全文获取类型
收费全文 | 49813篇 |
免费 | 5339篇 |
国内免费 | 4053篇 |
专业分类
电工技术 | 4084篇 |
技术理论 | 12篇 |
综合类 | 6410篇 |
化学工业 | 3671篇 |
金属工艺 | 608篇 |
机械仪表 | 2145篇 |
建筑科学 | 2935篇 |
矿业工程 | 1356篇 |
能源动力 | 2025篇 |
轻工业 | 1030篇 |
水利工程 | 1238篇 |
石油天然气 | 819篇 |
武器工业 | 930篇 |
无线电 | 6800篇 |
一般工业技术 | 2777篇 |
冶金工业 | 1975篇 |
原子能技术 | 422篇 |
自动化技术 | 19968篇 |
出版年
2024年 | 198篇 |
2023年 | 647篇 |
2022年 | 1210篇 |
2021年 | 1389篇 |
2020年 | 1533篇 |
2019年 | 1152篇 |
2018年 | 1029篇 |
2017年 | 1347篇 |
2016年 | 1563篇 |
2015年 | 1744篇 |
2014年 | 3301篇 |
2013年 | 3176篇 |
2012年 | 3901篇 |
2011年 | 3926篇 |
2010年 | 3081篇 |
2009年 | 3335篇 |
2008年 | 3478篇 |
2007年 | 3800篇 |
2006年 | 3410篇 |
2005年 | 3036篇 |
2004年 | 2665篇 |
2003年 | 2316篇 |
2002年 | 1713篇 |
2001年 | 1389篇 |
2000年 | 1095篇 |
1999年 | 749篇 |
1998年 | 551篇 |
1997年 | 439篇 |
1996年 | 359篇 |
1995年 | 293篇 |
1994年 | 259篇 |
1993年 | 195篇 |
1992年 | 150篇 |
1991年 | 124篇 |
1990年 | 78篇 |
1989年 | 80篇 |
1988年 | 71篇 |
1987年 | 53篇 |
1986年 | 45篇 |
1985年 | 50篇 |
1984年 | 60篇 |
1983年 | 43篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1977年 | 8篇 |
1965年 | 10篇 |
1964年 | 11篇 |
1961年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
In this paper we design a dynamic dictionary for
the priced information model initiated by Charikar et al. Assume that a set S consisting of n elements is given such that
each element has an associated price, a positive real number. The cost of performing an operation on elements of S is a function
of their prices. The cost of an algorithm is the sum of the costs of
all operations it performs. The objective is to design algorithms
which incur low cost. In this model we propose a dynamic dictionary, supporting
search, insert and delete, for keys drawn from a linearly ordered set.
As an application we show that the dictionary can be used in
computing the trapezoidal map of a set of line segments, a fundamental problem in
computational geometry. 相似文献
72.
新形势下的钻井信息化 总被引:3,自引:1,他引:2
介绍了我国石油行业在新的发展形势和管理模式下,钻井领域进行信息化的重要任务。在理清钻井业务流程的基础上,提出了以“钻井数据中心”为核心的钻井信息系统框架。从自动采集和人工采集两个方面阐明了钻井数据采集的范围和方式;从井筒网络、井场局域网、远程传输网和企业网等方面介绍了钻井信息化立体网络的构成,还介绍了钻井数据与甲方数据中心的数据交换方式、钻井数据中心的构建方法、以及钻井数据中心所支持的上层应用系统设计内容。提出了钻井信息化的发展方向,对我国钻井行业信息化有一定的指导意义。 相似文献
73.
Boeing has been working on the development and implementation of STEP AP 210 since its inception. Using a combination of internally funded activities, external government contracts and multi-company pilots, Boeing has developed prototype tools to utilize AP 210 and is poised to move these tools into production. This paper begins with a brief overview of STEP and AP 210. The status of available AP 210 vendor translators (data generators), along with viewers and analysis programs (data consumers) is covered. Discussion continues with present and planned usage of AP 210 in several companies with the primary emphasis on implementation at The Boeing Company. The document concludes with a summary of key points. 相似文献
74.
75.
A number of copolymers were synthesised by condensing the 2,4-dinitrophenylhydrazone of resacetophenone with substituted benzoic acids/ phenols and formaldehyde in the presence of sodium hydroxide or hydrochloric acid. The decomposition temperature, solubility and viscosity of the polymers have been determined. The ion-exchange properties have been studied by using a batch equilibrium method. The distribution of a number of metal ions between an aqueous solution and the resin have been measured. A wide range of pH and variable ionic strengths have been investigated. 相似文献
76.
P. Powell 《Information Systems Journal》1992,2(4):269-280
Abstract. Expert systems proliferate. They are now a usable and used tool in a variety of organizations. However, little research has been undertaken on the quantification of success or failure of expert system projects. By and large the only test carried out for expert system validation is one of comparison of the conclusions of the system with those of an expert or team of experts. While questioning the validity, this paper accepts that this method is being used and analyses whether or not the results obtained from this type of test should be a surprise. That is, what sort of results should be expected and to what extent do the reported ones live up to these expectations? Earlier research from the field of human information processing casts doubts on the success claims made for current expert systems. The implications of this research are then analysed in order to explore the possible redeeming features of expert systems which are not taken into account in such comparisons. The use of linear models as comparators for expert systems may prove beneficial. 相似文献
77.
Katherine A. B. Logan Michael J. S. Floate 《Journal of the science of food and agriculture》1985,36(11):1084-1092
For 30 acid upland and hill soils, with initial pH from 3.5 to 5.8, and loss on ignition from 14% to 94%, cation exchange capacity varied with pH according to the relationship CEC = m pH+C, where m and C are characteristic of each soil. The slope m depended on loss on ignition (LOI), and is given by: m=Δ CEC/Δ=0.22 LOI+1.92. Because of these relationships, CEC measured at the natural pH of the soil (in 0.025 M MgSO4 solution) is more relevant to field conditions than a conventional measurement at pH7. An improved method for estimating lime requirement (LR) of these soils was developed, based on the relationship found between LR and the difference in CEC (ΔCEC) between that at the natural pH of the soil and that at the target pH of 5.5: LR=1.12 ΔCEC+1.48. Lime requirement can therefore also be estimated from loss on ignition using the earlier relationships, and is given by: LR=(0.25 LOI+2.15) Δ+1.48, where Δ is the difference between the natural pH (in 0.025 M MgSO4) and the target pH. Predictions based on this agreed well with results for a further 10 soils. 相似文献
78.
数据广播是现阶段一种新的文化传媒体系,随着数字电视的不断发展完善,数据广播在信息产业飞速发展的今天,逐渐成为新时期信息传播的主要媒介方式,阐述数据广播在当今社会信息领域的存在形态、发展方向以及如何合理、高效地运营这样一种增值业务。 相似文献
79.
数值地形图的生成及其水文地貌特征评价 总被引:17,自引:2,他引:15
数值地形图(DEM)是利用地理信息系统(GIS)进行流域水文模拟的基础, 其精度直接影响模拟结果在没有现成的数值地形图时, 应用人员往往利用传统的地形图来生成它. 本文分别采用Arc/Info地理信息系统软件提供的哈奇逊法和不规则三角网五次插值法, 对一个实验流域的高程取样点进行插值, 生成了4种不同的数值地形图, 从凹洼分布、流域界定、河网提取、地面坡度和地形指数、以及地面径流汇成等方面, 对它们的水文地貌精度进行了比较. 结果表明, 两种方法都能生成由高程点群所反映的地形, 然而由于哈奇逊法能够结合流域的河网结构及其具有物理基础的水文地貌加强法来处理凹洼问题, 因此大大地提高了其所生成的流域数值地形图水文地貌特征精度. 相似文献
80.
CASE与MIS的开发 总被引:1,自引:0,他引:1
本文介绍CASE技术的基本思想与构成,CASE工具在MIS开发中的作用,概要介绍国内流行的CASE产品并对其作出评述。 相似文献