全文获取类型
收费全文 | 274961篇 |
免费 | 3407篇 |
国内免费 | 836篇 |
专业分类
化学 | 144208篇 |
晶体学 | 4194篇 |
力学 | 12152篇 |
综合类 | 1篇 |
数学 | 32334篇 |
物理学 | 86315篇 |
出版年
2021年 | 2064篇 |
2020年 | 2393篇 |
2019年 | 2657篇 |
2018年 | 3601篇 |
2017年 | 3371篇 |
2016年 | 5237篇 |
2015年 | 3606篇 |
2014年 | 5177篇 |
2013年 | 12578篇 |
2012年 | 10514篇 |
2011年 | 12478篇 |
2010年 | 8509篇 |
2009年 | 8143篇 |
2008年 | 11283篇 |
2007年 | 11347篇 |
2006年 | 10546篇 |
2005年 | 9672篇 |
2004年 | 8782篇 |
2003年 | 7614篇 |
2002年 | 7363篇 |
2001年 | 7731篇 |
2000年 | 5919篇 |
1999年 | 4634篇 |
1998年 | 3876篇 |
1997年 | 3757篇 |
1996年 | 3697篇 |
1995年 | 3259篇 |
1994年 | 3242篇 |
1993年 | 3341篇 |
1992年 | 3471篇 |
1991年 | 3593篇 |
1990年 | 3334篇 |
1989年 | 3278篇 |
1988年 | 3276篇 |
1987年 | 3154篇 |
1986年 | 2965篇 |
1985年 | 4100篇 |
1984年 | 4274篇 |
1983年 | 3381篇 |
1982年 | 3669篇 |
1981年 | 3571篇 |
1980年 | 3440篇 |
1979年 | 3539篇 |
1978年 | 3624篇 |
1977年 | 3518篇 |
1976年 | 3663篇 |
1975年 | 3312篇 |
1974年 | 3342篇 |
1973年 | 3379篇 |
1972年 | 2319篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Summary Using a saturated non-boiling hydrocarbon mixture, the influence of two parameters on the results of field ionization mass spectrometry (FI-MS) measurements was studied: (a) the potential difference between the FI emitter and the counterelectrode; (b) the emitter temperature.Variation of the potential difference had only a minor effect on the average molecular mass measured and had no evident effect on the relative ring number distribution in the sample. In contrast, when the emitter temperature was increased, higher average molecular masses were recorded. Moreover, the average molecular masses shifted to higher ring numbers. In order to control the relationship between the described influences during mixture analysis, measuring instructions have been developed that enable the quantitative analysis of unknown saturated samples. However, average molecular mass of the mixture must be known.
Entwicklung einer quantitativen FI-MS-Methode zur Charakterisierung von gesättigten hoch- und nichtsiedenden Kohlenwasserstoffgemischen相似文献
62.
63.
64.
D. N. Karimov E. A. Krivandina Z. I. Zhmurova B. P. Sobolev V. A. Bezhanov S. P. Chernov G. M. Shapochkin 《Crystallography Reports》2006,51(6):1009-1015
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region. 相似文献
65.
66.
The European Physical Journal C - The design constraints and the target physics performance of the ATLAS Electromagnetic Calorimeter are reviewed, and the construction status is summarized.... 相似文献
67.
S. Szegedi P. Raics M. Fayez-Hassan 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(2):429-433
Considering the importance of the X-ray production cross sections for the determination of the element concentrations in a
given material, we have measured them experimentally for Al Si, Sc, Ti, V, Fe, Co, Ni and Cu bombarded by protons with energies
ranging from 40 to 180 keV.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
68.
We consider the optimal service control of a multiclass M/G/1 queueing system in which customers are served nonpreemptively and the system cost rate is additive across classes and increasing convex in the numbers present in each class. Following Whittle's approach to a class of restless bandit problems, we develop a Langrangian relaxation of the service control problem which serves to motivate the development of a class of index heuristics. The index for a particular customer class is characterised as a fair charge for service of that class. The paper develops these indices and reports an extensive numerical investigation which exhibits strong performance of the index heuristics for both discounted and average costs. 相似文献
69.
Porous road surfaces offer an effective means of reducing the generation and propagation of noise from road traffic. However, the porosity of these surfaces can deteriorate over time, leading to a reduction in their noise reducing properties. Efficient methods are therefore required for monitoring this performance. Existing techniques for performing in-situ measurements of acoustic absorption are unsuitable for use within the traffic stream. Static measurements using time domain Maximum Length Sequence (MLS) based techniques have been demonstrated to offer advantages over traditional techniques, presenting the opportunity for measurements under dynamic conditions. This paper describes the design of a system for carrying out dynamic MLS-based measurements. Results are presented which demonstrate that stable dynamic measurements can be carried out at speeds of up to 30 km/h. 相似文献
70.
F. Prez-Willard C. Sürgers H. Von Lhneysen P. Pfundstein 《Physica E: Low-dimensional Systems and Nanostructures》2004,22(4):872-880
The electronic transport through nanostructured bismuth nanobridges has been investigated at low temperatures (T<2 K) and in magnetic fields B up to 8.5 T. The samples show reproducible resistance fluctuations as a function of B, superimposed on a large magnetoresistance of up to 50%. In addition, time-dependent resistance fluctuations in zero magnetic field demonstrate the presence of bistable scatterers in the constriction region of our samples, which are described by two-level systems. Their dynamics are shown to be sensitive to subtle modifications of the static scatterer configuration in their vicinity, which cannot be detected in the sample magnetofingerprint. 相似文献