全文获取类型
收费全文 | 107649篇 |
免费 | 2921篇 |
国内免费 | 1505篇 |
专业分类
电工技术 | 2088篇 |
技术理论 | 3篇 |
综合类 | 3797篇 |
化学工业 | 15530篇 |
金属工艺 | 6173篇 |
机械仪表 | 4574篇 |
建筑科学 | 4019篇 |
矿业工程 | 1520篇 |
能源动力 | 1881篇 |
轻工业 | 5290篇 |
水利工程 | 1737篇 |
石油天然气 | 1856篇 |
武器工业 | 165篇 |
无线电 | 11764篇 |
一般工业技术 | 19239篇 |
冶金工业 | 3971篇 |
原子能技术 | 488篇 |
自动化技术 | 27980篇 |
出版年
2024年 | 127篇 |
2023年 | 471篇 |
2022年 | 732篇 |
2021年 | 1080篇 |
2020年 | 793篇 |
2019年 | 689篇 |
2018年 | 15139篇 |
2017年 | 14115篇 |
2016年 | 10650篇 |
2015年 | 1552篇 |
2014年 | 1444篇 |
2013年 | 1701篇 |
2012年 | 4663篇 |
2011年 | 10988篇 |
2010年 | 9691篇 |
2009年 | 6848篇 |
2008年 | 8071篇 |
2007年 | 8997篇 |
2006年 | 1341篇 |
2005年 | 2292篇 |
2004年 | 1895篇 |
2003年 | 1856篇 |
2002年 | 1236篇 |
2001年 | 680篇 |
2000年 | 716篇 |
1999年 | 666篇 |
1998年 | 538篇 |
1997年 | 442篇 |
1996年 | 422篇 |
1995年 | 332篇 |
1994年 | 311篇 |
1993年 | 235篇 |
1992年 | 182篇 |
1991年 | 141篇 |
1990年 | 65篇 |
1989年 | 68篇 |
1988年 | 83篇 |
1987年 | 47篇 |
1986年 | 34篇 |
1968年 | 44篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1960年 | 32篇 |
1959年 | 36篇 |
1958年 | 38篇 |
1957年 | 37篇 |
1956年 | 36篇 |
1955年 | 66篇 |
1954年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
本文讨论了条形码中距离动态识别技术中扫描景深与扫描光束波长和条宽等要素之间的关系,提出了改善条形码读取距离的3种方法。为扩大条形码在工业过程控制、企业管理等领域的应用范围提供了理论依据。 相似文献
112.
113.
Voigt线型及其精确快速算法 总被引:1,自引:1,他引:0
通过把上半复平面分为4个区,并在每一区利用不同近似,建立了一种精确快速计算Voigt函数、修正的Voigt函数和Voigt函数偏导数的算法,其最大相对误差小于5×10-4.该算法是Line-by-Line大气透过率/辐射强度计算及其相关应用的有效算法. 相似文献
114.
115.
In connection with the specific features of high velocity aerated flow generated by hydraulic engineering structures, the mathematical model is developed for high turbulence air-water two-phase flow with the use of twin flow theoretical model in this paper. Furthermore the numerical method is proposed to treat bubbled flows. In addition, on the basis of air-water stratified twin flow model, the new calculation methods and free surface tracking technique are proposed to describe complicated movements of the free surface. Finally, the proposed model is used to calculate artificial aerated flows. The computed results coincide quite well with experimental results. This means that the proposed method can provide solid basis for practical engineering design. 相似文献
116.
Although the dams produce remarkable social and economic benefits, the threat made by unsafe dams to the life and property of people who live in the lower river area is un-negligible. Based on the monitoring data which reflect the safety condition of dams, the risk degree concept is proposed and the analysis system and model for evaluating risk degree (rate) are established in this paper by combining the reliability theory and field monitoring data. The analysis method for risk degree is presented based on Bayesian approach. A five-grade risk degree system for dam operation risk and corresponding risk degree is put forward according to the safety condition of dams. The operation risks of four cascade dams on some river are analyzed by the model and approach presented here and the result is adopted by the owner. 相似文献
117.
Fanggao Chang Tao Li Yongxia Ge Zhenping Chen Zhongshi Liu Xiping Jing 《Journal of Materials Science》2007,42(17):7109-7115
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x
Ho
x
)TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x
Ho
x
)TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The
local electron density and defect concentration estimated using positron annihilation technique conforms well to the features
found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model. 相似文献
118.
119.
从数据结构角度为旅游胜地设计导游系统。向游人提供景点的信息查询服务,根据指定的景点提供相关的景点信息。任意给定起点和终点,查询两点之间的最短路径。 相似文献
120.
Document caching and connection caching are extensively studied problems. In document caching, one has to maintain caches
containing documents accessible in a network. In connection caching, one has to maintain a set of open network connections
that handle data transfer. Previous work investigated these two problems separately while in practice the problems occur together:
In order to load a document, one has to establish a connection between network nodes if the required connection is not already
open. In this paper we present the first study that integrates document and connection caching. We first consider a very basic
model in which all documents have the same size and the cost of loading a document or establishing a connection is equal to
1. We present deterministic and randomized online algorithms that achieve nearly optimal competitive ratios unless the size
of the connection cache is extremely small. We then consider general settings where documents have varying sizes. We investigate
a FAULT model in which the loading cost of a document is 1 as well as a BIT model in which the loading cost is equal to the
size of the document. 相似文献