首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   150987篇
  免费   6274篇
  国内免费   3140篇
电工技术   4186篇
技术理论   10篇
综合类   6234篇
化学工业   23185篇
金属工艺   8430篇
机械仪表   7239篇
建筑科学   8034篇
矿业工程   2528篇
能源动力   3123篇
轻工业   7716篇
水利工程   2348篇
石油天然气   4646篇
武器工业   534篇
无线电   17178篇
一般工业技术   24771篇
冶金工业   6045篇
原子能技术   1031篇
自动化技术   33163篇
  2024年   188篇
  2023年   1060篇
  2022年   1698篇
  2021年   2464篇
  2020年   1950篇
  2019年   1726篇
  2018年   15996篇
  2017年   15225篇
  2016年   11687篇
  2015年   3199篇
  2014年   3446篇
  2013年   4050篇
  2012年   7343篇
  2011年   13739篇
  2010年   12044篇
  2009年   9153篇
  2008年   10328篇
  2007年   11314篇
  2006年   3946篇
  2005年   4518篇
  2004年   3391篇
  2003年   3140篇
  2002年   2454篇
  2001年   1845篇
  2000年   1926篇
  1999年   2065篇
  1998年   1855篇
  1997年   1501篇
  1996年   1450篇
  1995年   1084篇
  1994年   1033篇
  1993年   718篇
  1992年   553篇
  1991年   454篇
  1990年   322篇
  1989年   258篇
  1988年   239篇
  1987年   135篇
  1986年   97篇
  1985年   70篇
  1982年   39篇
  1968年   43篇
  1966年   42篇
  1965年   44篇
  1959年   37篇
  1958年   37篇
  1957年   36篇
  1956年   34篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
941.
Imitated GE ware was one of the most famous products of Jingdezhen porcelain field in Ming dynasty (AD 1368-1644). The exterior features of its body and glaze are very marvelous. Black foot, purple mouth and crazing glaze are the main features of imitated GE ware. Until now, the key conditions of resulting these features are not clearly identified. In order to find the critical elements for firing these features, instrumental neutron activation analysis (INAA) and wavelength-dispersive X-ray fluorescence (WDXRF) were used to determine the element abundance patterns of imitated GE ware body and glaze. The experimental data was compared with that of imitated Longquan celadon and of Longquan celadon. The analytical results indicated that Fe, Ti and Na were the critical elements. The body of imitated GE ware which contains high Fe and Ti are the basic conditions of firing its black body, black foot and purple mouth. The glaze of imitated GE ware which contains high Na is the main condition of producing its crazing glaze. Na is the critical element which enlarges the difference in expansion coefficients between the glaze and body of imitated GE ware. Furthermore, Zijin soil was added into kaolin to make the body rich in Fe and Ti. And something which was rich in Na was used to produce crazing glaze in the manufacturing process of imitated GE ware.  相似文献   
942.
Drawing Power Law Graphs Using a Local/Global Decomposition   总被引:1,自引:0,他引:1  
  相似文献   
943.
We present evidence for a close analogy between the nonlinear behaviour of a pulsed microwave-driven Josephson junction at low temperature and the experimentally observed behaviour of Josephson systems operated below the quantum transition temperature under similar conditions. We specifically address observations of Ramsey-type fringe oscillations, which can be understood in classical nonlinear dynamics as results of slow transient oscillations in a pulsed microwave environment. Simulations are conducted to mimic experimental measurements by recording the statistics of microwave-induced escape events from the anharmonic potential well of a zero-voltage state. Observations consistent with experimentally obtained Ramsey-type oscillations are found in the classical model. An erratum to this article can be found at  相似文献   
944.
The paper investigates correlations in a general theory of quantum measurement based on the notion of instrument. The analysis is performed in the algebraic formalism of quantum theory in which the observables of a physical system are described by a von Neumann algebra, and the states—by normal positive normalized functionals on this algebra. The results extend and generalise those obtained for the classical case where one deals with the full algebra of operators on a Hilbert space.  相似文献   
945.
The (2 w )! reversible transformations on w wires, i.e. reversible logic circuits with w inputs and w outputs, together with the action of cascading, form a group, isomorphic to the symmetric group S 2 w . Therefore, we investigate the group S n as well as one of its subgroups isomorphic to S n/2 × S n/2. We then consider the left cosets, the right cosets, and the double cosets generated by the subgroup. Each element of a coset can function as the representative of the coset. The coset can then be considered as the set of all group elements that differ from the representative by merely multiplying (either to the left or to the right or to both sides) by an arbitrary element of the subgroup. Different choices of the coset space and different choices of the coset representatives lead to six different syntheses for implementing an arbitrary reversible logic operation into hardware. Evaluation of all six methods, by means of three different cost functions (gate cost, switch cost, and quantum cost), leads to a best choice.  相似文献   
946.
An SQL extension is formalized for the management of spatio-temporal data, i.e. of spatial data that evolves with respect to time. The extension is dedicated to applications such as topography, cartography, and cadastral systems, hence it considers discrete changes both in space and in time. It is based on the rigid formalization of data types and of SQL constructs. Data types are defined in terms of time and spatial quanta. The SQL constructs are defined in terms of a kernel of few relational algebra operations, composed of the well-known operations of the 1NF model and of two more, Unfold and Fold. In conjunction with previous work, it enables the uniform management of 1NF structures that may contain not only spatio-temporal but also either purely temporal or purely spatial or conventional data. The syntax and semantics of the extension is fully consistent with the {SQL:2003} standard.  相似文献   
947.
A necessary and sufficient condition is given for a connected bipartite graph to be the incidence graph of a contact family of segments and points. We deduce that any four-connected three-colorable plane graph is the contact graph of a family of segments and that any four-colored planar graph without an induced C4 using four colors is the intersection graph of a family of straight line segments.  相似文献   
948.
Fast Recognition of Fibonacci Cubes   总被引:1,自引:0,他引:1  
Fibonacci cubes are induced subgraphs of hypercubes based on Fibonacci strings. They were introduced to represent interconnection networks as an alternative to the hypercube networks. We derive a characterization of Fibonacci cubes founded on the concept of resonance graphs. The characterization is the basis for an algorithm which recognizes these graphs in O(mlog n) time. A. Vesel supported by the Ministry of Science of Slovenia under the grant 0101-P-297.  相似文献   
949.
通过对活性炭载体进行不同条件的超声波处理获得了具有不同表面化学性质的载体,使用比表面积(BET)、酸碱滴定等技术手段对载体的物理化学性质进行了表征。将经过超声波处理的活性炭载体制备成Pt/C催化剂,并将催化剂直接用于催化反应,考察了活性炭载体的不同超声波处理条件对Pt/C催化剂性能的影响。实验发现,活性炭载体经过超声波处理后,表面灰分含量、pH值和中孔孔容有较大的变化;使用经过60min超声波处理后中孔孔容较大的活性炭作为载体制备的Pt/C催化剂,在催化加氢反应性能测试中显示了最高的催化活性。在此基础上,就活性炭载体的超声波处理对Pt/C催化剂活性的影响进行了讨论。  相似文献   
950.
The security of a deterministic quantum scheme for communication, namely the LM05 [1], is studied in presence of a lossy channel under the assumption of imperfect generation and detection of single photons. It is shown that the scheme allows for a rate of distillable secure bits higher than that pertaining to BB84 [2]. We report on a first implementation of LM05 with weak pulses.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号