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   313篇
  免费   53篇
  国内免费   97篇
系统科学   47篇
丛书文集   5篇
教育与普及   3篇
现状及发展   3篇
研究方法   2篇
综合类   403篇
  2024年   4篇
  2023年   13篇
  2022年   2篇
  2021年   7篇
  2020年   2篇
  2019年   4篇
  2018年   10篇
  2017年   9篇
  2016年   8篇
  2015年   8篇
  2014年   23篇
  2013年   30篇
  2012年   17篇
  2011年   24篇
  2010年   9篇
  2009年   19篇
  2008年   35篇
  2007年   38篇
  2006年   64篇
  2005年   27篇
  2004年   17篇
  2003年   28篇
  2002年   8篇
  2001年   10篇
  2000年   17篇
  1999年   6篇
  1998年   6篇
  1997年   6篇
  1996年   4篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1980年   1篇
排序方式: 共有463条查询结果,搜索用时 375 毫秒
41.
INTRODUCTIONKraft black liquor composition is very complicated. Generally, it is a complex and multiphase fluid, which consists of organic and inorganic components. The total solids content in black liquors has a great effect on its fluidity and deformation. To the wood black liquor, there have already been detailed researches on their flow properties and many theoretic or practical results have been concluded in the literatures [1-8]. But to non-wood black liquor, the previous researches…  相似文献   
42.
Based on analyzing the techniques and architecture of existing network Intrusion Detection System (IDS), and probing into the fundament of Immune System (IS), a novel immune model is presented and applied to network IDS, which is helpful to design an effective IDS. Besides, this paper suggests a scheme to represent the self profile of network. And an automated self profile extraction algorithm is provided to extract self profile from packets. The experimental results prove validity of the scheme and algorithm, which is the foundation of the immune model.  相似文献   
43.
44.
The butt welds of 4-mm thick 5A06 aluminum alloy plates were produced by adjustable-gap bobbin-tool friction stir travel with travel speeds of 200, 300, and 400 mm/min in this study. The microstructure was studied using optical microscopy and electron backscatter diffraction (EBSD). Tensile tests and microhardness measurements were performed to identify the effect of the travel speed on the joint mechanical properties. Sound joints were obtained at 200 mm/min while voids were present at different positions of the joints as the travel speed increased. The EBSD results show that the grain size, high angle grain boundaries, and density of geometrically necessary dislocations in different regions of the joint vary depending on the recovery and recrystallization behavior. Specific attention was given to the relationship between the local microstructure and mechanical properties. Microhardness measurements show that the average hardness of the stir zone (SZ) was greater than that of the base material, which was only affected slightly by the travel speed. The tensile strength of the joint decreased with increasing travel speed and the maximal strength efficiency reached 99%.  相似文献   
45.
Financial market model based on self-organized percolation   总被引:1,自引:0,他引:1  
Financial markets are typical complex systems in which the large-scale dynamical properties depend on the evolution of a large number of nonlinear-coupled subsys-tems. The efficient market hypothesis (EMH) based on rational expectation assumption (REA) considers the price of financial markets as random walk, thus the return dis-tribution obeys Gaussian form. However, the EMH suffers the impugnation on REA and the challenge of actual fi-nancial data that the real-life markets are of return…  相似文献   
46.
This paper introduces the design and development of a new computerized data acquisition system for the coal-fired magnetohydrodynamical (MHD) electrical power generation experiments. Compared to the previous system, it has a higher sampling rate and an improved simultaneity performance. It also improves the data collection method and sensor design for the measurement of Faraday voltages and Faraday currents. The system has been successfully used in many regular MHD generator tests. It provides an excellent base for the future research and development of the Coal-fired MHD electrical power generation.  相似文献   
47.
1.IntroductionTherearemanynumericalresultsaboutthenon-smoothintegralequationswherek(s,t)=k.(t)~k(s/t)/tandf(s)aregiven,uistheunknownsolution(e.g.[1-6]).Buttherearefewresultsaboutthehighorderandadaptivemethodscorrespondingly.Becauseoftheefficiencyinsolving…  相似文献   
48.
EC,ASMC and Macrophage Oxidize Human Low Density Lipoprotein   总被引:1,自引:0,他引:1  
Itisknownthatduringatherosclerosis (As)oxidizedlowdensitylipoprotein (ox LDL)playsanimportantrolethatistakenupbyarterialwallmacrophagesatanenhancedrate ,leadingtocellularcholesterolaccumulationandfoamcellformation .TheatherogenicityofoxidizedLDLalsoinvolv…  相似文献   
49.
The relationship of species and abundance between the diatoms in the water and sediments from the southern South China Sea (SCS) were discussed, and the key environmental controlling factors were also investigated. Studies show that the diatom abundance is high in both water and sediments in the southeast part of the southern SCS and the varying trend is similar, while in the northwest part, the abundance is low, and the varying trend is different. The dominant diatom species are Thalassionema nitzschioides and Nitzschia bicapitata in water, and T. nitzschioides and Chaetoceros messanensis in sediments. The diatom species of small size and thin shell in water are more than in the sediments, while the diatom species of large size and thick shell in water are less. The percentage of species T. nitzschioides is higher in water of southeast part than in that of northwest part, but it is similar in sediments of both areas. It is shown that the southwest monsoon is the important factor influencing diatom abundance and T. nitzschioides percentage, and when the southwest monsoon is well developed, the distribution of diatom abundance and T. nitzschioides percentage are consistent in both water and sediments of the study area.  相似文献   
50.
Insulin-like growth factor 1 (IGF-1) promotes osteoblasts differentiation and bone formation, and its expression is induced by mechanical stretch, thus IGF-1 has been considered an effector molecule that links mechanical stimulation and local tissue responses. In this study, a mechanical stretching device was designed to apply physiological level static or cyclic stretching stimulation to osteoblasts. Different isoforms of IGF-1 mRNA were amplified by RT-PCR from the cells using respective primers and these amplified products were sequenced. An iso-form of IGF-1 splicing product was found to be selectively produced by osteoblasts under stretching stimulation. This IGF-1 isoform had identical sequence with the mechano growth factor (MGF) which was originally identified in muscle cells. Regulations of the expression of the liver-type IGF (L.IGF-1) and MGF in osteoblasts under stretch stimulation were further studied using semi-quantitative RT-PCR. Stretch stimulation was found to promot the expression of IGF-1 (L.IGF-1 and MGF), and for both isoforms expression was more effectively stimulated by cyclic stretch than static stretch. MGF was detected only in osteoblasts subjected to mechanical stretch, suggesting MGF was a stretch sensitive growth factor. Expression of MGF peaked earlier than that of L.IGF-1, which was similar to their regulation in muscle and suggested similar roles of MGF and L.IGF-1 in bone as in muscle cells. The functions of MGF and LIGF-1 in osteoblasts shall be established by further experimental studies.  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