全文获取类型
收费全文 | 2602篇 |
免费 | 97篇 |
国内免费 | 15篇 |
专业分类
化学 | 1763篇 |
晶体学 | 12篇 |
力学 | 73篇 |
数学 | 391篇 |
物理学 | 475篇 |
出版年
2023年 | 15篇 |
2022年 | 33篇 |
2021年 | 65篇 |
2020年 | 45篇 |
2019年 | 40篇 |
2018年 | 38篇 |
2017年 | 37篇 |
2016年 | 94篇 |
2015年 | 79篇 |
2014年 | 73篇 |
2013年 | 159篇 |
2012年 | 157篇 |
2011年 | 184篇 |
2010年 | 103篇 |
2009年 | 105篇 |
2008年 | 166篇 |
2007年 | 165篇 |
2006年 | 165篇 |
2005年 | 149篇 |
2004年 | 145篇 |
2003年 | 111篇 |
2002年 | 110篇 |
2001年 | 37篇 |
2000年 | 28篇 |
1999年 | 30篇 |
1998年 | 19篇 |
1997年 | 17篇 |
1996年 | 33篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 27篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 25篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有2714条查询结果,搜索用时 312 毫秒
151.
Perusal of literature data and some new results concerning syndiotactic-specific polymerization of styrene suggest a reaction mechanism accounting for the steric control. Key features of the proposed mechanism are stereorigid ηn coordination of the growing chain end and diastereoselective coordination of the monomer imposed by direct interactions with the ancillary ligand of the metal complex, a pseudotetrahedral chiral Ti(III) or Zr(III) cation, which inverts its configuration after every syndiospecific insertion step. 相似文献
152.
Jérôme Deprince Manuel Bautista Stephan Fritzsche Javier García Timothy Kallman Claudio Mendoza Patrick Palmeri Pascal Quinet 《X射线光谱测定》2020,49(1):29-32
In the present work, we report an investigation of plasma environment effects on the atomic parameters associated with the K-vacancy states in highly charged iron ions within the astrophysical context of accretion disks around black holes. More particularly, the sensitivity of K-line X-ray fluorescence parameters (wavelengths, radiative transition probabilities, and Auger rates) in Fe XVII–Fe XXV ions has been estimated for plasma conditions characterized by an electron temperature ranging from 105 to 107 K and an electron density ranging from 1018 to 1022 cm−3. In order to do this, relativistic multiconfiguration Dirac-Fock atomic structure calculations have been carried out by considering a time averaged Debye-Hückel potential for both the electron–nucleus and electron–electron interactions. 相似文献
153.
154.
Riet Dams Elena Bernabe Anna Nicoletti Claudio Loda Luca Martini Damiano Papini 《Rapid communications in mass spectrometry : RCM》2010,24(17):2650-2654
The introduction of Quality by Design (QbD) in Drug Development has resulted in a greater emphasis on chemical process understanding, in particular on the origin and fate of impurities. Therefore, the identification and quantitation of low level impurities in new Active Pharmaceutical Ingredients (APIs) play a crucial role in project progression and this has created a greater need for sensitive and selective analytical methodology. Consequently, scientists are constantly challenged to look for new applications of traditional analytical techniques. In this context a normal‐phase liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) method was developed to determine the amount of a de‐fluorinated analogue impurity in Casopitant Mesylate, a new API under development in GlaxoSmithKline, Verona. Normal‐phase LC provided the selectivity needed between our target analyte and Casopitant, while a single quadrupole mass spectrometer was used to ensure the sensitivity needed to detect the impurity at <0.05%w/w. Standard solutions and samples were prepared in heptane/ethanol (50:50, v/v) containing 1% of 2 M NH3 in ethanol; the mobile phase consisted of heptane/ethanol (95:5, v/v) with isocratic elution (flow rate: 1.0 mL/min, total run time: 23 min). To allow the formation of ions in solutions under normal‐phase (apolar) conditions, a post‐column infusion of a solution of 0.1% v/v of formic acid in methanol was applied (flow rate: 200 µL/min). The analysis was carried out in positive ion mode, monitoring the impurity by single ion monitoring (SIM). The method was fully validated and its applicability was demonstrated by the analysis of real‐life samples. This work is an example of the need for selective and accurate methodology during the development of a new chemical entity in order to develop an appropriate control strategy for impurities to ultimately ensure patient safety. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
155.
Knut Bakke Claudio Furtado J. R. Nascimento 《The European Physical Journal C - Particles and Fields》2009,60(3):501-507
We investigate the relativistic and non-relativistic quantum dynamics of a neutral spin-1/2 particle subject to an external
electromagnetic field in the presence of a cosmic dislocation. We analyze the explicit contribution of the torsion in the
geometric phase acquired in the dynamics of this neutral spinorial particle. We discuss the influence of the torsion in the
relativistic geometric phase. Using the Foldy–Wouthuysen approximation, the non-relativistic quantum dynamics is studied and
the influence of the torsion on the Aharonov–Casher and He–McKellar–Wilkens effects are discussed.
An erratum to this article can be found at 相似文献
156.
Lucas Pizzuti Luciana A. Piovesan Alex F.C. Flores Frank H. Quina Claudio M.P. Pereira 《Ultrasonics sonochemistry》2009,16(6):728-731
An efficient and green synthesis of thiocarbamoyl-3,5-diaryl-4,5-dihydro-1H-pyrazoles via the condensation of chalcones with thiosemicarbazide in ethanol and KOH under ultrasound irradiation is reported. The products were isolated in good yields after short reaction times. 相似文献
157.
158.
159.
Pierluigi?Contucci Cristian?Giardinà Claudio?GibertiEmail author Giorgio?Parisi Cecilia?Vernia 《Journal of statistical physics》2011,143(1):1-10
We numerically investigate the spin glass energy interface problem in three dimensions. We analyze the energy cost of changing
the overlap from −1 to +1 at one boundary of two coupled systems (in the other boundary the overlap is kept fixed to +1).
We implement a parallel tempering algorithm that simulates finite temperature systems and works with both cubic lattices and
parallelepiped with fixed aspect ratio. We find results consistent with a lower critical dimension D
c
=2.5. The results show a good agreement with the mean field theory predictions. 相似文献