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   583489篇
  免费   7831篇
  国内免费   2709篇
电工技术   11633篇
技术理论   5篇
综合类   1417篇
化学工业   86215篇
金属工艺   23109篇
机械仪表   16953篇
建筑科学   13926篇
矿业工程   3366篇
能源动力   13713篇
轻工业   49301篇
水利工程   6056篇
石油天然气   10988篇
武器工业   255篇
无线电   68459篇
一般工业技术   110897篇
冶金工业   118437篇
原子能技术   12148篇
自动化技术   47151篇
  2021年   4708篇
  2019年   4363篇
  2018年   7049篇
  2017年   7097篇
  2016年   7558篇
  2015年   5482篇
  2014年   8974篇
  2013年   25210篇
  2012年   14988篇
  2011年   20451篇
  2010年   16433篇
  2009年   18341篇
  2008年   19373篇
  2007年   19681篇
  2006年   17371篇
  2005年   15784篇
  2004年   14833篇
  2003年   14265篇
  2002年   13873篇
  2001年   14273篇
  2000年   13461篇
  1999年   14184篇
  1998年   35967篇
  1997年   25104篇
  1996年   19418篇
  1995年   14322篇
  1994年   12807篇
  1993年   12627篇
  1992年   9279篇
  1991年   8786篇
  1990年   8669篇
  1989年   8558篇
  1988年   8025篇
  1987年   6817篇
  1986年   6809篇
  1985年   7744篇
  1984年   7253篇
  1983年   6651篇
  1982年   5990篇
  1981年   6364篇
  1980年   5738篇
  1979年   5890篇
  1978年   5772篇
  1977年   6465篇
  1976年   8673篇
  1975年   5059篇
  1974年   4811篇
  1973年   4773篇
  1972年   4052篇
  1971年   3590篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
71.
Reducible rank codes and their applications to cryptography   总被引:2,自引:0,他引:2  
We present a new family of so-called reducible rank codes which are a generalization of rank product codes . This family includes maximal rank distance (MRD) codes for lengths n>N in the field F/sub N/. We give methods for encoding and decoding reducible rank codes. A public key cryptosystem based on these codes and on the idea of a column scrambler is proposed. The column scrambler "mixes" columns of a generator (parity-check) matrix of a code. It makes the system more resistant to structural attacks such as Gibson's attacks. Possible attacks on the system are thoroughly studied. The system is found to be secure against known attacks for public keys of about 16 kbits and greater.  相似文献   
72.
73.
For more than half a century, in nearly all western states, the regulatory agencies (the State Engineer or equivalent) used impairment of other water rights as the primary criterion for approving or rejecting change applications to move water to higher-valued uses. In recent years, however, protests to change applications have been brought by 'stakeholders' who do not own water rights, but who argue that they are affected by water transfers. Under the impairment rule, these parties do not have statutory standing to protest successfully. But they have brought legal suits to block transfers, and the courts have considered whether additional criteria involving 'impacts on social welfare' are needed to evaluate transfers. State Supreme Court rulings on such suits in Utah and Nevada are reviewed as prototype cases. The Utah court held that additional 'social welfare' criteria must be utilized by the State Engineer in evaluating change applications, whereas the Nevada court held that such criteria were already incorporated in existing water statutes and administrative practice. The critical question raised in the paper is whether existing state regulatory agencies can effectively implement a real 'social welfare' criterion to evaluate change applications. The conclusion is that they probably cannot, and that if they try, water allocations will be politicized to a much greater extent than they are now, and efficient market transfers will be impeded if not completely prevented.  相似文献   
74.
This study examined reciprocal relationships between collective efficacy and team performance over a season of competition in women's intercollegiate ice hockey within weekends where the opponent was constant for 2 games. Collective efficacy beliefs within 12 teams were assessed prior to both games for at least 7 weekends. Team performance indexes produced an overall measure of performance for each game. The average influence of Saturday collective efficacy on Saturday performance was moderate and positive after controlling for Friday performance. The average influence of Friday performance on Saturday collective efficacy was small and positive after removing the influence of Friday collective efficacy from Friday performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
A biochar from casein and its properties   总被引:2,自引:0,他引:2  
A biochar was prepared by pyrolysis of casein. A helium and mercury porosimeter were used to measure the true and apparent densities of the chars respectively, elemental and IR analysis were used to characterize the chemical composition of char. A SEM was used to observe the char surfaces in order to verify the presence of porosity. The biochar has 9.02% of nitrogen, content of porosity is 20%. The experimental results show that it is possible to prepare chars with relatively high porosity from casein for the further preparation of activated carbon.  相似文献   
76.
Passivated single damascene copper SiO2 damascene lines were evaluated in combination with TiSiN and Ta(N)/Ta diffusion barriers. Leakage current, breakdown and time-dependent dielectric breakdown properties were investigated on a wafer level basis for temperatures ranging between room temperature and 150 °C. It is found that the leakage performance of the wafers with a TiSiN barrier is better at room temperature, but at 150 °C the performance levels out with Ta(N)/Ta. Time-dependent dielectric breakdown measurements at 150 °C show that the lifetime of the interconnect is higher with the selected Ta(N)/Ta barrier than for TiSiN.  相似文献   
77.
Efficient blue‐, green‐, and red‐light‐emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula CNPt(μ‐pz)2PtCN (where CN = 2‐(4′,6′‐difluorophenyl)pyridinato‐N,C2′, pz = pyrazole ( 1 ), 3‐methyl‐5‐tert‐butylpyrazole ( 2 ), and 3,5‐bis(tert‐butyl)pyrazole ( 3 )). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3 , solely determines the electroluminescence color of the organic light‐emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5‐bis(N‐carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m–2, a brightness of 3900 Cd m–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3 , respectively, also give high quantum efficiencies (~ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current‐density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low‐energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (~ 5 %) and brightness (~ 600 Cd m–2 at 10 V).  相似文献   
78.
Many organisations use decision models in their processes such as tables or trees to provide decision support to their operational divisions. For example, in fault management, customer contact centre operators usually use a decision model in the form of prescribed interviews. Based on the answers given by customers, the operator navigates through the decision model to reach an assessment of the problem. In order to achieve customer satisfaction and operational excellence, it is very important to constantly monitor the performance of a decision model not only on an overall level, but also on the level of individual decisions. In this paper we present a configurable business process analytics tool, known as the intelligent Universal Service Management System, that constantly monitors decision data and is capable of optimising the decisions based on high-level business objectives. We explain the various features of the software and show how it can be used to optimise decision processes. We also show how we can easily provide a customised version to monitor the performance of provision processes.  相似文献   
79.
Interest in real-time model-based control is increasing as more and more facilities are being asked to meet stricter effluent requirements while at the same time minimizing costs. It has been identified that biological process models and automated process control technologies are being used at wastewater treatments plants throughout the world and that great potential for optimising biotreatment may exist with the integration of these two technology areas. According to our experience, wastewater treatment plants are indeed looking for ways to successfully integrate their modelling knowledge into their process control structure; however, there are practical aspects of this integration that must be addressed if the benefits of this integration are to be realised. This paper discusses the practical aspects of monitoring, filtering and analysing real sensor data with an aim to produce a reliable real-time data stream that might be used within a model-based control structure. Several real case study examples are briefly discussed in this paper.  相似文献   
80.
The aim of this study was to evaluate the use of total coliforms (TC) and faecal coliforms (FC) using a membrane filtration method for precise monitoring of faecal pollution in Korean surface water. The samples were collected in Korea from both main rivers and their tributaries. Presumptive TC * FC were enumerated. The ratios of presumptive FC to TC were not constant, but varied widely, and TC were difficult to enumerate because of overgrowth by background colonies. For FC this was not the case. Seven hundred and three purified strains of presumptive TC * FC and their background colonies were biotyped using API 20E. Among 272 presumptive TC, non-faecal related species, Aeromonas hydrophila dominated (34.6%) and E. coli accounted for only 5.1%. In contrast, E. coli made up 89% of the 209 presumptive FC. Furthermore, of 164 background colonies on Endo Agar LES, 54.9% was A. hydrophila, while background colonies on m-FC Agar were few (58 strains), and despite their atypical colony appearance, most of them were biotyped as enteric bacteria. These results reveal that the detection of FC rather than TC using m-FC Agar is more appropriate for faecal pollution monitoring in eutrophicated surface water located in a temperate region.  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