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   361737篇
  免费   30919篇
  国内免费   16118篇
电工技术   21626篇
技术理论   45篇
综合类   25841篇
化学工业   60091篇
金属工艺   21145篇
机械仪表   23798篇
建筑科学   27917篇
矿业工程   11891篇
能源动力   9889篇
轻工业   24782篇
水利工程   6848篇
石油天然气   23627篇
武器工业   2849篇
无线电   40063篇
一般工业技术   39742篇
冶金工业   18632篇
原子能技术   3722篇
自动化技术   46266篇
  2024年   2352篇
  2023年   6070篇
  2022年   10205篇
  2021年   14129篇
  2020年   10845篇
  2019年   8809篇
  2018年   10270篇
  2017年   11458篇
  2016年   10612篇
  2015年   14298篇
  2014年   17856篇
  2013年   21236篇
  2012年   22999篇
  2011年   25461篇
  2010年   22491篇
  2009年   21329篇
  2008年   20974篇
  2007年   19942篇
  2006年   20304篇
  2005年   17863篇
  2004年   12112篇
  2003年   10793篇
  2002年   10000篇
  2001年   8905篇
  2000年   8832篇
  1999年   9403篇
  1998年   7188篇
  1997年   6138篇
  1996年   5814篇
  1995年   4787篇
  1994年   3894篇
  1993年   2631篇
  1992年   2075篇
  1991年   1574篇
  1990年   1234篇
  1989年   998篇
  1988年   832篇
  1987年   525篇
  1986年   410篇
  1985年   259篇
  1984年   207篇
  1983年   164篇
  1982年   128篇
  1981年   77篇
  1980年   99篇
  1979年   43篇
  1978年   17篇
  1977年   23篇
  1976年   28篇
  1959年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
本文利用简便的滴定过程模型,确立了微机模拟处理实验数据,方便、准确地求解络合滴定等当点的方法。设计了最佳实验条件模拟估计程序。该法测定Zn~(2+),Pb~(2+),Cu~(2+),Fe~(3+)结果的相对误差Δ<1%。pH=6-7时,测定Ca~(2+)的相对误差为-1.61%;σ<0.001mmol,(N=5)。  相似文献   
82.
Reversible watermarking scheme with image-independent embedding capacity   总被引:1,自引:0,他引:1  
Permanent distortion is one of the main drawbacks of all the irreversible watermarking schemes. Attempts to recover the original signal after the signal passes the authentication process are being made, starting just a few years ago. Some common problems, such as salt-and-pepper artefacts owing to intensity wraparound and low embedding capacity, can now be resolved. However, some significant problems remain unsolved. First, the embedding capacity is signal-dependent, i.e., capacity varies significantly depending on the nature of the host signal. The direct impact of this is compromised security for signals with low capacity. Some signals may be even non-embeddable. Secondly, while seriously tackled in irreversible watermarking schemes, the well-known problem of block-wise dependence, which opens a security gap for the vector quantisation attack and transplantation attack, are not addressed by researchers of the reversible schemes. This work proposes a reversible watermarking scheme with near-constant signal-independent embedding capacity and immunity to the vector quantisation attack and transplantation attack.  相似文献   
83.
任向红  樊秉安  李瑛 《粘接》2002,23(1):1-2,6
坑道水下堵漏剂的研制包括F-1、F-2和F-3型。其中F-1是一种有机堵漏剂,它可以在水中固化;F-2是一种无机防水堵漏剂,施工方便;F-3是速凝型,它可在瞬间固化,能对坑道的涌水口进行堵漏。  相似文献   
84.
85.
简要介绍了推力矢量控制技术的概念,分析了推力矢量控制的基本原理及特点.在简要分析其技术发展历程的基础上,给出了导弹推力矢量技术的现状和发展趋势.  相似文献   
86.
A series of new o‐phenylenediamine (OPD)/o‐phenetidine (PHT) copolymers with partly phenazine‐like structures has been successfully synthesized at three polymerization temperatures by chemically oxidative polymerization in four different polymerization media. The molecular structures and properties of the resulting OPD/PHT polymers were investigated by IR, UV–vis and high‐resolution 1H NMR spectroscopies, and DSC, in order to ascertain the effect of reaction temperature, comonomer ratio and acid medium. The copolymerization mechanism of OPD with PHT monomers has been proposed. It is found that the statistical OPD/PHT copolymer obtained at a temperature of 118 °C has a higher degree of polymerization than that obtained at 12–17 °C. The OPD content in the copolymers calculated from NMR spectroscopic analysis is higher than that in the feed OPD content, whereas the OPD content calculated from element analysis is slightly lower than the feed OPD content. It can be predicted that denitrogenation takes place in the OPD units during the polymerization process at OPD/PHT molar ratios of 90/10 and 100/0. These OPD/PHT copolymers exhibit a much better solubility than the OPD homopolymer, hence suggesting an incorporation of PHT units into the phenazine structure of the homopolymer. The thermal behavior of the copolymers was also studied. Copyright © 2004 Society of Chemical Industry  相似文献   
87.
88.
Diabetes mellitus is a common disease. It affects multiple organ systems. Adverse effects of hyperglycemia on infection, fracture healing, and bone remodeling have been recently reported. This study was conducted to evaluate the clinical and radiographic results of 93 total hip arthroplasties in 78 consecutive patients with diabetes. All femoral components were cemented using contemporary cementing techniques. Prophylactic antibiotics were given in each case. The mean follow-up period was 4.1 years (range, 2-6.5 years). Ninety-six percent of the hips were rated excellent or good. Radiolucencies were observed in only 3.7% of the stems, while 22.2% of the cups showed radiolucencies. There was a 4% revision incidence. There was no postoperative infection in this series--a distinct improvement from previously reported series. However, complications remained high at 24.3%. The most frequent complication was urinary tract infection (14.2%). The most serious complication was myocardial infarction. The authors believe total hip arthroplasty can be safely performed in patients with diabetes, provided that adequate medical and follow-up evaluations are performed. The medium-term clinical and radiographic follow-up evaluations are not inferior to reported series in patients without diabetes.  相似文献   
89.
90.
The growth of Li1+xMn2O4 via detonation reaction was investigated with respect to the presence of an energetic precursor, such as the metallic nitrate and the degree of confinement of the explosive charge. The detonation products were characterized by scanning electron microscopy. Powder X-ray diffraction and transmission electron microscopy were used to characterize the products. Li1+xMn2O4 with 1-2 μm spherical morphology and more uniform secondary particles, but with smaller primary particles of diameters from 20 to 60 nm and a variety of morphologies were found. The oxides produced by this cheap method affirmed the validity of detonation synthesis of nano-size powders.  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