全文获取类型
收费全文 | 3790篇 |
免费 | 378篇 |
国内免费 | 636篇 |
专业分类
化学 | 2388篇 |
晶体学 | 113篇 |
力学 | 201篇 |
综合类 | 71篇 |
数学 | 503篇 |
物理学 | 1528篇 |
出版年
2022年 | 65篇 |
2021年 | 60篇 |
2020年 | 74篇 |
2019年 | 66篇 |
2018年 | 61篇 |
2017年 | 84篇 |
2016年 | 109篇 |
2015年 | 124篇 |
2014年 | 123篇 |
2013年 | 215篇 |
2012年 | 161篇 |
2011年 | 190篇 |
2010年 | 187篇 |
2009年 | 202篇 |
2008年 | 237篇 |
2007年 | 254篇 |
2006年 | 242篇 |
2005年 | 181篇 |
2004年 | 148篇 |
2003年 | 108篇 |
2002年 | 120篇 |
2001年 | 130篇 |
2000年 | 124篇 |
1999年 | 101篇 |
1998年 | 65篇 |
1997年 | 64篇 |
1996年 | 58篇 |
1995年 | 52篇 |
1994年 | 40篇 |
1993年 | 48篇 |
1992年 | 74篇 |
1991年 | 45篇 |
1990年 | 57篇 |
1989年 | 39篇 |
1988年 | 49篇 |
1987年 | 41篇 |
1986年 | 40篇 |
1985年 | 51篇 |
1984年 | 42篇 |
1983年 | 38篇 |
1982年 | 34篇 |
1981年 | 35篇 |
1980年 | 49篇 |
1979年 | 40篇 |
1978年 | 27篇 |
1977年 | 41篇 |
1976年 | 26篇 |
1975年 | 29篇 |
1971年 | 24篇 |
1967年 | 26篇 |
排序方式: 共有4804条查询结果,搜索用时 922 毫秒
1.
Back Cover: Reactions of Group 4 Metallocenes with Monosubstituted Acetonitriles: Keteniminate Formation versus CC Coupling (Chem. Eur. J. 8/2015)
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)
2.
Becker Otwin Leopold-Wildburger Ulrike 《Central European Journal of Operations Research》2020,28(2):425-440
Central European Journal of Operations Research - This paper combines work to use a decision support tool for sustainable economic development, while acknowledging interdependent dynamics of... 相似文献
3.
4.
Wolfram Bremser Roland Becker Heinrich Kipphardt Petra Lehnik-Habrink Ulrich Panne Antje Töpfer 《Accreditation and quality assurance》2006,11(10):489-495
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment. 相似文献
5.
6.
Styrene (STY) is now produced industrially in fairly large quantities by the dehydrogenation of ethylbenzene (EB) using promoted iron oxide catalyst with superheated steam.In this case, small amount of carbon dioxide formed as a by-product was known to inhibit the catalytic activity of commercial catalyst. Recently, there have been some reports which carbon dioxide showed positive effects to promote catalytic activities on the reaction over several catalysts.In this study, we attempted to combine the dehydrogenation of EB to STY with the carbon dioxide shift-reaction. The combine reaction (EB + CO2 → STY + H2O + CO) can be considered as one of the ways of using CO2 resources and can yield simultaneously STY and Carbon oxide.Alumina oxide catalysts such as Al2O3, Na2O/Al2O3 and K2O/Al2O3 were prepared by the usual impregnation method with an aqueous solution of NaNO3 and KNO3, and then calcined at 650℃ for 5 h in a stream of air. The reaction condition is 600℃, flow of CO2 38ml/mon and space velocity (EB) 1.28h-1. 相似文献
7.
A. Hoffknecht O. Uwira A. Frank S. Schennach W. Spies M. Wagner S. Schippers A. Müller R. Becker M. Kleinod N. Angert P.H. Mokler 《Hyperfine Interactions》1998,114(1-4):257-261
The origin of the widely observed enhancement of rates for electron-ion recombination at very low energies is still unknown.
We investigated the recombination of Au25+ with free electrons in a merged-beams experiment at the UNILAC accelerator of the GSI in Darmstadt. At E
rel= 0 eV we found an enormous enhancement factor of 365 compared to the theory of radiative recombination. An increase of the
electron density by a factor of 10 had not much influence on the measured rate coefficient.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
T. Engel M. Würtz S. Borneis St. Becker I. Klaft A. Kohl T. Kühl F. Laeri D. Marx K. Meier R. Neumann F. Schmitt P. Seelig L. Völker 《Hyperfine Interactions》1997,108(1-3):251-258
Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening
is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser
systems specialized on the specific needs of laser spectroscopy at storage rings is reported.
Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different
Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast
qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator.
It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a
frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz.
This laser can be advantageous for laser cooling of ion beams.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
无偏的岭回归迭代算法 总被引:1,自引:0,他引:1
本文探讨线性模型的无偏的岭回归迭代算法,这种算法保持最小二乘法的性质,当存在较为严重的共线性时,它能给出较为精确的参数及其协差阵的估计值;当存在严格的共线性时,给出参数及其协差阵的无穷多解中的一个,这个解由初值决定。文章还给出了算法的收敛性及一些其它性质的证明。 相似文献
10.
报道了一种弥散型金属薄膜逾渗系统的制备方法和研究结果。从实验发现这种新型的逾渗系统具有异常的R-I关系、三次谐波系数与独特的电流临界规律。分析表明:这些特性与此类薄膜逾渗结构随电流增大而逐渐变化的过程有关,是由沿膜横向逐渐变化的局域隧道电流(LDTC)与跳跃电导(LDHC)效应引起的。 相似文献