全文获取类型
收费全文 | 40994篇 |
免费 | 1753篇 |
国内免费 | 1457篇 |
专业分类
化学 | 29188篇 |
晶体学 | 315篇 |
力学 | 859篇 |
综合类 | 11篇 |
数学 | 5898篇 |
物理学 | 7933篇 |
出版年
2023年 | 286篇 |
2022年 | 387篇 |
2021年 | 689篇 |
2020年 | 675篇 |
2019年 | 680篇 |
2018年 | 787篇 |
2017年 | 770篇 |
2016年 | 1505篇 |
2015年 | 1216篇 |
2014年 | 1297篇 |
2013年 | 2773篇 |
2012年 | 3018篇 |
2011年 | 3256篇 |
2010年 | 1887篇 |
2009年 | 1929篇 |
2008年 | 2532篇 |
2007年 | 2477篇 |
2006年 | 2170篇 |
2005年 | 2051篇 |
2004年 | 2139篇 |
2003年 | 1557篇 |
2002年 | 1436篇 |
2001年 | 888篇 |
2000年 | 749篇 |
1999年 | 587篇 |
1998年 | 474篇 |
1997年 | 379篇 |
1996年 | 467篇 |
1995年 | 338篇 |
1994年 | 311篇 |
1993年 | 365篇 |
1992年 | 307篇 |
1991年 | 214篇 |
1990年 | 210篇 |
1989年 | 170篇 |
1988年 | 170篇 |
1987年 | 159篇 |
1986年 | 153篇 |
1985年 | 251篇 |
1984年 | 219篇 |
1983年 | 171篇 |
1982年 | 158篇 |
1981年 | 157篇 |
1980年 | 127篇 |
1979年 | 123篇 |
1978年 | 103篇 |
1977年 | 110篇 |
1976年 | 95篇 |
1975年 | 97篇 |
1973年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
This paper deals with the unsupervised classification of univariate observations. Given a set of observations originating from a K-component mixture, we focus on the estimation of the component expectations. We propose an algorithm based on the minimization of the “K-product” (KP) criterion we introduced in a previous work. We show that the global minimum of this criterion can be reached by first solving a linear system then calculating the roots of some polynomial of order K. The KP global minimum provides a first raw estimate of the component expectations, then a nearest-neighbour classification enables to refine this estimation. Our method’s relevance is finally illustrated through simulations of various mixtures. When the mixture components do not strongly overlap, the KP algorithm provides better estimates than the Expectation-Maximization algorithm. 相似文献
62.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
63.
Oleg Palumbíny 《Czechoslovak Mathematical Journal》2003,53(2):467-477
The paper deals with oscillation criteria of fourth order linear differential equations with quasi-derivatives. 相似文献
64.
Monika Goikoetxea María J. Barandiaran José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5838-5846
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007 相似文献
65.
66.
Jiří Herec 《Czechoslovak Journal of Physics》2004,54(12):1473-1481
In this paper the quantum-statistical properties of light beams propagating in a directional nonlinear coupler are investigated.
This device is composed of a pair of linearly coupled nonlinear waveguides operating by means of degenerate parametric downconversion.
The possibility of generation of nonclassical states of light in single and compound modes, using the short-length approximation,
is discussed. Influence of linear and nonlinear mismatches for generation of nonclassical light is taken into account.
This work was supported by Project LN00A015, Research Project No. CEZ: J14/98 and the COST project OC P11.003 of the Czech
Ministry of Education. 相似文献
67.
Luc Martinon Stéphane Azoulay E. Peter Kündig 《Journal of organometallic chemistry》2004,689(23):3831-3836
A Pd-catalyzed three-component assembling of highly functionalized 4-benzyl-(and allyl-)pyrrolidines was achieved based on a combination of allyl amines, gem-diactivated alkenes, and unsaturated halides (or triflate). 相似文献
68.
Jocelyn Sabatier Serge Poullain Patrick Latteux Jean Luc Thomas Alain Oustaloup 《Nonlinear dynamics》2004,38(1-2):383-400
Robust speed control of a low damped electromechanical system with backlash is studied, controlled load angular speed being not measured. The proposed control strategy combines a Luenberger observer (load angular speed and load torque disturbance estimations) and a robust CRONE controller. The observer provides estimation of the load angular speed and of the disturbance torque applied on the load. Through the computation of only three independent parameters (as many as a PID controller), the CRONE controller permits to ensure the robust speed control of the load in spite of plant parametric variations and speed observation errors. The proposed control strategy is applied to a four mass experimental test bench. 相似文献
69.
Ccile Nouvel Philippe Dubois Edith Dellacherie Jean‐Luc Six 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2577-2588
The whole controlled synthesis of novel amphiphilic polylactide (PLA)‐grafted dextran copolymers was achieved. The control of the architecture of such biodegradable and potentially biocompatible copolymers has required a three‐step synthesis based on the “grafting from” concept. The first step consisted of the partial silylation of the dextran hydroxyl groups. This protection step was followed by the ring‐opening polymerization of D ,L ‐lactide initiated from the remaining OH functions of the partially silylated polysaccharide. The third step involved the silylether group deprotection under very mild conditions. Based on previous studies, in which the control of the first step was achieved, this study is focused on the last two steps. Experimental conditions were investigated to ensure a controlled polymerization of D ,L ‐lactide, in terms of grafting efficiency, graft length, and transesterification limitation. After polymerization, the final step was studied in order to avoid degradation of both polysaccharide backbone and polyester grafts. The chemical stability of dextran backbone was checked throughout each step of the synthesis. PLA‐grafted dextrans and PLA‐grafted (silylated dextrans) were proved to adopt a core‐shell conformation in various solvents. Furthermore, preliminary experiments on the potential use of these amphiphilic grafted copolymers as liquid/liquid interface stabilizers were performed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2577–2588, 2004 相似文献
70.