全文获取类型
收费全文 | 7214篇 |
免费 | 318篇 |
国内免费 | 79篇 |
专业分类
化学 | 4313篇 |
晶体学 | 221篇 |
力学 | 196篇 |
综合类 | 4篇 |
数学 | 1046篇 |
物理学 | 1831篇 |
出版年
2022年 | 74篇 |
2021年 | 68篇 |
2020年 | 94篇 |
2019年 | 144篇 |
2018年 | 102篇 |
2017年 | 99篇 |
2016年 | 144篇 |
2015年 | 125篇 |
2014年 | 187篇 |
2013年 | 565篇 |
2012年 | 317篇 |
2011年 | 360篇 |
2010年 | 242篇 |
2009年 | 214篇 |
2008年 | 247篇 |
2007年 | 254篇 |
2006年 | 221篇 |
2005年 | 181篇 |
2004年 | 176篇 |
2003年 | 203篇 |
2002年 | 171篇 |
2001年 | 101篇 |
2000年 | 96篇 |
1999年 | 66篇 |
1997年 | 70篇 |
1996年 | 79篇 |
1995年 | 85篇 |
1994年 | 82篇 |
1993年 | 84篇 |
1992年 | 98篇 |
1991年 | 88篇 |
1990年 | 76篇 |
1989年 | 110篇 |
1988年 | 76篇 |
1987年 | 70篇 |
1986年 | 81篇 |
1985年 | 126篇 |
1984年 | 119篇 |
1983年 | 93篇 |
1982年 | 98篇 |
1981年 | 101篇 |
1980年 | 85篇 |
1979年 | 98篇 |
1978年 | 74篇 |
1977年 | 101篇 |
1976年 | 79篇 |
1975年 | 86篇 |
1974年 | 92篇 |
1973年 | 97篇 |
1972年 | 57篇 |
排序方式: 共有7611条查询结果,搜索用时 31 毫秒
261.
C.N.R. Rao D.D. Sarma P.R. Sarode E.V. Sampathkumaran L.C. Gupta R. Vijayaraghavan 《Chemical physics letters》1980,76(3):413-415
The valence state of Yb in some of its intermetallics, YbNi2Ge2, YbCu2Si2 and YbPd2Si2 has been investigated by LIII(Yb) absorption edges and X-ray pnotoelectron spectra in the 4f and 4d regions. These studies establish the presence of mixed valence in all three systems and illustrate the utility of 4f and 4d spectra in the study of mixed valence in Yb compounds. 相似文献
262.
263.
264.
New Experimental Insight into the Nature of Metal−Metal Bonds in Digallium Compounds: J Coupling between Quadrupolar Nuclei
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Libor Kobera Scott A. Southern Dr. Gyandshwar Kumar Rao Prof. Dr. Darrin S. Richeson Prof. Dr. David L. Bryce 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9565-9573
Multiple bonding between atoms is of ongoing fundamental and applied interest. Here, we report a multinuclear (1H, 13C, and 71Ga) solid‐state magnetic resonance spectroscopic study of digallium compounds which have been proposed, albeit somewhat controversially, to contain single, double, and triple Ga?Ga bonds. Of particular relevance to the nature of these bonds, we have carried out two‐dimensional 71Ga J/D‐resolved NMR experiments which provide a direct measurement of J(71Ga,71Ga) spin–spin coupling constants across the gallium?gallium bonds. When placed in the context of clear‐cut experimental data for analogous singly, doubly, and triply bonded carbon spin pairs or boron spin pairs, the 71Ga NMR data clearly support the notion of a different bonding paradigm in the gallium systems. Our findings are consistent with an increasing role across the purported gallane–gallene–gallyne series for classical and/or slipped π‐type bonding orbitals. 相似文献
265.
Abstract On radiolysis tris(acetylacetonato) cobalt(III) in aqueous solutions is found to get reduced by reaction with (1) hydrated electrons, (2) H atoms, (3) OH radicals and (4) C2H2OH radicals. The bimolecular rate constants for the first three reactions, determined by competition kinetics are: 4 × 1010, 2.3 × 109 and 4.7 × 109 M?1sec?1 respectively. Absorption spectra of the irradiated solutions indicate the formation of bis(acetylacetonato) cobalt(II) from reaction (1), but not from (3). The total cobaltous yield in air-free solutions is given byG(Co++) = 5.6 and 6.5 at pH 6.5 and 1 respectively. It appears that Geaq- ∽ H + GoH ∽ 2.8 in neutral solutions. Considerations of material balance for the primary yields of radiolysis of water suggest the possibility that the so-called independent H-atoms in neutral solutions are probably excited water molecules or ion-pairs. 相似文献
266.
267.
268.
A simple and convenient methodology for the synthesis of N,N′-disubstituted ureas from primary amines by a heterogenized catalyst montmorillonitebipyridinepalladium (II)acetate for the first time at room temperature and atmospheric pressure is described. 相似文献
269.
P. R. Alapati D. M. Potukuchi N. V. S. Rao V. G. K. M. Pisipati A. S. Paranjpe U. R. K. Rao 《Liquid crystals》2013,40(11):1461-1479
Abstract We report X-ray diffraction, density, ultrasonic velocity and refractive index studies in the N(p-n-pentyloxy benzylidene) p-n-alkylaniline compounds, viz. 50.5, 50.6 and 50.7. The nematic-smectic A (NA) transition is found to be weak first order in 50.6 while it is second order in 50.5 and 50.7. The salient features observed are cybotactic clusters in the nematic phase in all the compounds, molecular tilt which was inferred due to the end alkyl chains tilt causing orienta-tional disorder (smaller orientational order parameters ‘s’ than expected) in smectic A phase, smectic F phase and large tilt angle variation in smectic C phase in a small temperature range in 50.5. The observed results are discussed in the light of available data in other n0.m compounds. 相似文献
270.
We report here our results on the spectroscopic and elemental analysis of femtosecond (fs) laser-modified regions in polymers of polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) in the context of defect formation and emission in the visible region. Different physical and chemical models are used to explain the changes in modified regions. We found that the emission intensity, recorded from the fs-modified regions of polymers, decreased over time to a constant value. We also demonstrate that these materials are suitable for the preparation of the microstructures en route for light guiding applications. The fs laser-irradiated regions exhibited paramagnetic behavior as was confirmed from electron spin resonance studies through the formation of peroxide-type free radicals. Raman mapping was performed in the modified regions which consisted of defects and found that the modulations in intensity are predominant in the central portion of the structure compared to edges. Elemental analysis has been performed in the modified regions using field emission scanning electron microscope instrument and energy-dispersive X-ray absorption spectroscopy to estimate the percentage contents of individual elements which resulted in defect formation such as paramagnetic and optical centers. 相似文献