全文获取类型
收费全文 | 17843篇 |
免费 | 1103篇 |
国内免费 | 508篇 |
专业分类
系统科学 | 1449篇 |
丛书文集 | 266篇 |
教育与普及 | 330篇 |
理论与方法论 | 322篇 |
现状及发展 | 946篇 |
研究方法 | 47篇 |
综合类 | 16089篇 |
自然研究 | 5篇 |
出版年
2024年 | 68篇 |
2023年 | 119篇 |
2022年 | 218篇 |
2021年 | 206篇 |
2020年 | 134篇 |
2019年 | 46篇 |
2018年 | 776篇 |
2017年 | 809篇 |
2016年 | 528篇 |
2015年 | 240篇 |
2014年 | 328篇 |
2013年 | 294篇 |
2012年 | 644篇 |
2011年 | 1357篇 |
2010年 | 1167篇 |
2009年 | 853篇 |
2008年 | 1006篇 |
2007年 | 1210篇 |
2006年 | 369篇 |
2005年 | 495篇 |
2004年 | 502篇 |
2003年 | 458篇 |
2002年 | 407篇 |
2001年 | 444篇 |
2000年 | 405篇 |
1999年 | 755篇 |
1998年 | 702篇 |
1997年 | 753篇 |
1996年 | 662篇 |
1995年 | 558篇 |
1994年 | 491篇 |
1993年 | 465篇 |
1992年 | 388篇 |
1991年 | 390篇 |
1990年 | 274篇 |
1989年 | 323篇 |
1988年 | 268篇 |
1987年 | 182篇 |
1986年 | 88篇 |
1985年 | 27篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1970年 | 3篇 |
1969年 | 4篇 |
1968年 | 2篇 |
1967年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
311.
设计了一种下一代互联网中的智能QoS组播路由算法,给定一个QoS组播请求和柔性QoS需求,包括带宽需求、组播端到端延迟区间,延迟抖动区间和出错率区间,寻找一棵QoS组播路由树.提出一种基于演化算法和单纯形算法的混合算法来构造满足上述需求且费用近优QoS柔性组播路由树,兼顾网络负载均衡.仿真结果表明,该算法是可行和有效的,明显优于基于传统遗传算法的QoS组播路由算法. 相似文献
312.
Large Deflection Buckling Spring-Piece (LDBSP) refers to the deformation of an end-fixed flat spring-piece under normal loadings. Plastic deformation usually appears in LDBSP.The static characteristic curve is very particular, because within its linear deflection region, the spring constant can be designed to be any value from minus to plus. With its obvious advantages of large liner deflection range, low spring constant, etc., the LDBSP has now been extensively applied to the exciting device, low-frequency shock absorbers and so on. The static characteristic curve of LDBSP belongs to the nonlinear problem of an arch with varying section. Therefore, it is difficult to obtain it theoretically. The formulae for designing LDBSP have not been set up yet. In this study,the authors apply similarity theory to analyze the liner deflection range A and the spring constant K, and derive the relationship of similarity criterion, finally obtain a set of formulae for designing LDBSP by model test and the least square method, which can be applied in engineering design.Through the research, it is proved that it is unnecessary to keep geometrical similarity of spring-piece shape. This fact extends the application scope of the formulae. The proposed formulae for designing LDBSP thereby can be applied for any dimensions within the range allowed. 相似文献
313.
GanShi-xin 《武汉大学学报:自然科学英文版》2004,9(1):13-17
This paper investigates some conditions which imply the strong laws of large numbers for Banach space valued random variable sequences. Some generalizations of the Marcinkiewicz- Zygmund theorem and the HoffmannJφrgensen and Pisier theorem are obtained. 相似文献
314.
ZhangNing LiuHai-lin YuZhu-xing XiongRui ShiJing 《武汉大学学报:自然科学英文版》2004,9(1):55-58
The characteristics of electronic transport properties: behaviors of magnetization curve and magnetic relaxation of a typical normal superconductor 2H-NbSe2 are investigated. The results show that Tc and △Tc of the samples are 7. 2,0. 18 K, indicating that superconducting energy gap at zero temperature is 1. 1 meV. No fish tail shape is found in the magnetization curves at several temperatures. The relationship between remnant magnetic moment and time reveals that the magnetic flux creep of the sample agrees with the Kim-Anderson thermal activation model with the relaxation rate S=0.000 36 at T=6 K. 相似文献
315.
Xiao Ling Yu Zu-yu Yang Chao Zhu Hua-yue Du Yu-min College of Resource Environmental Science Wuhan University Wuhan Hubei China 《武汉大学学报:自然科学英文版》2004,9(2):247-251
0 IntroductionChitosanisadeacetylatedderivativeofchitin ,containinginitsstructure glucosamineandacetylglucosamine joinedthroughβ (1→ 4 )linkages.ItisinsolubleinwaterandcommonorganicsolventsbutsolubleatapHunder 6 .5acidicmedia.Duetoitsexcellentbiodegradableandbiocompatiblecharacter,chi tosanhasbeenexaminedextensivelyinthepharmaceuticalindus tryforitspotentialinthedevelopmentofdrugdeliverysys tems[1 ,2 ] .Gelatinisabiodegradablepolymerofwidesafety ,pro ducedfromcollagen ,themostabundantprote… 相似文献
316.
ZHAO Wei HU Ke KIMOTO Akitsu MIZUYAMA Takahisa . Institute of Environmental Science Beijing Normal University Beijing China . College of Earth Sciences Jilin University Changchun Jilin China . Laboratory of Erosion Control Graduate School of Agriculture Kyoto University Kyoto Japan 《武汉大学学报:自然科学英文版》2004,9(4):527-532
0 IntroductionManystudieshavebeendoneonthesedimentdischargeinMt.Tanakami .Thosestudiesconcerntheamountofsedi mentsandfewdiscussionsabouttheprocessonly .Andthesedi mentyieldmechanismindevastatedslopeinMt.Tanakamiisnotfullyunderstood.Inordertorecordthewholeprocessofsoilero sionfromthebeginningofprecipitation ,totheendofsedimentmovement,asimulatingexperimentbyusingartificialrainiscon ducted .Basedonthisexperiment,andbyfurthercomparingwiththepreviousdataofsedimentsinthisarea,somebasicdataaboutc… 相似文献
317.
MAOCheng-ying LUYan-sheng 《武汉大学学报:自然科学英文版》2004,9(5):687-693
As the increasing popularity and complexity of Web applications and the emergence of their new characteristics. the testing and maintenance of large, complex Web applications are becoming more complex and difficult. Web applications generally contain lots of pages and are used by enormous users. Statistical testing is an effective way of ensuring their quality. Web usage can be accurately described by Markov chain which has been proved to be an ideal model for software statistical testing. The results of unit testing can b eutilized in the latter stages, wbich is an important strategy for bottom-to-top integration testing, and the other improvement of extended Markov chain model (FMM) is to present the error type vector which is treated as a part of page node. This paper also proposes the algorithm for generating test cases of usage paths. Finally, optional usage reliability evaluation methods and an incremental usability regression testing model for testing and evaluation are presented. 相似文献
318.
In this paper, the superluminal group velocity in a coaxial photonic crystal is studied. The simulation of the effective refraction index in coaxial photonic crystal is performed. The group velocity is calculated based on the transmission line equations and compared with experimental results. 相似文献
319.
提出了一种基于扫描线种子填充的二值图像快速聚类算法 .该算法步骤为 :对二值图像进行扫描 ,如果检测到了目标点 ,则将该点作为新的聚类的种子 ,将该种子扩展到整个目标区域 ,形成一个包含目标区域的聚类 .该算法的特点为 :只需一次扫描即可动态生成所有聚类 ,聚类总数动态生成 ,每一时刻只有一个聚类被处理 ,可提前进行一些后续处理 ,算法描述简单 ,易于编程实现 . 相似文献
320.
多传感器机器人数据采集与融合系统研究 总被引:1,自引:1,他引:1
根据多传感器机器人控制器数据采集量大、数据融合算法复杂、系统实时性强的特点 ,提出了基于ADμC812和TMS32 0F2 0 6的双CPU结构的机器人信息采集与数据融合系统结构 .介绍了该系统的硬件组成、基本工作原理以及接口电路 ,并给出了ADμC812子系统程序流程图 . 相似文献