全文获取类型
收费全文 | 1476篇 |
免费 | 19篇 |
国内免费 | 5篇 |
专业分类
化学 | 843篇 |
晶体学 | 32篇 |
力学 | 30篇 |
数学 | 98篇 |
物理学 | 497篇 |
出版年
2022年 | 17篇 |
2021年 | 26篇 |
2020年 | 19篇 |
2019年 | 23篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 35篇 |
2015年 | 24篇 |
2014年 | 39篇 |
2013年 | 115篇 |
2012年 | 73篇 |
2011年 | 86篇 |
2010年 | 47篇 |
2009年 | 45篇 |
2008年 | 52篇 |
2007年 | 55篇 |
2006年 | 66篇 |
2005年 | 45篇 |
2004年 | 46篇 |
2003年 | 28篇 |
2002年 | 40篇 |
2001年 | 24篇 |
2000年 | 20篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 26篇 |
1991年 | 16篇 |
1990年 | 20篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 25篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1976年 | 10篇 |
1975年 | 15篇 |
1973年 | 12篇 |
1971年 | 9篇 |
排序方式: 共有1500条查询结果,搜索用时 343 毫秒
91.
Polymer composite comprising polyvinylidene fluoride (PVDF) and potassium hexatitante (K2Ti6O13) was synthesized by solution casting. The effect of K2Ti6O13 on surface, thermal, and electrical properties of polymer composite were investigated. The addition of K2Ti6O13 with polymer leads to thermal degradation and transition of polymer composite from semi-crystalline to amorphous phase. The optimum results of contact angle for different loading wt% of K2Ti6O13 were directly correlated with the surface morphology. Our experimental results confirmed the incorporation of K2Ti6O13 in polymer by SEM micrographs. The evaluated dielectric properties (ε' = 424; tan δ = 2.14 at 130 °C and 100 Hz frequency for 20 wt% loading of K2Ti6O13) for polymer composite are higher in compared to pure polymer. The enhancement in dielectric constant and changing the surface properties of polymer composite can be used for the development of electrochemical storage device applications. 相似文献
92.
93.
S.S. Pote C.P. Joshi S.V. Moharil P.L. Muthal S.M. Dhopte 《Physica B: Condensed Matter》2011,406(6-7):1308-1311
Some compounds with fluorite structures in the system CaF2–YF3 were prepared by precipitation followed by thermal annealing at 1000 °C. Photoluminescence spectra of Ce3+ and Eu2+ were studied. In this host, Ce3+ exhibits PL, which is totally different from that observed for the constituent fluorides. Eu2+ emission, on the other hand, is almost the same as that for CaF2. The changes are explained in terms of the defect structure of Ca1?xYxF2+x. 相似文献
94.
95.
In this paper we obtain global controllability of a semilinear system involving monotone nonlinearities of both Lipschitzian and non-Lipschitzian types. 相似文献
96.
Base free Fe(CO)5 catalyzed one-pot synthesis of E/Z alkyl 3-formyl-3-alkyl/aryl/ferrocenyl-2-propenoates (retinoid esters) was achieved by the photolysis of alcoholic solution of terminal acetylenes and carbon monoxide. 8–10 Mol% of ironpentacarbonyl was used as a catalyst for significant transformations of retinoid esters. During the photolysis, alkynes reduced by the simultaneous double functionalization esterification and formylation and resulted in regioselective E/Z isomers of alkyl 3-formyl-3-alkyl/aryl/ferrocenyl-2-propenoates. The bi-functionalization of acetylene is quite unusual and is not observed frequently. The highest yield of the retinoid esters was achieved with 3° alcohols (96%, for E and Z isomers) while the least yield was observed with 1° alcohols (25%, for E and Z isomers). All retinoid esters are regiospecific and have exceptional biological significance to serve as key structural motifs in drug and pharmaceutical applications. 相似文献
97.
For the nonlinear recurrence relation
it is proved that the limit
exists and defines an entire function of 2 = 1(1-1). 相似文献
98.
This paper presents improved equivalent circuits for the analysis and design of acoustic plate wave devices. The method uses a mixed equivalent circuit for the interdigital transducer consisting of both active and passive sections placed on the surface of a piezoelectric plate. The values of the various circuit elements are obtained by carrying out a best fit between theoretical and experimental frequency dependence of the real and imaginary parts of transducer input impedance. Knowledge of the equivalent circuit parameters allows one to optimize design of the devices. The method has been successfully employed for the design of one-port shear-horizontal wave resonators on Y-X lithium niobate plates. The proposed method can also be utilized for determining acoustic wave velocity with high accuracy. 相似文献
99.
Reflection of zero-order normal acoustic waves excited in a thin piezoelectric plate from a set of conducting strips of a finite thickness is studied both theoretically and experimentally. The analysis shows that the effects produced by the short-circuiting of the plate surface and by the elastic load on the impedance ratio of adjacent plate segments are in opposition to each other. These effects can be commensurable, and, hence, for each wave type, there is a certain value of the strip thickness at which the reflection coefficient becomes equal to zero. The experimental results obtained for a shear horizontal normal wave (an SH 0 wave) propagating in a lithium niobate plate are in good agreement with the theory and justify the use of the equivalent-circuit model in analyzing the properties of reflectors of the type under study. 相似文献
100.