全文获取类型
收费全文 | 29554篇 |
免费 | 4840篇 |
国内免费 | 3256篇 |
专业分类
化学 | 21278篇 |
晶体学 | 362篇 |
力学 | 1721篇 |
综合类 | 295篇 |
数学 | 3220篇 |
物理学 | 10774篇 |
出版年
2024年 | 100篇 |
2023年 | 626篇 |
2022年 | 946篇 |
2021年 | 1026篇 |
2020年 | 1140篇 |
2019年 | 1091篇 |
2018年 | 912篇 |
2017年 | 892篇 |
2016年 | 1408篇 |
2015年 | 1374篇 |
2014年 | 1647篇 |
2013年 | 2122篇 |
2012年 | 2683篇 |
2011年 | 2705篇 |
2010年 | 1827篇 |
2009年 | 1622篇 |
2008年 | 1876篇 |
2007年 | 1778篇 |
2006年 | 1561篇 |
2005年 | 1363篇 |
2004年 | 1065篇 |
2003年 | 938篇 |
2002年 | 902篇 |
2001年 | 695篇 |
2000年 | 576篇 |
1999年 | 669篇 |
1998年 | 482篇 |
1997年 | 473篇 |
1996年 | 429篇 |
1995年 | 391篇 |
1994年 | 401篇 |
1993年 | 333篇 |
1992年 | 271篇 |
1991年 | 268篇 |
1990年 | 223篇 |
1989年 | 162篇 |
1988年 | 115篇 |
1987年 | 117篇 |
1986年 | 91篇 |
1985年 | 73篇 |
1984年 | 53篇 |
1983年 | 30篇 |
1982年 | 33篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1963年 | 7篇 |
1959年 | 12篇 |
1958年 | 11篇 |
1957年 | 19篇 |
1956年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
J. Song H. Jiang Z.J. Liu D.Y. Khang Y. Huang J.A. Rogers C. Lu C.G. Koh 《International Journal of Solids and Structures》2008,45(10):3107-3121
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. 相似文献
53.
Pengbo Jiang Tiexin Cheng Yan Liu Xianghao Cui Yingli Bi Kaiji Zhen 《Reaction Kinetics and Catalysis Letters》2004,82(1):49-56
The novel phase transfer catalysts S-8 [4-(dimethyloctylammonium) propansultan] and DB-X [1,4-bis(triethylmethylammonium)benzene dibromide] were synthesized and employed for high conversion synthesis of dichlorocyclopropane from various olefins.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
54.
Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining the optimal burn‐in time and optimal work size maximizing the long‐run average amount of work saved per time unit in the computer applications. Assuming that the underlying lifetime distribution of the computer has an initially decreasing or/and eventually increasing failure rate function, an upper bound for the optimal burn‐in time is derived for each fixed work size and a uniform (with respect to the burn‐in time) upper bound for the optimal work size is also obtained. Furthermore, it is shown that a non‐trivial lower bound for the optimal burn‐in time can be derived if the underlying lifetime distribution has a large initial failure rate. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
55.
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
56.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
57.
58.
Junchai Zhao Shichun Jiang Xiangling Ji Lijia An Bingzheng Jiang 《Journal of Polymer Science.Polymer Physics》2004,42(18):3496-3504
The surface morphologies of poly(styrene‐b‐4vinylpyridine) (PS‐b‐P4VP) diblock copolymer and homopolystyrene (hPS) binary blend thin films were investigated by atomic force microscopy as a function of total volume fraction of PS (?PS) in the mixture. It was found that when hPS was added into symmetric PS‐b‐P4VP diblock copolymers, the surface morphology of this diblock copolymer was changed to a certain degree. With ?PS increasing at first, hPS was solubilized into the corresponding domains of block copolymer and formed cylinders. Moreover, the more solubilized the hPS, the more cylinders exist. However, when the limit was reached, excessive hPS tended to separate from the domains independently instead of solubilizing into the corresponding domains any longer, that is, a macrophase separation occurred. A model describing transitions of these morphologies with an increase in ?PS is proposed. The effect of composition on the phase morphology of blend films when graphite is used as a substrate is also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3496–3504, 2004 相似文献
59.
Hydrogels containing benzo-18-crown-6 were used to modify microcantilevers for measurements of the concentration of Pb2+ in aqueous solutions. These microcantilevers undergo bending deflection upon exposure to solutions containing various Pb2+ concentrations as the result of a swelling of the hydrogels. It was found that a concentration of 10(-6) M Pb2+ can be detected using this technology. Other cations, such as Na+, have no effect on the deflection of this cantilever. The cation K+, which also complexes with benzo-18-crown-6, could interfere with Pb2+ detection, but only at high concentrations (> 10(-4) M). 相似文献
60.
Xiao Xiaohua Cao Yuguan Liu Xia Jiang Shengxiang 《Journal of inclusion phenomena and macrocyclic chemistry》2004,48(3-4):111-115
A PM3 calculation in vacuum of the inclusion complexation ofo-, m-, p-nitro-phenol with calix[n]arenes is performedsuccessfully. The pathways for inclusion process are describedand the most probable structures of the 1:1 complex are soughtthrough a potential energy scan. The energy differences betweenthe inclusion complexes and the hosts, by calculation, show thatthe most stable complexation is calix[4]-p-nitro phenol andcalix[6]-m-nitro phenol. 相似文献