全文获取类型
收费全文 | 1292篇 |
免费 | 75篇 |
国内免费 | 273篇 |
专业分类
化学 | 1139篇 |
晶体学 | 7篇 |
力学 | 70篇 |
综合类 | 1篇 |
数学 | 174篇 |
物理学 | 249篇 |
出版年
2023年 | 9篇 |
2022年 | 21篇 |
2021年 | 27篇 |
2020年 | 23篇 |
2019年 | 19篇 |
2018年 | 34篇 |
2017年 | 25篇 |
2016年 | 27篇 |
2015年 | 28篇 |
2014年 | 44篇 |
2013年 | 125篇 |
2012年 | 107篇 |
2011年 | 124篇 |
2010年 | 64篇 |
2009年 | 92篇 |
2008年 | 79篇 |
2007年 | 76篇 |
2006年 | 48篇 |
2005年 | 71篇 |
2004年 | 140篇 |
2003年 | 108篇 |
2002年 | 79篇 |
2001年 | 26篇 |
2000年 | 21篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1989年 | 8篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1967年 | 4篇 |
1959年 | 3篇 |
1929年 | 4篇 |
排序方式: 共有1640条查询结果,搜索用时 15 毫秒
11.
12.
The scope of this paper is to present a nonlinear error estimation and correction for Navier-Stokes and Reynolds-averaged Navier-Stokes equations. This nonlinear corrector enables better solution or functional output predictions at fixed mesh complexity and can be considered in a mesh adaptation process. After solving the problem at hand, a corrected solution is obtained by solving again the problem with an added source term. This source term is deduced from the evaluation of the residual of the numerical solution interpolated on the h/2 mesh. To avoid the generation of the h/2 mesh (which is prohibitive for realistic applications), the residual at each vertex is computed by local refinement only in the neighborhood of the considered vertex. One of the main feature of this approach is that it automatically takes into account all the properties of the considered numerical method. The numerical examples point out that it successfully improves solution predictions and yields a sharp estimate of the numerical error. Moreover, we demonstrate the superiority of the nonlinear corrector with respect to linear corrector that can be found in the literature. 相似文献
13.
14.
描述了在过剩压驱动下金刚石晶种外延生过程中,大量伴生的石墨再结晶现象。再结晶石墨抑制了金刚石的自发成核;它们分布于合成腔触媒金属的低温区,结晶数量多,晶粒片状分层,尺寸大,但出现乱层晶体结构;同时产生一定数量的无定形碳。分析认为,这与长时间的低过剩压驱动,触媒金属内有足够的碳源供给,并具备在高温高压下石墨充分结晶但又达不到完全石墨化条件有关。还讨论了在低过剩压驱动下,促进金刚石晶体外延生长的碳源可能是活化的碳原子,而不是具有乱层结构特征的再结晶石墨。 相似文献
15.
Relativistic symmetries in the Rosen-Morse potential and tensor interaction using the Nikiforov-Uvarov method 下载免费PDF全文
Approximate analytical bound-state solutions of the Dirac particle in the fields of attractive and repulsive Rosen- Morse (RM) potentials including the Coulomb-like tensor (CLT) potential are obtained for arbitrary spin-orbit quantum number κ. The Pekeris approximation is used to deal with the spin-orbit coupling terms κ(κ± 1)r 2 . In the presence of exact spin and pseudospin (p-spin) symmetries, the energy eigenvalues and the corresponding normalized two-component wave functions are found by using the parametric generalization of the Nikiforov-Uvarov (NU) method. The numerical results show that the CLT interaction removes degeneracies between the spin and p-spin state doublets. 相似文献
16.
17.
S. Bagˇcı H.M. Tütüncü S. Duman E. Bulut M. Özacar G.P. Srivastava 《Journal of Physics and Chemistry of Solids》2014
We have performed an ab initio study of structural, electronic, magnetic, vibrational and thermal properties of the cubic spinel LiMn2O4 by employing the density functional theory, the linear-response formalism, and the plane-wave pseudopotential method. An analysis of the electronic structure with the help of electronic density of states shows that the density of states at the Fermi level (N (EF)) is found to be governed by the Mn 3d electrons with some contributions from the 2p states of O atoms. It is important to note that the contribution of Mn 3d states to N(EF) is as much as 85%. From our phonon calculations, we have obtained that the main contribution to phonon density of states (below 250 cm−1) comes from the coupled motion of Mn and O atoms while phonon modes between 250 cm−1 and 375 cm−1 are characterized by the vibrations of all the three types of atoms. The contribution from Li increases rapidly at higher frequency (above 375 cm−1) due to the light mass of this atom. Finally, the specific heat and the Debye temperature at 300 K are calculated to be 249.29 J/mol K and 820.80 K respectively. 相似文献
18.
Charge ordering modulations in a Bi<sub>0.4</sub>Ca<sub>0.6</sub>MnO<sub>3</sub> film with a thickness of 110 nm 下载免费PDF全文
The low temperature sample stage in a transmission electron microscope is used to investigate the charge ordering behaviours in a Bi 0.4 Ca 0.6 MnO 3 film with a thickness of 110 nm at 103 K.Six different types of superlattice structures are observed using the selected-area electron diffraction(SAED) technique,while three of them match well with the modulation stripes in high-resolution transmission electron microscopy(HRTEM) images.It is found that the modulation periodicity and direction are completely different in the region close to the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface from those in the region a little further from the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface,and the possible reasons for this are discussed.Based on the experimental results,structural models are proposed for these localized modulated structures. 相似文献
19.
The dipole moments of the ground and excited states of 4′-(hexyloxy)-4-biphenylcarbonitrile and 4-isothiocyanatophenyl 4-pentylbicyclo [2.2.2] octane-1-carboxylate nematic liquid crystals and their mixtures prepared in chloroform and dichloromethane were studied at room temperature. The dipole moments of the ground states of the all samples were calculated according to the Guggenheim–Smith method. The dipole moments of their excited states were determined with the help of the Lippert equation by measuring the absorption and fluorescence spectra, solvent polarity and refractive index values. It was determined that dipole moments of the excited states were higher than those of the ground states. Moreover, the dipole moments of the ground and excited states of two nematic liquid crystals were also estimated by using molecular mechanic method (Gaussian09 program (DFT/B3LYP 6-31G(dp)). The results obtained are interpreted in detail. 相似文献
20.
Guiffo-Soh G Hernandez B Coïc YM Boukhalfa-Heniche FZ Fadda G Ghomi M 《The journal of physical chemistry. B》2008,112(4):1282-1289
Circular dichroism (CD) and Raman scattering were applied to the aqueous solution of minimalist LK peptides constructed with successive KL repeats leading to the following generic primary sequence: (KL)nK. Three peptides of this family, a 3-mer (n=1), a 9-mer (n=4), and a 15-mer (n=7), are analyzed in this report. Raman spectra of the 3-mer (KLK, a random chain) and its labile-hydrogen deuterated species yield a set of interesting information for analyzing longer peptides of this series. Although the CD spectrum of the 9-mer (KLKLKLKLK) reveals a signal traditionally assigned to a random structure, the corresponding Raman spectrum allows finding a mixture of conformations in solution, adopting predominantly beta-type structures. This fact proves the utility of Raman spectroscopy to eliminate eventual ambiguity concerning conformational assignments in peptides based only on the use of CD technique. Finally, the 15-mer (KLKLKLKLKLKLKLK) gives rise to CD and Raman spectra clearly assignable to a beta-type structure. On the basis of all the observed results on the 15-mer, we can confirm that this peptide may exist as isolated beta-strands at low concentration (sub-micromolar), flat-oriented at the air/water interface, whereas at high concentrations (millimolar), non-H-bonded immersible aggregates might be formed. A hypothetical model for these beta-strand aggregates could be proposed as stabilized by an interior hydrophobic core and a hydrophilic external face, formed by leucine and lysine side chains, respectively. 相似文献