全文获取类型
收费全文 | 87999篇 |
免费 | 7019篇 |
国内免费 | 6072篇 |
专业分类
化学 | 27187篇 |
晶体学 | 1849篇 |
力学 | 3676篇 |
综合类 | 459篇 |
数学 | 23479篇 |
物理学 | 44440篇 |
出版年
2023年 | 248篇 |
2022年 | 275篇 |
2021年 | 555篇 |
2020年 | 833篇 |
2019年 | 1201篇 |
2018年 | 1136篇 |
2017年 | 861篇 |
2016年 | 630篇 |
2015年 | 590篇 |
2014年 | 1353篇 |
2013年 | 2614篇 |
2012年 | 1419篇 |
2011年 | 2090篇 |
2010年 | 2615篇 |
2009年 | 7268篇 |
2008年 | 8389篇 |
2007年 | 7023篇 |
2006年 | 6295篇 |
2005年 | 4402篇 |
2004年 | 4168篇 |
2003年 | 4398篇 |
2002年 | 5568篇 |
2001年 | 4037篇 |
2000年 | 3798篇 |
1999年 | 3608篇 |
1998年 | 2989篇 |
1997年 | 2109篇 |
1996年 | 1869篇 |
1995年 | 2287篇 |
1994年 | 2247篇 |
1993年 | 1664篇 |
1992年 | 1174篇 |
1991年 | 881篇 |
1990年 | 712篇 |
1989年 | 642篇 |
1988年 | 603篇 |
1987年 | 442篇 |
1985年 | 980篇 |
1984年 | 634篇 |
1983年 | 498篇 |
1982年 | 655篇 |
1981年 | 809篇 |
1980年 | 728篇 |
1979年 | 565篇 |
1978年 | 591篇 |
1977年 | 549篇 |
1976年 | 544篇 |
1975年 | 318篇 |
1974年 | 357篇 |
1973年 | 465篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
141.
The dielectric responses (i.e. the refractive indices and the second order nonlinear susceptibilities) of all orthorhombic rare earth molybdates have been studied on the basis of the relationship between dielectric responses and the average atomic number of constituent atoms of crystals. Both the linear and second order nonlinear optical responses at 1.064 μm decrease with increasing atomic number from La to Lu. 相似文献
142.
Bond covalency and valence of elements in HgBa2Can−1CunO2n+2+δ (n=1, 2, 3, 4) were calculated and their relationship with Tc was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest Tc sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher Tc. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples. 相似文献
143.
Electrical impedance measurements of Na3H(SO4)2 were performed as a function of both temperature and frequency. The electrical conductivity and dielectric relaxation have been evaluated. The temperature dependence of electrical conductivity reveals that the sample crystals transformed to the fast ionic state in the high temperature phase. The dynamical disordering of hydrogen and sodium atoms and the orientation of SO4 tetrahedra results in fast ionic conductivity. In addition to the proton conduction, the possibility of a Na+ contribution to the conductivity in the high temperature phase is proposed. The frequency dependence of AC conductivity is proportional to ωs. The value of the exponent, s, lies between 0.85 and 0.46 in the room temperature phase, whereas it remains almost constant, 0.6, in the high-temperature phase. The dielectric dispersion is examined using the modulus formalism. An Arrhenius-type behavior is observed when the crystal undergoes the structural phase transition. 相似文献
144.
R.S. Gonnelli A. CalzolariD. Daghero G.A. UmmarinoV.A. Stepanov P. FinoG. Giunchi S. CeresaraG. Ripamonti 《Journal of Physics and Chemistry of Solids》2002,63(12):2319-2323
We studied the voltage and temperature dependency of the dynamic conductance of normal metal-MgB2 junctions obtained either with the point-contact technique (with Au and Pt tips) or by making Ag-paint spots on the surface of MgB2 samples. The fit of the conductance curves with the generalized BTK model gives evidence of pure s-wave gap symmetry. The temperature dependency of the gap, measured in Ag-paint junctions (dirty limit), follows the standard BCS curve with 2Δ/kBTc=3.3. In out-of-plane, high-pressure point-contacts we obtained almost ideal Andreev reflection characteristics showing a single small s-wave gap Δ=2.6±0.2 meV (clean limit). 相似文献
145.
The high-temperature cubic phase of non-stoichiometric strontium ferrite SrFeOx (2.5≤x≤3.0) has been studied by in situ neutron powder diffraction in air over the temperature range 300-1273 K. The composition of SrFeOx changes within the range 2.56≤x≤2.81 from 1273 to 673 K, respectively.Rietveld refinements of the diffraction patterns show that the high-temperature cubic phase of SrFeOx is consistent with a face-centred Fm3c structure. This structure leads to agreement with previous density measurements. This cell allows the high-temperature structure of SrFeOx to be described in terms of a solid solution of the composition end members. Cubic SrFeOx at high temperature is found to closely obey Vegard's law. The density of cubic SrFeOx is also found to exhibit a linear relationship with composition. 相似文献
146.
147.
对观赏南瓜色素的提取及性质进行了初步的探索,研究了光、温度、pH、氧化剂、还原剂、常用的食品添加剂对色素的影响.结果表明:观赏南瓜色素对光和热都比较稳定;适宜在pH值4-12之间使用;耐氧化性和耐还原性均较好;Vc对色素有一定的消色作用;柠檬酸三钠对色素有增色作用;色素对常用的食品添加剂有较强稳定性. 相似文献
148.
149.
Given a principal value convolution on the Heisenberg group Hn = Cn×R, we study the relation between its Laguerre expansion and the Fourier-Bessel expansion of its limit on Cn. We also calculate the Dirichlet kernel for the Laguerre expansion on the group Hn. 相似文献
150.
We study the growth morphology of thin macrostructure films which is known to be largely affected by the deposition conditions as thin film nucleation and formation is dependent on the kinetic energy and chemical free energy of the atoms. The ion-beam sputtering technique used for depositing thin layers is due to the advantage over other techniques, e.g. the independent control of many process parameters, such as the pressure and/or the energy of the ion-beam and the substrate temperature. Therefore, the dependence of various sputtering parameters such as: (i) sputtering pressure and/or the rate of deposition and (ii) the effect of substrate temperature on the growth has been studied by depositing a single layer of Al. The variations show some interesting dependencies on the structural parameters for the Al layer deposited which has been understood in terms of thin film growth and nucleation theory. 相似文献