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   23774篇
  免费   2584篇
  国内免费   1207篇
电工技术   1586篇
综合类   2507篇
化学工业   2878篇
金属工艺   649篇
机械仪表   1206篇
建筑科学   2983篇
矿业工程   1009篇
能源动力   708篇
轻工业   1068篇
水利工程   951篇
石油天然气   862篇
武器工业   298篇
无线电   2274篇
一般工业技术   1413篇
冶金工业   1749篇
原子能技术   204篇
自动化技术   5220篇
  2024年   65篇
  2023年   216篇
  2022年   373篇
  2021年   492篇
  2020年   592篇
  2019年   533篇
  2018年   535篇
  2017年   739篇
  2016年   913篇
  2015年   904篇
  2014年   1372篇
  2013年   1247篇
  2012年   1518篇
  2011年   1807篇
  2010年   1347篇
  2009年   1445篇
  2008年   1401篇
  2007年   1623篇
  2006年   1506篇
  2005年   1264篇
  2004年   1057篇
  2003年   985篇
  2002年   825篇
  2001年   739篇
  2000年   554篇
  1999年   420篇
  1998年   290篇
  1997年   244篇
  1996年   190篇
  1995年   187篇
  1994年   173篇
  1993年   107篇
  1992年   95篇
  1991年   76篇
  1990年   83篇
  1989年   38篇
  1988年   45篇
  1987年   41篇
  1986年   33篇
  1985年   143篇
  1984年   238篇
  1983年   282篇
  1982年   201篇
  1981年   310篇
  1980年   120篇
  1979年   44篇
  1978年   41篇
  1977年   15篇
  1975年   23篇
  1974年   22篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
A data acquisition system for time resolved X-ray scattering experiments using linear, quadrant or area gas proportional detectors with delay line readout based on commercially available hardware (National Instruments) is described. The system can easily be configured for recording data from point detectors (e.g. photomultipliers and photodiodes) and/or ancillary data only. Applications involving measurements with two different types of time to digital converters illustrate the features and performances of the system.  相似文献   
42.
D. P. Phillips, T. E. Ruth, and L. M. Wagner (1993) reported that 1969-1990 California mortality data show that Chinese Americans are particularly vulnerable to diseases that Chinese astrology and traditional Chinese medicine associate with their birth years. For example, because fire is associated with the heart, a Chinese person born in a fire year (such as 1937) is more likely to die of heart disease than is a Chinese person born in a nonfire year. However, many diseases were excluded from this study, some diseases that were included have ambiguous links to birth years, and the statistical tests were indirect. A more complete statistical analysis and independent California mortality data for the years 1960-1968 and 1991-2002 did not replicate the original results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
43.
Provides the biography of David W. Johnson and announces that he has won the Award for Distinguished Contributions of Applications of Psychology to Education and Training for programmatic research, comprehensive research reviews, and revision of theory over four decades of persistence that have provided the knowledge foundation for cooperative learning, constructive controversy, conflict resolution, and peer mediation training. A selected bibliography is also provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
44.
In this letter, a block code that minimizes the peak‐to‐average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. It is shown that peak envelope power is invariant to cyclic shift and codeword inversion. The systematic encoding rule for the proposed code is composed of searching for a seed codeword, shifting the register elements, and determining codeword inversion. This eliminates the look‐up table for one‐to‐one correspondence between the source and the coded data. Computer simulation confirms that OFDM systems with the proposed code always have the minimum PAPR.  相似文献   
45.
稀土改善09CuPTiRE耐候钢耐蚀性的作用机理   总被引:9,自引:2,他引:7  
林勤  陈帮文  郭锋  郭英  孙学义  张志平 《稀土》2003,24(5):26-28
应用扫描电镜(SEM)、离子探针(IMA)、X射线光电子能谱(XPS)和交流阻抗法研究含不同稀土耐候钢稀土提高耐大气腐蚀作用机理。结果表明,合适的稀土含量可显著提高钢的耐腐蚀性,稀土能促进Si、Cu和P在内锈层中以Si~(4+)、Cu~+和P~(5+)形态富集,并观察到锈层中的稀土。钢中加入稀土形成了致密连续厚而粘附性好的含硅铜稀土的复合铁锈层,从而提高了抗大气腐蚀性能。  相似文献   
46.
对小型中间下料预焙电解槽技术条件摆布的原则和具体数据进行了探讨,提出了尽可能利用从大型预焙槽上得出的先进经验,并消化吸收,掌握好各种条件的平衡,以取得好经济技术指标的观点。  相似文献   
47.
The 1977 Broadcasting‐Satellite Service (BSS) Plan for Region 1 & 3 had been widely acknowledged to be out‐of‐date by the late 1980s. Development of digital modulation in the early 1990s provided an opportunity to update the technical provisions of the Plan to make it more economically viable. After a decade of work and three World Radiocommunication Conferences (WRCs), the revision of Region 1 & 3 BSS Plan was finally completed in 2003. The new Plan increased channel assignments from 5 to 10 analog‐equivalent channels for each country in Region 1, and from 4 to 12 channels for each country in Region 3. Yet, despite the increase in capacity, the new Plan is surprisingly similar to the original one in terms of the technical parameters. It is still based on national coverage, and the channel plan, orbital location, orbital spacing, and polarization are also the same. As a result, the new Plan is no more economically viable to implement than the old. To create economically viable BSS systems would most likely require modifications to the assignment in the Plan. Yet, modification procedures were made more difficult to apply after replanning. Less future implementation of BSS networks than would otherwise have occurred can be expected, and an inefficient usage of these frequency bands will likely result. On the other hand, less implemented systems will mean more capacity set aside for future use. This is important for countries that currently do not have satellite operations. In the end, BSS replanning reflects the eternal conflict between efficient usage and guaranteed future access. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
48.
本文介绍了一种作业效率高、省时省力新型的转炉炉底车,其特点是转盘转动灵活,炉底车上项盘径向任意方向均能平稳倾斜一定角度,以保证炉底圆周所受项力均匀可靠,满足炉底安装要求。  相似文献   
49.
In many legal proceedings, fact finders scrutinize the demeanor of a defendant or witness, particularly his or her nonverbal behavior, for indicators of deception. This meta-analysis investigated directly observable nonverbal correlates of deception as a function of different moderator variables. Although lay people and professionals alike assume that many nonverbal behaviors are displayed more frequently while lying, of 11 different behaviors observable in the head and body area, only 3 were reliably associated with deception. Nodding, foot and leg movements, and hand movements were negatively related to deception in the overall analyses weighted by sample size. Most people assume that nonverbal behaviors increase while lying; however, these behaviors decreased, whereas others showed no change. There was no evidence that people avoid eye contact while lying, although around the world, gaze aversion is deemed the most important signal of deception. Most effect sizes were found to be heterogeneous. Analyses of moderator variables revealed that many of the observed relationships varied as a function of content, motivation, preparation, sanctioning of the lie, experimental design, and operationalization. Existing theories cannot readily account for the heterogeneity in findings. Thus, practitioners are cautioned against using these indicators in assessing the truthfulness of oral reports. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
50.
Presents a reply by B. Fowers and B. Davidov to Islam's comments (see record 2007-14606-019) regarding their article (see record 2006-11202-002). Islam noted that virtues are often presented as universally valid character strengths, yet formulations of virtues are always embedded in a particular cultural context, a point we took pains to make in our article. We focus our response on Islam's important suggestion that this tension between universal human characteristics and the particulars of cultural context is indissoluble. Whereas he suggested this tension leads to contradiction and paradox, we see it as a fertile dialectic. The virtue of openness to the other is also subject to the same tension of abstract formulation and particular application. Although we formulated this virtue in a very general way, any instantiation of it would be shaped by the particulars of the cultural context and the situation in which it is exercised. We introduced the concept of dialogue because it is constituted not only by differences between individuals or groups but even more fundamentally by the dialectical relationship between those differences in cultural particularities and the universal human capacities for reason, curiosity, and social engagement, among others. Dialogue acknowledges the indissoluble otherness one finds in those culturally different from oneself, and yet real interchange can only occur because participants in dialogue exercise the cognitive flexibility characteristic of human beings and recognize a shared humanity with the other. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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