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   3232篇
  免费   65篇
  国内免费   9篇
电工技术   38篇
综合类   1篇
化学工业   460篇
金属工艺   66篇
机械仪表   31篇
建筑科学   14篇
矿业工程   3篇
能源动力   90篇
轻工业   69篇
水利工程   15篇
石油天然气   19篇
无线电   242篇
一般工业技术   404篇
冶金工业   1611篇
原子能技术   2篇
自动化技术   241篇
  2023年   10篇
  2022年   33篇
  2021年   39篇
  2020年   27篇
  2019年   35篇
  2018年   57篇
  2017年   45篇
  2016年   42篇
  2015年   29篇
  2014年   63篇
  2013年   155篇
  2012年   78篇
  2011年   94篇
  2010年   71篇
  2009年   62篇
  2008年   73篇
  2007年   85篇
  2006年   47篇
  2005年   54篇
  2004年   41篇
  2003年   53篇
  2002年   44篇
  2001年   30篇
  2000年   33篇
  1999年   79篇
  1998年   505篇
  1997年   296篇
  1996年   206篇
  1995年   105篇
  1994年   108篇
  1993年   108篇
  1992年   31篇
  1991年   45篇
  1990年   53篇
  1989年   41篇
  1988年   31篇
  1987年   31篇
  1986年   34篇
  1985年   28篇
  1984年   19篇
  1983年   16篇
  1982年   19篇
  1981年   27篇
  1980年   32篇
  1979年   15篇
  1978年   12篇
  1977年   44篇
  1976年   85篇
  1975年   9篇
  1973年   6篇
排序方式: 共有3306条查询结果,搜索用时 203 毫秒
31.
32.
Four experiments contrasted the cue-familiarity hypothesis of feeling-of-knowing judgments (FKJs) and tip-of-the-tongue feelings (TOTs) to the target-retrievability hypothesis. Familiarity of the cues was contrasted to memorability of the targets in a paired-associate design (e.g., A-B A-B, A-B A-B', A-B A-D, A-B C-D), in which the number of repetitions of the cue A terms was dissociated from the memorability of the target B terms. Little support was found for the target-retrievability hypothesis, because in none of the 4 experiments were FKJs related to target memorability. In one experiment, an omnibus retrieval hypothesis (which implicates total retrieval rather than just correct retrieval) and the cue-familiarity hypothesis produced isomorphic predictions that were borne out by the FKJ and TOT results. All 4 experiments supported the cue-familiarity hypothesis, because FKJs and TOTs were directly related to the number of presentations (and thereby the familiarity) of the cues.  相似文献   
33.
BACKGROUND: The efficacy of breast self-examination in helping to reduce mortality from breast cancer has not been rigorously demonstrated. PURPOSE: To assess efficacy, a large, randomized trial was initiated in Shanghai, China. METHODS: From October 1989 to October 1991, 267040 current and retired female employees associated with 520 factories in the Shanghai Textile Industry Bureau were randomly assigned on the basis of factory to either a self-examination instruction group (133375 women) or a control group (133665 women). The women were born within the period from 1925 through 1958. Women in the instruction group were given intensive training in breast self-examination, including the use of silicone breast models and personalized instruction, plus two subsequent reinforcement sessions and multiple reminders to practice the technique. Women in the control group were asked to attend training sessions on the prevention of low back pain. All women have been followed for the development of breast diseases and for death from breast cancer. RESULTS: A high level of participation during the first 4-5 years of the trial was documented among women in the instruction group. Randomly sampled women in this group demonstrated greater proficiency in detecting lumps in breast models than did randomly sampled women in the control group. Approximately equal numbers of breast cancers were detected in the two groups (331 in the instruction group and 322 in the control group) through 1994, which is the last year for which case-finding efforts have been completed. The breast cancers detected in the instruction group were not diagnosed at an appreciably earlier stage or smaller size than those in the control group. More benign breast lesions were detected in the instruction group than in the control group (1457 versus 623, respectively), suggesting a higher index of suspicion for women who received training. Cumulative breast cancer mortality rates through 5 years from entry into the study were nearly equivalent for the two groups. CONCLUSIONS: Breast self-examination has not led to a reduction in mortality from breast cancer in this study cohort in the first several years since the trial began. A shift toward the diagnosis of disease at a less advanced stage in women given instruction has also not been demonstrated. Longer follow-up of participants in this trial is required before final assessment can be made of the efficacy of breast self-examination. IMPLICATIONS: At this time, there is insufficient evidence to recommend for or against the teaching of breast self-examination.  相似文献   
34.
35.
The scalar transform is a new representation for signals, offering a perspective that is different from the Fourier transform. We introduce the notion of a scalar periodic function. These functions are then represented through the discrete scale series. We also define the notion of a strictly scale-limited signal. Analogous to the Shannon interpolation formula, we show that such signals can be exactly reconstructed from exponentially spaced samples of the signal in the time domain. As an interesting, practical application, we show how properties unique to the scale transform make it very useful in computing depth maps of a scene  相似文献   
36.
The presentations made, as well as the discussions, in the panels at the workshop, Thermal Challenges in Next Generation Electronic Systems (THERMES), are summarized in this paper. The panels dealt with diverse topics including thermal management roadmaps, microscale cooling systems, numerical modeling from the component to system levels, hardware for future high performance and Internet computing architectures, and transport issues in the manufacturing of electronic packages. The focus of the panels was to identify barriers to further progress in each area that require the attention of the research community.  相似文献   
37.
38.
39.
2',4'-Dihydroxyacetophenone, also known as resoacetophenone, is a commercially important intermediate which is generally prepared by the acylation of resorcinol with acetic acid in the presence of a molar excess of zinc chloride, which leads to waste disposal problems. The most frequently used acylating agents such as acetic anhydride and acetyl chloride have several disadvantages and need to be replaced by cheap and benign agents. In this connection, acetic acid is a better choice but with a non-polluting and reusable catalyst. The synthesis of 2',4'-dihydroxyacetophenone from resorcinol and acetic acid was carried out in the presence of a variety of solid acid catalysts such as montmorillonite clay (K-10), dodecatungstophosphoric acid (DTP) supported on K-10, sulfated zirconia and ion exchange resins. Amongst these catalysts, Amberlyst-36, an ion exchange resin, was found to be the most effective. The effects of various parameters on the rate of reaction and selectivity were investigated to establish the intrinsic kinetics of the reaction. It was possible to deduce the adsorption equilibrium constant and rate constant simultaneously for the reaction including the corresponding energies of activation. The catalyst is reusable. The process is in consonance with the principles of green chemistry. Electronic Publication  相似文献   
40.
In this paper we report the impact of hot-carrier stress on analog performance of n- and p-MOSFET's with conventional oxide, NH3-nitrided oxide (RTN) and reoxidized nitrided oxide (RTN/RTO) as gate dielectrics. Changes due to hot-carrier stress in crucial analog parameters viz., drain output resistance, voltage gain, and input offset voltage of a source coupled differential MOSFET pair are investigated. Results show that RTN/RTO gate dielectrics suppress degradation of analog parameters in n-MOSFET's but increase it slightly in p-MOSFET's, as compared to conventional oxide MOSFET's  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