全文获取类型
收费全文 | 1700篇 |
免费 | 77篇 |
国内免费 | 14篇 |
专业分类
化学 | 1029篇 |
晶体学 | 3篇 |
力学 | 37篇 |
数学 | 358篇 |
物理学 | 364篇 |
出版年
2023年 | 9篇 |
2022年 | 18篇 |
2021年 | 30篇 |
2020年 | 37篇 |
2019年 | 35篇 |
2018年 | 24篇 |
2017年 | 29篇 |
2016年 | 66篇 |
2015年 | 46篇 |
2014年 | 53篇 |
2013年 | 102篇 |
2012年 | 104篇 |
2011年 | 122篇 |
2010年 | 89篇 |
2009年 | 70篇 |
2008年 | 86篇 |
2007年 | 77篇 |
2006年 | 51篇 |
2005年 | 71篇 |
2004年 | 63篇 |
2003年 | 51篇 |
2002年 | 53篇 |
2001年 | 34篇 |
2000年 | 26篇 |
1999年 | 21篇 |
1998年 | 24篇 |
1997年 | 16篇 |
1996年 | 23篇 |
1995年 | 19篇 |
1994年 | 21篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1972年 | 10篇 |
1966年 | 7篇 |
1916年 | 11篇 |
1913年 | 8篇 |
排序方式: 共有1791条查询结果,搜索用时 15 毫秒
211.
A European interlaboratory collaborative study was conducted to validate a method for the quantitative determination of lipophilic
marine biotoxins based on high-performance liquid chromatography–tandem mass spectrometry. During this study, the diarrhetic
shellfish poisoning toxins okadaic acid, dinophysis toxin1 and 2 including their esters, the azaspiracids 1-3, pectenotoxin2,
and the yessotoxins were investigated at concentration levels near the limit of quantification and near the legal limit. Naturally
contaminated blue mussels, both raw and cooked and spiked extracts of clams and oysters were studied and results were obtained
for 16 test samples from 16 laboratories representing eight different countries. This article summarizes the study outcome
concerning validation key parameters like specificity, linearity, limit of detection, accuracy/recovery, and precision. Further,
influences of cooking of mussels before homogenization or hydrolysis on method robustness have been evaluated. 相似文献
212.
The classical Strong Szegö-Widom Limit Theorem describes the asymptotic behavior of the determinants of the finite sections PnT(a)Pn of Toeplitz operators, i.e., of operators which have constant entries along each diagonal. We generalize these results to operators which have almost periodic sequences as their diagonals. 相似文献
213.
Oscar Salas-Solano Kunnel Babu SungAe Suhr Park Xinfeng Zhang Li Zhang Zoran Sosic Boris Boumajny Ming Zeng Kuang-Chuan Cheng Angelia Reed-Bogan Stacey Cummins-Bitz David A. Michels Monica Parker Paulina Bonasia Mingfang Hong Steven Cook Margaret Ruesch David Lamb Dora Bolyan Steffen Kiessig Darren Allender Brian Nunnally 《Chromatographia》2011,73(11-12):1137-1144
Interlaboratory comparisons are essential to bringing emerging technologies into biopharmaceutical industry practice and regulatory acceptance. As a result, an international team including 12 laboratories from 10 independent biopharmaceutical companies in the United States and Switzerland was formed to evaluate the precision and robustness of capillary isoelectric focusing (CIEF) to assess the charge heterogeneity of monoclonal antibodies. The different laboratories determined the apparent pI and the relative distribution of the charge isoforms of a representative monoclonal antibody (rMAb) sample using the same CIEF method. Statistical evaluation of the data was performed to determine within and between-laboratory consistencies and outlying information. The apparent pI data generated for each charge variant peak showed very good precision between laboratories with percentage of RSD values of ??0.5%. Similarly, the percentage of RSD for the rMAb charge variants percent peak area values are ??4.4% across different laboratories with different analysts using different lots of ampholytes and multiple instruments. Taken together, these results validate the appropriate use of CIEF in the biopharmaceutical industry in support of regulatory submissions. 相似文献
214.
Barkleit A Tsushima S Savchuk O Philipp J Heim K Acker M Taut S Fahmy K 《Inorganic chemistry》2011,50(12):5451-5459
Thermodynamic parameters for the complexation of Eu(3+) with pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) as a model system for polymerizable metal-complexing humic acids were determined using temperature-dependent time-resolved laser-induced fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC). At low metal and ligand concentrations (<50 μM Eu(3+), <1 mM BTC), a 1:1 monomeric Eu-BTC complex was identified in the range of 25-60 °C. At elevated concentrations (>500 μM Eu(3+) and BTC) a temperature-dependent polymerization was observed, where BTC monomers are linked via coordinating shared Eu(3+) ions. The two methods lead to comparable thermodynamic data (ΔH = 18.5 ± 1.5/16.5 ± 0.1 kJ mol(-1); ΔS = 152 ± 5/130 ± 5 J mol(-1) K(-1); TRLFS/ITC) in the absence of polymerization. With the onset of polymerization, TRLFS reveals the water coordination number of the lanthanide, whereas calorimetry is superior in determining the thermodynamic data in this regime. Evaluating the heat uptake kinetics, the monomer and polymer formation steps could be separated by "time-resolved" ITC, revealing almost identical binding enthalpies for the sequential reactions. Structural features of the complexes were studied by Fourier-transform infrared (FTIR) spectroscopy in combination with density functional theory (DFT) calculations showing predominantly chelating coordination with two carboxylate groups in the monomeric complex and monodentate binding of a single carboxylate group in the polymeric complex of the polycarboxylate with Eu(3+). The data show that pyromellitic acid is a suitable model for the study of metal-mediated polymerization as a crucial factor in determining the effect of humic acids on the mobility of heavy metals in the environment. 相似文献
215.
Barkleit A Geipel G Acker M Taut S Bernhard G 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(1):549-552
For the first time Am(III) complexation with a small organic ligand could be identified and characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature and trace metal concentration. With pyromellitic acid (1,2,4,5-benzene-tetracarboxylic acid, BTC) as ligand spectroscopic characteristics for the Am-BTC complex system were determined at pH 5.0, an ionic strength of 0.1 M (NaClO4) and room temperature. The fluorescence lifetimes were determined to be 23.2±2.2 ns for Am3+(aq) and 27.2±1.2 ns for the Am-BTC 1:1 complex; the emission maximum for the 5D1-(7)F1 transition is 691 nm for both species. The complex stability constant for the Am-BTC 1:1 complex was calculated to be logβ110=5.42±0.16. 相似文献
216.
Steffen Oroszi Torsten Jakob Christian Wilhelm Hauke Harms Thomas Maskow 《Journal of Thermal Analysis and Calorimetry》2011,104(1):223-231
Isothermal microcalorimetry can be used to investigate the photosynthetic energy conversion of autotrophic organisms. In this
study, for the first time a diatom alga was used to compare the calorimetrically measured heat flux with measurements of the
photosynthetic performance by oxygen evolution and pulse-amplitude modulated fluorescence. The presented experimental setup
proved suitable to compare calorimetric data with those of conventional methods of the determination of photosynthesis rates.
Special attention was paid to the contribution of energy dissipation via non-photochemical quenching (NPQ) of chlorophyll
fluorescence to the metabolic energy balance. This was achieved by a combination of different light conditions and the use
of an inhibitor of NPQ. Although NPQ is an important photoprotective mechanism in diatoms, the inhibition of NPQ resulted
in an activation of alternative, energy dissipating pathways for absorbed radiation which completely compensated for the fraction
of energy dissipation by NPQ. 相似文献
217.
Hedberg C Dekker FJ Rusch M Renner S Wetzel S Vartak N Gerding-Reimers C Bon RS Bastiaens PI Waldmann H 《Angewandte Chemie (International ed. in English)》2011,50(42):9832-9837
A matter of common sense: A common recognition motif consisting of a negatively charged group five to six bonds away (red) from the (thio)ester functionality (green) and a positively charged tail group ten to twelve bonds away (blue) was identified in two native acyl protein thioesterase?1 (APT1) substrates. This similarity led to the design of potent inhibitors of the Ras-depalmitoylating enzyme APT1. 相似文献
218.
219.
Steffen Borchers Sandro Bosio Rolf Findeisen Utz-Uwe Haus Philipp Rumschinski Robert Weismantel 《Mathematical Methods of Operations Research》2011,73(3):381-400
This paper focuses on combinatorial feasibility and optimization problems that arise in the context of parameter identification
of discrete dynamical systems. Given a candidate parametric model for a physical system and a set of experimental observations,
the objective of parameter identification is to provide estimates of the parameter values for which the model can reproduce
the experiments. To this end, we define a finite graph corresponding to the model, to each arc of which a set of parameters
is associated. Paths in this graph are regarded as feasible only if the sets of parameters corresponding to the arcs of the
path have nonempty intersection. We study feasibility and optimization problems on such feasible paths, focusing on computational
complexity. We show that, under certain restrictions on the sets of parameters, some of the problems become tractable, whereas
others are NP-hard. In a similar vein, we define and study some graph problems for experimental design, whose goal is to support
the scientist in optimally designing new experiments. 相似文献
220.
Berger Moritz Welchowski Thomas Schmitz-Valckenberg Steffen Schmid Matthias 《Advances in Data Analysis and Classification》2019,13(4):965-990
Advances in Data Analysis and Classification - Cause-specific hazard models are a popular tool for the analysis of competing risks data. The classical modeling approach in discrete time consists of... 相似文献