全文获取类型
收费全文 | 30469篇 |
免费 | 2949篇 |
国内免费 | 2574篇 |
专业分类
化学 | 20854篇 |
晶体学 | 268篇 |
力学 | 1221篇 |
综合类 | 236篇 |
数学 | 4897篇 |
物理学 | 8516篇 |
出版年
2024年 | 57篇 |
2023年 | 318篇 |
2022年 | 656篇 |
2021年 | 788篇 |
2020年 | 871篇 |
2019年 | 1021篇 |
2018年 | 849篇 |
2017年 | 759篇 |
2016年 | 1284篇 |
2015年 | 1299篇 |
2014年 | 1491篇 |
2013年 | 2060篇 |
2012年 | 2280篇 |
2011年 | 2618篇 |
2010年 | 1748篇 |
2009年 | 1673篇 |
2008年 | 2110篇 |
2007年 | 1918篇 |
2006年 | 1882篇 |
2005年 | 1692篇 |
2004年 | 1341篇 |
2003年 | 1063篇 |
2002年 | 1162篇 |
2001年 | 753篇 |
2000年 | 598篇 |
1999年 | 476篇 |
1998年 | 355篇 |
1997年 | 308篇 |
1996年 | 297篇 |
1995年 | 232篇 |
1994年 | 192篇 |
1993年 | 164篇 |
1992年 | 143篇 |
1991年 | 124篇 |
1990年 | 102篇 |
1989年 | 81篇 |
1988年 | 80篇 |
1987年 | 67篇 |
1986年 | 60篇 |
1985年 | 87篇 |
1984年 | 64篇 |
1983年 | 41篇 |
1982年 | 62篇 |
1981年 | 51篇 |
1980年 | 52篇 |
1979年 | 45篇 |
1978年 | 58篇 |
1977年 | 44篇 |
1976年 | 51篇 |
1974年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Yong Joon Park Min Gyu KimYoung-Sik Hong Xianglan WuKwang Sun Ryu Soon Ho Chang 《Solid State Communications》2003,127(7):509-514
Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO2 structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2. Indeed, Li[Ni0.50Mn0.50]O2 compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni0.17Li0.22Mn0.61]O2 and Li[Ni0.25Li0.17Mn0.58]O2 compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni2+ and about Ni3+, while the oxidation state of Mn ion sustains Mn4+ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2, in which Ni ion changes between Ni2+ and NI4+. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process. 相似文献
52.
53.
54.
在随机删失下研究了乘积限过程和累积失效率过程的振动模的局部性质 .给出了这两个过程的振动模的重对数律 ,并应用这些结果得到了几种核密度估计和Bahadur-Kiefer过程的精确收敛速度 相似文献
55.
Zi‐Cai Li Tzon‐Tzer Lu Hung‐Tsai Huang Alexander H.‐D. Cheng 《Numerical Methods for Partial Differential Equations》2007,23(1):93-144
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
56.
57.
Transfer matrix approach of vibration isolation analysis of periodic composite structure 总被引:1,自引:0,他引:1
Wang Yong Huang Qibai Zhou Minggang Xu Zhisheng 《Archive of Applied Mechanics (Ingenieur Archiv)》2007,77(7):461-471
The transmission properties of elastic waves propagating in a three-dimensional composite structure embedded periodically
with spherical inclusions are analyzed by the transfer matrix method in this paper. Firstly, the periodic composite structures
are divided into many layers, the transfer matrix of monolayer structure is deduced by the wave equations, and the transfer
matrix of the entire structure is obtained in the case of boundary conditions of displacement and stress continuity between
layers. Then, the effective impedance of the structure is analyzed to calculate its reflectivity and transmissivity of vibration
isolation. Finally, numerical simulation is carried out; the experiment results validate the accuracy and feasibility of the
method adopted in the paper and some useful conclusions are obtained.
Project (No. 50075029) supported by the National Natural Science Foundation of China. 相似文献
58.
Timur Zharnikov Alexander Yakovlev Semion Kuchanov 《Journal of Polymer Science.Polymer Physics》2003,41(9):892-902
The problem of finding conditions of the loss of thermodynamic stability by the reaction system was solved on the basis of the developed theory of living free‐radical copolymerization. The spinodal's calculations were carried out for a significant number of systems differing in the values of kinetic, stoichiometric, and thermodynamic parameters. Analysis of the results of such calculations revealed some regularities in the spinodal curves' behavior and permitted us to classify their possible topological types. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 892–902, 2003 相似文献
59.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
60.
Alexander J. Zaslavski 《Journal of Mathematical Analysis and Applications》2007,335(2):962-973
The Tonelli existence theorem in the calculus of variations and its subsequent modifications were established for integrands f which satisfy convexity and growth conditions. In this paper we consider a large class of optimal control problems which is identified with a complete metric space of integrands without convexity assumptions and show that for a generic integrand the corresponding optimal control problem possesses a unique solution and this solution is Lipschitzian. 相似文献