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   66233篇
  免费   3615篇
  国内免费   92篇
电工技术   508篇
综合类   141篇
化学工业   15024篇
金属工艺   1266篇
机械仪表   1305篇
建筑科学   2054篇
矿业工程   145篇
能源动力   1658篇
轻工业   11510篇
水利工程   632篇
石油天然气   323篇
武器工业   7篇
无线电   2762篇
一般工业技术   10494篇
冶金工业   12581篇
原子能技术   318篇
自动化技术   9212篇
  2024年   125篇
  2023年   572篇
  2022年   1410篇
  2021年   2070篇
  2020年   1402篇
  2019年   1581篇
  2018年   2482篇
  2017年   2423篇
  2016年   2588篇
  2015年   1870篇
  2014年   2472篇
  2013年   4956篇
  2012年   3958篇
  2011年   4055篇
  2010年   3175篇
  2009年   2945篇
  2008年   2773篇
  2007年   2499篇
  2006年   1889篇
  2005年   1600篇
  2004年   1387篇
  2003年   1348篇
  2002年   1183篇
  2001年   920篇
  2000年   844篇
  1999年   888篇
  1998年   4044篇
  1997年   2688篇
  1996年   1787篇
  1995年   1070篇
  1994年   850篇
  1993年   870篇
  1992年   344篇
  1991年   325篇
  1990年   259篇
  1989年   267篇
  1988年   273篇
  1987年   240篇
  1986年   215篇
  1985年   247篇
  1984年   209篇
  1983年   164篇
  1982年   197篇
  1981年   228篇
  1980年   238篇
  1979年   117篇
  1978年   121篇
  1977年   385篇
  1976年   778篇
  1973年   109篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
54.
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program.  相似文献   
55.
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values.  相似文献   
56.
Generation of Technology-Independent Retargetable Analog Blocks   总被引:1,自引:0,他引:1  
This paper introduces a complete methodology for retargeting of analog cells to different sets of specifications. This methodology is technology-independent, thus allowing the migration, from one technology to another, of the circuit under retargeting. Careful integration of the device sizing and layout generation tasks via the incorporation of layout constraints during the sizing process allows to generate fully functional designs in a few minutes. The methodology is illustrated via the retargeting of a fully-differential Miller-compensated two-stage operational amplifier for a new set of specifications and two different technological processes.An erratum to this article can be found at  相似文献   
57.
58.
In three experiments subjects performed one of five tasks after an initial study phase. Results showed that performance on conceptually driven retention tasks (those requiring the processing of meaning) was consistently dissociated from that on data-driven tasks (those relying more on analysis of physical features). Performance on conceptually driven tasks of free recall, semantic cued recall, and a task of answering general knowledge questions was enhanced most when target items had been generated rather than read at study (Experiment 1) and when subjects formed mental images of item referents at study (Experiment 3). Conversely, the data driven tasks of word fragment completion and recall using graphemic cues were performed best when subjects read rather than generated items at input (Experiment 1) and when the physical features of study and test items matched in terms of modality (Experiment 2) and typography (Experiment 3). These findings indicate that dissociations among memory tasks are better explained in terms of the degree of overlap between mental operations at study and test than in terms of various memory systems underlying different tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
59.
Non-deterministic exponential time has two-prover interactive protocols   总被引:2,自引:1,他引:1  
We determine the exact power of two-prover interactive proof systems introduced by Ben-Or, Goldwasser, Kilian, and Wigderson (1988). In this system, two all-powerful noncommunicating provers convince a randomizing polynomial time verifier in polynomial time that the inputx belongs to the languageL. We show that the class of languages having tow-prover interactive proof systems is nondeterministic exponential time.We also show that to prove membership in languages inEXP, the honest provers need the power ofEXP only.The first part of the proof of the main result extends recent techniques of polynomial extrapolation used in the single prover case by Lund, Fortnow, Karloff, Nisan, and Shamir.The second part is averification scheme for multilinearity of a function in several variables held by an oracle and can be viewed as an independent result onprogram verification. Its proof rests on combinatorial techniques employing a simple isoperimetric inequality for certain graphs:  相似文献   
60.
Conducted a study of client expectations of psychological services in Yucatán, Mexico, under the sponsorship of a grant from the Organization of American States. The Expectations about Counseling–Brief form (EAC-B) questionnaire was translated and administered to 488 subjects across age, sex, and experience with psychological services. Subsequent analyses supported the reliability and robustness of the Spanish EAC-B, with factor structure similar to the EAC-B in English. Some relation was found among age, sex, prior counseling experience, and expectations about counseling. Implications of these data for future research and comparison with U.S. subjects are discussed. (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