全文获取类型
收费全文 | 2527篇 |
免费 | 528篇 |
国内免费 | 432篇 |
专业分类
电工技术 | 170篇 |
综合类 | 298篇 |
化学工业 | 38篇 |
金属工艺 | 17篇 |
机械仪表 | 90篇 |
建筑科学 | 90篇 |
矿业工程 | 30篇 |
能源动力 | 23篇 |
轻工业 | 28篇 |
水利工程 | 34篇 |
石油天然气 | 14篇 |
武器工业 | 16篇 |
无线电 | 457篇 |
一般工业技术 | 106篇 |
冶金工业 | 82篇 |
原子能技术 | 6篇 |
自动化技术 | 1988篇 |
出版年
2024年 | 16篇 |
2023年 | 61篇 |
2022年 | 85篇 |
2021年 | 107篇 |
2020年 | 148篇 |
2019年 | 116篇 |
2018年 | 104篇 |
2017年 | 121篇 |
2016年 | 140篇 |
2015年 | 170篇 |
2014年 | 202篇 |
2013年 | 171篇 |
2012年 | 223篇 |
2011年 | 213篇 |
2010年 | 193篇 |
2009年 | 168篇 |
2008年 | 197篇 |
2007年 | 189篇 |
2006年 | 141篇 |
2005年 | 127篇 |
2004年 | 116篇 |
2003年 | 89篇 |
2002年 | 80篇 |
2001年 | 52篇 |
2000年 | 44篇 |
1999年 | 30篇 |
1998年 | 18篇 |
1997年 | 32篇 |
1996年 | 19篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 9篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1962年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3487条查询结果,搜索用时 15 毫秒
1.
Somnath Karmakar 《Polycyclic Aromatic Compounds》2019,39(2):159-171
Eigensolutions of {X( = C,B,N),Y( = C,B,N)}-cyclacene graphs with next nearest neighbor (nnn) interactions have been obtained in analytical forms by adapting n-fold rotational symmetry followed by two-fold rotational symmetry (or a plane of symmetry). Expressions of eigensolution indicate the subspectral relationship among such cyclacenes with an even number of hexagonal rings e.g., eigenvalues of {X,Y}-di-cyclacene are found in the eigenspectra of all such even cyclacenes. Total π-electron energies and highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gaps are calculated using the analytical expressions obtained and are found to vary negligibly with the variation of nnn interactions in such cyclacenes. Total π-electron energy is found to increase due to increase in restriction intensity of nnn interactions, whereas the HOMO–LUMO gap of polyacenecs having the even number of hexagonal rings and with one electron at each site (atom) decreases with increase in the restriction intensity since such systems contain degenerate half-filled HOMO (bonding or nonbonding) that are much more vulnerable for perturbations imposed through nnn interactions. 相似文献
2.
3.
4.
毛家河水电站库区岩溶发育特征及邻谷渗漏分析 总被引:1,自引:0,他引:1
毛家河水电站位于碳酸盐岩地区,库首距左岸邻谷可渡河14—23km、距右岸邻谷北盘江干流14.8km,水库两岸大型落水洞、溶洞及地下岩溶管道相对较为发育。为初步判断水库存在邻谷渗漏的可能性,对水库两岸可溶岩地层岩溶发育形态、特征及规律进行了勘察,并根据现场地质调查资料对3条可疑渗漏带进行了分析论证。 相似文献
5.
FloorControl是在大型网络实时交互平台下对共享资源进行控制管理的一项技术。FloorControl的概念分为机制和策略两个部分,协议属于机制,而策略则是具体的控制办法。本文着重介绍了在共享应用中使用FloorControl的技术要点,分析了目前常用的FloorControl协议,并给出了若干具体的FloorControl策略,这些策略的共同作用结果是具有公平、灵活和协同性。 相似文献
6.
We study the application of the geographic nearest neighbor approach to two problems. The first problem is the construction of an approximately minimum length rectilinear Steiner tree for a set ofn points in the plane. For this problem, we introduce a variation of a subgraph of sizeO(n) used by YaO [31] for constructing minimum spanning trees. Using this subgraph, we improve the running times of the heuristics discussed by Bern [6] fromO(n
2
log
n) toO(n log2
n). The second problem is the construction of a rectilinear minimum spanning tree for a set ofn noncrossing line segments in the plane. We present an optimalO(n logn) algorithm for this problem. The rectilinear minimum spanning tree for a set of points can thus be computed optimally without using the Voronoi diagram. This algorithm can also be extended to obtain a rectilinear minimum spanning tree for a set of nonintersecting simple polygons.The results in this paper are a part of Y. C. Yee's Ph.D. thesis done at SUNY at Albany. He was supported in part by NSF Grants IRI-8703430 and CCR-8805782. S. S. Ravi was supported in part by NSF Grants DCI-86-03318 and CCR-89-05296. 相似文献
7.
A Novel Segmentation and Feedback Model for Resolving Contention in Optical Burst Switching 总被引:2,自引:0,他引:2
A novel segmentation and feedback model (SFM) applied to resolve contention is proposed. Simulation and performance analyses show that the SFM effectively avoids contentions in optical burst switching (OBS). The long delay time of deflection routing and the immature technology of wavelength converters and optical buffers are not deployed in the SFM. The SFM does not only realize fast switching but also allows preemption by higher priority bursts. 相似文献
8.
EuLisp has an integrated object system with reflective capabilities. We discuss some example applications which use these facilities to experiment with some advanced and powerful concepts, namely, finalization, virtual shared memory and persistence. A secondary goal is to attempt to illustrate the additional possibilities of metaobject programming over non-metalevel techniques. 相似文献
9.
Bakermans-Kranenburg M. J.; van Uzendoorn M. H.; Bokhorst C. L.; Schuengel C. 《Canadian Metallurgical Quarterly》2004,18(3):545
In this first behavior genetic study on infant-father attachment, we estimated genetic and environmental influences on infant-father attachment behaviors and on temperamental dependency, both assessed with the Attachment Q-Sort (AQS; B. E.Vaughn & E. Waters, 1990; E. Waters, 1995). Mothers of mono- and dizygotic twins (N = 56 pairs) sorted the AQS with a focus on the infant's behaviors in the presence of the father. Genetic modeling showed that attachment was largely explained by shared environmental (59%) and unique environmental (41%) factors. For dependency, genetic factors explained 66% of the variance, and unique environmental factors including measurement error explained 34%. Attachment to father appears to be, to a significant degree, a function of the environment that twins share. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.