全文获取类型
收费全文 | 183474篇 |
免费 | 37968篇 |
国内免费 | 27028篇 |
专业分类
化学 | 120814篇 |
晶体学 | 2141篇 |
力学 | 12305篇 |
综合类 | 631篇 |
数学 | 22484篇 |
物理学 | 90095篇 |
出版年
2024年 | 741篇 |
2023年 | 2787篇 |
2022年 | 4305篇 |
2021年 | 4541篇 |
2020年 | 5092篇 |
2019年 | 5412篇 |
2018年 | 4849篇 |
2017年 | 5088篇 |
2016年 | 7215篇 |
2015年 | 7168篇 |
2014年 | 8140篇 |
2013年 | 11657篇 |
2012年 | 13353篇 |
2011年 | 16261篇 |
2010年 | 15720篇 |
2009年 | 15603篇 |
2008年 | 9563篇 |
2007年 | 8612篇 |
2006年 | 7862篇 |
2005年 | 7454篇 |
2004年 | 7383篇 |
2003年 | 5710篇 |
2002年 | 5277篇 |
2001年 | 5236篇 |
2000年 | 4079篇 |
1999年 | 4650篇 |
1998年 | 4011篇 |
1997年 | 3645篇 |
1996年 | 4112篇 |
1995年 | 4155篇 |
1994年 | 4123篇 |
1993年 | 4037篇 |
1992年 | 3596篇 |
1991年 | 3146篇 |
1990年 | 2647篇 |
1989年 | 2513篇 |
1988年 | 2279篇 |
1987年 | 1485篇 |
1986年 | 1557篇 |
1985年 | 1176篇 |
1984年 | 1219篇 |
1983年 | 511篇 |
1982年 | 1022篇 |
1981年 | 837篇 |
1980年 | 842篇 |
1979年 | 572篇 |
1978年 | 569篇 |
1977年 | 664篇 |
1976年 | 1080篇 |
1972年 | 549篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
M. V. Kartikeyan G. Singh E. Borie B. Piosczyk M. Thumm 《International Journal of Infrared and Millimeter Waves》2006,27(5):657-670
The feasibility of an 84 GHz, 500 kW, CW gyrotron for ECRH on an experimental tokamak will be presented in this paper. Mode
competition and mode selection procedures are carefully investigated by considering various candidate modes and the TE10,4 mode is chosen as the operating mode. A conventional cylindrical cavity resonator with weak input and output tapers and parabolic
roundings is considered for interaction studies. Self-consistent, both single mode and time-dependent, calculations are carried
out and power and efficiencies are computed for a typical set of beam parameters. The results show that an output power of
well over 500 kW, CW and efficiency around 40% can be reached without a depressed collector. 相似文献
82.
83.
This paper presents an instance of using FD-TD method to analyze the aperture field of circular groove guide horn antenna. This process is one part of a hybrid method to solve the radiation field of aperture antenna. To verify the calculated aperture field the radiation pattern is computed from it and compared with the measured one. Good agreement is reached. 相似文献
84.
The object of this note is to prove the followingTheorem Let{a_n}and{b_n}be sequences of real numbers such that0<∑∑a_n~2<+∞and0<∑b_n~2<+∞.Then we have the inequalitysum from m=1 to∞sum from n=1 to∞a_mb_n/m+n<{sum from n=1 to∞(π-θ/n~(1/2)a_n~2}~1/2{sum from n=1 to∞(π-θ/n~(1/2)b_n~2}~1/2 (1)whereθ=3/2~(1/2)-1=1.121320343. 相似文献
85.
Gang Wang Xiulin Zhu Zhenping Cheng Jian Zhu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2912-2921
A series of (di)picolinic acids and their derivates are investigated as novel complexing tridentate or bidentate ligands in the iron‐mediated reverse atom transfer radical polymerization of methyl methacrylate in N,N‐dimethylformamide at 100 °C with 2,2′‐azobisisobutyrontrile as an initiator. The polymerization rates and polydispersity indices (1.32–1.8) of the resulting polymers are dependent on the structures of the ligands employed. Different iron complexes may be involved in iron‐mediated reverse atom transfer radical polymerization, depending on the type of acid used. 1H NMR spectroscopy has been used to study the structure of the resulting polymers. Chain‐extension reactions have been performed to further confirm the living nature of this catalytic system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2912–2921, 2006 相似文献
86.
Qipeng Guo Fei Chen Ke Wang Ling Chen 《Journal of Polymer Science.Polymer Physics》2006,44(21):3042-3052
An amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) (PEO–PDMS) diblock copolymer was used to template a bisphenol A type epoxy resin (ER); nanostructured thermoset blends of ER and PEO–PDMS were prepared with 4,4′‐methylenedianiline (MDA) as the curing agent. The phase behavior, crystallization, hydrogen‐bonding interactions, and nanoscale structures were investigated with differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, and small‐angle X‐ray scattering. The uncured ER was miscible with the poly(ethylene oxide) block of PEO–PDMS, and the uncured blends were not macroscopically phase‐separated. Macroscopic phase separation took place in the MDA‐cured ER/PEO–PDMS blends containing 60–80 wt % PEO–PDMS diblock copolymer. However, the composition‐dependent nanostructures were formed in the cured blends with 10–50 wt % PEO–PDMS, which did not show macroscopic phase separation. The poly(dimethylsiloxane) microdomains with sizes of 10–20 nm were dispersed in a continuous ER‐rich phase; the average distance between the neighboring microdomains was in the range of 20–50 nm. The miscibility between the cured ER and the poly(ethylene oxide) block of PEO–PDMS was ascribed to the favorable hydrogen‐bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3042–3052, 2006 相似文献
87.
In this paper we give a realization of some symmetric space G/K as a closed submanifold P of G. We also give several equivalent representations of the submanifold P. Some properties of the set gK∩P are also discussed, where gK is a coset space in G. 相似文献
88.
89.
90.
In developing travel demand models it is generally assumed that the base-year data used in developing the parameters, as well as the forecasted data to be used as independent variables for the design year, are of acceptable quality. The purpose of this paper is to present the application of error propagation theory in assesing the predictive quality of one type of travel demand forecasting model (multinomial logit models) and to demonstrate how error considerations can be used as a tool for identifying the optimal model. The general conclusions of this study are that: (1) it is indeed possible to quantify errors in dependent variables in logit models as a consequence of errors in independent variables; and (2) error consideration can be used as a tool for identifying the optimal model from a set of candidate models. Further research is recommended to develop better insights into the phenomenon of error propagation so that the consideration of errors can be a factor in decisions on model selection. 相似文献