首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   20689篇
  免费   1354篇
  国内免费   131篇
电工技术   131篇
综合类   359篇
化学工业   5041篇
金属工艺   460篇
机械仪表   315篇
建筑科学   546篇
矿业工程   55篇
能源动力   565篇
轻工业   4018篇
水利工程   171篇
石油天然气   411篇
武器工业   6篇
无线电   1378篇
一般工业技术   2379篇
冶金工业   1998篇
原子能技术   105篇
自动化技术   4236篇
  2024年   38篇
  2023年   158篇
  2022年   652篇
  2021年   784篇
  2020年   454篇
  2019年   521篇
  2018年   608篇
  2017年   616篇
  2016年   666篇
  2015年   510篇
  2014年   887篇
  2013年   1380篇
  2012年   1340篇
  2011年   1742篇
  2010年   1289篇
  2009年   995篇
  2008年   1144篇
  2007年   817篇
  2006年   652篇
  2005年   564篇
  2004年   598篇
  2003年   544篇
  2002年   497篇
  2001年   326篇
  2000年   291篇
  1999年   309篇
  1998年   838篇
  1997年   595篇
  1996年   367篇
  1995年   245篇
  1994年   204篇
  1993年   295篇
  1992年   153篇
  1991年   91篇
  1990年   94篇
  1989年   90篇
  1988年   85篇
  1987年   68篇
  1986年   35篇
  1985年   42篇
  1984年   31篇
  1983年   25篇
  1982年   27篇
  1981年   22篇
  1980年   35篇
  1977年   32篇
  1976年   52篇
  1965年   97篇
  1963年   54篇
  1957年   28篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
尹趣 《世界电信》2004,17(12):30-35
欧洲主要电信运营商所处国度的经济和人口布局情况不同,竞争环境也有差别,在专线资费方面的做法也有许多不同之处。考虑到地区之间竞争的差异。目前多数国家都取消了地区交叉补贴的做法,但还有一部分国家仍然坚持统一费率。在资费方面的基本促销手段为接合同年限和用户的支出额打折。从2000年到2003年资费演变的基本情况是;接入费扣2Mbit/s以下较低速率的专线租费保持平稳略有下降,较高速率专线的租费则有较大的下调幅虚。  相似文献   
42.
43.
Currently there are design barriers inhibiting the implementation of high-precision digital signal processing (DSP) objects with field programmable logic (FPL) devices. This paper explores overcoming these barriers by fusing together the popular distributed arithmetic (DA) method with the residue number system (RNS) for use in FPL-centric designs. The new design paradigm is studied in the context of a high-performance filter bank and a discrete wavelet transform (DWT). The proposed design paradigm is facilitated by a new RNS accumulator structure based on a carry save adder (CSA). The reported methodology also introduces a polyphase filter structure that results in a reduced look-up table (LUT) budget. The 2C-DA and RNS-DA are compared, in the context of a FPL implementation strategy, using a discrete wavelet transform (DWT) filter bank as a common design theme. The results show that the RNS-DA, compared to a traditional 2C-DA design, enjoys a performance advantage that increases with precision (wordlength).  相似文献   
44.
身份管理渐行其道   总被引:1,自引:0,他引:1  
张杰 《世界电信》2004,17(3):39-42
目前人们面临的网络安全问题越来越严峻,不仅包括计算机病毒、垃圾电子邮件等的挑战,对信息资源的有效存取保护要求也在提高。身份管理技术能对用户身份标识进行集中与简化管理,实现安全、简便登录等功能,不但削减了投入和维护成本,还提高了效率,因此近来得到迅速发展。2003年的调查显示,身份管理在安全产品市场增幅达45%;在各企业应用普及率已达到17.9%。但身份管理还需要解决提高单点登录安全性,实施多方可靠数字身份以及本身复杂性等问题。  相似文献   
45.
The objective of this research was to study the removal of cadmium and lead from an aqueous solution through a biological treatment. For this purpose a glass-ceramic material was manufactured from industrial and urban wastes. Biofilms of microorganisms found in wastewater were developed on its surface, and continuous tests were conducted in the presence and absence of the biofilm to analyze the glass-ceramic's ability to remove the heavy metals from an aqueous environment. The results suggest that this bioremediation process, developed on an industrial scale, could represent an alternative to the chemical processes currently used.  相似文献   
46.
47.
Reaction of bacterial adhesins with complementary receptors on the surfaces of mucosal respiratory, gastrointestinal and genitourinary cells leads to bacterial adhesion to the human body. This is the first step in the sequence of events leading to infection. It has been observed that subinhibitory concentrations (sub-MICs) of some antibiotics are able to reduce bacterial adhesion. The pharmacokinetic curves of antibiotics show that these sub-MICs are present in tissues during a typical course of therapy. This study investigated the ability of sub-MICs of seven macrolides and four fluoroquinolones to reduce adhesiveness of Staphylococcus aureus to human buccal cells. The literature generally reports data for only one antibiotic at a time. To obtain an overall view of the findings of eleven antibiotics together, the data have been normalized according to the molecular weight of each antibiotic and the dose-effect curves determined.  相似文献   
48.
49.
50.
The neuronal cytoskeleton is one of the most profoundly altered organelles in late life neuro-degenerative disorders that are characterized by progressive impairments in cognitive abilities. The elucidation of the protein building blocks of these organelles as well as advances in understanding how these proteins become altered in Alzheimer's disease (AD) and other less common dementing illnesses, i.e., diffuse Lewy body disease (DLBD) or the Lewy body variant of AD (LBVAD), will provide insights into the molecular basis of these disorders. Within, we review evidence that normal adult human tau is abnormally phosphorylated and converted into the subunits of AD paired helical filaments (PHFs), and that Lewy bodies (LBs) represent accumulation of altered neurofilament (NF) triplet subunits. Although the precise biological consequences of PHF and LB formation in neurons is unknown, growing evidence suggests that the formation of PHFs and LBs from normal neuronal cytoskeletal proteins could have deleterious effects on neuronal function and survival. Finally, insights into the composition of PHFs and LBs could lead to the development of novel strategies for the timely and accurate diagnosis of AD, DLBD and the LBVAD.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号