全文获取类型
收费全文 | 44599篇 |
免费 | 6391篇 |
国内免费 | 4151篇 |
专业分类
化学 | 29475篇 |
晶体学 | 602篇 |
力学 | 1872篇 |
综合类 | 189篇 |
数学 | 1445篇 |
物理学 | 21558篇 |
出版年
2024年 | 81篇 |
2023年 | 424篇 |
2022年 | 1247篇 |
2021年 | 1211篇 |
2020年 | 1447篇 |
2019年 | 1363篇 |
2018年 | 1273篇 |
2017年 | 1438篇 |
2016年 | 2129篇 |
2015年 | 2035篇 |
2014年 | 2390篇 |
2013年 | 4192篇 |
2012年 | 2878篇 |
2011年 | 3085篇 |
2010年 | 2493篇 |
2009年 | 2982篇 |
2008年 | 2827篇 |
2007年 | 3051篇 |
2006年 | 2719篇 |
2005年 | 2282篇 |
2004年 | 1991篇 |
2003年 | 1729篇 |
2002年 | 1363篇 |
2001年 | 1199篇 |
2000年 | 1129篇 |
1999年 | 955篇 |
1998年 | 807篇 |
1997年 | 694篇 |
1996年 | 629篇 |
1995年 | 537篇 |
1994年 | 452篇 |
1993年 | 385篇 |
1992年 | 354篇 |
1991年 | 231篇 |
1990年 | 160篇 |
1989年 | 145篇 |
1988年 | 188篇 |
1987年 | 107篇 |
1986年 | 80篇 |
1985年 | 75篇 |
1984年 | 68篇 |
1983年 | 27篇 |
1982年 | 60篇 |
1981年 | 42篇 |
1980年 | 45篇 |
1979年 | 27篇 |
1978年 | 21篇 |
1976年 | 15篇 |
1973年 | 23篇 |
1972年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Jean-Marcel Colmont François Rohart Jean-Pierre Bouanich 《Journal of Molecular Spectroscopy》2006,238(1):98-107
Extensive experiments on the K = 3 component of the J = 12-11 rotational transition of acetonitrile CH3C14N, located near 220.7 GHz, were performed at different temperatures in the range 235-350 K. They allow determining the N2-, H2-, and He-broadening coefficients, as well as their temperature dependences. More specific measurements on all the K-components of the involved transition perturbed by N2 at 303 K allow to point out a clear decreasing of the broadening coefficient with increasing K. Narrowing effects are clearly observed, and experimental lines were analysed both with Voigt and speed dependent Voigt profiles; but no exhaustive lineshape study was carried out. All the experimental parameters are compared with results derived from a semiclassical calculation of collisional interactions, including electrostatic, induction, and dispersion energy contributions. 相似文献
152.
薄原子蒸汽膜的单光子Dcike窄化吸收光谱可以拓展到双光子情形,以级联三能级系统为例,从理论上得到了亚多普勒结构的双光子吸收光谱,其线型表现出和单光子过程相似的与膜厚和探测光波长的比值(L/λ)相关的周期性.当L/λ=(2n+1)/2(膜厚为半波长的奇数倍)时,吸收谱线窄化现象明显.当L/λ=2n/2(膜厚为半波长的偶数倍)时,单光子情形的谱线窄化现象消失,而双光子情形的谱线仍表现为亚多普勒结构,尤其在异侧入射的情形下,可以获得极窄的双光子谱线结构. 这种结构来自原子与腔壁碰撞的消激发效应和双光子过程的抽运-探测机制的贡献.
关键词:
薄原子蒸汽膜
双光子光谱
Dicke窄化 相似文献
153.
A current interpretation of XPS spectra of Ni metal assumes that the main 6 eV satellite is due to a two hole c3d94s2 (c is a core hole) final state effect. We report REELS observation in AES at low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6 eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd9L and the unscreened cd8 final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH)2, NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni2+ and Ni3+ simulate the main line and satellite structures for Ni(OH)2 and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed. 相似文献
154.
M.Yu. Tretyakov V.V. Parshin M.A. Koshelev A.P. Shkaev A.F. Krupnov 《Journal of Molecular Spectroscopy》2006,238(1):91-97
Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′ka′, kc′-Jka, kc = 51,5-42,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 31,3-22,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given. 相似文献
155.
Due to the discovery of Au as a catalyst for low temperature CO oxidation, the adsorption of CO on Au surfaces has attracted a lot of attention recently. On stepped and rough single crystal surfaces as well as on deposited particles two characteristic desorption states above 100 K have been observed via TPD. We have studied Au deposits on graphite in order to elucidate the nature of these desorption peaks in more detail. For this purpose, Au was deposited at 100 K and 300 K on HOPG as a weakly interacting support. In analogy to other supports, we obtain two desorption states (∼140 K and ∼170 K) whose relative intensities depend strongly on the deposition temperature with the high temperature peak being much more pronounced for the 100 K deposits. After annealing to 600 K, both states drastically lose intensity. XP spectra, on the other hand, show virtually no decrease of the Au 4f intensity as would be expected for desorption or significant changes of the particle morphologies. We conclude that both desorption peaks are defect-related and connected with under-coordinated Au atoms that are lost for the most part upon annealing. These sites could be located at the perimeter of dendritic islands or on small, defect-rich particles in addition to larger particles not adsorbing CO at 100 K. Preliminary STM results are in favour of the second interpretation. 相似文献
156.
We have performed total-energy calculations to study theoretical scanning tunneling microscopy (STM) images of the Si(1 1 1)3 × 2 surfaces induced by the adsorption of alkaline-earth metals (AEMs). Previously, in a series of works on Ba/Si(1 1 1) system, we have found that the observed Si(1 1 1)3 × 1-Ba LEED phase indeed has a 3 × 2 periodicity with a Ba coverage of 1/6 ML and the HCC substrate structure. Based on results of the Ba case, we proposed that the HCC structure is also adopted for other AEM atoms, which was confirmed by our recent work. In this paper, we mainly report the STM simulations for different AEM systems to compare with existing experimental data. We discuss the difference in the detailed STM images for different AEM adsorbates. Especially, the difference in filled-state images between Mg and other AEM atoms is attributed to the strong Mg-Si interaction. 相似文献
157.
Cr-doped mullites were prepared from single-phase precursors containing up to 9.60 wt% Cr2O3 using a sol-gel technique followed by thermal treatment. Particle induced X-ray emission spectroscopy and X-ray powder diffraction were used to characterize the samples. Mullites were orthorhombic, space group Pbam. Cr doping caused the increase of unit-cell parameters. Strongest expansion was noticed along c-axis followed by a and b (Δc/c=0.089, Δa/a=0.061, Δb/b=0.045% per mole Cr2O3). A second phase, namely θ-(Al,Cr)2O3, was revealed by XRD in the sample containing 9.60 wt% Cr2O3. The structure of mullites was refined by the Rietveld method, location of Cr3+ was performed by the EPR spectroscopy. At low chromium doping level (Cr2O3 content less than ∼5 wt%) Cr3+ ions were substituted for Al3+ in the AlO6 octahedra of the mullite structure (M1 site). For higher doping level, Cr3+ ions were additionally substituted for Al3+ in the AlO6 octahedra of the second phase [θ-(Al,Cr)2O3 at 1400 °C, or α-(Al,Cr)2O3 at 1600 °C] which segregated in the system. Substitution of Cr3+ for Al3+ on M1 site in the mullite structure resulted in increase of average distances in (M1)O6 octahedron and decrease of average distances in T*O4 tetrahedron, while average distances in TO4 tetrahedron stayed almost constant. 相似文献
158.
M. Esmaeelpour 《Applied Surface Science》2006,252(18):6353-6359
This research investigates the effect of ion implantation dosage level and further thermal treatment on the physical characteristics of chromium coatings on Si(1 1 1) substrates. Chromium films had been exposed to nitrogen ion fluencies of 1 × 1017, 3 × 1017, 6 × 1017 and 10 × 1017 N+ cm−2 with a 15 keV energy level. Obtained samples had been heat treated at 450 °C at a pressure of 2 × 10−2 Torr in an argon atmosphere for 30 h. Atomic force microscopy (AFM) images showed significant increase in surface roughness as a result of nitrogen ion fluence increase. Secondary ion mass spectroscopy (SIMS) studies revealed a clear increased accumulation of Cr2N phase near the surface as a result of higher N+ fluence. XRD patterns showed preferred growth of [0 0 2] and [1 1 1] planes of Cr2N phase as a result of higher ion implantation fluence. These results had been explained based on the nucleation-growth of Cr2N phase and nitrogen atoms diffusion history during the thermal treatment process. 相似文献
159.
160.