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   12383篇
  免费   1832篇
  国内免费   1036篇
电工技术   905篇
综合类   1972篇
化学工业   1498篇
金属工艺   294篇
机械仪表   699篇
建筑科学   1217篇
矿业工程   586篇
能源动力   276篇
轻工业   1339篇
水利工程   590篇
石油天然气   474篇
武器工业   163篇
无线电   875篇
一般工业技术   970篇
冶金工业   490篇
原子能技术   38篇
自动化技术   2865篇
  2024年   25篇
  2023年   128篇
  2022年   256篇
  2021年   370篇
  2020年   391篇
  2019年   369篇
  2018年   356篇
  2017年   486篇
  2016年   467篇
  2015年   529篇
  2014年   745篇
  2013年   805篇
  2012年   1007篇
  2011年   1031篇
  2010年   866篇
  2009年   884篇
  2008年   757篇
  2007年   1001篇
  2006年   845篇
  2005年   747篇
  2004年   589篇
  2003年   503篇
  2002年   389篇
  2001年   320篇
  2000年   234篇
  1999年   218篇
  1998年   163篇
  1997年   142篇
  1996年   101篇
  1995年   109篇
  1994年   99篇
  1993年   76篇
  1992年   44篇
  1991年   43篇
  1990年   29篇
  1989年   36篇
  1988年   18篇
  1987年   9篇
  1986年   8篇
  1985年   5篇
  1984年   4篇
  1983年   3篇
  1981年   3篇
  1979年   5篇
  1977年   3篇
  1962年   3篇
  1958年   3篇
  1957年   4篇
  1955年   2篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 142 毫秒
991.
对地空导弹将要拦截的目标进行识别,其主要思想是在综合多个因素的基础上给出待识别目标相对于已有目标集中各目标的隶属程度,通过隶属度排序,决定目标的种类,以便于为防空作战决策提供科学依据.最后通过实例说明该模型的合理性和有效性.  相似文献   
992.
The characterization of sulfonated polyetherketone (SPEK-C) films was investigated by using positron annihilation lifetime spectroscopy (PALS) and atomic force microscopy (AFM). It was found that free volume radius and intensity depend on the variation of sulfonation degree and solvent evaporation time of the films. Pore size and distribution determined from PALS and AFM measurements showed reasonable agreement.  相似文献   
993.
石质文物风化程度的超声波CT检测   总被引:1,自引:0,他引:1  
我国是一个具有悠久历史的文明古国,拥有大量的具有重要历史意义和价值的文化遗产,然而,由于长期的风化作用,导致它们损伤严重,亟须对其风化程度进行评价。超声波测试具有检测分辨率高,对被测物无损伤等特点,使其成为检测石质文物风化程度的有力手段。从理论和办法上,对运用超卢穿透波CT检测石质文物风化程度的方法进行了探讨,提出了一套利用超声波CT法检测现场石质文物风化程度和文物材料丰要力学参数分布状况的方法。利用这套方法对浙江省义乌市南宋古桥——古月桥桥身条石的风化程度进行测试,取得了较好的效果。  相似文献   
994.
基于实例的推理是人工智能中一项重要推理技术,而推理的核心是检索.介绍了产品设计的相似度计算方法,以及实例特征参数权系数值的确定方法,最后给出产品设计实例库三级检索算法.  相似文献   
995.
This article provides a justification for continuous measurements being more informative than pass/fail data. Namely, more information is provided for the same sample size or a smaller sample size is required for the same information. In the article, inference of the conformance probability, the probability of measurements meeting specifications, is considered. It is shown that continuous measurements provide dramatic advantages, especially when the conformance probability is high.  相似文献   
996.
Two sets of traditional Greek sheep milk yoghurt were produced: the first one (YC) using normal yoghurt culture (Lactobacillus delbrueckii subsp. bulgaricus ?10.13 and Streptococcus thermophilus ?10.7) and the second (PR) with the same normal culture mixed with Lactobacillus paracasei subsp. paracasei DC412. YC and PR had similar physicochemical properties and proteolysis patterns throughout storage. Both products showed similar peptide profiles by RP-HPLC but quantitative differences were observed in respect to storage time. Single-strain cultures of the microorganisms used showed similar peptide profiles for both lactobacilli, yet L. delbrueckii subsp. bulgaricus was the most proteolytic of all three microorganisms. The peptide content and the ACE-inhibitory activity of the water-soluble extracts of yoghurts, YC and PR, increased throughout storage. Major peptides were identified from yoghurt PR and from the separate cultures of L. delbrueckii subsp. bulgaricus and L. paracasei subsp. paracasei. Most of these peptides were derived from β-casein. A peptide, β-CN f114-121, with well-established ACE-inhibitory and opiate-like activity was identified in yoghurt PR. Further identified peptides were regarded as potential ACE-inhibitors according to their sequence.  相似文献   
997.
The mature peptide of Thermomonospora fusca xylanase A (TfxA) was successfully expressed in Pichia pastoris under the control of AOX1 promoter. The activity of recombinant T. fusca xylanase A (reTfxA) in culture supernatant was 117.3 ± 2.4 U/mg, which is 3 times higher than that of the native TfxA. The optimal temperature and pH for reTfxA were 60 °C and 6.0, respectively. When treated at 70 °C and pH 6.0 for 2 min, the residual activity of the reTfxA was 70%. The reTfxA was very stable over a wide pH range (5.0–9.0). After incubation over pH 5.0–9.0 at 25 °C for 1 h, all the residual activity of reTfxA was over 80%. The Km and kcat values for reTfxA were 2.45 mg/ml and 139 s−1, respectively. HPLC analysis revealed that xylobiose (X2) was the main hydrolysis product released from birchwood xylan and wheat bran insoluble xylan by reTfxA. Hydrolysis results of xylooligosaccharides showed that reTfxA was an endo-acting xylanase and xylobiose, xylotriose (X3), xylotetraose (X4), xylopentaose (X5), and xylohexaose (X6) could be hydrolysed. This is the first report on the expression of reTfxA in yeast and on the determining and quantifying of the hydrolysis products released from xylans and xylooligosaccharides by reTfxA.  相似文献   
998.
A classical question for memory researchers is whether memories vary in an all-or-nothing, discrete manner (e.g., stored vs. not stored, recalled vs. not recalled), or whether they vary along a continuous dimension (e.g., strength, similarity, or familiarity). For yes-no classification tasks, continuous- and discrete-state models predict nonlinear and linear receiver operating characteristics (ROCs), respectively (D. M. Green & J. A. Swets, 1966; N. A. Macmillan & C. D. Creelman, 1991). Recently, several authors have assumed that these predictions are generalizable to confidence ratings tasks (J. Qin, C. L. Raye, M. K. Johnson, & K. J. Mitchell, 2001; S. D. Slotnick, S. A. Klein, C. S. Dodson, & A. P. Shimamura, 2000; and A. P. Yonelinas, 1999). This assumption is shown to be unwarranted by showing that discrete-state ratings models predict both linear and nonlinear ROCs. The critical factor determining the form of the discrete-state ROC is the response strategy adopted by the classifier. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
999.
When participants studied a list of paired associates for several study-test cycles, their judgments of learning (JOLs) exhibited relatively good calibration on the 1st cycle, with a slight overconfidence. However, a shift toward marked underconfidence occurred from the 2nd cycle on. This underconfidence-with-practice (UWP) effect was very robust across several experimental manipulations, such as feedback or no feedback regarding the correctness of the answer, self-paced versus fixed-rate presentation, different incentives for correct performance, magnitude and direction of associative relationships, and conditions producing different degrees of knowing. It was also observed both in item-by-item JOLs and in aggregate JOLs. The UWP effect also occurred for list learning and for the memory of action events. Several theoretical explanations for this counterintuitive effect are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
1000.
A short review of the works concerning parameter estimation in kinetic experiments was performed. An adaptive random search algorithm was applied to evaluate the parameters and parameter confidence intervals of Langmuir-Hinshelwood models. The kinetic parameters were determined using the Box - Draper criterion. The parameter confidence regions were found by using the likelihood ratio. Three heterogeneously catalyzed hydrogenations were studied.  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