全文获取类型
收费全文 | 217425篇 |
免费 | 2560篇 |
国内免费 | 632篇 |
专业分类
化学 | 111646篇 |
晶体学 | 3539篇 |
力学 | 9733篇 |
综合类 | 6篇 |
数学 | 23553篇 |
物理学 | 72140篇 |
出版年
2021年 | 2057篇 |
2020年 | 2234篇 |
2019年 | 2495篇 |
2018年 | 3171篇 |
2017年 | 3045篇 |
2016年 | 4399篇 |
2015年 | 2749篇 |
2014年 | 4327篇 |
2013年 | 10258篇 |
2012年 | 8266篇 |
2011年 | 9799篇 |
2010年 | 6743篇 |
2009年 | 6447篇 |
2008年 | 8567篇 |
2007年 | 8750篇 |
2006年 | 8234篇 |
2005年 | 7344篇 |
2004年 | 6766篇 |
2003年 | 5931篇 |
2002年 | 5714篇 |
2001年 | 6560篇 |
2000年 | 5045篇 |
1999年 | 3878篇 |
1998年 | 3099篇 |
1997年 | 3135篇 |
1996年 | 2872篇 |
1995年 | 2681篇 |
1994年 | 2527篇 |
1993年 | 2419篇 |
1992年 | 2782篇 |
1991年 | 2738篇 |
1990年 | 2663篇 |
1989年 | 2459篇 |
1988年 | 2493篇 |
1987年 | 2486篇 |
1986年 | 2318篇 |
1985年 | 3017篇 |
1984年 | 3273篇 |
1983年 | 2683篇 |
1982年 | 2844篇 |
1981年 | 2806篇 |
1980年 | 2679篇 |
1979年 | 2785篇 |
1978年 | 2867篇 |
1977年 | 2866篇 |
1976年 | 2922篇 |
1975年 | 2699篇 |
1974年 | 2661篇 |
1973年 | 2799篇 |
1972年 | 1772篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
S. Park T. U. Kampen T. Kachel P. Bressler W. Braun D. R. T. Zahn 《Applied Surface Science》2002,190(1-4):376-381
The interaction of Ag and In with a thin film of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was studied by near-edge X-ray absorption fine structure (NEXAFS). Upon Ag deposition on a PTCDA film of 20 nm thickness the relative intensities and lineshapes, as well as the angular dependence of the spectra remains unchanged, illustrating the formation of a chemically unreactive Ag/PTCDA interface. On the other hand, the adsorption of 0.3 nm In strongly decreases the intensity of the π* resonances in C and O K-edge NEXAFS spectra. This is attributed to a strong charge transfer between In and PTCDA, leading to a redistribution of the charge in the molecule. However, the absence of a strong shift or new features and negligible dependence of peak intensities corresponding to π* resonances on the In thickness indicate that the interaction between In and PTCDA is not accompanied by a covalent bond formation. 相似文献
982.
M. Le Vassor D’yerville D. Monge D. Cassagne J. P. Albert 《Optical and Quantum Electronics》2002,34(5-6):445-454
We present here a tight-binding-like modelling of two-dimensional (2D) photonic crystals (PCs). Adopted from solid-state physics,
the concept of generalized Wannier functions is used to construct a localized state basis that allows a parameter-free ab
initio study of defects in PCs. We demonstrate here for a 2D triangular lattice of dielectric rods in air, the existence of
this localized basis and the possibility to study large scale complex dielectric structures deviating from periodicity. Specific
numerical simulations on a split waveguide embedded in this triangular lattice are performed, and they demonstrate the superiority
of this method over plane wave based techniques. 相似文献
983.
984.
985.
986.
Mukund G. Kulkarni Attrimuni P. Dhondge Dnyaneshwar D. Gaikwad Ajit S. Borhade Sanjay W. Chavhan 《Tetrahedron letters》2006,47(6):1003-1005
A two-step synthetic sequence for an efficient synthesis of 3-allylindoles is described. 相似文献
987.
We consider a class of Lagrangian theories where part of the coordinates does not have any time derivatives in the Lagrange function (we call such coordinates degenerate). We advocate that it is reasonable to reconsider the conventional definition of singularity based on the usual Hessian and, moreover, to simplify the conventional hamiltonization procedure. In particular, in such a procedure, it is not necessary to complete the degenerate coordinates with the corresponding conjugate momenta. 相似文献
988.
Results are presented of an analytic construction and investigation of adaptive data classification algorithms for intermittent turbulence. A decision making rule is presented, relationships are derived to estimate the classification accuracy. A three-level procedure is described for processing the intermittency, including the calculation algorithms for the initial point, self-teaching, and optimal classification. It is shown that the method proposed permits realization of total automation of intermittency data processing.Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 18, pp. 119–123, 1987. 相似文献
989.
Auditory filter characteristics and consonant recognition for hearing-impaired listeners 总被引:1,自引:0,他引:1
To examine the association between frequency resolution and speech recognition, auditory filter parameters and stop-consonant recognition were determined for 9 normal-hearing and 24 hearing-impaired subjects. In an earlier investigation, the relationship between stop-consonant recognition and the articulation index (AI) had been established on normal-hearing listeners. Based on AI predictions, speech-presentation levels for each subject in this experiment were selected to obtain a wide range of recognition scores. This strategy provides a method of interpreting speech-recognition performance among listeners who vary in magnitude and configuration of hearing loss by assuming that conditions which yield equal audible spectra will result in equivalent performance. It was reasoned that an association between frequency resolution and consonant recognition may be more appropriately estimated if hearing-impaired listeners' performance was measured under conditions that assured equivalent audibility of the speech stimuli. Derived auditory filter parameters indicated that filter widths and dynamic ranges were strongly associated with threshold. Stop-consonant recognition scores for most hearing-impaired listeners were not significantly poorer than predicted by the AI model. Furthermore, differences between observed recognition scores and those predicted by the AI were not associated with auditory filter characteristics, suggesting that frequency resolution and speech recognition may appear to be associated primarily because both are degraded by threshold elevation. 相似文献
990.
S. D. Borkute U. H. Nagvekar S. A. Balakrishnan R. S. Mani 《Journal of Radioanalytical and Nuclear Chemistry》1987,119(4):297-302
A novel method to eliminate T3 from gross sera/plasma based on prior treatment with 8-anilino-1-naphthalene sulphonic acid has been standardized. This method is rapid with a minimum loss of protein and uses only small quantities of charcoal. The treated sera have been tested for acceptance in the RIA system for routine assays. 相似文献