全文获取类型
收费全文 | 303313篇 |
免费 | 35875篇 |
国内免费 | 14091篇 |
专业分类
电工技术 | 19199篇 |
技术理论 | 17篇 |
综合类 | 21169篇 |
化学工业 | 56634篇 |
金属工艺 | 16673篇 |
机械仪表 | 18743篇 |
建筑科学 | 22659篇 |
矿业工程 | 8251篇 |
能源动力 | 8543篇 |
轻工业 | 27765篇 |
水利工程 | 5808篇 |
石油天然气 | 15496篇 |
武器工业 | 2773篇 |
无线电 | 35346篇 |
一般工业技术 | 38553篇 |
冶金工业 | 12284篇 |
原子能技术 | 2976篇 |
自动化技术 | 40390篇 |
出版年
2024年 | 1165篇 |
2023年 | 4104篇 |
2022年 | 8121篇 |
2021年 | 11177篇 |
2020年 | 9615篇 |
2019年 | 9364篇 |
2018年 | 9965篇 |
2017年 | 11571篇 |
2016年 | 11194篇 |
2015年 | 14639篇 |
2014年 | 17438篇 |
2013年 | 20797篇 |
2012年 | 21367篇 |
2011年 | 22462篇 |
2010年 | 20778篇 |
2009年 | 19823篇 |
2008年 | 19118篇 |
2007年 | 18058篇 |
2006年 | 17370篇 |
2005年 | 14422篇 |
2004年 | 10512篇 |
2003年 | 9576篇 |
2002年 | 9530篇 |
2001年 | 8348篇 |
2000年 | 6878篇 |
1999年 | 5873篇 |
1998年 | 3921篇 |
1997年 | 3225篇 |
1996年 | 2978篇 |
1995年 | 2363篇 |
1994年 | 1939篇 |
1993年 | 1276篇 |
1992年 | 1079篇 |
1991年 | 774篇 |
1990年 | 589篇 |
1989年 | 499篇 |
1988年 | 353篇 |
1987年 | 261篇 |
1986年 | 208篇 |
1985年 | 107篇 |
1984年 | 84篇 |
1983年 | 83篇 |
1982年 | 73篇 |
1981年 | 62篇 |
1980年 | 63篇 |
1979年 | 30篇 |
1978年 | 6篇 |
1965年 | 3篇 |
1959年 | 15篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
By exploiting a general cyclostationary (CS) statistics-based framework, this letter develops a rigorous and unified asymptotic (large sample) performance analysis setup for a class of blind feedforward timing epoch estimators for linear modulations transmitted through time nonselective flat-fading channels. Within the proposed CS framework, it is shown that several estimators proposed in the literature can be asymptotically interpreted as maximum likelihood (ML) estimators applied on a (sub)set of the second- (and/or higher) order statistics of the received signal. The asymptotic variance of these ML estimators is established in closed-form expression and compared with the modified Crame/spl acute/r-Rao bound. It is shown that the timing estimator proposed by Oerder and Meyr achieves asymptotically the best performance in the class of estimators which exploit all the second-order statistics of the received signal, and its performance is insensitive to oversampling rates P as long as P/spl ges/3. Further, an asymptotically best consistent estimator, which achieves the lowest asymptotic variance among all the possible estimators that can be derived by exploiting jointly the second- and fourth-order statistics of the received signal, is also proposed. 相似文献
23.
Data mining extracts implicit, previously unknown, and potentially useful information from databases. Many approaches have been proposed to extract information, and one of the most important ones is finding association rules. Although a large amount of research has been devoted to this subject, none of it finds association rules from directed acyclic graph (DAG) data. Without such a mining method, the hidden knowledge, if any, cannot be discovered from the databases storing DAG data such as family genealogy profiles, product structures, XML documents, task precedence relations, and course structures. In this article, we define a new kind of association rule in DAG databases called the predecessor–successor rule, where a node x is a predecessor of another node y if we can find a path in DAG where x appears before y. The predecessor–successor rules enable us to observe how the characteristics of the predecessors influence the successors. An approach containing four stages is proposed to discover the predecessor–successor rules. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 621–637, 2006. 相似文献
24.
介绍了一种新的探测雷达最小作用距离的方法,打破了传统的最小跟踪距离受发射脉宽局限的限制,重点介绍对发射线性调频信号的雷达的近距离探测方法,并给出了仿真计算结果。 相似文献
25.
26.
A central event in the life of a cellular system is the interaction between the exterior and the interior compartments. Biochemical signals arrive at the cellular surface, bind to their membrane bound receptor followed by a conformational change triggering the release of an internal chemical or electrical signal.This basic principle is followed by all our perceptive abilities like sense of smell or taste, but also by different signal transduction pathways involved in nerve conductivity, vision, sense of touch or hearing. To follow and mimic this principle of parallel registration is one of the aims of modern nanobiotechnology. If we are able to specifically biofunctionalize small arrays of a solid surface, which could be an electrode or a semiconductor, this approach will enable us to build up devices called “biochips” or “biosensors” that allow the determination of bioactive molecules with high specificity at lowest concentrations. Potential pharmacological active substrates might be screened as well as new receptors may be determined. Applications in genomics as well as proteomics are realistic. The major prerequisite for such a broad spectrum of applications is the fabrication of receptive surfaces. Biomolecules have to be surface‐adsorbed in a highly reproducible, oriented and well organised fashion, a task which in biology is taken by the cellular membranes as external or internal receptive surfaces. The physical principles like hydrogen bonds, electrostatic or hydrophobic interactions that lead to such an organized surface are well known. To synthesize molecular building blocks and to position them onto an otherwise unspecific surface is one of the challenges of nanobiotechnology combining biological knowledge and chemical skills with biophysical techniques that allow to handle or analyze even single molecules. 相似文献
27.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
28.
29.
燕善敏 《徐州工程学院学报》2003,(6)
行政法学的研究应该尽量放宽视角,适应将来法治建设的需要。我们必须把行政行为的概念放到整个法治体系中甚至整个社会的发展中去研究。 相似文献
30.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献