全文获取类型
收费全文 | 1144篇 |
免费 | 63篇 |
国内免费 | 80篇 |
专业分类
化学 | 503篇 |
晶体学 | 3篇 |
力学 | 46篇 |
综合类 | 1篇 |
数学 | 171篇 |
物理学 | 563篇 |
出版年
2024年 | 1篇 |
2023年 | 24篇 |
2022年 | 19篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 38篇 |
2016年 | 43篇 |
2015年 | 34篇 |
2014年 | 61篇 |
2013年 | 74篇 |
2012年 | 39篇 |
2011年 | 70篇 |
2010年 | 60篇 |
2009年 | 82篇 |
2008年 | 76篇 |
2007年 | 86篇 |
2006年 | 64篇 |
2005年 | 61篇 |
2004年 | 51篇 |
2003年 | 43篇 |
2002年 | 39篇 |
2001年 | 32篇 |
2000年 | 34篇 |
1999年 | 25篇 |
1998年 | 28篇 |
1997年 | 27篇 |
1996年 | 22篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有1287条查询结果,搜索用时 265 毫秒
91.
Sebastián Lorca 《Journal of Mathematical Analysis and Applications》2004,295(1):276-286
We study the existence of positive solutions to the elliptic equation ε2Δu(x,y)−V(y)u(x,y)+f(u(x,y))=0 for (x,y) in an unbounded domain subject to the boundary condition u=0 whenever is nonempty. Our potential V depends only on the y variable and is a bounded or unbounded domain which may coincide with . The positive parameter ε is tending to zero and our solutions uε concentrate along minimum points of the unbounded manifold of critical points of V. 相似文献
92.
There are various methods to evaluate voice parameters. Original software was used to assess the voice quality by the staff of AUDIO-Fon centr Brno, Czech Republic. A group of hereditary deaf persons was examined. Deaf persons have all of the biological conditions to make voice except for the possibility of acoustic feedback. We examined the voices of 35 persons (20 men and 15 women) with hereditary profound hearing impairments, and we compared voice parameters with the voice of intact persons. To measure we used special software called voice field measurements (VFMs). The program graphically records voice frequency and intensity. VFM is an objective method that enables the assessment of basic physical voice characteristics. It is suitable for the examination of both intact and disturbed voice. The voice of the deaf has a higher basic voice frequency in men as well as in women. This type of voice production, ie, childlike voice, which is fixed only by a motor stereotype, is much more demanding for a mature larynx. Hearing influences both the voice development and speech production. The voice of persons with hearing impairments has a higher basic voice frequency regardless of their sex. This type of voice production, which is fixed only by a motor stereotype, ie, child voice, is much more demanding for a larynx of an adult. Thus, phonation of deaf people is more demanding and their voice production needs greater effort. Deaf people, despite an intact phonic apparatus, cannot produce more than one type of voice. They cannot modulate their voices concerning the frequency and dynamics. They cannot change their voices continually. The voice is limited in both of these parameters (frequency and dynamics). If a deaf person wants to change a voice characteristic, it is possible only by discontinuous changes-"skipping." 相似文献
93.
Ilya?KuselmanEmail author Alexander?Weisman Wolfhard?Wegscheider 《Accreditation and quality assurance》2003,8(11):530-531
The current situation in the pharmaceutical industry is discussed, when the traceability of measurement (analytical) results to certified values of pharmacopoeial reference standards is required, without evaluating their uncertainties. It is shown that the evaluation of measurement uncertainty is necessary for understanding the level of confidence of the analytical results and their comparability, particularly during preparation and characterisation of the reference standards.Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher. Apart from exceptional circumstances, they are not submitted to the usual referee procedure and go essentially unaltered. 相似文献
94.
采用传统陶瓷烧结工艺,在无压还原气氛下低温制备出透明性良好的掺Yb3+氧化镧钇透明激光陶瓷,测试了其在室温下的吸收光谱、发射光谱和荧光寿命.结果表明,掺Yb3+氧化镧钇透明激光陶瓷的吸收系数随着Yb3+掺杂浓度的增加而增大,最强吸收峰974nm处的吸收截面为0.90~1.12×10-20 cm2;主发射峰1 032 nm和1 075 nm处的发射截面分别为1.05×10-20 cm2和0.87×10-20 cm2; Yb3+掺杂浓度为5at.%时荧光寿命为1.38 ms,并随Yb3+掺杂浓度的增加而减小;当Yb3+掺杂浓度超过10at.%时,样品中存在严重的浓度猝灭.产生浓度猝灭的原因是高掺杂时离子间存在合作上转换和能量转移. 相似文献
95.
96.
The fluorescence property of xTbF3-BaF2-AlF3-GeO2+ySmF3 (x=0.01-40 mol%, y=0-5 wt%) glasses were investigated. The enhancement of Sm3+ fluorescence was recognized in the presence of Tb3+. Increasing Tb3+ content, the emission color changed from green to orange. When the intensity of fluorescence at 540 nm originated from Tb3+ is compared with that at 600 nm originated from Sm3+, the information about the concentration quenching of Tb3+ and Sm3+ was obtained. From these results, rare earth ions were dispersed identically in the glasses. After heating to 673 K or cooling to 77 K, the emission color of 20TbF3-20BaF2-10AlF3-50GeO2/mol%+0.05 wt% SmF3 glass was reversibly changed from orange to green. In addition, while the emission from 10TbF3-20BaF2-10AlF3-60GeO2+0.01 wt% SmF3 glass was green, its crystallized sample, prepared by annealing at 1073 K, exhibited an orange emission due to Sm3+ at room temperature. 相似文献
97.
Solubility of disodium 5′-guanylate in water + ethanol binary solvent mixtures was determined by a gravimetric method in the temperature range from 283.15 K to 323.15 K, pH range from 8 to 10 and at different water/ethanol mole ratios. The effects of pH, temperature and water/ethanol mole ratio on the solubility were investigated in detail. The modified Apelblat model and the combined nearly ideal binary solvent (CNIBS)/Redlich-Kister model were selected to correlate the experimental data. The results showed that the experimental data was satisfactorily correlated by the (CNIBS)/Redlich-Kister model, but for the modified Apelblat model, the correlation was not so satisfactory in some cases. 相似文献
98.
99.
Gongming WEI 《数学年刊B辑(英文版)》2008,29(3)
A 2-coupled nonlinear Schr(o)dinger equations with bounded varying potentials and strongly attractive interactions is considered.When the attractive interaction is strong enough,the existence of a ground state for sufficiently small Planck constant is proved.As the Planck constant approaches zero,it is proved that one of the components concentrates at a minimum point of the ground state energy function which is defined in Section 4. 相似文献
100.
Yves Van Ingelgem Els Tourwé Orlin Blajiev Rik Pintelon Annick Hubin 《Electroanalysis》2009,21(6):730-739
Electrochemical impedance spectroscopy (EIS) is a powerful technique to study electrochemical processes and to perform screening tasks. Recently an integrated measuring and modeling methodology for EIS based on a multisine excitation signal was developed. A key issue in this methodology is the data analysis, allowing us to rapidly quantify the reliability of the measured data. In this paper, a comparison is made between classical single‐sine and the proposed multisine measurements on the same system. The fitting of the impedance data obtained by single‐or multisine excitation and using different weighting factors is also discussed. In addition to the advantages reported in earlier work, it is concluded that, of all investigated frequencies, the odd random phase multisine excitation yields the highest quality data in the shortest measurement time. 相似文献