全文获取类型
收费全文 | 19583篇 |
免费 | 882篇 |
国内免费 | 101篇 |
专业分类
化学 | 13474篇 |
晶体学 | 123篇 |
力学 | 449篇 |
数学 | 2961篇 |
物理学 | 3559篇 |
出版年
2023年 | 124篇 |
2022年 | 179篇 |
2021年 | 281篇 |
2020年 | 384篇 |
2019年 | 405篇 |
2018年 | 240篇 |
2017年 | 239篇 |
2016年 | 619篇 |
2015年 | 573篇 |
2014年 | 664篇 |
2013年 | 1060篇 |
2012年 | 1164篇 |
2011年 | 1302篇 |
2010年 | 765篇 |
2009年 | 678篇 |
2008年 | 1072篇 |
2007年 | 1060篇 |
2006年 | 981篇 |
2005年 | 919篇 |
2004年 | 792篇 |
2003年 | 656篇 |
2002年 | 625篇 |
2001年 | 314篇 |
2000年 | 303篇 |
1999年 | 279篇 |
1998年 | 244篇 |
1997年 | 234篇 |
1996年 | 272篇 |
1995年 | 251篇 |
1994年 | 222篇 |
1993年 | 218篇 |
1992年 | 207篇 |
1991年 | 179篇 |
1990年 | 178篇 |
1989年 | 177篇 |
1988年 | 151篇 |
1987年 | 127篇 |
1986年 | 117篇 |
1985年 | 169篇 |
1984年 | 170篇 |
1983年 | 130篇 |
1982年 | 156篇 |
1981年 | 163篇 |
1980年 | 137篇 |
1979年 | 144篇 |
1978年 | 168篇 |
1977年 | 117篇 |
1976年 | 109篇 |
1975年 | 122篇 |
1974年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Experiments for the determination of mono-, di and tri-butyltin (MBT, DBT and TBT) by hydride generation/gas chromatography/atomic absorption spectrometry in various matrices (sediment, suspended matter, mussel, algae and water) have revealed that poor butyltin recoveries are obtained in sediments displaying high sulphur and hydrocarbon contents; very poor recoveries were also observed for TBT in sediments with high chlorophyll pigment contents as well as in algal samples. It was however not clear whether the hydride generatin was inhibited by these infering compounds, as was previously assumed in the case of hydrocarbons, or whether interferences affected the atomization rate. Further studies were performed to solve this problem in order to validate this method in the case of analyses of, for example, oil-contaminated sediment and algae. This paper presents the results obtained. It is concluded here that the poor recoveries were due to an inhibition of hydride generation rather than to interference at the atomization stage. 相似文献
42.
43.
44.
Klaus Anderle Richard Birenheide Martin J. A. Werner Joachim H. Wendorff 《Liquid crystals》1991,9(5):691-699
Polarized light leads to an effective reorientation of the optic axis in the glassy state of liquid-crystalline side chain polymers containing azobenzene mesogenic groups, via a trans-cis and cis-trans isomerization. Using a combination of U V and IR dichroitic studies it is shown for copolymers consisting of chromophores (azobenzene) and non-chromophores (phenylbenzoate) that only the chromophores are reoriented by light as far as the glassy state is concerned. Individual chromophores are thus addressed by photoselection. Photoselection in the fluid nematic state, on the other hand, leads also to a reorientation of the non-chromophores. 相似文献
45.
Martin Schechter 《Mathematical Methods in the Applied Sciences》1994,17(4):229-238
We show how saddle point techniques can be used to obtain new results for general resonance problems of the type considered by Landesman and Lazer. 相似文献
46.
Background
Repeated execution of a tactile task enhances task performance. In the present study we sought to improve tactile performance with unattended activation-based learning processes (i.e., focused stimulation of dermal receptors evoking neural coactivation (CA)). Previous studies show that the application of CA to a single finger reduced the stationary two-point discrimination threshold and significantly increased tactile acuity. These changes were accompanied by an expansion of the cortical finger representation in primary somatosensory cortex (SI). Here we investigated the effect of different types of multifinger CA on the tactile performance of each finger of the right hand. 相似文献47.
This paper establishes a general ABC inventory classification system as the foundation for a normative model of the maintenance cost structure and stock turnover characteristics of a large, multi-item inventory system with constant demand. For any specified number of inventory classes, the model allows expression of the overall system combined ordering and holding cost in terms of (i) the re-ordering frequencies for the items in each inventory class and (ii) the inventory class structure, that is, the proportion of the total system's items that are in each inventory class. The model yields a minimum total maintenance cost function, which reflects the effect of class structure on inventory maintenance costs and turnover. If the Pareto curve (a.k.a. Distribution-by-value function) for the inventory system can be expressed (or approximated) analytically, the model can also be used to determine an optimal class structure, as well as an appropriate number of inventory classes. A special case of the model produces a simply structured, class-based ordering policy for minimizing total inventory maintenance costs. Using real data, the cost characteristics of this policy are compared to those of a heuristic, commonly used by managers of multi-item inventory systems. This cost comparison, expressed graphically, underscores the need for normative modelling approaches to the problem of inventory cost management in large, multi-item systems. 相似文献
48.
Martin I. Karakhanyan 《Journal of Contemporary Mathematical Analysis (Armenian Academy of Sciences)》2007,42(3):146-150
The paper proves some general facts on commutators that refer to Fuglede-Putnam classical theorem in the spectral theory of not necessarily selfadjoint operators. 相似文献
49.
50.
It is shown that the law of an SDE driven by fractional Brownian motion with Hurst parameter greater than 1/2 has a smooth density with respect to Lebesgue measure, provided that the driving vector fields satisfy Hörmander’s condition. The main new ingredient of the proof is an extension of Norris’ lemma to this situation. 相似文献