全文获取类型
收费全文 | 39398篇 |
免费 | 763篇 |
国内免费 | 176篇 |
专业分类
化学 | 20151篇 |
晶体学 | 460篇 |
力学 | 1262篇 |
综合类 | 12篇 |
数学 | 6423篇 |
物理学 | 12029篇 |
出版年
2023年 | 148篇 |
2022年 | 341篇 |
2021年 | 705篇 |
2020年 | 792篇 |
2019年 | 1038篇 |
2018年 | 1373篇 |
2017年 | 1393篇 |
2016年 | 1918篇 |
2015年 | 1094篇 |
2014年 | 1647篇 |
2013年 | 2570篇 |
2012年 | 2560篇 |
2011年 | 2857篇 |
2010年 | 2450篇 |
2009年 | 2297篇 |
2008年 | 2607篇 |
2007年 | 2456篇 |
2006年 | 2267篇 |
2005年 | 1664篇 |
2004年 | 1237篇 |
2003年 | 808篇 |
2002年 | 760篇 |
2001年 | 562篇 |
2000年 | 782篇 |
1999年 | 528篇 |
1998年 | 605篇 |
1997年 | 593篇 |
1996年 | 277篇 |
1995年 | 178篇 |
1994年 | 142篇 |
1993年 | 106篇 |
1992年 | 98篇 |
1991年 | 89篇 |
1990年 | 83篇 |
1989年 | 45篇 |
1988年 | 52篇 |
1987年 | 59篇 |
1986年 | 52篇 |
1985年 | 79篇 |
1984年 | 65篇 |
1983年 | 47篇 |
1982年 | 64篇 |
1981年 | 60篇 |
1980年 | 52篇 |
1979年 | 47篇 |
1978年 | 54篇 |
1977年 | 53篇 |
1976年 | 52篇 |
1974年 | 40篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Colloid Journal - It has been found that the addition of ammonia water to a gold sol obtained by the Duff method induces the growth of the gold particles. The growth kinetics of such particles in... 相似文献
33.
34.
Journal of Structural Chemistry - Thermodynamic characteristics are calculated for aqueous alkanolamine solutions that are obtained by substituting alkyl radicals for the protons in the amino group... 相似文献
35.
36.
Driven and non-equilibrium quantum states of matter have attracted growing interest in both theoretical and experimental studies in condensed matter physics. Recent progress in realizing transient collective states in driven or pumped Dirac materials (DMs) is reviewed herein. In particular, the focus is on optically pumped DMs which are a promising platform for transient excitonic instabilities. Optical pumping combined with the linear (Dirac) dispersion of the electronic spectrum offers a knob for tuning the effective interaction between the photoexcited electrons and holes, and thus provides a way of reducing the critical coupling for excitonic instability. As a result, a transient excitonic condensate could be achieved in a pumped DM while it is not feasible in equilibrium. A unifying theoretical framework is provided for describing transient collective states in 2D and 3D DMs. The experimental signatures are described and numerical estimates of the size of the dynamically induced excitonic gaps and the values of the critical temperatures for several specific systems, are summarized. In addition, general guidelines for identifying promising material candidates are discussed. Finally, comments are provided regarding recent experimental efforts in realizing transient excitonic condensate in pumped DMs, and outstanding issues and possible future directions are outlined. 相似文献
37.
Dehghanpour-Sahron Ja’far Mahdavi-Amiri Nezam 《4OR: A Quarterly Journal of Operations Research》2021,19(4):473-499
4OR - Partitioning a given data-set into subsets based on similarity among the data is called clustering. Clustering is a major task in data mining and machine learning having many applications... 相似文献
38.
Alexander J. Marshall 《Analytica chimica acta》2004,527(1):13-20
Holographic sensors for monitoring ionic strength have been fabricated from charged sulphonate and quaternary ammonium monomers, incorporated into thin, polymeric hydrogel films which were transformed into volume holograms. The diffraction wavelength or reflected colour of the holograms was used to characterise their swelling or de-swelling behaviour as a function of ionic strength in various media. The effects of co-monomer structure, buffer composition, ion composition, pH and temperature were evaluated, whilst the reversibility and reproducibility of the sensor was also assessed. An acrylamide-based hologram containing equal molar amounts of negatively and positively charged monomers was shown to be able to quantify ionic strength independent of the identity of the ionic species present in the test solution. The sensor was fully reversible, free of hysteresis and exhibited little response to pH between 3 and 9 and temperature within the range 20-45 °C. The system was successfully used to quantify the ionic strength of milk solutions, which contain a complex mixture of ions and biological components. 相似文献
39.
Alexander Zeller 《Journal of organometallic chemistry》2006,691(21):4379-4385
The ethylene polymerization reaction of a neutral nickel catalyst was studied by DFT calculations at the Becke3LYP/6-31G(d) level of theory. As in related cases a β-agostic bond stabilizes the nickel alkyl ground states. Transition states for the insertion of the olefin show a distinct α-agostic interaction, which has not been observed for late metal polymerization catalysts before. An ethylene-alkyl complex was identified as the resting state of the reaction. The overall barrier height of the reaction amounts to 17.54 kcal/mol, which slightly increases to 17.60 kcal/mol for the polymerization of deuterated ethylene. Therefore, a small positive kinetic isotope effect (kH/kD = 1.09) can be calculated, which is caused by the α-agostic interaction in the transition state. A comparison to other late metal based polymerization systems reveals that the ethylene coordination step of highly active catalysts is significantly lower in energy compared to catalysts which are only moderately active. 相似文献
40.
Planar laser-induced fluorescence visualisation is used to investigate nonuniformities in the flow of a hypersonic conical nozzle. Possible causes for the nonuniformity are outlined and investigated, and the problem is shown to be due to a small step at the nozzle throat. Entrainment of cold boundary layer gas is postulated as the cause of the signal nonuniformity.
PACS 47.80.Jk, 47.40.Ki, 47.60.+i 相似文献