全文获取类型
收费全文 | 18155篇 |
免费 | 3325篇 |
国内免费 | 2452篇 |
专业分类
化学 | 13868篇 |
晶体学 | 216篇 |
力学 | 1107篇 |
综合类 | 139篇 |
数学 | 2365篇 |
物理学 | 6237篇 |
出版年
2024年 | 33篇 |
2023年 | 349篇 |
2022年 | 484篇 |
2021年 | 619篇 |
2020年 | 814篇 |
2019年 | 806篇 |
2018年 | 683篇 |
2017年 | 580篇 |
2016年 | 905篇 |
2015年 | 984篇 |
2014年 | 1090篇 |
2013年 | 1362篇 |
2012年 | 1630篇 |
2011年 | 1686篇 |
2010年 | 1241篇 |
2009年 | 1157篇 |
2008年 | 1178篇 |
2007年 | 1023篇 |
2006年 | 972篇 |
2005年 | 833篇 |
2004年 | 710篇 |
2003年 | 621篇 |
2002年 | 778篇 |
2001年 | 568篇 |
2000年 | 429篇 |
1999年 | 393篇 |
1998年 | 314篇 |
1997年 | 256篇 |
1996年 | 256篇 |
1995年 | 213篇 |
1994年 | 180篇 |
1993年 | 131篇 |
1992年 | 121篇 |
1991年 | 114篇 |
1990年 | 82篇 |
1989年 | 69篇 |
1988年 | 57篇 |
1987年 | 34篇 |
1986年 | 35篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 5篇 |
1981年 | 18篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1974年 | 5篇 |
1957年 | 5篇 |
1930年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
YBa2Cu3O7-δ and Tl2Ba2CaCu2O8 thin films for microwave filters were synthesized by pulsed laser deposition and the two-step thalliation process. Substrate
quality requirements and the relation of thin film morphology, microstructure with microwave surface resistance were discussed. 相似文献
102.
103.
Nano-sized oxide structures resulted from localized electrochemical oxidation induced by a negatively biased atomic force microscopy (AFM) tip operated with the non-contact mode were fabricated on p-GaAs(1 0 0) surface. The geometrical characteristics of the oxide patterns and their dependences on various fabrication parameters, e.g., the anodization time, the biased voltages, the tip scanning rates, as well as the formation mechanism and relevant growth kinetics are investigated. Results indicate that the height of the protruded oxide dots grow exponentially as a function of time in the initial stage of oxidation and soon reaches a maximum height depending linearly with the anodized voltages, in according with the behaviors predicted by space charge limited local oxidation mechanism. In addition, selective micro-Auger analysis of the anodized region reveals the formation of Ga(As)Ox, indicating the prominent role played by the field-induced nanometer-size water meniscus in producing the nanometer-scale oxide dots and bumps on p-GaAs(1 0 0) surface. 相似文献
104.
105.
Triterpenoid Constituents of Huperzia miyoshiana 总被引:1,自引:0,他引:1
Thirteen triterpenoids, including three new ones, miyoshianois A (1), B (2) and C (3), were isolated from Huperzia miyoshiana. The structures of these new compounds were established as 3-O-dihydroferuloyltohogenol (1), 16-oxo-3β,21β-dihydrox-y-serrat-14-en-24-ferulate (2) and 16-oxo-3a, 21β-dihydroxy-serrat-14-en-24-ferulate (3), respectively, on the basis of their spectroscopic analysis. 相似文献
106.
Ying‐Ling Liu Chuan‐Shao Wu Yie‐Shun Chiu Wen‐Hsuan Ho 《Journal of polymer science. Part A, Polymer chemistry》2003,41(15):2354-2367
A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′‐diaminodiphenylmethane with the sol–gel reaction of a phosphorus‐containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with 3‐glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, 1H and 31P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass‐transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003 相似文献
107.
We study a GI/M/c type queueing system with vacations in which all servers take vacations together when the system becomes empty. These servers keep taking synchronous vacations until they find waiting customers in the system at a vacation completion instant.The vacation time is a phase-type (PH) distributed random variable. Using embedded Markov chain modeling and the matrix geometric solution methods, we obtain explicit expressions for the stationary probability distributions of the queue length at arrivals and the waiting time. To compare the vacation model with the classical GI/M/c queue without vacations, we prove conditional stochastic decomposition properties for the queue length and the waiting time when all servers are busy. Our model is a generalization of several previous studies. 相似文献
108.
A fourth‐order compact finite difference scheme on the nine‐point 2D stencil is formulated for solving the steady‐state Navier–Stokes/Boussinesq equations for two‐dimensional, incompressible fluid flow and heat transfer using the stream function–vorticity formulation. The main feature of the new fourth‐order compact scheme is that it allows point‐successive overrelaxation (SOR) or point‐successive underrelaxation iteration for all Rayleigh numbers Ra of physical interest and all Prandtl numbers Pr attempted. Numerical solutions are obtained for the model problem of natural convection in a square cavity with benchmark solutions and compared with some of the accurate results available in the literature. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
109.
110.
Analytic solutions of an iterative functional equation 总被引:4,自引:0,他引:4