全文获取类型
收费全文 | 15337篇 |
免费 | 2733篇 |
国内免费 | 2235篇 |
专业分类
化学 | 10868篇 |
晶体学 | 251篇 |
力学 | 904篇 |
综合类 | 158篇 |
数学 | 1741篇 |
物理学 | 6383篇 |
出版年
2024年 | 57篇 |
2023年 | 275篇 |
2022年 | 517篇 |
2021年 | 569篇 |
2020年 | 708篇 |
2019年 | 663篇 |
2018年 | 602篇 |
2017年 | 547篇 |
2016年 | 798篇 |
2015年 | 832篇 |
2014年 | 939篇 |
2013年 | 1250篇 |
2012年 | 1530篇 |
2011年 | 1481篇 |
2010年 | 1060篇 |
2009年 | 1028篇 |
2008年 | 1167篇 |
2007年 | 1004篇 |
2006年 | 824篇 |
2005年 | 706篇 |
2004年 | 532篇 |
2003年 | 458篇 |
2002年 | 421篇 |
2001年 | 367篇 |
2000年 | 299篇 |
1999年 | 257篇 |
1998年 | 187篇 |
1997年 | 154篇 |
1996年 | 161篇 |
1995年 | 117篇 |
1994年 | 129篇 |
1993年 | 101篇 |
1992年 | 92篇 |
1991年 | 82篇 |
1990年 | 67篇 |
1989年 | 67篇 |
1988年 | 44篇 |
1987年 | 25篇 |
1986年 | 41篇 |
1985年 | 35篇 |
1984年 | 32篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Olga Ordeig Craig E Banks Trevor J Davies F Javier del Campo Francesc Xavier Mu?oz Richard G Compton 《Analytical sciences》2006,22(5):679-683
Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide ions and are shown to be analytical useful. Two types of ultra-microelectrode arrays are used; the first consist of 256 individual electrodes of 5 microm in radius, 170 of which are electrochemically active in a cubic arrangement which are separated from their nearest neighbour by a distance of 100 microm. The second array compromises 2597 electrodes of 2.5 microm in radius and of which 1550 of which are electrochemically active in a hexagonal arrangement separated by the nearest neighbour by 55 microm. Well defined voltammetric waves are found with peak currents proportional to the concentration of hydroxide ions in the range 50 microM to 1 mM. Detection limits of 20 microM using the 170 ultra-microelectrode and 10 microM with the 1550 ultra-microelectrode array are shown to be possible but with a higher sensitivity of 4 mA M(-1) observed using the 1550 ultra-microelectrode array compared to 1.2 mA M(-1) with the 170 ultra-microelectrode array. 相似文献
42.
This paper addresses a kind of risk decision-making problem existing widely in public administration and business management, which is characterized by (1) occurrence probabilities of states of nature can be estimated by analysing historical observations, but historical observations of different objects are unhomogeneous, (2) the relation between observations and occurrence probabilities of states of nature are affected by some qualitative and quantitative indicators, (3) it is a real-time decision-making problem, that is, there are many decisions for different objects to be made in a limited time, (4) considering decision's execution, impact of resource constrains is an important issue in decision-making process. In this paper, we develop a rule-based approach to address the problem. In the proposed approach, a two-step clustering method is employed to classify objects into categories, and observations in each category can be approximately viewed as homogeneous. For objects in each category, occurrence probabilities of states of nature are estimated by logistic regression, and the decision rule is obtained through solving an optimization model, which is to minimize the total decision risks while satisfying resource constrains. Effect and efficacy of our approach are illustrated through its application to China's customs inspection decision. 相似文献
43.
Model and empirical study on some collaboration networks 总被引:8,自引:0,他引:8
Pei-Pei Zhang Kan Chen Yue He Tao Zhou Bei-Bei Su Yingdi Jin Hui Chang Yue-Ping Zhou Li-Cheng Sun Bing-Hong Wang Da-Ren He 《Physica A》2006,360(2):599-616
In this paper we present an empirical study of a few practical systems described by cooperation networks, and propose a model to understand the results obtained. We study four non-social systems, which are the Bus Route Networks of Beijing and Yangzhou, the Travel Route Network of China, Huai-Yang recipes of Chinese cooked food, and a social system, which is the Collaboration Network of Hollywood Actors. In order to explain the results related to the degree distribution, act-degree distribution and act-size distribution (especially about the degree distribution, which may be better fitted using a stretched exponential distribution (SED)), we suggest a simple model to show a possible evolutionary mechanism for the emergence of such networks. The analytic and numerical results obtained from the model are in good agreement with the empirical results. 相似文献
44.
Francisco-Javier Muñoz-Delgado Victoriano Ramirez-González Paul Sablonnière 《分析论及其应用》1995,11(1):62-71
In this work we study linear polynomial operators preserving some consecutive i-convexities and leaving invariant the polynomials
up to a certain degree. First, we study the existence of an incom patibility between the conservation of certain i-convexities
and the invariance of a space of polynomials. Interpolation properties are obtained and a theorem by Berens and DeVore about
the Bernstein's operator is extended. Finally, from these results a generalized Bernstein's operator is obtained.
This work was supported by Junta de Andalucia. Grupo de investigación: Matemática Aplicada. Código: 1107 相似文献
45.
46.
47.
48.
Rong‐Min Wang Nai‐Pu He Yu‐Feng He Yun‐Tao Xie Yun‐Pu Wang Eishun Tsuchida 《先进技术聚合物》2005,16(8):638-641
Water‐soluble low molecular weight chitosan of nanometer level and its copper complexes were prepared, and characterized by IR spectra, elemental analysis and gel permeation chromatography (GPC). The modes and mechanism of these copper complexes interaction with DNA were studied by a fluorescent probe method and electrophoresis analysis. It is suggested that there are electrostatic and intercalation modes of copper complexes interacting with DNA. At first, the cationic complex electrostaticly binds to the negatively charged phosphate backbone of DNA, and then a portion of the complex intercalates between the base pairs on the DNA duplex strand. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
49.
Xu Wen-Yang Guo Chang-Jie Do Tao 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(4):325-331
A member of the novel family of crystalline microporous aluminophosphates, AlPO4-12, was synthesized by hydrothermal crystallization using different aluminum-containing compounds. Three new crystalline phases were obtained by varying the composition of the reaction mixture. The effect of the synthesis conditions on the hudrothermal process and the kinetics of crystallization are discussed. The apparent activation energies obtained for AlPO4-12 are 20.9 and 14.6 kcal/mol for nucleation and crystallization, respectively. The adsorption isotherms of one AlPO4-12 product were measured. 相似文献
50.