全文获取类型
收费全文 | 166篇 |
免费 | 13篇 |
专业分类
化学 | 143篇 |
力学 | 1篇 |
数学 | 23篇 |
物理学 | 12篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 10篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 11篇 |
2011年 | 16篇 |
2010年 | 14篇 |
2009年 | 8篇 |
2008年 | 21篇 |
2007年 | 9篇 |
2006年 | 2篇 |
2005年 | 8篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1965年 | 2篇 |
1926年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有179条查询结果,搜索用时 281 毫秒
91.
We study two approaches to replace a finite mathematical programming problem with inequality constraints by a problem that contains only equality constraints. The first approach lifts the feasible set into a high-dimensional space by the introduction of quadratic slack variables. We show that then not only the number of critical points but also the topological complexity of the feasible set grow exponentially. On the other hand, the second approach bases on an interior point technique and lifts an approximation of the feasible set into a space with only one additional dimension. Here only Karush–Kuhn–Tucker points with respect to the positive and negative objective function in the original problem give rise to critical points of the smoothed problem, so that the number of critical points as well as the topological complexity can at most double. 相似文献
92.
In the screening of complex mixtures, for example combinatorial libraries, natural extracts, and metabolic incubations, different
approaches are used for integrated bioaffinity screening. Four major strategies can be used for screening of bioactive mixtures
for protein targets—pre-column and post-column off-line, at-line, and on-line strategies. The focus of this review is on recent
developments in post-column on-line screening, and the role of mass spectrometry (MS) in these systems. On-line screening
systems integrate separation sciences, mass spectrometry, and biochemical methodology, enabling screening for active compounds
in complex mixtures. There are three main variants of on-line MS based bioassays: the mass spectrometer is used for ligand
identification only; the mass spectrometer is used for both ligand identification and bioassay readout; or MS detection is
conducted in parallel with at-line microfractionation with off-line bioaffinity analysis. On the basis of the different fields
of application of on-line screening, the principles are explained and their usefulness in the different fields of drug research
is critically evaluated. Furthermore, off-line screening is discussed briefly with the on-line and at-line approaches. 相似文献
93.
Roland Hord Gerhard Cordier Kathrin Hofmann Alexander Buckow Gwendolyne Pascua Hubertus Luetkens Prof. Dr. Lambert Alff Prof. Dr. Barbara Albert 《无机化学与普通化学杂志》2011,637(9):1114-1117
Through low‐temperature synthesis in CsOH flux, lanthanum cuprate La2CuO4 can be obtained in a metastable form, the so‐called T′ modification (tetragonal, I4/mmm, no. 139, a = 400.95(2) pm, c = 1254.08(7) pm). When heated, this T′ phase transforms into a K2NiF4‐type modification, whose crystal structure was now refined from X‐ray powder data (tetragonal, I4/mmm, no. 139, a = 383.29(3) pm, c = 1331.3(2) pm at T = 1073 K). The well‐known orthorhombic phase (s.g. Cmce, no. 64, a = 536.14(3) pm, b = 1315.53(8) pm, c = 540.20(3) pm) – usually obtained via conventional solid state synthesis – was observed to form upon cooling from the K2NiF4‐type modification. High‐temperature powder diffractometry allowed crystal structure refinements for all of the three phases. 相似文献
94.
Jan W. Post Hubertus V.M. Hamelers Cees J.N. Buisman 《Journal of membrane science》2009,330(1-2):65-72
Reverse electrodialysis is a membrane-based technique for production of sustainable electricity from controlled mixing of a diluted electrolyte solution (e.g., river water) and a concentrated electrolyte solution (e.g., sea water). Reverse electrodialysis has been investigated with pure sodium chloride solutions. In practice, however, in most cases also other ions are present in both feed solutions. In the present paper, the effect of multivalent ions on the performance of a reverse electrodialysis stack was investigated. Results show that, besides a higher stack resistance in presence of multivalent ions, especially the presence of multivalent ions in the dilute solution has a lowering effect on the stack voltage. This can be explained by an observed transport of these ions from the diluted electrolyte solution to the concentrated electrolyte solution. In order to prevent or hamper this transport against the activity gradient, monovalent-selective membranes can be used. This shows indeed better results with respect to the stack voltage. Therefore, it would be beneficial to use monovalent-selective membranes in reverse electrodialysis, especially in the case of a relatively high content of multivalent ions in the dilute (i.e., in the first stages of the installation where the sodium chloride content in the dilute is still relatively low). 相似文献
95.
96.
97.
Design,synthesis and biological activity of rigid cannabinoid CB1 receptor antagonists 总被引:1,自引:0,他引:1
Stoit AR Lange JH Hartog AP Ronken E Tipker K Stuivenberg HH Dijksman JA Wals HC Kruse CG 《Chemical & pharmaceutical bulletin》2002,50(8):1109-1113
The design, synthesis and biological activities of potent pyrazole-based tricyclic CB1 receptor antagonists (2) are described. The key synthetic step involves the ring closure of the lithiated alpha, gamma-keto ester adduct (4). The optimal nitroderivative (28) in this series exhibits a high CB1 receptor affinity (pKi=7.2) as well as very potent antagonistic activity (pA2=8.8) in vitro. The regioselectivity of the pyrazole ring closure is shown to depend strongly on the aromatic substitution pattern of the applied arylhydrazine. 相似文献
98.
99.
Catalin Vasile Maftei Martin Heiko Franz Christian Kleeberg Ion Neda 《Molecules (Basel, Switzerland)》2021,26(11)
The substance class of the well-known Cinchona alkaloids is widened by 6′-Amino-cinchonine and 6′-Amino-cinchonidine, novel compounds which incorporate a primary amino function in the quinolinic ring system. These key intermediates open the field for a range of fruitful chemistry. Here is described a short and direct pathway for the synthesis of triazole containing derivatives of the above-mentioned substances using the [3 + 2] Huisgen cycloaddition. For this purpose, the amines were first converted into the corresponding azides. Based on this, non-substituted and silyl-protected triazoles were synthesized as examples. Furthermore, didehydrated derivatives of quincorine and quincoridine were used as addition partners, resulting in compounds that carry the quinuclidine ring of the cinchona alkaloids at both ends. Some of these compounds were examined radiographically to investigate the position of the quinuclidine ring to the triazole. The solid-state structures of compounds 10, 11 and 28 were determined by X-ray diffraction analyses. 相似文献
100.
Monique G.M. de Sain-van der Velden Maria van der Ham Judith J. Jans Gepke Visser Peter M. van Hasselt Hubertus C.M.T. Prinsen Nanda M. Verhoeven-Duif 《Analytica chimica acta》2015
Methylmalonic acid (MMA) and total homocysteine (tHCYS) concentrations are used to detect acquired and inborn errors of cobalamin (vitamin B12, Cbl) metabolism and to evaluate the effect of therapeutic interventions. Dried blood spot sampling offers a patient-friendly and easy alternative to plasma sampling. However, dried blood spot concentrations are not necessarily equal to plasma concentrations. Therefore, the objective of this work was to establish the relationship between MMA and tHYS dried blood spot and plasma concentrations to facilitate clinical implementation of dried blood spot sampling. MMA and tHCYS in both plasma and DBS were validated on ultra performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS). While position of the punch (in DBS) did affect tHCYS concentration, no influence of hematocrit (Ht) and blood volume on both MMA and tHCYS concentrations was observed. The plasma assay performed better than the DBS assay by most criteria. However, the DBS matrix was superior for tHCYS stability. Paired plasma and DBS samples were obtained from patients suspected for Cbl deficiency and from patients with a known inborn error of metabolism affecting MMA or tHCYS concentration. Based on the strong correlation of tHCYS in both matrices (y = 0.46 ± 1.12 (r2 = 0.91)), determination of tHCYS in plasma can be replaced by tHCYS in DBS. However, for MMA, a correlation in the higher (pathological) range of MMA exist, but no correlation was observed in the lower ranges. Therefore the added value of MMA concentrations in DBS is currently unknown and should be further investigated. 相似文献