全文获取类型
收费全文 | 12504篇 |
免费 | 2220篇 |
国内免费 | 1485篇 |
专业分类
化学 | 8704篇 |
晶体学 | 166篇 |
力学 | 874篇 |
综合类 | 115篇 |
数学 | 1405篇 |
物理学 | 4945篇 |
出版年
2024年 | 25篇 |
2023年 | 288篇 |
2022年 | 493篇 |
2021年 | 513篇 |
2020年 | 521篇 |
2019年 | 533篇 |
2018年 | 439篇 |
2017年 | 400篇 |
2016年 | 653篇 |
2015年 | 610篇 |
2014年 | 703篇 |
2013年 | 852篇 |
2012年 | 1132篇 |
2011年 | 1102篇 |
2010年 | 851篇 |
2009年 | 793篇 |
2008年 | 777篇 |
2007年 | 687篇 |
2006年 | 707篇 |
2005年 | 616篇 |
2004年 | 402篇 |
2003年 | 336篇 |
2002年 | 331篇 |
2001年 | 255篇 |
2000年 | 237篇 |
1999年 | 243篇 |
1998年 | 206篇 |
1997年 | 225篇 |
1996年 | 207篇 |
1995年 | 186篇 |
1994年 | 149篇 |
1993年 | 106篇 |
1992年 | 97篇 |
1991年 | 89篇 |
1990年 | 85篇 |
1989年 | 71篇 |
1988年 | 54篇 |
1987年 | 29篇 |
1986年 | 45篇 |
1985年 | 32篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Xe-Kr laser induced collisional ionization system and experimental preparation of its initial state: Four-photon resonant excitation
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper proposes a novel one-colour Xe-Kr laser induced collisional ionization system. Considering the level scheme of the system, it finds that the initial state of the reaction--the four 4f levels with even J of Xe-can be prepared through method of four-photon resonant excitation by dye laser with wavelength of -440 nm. Absorption of an additional photon (the transfer laser) of the same wavelength will complete the laser induced collisional ionization process. The resonance enhanced ionization spectrum of Xe by four laser photons at -440nm is measured through time-of-flight mass spectrometry, this aims at the preparation of the initial state of the system proposed. The Stark broadening of the measured spectrum is observed and consistent with the previous study. Analysis of the measured resonance ionization spectrum implies the feasibility of -440 nm four-photon resonant excitation of the initial 4f state of the Xe Kr system proposed in this paper, which prepares for a further experiment of laser induced collisional ionization. 相似文献
992.
A protocol for controlled remote implementation of a partially unknown operation on an arbitrary quantum state is proposed.
In this protocol, a task can be performed using a GHZ state shared among three distant parties: Alice, Bob and the controller
Charlie. This protocol is also generalized to the multi-party control system based on sharing an N-qubit GHZ state.
Supported by the Natural Science Youth Teacher Foundation of Xuzhou Institute of Technology, China (Grant No. XKY2007317) 相似文献
993.
The emergent light distribution of a new type of contact laser scalpel is measured in three different states using a light sensor. The relationship between the angle and the light intensity is analyzed. The results show that the strongest light is emitted from two sides and the front of the scalpel. The light from the front mainly plays a role of cutting. The light from two sides contributes to stanch the wound so as to remain a clear visual field during the surgery. It also helps to increase the cutting efficiency. 相似文献
994.
Ai Hua Fan 《Journal d'Analyse Mathématique》2002,86(1):271-287
Let β > 1 be a Pisot number andg be a positive Hölder continuous function with period one and g(0) = 1. The multiperiodic functionG(ξ)=Π n=0 ∞ g(ξ/βn) is studied and the asymptotic behaviour ofI G(T) = ∫ 0 T G(ξ)dξ investigated. We prove that the limit of logI(T)/ logT exists asT tends to infinity. We also provide a method to calculate this limit for the caseg(ξ) = cos2 2πξ, corresponding to the Fourier transform of the Bernoulli convolution associated to the golden number (or some of its generalizations). 相似文献
995.
Xiaoli Li Guangmin Wu Jun Shen Fan Yang Jue Wang 《Journal of Sol-Gel Science and Technology》2002,25(3):235-242
When designing a cut-off interference filter, extra layers are needed to add on each side of periodic symmetrical multilayer to match the incident medium and the substrate. In this paper, we use sol-gel film with adjustable refractive index as the match layer. The influence of the refractive index and thickness of the match layer on the film system is discussed in detail. As an example, a special filter which is transparent (>80%) at the wavelength 3–5 m and high reflective (>90%) at the wavelength 1.3 m is designed. Finally a series of optimized film parameters are presented. The whole design process is a good reference to the other multilayer special filter made by sol-gel process. 相似文献
996.
In near neutral medium, the resonance Rayleigh scattering (RRS) intensities of an alone cationic surfactant and nucleic acid are very weak. However, when they combine with each other to form a complex, the RRS intensity of the solution is enhanced greatly. In this paper the reactions of five cationic surfactants with nucleic acids have been studied. The results show that the reaction conditions and RRS spectral characteristics of these reactions are similar, but their sensitivities are obviously different. Among them, the sensitivity of cetyldimethyl benzylammonium chloride (CDBAC) with an aryl and large molecular weight is the highest, while that of cetyl-trimethylammonium bromide (CTAB) without aryl and with small molecular weight is the lowest. The detection limits for ctDNA and yRNA of the former are 6.6 and 29.4 ng · mL-1, while that of the latter are 13.3 and 53.6 ng · mL-1. The method has better selectivity and can be applied to the determination of trace amounts of nucleic acids. Furthermore, i 相似文献
997.
[reaction: see text] New affinity reagents were synthesized using alkene metathesis to directly modify the MeBmt side chain of cyclosporin A. The reagents were used to detect novel cyclophilins from cellular extracts. 相似文献
998.
The reaction of a nickel dithiolene complex (1) and ethylene is a two-step process, in which the trans-product (2) forms first in the direct addition of the olefin to 1, while the more thermodynamically stable cis-product (3) involves isomerization of 2. The introduction of electron-withdrawing groups (cyano or trifluoromethyl) not only significantly lowers the activation energy (TS1) for the formation of trans-product, but it also strongly stabilizes the products (2, 3) such that they are favored by the free energy. However, these substituents leave the barrier for the conformational transformation step (TS2) nearly unchanged. On reduction, the previously favored adduct is now strongly disfavored. 相似文献
999.
1000.
Qi JH Zhang XY Zhang RS Liu MC Hu ZD Xue HF Fan BT 《SAR and QSAR in environmental research》2000,11(2):117-131
It is proposed for the first time a method of prediction of the programmed-temperature retention times of components of naphthas in capillary gas chromatography using artificial neural networks. People are used to predict the programmed-temperature retention time using many formulas such as the integral formula, which requires that four parameters must be determined by calculation or experiments. However the results obtained by the formula are not so good to meet the demand of industry. In order to predict retention time accurately and conveniently, artificial neural networks using five-fold cross-validation and leave-20%-out methods have been applied. Only two parameters: density and isothermal retention index were used as input vectors. The average RMS error for predicted values of five different networks was 0.18, whereas the RMS error of predictions by the integral formula was 0.69. Obviously, the predictions by neural networks were much better than predictions by the formula, and neural networks need fewer parameters than the formula. So neural networks can successfully and conveniently solve the problem of predictions of programmed-temperature retention times, and provide useful data for analysis of naphthas in petrochemical industry. 相似文献