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   2992篇
  免费   87篇
  国内免费   33篇
电工技术   55篇
综合类   37篇
化学工业   261篇
金属工艺   112篇
机械仪表   43篇
建筑科学   72篇
矿业工程   9篇
能源动力   48篇
轻工业   164篇
水利工程   27篇
石油天然气   12篇
武器工业   7篇
无线电   106篇
一般工业技术   213篇
冶金工业   1780篇
原子能技术   34篇
自动化技术   132篇
  2023年   7篇
  2022年   11篇
  2021年   18篇
  2020年   17篇
  2019年   25篇
  2018年   30篇
  2017年   26篇
  2016年   36篇
  2015年   17篇
  2014年   32篇
  2013年   66篇
  2012年   64篇
  2011年   111篇
  2010年   83篇
  2009年   77篇
  2008年   97篇
  2007年   79篇
  2006年   58篇
  2005年   65篇
  2004年   52篇
  2003年   28篇
  2002年   34篇
  2001年   32篇
  2000年   36篇
  1999年   59篇
  1998年   534篇
  1997年   309篇
  1996年   197篇
  1995年   134篇
  1994年   108篇
  1993年   99篇
  1992年   24篇
  1991年   23篇
  1990年   31篇
  1989年   37篇
  1988年   38篇
  1987年   27篇
  1986年   21篇
  1985年   28篇
  1984年   7篇
  1983年   10篇
  1982年   15篇
  1981年   18篇
  1980年   22篇
  1979年   13篇
  1978年   9篇
  1977年   65篇
  1976年   129篇
  1971年   6篇
  1967年   10篇
排序方式: 共有3112条查询结果,搜索用时 46 毫秒
71.
To optimize the growth promoting effect of growth hormone (GH), 65 previously untreated girls with Turner syndrome (TS), chronological age (CA) 2-11 yr, were randomized into 3 dosage regimen groups: A, B, and C, with a daily recombinant-human GH dose during 4 study years of 4-4-4-4, 4-6-6-6, and 4-6-8-8 IU/m2 b.s. The first GH dosage increase in groups B and C resulted in a significantly higher mean height velocity (HV) compared with constant dose group A. During the third year, when the dose was raised again only in group C, mean HV was significantly higher in groups B and C than in group A, and in group C compared with group B. In year 4 only group C mean HV remained significantly higher than group A. The pattern of change in HSDSCA (Dutch-Swedish-Danish Turner references) was identical; however, in year 4 mean delta HSDSCA in group B also remained significantly higher than group A. After 4 yr GH treatment, the following was determined. 1) The mean delta HSDSCA was significantly higher for groups B and C compared with group A, but not significantly different between groups B and C. 2) Although significantly higher compared with estimated values for untreated Dutch girls with TS, bone maturation of the GH treated girls was not significantly different between groups. 3) It was positively related with the degree of bone age (BA) retardation at start of study and negatively with baseline CA. 4) Both the modified Index of Potential Height (mIPHRUS) and a recently developed Turner-specific final height (FH) prediction method (PTSRUS), based on regression coefficients for H, CA, and bone age, showed significant increases in mean FH prediction, without significant differences between groups. PTSRUS values were markedly higher than the mIPHRUS values. Dose dependency could be shown for the area under the curve (AUC) for GH, but delta HSDSCA was not linearly related with AUC. Baseline GH binding protein (BP) levels were in 84% of the cases within the normal age range; the decrease in mean levels after 6 months GH was not significant. Mean insulin-like growth factor I (IGF-I) and IGFBP-3 plasma levels increased significantly, without significant differences between groups. delta HSDSCA during GH was dependent on IGF-I plasma levels at baseline and during the study period, beta-0.002 and beta-0.0004. Thus, a stepwise GH-dosing approach reduced the "waning" effect of the growth response after 4 yr treatment without undue bone maturation. FH prediction was not significantly different between treatment groups. Irrespective of the GH dose used, initiation of GH treatment at a younger age was beneficial after 4 yr GH when expressed as actual cm gained or as gain in FH prediction, but was not statistically significant when expressed as delta HSDSCA over the study period.  相似文献   
72.
This article elucidates the clinical applicability and state of the art of ambulatory urodynamics. Ambulatory urodynamics have evolved into practical investigations like EAC, HFM, and EAC combined with renal pelvimetry. EAC has been shown to be the method of preference if detrusor overactivity is involved. Conventional filling cystometry has proved to be an unreliable way to exclude detrusor instability. De novo instability after suspension surgery often indicates that an existing detrusor overactivity was not identified preoperatively. EAC including flowmetry has shown considerable variance in obstructive and contractility parameters in males with LUTS indicative for BPH. This raises doubt whether the clinical flow analysis is the suitable "gold standard" as advocated by the ICS. For a real break through of EAC, less complex automatic analysis is necessary. HFM is a newer method within the range of ambulatory urodynamic tests. It has not yet been completely evaluated. But, because the technique is analogous to the office flowmetry, noninvasive and very well accepted by the patients, it is expected to be widely used. This expectation is strengthened by the fact that HFM seems to show individual therapeutic efficacy of drugs, such as alpha-blockers. As a research tool to evaluate efficacy, it is far more powerful than conventional methods because of the reduction of within-patient standard deviation to about 10%. Finally, EAC combined with pelvimetry offers a promising method for the clinical evaluation of a combined dysfunction of upper and lower urinary tract.  相似文献   
73.
This paper describes a study of the effects of the overall spatial resolution, polynomial degree and computational grid directionality on the accuracy of numerical solutions of a highly anisotropic thermal diffusion equation using the spectral element spatial discretization method. The high-order spectral element macroscopic modeling code SEL/HiFi has been used to explore the parameter space. It is shown that for a given number of spatial degrees of freedom, increasing polynomial degree while reducing the number of elements results in exponential reduction of the numerical error. The alignment of the grid with the direction of anisotropy is shown to further improve the accuracy of the solution. These effects are qualitatively explained and numerically quantified in 2- and 3-dimensional calculations with straight and curved anisotropy.  相似文献   
74.
Anomaly detection allows for the identification of unknown and novel attacks in network traffic. However, current approaches for anomaly detection of network packet payloads are limited to the analysis of plain byte sequences. Experiments have shown that application-layer attacks become difficult to detect in the presence of attack obfuscation using payload customization. The ability to incorporate syntactic context into anomaly detection provides valuable information and increases detection accuracy. In this contribution, we address the issue of incorporating protocol context into payload-based anomaly detection. We present a new data representation, called \({c}_n\)-grams, that allows to integrate syntactic and sequential features of payloads in an unified feature space and provides the basis for context-aware detection of network intrusions. We conduct experiments on both text-based and binary application-layer protocols which demonstrate superior accuracy on the detection of various types of attacks over regular anomaly detection methods. Furthermore, we show how \({c}_n\)-grams can be used to interpret detected anomalies and thus, provide explainable decisions in practice.  相似文献   
75.
针对光谱测试系统对光源稳定性越来越高的要求,介绍了一种以单片机为核心的高稳定性的钨灯电源系统.它以C8051F410单片机为核心,采用增量式PID控制算法,通过控制单片机的D/A输出来调整MOS场效应管的导通情况,从而达到稳定钨灯工作电流的目的,保证钨灯的发光稳定.通过实验验证,新设计的电源具有控制精度高、稳定性好、性能可靠等优点,可应用于光谱测试系统中.  相似文献   
76.
针对矿山电力传动系统的特点和要求 ,根据遗传算法和模糊控制理论 ,研究和设计了一种基于遗传算法的自寻优模糊控制器。仿真研究和实时控制结果表明 ,该控制器设计的调速系统具有响应速度快、空载和负载情况下无静差、无超调、鲁棒性强等特点 ,且结构简单 ,易于实现实时控制。  相似文献   
77.
78.
设计的功能是以人为本,丰富和升华人们的生理体验和心理体验以提升生活品质,传递信息和新的思维方式;设计作品的优劣从某种角度来说是设计思维深入程度决定的;设计思维是以个人对世界的认识为基础的;人对世界认识的程度实际上也就是设计思维深入的程度,因此我们应弄清自己思维的渊源,树立正确的世界观。  相似文献   
79.
设计的功能是以人为本,丰富和升华人们的生理体验和心理体验以提升生活品质,传递信息和新的思维方式;设计作品的优劣从某种角度来说是设计思维深入程度决定的;设计思维是以个人对世界的认识为基础的;人对世界认识的程度实际上也就是设计思维深入的程度,因此我们应弄清自己思维的渊源,树立正确的世界观。  相似文献   
80.
Status and results of a research project are reported, which aims at developing calorimetric low temperature detectors for heavy ions. The special conditions for the detection of energetic heavy ions are discussed. The response of an aluminium transition edge calorimeter, operated at about1.5K, to the impact of heavy ions was investigated. The observed energy resolutions E/E=3.9×10–3for5.9MeV/u 208 Pb-ions, E/E=1.6×10–3for4.8MeV/u 58 Ni-ions and E/E=4.3×10–3for100MeV/u 20 Ne-ions are most probably not yet limited by the intrinsic detector resolution. The present results already represent an improvement over conventional solid state detectors and ionization chambers.  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