全文获取类型
收费全文 | 30694篇 |
免费 | 84篇 |
国内免费 | 80篇 |
专业分类
系统科学 | 294篇 |
丛书文集 | 514篇 |
教育与普及 | 83篇 |
理论与方法论 | 125篇 |
现状及发展 | 12809篇 |
研究方法 | 1152篇 |
综合类 | 15283篇 |
自然研究 | 598篇 |
出版年
2013年 | 188篇 |
2012年 | 394篇 |
2011年 | 1030篇 |
2010年 | 159篇 |
2008年 | 469篇 |
2007年 | 523篇 |
2006年 | 555篇 |
2005年 | 547篇 |
2004年 | 587篇 |
2003年 | 548篇 |
2002年 | 479篇 |
2001年 | 892篇 |
2000年 | 899篇 |
1999年 | 534篇 |
1992年 | 546篇 |
1991年 | 469篇 |
1990年 | 497篇 |
1989年 | 453篇 |
1988年 | 480篇 |
1987年 | 487篇 |
1986年 | 454篇 |
1985年 | 650篇 |
1984年 | 488篇 |
1983年 | 398篇 |
1982年 | 320篇 |
1981年 | 346篇 |
1980年 | 434篇 |
1979年 | 928篇 |
1978年 | 762篇 |
1977年 | 732篇 |
1976年 | 628篇 |
1975年 | 695篇 |
1974年 | 880篇 |
1973年 | 791篇 |
1972年 | 769篇 |
1971年 | 946篇 |
1970年 | 1288篇 |
1969年 | 952篇 |
1968年 | 862篇 |
1967年 | 902篇 |
1966年 | 872篇 |
1965年 | 606篇 |
1964年 | 198篇 |
1959年 | 346篇 |
1958年 | 564篇 |
1957年 | 398篇 |
1956年 | 372篇 |
1955年 | 305篇 |
1954年 | 332篇 |
1948年 | 275篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
321.
介绍了一种新型的指纹识别装置(晶体传感器的指纹识别装置),并借此分析和研究了指纹识别系统的识别原理和设计方法,这些原理和方法对指导和优化指纹识别系统的设计提供了依据。 相似文献
322.
Localization of a Robotic Capsule for GI Motility Inspection with a Portable Ultrasonic System 总被引:5,自引:0,他引:5
IntroductionResearchesonmicromedicaldeviceandmicromedicalrobot,especiallytheinvivoinspectionsystemworkinginalimentarycanalorinbloodvesselwithlittledamageornondamagetohumanbodyhavebeenundertakenandreportedbyexpertsinmanycountries.Thesesystemsusuallyownmanyadvantagessuchas:smallvolume,lowpowerconsumption,littleinterferencetoworkingsurroundings,socangreatlyenlargethescopesofmedicalexaminationandrelievethepatientsofdiscomfortcausedbynormalprocedures.Thecapsuleendoscope“NORIKAsystem”developedby… 相似文献
323.
科技创新是时代发展的永恒主题 总被引:2,自引:0,他引:2
王勤 《科技情报开发与经济》2004,14(6):192-193
从科技创新的基本特征、类型分析入手,总结介绍了国际科技创新的发展经验与启示,并结合我国国情,提出现阶段我国科技创新的战略框架和基本对策。 相似文献
324.
在室内装潢方面,人们较注重室内布局和装饰,而对给水管道则极少关注.应引起足够的重视。在建筑给水系统中由新型塑料管材替代金属管材已成为趋势。所以,室内给水管应选用新型塑料管材,并且应根据新型塑料管材的特点进行施工。确保给水系统的安装质量。 相似文献
325.
高文华 《科技情报开发与经济》2004,14(6):304-305
以新长铁路为例,从施工前、施工中及施工后的具体情况出发,对过江光缆施工技术进行了详细的说明,就如何减小风险提出了一些建议。 相似文献
326.
1 Introduction
Over the past several years, the preparation and characterization ofnanoscale magnetic materials, especially one-dimensional (1D) nanostructure, have attracted much attention as the nanomaterials would allow investigating the fundamental aspects of magnetic-ordering phenomena in magnetic materials with reduced dimensions and could lead to new potential applications such as data storage technology[1-6]. 相似文献
327.
Rodney G.Downey ;Judith Egan ;Michael R.Fellows ;Frances A.Rosamond ;Peter Shaw 《清华大学学报》2014,(4):329-337
The main purpose of this paper is to exposit two very different, but very general, motivational schemes in the art of parameterization and a concrete example connecting them. We introduce a dynamic version of the DOMINATING SET problem and prove that it is fixed-parameter tractable(FPT). The problem is motivated by settings where problem instances evolve. It also arises in the quest to improve a natural greedy heuristic for the DOMINATING SET problem. 相似文献
328.
Foam nests have evolved independently in several amphibian groups as an adaptive response to prevent predation and desiccation in dry environments. Nests are normally laid on ponds, or in underground galleries, humid forest leaf litter or terrestrial bromeliads. They are built when males or females beat a foam precursor associated with the egg masses extruded by the female. The spawning process requires the synchronic actions of the mating pair to obtain a hemispheric nest that protects the offspring. Herein, we describe the spawning behaviour of Engystomops pustulatus based on videos from 13 nesting couples from the lowlands of western Ecuador. Three variables were measured as indicators of male effort: duration of mixing events, duration of resting periods, and number of kicks per mixing event. We consider that not only male physical effort but also female behaviour influences nest structure. We suggest that nest building requires prolonged and intense physical activity by the male as well as the female’s steady position during spawning and female’s oviposition site selection. Nest building has two phases. In the first phase, the duration of resting periods, the duration of mixing events, and the number of kicks increase and are highly variable. During the second phase the three variables stabilise until the end. The volume of the nest increased mainly during the second phase. In four nesting events we observed kicking movements by the female. To our knowledge, this is the first time that female kicking has been observed in leptodactylid frogs. The function of this behaviour is unknown but our observations suggest that it may be triggered by insufficient male effort. Traditionally, female mate choice in Engystomops has been explained under models of indirect benefits exclusively. We argue that the prolonged male activity during nesting could influence female fitness directly. This will allow the operation of sexual selection via direct benefits. 相似文献
329.
330.