74.
本文研究作为双层桥模型的梁方程耦合系统,利用Leray-Schauder不动点定理,得到了一个关于这种系统的解的存在性定理,它类似于McKenna和Walter文2中关于吊桥方程的一个定理。 相似文献
75.
76.
V. Dzhunushaliev 《Foundations of Physics》2002,32(7):1069-1090
An approximate model of a spacetime foam is presented. It is supposed that in the spacetime foam each quantum handle is like to an electric dipole and therefore the spacetime foam is similar to a dielectric. If we neglect of linear sizes of the quantum handle then it can be described with an operator containing a Grassman number and either a scalar or a spinor field. For both fields the Lagrangian is presented. For the scalar field it is the dilaton gravity + electrodynamics and the dilaton field is a dielectric permeability. The spherically symmetric solution in this case give us the screening of a bare electric charge surrounded by a polarized spacetime foam and the energy of the electric field becomes finite one. In the case of the spinor field the spherically symmetric solution give us a ball of the polarized spacetime foam filled with the confined electric field. It is shown that the full energy of the electric field in the ball can be very big. 相似文献
77.
78.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献
79.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
80.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献