全文获取类型
收费全文 | 3283篇 |
免费 | 237篇 |
国内免费 | 55篇 |
专业分类
化学 | 2356篇 |
晶体学 | 33篇 |
力学 | 139篇 |
数学 | 372篇 |
物理学 | 675篇 |
出版年
2023年 | 19篇 |
2022年 | 30篇 |
2021年 | 105篇 |
2020年 | 107篇 |
2019年 | 141篇 |
2018年 | 143篇 |
2017年 | 96篇 |
2016年 | 188篇 |
2015年 | 140篇 |
2014年 | 167篇 |
2013年 | 348篇 |
2012年 | 213篇 |
2011年 | 201篇 |
2010年 | 158篇 |
2009年 | 154篇 |
2008年 | 181篇 |
2007年 | 182篇 |
2006年 | 138篇 |
2005年 | 96篇 |
2004年 | 92篇 |
2003年 | 67篇 |
2002年 | 81篇 |
2001年 | 63篇 |
2000年 | 55篇 |
1999年 | 47篇 |
1998年 | 24篇 |
1997年 | 19篇 |
1996年 | 15篇 |
1995年 | 14篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 15篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 14篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1973年 | 7篇 |
1971年 | 6篇 |
1862年 | 8篇 |
排序方式: 共有3575条查询结果,搜索用时 171 毫秒
1.
2.
3.
Zinc polyoxometalate on activated carbon: an efficient catalyst for selective oxidation of alcohols with hydrogen peroxide 下载免费PDF全文
[PW11ZnO39]5? was immobilized on activated carbon and characterized using Fourier transform infrared, X‐ray diffraction, Brunauer–Emmett–Teller and elemental analysis techniques. Effective oxidation of various alcohols with hydrogen peroxide was performed in the presence of this catalyst. Easy separation of the catalyst from the reaction mixture, cheapness, high activity and selectivity, stability as well as retained activity in subsequent catalytic cycles make this supported catalyst suitable for small‐scale synthesis. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
4.
5.
The main result of the paper is a theorem, using which a new proof of Roth’s theorem is obtained, a new solvability criterion
for the matrix equation AX-YB = C is proved, a formula for a particular solution of the latter is derived, and the least of
the orders of square nonsingular matrices containing a given rectangular matrix as a submatrix is determined. Bibliography:
5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 323, 2005, pp. 15–23. 相似文献
6.
Al.Th. Kermanidis D.G. Stamatelos G.N. Labeas Sp.G. Pantelakis 《Theoretical and Applied Fracture Mechanics》2006,45(2):148-158
The synergetic effect of corrosion and corrosion induced hydrogen embrittlement damage processes which occur at local scale has been found to result in a dramatic macroscopic tensile ductility loss of the 2024 aluminum alloy. In the present work, the tensile behaviour of corroded 2024 T351 specimens has been estimated on the basis of FE analysis by taking into account the local material properties in the damaged areas. A parametric study is involved to account for the effect of thickness in the results. Calculated tensile properties obtained with the analysis agree well with experimental data. 相似文献
7.
Polyvinyl alcohol (PVA)-based proton conducting polymer electrolytes have been prepared by the solution cast technique. The
conductivity is observed to increase from 10−9 to 10−4 S cm−1 as a result of orthophosphoric acid (H3PO4) addition. The plot of conductivity vs temperature shows that a phase transition occurred at 343 K in the sample PVA-33 wt%
H3PO4. The β-relaxation peak is observed at 313 K. The glass transition temperature of PVA-33 wt% H3PO4 is 343 K. Orthophosphoric acid seems to play a dual role, i.e., as a proton source and as a plasticizer. The ac conductivity
σ
ac = Aω
s was also calculated in the temperature range from 303 to 353 K. The conduction mechanism was inferred by plotting the graph
of s vs T from which the conduction mechanism for sample PVA-17 wt% H3PO4 was inferred to occur by way of the overlapping large polaron tunneling (OLPT) model and the conduction mechanism for the
sample PVA-33 wt% H3PO4 by way of the correlated barrier height (CBH) model. 相似文献
8.
L. V. Giurgiu M. N. Grecu X. Filip O. Raita Al. Darabont D. Gavre J. Blasco 《Applied magnetic resonance》2003,24(3-4):351-360
We report an electron paramagnetic resonance (EPR) investigation of the spin dynamics in the paramagnetic regime of the colossal magnetoresistive manganites La2/3Ca1/3Mn1?x Me x O3 (Me=Al, In;x≤0.05). The temperature dependences of the EPR linewidth and integral intensity have been analyzed in terms of the bottleneck spin relaxation and small-polaron hopping models. The exchange coupling integral between Mn3+ and Mn4+ ions and the polaron activation energy decrease with increasing doping level. A discussion is given concerning the factors which could explain the observed changes. 相似文献
9.
Majid Vaezzadeh Ehsan Noruzifar Ghanati Faezeh Mohsen Salehkotahi Reza Mehdian 《Journal of magnetism and magnetic materials》2006
Experimental results of applying a steady magnetic field (20 and 30 mT) on agricultural plants reveal that their growth is more than that of control plants. Considering that these plants have ferritin cells, and each ferritin cell has 4500 Fe atoms, it is obvious that they have an outstanding role in the plants’ growth. As the last spin magnetic moment (SMM) of the Fe atom posed to an external magnetic field (EMF), the composition of SMM and EMF create an oscillator in the system. Then we have a moment of force on ferritin cells. This oscillator exerts its energy, then damps and finally locates in the field direction. The relaxed energy increased the internal temperature (i.e., the effective temperature of the magnetic spin system of plant) so that it is situated in a proper temperature for growing. This phenomenon (temperature increasing) occurs in the initial minutes of applying the magnetic field. So it depends on the number of times of locating the plant in magnetic field in a day (n). If this number (n) passes the critical value, the plant reaches a burning temperature and growth is perturbed. In this paper, the plant growth rate and critical temperature in a steady magnetic field were investigated and formulated theoretically. An innovative result in this research is as follows: if a plant's environment was in the dormant temperature, we could increase the internal temperature of the plant by applying a magnetic field n times in a day (for growth). 相似文献
10.