全文获取类型
收费全文 | 434篇 |
免费 | 18篇 |
国内免费 | 3篇 |
专业分类
化学 | 324篇 |
晶体学 | 21篇 |
力学 | 8篇 |
数学 | 61篇 |
物理学 | 41篇 |
出版年
2023年 | 5篇 |
2022年 | 18篇 |
2021年 | 22篇 |
2020年 | 20篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 13篇 |
2016年 | 12篇 |
2015年 | 19篇 |
2014年 | 16篇 |
2013年 | 17篇 |
2012年 | 26篇 |
2011年 | 31篇 |
2010年 | 21篇 |
2009年 | 15篇 |
2008年 | 33篇 |
2007年 | 24篇 |
2006年 | 15篇 |
2005年 | 19篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 7篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有455条查询结果,搜索用时 15 毫秒
81.
The electrical conductivities of (1−x) Li2O · x BaO · 2 SiO2, (1−x) Na2O · x MgO ·2 SiO2, (1−x) Na2O · x CaO · SiO2 and (1−x) Na2O · x BaO · 2SiO2 glasses were measured at temperature ranging from room temperature to 450°C. The transport numbers for Na+ ion in (1−x) Na2O · x BaO · 2 SiO2 glasses were measured. It was found that the alkali ion carried a significant part of the current in these glasses except one that had no alkali ions, and the conductivity decreased markedly as the alkali oxide was substituted by an alkaline earth oxide. The results of conductivity measurements combined with the data hitherto reported on mixed alkali glasses led to the proposal that the so-called mixed alkali effect could be explained on the basis of the independent path model in which it is assumed that cations can move only through vacant sites left by those of the same type. 相似文献
82.
83.
Gugliuzza A Aceto MC Macedonio F Drioli E 《The journal of physical chemistry. B》2008,112(34):10483-10496
Next generation PEEK-WC membranes have been fabricated by using an innovative self-assembly technique. Patterned architectures have been achieved via a solvent-reduced and water-assisted process, resulting in honeycomb packed geometry. The membranes exhibit monodisperse pores with size and shape comparable to those left by templating water droplets. Influencing factors for the formation of self-assembled poly-(etheretherketone) with Cardo [PEEK-WC] membranes have been evaluated, identifying the critical parameters for nucleation, growth, and propagation of the droplet-mobile arrays through the overall films. Structure-transport relationships have been discussed according to the results achieved from the implementation of membrane distillation processes, yielding indication about the suitability of self-assembled PEEK-WC films to work as interfaces in contactor operations. 相似文献
84.
Mincsovics Emil Pápai Katalin Ludányi Krisztina Dávid Ádám Zoltán Budai Marianna Antal István Klebovich Imre 《平面色谱法杂志一现代薄层色谱法》2008,21(5):361-366
JPC – Journal of Planar Chromatography – Modern TLC - The newly developed experimental OPLC separation unit 100 (OSU 100) has been used for fully on-line multiple hyphenation using the... 相似文献
85.
Temiloluwa T. Adejumo Marianna Danopoulou Leandros P. Zorba Dr. Andrej Pevec Dr. Matija Zlatar Dr. Dušanka Radanović Milica Savić Prof. Dr. Maja Gruden Prof. Dr. Katarina K. Anđelković Prof. Dr. Iztok Turel Dr. Božidar Čobeljić Prof. Dr. Georgios C. Vougioukalakis 《欧洲无机化学杂志》2023,26(33):e202300193
Two new Zn(II) complexes bearing tridentate hydrazone-based ligands with NNO or NNS donor atoms were synthesised and characterised by elemental analysis, infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies, and single crystal X-ray diffraction methods. These complexes, together with four previously synthesised analogues, having hydrazone ligands with a NNO donor set of atoms, were successfully employed as catalysts in the ketone-amine-alkyne (KA2) coupling reaction, furnishing tetrasubstituted propargylamines, compounds with unique applications in organic chemistry. DFT calculations at the CAM-B3LYP/TZP level of theory were performed to elucidate the electronic structure of the investigated Zn(II) complexes, excellently correlating the structure of the complexes to their catalytic reactivity. 相似文献
86.
Enantiomeric separation of new phytoalexin analogs with cyclofructan chiral stationary phases in normal‐phase mode 下载免费PDF全文
Marianna Moskaľová Ján Petrovaj Taťána Gondová Mariana Budovská Daniel W. Armstrong 《Journal of separation science》2016,39(19):3669-3676
For the first time, three different derivatized cyclofructan chiral stationary phases were used for the direct high‐performance liquid chromatographic enantiomeric separation of 11 new racemic analogs of a natural indole phytoalexin. This class of compounds is known to have significant antiproliferative activity and other potentially useful pharmacological properties. The effect of various experimental factors was investigated to optimize the separations in the normal‐phase mode. It was found that the nature of polar modifier and additive in the mobile phase have significant impact on the enantioseparations. Better chiral recognition of analyzed compounds was achieved on (R)‐naphthylethyl carbamate cyclofructan 6 than on isopropyl carbamate cyclofructan 6 and dimethylphenyl carbamate cyclofructan 7. The thermodynamic parameters showed that the chiral separation was enthalpy controlled in all cases. 相似文献
87.
Georgakopoulos CG Vonaparti A Stamou M Kiousi P Lyris E Angelis YS Tsoupras G Wuest B Nielen MW Panderi I Koupparis M 《Rapid communications in mass spectrometry : RCM》2007,21(15):2439-2446
A new combined doping control screening method for the analysis of anabolic steroids in human urine using liquid chromatography/electrospray ionization orthogonal acceleration time-of-flight mass spectrometry (LCoaTOFMS) and gas chromatography/electron ionization orthogonal acceleration time-of-flight mass spectrometry (GCoaTOFMS) has been developed in order to acquire accurate full scan MS data to be used to detect designer steroids. The developed method allowed the detection of representative prohibited substances, in addition to steroids, at concentrations of 10 ng/mL for anabolic agents and metabolites, 30 ng/mL for corticosteroids, 500 ng/mL for stimulants and beta-blockers, 250 ng/mL for diuretics, and 200 ng/mL for narcotics. Sample preparation was based on liquid-liquid extraction of hydrolyzed human urine, and the final extract was analyzed as trimethylsilylated derivatives in GCoaTOFMS and underivatized in LCoaTOFMS in positive ion mode. The sensitivity, mass accuracy, advantages and limitations of the developed method are presented. 相似文献
88.
Performance of idealized column structures under high pressure 总被引:1,自引:0,他引:1
We have examined the influence of the longitudinal temperature and pressure gradients in columns operated under very high pressures on the coefficients of the van Deemter equation under the idealized condition of complete radial uniformity. These gradients change the diffusion coefficients over the length of the column, and the equation takes a new form, where the classical linear C-term is replaced by more complex forms that capture the effects of these axial gradients. The details of the derivations are shown and the implications are discussed. 相似文献
89.
Flamini G Tebano M Cioni PL Ceccarini L Ricci AS Longo I 《Journal of chromatography. A》2007,1143(1-2):36-40
A novel microwave method has been applied to the hydrothermal extraction of essential oil from plants. An insulated microwave coaxial antenna was introduced inside a 1000 ml glass flask containing dry Laurus nobilis L. leaves and tap water. Microwave power up to 800 W at 2450 MHz was emitted in continuous wave regime (CW) or in pulsed regime (PR) at 8 kW peak power. Stirring with a magnetic bar and a Clevenger refrigerator connected to the flask enabled to complete the extraction in 1 h. The results of the in situ microwave extraction were compared with those obtained by heating the same reactor with a conventional electric mantle by gas chromatography-mass spectrometry (GC-MS) analysis. Differences were observed both in the composition of the essential oil and from the energetic point of view. The essential oil obtained with microwave (MW) methods contained substantially higher amounts of oxygenated compounds and lower amounts of monoterpenes than conventional method. The in situ microwave heating is safe and versatile; it presents time and energy saving advantages, and therefore it can be considered useful also for industrial applications. 相似文献
90.
Marianna A. Shubov 《Mathematische Nachrichten》2002,241(1):125-162
We develop spectral and asymptotic analysis for a class of nonselfadjoint operators which are the dynamics generators for the systems governed by the equations of the spatially nonhomogeneous Timoshenko beam model with a 2–parameter family of dissipative boundary conditions. Our results split into two groups. We prove asymptotic formulas for the spectra of the aforementioned operators (the spectrum of each operator consists of two branches of discrete complex eigenvalues and each branch has only two points of accumulation: +∞ and —∞), and for their generalized eigenvectors. Our second main result is the fact that these operators are Riesz spectral. To obtain this result, we prove that the systems of generalized eigenvectors form Riesz bases in the corresponding energy spaces. We also obtain the asymptotics of the spectra and the eigenfunctions for the nonselfadjoint polynomial operator pencils associated with these operators. The pencil asymptotics are essential for the proofs of the spectral results for the aforementioned dynamics generators. 相似文献