全文获取类型
收费全文 | 19172篇 |
免费 | 1663篇 |
国内免费 | 735篇 |
专业分类
电工技术 | 373篇 |
综合类 | 1294篇 |
化学工业 | 6134篇 |
金属工艺 | 359篇 |
机械仪表 | 1425篇 |
建筑科学 | 1253篇 |
矿业工程 | 1875篇 |
能源动力 | 260篇 |
轻工业 | 913篇 |
水利工程 | 294篇 |
石油天然气 | 1568篇 |
武器工业 | 112篇 |
无线电 | 625篇 |
一般工业技术 | 2053篇 |
冶金工业 | 501篇 |
原子能技术 | 110篇 |
自动化技术 | 2421篇 |
出版年
2024年 | 55篇 |
2023年 | 139篇 |
2022年 | 339篇 |
2021年 | 430篇 |
2020年 | 469篇 |
2019年 | 355篇 |
2018年 | 395篇 |
2017年 | 484篇 |
2016年 | 531篇 |
2015年 | 653篇 |
2014年 | 963篇 |
2013年 | 1042篇 |
2012年 | 1493篇 |
2011年 | 1459篇 |
2010年 | 1047篇 |
2009年 | 1094篇 |
2008年 | 1113篇 |
2007年 | 1381篇 |
2006年 | 1289篇 |
2005年 | 1078篇 |
2004年 | 1003篇 |
2003年 | 854篇 |
2002年 | 741篇 |
2001年 | 683篇 |
2000年 | 542篇 |
1999年 | 435篇 |
1998年 | 328篇 |
1997年 | 278篇 |
1996年 | 192篇 |
1995年 | 174篇 |
1994年 | 128篇 |
1993年 | 82篇 |
1992年 | 80篇 |
1991年 | 61篇 |
1990年 | 41篇 |
1989年 | 31篇 |
1988年 | 24篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 24篇 |
1983年 | 8篇 |
1982年 | 16篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1977年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
21.
In this work, we study dynamic provisioning of multicast sessions in a wavelength-routed sparse splitting capable WDM network
with an arbitrary mesh topology where the network consists of nodes with full, partial, or no wavelength conversion capabilities
and a node can be a tap-and-continue (TaC) node or a splitting and delivery (SaD) node. The objectives are to minimize the
network resources in terms of wavelength-links used by each session and to reduce the multicast session blocking probability.
The problem is to route the multicast session from each source to the members of every multicast session, and to assign an
appropriate wavelength to each link used by the session. We propose an efficient online algorithm for dynamic multicast session
provisioning. To evaluate the proposed algorithm, we apply the integer linear programming (ILP) optimization tool on a per
multicast session basis to solve off-line the optimal routing and wavelength assignment given a multicast session and the
current network topology as well as its residual network resource information. We formulate the per session multicast routing
and wavelength assignment problem as an ILP. With this ILP formulation, the multicast session blocking probability or success
probability can then be estimated based on solving a series of ILPs off-line. We have evaluated the effectiveness of the proposed
online algorithm via simulation in terms of session blocking probability and network resources used by a session. Simulation
results indicate that our proposed computationally efficient online algorithm performs well even when a fraction of the nodes
are SaD nodes. 相似文献
22.
Until recently, numerical simulations of discontinuities in highly super-Alfvénic plasmas have been severely limited by comparatively crude resolution and accuracy. Significant progress in the numerical simulation of such plasmas was achieved with the recently implemented Central Weighted Essentially Non-Oscillatory (CWENO) scheme. Combining this technique with that of adaptive mesh refinement (AMR), we have developed a third-order numerical scheme, which is able to efficiently capture strong gradients on spatial scales being small compared to the overall scale of the plasma system considered. Here, we first describe important algorithmic aspects of the scheme as well as the physics included in it. Second, we present the results of various performance tests. And, third, we illustrate its application to ‘real world problems’ using the example of the dynamics of a Sedov-type explosion. 相似文献
23.
We describe a Gauss–Seidel algorithm for optimizing a three‐dimensional unstructured grid so as to conform to a given metric. The objective function for the optimization process is based on the maximum value of an elemental residual measuring the distance of any simplex in the grid to the local target metric. We analyse different possible choices for the objective function, and we highlight their relative merits and deficiencies. Alternative strategies for conducting the optimization are compared and contrasted in terms of resulting grid quality and computational costs. Numerical simulations are used for demonstrating the features of the proposed methodology, and for studying some of its characteristics. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
24.
25.
Patricio Toro Raúl Quijada Omar Murillo Mehrdad Yazdani‐Pedram 《Polymer International》2005,54(4):730-734
The mechanical, morphological behavior and water absorption characteristics of polypropylene (PP) and silica, or PP and rice‐husk, composites have been studied. The silica used in this study as filler was a commercial type produced from soluble glass or rice husks. The compatibilizing effect of PP grafted with monomethyl itaconate (PP‐g‐MMI) and/or with vinyltriethoxysilane (PP‐g‐VTES) as polar monomers on the mechanical properties and water absorption was also investigated. In general, a high loading of the studied fillers in the polymer matrix increases the stiffness and the water absorption capacity. This effect is more noticeable in the tensile modulus of the PP/silica composite with PP‐g‐VTES as compatibilizer. However, the increase of the rice‐husk charge as a natural filler in the PP matrix decreases the stiffness, and in the presence of PP‐g‐MMI as compatibilizer in PP/rice‐husk, the tensile modulus and water absorption of the composite were improved. The better adhesion and phase continuity in the PP/silica and PP/rice‐husk composites with different compatibilizers was confirmed by the morphological study. Copyright © 2004 Society of Chemical Industry 相似文献
26.
胜利炼油厂重油加氢 (VRDS)装置的常压分馏塔为填料塔 ,2 0 0 1年检修开工后该系统出现异常 ,经过查找分析 ,确定轻烃 /产品减压渣油换热器和柴油汽提塔重沸器内漏是装置异常的主要原因 相似文献
27.
28.
某铅锌矿选矿尾矿综合利用试验研究 总被引:2,自引:0,他引:2
针对选矿尾矿的特性,采用高选择性的3ACH捕收剂、F—1抑制剂,回收了绢云母含量分别达96%和64%以上的一、二级绢云母产品。经应用试验表明:绢云母一级品在橡胶中的补强性能基本达到了沉淀法白炭黑水平,二级品也全面超过硅铝炭黑的补强性能。 相似文献
29.
30.
Nestor A. Calvo Sergio R. Idelsohn 《International journal for numerical methods in engineering》2002,55(12):1439-1449
There has been some degree of success in all‐hexahedral meshing. Standard methods start with the object geometry defined by means of an all‐quadrilateral mesh, followed by the use of the combinatorial dual to the mesh in order to define the internal connectivities among elements. For all of the known methods using the dual concept, it is necessary to first prevent or eliminate self‐intersecting (SI) dual lines of the given quadrilateral mesh. The relevant features of SI lines are studied, giving a method to remove them, which avoids deforming the original geometry. Some examples of resulting meshes are shown where the current meshing method has been successfully applied. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献