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   32930篇
  免费   2466篇
  国内免费   1109篇
电工技术   1506篇
技术理论   3篇
综合类   1665篇
化学工业   5620篇
金属工艺   1820篇
机械仪表   1804篇
建筑科学   2569篇
矿业工程   782篇
能源动力   840篇
轻工业   2211篇
水利工程   513篇
石油天然气   1458篇
武器工业   206篇
无线电   3399篇
一般工业技术   4457篇
冶金工业   2750篇
原子能技术   305篇
自动化技术   4597篇
  2024年   100篇
  2023年   464篇
  2022年   758篇
  2021年   1204篇
  2020年   928篇
  2019年   737篇
  2018年   905篇
  2017年   934篇
  2016年   856篇
  2015年   1095篇
  2014年   1363篇
  2013年   1893篇
  2012年   1953篇
  2011年   2117篇
  2010年   1880篇
  2009年   1734篇
  2008年   1770篇
  2007年   1788篇
  2006年   1693篇
  2005年   1577篇
  2004年   1137篇
  2003年   996篇
  2002年   1016篇
  2001年   769篇
  2000年   831篇
  1999年   877篇
  1998年   736篇
  1997年   617篇
  1996年   618篇
  1995年   491篇
  1994年   433篇
  1993年   339篇
  1992年   318篇
  1991年   186篇
  1990年   187篇
  1989年   166篇
  1988年   142篇
  1987年   127篇
  1986年   91篇
  1985年   87篇
  1984年   76篇
  1983年   78篇
  1982年   70篇
  1981年   54篇
  1980年   53篇
  1979年   46篇
  1978年   38篇
  1977年   43篇
  1976年   28篇
  1975年   33篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
Blood product transfusion is a financial concern for hospitals and patients. Efficient utilization of this dwindling resource is a critical problem if hospitals are to maximize patient care while minimizing costs. Traditional statistical models do not perform well in this domain. An additional concern is the speed with which transfusion decisions and planning can be made. Rapid assessment in the emergency room (ER) necessarily limits the amount of usable information available (with respect to independent variables available). This study evaluates the efficacy of using artificial neural networks (ANNs) to predict the transfusion requirements of trauma patients using readily available information. A total of 1016 patient records are used to train and test a backpropagation neural network for predicting the transfusion requirements of these patients during the first 2, 2-6, and 6-24 h, and for total transfusions. Sensitivity and specificity analysis are used along with the mean absolute difference between blood units predicted and units transfused to demonstrate that ANNs can accurately predict most ER patient transfusion requirements, while only using information available at the time of entry into the ER.  相似文献   
72.
丁辉 《铜业工程》2003,(3):23-24
本文介绍了贵冶失重给料螺旋的性能、生产准备、点检维修、技术攻关、缺陷改进。  相似文献   
73.
Although continuing care is strongly related to positive treatment outcomes for substance use disorder (SUD), participation rates are low and few effective interventions are available. In a randomized clinical trial with 150 participants (97% men), 75 graduates of a residential Veterans Affairs Medical Center SUD program who received an aftercare contract, attendance prompts, and reinforcers (CPR) were compared to 75 graduates who received standard treatment (STX). Among CPR participants, 55% completed at least 3 months of aftercare, compared to 36% in STX. Similarly, CPR participants remained in treatment longer than those in STX (5.5 vs. 4.4 months). Additionally, CPR participants were more likely to be abstinent compared to STX (57% vs. 37%) after 1 year. The CPR intervention offers a practical means to improve adherence among individuals in SUD treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
74.
丁翔宇 《物探装备》2003,13(1):55-58
在对RTK技术进行简要介绍的基础上,叙述了这一技术在黄土塬地区地震勘探测量中的应用,及所取得的良好测量资料。  相似文献   
75.
杨晓江  丁广友 《河南冶金》2003,11(5):13-14,21
对唐钢薄板坯连铸机生产的SS400钢的生产工艺进行了分析,认为薄板坯连铸机生产的SS400钢,在采取了精炼站在线定氧,将钢水全氧控制在25×10~(-6)左右,同时连铸采取保护浇注和轻压下等技术后,能够确保薄板坯连铸SS400钢的顺利浇注,轧制的板带材表面质量良好,机械性能符合要求。  相似文献   
76.
扇形段电磁搅拌对82B钢连铸坯成分和组织的影响   总被引:3,自引:1,他引:2  
进行了结晶器搅拌和结晶器 +扇形段电磁搅拌连铸 82B钢 2 80mm× 380mm方坯的工业试验。结果表明 ,扇形段搅拌降低和改善了铸坯的中心偏析、疏松和夹杂物分布。 82B钢铸坯经扇形段搅拌后 ,中心部位碳含量峰值明显减小 ,碳偏析指数降低 5 7%~ 1 0 8% ,铸坯成分的方差值 (σ)减小 32 %~ 34 9%。  相似文献   
77.
This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100-150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.
Copper containing faujasite has been successfully prepared for the first time using a direct synthesis method. Faujasite type zeolite can be prepared in the presence of copper species by tuning the synthesis conditions. Ammonium hydroxide was used to form a copper complex that was later mixed with the reacting gel. Sodium is required to obtain copper faujasite. The complete elimination of sodium ions from the starting gel produces amorphous material. Crystallization took place at 358 K for 11 days. Crystallization temperature of 373 K produces ANA type zeolite as an impurity. Increasing by two times the amount of copper complex added to the reacting gel increases the crystallization time of Cu-FAU from 11 to 20 days (the crystallization rate decreases). The copper containing faujasite obtained was characterized by XRD, FESEM, EDX, EPR, FT-IR, TPR, and BET. According to the XRD pattern only FAU type zeolite was obtained. According to TPR experiments, the reduction temperature for Cu2+ ions present in Cu-FAU prepared by direct synthesis was 70 K more than for Cu-FAU prepared by ion-exchange. This difference can be due to the different location of the copper ions in the supercages or in the sodalite cages of the faujasite.  相似文献   
79.
Introduction     
Concluding remarks With this brief exposition of the areas covered in this special double issue on Eurotra, we shall now conclude our introduction. We hope that the volume will achieve its goals, as outlined above, at least to some extent. Certainly, much more could be said about a wide range of topics which have been covered in the lifetime or the project so far. For instance, these article, mainly written by linguists, deliberately neglect the software implementation and environment aspects of the prototype Eurotra Translation System, as well as a number of peripheral tools and components of the system that are available to the user, such as lexical data bases, text-handling mechanisms and the like. The reader interested in aspects of this kind is referred to Raw et al. 1989 for a very brief introduction, and to the Eurotra software team at the Commission of the European Communities (DG XIII, Luxembourg) for more details. However, one goal that we do hope to come close to achieving is to give a fair overview of the Eurotra linguistic theory of translation and the mainstream and sideline formalisms expressing variant versions of it. If we have come anywhere near achieving that, our gratitude is due to the numerous Eurotra colleagues who have supported us in preparing this volume, and to the editor of this journal.  相似文献   
80.
对采用粉末冶金与化学热处理相结合的方法研制的电触头材料进行了理化性能、显微组织和抗氧化性能试验,探讨其机理及对性能的影响因素。试验表明:所研制的触头的理化性能基本达到了国标规定的相近触头的指标,其显微组织和抗氧比性能则优于国标规定。A_(c4)加速模拟电寿命试验的结果证实该种触头材料应用前景良好。  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