首页 | 官方网站   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   1002篇
  免费   76篇
  国内免费   35篇
工业技术   1113篇
  2023年   9篇
  2022年   2篇
  2021年   16篇
  2020年   18篇
  2019年   15篇
  2018年   11篇
  2017年   19篇
  2016年   26篇
  2015年   24篇
  2014年   53篇
  2013年   52篇
  2012年   53篇
  2011年   70篇
  2010年   63篇
  2009年   64篇
  2008年   58篇
  2007年   86篇
  2006年   47篇
  2005年   56篇
  2004年   57篇
  2003年   49篇
  2002年   42篇
  2001年   23篇
  2000年   27篇
  1999年   19篇
  1998年   22篇
  1997年   18篇
  1996年   20篇
  1995年   21篇
  1994年   9篇
  1993年   8篇
  1992年   2篇
  1991年   12篇
  1990年   5篇
  1989年   9篇
  1988年   5篇
  1987年   3篇
  1986年   4篇
  1985年   3篇
  1984年   4篇
  1983年   2篇
  1982年   2篇
  1981年   1篇
  1980年   2篇
  1974年   1篇
  1973年   1篇
排序方式: 共有1113条查询结果,搜索用时 15 毫秒
1.
Certified reference materials are an essential tool for calibration of testing equipment, validation of analytical methods and ensuring quality of test results. Due to lack of national low temperature reference materials, Decahydronaphthalene reference material for flash point measurements according to ISO 13736has been developed by the National Metrology Institute of Egypt (NIS). This article describes production steps of the reference material. Certification of the material was carried out by interlaboratory comparisons, where between bottles homogeneity and stability studies were conducted in explosion protection department at PTB, Germany. The interlaboratory results were statistically analyzed, and robust mean was calculated as assigned value. The certified value and expanded measurement uncertainty (k = 2) was found 55.7 °C ± 1.2 °C, respectively.  相似文献   
2.
This paper presents a 5.7–6.0 GHz Phase-Locked Loop (PLL) design using a 130 nm 2P6M CMOS process. We propose to suppress reference spur through reducing the current mismatch in charge pump (CP), controlling the delay time in phase frequency detector (PFD), and using a smaller VCO gain (KVCO). With a reference frequency of 32.768 MHz, chip measurement results show that the frequency tuning range is 5.7–6.0 GHz, the reference spur is −68 dBc, the phase noise levels are −109 dBc/Hz and −135 dBc/Hz at 1 MHz and 10 MHz offset respectively for 5.835 GHz. Compared with existing designs in the literature, this work’s reference spur is improved by at least 17% and its phase noise is the lowest. Under a 1.5 V supply voltage, the power dissipation with an output buffer of the PLL is 12 mW.  相似文献   
3.
孟祥武  苏醒  骆婧 《室内设计》2019,(1):104-110
生土建筑形式多样,不仅是中国传 统建筑重要的组成部分,在世界范围内也有 广泛分布。在全球能源危机背景下,生土建 筑材料的生态性能又一次受到世人瞩目。我 国研究生土建筑时间较早,但相较于发达国 家,在研究探索与经验累积等方面还存在一 定差距。本文从研究机构、教育模式、规范 标准三个不同层面对国内外生土建筑研究进 行分析判断,寻找出目前国内外生土建筑发 展的现状和需要改进之处,总结国外先进研 究经验,以高校教育作为理论支撑、规范标 准作为实践场地、研究机构作为理论与实践 结合的统筹研究单位,使三方面形成集“产 学研”为一体的完整链条,为我国生土建筑 的进一步发展提供依据。  相似文献   
4.
马蒙 《核动力工程》2020,41(1):122-126
分析反应堆压力容器(RPV)锻件制造过程中关键化学元素含量及基准无塑性转变温度(RTNDT)数值,通过引入修正淬透性系数,建立了反映RTNDT变化规律的修正淬透性系数函数表达式,并给出了实例验证,结果表明,通过本文建立的修正淬透性系数函数式可以比较精确地预估RPV锻件的RTNDT值。   相似文献   
5.
The planning of Physical Cell Identities (PCI) has a strong impact on the performance of Long Term Evolution cellular networks. Although several PCI planning schemes have been proposed in the literature, no study has quantified the performance gains obtained by these schemes. In this paper, a comprehensive performance analysis is carried out to quantify the impact of PCI planning on user quality of service and network capacity in the downlink of LTE. First, an analytical model for the influence of PCI planning on reference signal collisions is developed. Based on this model, different PCI planning schemes are tested on a dynamic system-level simulator implementing a macrocellular scenario. During the analysis, both Voice-over-IP and full buffer services over time-synchronized and non-time synchronized networks are considered. Results show that call blocking and dropping for real-time services and user throughput for non-real time services can be significantly improved by a proper PCI plan.  相似文献   
6.
为了减少测试数据和测试时间,该文提出一种基于镜像对称参考切片的多扫描链测试数据压缩方法.采用两个相互镜像对称的参考切片与扫描切片做相容性比较,提高了相容概率.若扫描切片与参考切片相容,只需要很少的几位编码就可以表示这个扫描切片,并且可以并行载入多扫描链;若不相容,参考切片被该扫描切片替换.提出一种最长相容策略,用来处理扫描切片与参考切片同时满足多种相容关系时的选取问题.根据 Huffman 编码原理确定不同相容情况的编码码字,可以进一步提高测试数据的压缩率.实验结果表明所提方法的平均测试数据压缩率达到了69.13%.  相似文献   
7.
国内外雨水花园研究综述   总被引:2,自引:0,他引:2  
系统归纳国内外雨水花园的研究现状,明确了国内的研究内容主要涉及雨水花园的起源与发展、国外优秀案例介绍、雨水花园的营造技术、雨水花园场地试验及模型构建等;国外的研究内容主要涉及雨水花园的水文模拟研究、土壤渗透力研究、污染物滞留能力研究、不同植物应用对水文的影响、建造及应用等,为今后的雨水花园研究工作奠定基础和提供借鉴。  相似文献   
8.
The potential usefulness of FDA's U.S. Total Diet Study (TDS) selenium (Se) data to the nutrition community was evaluatedas part of the TDS modernization program. TDS Se data collected from 2003 – 2010 was evaluated by comparing these data to Se concentration data in USDA's Standard Reference 26 (SR26) Database. We also evaluated trends in Se concentrations over time and differences in Se concentrations by Market Basket (MB). Comparable SR26 foods were identified for most TDS foods; however, for many TDS foods, there was more than one match in SR26. TDS was found to be a unique source of analytical Se concentration data for four food mixtures and for several SR26 foods with imputed Se concentrations. Se concentrations in TDS foods were similar to analyzed Se concentrations in most corresponding SR26 foods. Se concentrations in whole wheat bread were significantly higher in MB 2 (U.S. West Region, collected in the winter) than in MB 1 (U.S. North Central Region, collected in the fall), 3 (U.S. South Region, collected in the spring), and 4 (U.S. North East Region, collected in the summer). Se concentrations in whole wheat bread were also significantly higher in MB 4 than in MB 3. Se concentrations in boiled eggs were significantly higher in MB 2 than in other market baskets. The U.S. Total Diet Study suspended analysis of Se in 2010, but FDA is evaluating the potential benefits of adding Se analysis back to the TDS program. Results of this study demonstrate the potential value of TDS concentration data for Se and other nutrients to the U.S. nutrition community. However, it is clear that TDS data on generic foods (e.g. tuna, canned in water) are less useful than TDS data on more specifically defined foods (e.g. tuna, white, canned in water). Potential geographical and/or seasonal differences in Se contents of some foods may warrant additional investigation.  相似文献   
9.
The GERG-2008 equation of state is the approved ISO standard (ISO 20765-2) for the calculation of thermophysical properties of natural gas mixtures. The composition of natural gas can vary considerably due to the diversity of origin. Further diversification was generated by adding hydrogen, biogas, or other non-conventional energy gases. In this work, high-precision experimental (p, ρ, T) data for two gravimetrically prepared synthetic natural gas mixtures are reported. One mixture resembled a conventional natural gas of 11 components (11 M) with a nominal mixture composition (amount-of-substance fraction) of 0.8845 for methane as the matrix compound with the other compounds being 0.005 for oxygen, 0.04 for nitrogen, 0.015 for carbon dioxide, 0.04 for ethane, 0.01 for propane, 0.002 each for n- and isobutane, and ultimately 0.0005 each for isopentane, n-pentane, and n-hexane. The other mixture was a 13-component hydrogen-enriched natural gas with a low calorific value featuring a nominal composition of 0.7885 for methane, 0.03 for hydrogen, 0.005 for helium, 0.12 for nitrogen, 0.04 for carbon dioxide, 0.0075 for ethane, 0.003 for propane, 0.002 each for n- and isobutane, and 0.0005 each for neopentane, isopentane, n-pentane, and n-hexane. Density measurements were performed in an isothermal operational mode at temperatures between 260 and 350 K and at pressures up to 20 MPa by using a single-sinker densimeter with magnetic suspension coupling. The data were compared with the corresponding densities calculated from both GERG-2008 and AGA8-DC92 equations of state to test their performance on real mixtures. The average absolute deviation from GERG-2008 (AGA8-DC92) is 0.027% (0.078%) for 11 M and 0.095% (0.062%) for the 13-component H2-enriched mixture, respectively. The corresponding maximum relative deviation from GERG-2008 (AGA8-DC92) amounts to 0.095% (0.127%) for 11 M and 0.291% (0.193%) for the H2-enriched mixture.  相似文献   
10.
标准物质是保证准确量值和量值溯源的重要工具,标准物质的有效控制和管理是确保实验室检测数据准确的关键步骤,关系着实验室质量控制水平。对标准物质进行有效的管理控制,充分发挥标准物质的功能,是当前检测实验室急需解决的关键问题。本文主要探究了从标准物质的购买、验收及验证、储存管理、配制、标识、使用、期间核查、失效后处理等全过程进行系统地控制,保证标准物质的质量,确保标准物质在质量控制、校准测量仪器、评价测量分析方法、赋予物质特性量值、考核评价检测人员的技术能力、产品检测过程等方面起到重要作用,从而达到提高检测实验室检测数据的准确性和检测技术能力水平的目的。  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-23

京公网安备 11010802026262号