全文获取类型
收费全文 | 8542篇 |
免费 | 244篇 |
国内免费 | 59篇 |
专业分类
化学 | 4915篇 |
晶体学 | 76篇 |
力学 | 332篇 |
综合类 | 16篇 |
数学 | 1353篇 |
物理学 | 2153篇 |
出版年
2022年 | 55篇 |
2021年 | 79篇 |
2020年 | 110篇 |
2019年 | 103篇 |
2018年 | 94篇 |
2017年 | 93篇 |
2016年 | 199篇 |
2015年 | 189篇 |
2014年 | 186篇 |
2013年 | 378篇 |
2012年 | 384篇 |
2011年 | 438篇 |
2010年 | 327篇 |
2009年 | 249篇 |
2008年 | 390篇 |
2007年 | 361篇 |
2006年 | 370篇 |
2005年 | 332篇 |
2004年 | 287篇 |
2003年 | 231篇 |
2002年 | 270篇 |
2001年 | 226篇 |
2000年 | 178篇 |
1999年 | 123篇 |
1998年 | 124篇 |
1997年 | 104篇 |
1996年 | 125篇 |
1995年 | 120篇 |
1994年 | 120篇 |
1993年 | 123篇 |
1992年 | 134篇 |
1991年 | 120篇 |
1990年 | 112篇 |
1989年 | 77篇 |
1988年 | 99篇 |
1987年 | 74篇 |
1986年 | 89篇 |
1985年 | 95篇 |
1984年 | 90篇 |
1983年 | 98篇 |
1982年 | 85篇 |
1981年 | 84篇 |
1980年 | 79篇 |
1979年 | 80篇 |
1978年 | 78篇 |
1977年 | 84篇 |
1976年 | 83篇 |
1975年 | 64篇 |
1974年 | 69篇 |
1973年 | 65篇 |
排序方式: 共有8845条查询结果,搜索用时 750 毫秒
201.
202.
We investigate the dynamics and mechanism of the IR-driven cis-trans isomerization of nitrous acid (HONO) in a low-temperature krypton matrix applying ultrafast time resolved IR spectroscopy. After excitation of the OH-stretching mode the trans HONO state decays biexponentially on a 8 and 260 ps time scale. The initially excited cis HONO state decays on a 20 ps time scale. Cis HONO isomerizes with 10% quantum yield on a 20 ps time scale to trans HONO. The quantum yield we observe is significantly smaller than the previously reported 100%, which could imply that additional, much slower reaction channels exist. We furthermore developed a four-dimensional model of the system, which includes the three proton intramolecular degrees of freedom of HONO fully quantum mechanically and one intermolecular translational degree of freedom of the molecule in the crystal cage. We find that cis-trans isomerization necessarily is accompanied by a translation of the molecule as a whole in the crystal cage. The translational degree of freedom tunes the intramolecular proton states of HONO with respect to each other. When resonances occur, the proton states might couple and transfer population. We suggest a possible reaction pathway, where the cis OH-stretch excited state first couples to a high cis torsional mode, which then may transfer almost instantaneously to the trans side. The model qualitatively explains all experimental observations. 相似文献
203.
J. Kučera J. Kučera A. R. Byrne A. R. Byrne J. Mizera J. Mizera M. Lučaníková M. Lučaníková Z. Řanda Z. Řanda 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):251-257
Summary Radiochemical neutron activation procedures using liquid-liquid extraction with tetraphenylarsonium chloride in chloroform
from 1M HCl and solid extraction with ALIQUAT 336 incorporated in a polyacrylonitrile binding matrix from 0.1M HCl were developed
for accurate determination of rhenium in biological and environmental samples at the sub-ng . g-1 level. Concentrations of Re in the range of 0.1 to 2.4 ng . g-1 were determined in several botanical reference materials (RM), while in a RM of road dust a value of ~10 ng . g-1 was found. Significantly elevated values of Re, up to 90 ng . g-1 were found in seaweed (brown algae). Results for Re in the brown algae Fucus vesiculosus in which elevated 99Tc values had previously been determined suggested possible competition between Re and Tc in the accumulation process. 相似文献
204.
A precise x-ray fluorescence method for the determination of sulphur in coat. The sample is mixed with calcium oxide and active carbon and is gradually heated to 900°C. After coding, lithium tetraborate and lead oxide are added and a prepared. The Pb Mα line is used as an internal standard for the KKα line. The results for coal have a relative standard deviation of approximately 1% and exhibit. 相似文献
205.
206.
LoSecco JM Bionta RM Biewitt G Bratton CB Casper D Chrysicopoulou P Claus R Cortez BG Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Haines TJ Jones TW Kielczewska D Kropp WR Learned JG Lehmann E Park HS Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak L Svoboda R van der Velde JC Wuest C 《Physical review letters》1985,54(21):2299-2301
207.
F. J. Coetzer T. C. Kotzé P. B. Kotzé F. J. Mostert P. van der Westhuizen 《Zeitschrift für Physik A Hadrons and Nuclei》1985,320(3):359-362
Detailed measurements on the 5p 4 S 3 2/0 and 5p~' 2 D 5 2/0 levels in Kr II are reported. Cascade effects were taken into account with the aid of the arbitrarily normalized decay curve (ANDC) technique. Experimental values are compared to values obtained by other investigators as well as to theoretical values. 相似文献
208.
209.
NMR spectra have been measured of the Li+, Na+ and K+ ion pairs of the indenyl carbanion in 1,2-dimethoxyethane and tetrahydrofuran as a function of temperature. The changes of the chemical shifts are explained in terms of the detailed structure of the ion pairs. The results in both solvents strongly suggest that in indenyl-Li+ the counterion is predominantly located over the six-membered ring. In THF the preferred position of the cations Na+ and K+ in the contact ion pairs seems to be the five-membered ring. 相似文献
210.
Büttner K Bernhardt J Scharf C Schmid R Mäder U Eymann C Antelmann H Völker A Völker U Hecker M 《Electrophoresis》2001,22(14):2908-2935
Proteomics relying on two-dimensional (2-D) gel electrophoresis of proteins followed by spot identification with mass spectrometry is an excellent experimental tool for physiological studies opening a new perspective for understanding overall cell physiology. This is the intriguing outcome of a method introduced by Klose and O'Farrell independently 25 years ago. Physiological proteomics requires a 2-D reference map on which most of the main proteins were identified. In this paper, we present such a reference map with more than 300 entries for Bacillus subtilis proteins with an isoelectric point (pI) between 4 and 7. The most abundant proteins of exponentially growing cells were compiled and shown to perform mainly housekeeping functions in glycolysis, tricarboxylic acid cycle (TCC), amino acid biosynthesis and translation as well as protein quality control. Furthermore, putative post-translational modifications were shown at a large scale, with 47 proteins in total forming more than one spot. In a few selected cases evidence for phosphorylation of these proteins is presented. The proteome analysis in the standard pI range was complemented by either stretching the most crowded regions in a narrow pH gradient 4.5-5.5, or by adding other fractions of the total B. subtilis proteome such as alkaline proteins as well as extracellular proteins. A big challenge for future studies is to provide an experimental protocol covering the fraction of intrinsic membrane proteins that almost totally escaped detection by the experimental procedure used in this study. 相似文献