全文获取类型
收费全文 | 33273篇 |
免费 | 1429篇 |
国内免费 | 1452篇 |
专业分类
化学 | 10472篇 |
晶体学 | 254篇 |
力学 | 430篇 |
综合类 | 80篇 |
数学 | 15859篇 |
物理学 | 4328篇 |
无线电 | 4731篇 |
出版年
2024年 | 31篇 |
2023年 | 421篇 |
2022年 | 282篇 |
2021年 | 380篇 |
2020年 | 547篇 |
2019年 | 722篇 |
2018年 | 651篇 |
2017年 | 538篇 |
2016年 | 621篇 |
2015年 | 817篇 |
2014年 | 1227篇 |
2013年 | 1928篇 |
2012年 | 1460篇 |
2011年 | 2415篇 |
2010年 | 1848篇 |
2009年 | 2349篇 |
2008年 | 2495篇 |
2007年 | 2322篇 |
2006年 | 1818篇 |
2005年 | 1408篇 |
2004年 | 1240篇 |
2003年 | 1187篇 |
2002年 | 1378篇 |
2001年 | 742篇 |
2000年 | 659篇 |
1999年 | 729篇 |
1998年 | 616篇 |
1997年 | 507篇 |
1996年 | 557篇 |
1995年 | 563篇 |
1994年 | 474篇 |
1993年 | 411篇 |
1992年 | 371篇 |
1991年 | 269篇 |
1990年 | 237篇 |
1989年 | 267篇 |
1988年 | 169篇 |
1987年 | 155篇 |
1986年 | 146篇 |
1985年 | 197篇 |
1984年 | 165篇 |
1983年 | 110篇 |
1982年 | 154篇 |
1981年 | 130篇 |
1980年 | 82篇 |
1979年 | 74篇 |
1978年 | 71篇 |
1977年 | 58篇 |
1976年 | 47篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
191.
192.
193.
较为详细地介绍AT91SAM7S64芯片的I2C接口控制器中外围数据控制器(PDC)的使用方式,并将其与AT24C04之间的通信作为实例给出完整的应用开发流程和软硬件详细描述。该方法的可行性已经为工程实践和实际产品所证实。该操作也可推广到其他AT91SAM7S系列ARM处理器与其他I2C接口器件间的通信。并对其他拥有外围数据控制器的接口开发有一定的借鉴意义。 相似文献
194.
195.
196.
197.
Homogeneously prepared tosylcelluloses (TC) with degrees of substitution (DS) of DSTos 0.1–1.8 were used as intermediates for the synthesis of methylaminocelluloses (MAC) by nucleophilic substitution with methylamine. TC with DSTos up to 1.1 were shown to be valuable intermediates for selective synthesis of MAC with DSMA varying from 0.1 to approximately 1. No nucleophilic substitution was observed at higher DSTos. At the chosen reaction conditions (60 °C, 48 h) residual tosyl moieties remained unchanged and little hydrolysis took place. The samples obtained were characterized by means of elemental analysis, FTIR and 13C CP/MAS NMR spectroscopy. 13C CP/MAS NMR spectroscopy was found to be an efficient tool for quantification of DSMA. Furthermore, the swelling behaviour in water was investigated and preliminary tests concerning the bilirubin adsorption capacity of MAC were carried out. 相似文献
198.
Parameters of Gaussian multivariate models are often estimated using the maximum likelihood approach. In spite of its merits, this methodology is not practical when the sample size is very large, as, for example, in the case of massive georeferenced data sets. In this paper, we study the asymptotic properties of the estimators that minimize three alternatives to the likelihood function, designed to increase the computational efficiency. This is achieved by applying the information sandwich technique to expansions of the pseudo-likelihood functions as quadratic forms of independent normal random variables. Theoretical calculations are given for a first-order autoregressive time series and then extended to a two-dimensional autoregressive process on a lattice. We compare the efficiency of the three estimators to that of the maximum likelihood estimator as well as among themselves, using numerical calculations of the theoretical results and simulations. 相似文献
199.
Matthew D. Horton 《Linear algebra and its applications》2007,425(1):130-142
After defining and exploring some of the properties of Ihara zeta functions of digraphs, we improve upon Kotani and Sunada’s bounds on the poles of Ihara zeta functions of undirected graphs by considering digraphs whose adjacency matrices are directed edge matrices. 相似文献
200.
Yasufumi Hashimoto 《Journal of Number Theory》2007,122(2):324-335
In [P. Sarnak, Class numbers of indefinite binary quadratic forms, J. Number Theory 15 (1982) 229-247], it was proved that the Selberg zeta function for SL2(Z) is expressed in terms of the fundamental units and the class numbers of the primitive indefinite binary quadratic forms. The aim of this paper is to obtain similar arithmetic expressions of the logarithmic derivatives of the Selberg zeta functions for congruence subgroups of SL2(Z). As applications, we study the Brun-Titchmarsh type prime geodesic theorem and the asymptotic formula of the sum of the class number. 相似文献