全文获取类型
收费全文 | 247197篇 |
免费 | 5065篇 |
国内免费 | 776篇 |
专业分类
化学 | 138801篇 |
晶体学 | 2643篇 |
力学 | 9577篇 |
综合类 | 8篇 |
数学 | 32147篇 |
物理学 | 69862篇 |
出版年
2021年 | 1839篇 |
2020年 | 2223篇 |
2019年 | 2206篇 |
2018年 | 2700篇 |
2017年 | 2499篇 |
2016年 | 4888篇 |
2015年 | 4128篇 |
2014年 | 4717篇 |
2013年 | 12509篇 |
2012年 | 11226篇 |
2011年 | 12806篇 |
2010年 | 7926篇 |
2009年 | 7641篇 |
2008年 | 11505篇 |
2007年 | 11408篇 |
2006年 | 10718篇 |
2005年 | 10076篇 |
2004年 | 8989篇 |
2003年 | 7574篇 |
2002年 | 7196篇 |
2001年 | 7382篇 |
2000年 | 5862篇 |
1999年 | 4393篇 |
1998年 | 3377篇 |
1997年 | 3257篇 |
1996年 | 3449篇 |
1995年 | 2884篇 |
1994年 | 2882篇 |
1993年 | 2723篇 |
1992年 | 3072篇 |
1991年 | 2908篇 |
1990年 | 2681篇 |
1989年 | 2533篇 |
1988年 | 2539篇 |
1987年 | 2428篇 |
1986年 | 2292篇 |
1985年 | 3412篇 |
1984年 | 3356篇 |
1983年 | 2671篇 |
1982年 | 2915篇 |
1981年 | 2800篇 |
1980年 | 2685篇 |
1979年 | 2628篇 |
1978年 | 2694篇 |
1977年 | 2594篇 |
1976年 | 2608篇 |
1975年 | 2523篇 |
1974年 | 2452篇 |
1973年 | 2531篇 |
1972年 | 1414篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Fotios C. Paliogiannis 《Rendiconti del Circolo Matematico di Palermo》1995,44(1):21-44
In this paper, the spectral theorem and related characterizations of the spectrum and the spectral projections for bounded self adjoint and normal operators on a Hilbert space, are proved in purely topological —function theoretic terms. The basis for such a development, is the Gelfand—Naimark theorem for commutativeC *-algebras and the fact that the structure space of the (abelian) von Neumann algebra generated by the operator is a Stonean space. 相似文献
992.
993.
This paper deals with a model of time-dependent double diffusive convection in Darcy flow. In particular it is concerned with the spatial decay of solutions when the flow is confined to a semi-infinite cylinder. Decay bounds for an energy expression are derived. 相似文献
994.
995.
We have studied hydrogen adsorption on the Ge(1 1 1) c(2 × 8) surface using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES). We find that atomic hydrogen preferentially adsorbs on rest atom sites. The neighbouring adatoms appear higher in STM images, which clearly indicates a charge transfer from the rest atom states to the adatom states. The surface states near the Fermi-level have been followed by ARPES as function of H exposure. Initially, there is strong emission from the rest atom states but no emission at the Fermi-level which confirms the semiconducting character of the c(2 × 8) surface. With increasing H exposure a structure develops in the close vicinity of the Fermi-level. The energy position clearly indicates a metallic character of the H-adsorbed surface. Since the only change in the STM images is the increased brightness of the adatoms neighbouring a H-terminated rest atom, we identify the emission at the Fermi-level with these adatom states. 相似文献
996.
X-ray reflectivity (XRR), X-ray fluorescence (XRF) and small angle X-ray scattering (SAXS) techniques are used to the monitoring of Cu/porous low κ processes, which are developed for the next generation (≤65 nm) integrated circuits. Sensitivity of XRR and XRF is sufficient to detect drifts of the copper barrier layer, copper seed layer and Cu CMP (chemical-mechanical polishing) processes. Their metrology key parameters comply with production requirements. SAXS allows determining the pore structure of low κ films: average pore size and pore size distribution. 相似文献
997.
Z.J. Liu H.H. Long W.C. Ye X.X. Zou Z.L. Qin E.P. Li J.S. Chen 《Journal of magnetism and magnetic materials》2006
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated. 相似文献
998.
Nickel and cobalt films illustrate alternative Bloch lines with cap switches. The strip magnetic domains become zigzag and bubbling cells for Ni and Co films, respectively, under an external field of 1.5 T. The magnetoresistances (MR) for currents parallel (CIW) to the domain walls is 15% less than those of the perpendicular (CPW) case. We also studied the magneto size effect by applying the magnetic field normal to the surface, from which the Sondheimer oscillation appears attributing to periodic striking of the surface for electrons traveling in circular motion on a plane canting to the surface. The experiments can be expressed by the magneto size effect inherited with very small specularity parameters. 相似文献
999.
1000.
Inmaculada García Cuesta José Sánchez-Marín Alfredo M J Sánchez de Merás 《Chemphyschem》2006,7(2):508-513
Investigations into the charge-separated states and electron-transfer transitions in tetracyanoethylene (TCNE) complexes have recently generated much interest. In this work we present theoretical calculations showing that the most stable structure of the dianion TCNE2- has D2d symmetry in vacuum as well as in the solvents dichloromethane and acetonitrile. By means of the coupled cluster linear response, we compute the vertical electronic spectrum in both the gas phase and solution. The theoretical results are compared to the experimental data and good agreement is achieved. 相似文献