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   24874篇
  免费   321篇
  国内免费   12篇
电工技术   181篇
综合类   17篇
化学工业   5073篇
金属工艺   472篇
机械仪表   486篇
建筑科学   714篇
矿业工程   49篇
能源动力   454篇
轻工业   3922篇
水利工程   254篇
石油天然气   101篇
武器工业   6篇
无线电   1122篇
一般工业技术   4105篇
冶金工业   5148篇
原子能技术   125篇
自动化技术   2978篇
  2024年   278篇
  2023年   240篇
  2022年   277篇
  2021年   588篇
  2020年   516篇
  2019年   548篇
  2018年   951篇
  2017年   884篇
  2016年   924篇
  2015年   705篇
  2014年   1007篇
  2013年   1791篇
  2012年   1379篇
  2011年   1253篇
  2010年   1021篇
  2009年   993篇
  2008年   966篇
  2007年   901篇
  2006年   631篇
  2005年   456篇
  2004年   488篇
  2003年   427篇
  2002年   402篇
  2001年   285篇
  2000年   285篇
  1999年   335篇
  1998年   1656篇
  1997年   1143篇
  1996年   723篇
  1995年   387篇
  1994年   307篇
  1993年   366篇
  1992年   134篇
  1991年   116篇
  1990年   100篇
  1989年   111篇
  1988年   100篇
  1987年   93篇
  1986年   99篇
  1985年   121篇
  1984年   72篇
  1983年   71篇
  1982年   92篇
  1981年   98篇
  1980年   87篇
  1979年   50篇
  1978年   46篇
  1977年   162篇
  1976年   288篇
  1975年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Enhancement of the basic properties of the X zeolite with FAU framework has been carried out during synthesis, without further treatment such as ion-exchange or impregnation. Control of the washing stage enables retention of the optimum amount of alkaline hydroxides, which increases the basic catalytic activity of X zeolite in the alkylation of toluene. This alkaline hydroxides neither affect the FAU framework nor the silicon/aluminium molar ratio of the X zeolite. The optimum (Na + K)/Al molar ratio of the improved catalyst was 1.06 corresponding to a washing volume of 200 mL. This X zeolite presented better catalytic activity than a cesium-zeolite prepared by ion-exchange. The presence of hydroxysodalite impurity in the X zeolite increased the amount of impregnated alkaline hydroxides but not the catalytic activity. The present study shows that it is possible to increase the basic properties of the X zeolite directly in the synthesis process.  相似文献   
22.
m.k 《电脑》2014,(4):152-153
正自2月在第十届AAITF展会上公布了今年陆续发售的众多全新产品后,笔者一直关注着芬朗公司的具体动向。本月中旬,笔者受邀前往广州车元素旗舰店测试芬朗Feelart推出不久的性价比型两分频套装喇叭——SP-6.5A。外观工艺简单介绍一下SP-6.5A的外观,其实从产品系列来讲,SP-6.5在芬朗的产品线中属于第三梯队的极速摇滚系列,该系列的产品定位是为满足车主在进入汽车音响改装之门后对音色声效  相似文献   
23.
The influence of temperature on the gas chromatographic separation ofcis-trans isomers of the methyl esters of some monounsaturated fatty acids was studied on capillary columns coated with Apiezon L, BDS and DEGS. As far as methyl oleate and methyl elaidate are concerned, the separation is better at lower temperatures on Apiezon L (180–210 C) and at higher temperatures on polyester phases (BDS, DEGS; 150–180 C). The influence of temperature on the separation ofcis-trans isomers on the three stationary phases under study is explained by the higher values of δECL/δt forcis isomers. The variation of the equivalent carbon chain length with temperature can be used for the identification ofcis-trans isomers in natural mixtures.  相似文献   
24.
Pardo  A.  Merino  M.C.  López  M.D.  Escalera  M.D.  Viejo  F. 《Oxidation of Metals》2003,59(1-2):1-21
A study was made on the influence of the SiCp proportion and the matrix concentration of four composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) on their oxidation behavior. Gravimetric tests were used in a kinetics study of the corrosion process at different temperatures (350, 400, 450, and 500°C). The influence of corrosion on mechanical properties was evaluated by hardness measurements. The nature of corrosion products and the influence of the microstructure on the morphology and growth of the oxidation layer were analyzed by SEM and low-angle XRD. The extent of the damage due to oxidation for Al/SiCp composites increases with the SiCp concentration due to the increase of nucleation sites. One of these nucleation sites is in the interface region between the matrix and the particles. Oxidation was influenced more by the percentage of alloy elements in the matrix than by the proportion of SiCp reinforcement. The presence of Cu and Ni in the matrix favors the oxidation process through the formation of different intermetallic compounds.  相似文献   
25.
OBJECTIVE: a) To find the reasons for inadequate use of Hospital Casualty Departments (HCDs); b) to discover the general population's levels of information concerning non-hospital Emergency Services (NESs); c) to analyse the relationship between the type of Primary Care Centre (PCC), i.e. whether reformed or not, and inadequate use of HCDs. DESIGN: A crossover study. SETTING: The Germans Trias i Pujol Hospital Casualty Department, Badalona. PATIENTS: A random sample of 321 patients over 14 years old, who were attended for pathologies considered emergencies not requiring hospital treatment. MEASUREMENTS AND MAIN RESULTS: The variables gathered were: age, gender, where the patient came from, reason for hospital use, knowledge of NESs and subsequent referral. 83.2% of patients attended on their own initiative. The main reasons given were "advantages of a hospital" and "the persistence of symptoms." 49% of the patients stated they knew of the NESs. 80% of the patients proceeded from PCCs which had not been reformed. There were no statistically significant differences (p > 0.05) when the variables "reason for use" and "knowledge of NESs" were compared in relation to where the patient came from (i.e. reformed or non-reformed PCC). CONCLUSIONS: General practitioners in reformed PCCs are less likely to refer to HCDs. Knowledge and use of NESs should be actively supported.  相似文献   
26.
In spite of the names and works of practically all the early 19th Century Spanish specialists in urinary tract being widely known, there are still in my opinion several names and writings, either forgotten or misplaced in newspaper libraries, archives and general libraries, awaiting to be discovered. The second half of the 19th Century was a prolific age in every aspect of Spanish life, most particularly literature. In Medicine, apart from the well known professional writings, the number of scientific journals and publications, whether in the form of brochures or divulgative articles, that came to light was countless. Computer management of collections currently under implementation in many registers, will allow their location and the finding of new texts. One of these long forgotten pioneers, is Doctor Alejandro Settier (1858-1915), a Valencian practitioner who describes himself as a "disciple of the Paris hospitals and specialist in genitourinary tract disorders", who practised in Madrid between 1883 and 1890. Surprisingly, and in spite of him being the most prolific author in urological issues during the last century (my investigations show he is the author of 2 books, 3 brochures and 40 articles in journals), neither his name nor his work, as far as we know, are mentioned by none of the historians consulted, which is nothing but highly surprising if we also take into consideration that Alejandro Settier was the founder of the first Spanish monographic journal for urinary disorders: "Gaceta de enfermedades de los órganos génito-urinarios" (Gazette of genitourinary organs disorders), Madrid 1887, which in spite of its short existence, can be considered as the first scientific periodical publication in our specialty.  相似文献   
27.
In this paper we present Turk-2, a hybrid multi-modal chess player with a robot arm and a screen-based talking head. Turk-2 can not only play chess, but can see and hear the opponent, can talk to him and display emotions. We were interested to find out if a simple embodiment with human-like communication capabilities enhances the experience of playing chess against a computer. First, give an overview of the development road to multi-modal communication with computers. Then we motivate our research with a hybrid system, we introduce the architecture of Turk-2, we describe the human experiments and its evaluation. The results justify that multi-modal interaction makes game playing more engaging, enjoyable – and even more effective. These findings for a specific game situation provide yet another evidence of the power of human-like interaction in turning computer systems more attractive and easier to use.  相似文献   
28.
29.
The present paper deals with the problem of solving the (\(n^2 - 1\))-puzzle and cooperative path-finding (CPF) problems sub-optimally by rule-based algorithms. To solve the puzzle, we need to rearrange \(n^2 - 1\) pebbles in the \(n \times n\)-sized square grid using one vacant position to achieve the goal configuration. An improvement to the existing polynomial-time algorithm is proposed and experimentally analyzed. The improved algorithm represents an attempt to move pebbles in a more efficient way compared to the original algorithm by grouping them into so-called snakes and moving them together as part of a snake formation. An experimental evaluation has shown that the snakeenhanced algorithm produces solutions which are 8–9 % shorter than the solutions generated by the original algorithm. Snake-like movement has also been integrated into the rule-based algorithms used in solving CPF problems sub-optimally, which is a closely related task. The task in CPF consists in moving a group of abstract robots on an undirected graph to specific vertices. The robots can move to unoccupied neighboring vertices; no more than one robot can be placed in each vertex. The (\(n^2 - 1\))-puzzle is a special case of CPF where the underlying graph is a 4-connected grid and only one vertex is vacant. Two major rule-based algorithms for solving CPF problems were included in our study—BIBOX and PUSH-and-SWAP (PUSH-and-ROTATE). The use of snakes in the BIBOX algorithm led to consistent efficiency gains of around 30 % for the (\(n^2 - 1\))-puzzle and up to 50 % in for CPF problems on biconnected graphs with various ear decompositions and multiple vacant vertices. For the PUSH-and-SWAP algorithm, the efficiency gain achieved from the use of snakes was around 5–8 %. However, the efficiency gain was unstable and hardly predictable for PUSH-and-SWAP.  相似文献   
30.
Formal translations constitute a suitable framework for dealing with many problems in pattern recognition and computational linguistics. The application of formal transducers to these areas requires a stochastic extension for dealing with noisy, distorted patterns with high variability. In this paper, some estimation criteria are proposed and developed for the parameter estimation of regular syntax-directed translation schemata. These criteria are: maximum likelihood estimation, minimum conditional entropy estimation and conditional maximum likelihood estimation. The last two criteria were proposed in order to deal with situations when training data is sparse. These criteria take into account the possibility of ambiguity in the translations: i.e., there can be different output strings for a single input string. In this case, the final goal of the stochastic framework is to find the highest probability translation of a given input string. These criteria were tested on a translation task which has a high degree of ambiguity.  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