全文获取类型
收费全文 | 795篇 |
免费 | 22篇 |
国内免费 | 3篇 |
专业分类
化学 | 561篇 |
晶体学 | 5篇 |
力学 | 10篇 |
数学 | 150篇 |
物理学 | 94篇 |
出版年
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 25篇 |
2015年 | 20篇 |
2014年 | 13篇 |
2013年 | 27篇 |
2012年 | 34篇 |
2011年 | 39篇 |
2010年 | 39篇 |
2009年 | 19篇 |
2008年 | 50篇 |
2007年 | 54篇 |
2006年 | 55篇 |
2005年 | 43篇 |
2004年 | 28篇 |
2003年 | 31篇 |
2002年 | 23篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1972年 | 5篇 |
1970年 | 7篇 |
1968年 | 4篇 |
1964年 | 5篇 |
1959年 | 3篇 |
排序方式: 共有820条查询结果,搜索用时 46 毫秒
81.
Jeff Op de Beeck Wim De Malsche Joris Vangelooven Han Gardeniers Gert Desmet 《Journal of chromatography. A》2010,1217(39):6077-6084
We report on the possibility to perform HDC in micropillar array columns and the potential advantages of such a system. The HDC performance of a pillar array column with pillar diameter = 5 μm and an interpillar distance of 2.5 μm has been characterized using both a low MW tracer (FITC) and differently sized polystyrene bead samples (100, 200 and 500 nm). The reduced plate height curves that were obtained for the different investigated markers all overlapped very well, and attained a minimum value of about hmin = 0.3 (reduction based on the pillar diameter), corresponding to 1.6 μm in absolute value and giving good prospects for high efficiency separations. The obtained reduced retention time values were in fair agreement with that predicted by the Di Marzio and Guttman model for a flow between flat plates, using the minimal interpillar distance as characteristic interplate distance. 相似文献
82.
Xavi Illa Wim De Malsche Han Gardeniers Gert Desmet Albert Romano-Rodríguez 《Journal of chromatography. A》2010,1217(37):5817-5821
An experimental study of a micromachined non-porous pillar array column performance under non-retentive conditions is presented. The same pillar structure has been fabricated in cyclo-olefin polymer (COP) chips with three different depths via hot embossing and pressure-assisted thermal bonding. The influence of the depth on the band broadening along with the already known contribution arising from the top and bottom cover plates has been studied. The experimental results exhibit reduced plate heights as low as 0.2, which are in agreement with the previous experimental work. Moreover, the constant values of the reduced Van Deemter expression are also in accordance with the previous studies. A more exhaustive study of the C-term band broadening is also presented, showing that comparing the space between the pillars with different open tubular rectangular channels offers a good estimation of the C-term band broadening that is obtained experimentally. These experimental results, hence, confirm that micromachined pillar array columns fabricated in COP can achieve the same performance as the ones fabricated in silicon for the presently studied pillar channel design. 相似文献
83.
Frederik Detobel Ken Broeckhoven Joke Wellens Bert Wouters Remco Swart Mario Ursem Gert Desmet Sebastiaan Eeltink 《Journal of chromatography. A》2010,1217(18):3085-3090
An experimental study was performed to investigate the effects of column parameters and gradient conditions on the separation of intact proteins using styrene-based monolithic columns. The effect of flow rate on peak width was investigated at constant gradient steepness by normalizing the gradient time for the column hold-up time. When operating the column at a temperature of 60 °C a small C-term effect was observed in a flow rate range of 1–4 μL/min. However, the C-term effect on peak width is not as strong as the decrease in peak width due to increasing flow rate. The peak capacity increased according to the square root of the column length. Decreasing the macropore size of the polymer monolith while maintaining the column length constant, resulted in an increase in peak capacity. A trade-off between peak capacity and total analysis time was made for 50, 100, and 250 mm long monolithic columns and a microparticulate column packed with 5 μm porous silica particles while operating at a flow rate of 2 μL/min. The peak capacity per unit time of the 50 mm long monolithic column with small pore size was superior when the total analysis time is below 120 min, yielding a maximum peak capacity of 380. For more demanding separations the 250 mm long monolith provided the highest peak capacity in the shortest possible time frame. 相似文献
84.
Vikram Kestens Gert Roebben Thomas Linsinger 《Accreditation and quality assurance》2010,15(5):269-281
Based on a standard test method for purity by differential scanning calorimetry (DSC), ASTM E 928, a purity determination
method for highly pure polycyclic aromatic hydrocarbons (PAHs) has been developed and validated. The robustness of the developed
method was investigated by determining, under varying measurement conditions, the purity of two PAH certified reference materials
(CRMs), benzo[c]phenanthrene and dibenzo[a,h]anthracene. The repeatability and intermediate precision of the developed method was determined by analysing the purity of
benzo[c]phenanthrene and dibenzo[a,h]anthracene and PAH candidate CRMs indeno[1,2,3-c,d]pyrene, 6-methylchrysene and benzo[a]pyrene. The trueness of the method was studied using the same (candidate) CRMs and a series of 42 other PAH CRMs. For each
of the five (candidate) CRMs, a full measurement uncertainty budget was developed. Also for PAH materials for which the DSC
purity determination method has not been explicitly validated, the relative expanded measurement uncertainty was estimated. 相似文献
85.
Gerd Vanhoenacker Alberto Dos Santos Pereira Takashi Kotsuka Deirdre Cabooter Gert Desmet Pat Sandra 《Journal of chromatography. A》2010,1217(19):3217-3222
The performance of a polymeric stationary phase with reversed-phase properties (ET-RP1) was evaluated for LC separations at elevated temperature. The most significant observation was that the reduced plate height (h) decreased from 3.4 at 25 °C (optimal flow 0.5 mL/min) to 2.4 at 150 °C (optimal flow 2.5 mL/min) which is comparable to the efficiency obtained with silica-based reversed-phase columns of 4.6 mm ID operated at 0.8 mL/min. The phase showed no deterioration after long use at 150 °C within the pH range 1–9. Catalytic activity originating from the stationary phase material, e.g. as experienced on zirconium columns operated at elevated temperature, was absent. The performance of ET-RP1 is illustrated with the analysis of some pharmaceutical samples by LC and LC–MS. Operation at elevated temperature also allows to reduce the amount of organic modifier or to replace acetonitrile and methanol by the biodegradable ethanol. 相似文献
86.
Supervised learning methods are powerful techniques to learn a function from a given set of labeled data, the so-called training data. In this paper the support vector machines approach is applied to an image classification task. Starting with the corresponding Tikhonov regularization problem, reformulated as a convex optimization problem, we introduce a conjugate dual problem to it and prove that, whenever strong duality holds, the function to be learned can be expressed via the dual optimal solutions. Corresponding dual problems are then derived for different loss functions. The theoretical results are applied by numerically solving a classification task using high dimensional real-world data in order to obtain optimal classifiers. The results demonstrate the excellent performance of support vector classification for this particular problem. 相似文献
87.
Bart J. Crielaard Cristianne J. F. Rijcken Lingdong Quan Steffen vanderWal Isil Altintas Martin vanderPot John A. W. Kruijtzer Rob M. J. Liskamp Raymond M. Schiffelers Cornelus F. vanNostrum Wim E. Hennink Dong Wang Twan Lammers Gert Storm 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(29):7366-7370
88.
Gideon Steyl Gert J. Kruger Andreas Roodt 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(10):m473-m475
The molecules of the title complex, [Rh(Trop)(CO)2] (Trop is 2‐hydroxycyclohepta‐2,4,6‐trienonate, C7H5O2), exhibit symmetrical but non‐crystallographic square‐planar molecular geometry, with Rh—C distances of 1.825 (10) and 1.826 (9) Å, Rh—O distances of 2.021 (5) and 2.032 (5) Å, and an O—Rh—O bite angle of 79.4 (2)°. Strong Rh⋯Rh and Rh⋯C intermolecular interactions of 3.683 (3) and 3.650 (5) Å, respectively, are also observed. 相似文献
89.
90.
Given an optimization problem with a composite of a convex and componentwise increasing function with a convex vector function as objective function, by means of the conjugacy approach based on the perturbation theory, we determine a dual to it. Necessary and sufficient optimality conditions are derived using strong duality. Furthermore, as special case of this problem, we consider a location problem, where the “distances” are measured by gauges of closed convex sets. We prove that the geometric characterization of the set of optimal solutions for this location problem given by Hinojosa and Puerto in a recently published paper can be obtained via the presented dual problem. Finally, the Weber and the minmax location problems with gauges are given as applications. 相似文献