全文获取类型
收费全文 | 157524篇 |
免费 | 12355篇 |
国内免费 | 8950篇 |
专业分类
化学 | 78724篇 |
晶体学 | 1554篇 |
力学 | 11721篇 |
综合类 | 658篇 |
数学 | 41284篇 |
物理学 | 44888篇 |
出版年
2024年 | 257篇 |
2023年 | 1631篇 |
2022年 | 2740篇 |
2021年 | 2967篇 |
2020年 | 3022篇 |
2019年 | 2998篇 |
2018年 | 12402篇 |
2017年 | 12030篇 |
2016年 | 9267篇 |
2015年 | 4548篇 |
2014年 | 4732篇 |
2013年 | 6130篇 |
2012年 | 10656篇 |
2011年 | 17184篇 |
2010年 | 10290篇 |
2009年 | 10594篇 |
2008年 | 11365篇 |
2007年 | 12932篇 |
2006年 | 4479篇 |
2005年 | 4929篇 |
2004年 | 4430篇 |
2003年 | 4182篇 |
2002年 | 3134篇 |
2001年 | 2113篇 |
2000年 | 1998篇 |
1999年 | 2018篇 |
1998年 | 1760篇 |
1997年 | 1512篇 |
1996年 | 1610篇 |
1995年 | 1335篇 |
1994年 | 1210篇 |
1993年 | 1105篇 |
1992年 | 914篇 |
1991年 | 818篇 |
1990年 | 681篇 |
1989年 | 612篇 |
1988年 | 491篇 |
1987年 | 444篇 |
1986年 | 388篇 |
1985年 | 392篇 |
1984年 | 268篇 |
1983年 | 225篇 |
1982年 | 206篇 |
1981年 | 159篇 |
1980年 | 131篇 |
1979年 | 100篇 |
1978年 | 96篇 |
1977年 | 75篇 |
1975年 | 75篇 |
1973年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Using the multipoles method, we formulate the problems of radiation (both heave and sway) of water waves by a submerged sphere
in deep as well as in uniform finite depth water with an ice-cover, with the ice-cover being modelled as an elastic plate
of very small thickness. In each case this leads to an infinite system of linear equations which are solved numerically by
standard techniques. The added-mass and damping coefficients for a heaving and swaying sphere are obtained and depicted graphically
against the wave number for various values of the radius of the submerged sphere and flexural rigidity of the ice-cover to
show the effect of the presence of ice-cover on these quantities. When the flexural rigidity is taken to be zero, the numerical
results for the added-mass and damping coefficient for water with a free surface are recovered. 相似文献
82.
Alexander Linkov Liliana Rybarska-Rusinek 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(10):821-831
The paper presents a general method to find asymptotics for a (multi-)wedge system containing a thin wedge. It employs separation
of the symmetric and anti-symmetric parts of the boundary displacements and tractions of the wedge. The method is applicable
when the angle of the thin wedge turns to zero. A physical interpretation of the derived equations is obtained by using power
expansions of non-polynomial functions, which appear after the Mellin transform. We establish that the first term in the expansion
of the symmetric part corresponds to shear, while the first term of the anti-symmetric part describes deflection of the wedge
axis. Numerical experiments, performed by using a code developed on the basis of the theory, show that using only the first
terms of the expansions insignificantly influence accuracy: the approximate results coincide with the exact values of roots
to the third significant digit even for the wedge angle of 30°. 相似文献
83.
A novel algorithm, alternatively minimizing coupled vector (COV) resolution error and PARAFAC error algorithm, is proposed in this paper. This algorithm can overcome the problem of slow convergence and is insensitive to the estimation of component number, such problems are unavoidable while using the traditional parallel factors analysis (PARAFAC) algorithm. In other words, this algorithm is capable of improving the computing speed and providing accurate resolutions provided that the number of factors used in the computation is no less than that of the actual underlying ones. The characteristic performances were demonstrated with a novel fluorescence data array. 相似文献
84.
Yirang Yuan 《Numerical Methods for Partial Differential Equations》2003,19(5):665-681
For the coupled system of multilayer fluid dynamics in porous media, the modified characteristic finite difference fractional steps method applicable to parallel arithmetic is put forward and two‐dimensional and three‐dimensional schemes are used to form a complete set. Some techniques, such as calculus of variations, energy method, piecewise biquadratic interpolation, multiplicative commutation rule of difference operators, decomposition of high order difference operators and prior estimates are adopted. Optimal order estimates in L2 norm are derived to determine the error in the approximate solution. This method has already been applied to the numerical simulation of multilayer fluid dynamics in porous media. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 665–681, 2003. 相似文献
85.
Chen Yongnian 《模糊系统与数学》1995,(1)
ANTIFUZZYVECTORSPACES(Ⅱ)ChenYongnian(DepartmentofMathematics,XinjiangNormalUniversity,830054,Xinjiang,P.R.China)ANTIFUZZYVECT... 相似文献
86.
Two homologous series of mesogenic materials which incorporate a 1,4-tetrafluorophenylene moiety and a terminal cyano- or nitro-substituent have been synthesized by using palladiumcatalysed coupling procedures. The compounds exhibit nematic and/or smectic A phases. 相似文献
87.
88.
89.
Qian-huo Chen 《Journal of Non》2007,353(4):374-378
A sort of decorated nano ZnO organic sols have been successively prepared by pulsed laser ablation at the interface of ZnO target and a flowing liquid containing polymers. It is found that the decorated nano ZnO ethanol sols, the decorated nano ZnO-PS (polystyrene) cyclohexane sols and the decorated nano ZnO-PMMA (polymethyl methacrylate) ethyl butyrate sols all have strong fluorescence emission at 329 nm and 411 nm, 308 nm and 317 nm, and at 330 nm and 400 nm, respectively. The results show the decorating for nano ZnO will intensely affect their luminescence, and the wavelength and intensity of luminescence can be adjusted or controlled by the different decoration. 相似文献
90.
Kan‐Yi Pu Yi Chen Xiao‐Ying Qi Chun‐Yang Qin Qing‐Quan Chen Hong‐Yu Wang Yun Deng Qu‐Li Fan Yan‐Qin Huang Shu‐Juan Liu Wei Wei Bo Peng Wei Huang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3776-3787
In this contribution, we demonstrate a new effective methodology for constructing highly efficient and durable poly(p‐phenyleneethynylene) (PPE) containing emissive material with nonaggregating and hole‐facilitating properties through the introduction of hole‐transporting blocks into the PPE system as the grafting coils as well as building the energy donor–acceptor architecture between the grafting coils and the PPE backbone. Poly(2‐(carbazol‐9‐yl)ethyl methacrylate) (PCzEMA), herein, is chosen as the hole‐transporting blocks, and incorporated into the PPE system as the grafting coils via atom transfer radical polymerization. The chemical structure of the resultant copolymer, PPE‐g‐PCzEMA, was characterized by NMR and gel permeation chromatography, showing that the desirable copolymer was obtained with the narrow polydispersity. The increased thermal stability of PPE‐g‐PCzEMA was confirmed by thermogravimetric analysis and differential scanning calorimetry along with its macroinitiator. The optoelectronic properties of this copolymer were studied in detail by ultraviolet‐visible absorption, photoluminescence emission and excitation spectra, and cyclic voltammogram (CV). The results indicate that PPE‐g‐PCzEMA exhibits the solid‐state luminescent property dominated by individual lumophores, and also the energy transfer process from the PCzEMA blocks to the PPE backbone with a relatively higher energy transfer efficiency in the solid‐state compared to that of the solution state. Additionally, the hole‐injection property is greatly facilitated due to the presence of PCzEMA, as confirmed by CV profiles. All these data indicate that PPE‐g‐PCzEMA is a good candidate for use in optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3776–3787, 2007 相似文献