全文获取类型
收费全文 | 647篇 |
免费 | 41篇 |
国内免费 | 8篇 |
专业分类
化学 | 437篇 |
晶体学 | 3篇 |
力学 | 36篇 |
数学 | 114篇 |
物理学 | 106篇 |
出版年
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 35篇 |
2020年 | 20篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 13篇 |
2016年 | 31篇 |
2015年 | 24篇 |
2014年 | 20篇 |
2013年 | 45篇 |
2012年 | 51篇 |
2011年 | 58篇 |
2010年 | 32篇 |
2009年 | 24篇 |
2008年 | 41篇 |
2007年 | 41篇 |
2006年 | 38篇 |
2005年 | 25篇 |
2004年 | 17篇 |
2003年 | 39篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 8篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1923年 | 1篇 |
排序方式: 共有696条查询结果,搜索用时 15 毫秒
121.
Victoria F. Samanidou Dimitrios E. Giannakis Antonia Papadaki 《Journal of separation science》2009,32(9):1302-1311
Herein a quantitative method for the determination of seven penicillins in bovine plasma and veterinary drugs has been developed. Amoxicillin (AMO), ampicillin (AMP), penicillin G (PENG), penicillin V (PENV), oxacillin (OXA), cloxacillin (CLO) and dicloxacillin (DICLO) were separated on a Perfectsil ODS‐2 (250×4 mm, 5 μm) column, using gradient elution, with a mobile phase of 0.1% v/v TFA and ACN–methanol (90:10 v/v). PDA detection was used at 240 nm. Penicillins were isolated from bovine plasma by SPE on Lichrolut RP‐18 cartridges with mean recoveries from 85.7 to 113.5%. Colchicine (3 ng/μL) was used as an internal standard. The developed method was validated in terms of selectivity, linearity, accuracy, precision, stability and sensitivity. Repeatability (n = 5) and between‐day precision (n = 5) revealed RSD < 12%. The detection limits in the bovine plasma were estimated as 18 ng for AMO and AMP, 25 for PENG, PENV and OXA, 3 ng for CLO and 12 ng for DICLO. Spiked plasma samples were stable for 1 wk, except for AMP and CLO, which were stable for 3 wk and OXA for 4 wk. AMO, PENG and PENV were stable for two freeze–thaw cycles, OXA, CLO and DICLO for four, while AMP only for one. 相似文献
122.
A series of epoxy cured samples, with different molar composition of 1,4-butanediol diglycidyl ether (EP), cis-1,2-cyclohexanedicarboxylic anhydride (CH) and triethylamine (TEA) as initiator, was studied by Electrical Impedance Spectroscopy (EIS) in the frequency range 10−2-105 Hz. The resistivity of the system was evaluated by using the complex impedance analysis method. Resistivity values in the range between 107 and 1013 Ω cm were obtained and related to the composition (molar fraction xEP or xCH) of the epoxy system. The gel formation characteristics of the samples were obtained as theoretically described by Flory. 相似文献
123.
Kararizou E Likomanos D Gkiatas K Markou I Triantafyllou N Kararizos G 《Magnetic resonance imaging》2006,24(2):205-207
Gliomatosis cerebri (GC) is characterized by a diffuse infiltration of neoplastic glial cells with preservation of neuronal architecture. It can be very difficult to diagnose during life because the clinical manifestations are protean and tests are often nondiagnostic. The diagnosis of GC needs to be based on radiological, clinical and pathological criteria. We present a patient with GC, which initially presented as acute stroke attack. We discuss the usefulness of noninvasive methods, such a MR spectroscopy, in the diagnosis, grading and management of GC. 相似文献
124.
Dimitrios S. Sophianopoulos Konstantinos S. Papachristou 《Archive of Applied Mechanics (Ingenieur Archiv)》2012,82(10-11):1653-1662
The linearized buckling response of uniform steel beam-columns resting on a Pasternak foundation type is dealt with in this work. The corresponding two-point boundary value problem depends on the two parameters associated with the foundation model, that is, shear layer constant and Winkler spring coefficient, as well as on the axial loading. The fourth-order differential equation of buckling and the consequent characteristic one yield exact values of the buckling loads, which may lead to shape functions, being either one sinusoidal waveform or the sum of two different waveforms. The former case is associated with a single-mode response, while the latter with mode coupling. The conditions for which each of these cases characterizes the beam-column behavior are fully assessed and the dependence on the combination of the aforementioned parameters on the response is discussed in detail. It is found that regardless of the order of coupling, the corresponding mode is not related to rational values of buckling loads and hence this unfavorable phenomenon is excluded in structural design. 相似文献
125.
Dimitrios I. Papadimitriou 《International Journal of Computational Fluid Dynamics》2016,30(3):272-284
A new algorithm for the solution of the unsteady adjoint equations is proposed in this article, aiming at overcoming the excessive computational cost and memory requirements of the conventional adjoint approach for the optimisation of unsteady problems in computational mechanics. The total cost is equal to four times the cost of the unsteady state solution, which is twice the cost of the conventional backward-in-time adjoint calculation but the memory requirements are very small, equivalent to those of a steady-state problem, while stability is acceptable. The proposed algorithm is validated in the case of the 1D unsteady Burgers equation with non-smooth source terms. 相似文献
126.
Legendre Pseudospectral Approximation of Boussinesq Systems and Applications to Wave Breaking 下载免费PDF全文
Magnar Bjø rkavå g Henrik Kalisch Zahra Khorsand & Dimitrios Mitsotakis 《数学研究》2016,49(3):221-237
In this paper, we propose a spectral projection of a regularized Boussinesq
system for wave propagation on the surface of a fluid. The spectral method is based
on the use of Legendre polynomials, and is able to handle time-dependent Dirichlet
boundary conditions with spectral accuracy.The algorithm is applied to the study of undular bores, and in particular to the onset
of wave breaking connected with undular bores. As proposed in [2], an improved
version of the breaking criterion recently introduced in [5] is used. This tightened
breaking criterion together with a careful choice of the relaxation parameter yields
rather accurate predictions of the onset of breaking in the leading wave of an undular
bore. 相似文献
127.
Philip Jackson Dimitrios Hariskos Roland Wuerz Wiltraud Wischmann Michael Powalla 《固体物理学:研究快报》2014,8(3):219-222
We report on the interaction between intentional potassium doping of thin film Cu(In,Ga)Se2 (CIGS) solar cells, CIGS absorber composition, and device efficiency. Up to now high efficiency CIGS solar cells could not be produced with a gallium/(gallium + indium) ratio higher than 35%. The new doping process step does not only increase solar cell conversion efficiencies up to 20.8%, but also allows a shift in the CIGS absorber composition towards higher gallium content whilst maintaining this high efficiencies level. We find that the saturation of the open circuit voltages for higher gallium content that is normally observed can partially be overcome by the new doping procedure. This observation leads us to the conclusion that even on this high performance level CIGS solar cells still hold a potential for further development beyond the record values reported here. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
128.
Imaging and manipulation of biological structures with the AFM 总被引:11,自引:0,他引:11
Fotiadis D Scheuring S Müller SA Engel A Müller DJ 《Micron (Oxford, England : 1993)》2002,33(4):385-397
Many biologists have dreamt of physically touching and manipulating the biomolecules they were investigating. With the invention of the atomic force microscope (AFM), this dream has come true. Here, recent applications of the AFM to image and to manipulate biological systems at the nanometer scale are reviewed. Macromolecular biological assemblies as well as individual biomolecules can be subjected to controlled nanomanipulation. Examples of AFM application in imaging and nanomanipulation include the extraction of chromosomal DNA for genetic analysis, the disruption of antibody--antigen bonds, the dissection of biological membranes, the nanodissection of protein complexes, and the controlled modulation of protein conformations. Also reviewed is the novel combination of single molecule imaging and force spectroscopy which allows biomolecules to be imaged, and inter- and intramolecular forces to be measured. Future application of these nanotechniques will reveal new information on the structure, function and assembly of biomolecules. 相似文献
129.
Hatzakis NS Wei L Jorgensen SK Kunding AH Bolinger PY Ehrlich N Makarov I Skjot M Svendsen A Hedegård P Stamou D 《Journal of the American Chemical Society》2012,134(22):9296-9302
Allosteric regulation of enzymatic activity forms the basis for controlling a plethora of vital cellular processes. While the mechanism underlying regulation of multimeric enzymes is generally well understood and proposed to primarily operate via conformational selection, the mechanism underlying allosteric regulation of monomeric enzymes is poorly understood. Here we monitored for the first time allosteric regulation of enzymatic activity at the single molecule level. We measured single stochastic catalytic turnovers of a monomeric metabolic enzyme (Thermomyces lanuginosus Lipase) while titrating its proximity to a lipid membrane that acts as an allosteric effector. The single molecule measurements revealed the existence of discrete binary functional states that could not be identified in macroscopic measurements due to ensemble averaging. The discrete functional states correlate with the enzyme's major conformational states and are redistributed in the presence of the regulatory effector. Thus, our data support allosteric regulation of monomeric enzymes to operate via selection of preexisting functional states and not via induction of new ones. 相似文献
130.
Haschemi Nassab M Mitschke A Suchy MT Gutzki FM Zoerner AA Rhein M Hillemacher T Frieling H Jordan J Tsikas D 《The Analyst》2012,137(10):2480-2485
Common ethanol detection methods are not applicable to cell culture media and microdialysates due to interference with medium constituents including amino acids and pH indicators. We present a novel GC-MS method for the accurate and precise analysis of ethanol in cell cultures and microdialysates. The method is based on the carbonate-catalyzed extractive pentafluorobenzoylation of ethanol and deuterium-labelled ethanol serving as the internal standard and on their GC-MS analysis in the electron-capture negative-ion chemical ionization mode. The method was used to optimize experimental conditions in a custom-made ethanol vapour system utilized for studies examining ethanol influences on neuronal cell lines and in microdialysis. 相似文献