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   1857篇
  免费   44篇
  国内免费   6篇
电工技术   30篇
化学工业   282篇
金属工艺   33篇
机械仪表   42篇
建筑科学   26篇
矿业工程   1篇
能源动力   78篇
轻工业   43篇
水利工程   8篇
石油天然气   35篇
无线电   475篇
一般工业技术   333篇
冶金工业   174篇
原子能技术   14篇
自动化技术   333篇
  2023年   15篇
  2022年   64篇
  2021年   41篇
  2020年   46篇
  2019年   43篇
  2018年   50篇
  2017年   49篇
  2016年   34篇
  2015年   46篇
  2014年   57篇
  2013年   140篇
  2012年   73篇
  2011年   66篇
  2010年   78篇
  2009年   56篇
  2008年   59篇
  2007年   55篇
  2006年   62篇
  2005年   55篇
  2004年   46篇
  2003年   44篇
  2002年   48篇
  2001年   27篇
  2000年   40篇
  1999年   36篇
  1998年   68篇
  1997年   51篇
  1996年   31篇
  1995年   39篇
  1994年   37篇
  1993年   36篇
  1992年   22篇
  1991年   30篇
  1990年   29篇
  1989年   23篇
  1988年   18篇
  1987年   17篇
  1986年   19篇
  1985年   24篇
  1984年   12篇
  1983年   9篇
  1982年   14篇
  1981年   8篇
  1980年   13篇
  1979年   10篇
  1978年   7篇
  1977年   10篇
  1976年   9篇
  1974年   11篇
  1973年   10篇
排序方式: 共有1907条查询结果,搜索用时 12 毫秒
101.
In this paper, we consider the following question: what is the worst possible page-replacement strategy? Our goal is to devise an online strategy that has the highest possible fraction of page faults as compared to the worst offline strategy. We show that there is no deterministic, online page-replacement strategy that is competitive with the worst offline strategy. We give a randomized strategy based on the “most-recently-used” heuristic and show that this strategy is the worst possible online page-replacement strategy.  相似文献   
102.
Agrawal  D.P. 《Electronics letters》1974,10(8):121-122
A binary-coded-decimal adder/subtractor is proposed that uses the carry-look-ahead technique, resulting in a significant increase in speed. With slight modification, it is possible to use it for binary operation as well.  相似文献   
103.
Microwave synthesis of nano-sized BaTiO3 and decrystallized titania, and microwave sintering of electroceramics including BaTiO3, Ba(Zn1/3Ta2/3)O3 (BZT), lead zirconate–titanate (i.e. Pb(Zr x Ti1?x )O3, or PZT), etc., as well as multilayer ceramic capacitors based on X7R, C0G, and ferrite multilayer chip inductors are presented. The results indicate that microwave processing significantly accelerated synthesis and sintering kinetics. As a result, processing time can be saved up to 90%, with the product properties comparable to or better than that of the conventional products.  相似文献   
104.
105.
We report molecular changes in leaves of rice plants (Oryza sativa L. - reference crop plant and grass model) exposed to ultra low-dose ionizing radiation, first using contaminated soil from the exclusion zone around Chernobyl reactor site. Results revealed induction of stress-related marker genes (Northern blot) and secondary metabolites (LC-MS/MS) in irradiated leaf segments over appropriate control. Second, employing the same in vitro model system, we replicated results of the first experiment using in-house fabricated sources of ultra low-dose gamma (γ) rays and selected marker genes by RT-PCR. Results suggest the usefulness of the rice model in studying ultra low-dose radiation response/s.  相似文献   
106.
Two chemically different phases, hexagonal BN and AIN, were simultaneously produced by chemical vapor deposition (CVD) using an impinging jet reactor and the BCl3─AlCl3─NH3─Ar reagent system. The microstructure of the BN + AIN composite coatings was strongly dependent on temperature, pressure, and BCl3 and AlCl3 concentrations. The growth characteristics of BN and AIN in the codeposition system were similar to those expected from the single-phase deposition processes (i.e., BN-CVD and AIN-CVD), except the growth of AIN whiskers was accentuated, and competition between BN and AIN deposition in the composites was suspected to be the cause of less-crystalline deposits. In both BN + AIN-CVD and AIN-CVD, the growth of AIN whiskers became more apparent with increasing pressure or temperature. The codeposition behavior observed experimentally was compared with thermodynamic predictions.  相似文献   
107.
The X-ray diffraction pattern for potassium-zirconium phosphate is significantly improved when the material is prepared by the sol-gel route rather than the powder method. Peaks at high, low, and intermediate angles are presented and compared for the two methods. It is assumed that the more nearly homogeneous mixing of the elements in the sol-gel process is responsible for the significant improvement in crystallinity.  相似文献   
108.
BACKGROUND: Iron, folate, and vitamin B12 deficiencies have adverse effects on pregnancy outcome. In India, data on the concomitant prevalence of these deficiencies among pregnant women are meager. OBJECTIVE: We conducted a community-based study to assess the prevalence of deficiencies of iron, folate, and vitamin B12 among pregnant women in a rural block of Haryana State. METHODS: The study was approved by the ethics committee of the All India Institute of Medical Sciences, New Delhi. A total of 283 pregnant women were enrolled in the study. After oral informed consent had been obtained from the women, blood was drawn from the antecubital vein for estimation of the levels of serum ferritin by enzyme-linked immunosorbent assay (levels < 12 ng/ mL were considered as indicative of poor iron stores); serum folate was determined by radioimmunoassay (levels <3 ng/mL were considered as indicative of poor folate stores); and serum vitamin B12 was estimated by the microbiologic method (levels < 200 pg/mL were considered as indicative of poor vitamin B12 stores). RESULTS: The results indicated that 67.7%, 26.3%, and 74.1% of the women had poor iron, folate, and vitamin B12 stores, respectively. Concomitant deficiencies of iron, folate, and vitamin B12 occurred in 16.2% of the women. We found that 59.9% of the women were consuming less than 75% of the recommended daily caloric allowance (2175 kcal), indicating an overall poor food intake. This could be one of the predominant reasons for poor iron, folate, and vitamin B12 stores among the women. CONCLUSIONS: Our findings suggest that apart from iron and folate, vitamin B12 deficiencies may play an important role in causing anemia.  相似文献   
109.
Water Resources Management - The present study investigates and evaluate the scope and potential of modern computing tools and techniques such as ensembled machine learning methods in estimating...  相似文献   
110.
Xiao X  Puri IK  Agrawal AK 《Applied optics》2002,41(10):1922-1928
We focus on the utility of rainbow schlieren as a tool for measuring the temperature of axisymmetric partially premixed flames (PPFs). Methane-air PPFs are established on a coannular burner. The flames involve two spatially distinct reaction zones, one in an inner premixed region that has a curved tip and a spatially planar wing portion and another that involves an outer nonpremixed zone in which intermediate species burn in air. Schlieren images are found to visualize clearly these PPF characteristics through light deflection by steep refractive-index gradients in the two reaction zone fronts. The temperature distributions of two flames established at fuel-rich mixture equivalence ratios of phi(r) = 1.5 and 2.0, with bulk-averaged velocities, Vreac = 60 cm s(-1) and Vair = 50 cm s(-1), are inferred from color schlieren images, and a measurement error analysis is performed. Errors arise from two sources. One lies in the process of inferring the temperature from the refractive-index measurement by making assumptions regarding the local composition of the flame. We have shown through simulations that the average temperature deviations due to these assumptions are 1.7% for the phi(r) = 1.5 flame and 2.3% for the phi(r) = 2.0 flame. Another source involves the local uncertainty in the measurement of the transverse ray displacement at the filter plane that is used to determine the refractive index and thereafter the flame temperature. We have ascertained that a maximum error of 4.3% in the temperature determination can be attributed to this local measurement uncertainty. This investigation demonstrates the capability of the schlieren technique for providing not only qualitative displays of the PPFs but also full-field-of-view temperature measurements that are accurate, spatially resolved, and nonintrusive.  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