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   2044篇
  免费   65篇
  国内免费   9篇
电工技术   48篇
综合类   1篇
化学工业   402篇
金属工艺   43篇
机械仪表   38篇
建筑科学   64篇
矿业工程   3篇
能源动力   116篇
轻工业   138篇
水利工程   32篇
石油天然气   11篇
无线电   286篇
一般工业技术   467篇
冶金工业   194篇
原子能技术   26篇
自动化技术   249篇
  2024年   10篇
  2023年   28篇
  2022年   39篇
  2021年   67篇
  2020年   49篇
  2019年   46篇
  2018年   77篇
  2017年   54篇
  2016年   69篇
  2015年   38篇
  2014年   58篇
  2013年   145篇
  2012年   79篇
  2011年   93篇
  2010年   85篇
  2009年   111篇
  2008年   93篇
  2007年   72篇
  2006年   48篇
  2005年   42篇
  2004年   27篇
  2003年   39篇
  2002年   34篇
  2001年   28篇
  2000年   20篇
  1999年   32篇
  1998年   43篇
  1997年   39篇
  1996年   44篇
  1995年   21篇
  1994年   27篇
  1993年   22篇
  1992年   24篇
  1991年   23篇
  1990年   19篇
  1989年   21篇
  1988年   25篇
  1987年   21篇
  1986年   22篇
  1985年   41篇
  1984年   34篇
  1983年   40篇
  1982年   21篇
  1981年   24篇
  1980年   22篇
  1979年   17篇
  1978年   17篇
  1977年   13篇
  1976年   16篇
  1975年   15篇
排序方式: 共有2118条查询结果,搜索用时 0 毫秒
31.
This paper reports on a microfluidic device for the screening of organophosphonate nerve agent degradation products. The miniaturized system relies on an efficient chip-based separation of alkyl methylphosphonic acids (breakdown products of Sarin, Soman, and VX nerve agents) followed by their sensitive contactless conductivity detection. Experimental parameters relevant to the separation and detection processes have been optimized to yield high sensitivity (with 48-86 microg L(-1) detection limits), fast response (50 s for a three alkyl methylphosphonic acid mixture), high precision (RSD = 3.8-5.0%), and good linearity (over the 0.3-100 mg L(-1) range). Applicability to natural (river) water samples is demonstrated. The new microsystem offers promise for monitoring degradation products of chemical warfare agents, with advantages of speed/warning, efficiency, portability, sample size, and cost compared to conventional ion chromatography or capillary electrophoresis systems.  相似文献   
32.
The Ferroelectric relaxor ternary system 0.5PZN-(0.5 – x)PFN-xBZN was prepared using the columbite precursor method. The stability of the perovskite phase was studied as a function of BZN content in the system. It was observed that BZN is a good stabilizer of perovskite phase because of the high value of electronegativity difference between its cation and anion. It has also been observed that addition of BZN increases the dielectric maxima peak value and decrease the Curie temperature of the ceramics. The ternary composition 0.5PZN-0.425PFN-0.075BZN has been identified for MLCs applications. It has a T c of around room temperature with a peak dielectric constant 6400 and tan 0.05. The mechanical properties of relaxor materials have also been studied and reported.  相似文献   
33.
34.
This paper presents and studies the Canadian Truck Driver Scheduling Problem (CAN-TDSP), which is the problem of determining whether a sequence of locations can be visited within given time windows in such a way that driving and working activities of truck drivers comply with Canadian Commercial Vehicle Drivers Hours of Service Regulations. Canadian regulations comprise the provisions found in US hours of service regulations as well as additional constraints on the maximum amount of driving and the minimum amount of off-duty time on each day. We present two heuristics and an exact approach for solving the CAN-TDSP. Computational experiments demonstrate the effectiveness of our approaches and indicate that Canadian regulations are significantly more permissive than US hours of service regulations.  相似文献   
35.
In this paper we have proposed a dynamic pricing scheme for the contributing peers in the Video on Demand (VoD) system. The scheme provides an effective mechanism to maximize the profit through the residual resources of the contributing peers. A utilization function is executed for each contributing peer to estimate the utility factor based on the parameters such as initial setup cost, holding cost, chaining cost and salvage cost. In this paper, we urge an effective dynamic pricing algorithm that efficiently utilizes a range of parameters with a varying degree of complexity. The key findings of the algorithm are (i) each contributing peers are benefitted by the monetary based on its resource contributions to the VoD system and (ii) a high degree of social optimum is established by proficiently aggregating the contributing peer’s resources with the overall resources of the VoD system. We validate our claim by simulating the proposed dynamic pricing scheme with other standard pricing schemes such as altruism, cost model and game theory perspective. The result of our dynamic pricing scheme shows the best utility factor than other standard pricing schemes.  相似文献   
36.
Wireless Personal Communications - Cluster analysis is a commonly used technique by investors to create a diversified portfolio. The approach aims at maximizing returns for a tolerable degree of...  相似文献   
37.
Wireless Personal Communications - This paper analyzes the performance of two-way OFDMA based cooperative device-to-device communication (C-D2D) framework in a heterogeneous cellular network. In...  相似文献   
38.
Both enzymatic and nonenzymatic PTMs of proteins involve chemical modifications. Some of these modifications are prerequisite for the normal functioning of cell, while other chemical modifications render the proteins as “neo-self” antigens, which are recognized as “non-self” leading to aberrant cellular and humoral immune responses. However, these modifications could be a secondary effect of autoimmune diseases, as in the case of type I diabetes, hyperglycemia leads to protein glycation. The enigma of chemical modifications and immune response is akin to the “chick-and-egg” paradox. Nevertheless, chemical modifications regulate immune response. In some of the well-known autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis, chemically modified proteins act as autoantigens forming immune complexes. In some instances, chemical modifications are also involved in regulating immune response during pathogen infection. Further, the usefulness of proteomic analysis of immune complexes is briefly discussed.  相似文献   
39.
Low Cycle Fatigue (LCF) on smooth hour glass specimens and Fatigue Crack Propagation (FCP) studies on Single Edge Notch (SEN) specimens were carried out at room temperature on four Cu-Al polycrystalline alloys to investigate the effects of Stacking Fault Energy (SFE) and mechanical property variations on fatigue characteristics. Significant improvements in fatigue properties were observed for alloys of low SFE. A microhardness technique was used to delineate the fatigue plastic zone ahead of stopped cracks at several stress intensity ranges for all the alloys. Planar slip was associated with a less than a second power dependence of plastic zone size on the stress intensity range. Transmission Electron Microscopy (TEM) was used to observe the substructures that developed both in LCF at different strain ranges and also ahead of fatigue cracks at different stress intensity ranges. Fractography was carried out to study the micromechanisms of crack propagation using a two stage replication technique. The experimental results were in good agreement with a theoretical model for FCP developed previously by the authors which incorporates mechanical and microstructural variables.  相似文献   
40.
A considerable amount of tunnelling has been going on in India for various projects such as hydroelectric power, irrigation, roads and railways. Most of these projects are located in Himalayas, far awa...  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