全文获取类型
收费全文 | 624篇 |
免费 | 21篇 |
国内免费 | 11篇 |
专业分类
化学 | 430篇 |
晶体学 | 5篇 |
力学 | 10篇 |
数学 | 90篇 |
物理学 | 121篇 |
出版年
2023年 | 2篇 |
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 21篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 34篇 |
2011年 | 47篇 |
2010年 | 34篇 |
2009年 | 24篇 |
2008年 | 42篇 |
2007年 | 48篇 |
2006年 | 34篇 |
2005年 | 34篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 18篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有656条查询结果,搜索用时 15 毫秒
61.
Distribution of the strength of acid sites in mildly steamed HZSM-5 studied by IR spectroscopy 总被引:1,自引:0,他引:1
Jerzy Datka Barbara Gil Pawel Baran Brigitte Staudte 《Reaction Kinetics and Catalysis Letters》2002,77(2):209-217
Steaming resulted in modification of the distribution of acid strength of OH groups. The contribution of less acidic sites increased and new, very strongly acidic hydroxyls characterized by IR band at 3590 cm-1 appeared. 相似文献
62.
A new location problem is formulated and solved. It is the continuous version of the grey pattern problem which is a special case of the Quadratic Assignment Problem. The problem is a minimization of a convex function subject to non-convex constraints and has infinitely many optimal solutions. We propose several mathematical programming formulations that are suitable for a multi-start heuristic algorithm. In addition to solving these formulations by the Solver in Excel and Mathematica, a special Nelder–Mead algorithm is proposed. This special algorithm provided the best results. One suggested modification may improve the performance of the Nelder–Mead algorithm for other optimization problems as well. 相似文献
63.
We present the results on the partitioning of doxorubicin (DOX), a potent anticancer drug, through the model membrane system, self-assembled monolayers (SAMs) on gold electrodes. The monolayers were formed from alkanethiols of comparable length with different ω-terminal groups facing the aqueous electrolyte: the hydrophobic -CH(3) groups for the case of dodecanethiol SAMs or hydrophilic -OH groups of mercaptoundecanol SAMs. The electrochemical experiments combined with the surface plasmon resonance (SPR) and gravimetric studies show that doxorubicin is likely adsorbed onto the surface of hydrophilic monolayer, while for the case of the hydrophobic one the drug mostly penetrates the monolayer moiety. The adsorption of the drug hinders further penetration of doxorubicin into the monolayer moiety. 相似文献
64.
Zhang S Majewski PW Keskar G Pfefferle LD Osuji CO 《Langmuir : the ACS journal of surfaces and colloids》2011,27(18):11616-11621
Lyotropic nanowire dispersions are attractive precursors for semiconductor device fabrication because they permit the alignment control of active nanomaterials. The reliable production of nanowire-based mesophases, however, is very challenging in practice. We show that appropriately functionalized high-aspect-ratio nanowires of single-crystal ZnO spontaneously form nematic phases in organic and aqueous media. These systems show isotropic, biphasic, and nematic phases on increasing concentration, in reasonable agreement with Onsager's theory for rigid rods interacting via excluded volume. Suspensions were readily processed to produce films with large-area monodomains of aligned nanowires. Imprints of the director field in quiescently dried films display a propensity for bend deformation in the organic mesophase versus splay deformation in the aqueous case, suggesting that system elasticity may be tuned via surface functionalization. These results provide critical insight for the utilization of semiconductor nanowires as novel mesogens and further enable the use of solution-based routes for fabricating optoelectronic devices. 相似文献
65.
A new approach to the rapid determination of amoxicillin (AMO) in human plasma followed by solid phase microextraction (SPME) fiber coatings based on conducting polymers (polypyrrole and polythiophene) and high performance liquid chromatography (HPLC) has been described. The porous structures of the electrochemically deposited polymer coatings have been characterized by scanning electron microscopy (SEM). The experimental parameters relating to the extraction efficiency of the SPME fibers such as pH, extraction time and desorption conditions (solvents, time) were studied and selected. The SPME/HPLC-UV method was linear over a working range of 1-50 μg ml(-1). The inter-day accuracy (expressed as coefficients of variations, CVs) was less than 15% and precision (expressed as the relative standard deviations, RSDs) with percentage values was less than 5.9%. Amoxicillin was found to be stable in the human plasma at room temperature (20 °C) within 8 hours. The developed method was successfully applied to the analysis of real human plasma samples. The limit of detection and limit of quantification for amoxicillin in plasma were 1.21 μg ml(-1) and 3.48 μg ml(-1), respectively. 相似文献
66.
67.
Pawel Winter 《Operations Research Letters》2005,33(4):395-402
We give a number of structural results for the problem of constructing a minimum-length 2-connected network for a set of terminals in a graph, where edge-weights satisfy the triangle inequality. A new algorithmic framework, based on our structural results, is given. 相似文献
68.
Pawel J. Kulesza Silvia Zamponi Marcin A. Malik Krzysztof Miecznikowski Mario Berrettoni Roberto Marassi 《Journal of Solid State Electrochemistry》1997,1(1):88-93
Using Prussian blue (PB) electrodeposited on gold-covered foil as a model system, we have demonstrated the usefulness of
the time-derivative measurements of absorbance versus potential (linear potential-scan voltabsorptometry) for spectroelectrochemical
characterization of thin electrochromic films. The time-derivative signals were monitored for PB at 680 and 420 nm in potassium,
sodium and lithium electrolytes. Information obtained from cyclic voltabsorptometry is equivalent or complementary to that
from conventional cyclic voltammetry. In the case of PB films investigated in lithium electrolyte, the voltabsorptometric
time-derivative peaks are better defined than the respective voltammetric peaks. The combination of voltabsorptometry with
voltammetry enables molar absorptivity and/or film loading to be determined. Also, concentration changes of differently colored
mixed-valence redox centers can be monitored as a function of applied potential.
Received: 16 January 1997 / Accepted: 11 March 1997 相似文献
69.
70.
Pawel Winter 《BIT Numerical Mathematics》1985,25(3):485-496
The generalized Steiner problem (GSP) is concerned with the determination of a minimum cost subnetwork of a given network where some (not necessarily all) vertices satisfy certain pairwise (vertex or edge) connectivity requirements.The GSP has applications to the design of water and electricity supply networks, communication networks and other large-scale systems where connectivity requirements ensure the communication between the selected vertices when some vertices and/or edges can become inoperational due to scheduled maintenance, error, or overload.The GSP is known to beNP-complete. In this paper we show that if the subnetwork is required to be biconnected or respectively edge-biconnected, and the underlying network is outerplanar, the GSP can be solved in linear time. 相似文献