全文获取类型
收费全文 | 1390篇 |
免费 | 35篇 |
国内免费 | 6篇 |
专业分类
化学 | 968篇 |
晶体学 | 6篇 |
力学 | 25篇 |
数学 | 213篇 |
物理学 | 219篇 |
出版年
2023年 | 9篇 |
2022年 | 33篇 |
2021年 | 35篇 |
2020年 | 30篇 |
2019年 | 24篇 |
2018年 | 33篇 |
2017年 | 20篇 |
2016年 | 50篇 |
2015年 | 34篇 |
2014年 | 41篇 |
2013年 | 74篇 |
2012年 | 63篇 |
2011年 | 72篇 |
2010年 | 44篇 |
2009年 | 39篇 |
2008年 | 72篇 |
2007年 | 53篇 |
2006年 | 45篇 |
2005年 | 43篇 |
2004年 | 39篇 |
2003年 | 43篇 |
2002年 | 39篇 |
2001年 | 19篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 12篇 |
1997年 | 18篇 |
1996年 | 18篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1987年 | 8篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 8篇 |
1918年 | 8篇 |
1901年 | 11篇 |
1895年 | 6篇 |
1894年 | 6篇 |
1888年 | 6篇 |
1885年 | 9篇 |
排序方式: 共有1431条查询结果,搜索用时 19 毫秒
1.
A. A. Sonzogni A. S. M. A. Romo H. O. Mosca S. J. Nassiff 《Journal of Radioanalytical and Nuclear Chemistry》1993,170(1):143-156
The stacked foil technique was used in combination with γ-ray spectroscopy to obtain excitation functions for the production of different nuclei using natural vanadium as target and 85 MeV α-particles and 46.5 MeV deuterons as projectiles. The data are compared with theoretical predictions provided by an equilibrium and pre-equilibrium reaction model. In most cases the theoretical predictions seriously under-estimated the measured cross sections. 相似文献
2.
K. Daum W. Rhode P. Bareyre R. Barloutaud G. Chardin B. Degrange J. Ernwein B. Kuznik H. Meyer L. Mosca L. Moscoso O. Perdereau M. Schubnell S. Tisserant Y. Wei 《Zeitschrift fur Physik C Particles and Fields》1995,66(3):417-428
The combined analysis of the final event set of data on neutrino interactions inside the detector, upward going stopping muons and horizontal muons recorded in the Fréjus experiment is presented. The absolute atmospheric neutrino spectra in the energy range
for electron neutrinos and
for muon neutrinos are determined. Based on the parameterization of Volkova for thev
µ
a spectral index of =2.66±0.05 is obtained from the ratio of horizontal muons over upward going stopping muons and from the measurement of the energy loss of horizontal muons inside the detector. The neutrino spectra are compared with various flux calculations. They do not show any evidence for neutrino oscillations in agreement with earlier analyses of the Fréjus data.Now atUniversity of Michigan, Ann Arbor, USA 相似文献
3.
A number of polyfunctionalized cis-bicycio ¦3.3.0¦octanes have been synthesized starting from the tricyclic key intermediate which was obtained by the intramolecular cyclopropanation reaction of the diazo keto ester . Selected stereocontrolled transformations of using nucleophiles and electrophiles have been studied for the preparation of the title compounds. 相似文献
4.
On the biogenesis of betacyanins. Expaiments with [2-14C]-dopaxanthine Labelled dopaxanthine is prepared from betanin by a double exchange procedure replacing first its cyclodopa part by diethylamine and effecting the second exchange with 2-[14C]-dopa on the purified intermediate ‘DEA-betalain’; the specific activity delivered with the dopa allowed accurate determination of ? in the electronic spectrum of dopaxanthine (λmax 488 nm, ? = 41.800). The C(2)-labelled dopaxanthine is incubated into the fruits of Opuntia bergeriana. The incorporation rates into betanin are found to correspond approximately to those obtained in earlier experiments with labelled dopa alone: Only 1--5% of the label showed up in the cyclodopa moiety of the betanin (which is isolated as cyclodopa-glucoside) whereas 99--95% of the radioactivity was associated with the betalamic acid part (recovered in form of indicaxanthine). 相似文献
5.
6.
Hugo Bonau 《Macromolecular Symposia》1992,57(1):243-252
Since the end of 1990, the “Arbeitsqemeinschaft PVC Bodenbelags Recycling (Society for the recycling of PVC floorings, AgPR)” collects and recycles PVC floor coverings in Germany. AgPR is an activity as well of PVC producers as of PVC floor covering manufacturers. 19 European companies participate in this venture. AgPR collects used floorings in several areas of Germany. It also pays 150 DM/t of PVC flooring delivered to its recycling plant in Großefehn. This plant has a capacity for recycling 5000 t/a. The used floor coverings are comminuted, ground to powder size and after that reused to manufacture new floor coverings. 相似文献
7.
Roberto Mattioli Daniel Di Risola Rodolfo Federico Alessia Ciogli Francesco Gasparrini Claudio Villani Mario Fontana Anna Maggiore Maria dErme Luciana Mosca Antonio Francioso 《Molecules (Basel, Switzerland)》2022,27(7)
trans-Resveratrol is a natural bioactive compound with well-recognized health promoting effects. When exposed to UV light, this compound can undergo a photochemically induced trans/cis isomerization and a 6π electrochemical cyclization with the subsequent formation of 2,4,6-trihydroxyphenanthrene (THP). THP is a potentially harmful compound which can exert genotoxic effects. In this work we improved the chromatographic separation and determination of the two resveratrol isomers and of THP by using a non-commercial pentafluorophenyl stationary phase. We assessed the effect of natural deep eutectic solvents (NaDES) as possible photo-protective agents by evaluating cis-resveratrol isomer and THP formation under different UV-light exposure conditions with the aim of enhancing resveratrol photostability and inhibiting THP production. Our results demonstrate a marked photoprotective effect exerted by glycerol-containing NaDES, and in particular by proline/glycerol NaDES, which exerts a strong inhibitory effect on the photochemical isomerization of resveratrol and significantly limits the formation of the toxic derivative THP. Considering the presence of resveratrol in various commercial products, these results are of note in view of the potential genotoxic risk associated with its photochemical degradation products and in view of the need for the development of green, eco-sustainable and biocompatible resveratrol photo-stable formulations. 相似文献
8.
Influence of the carrier gas on HfCl4-H2O and ZrCl4-H2O atomic layer processes was investigated. The growth rates of HfO2 and ZrO2 decreased with increasing flow rate and pressure of the N2 carrier gas. Data of real-time quartz crystal microbalance measurements demonstrated that the effect observed was mainly due to influence of carrier gas on surface reactions and the role of overlapping the precursor pulses was negligible. At the same increase of the carrier gas mass flow, the increase of the linear flow rate led to more significant changes of thin-film properties than the increase of the carrier gas pressure did. Thin films with higher density, higher refractive index and, particularly, lower concentration of residual chlorine were obtained at higher carrier gas flow rates. Increase of the carrier gas flow rate also resulted in a higher concentration of a metastable phase in HfO2 thin films deposited at 300 °C. 相似文献
9.
Menzel D Fastl H Graf R Hellbrück J 《The Journal of the Acoustical Society of America》2008,123(5):2477-2479
This experiment investigates the effect of images of differently colored sports cars on the loudness of a simultaneously perceived car sound. Still images of a sports car, colored in red, light green, blue, and dark green, were displayed to subjects during a magnitude estimation task. The sound of an accelerating sports car was used as a stimulus. Statistical analysis suggests that the color of the visual stimulus may have a small influence on loudness judgments. The observed loudness differences are generally equivalent to a change in sound level of about 1 dB, with maximum individual differences of up to 3 dB. 相似文献
10.
Cycloadditions of α,β-unsaturated acyl cyanides (=2-oxonitriles) 1 – 6 to styrene and its p-substituted derivatives 7a – f , h are of inverse electron demand and provide, under mild conditions, regio- and stereoselectively 2-aryl-3,4-dihydro-2H-pyran-6-carbonitriles 8 – 13 , generally in good yield. Rates for the cycloaddition of acryloyl cyanide 1 to p-substituted styrenes, determined in competition reactions of substrate pairs relative to that of styrene, increase in the order of electron-donating ability NO2<Cl<H<AcO<Me<AcNH<MeO of the p-substituent. Linear correlation of log (kX/kH), and σp+ substituent constants (a Hammett-type plot), gives a reaction constant ρp+ of −1.47±0.17, supporting a concerted mechanism. 相似文献