全文获取类型
收费全文 | 11039篇 |
免费 | 1530篇 |
国内免费 | 1453篇 |
专业分类
化学 | 8751篇 |
晶体学 | 465篇 |
力学 | 316篇 |
综合类 | 72篇 |
数学 | 115篇 |
物理学 | 4303篇 |
出版年
2024年 | 24篇 |
2023年 | 143篇 |
2022年 | 436篇 |
2021年 | 415篇 |
2020年 | 511篇 |
2019年 | 425篇 |
2018年 | 367篇 |
2017年 | 396篇 |
2016年 | 535篇 |
2015年 | 486篇 |
2014年 | 493篇 |
2013年 | 885篇 |
2012年 | 598篇 |
2011年 | 789篇 |
2010年 | 614篇 |
2009年 | 680篇 |
2008年 | 633篇 |
2007年 | 776篇 |
2006年 | 715篇 |
2005年 | 595篇 |
2004年 | 511篇 |
2003年 | 442篇 |
2002年 | 360篇 |
2001年 | 284篇 |
2000年 | 275篇 |
1999年 | 243篇 |
1998年 | 199篇 |
1997年 | 204篇 |
1996年 | 178篇 |
1995年 | 125篇 |
1994年 | 115篇 |
1993年 | 91篇 |
1992年 | 102篇 |
1991年 | 54篇 |
1990年 | 53篇 |
1989年 | 45篇 |
1988年 | 34篇 |
1987年 | 37篇 |
1986年 | 32篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1972年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
M. Gutowski I. Dabkowska J. Rak S. Xu J.M. Nilles D. Radisic K.H. Bowen Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):431-439
The photoelectron spectra (PES) of anions of uracil-glycine and uracil-phenylalanine complexes reveal broad features with
maxima at 1.8 and 2.0 eV. The results of ab initio density functional B3LYP and second order M?ller-Plesset theory calculations indicate that the excess electron occupies a
π* orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT)
from the carboxylic group of glycine to the O8 atom of uracil. As a result, the four most stable structures of the anion of
uracil-glycine complex can be characterized as the neutral radical of hydrogenated uracil solvated by the anion of deprotonated
glycine. The similarity between the PES spectra for the uracil complexes with glycine and phenylalanine suggests that the
BFPT is also operative in the case of the latter anionic species. The BFPT to the O8 atom of uracil may be related to the
damage of nucleic acid bases by low energy electrons because the O8 atom is involved in a hydrogen bond with adenine in the
standard Watson-Crick pairing scheme.
Received 6 April 2002 Published online 13 September 2002 相似文献
12.
Tony Donnelly 《Applied Surface Science》2006,252(13):4445-4448
Ultra-thin (0.5-5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a 26 ns KrF excimer laser at 1 J cm−2. The deposition was controlled using a Langmuir ion probe and a quartz crystal thickness monitor. Transmission electron microscopy showed that the films are not continuous, but are structured on nanometer size scales. Optical absorption spectra showed the expected surface plasmon resonance feature, which shifted to longer wavelength and increased in strength as the equivalent film thickness was increased. It is shown that Maxwell Garnett effective medium theory can be used to calculate the main features of optical absorption spectra. 相似文献
13.
The Li oxides species formed on Li over-deposited V2O5 thin film surfaces have been studied by using X-ray and UV induced photoelectron spectroscopy (XPS and UPS). The photoelectron spectroscopic data show that the Li over-deposited V2O5 system itself is not stable. Further chemical decomposition reactions are taken place even under UHV conditions and lead to form Li2O and Li2O2 compounds on the surface. The formation of Li2O2 causes to arise an emission line at about 11.3 eV in the valence band spectra. 相似文献
14.
A short and efficient RCM route is reported for the construction of the key nine-membered B ring of eleutherobin starting from the readily available 1,2,5,6-diisopropylidene-d-glucose. 相似文献
15.
燃煤烟气中AsSePb的形态分布及SCl元素对其形态分布的影响 《燃料化学学报》2003,48(11):1298-1309
基于化学热力学平衡分析方法,计算分析了燃煤烟气中重金属As、Se、Pb的形态分布规律,研究了S、Cl等元素对As、Se、Pb的形态分布规律的影响。结果表明,氧化性气氛下,As以As2O5、As4O6、AsO等氧化物的形式存在;Se主要以SeO2形式存在;Pb在1000 K以下主要是固态PbSO4,1200 K以上为气态PbO。还原性气氛下,As在较低温度时为固态As2S2,900-1400 K以As2、AsS、AsN气体共存,2000 K以上全部转化为气态AsO。Se在1100 K以下主要以气态H2Se存在,1100 K开始生成SeS和Se2气体,1800 K时主要是气态Se和少量气态SeO;Pb在中低温时主要是PbS,1800 K以上气态Pb为主要存在形态。S在还原性气氛下增大了AsS(g)、PbS(g)、SeS(g)的比例,氧化性气氛下对As、Se、Pb形态分布基本无影响;Cl无论在氧化还是还原气氛下对As、Se影响均较小,但对Pb的形态分布影响较大。 相似文献
16.
17.
《Magnetic resonance in chemistry : MRC》2003,41(9):731-734
An NMR study of one new and several known abietane diterpenes isolated from the roots of Aegiphila lhotzkyana is described. In addition to 1D NMR, several 2D shift‐correlated NMR pulse sequences (1H–1H‐COSY, NOESY, HMQC and HMBC) were used to establish all the structures, and unambiguously perform the 1H and 13C chemical shift assignments of the new natural diterpene and three derivatives, the NMR data for which have not been reported previously. Revision of current data assignment for teuvincenone H is also suggested. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
18.
Dinesh Topwal U. Manju Sugata Ray S. Raj D. D. Sarma S. R. Krishnakumar M. Bertolo S. La Rosa G. Cautero 《Journal of Chemical Sciences》2006,118(1):87-92
Disordered Sr2FeMoO6 shows a drastic reduction in saturation magnetization compared to highly ordered samples, moreover magnetization as a function
of the temperature for different disordered samples shows qualitatively different behaviours. We investigate the origin of
such diversity by performing spatially resolved photoemission spectroscopy on various disordered samples. Our results establish
that extensive electronic inhomogeneity, arising most probably from an underlying chemical inhomogeneity in disordered samples, is
responsible for the observed magnetic inhomogeneity. It is further pointed out that these inhomogeneities are connected with
composition fluctuations of the type Sr2Fe1+x
Mo1-x
O6 with Fe-rich (x > 0) and Mo-rich (x < 0) regions.
Dedicated to Prof J Gopalakrishnan on his 62nd birthday. 相似文献
19.
In photochemical vapor deposition of aluminum film on silicon using dimethylaluminum hydride, (CH3)2AlH, a surface reaction dominated below a (CH3)2AlH pressure of 0.3 m Torr at 200°C, which was induced only with the 160 nm band emitted from a deuterium lamp. A gas-phase reaction occurred above 0.3 mTorr at 200°C, which could be induced by both 160 nm and 240 nm emission bands from the lamp. To distinguish between surface ad gas-phase reactions, a thickness profile was used. At 240°C the surface reaction could be induced even by the 240 nm band, while the deposits formed under illumination of the two bands were thinner than those obtained with only the 240 nm band, indicating occurrence of vacuum ultraviolet (VUV)-enhanced desorption. The mechanism responsible for the observed wavelength dependence in unclear. The electrical resistivity of the films deposited at 200°C was 4.5 μΩ cm, which did not change with wavelength. 相似文献
20.
Gabor Schmera Adi Bulsara David Pierson Frank Moss Enrico Di Cera 《Journal of statistical physics》1993,71(5-6):1179-1190
We consider the class of experiments which can be characterized by a Fokker-PIanck dynamics corresponding to the overdamped motion of a state point in a suitable stochastic potential. We assume that the general form of the potential is known (or can be guessed with reasonable accuracy), but that its parameters are to be determined experimentally by measurements made with a noisy instrument. This possible method for determining the potential parameters, which exploits the system's own internal stochastic motion in order to explore rapidly its available parameter space, is substantially more efficient than traditional methods involving time averages of single point measurements, and yet does not appear to have been previously considered. The method could be important when, for example, the experiment must be completed in a limited time owing either to the expense of the experimental materials or to the temporary stationarity of the preparation, situations which are commonly encountered in experimental biochemistry and biology. 相似文献