全文获取类型
收费全文 | 29291篇 |
免费 | 3859篇 |
国内免费 | 2315篇 |
专业分类
电工技术 | 1890篇 |
技术理论 | 3篇 |
综合类 | 3650篇 |
化学工业 | 2261篇 |
金属工艺 | 353篇 |
机械仪表 | 1206篇 |
建筑科学 | 5096篇 |
矿业工程 | 1471篇 |
能源动力 | 849篇 |
轻工业 | 2010篇 |
水利工程 | 2222篇 |
石油天然气 | 1364篇 |
武器工业 | 259篇 |
无线电 | 3157篇 |
一般工业技术 | 2308篇 |
冶金工业 | 1399篇 |
原子能技术 | 195篇 |
自动化技术 | 5772篇 |
出版年
2024年 | 167篇 |
2023年 | 510篇 |
2022年 | 1055篇 |
2021年 | 1092篇 |
2020年 | 1238篇 |
2019年 | 1070篇 |
2018年 | 1002篇 |
2017年 | 1186篇 |
2016年 | 1302篇 |
2015年 | 1330篇 |
2014年 | 1940篇 |
2013年 | 2019篇 |
2012年 | 2197篇 |
2011年 | 2441篇 |
2010年 | 1850篇 |
2009年 | 1741篇 |
2008年 | 1725篇 |
2007年 | 2007篇 |
2006年 | 1712篇 |
2005年 | 1440篇 |
2004年 | 1205篇 |
2003年 | 1008篇 |
2002年 | 734篇 |
2001年 | 624篇 |
2000年 | 492篇 |
1999年 | 456篇 |
1998年 | 350篇 |
1997年 | 290篇 |
1996年 | 247篇 |
1995年 | 216篇 |
1994年 | 184篇 |
1993年 | 127篇 |
1992年 | 79篇 |
1991年 | 87篇 |
1990年 | 70篇 |
1989年 | 54篇 |
1988年 | 49篇 |
1987年 | 24篇 |
1986年 | 28篇 |
1985年 | 15篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 11篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1966年 | 4篇 |
1964年 | 3篇 |
1959年 | 4篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Min Xu 《Information Processing Letters》2007,101(5):185-189
For a given connected graph G of order n, a routing R in G is a set of n(n−1) elementary paths specified for every ordered pair of vertices in G. The vertex (resp. edge) forwarding index of G is the maximum number of paths in R passing through any vertex (resp. edge) in G. Choudum and Sunitha [S.A. Choudum, V. Sunitha, Augmented cubes, Networks 40 (2002) 71-84] proposed a variant of the hypercube Qn, called the augmented cube AQn and presented a minimal routing algorithm. This paper determines the vertex and the edge forwarding indices of AQn as and 2n−1, respectively, which shows that the above algorithm is optimal in view of maximizing the network capacity. 相似文献
52.
The MultiDimER model is a conceptual model used for representing a multidimensional view of data for Data Warehouse (DW) and
On-Line Analytical Processing (OLAP) applications. This model includes a spatial extension allowing spatiality in levels,
hierarchies, fact relationships, and measures. In this way decision-making users can represent in an abstract manner their
analysis needs without considering complex implementation issues and spatial OLAP tools developers can have a common vision
for representing spatial data in a multidimensional model. In this paper we propose the transformation of a conceptual schema
based on the MultiDimER constructs to an object-relational schema. We based our mapping on the SQL:2003 and SQL/MM standards
giving examples of commercial implementation using Oracle 10g with its spatial extension. Further we use spatial integrity
constraints to ensure the semantic equivalence of the conceptual and logical schemas. We also show some examples of Oracle
spatial functions, including aggregation functions required for the manipulation of spatial data. The described mappings to
the object-relational model along with the examples using a commercial system show the feasibility of implementing spatial
DWs in current commercial DBMSs. Further, using integrated architectures, where spatial and thematic data is defined within
the same DBMS, facilitates the system management simplifying data definition and manipulation.
相似文献
Esteban ZimányiEmail: |
53.
单苯环氯取代指数法预测二噁类化合物PCDDs的正辛醇/水分配系数 总被引:1,自引:0,他引:1
采用单苯环氯取代指数作为氯代二苯并二口恶口英类化合物 (PCDDs)的分子结构描述符 ,通过正向逐步线性回归方法建立了PCDDs的logKow与分子结构描述符之间的定量关系模型。与文献报道的MOD模型相比 ,该模型不仅具有显著的相关性 (n =43,Radj=0 898,SE =0 195 ,在α =0 0 5时 ,F =2 0 45 5 ,p =0 0 0 0 0 ) ,而且对于分子结构具有更好的区分能力。利用建立的模型 ,对没有logKow文献值的其他 33种PCDDs化合物给出了预测值 相似文献
54.
针对已有的灰色关联度模型仅适用于实数序列而不能应用于区间灰数序列的情况,通过引入决策者心态指标,将区间灰数序列转化为决策者心态指标序列,并且当决策者的心态指标确定时,心态指标序列就转化为实数序列,于是通过对体现决策者心态的实数序列建立灰色关联度模型,得到了反映出决策者心态的灰色关联度,从而构建了基于心态指标的区间灰数关联度模型。决策者处于不同心态时,可以通过调整其心态计算灰关联度,从而使建立的关联度模型更加符合实际。最后,通过计算实例说明了模型的可行性。 相似文献
55.
The long term monitoring of aquatic ecosystems based on chemical analysis is expensive resulting in a lack of time series data for management purposes thus necessitating the need for new cost effective methodologies. This study developed a fish‐based index of biotic integrity (FIBI) for monitoring environmental conditions in riverine ecosystems within the Lake Victoria Basin, Kenya. The fish fauna in the basin is poorly studied, less diverse and ecologically specialized than the temperate fauna that provided the origins of the Index of Biotic Integrity. Fish samples were collected by electrofishing from 24 sites during baseflow periods in February, March and July 2004. Validation data were collected from 7 sites with varying levels of degradation. Fish samples were identified, counted and grouped into different trophic groups, relative tolerance to pollution, habitat guild and whether exotic or native to riverine environment. Thirty‐three candidate metrics were evaluated for responsiveness to habitat quality and twelve were selected for inclusion in the final index. The index classified 6 of the 7 validation sites according to their levels of degradation. As a bioassessment tool, the index was useful in laying the basis for long‐term monitoring of rivers in the Lake Victoria drainage basin. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
56.
在客源时间分布上,计算乌镇游客游览时间强度指数,得到游客游览时间主要集中在二、三季度,并以7、8月份为最高峰。而在客源市场的分布上,鸟镇已经形成了以浙江为核心,上海、北京等地为一级,安徽、河南等地为二级的国内客源市场。在长三角古村落旅游发展迅速的今天,乌镇与周边的周庄、同里等古镇的竞争日益激烈,而旅游产品的创新、加大宣传迅速占领国内二级客源市场等措施将有助于乌镇在竞争中脱颖而出,占领主导地位。 相似文献
57.
Tarasankar Pal 《Materials and Manufacturing Processes》2006,21(3):315-317
Cetylpyridinium chloride (CPC)-stabilized gold organosol in toluene has been prepared by using a two-phase (water-toluene) extraction of AuCl4- followed by its reduction with sodium borohydride in the presence of the surfactant, CPC. The surfactant-stabilized gold nanoparticles were exploited to examine their optical properties when exposed to various solvent systems by measuring the changes in the localized surface plasmon resonance (LSPR) spectrum. 相似文献
58.
杨婷 《安徽建筑工业学院学报》2006,14(6):59-62,98
高速铁路已成为区域大城市之间联系的重要纽带.高速铁路市区段的建设对城市的发展将产生深远影响.基于合肥城市发展的特征,重点从城市空间结构的视角,对合肥城市高速铁路走向进行多方案比较研究,并提出适宜的方案.进而指出,高速铁路市区段的选线应与城市规划相协调,引导城市良好空问结构的形成. 相似文献
59.
LIXue-mei ZHANGTao 《中国矿业大学学报(英文版)》2005,15(1):72-76
The comprehensive transportation project involves with many different transportation methods, such as railway, highway, waterway, airline, and pipeline, which have their special characteristics. To evaluate the transportation project with different transportation methods under the same system, the integrated evaluation method should be built up on the basis of a common index system. This paper suggests a feasible integrated evaluation method including index system establishing, indices transacting, the index weight distributing, and weighted value integrating. 相似文献
60.
《中国科学E辑(英文版)》2005,(Z2)
Land surface evapotranspiration is one of the most important components in water cycle between earth and atmosphere, and plays a very important role in the atmosphere, hydrosphere, and biosphere of the planet. It is an urgent task to understand the evapotranspiration process over different surface types and conditions in agriculture, hydrogeology, forest, and ecology for the purpose of using water resources properly. Additionally, land surface evapotranspiration is a key parameter in the synop… 相似文献