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   5511篇
  免费   101篇
  国内免费   2篇
电工技术   47篇
综合类   1篇
化学工业   841篇
金属工艺   44篇
机械仪表   67篇
建筑科学   100篇
矿业工程   64篇
能源动力   86篇
轻工业   359篇
水利工程   33篇
石油天然气   6篇
无线电   452篇
一般工业技术   682篇
冶金工业   2438篇
原子能技术   44篇
自动化技术   350篇
  2021年   22篇
  2020年   26篇
  2019年   42篇
  2018年   50篇
  2017年   54篇
  2016年   51篇
  2015年   49篇
  2014年   71篇
  2013年   173篇
  2012年   92篇
  2011年   139篇
  2010年   100篇
  2009年   96篇
  2008年   144篇
  2007年   125篇
  2006年   102篇
  2005年   112篇
  2004年   96篇
  2003年   82篇
  2002年   92篇
  2001年   68篇
  2000年   96篇
  1999年   140篇
  1998年   791篇
  1997年   458篇
  1996年   279篇
  1995年   191篇
  1994年   183篇
  1993年   164篇
  1992年   85篇
  1991年   73篇
  1990年   86篇
  1989年   95篇
  1988年   65篇
  1987年   84篇
  1986年   56篇
  1985年   76篇
  1984年   66篇
  1983年   59篇
  1982年   65篇
  1981年   51篇
  1980年   51篇
  1979年   40篇
  1978年   57篇
  1977年   83篇
  1976年   150篇
  1975年   34篇
  1974年   37篇
  1972年   34篇
  1971年   26篇
排序方式: 共有5614条查询结果,搜索用时 31 毫秒
31.
We have determined the nucleotide and encoded amino acid sequences of the capsid, membrane precursor, membrane, envelope, and nonstructural NS1 protein genes of a dengue-2 virus (D2-04) isolated from a patient in Hainan, China. The sequenced region contains a gene organization similar to that of other flaviviruses. The overall amino acid sequence similarity between D2-04 and other dengue-2 viruses is greater than 92%, whereas that between D2-04 and members of the other dengue serotypes is about 65%.  相似文献   
32.
A hyperdynamic circulatory state with elevated cardiac output, decreased peripheral vascular resistance, and sodium retention occurs in patients with portal cirrhosis. Surgical portal-systemic shunts and transjugular intrahepatic portal-systemic shunts (TIPS) have been shown to worsen the high-output state in these patients. However, clinical evidence of high-output congestive heart failure has been reported only rarely to complicate cirrhosis. We describe a patient who developed high-output congestive heart failure with markedly elevated filling pressures after TIPS and had complete resolution of heart failure after liver transplantation.  相似文献   
33.

RILEM Bulletin

Fourth International Conference on Durability of Building Materials and Components  相似文献   
34.
White WJ  Lawrie RA 《Meat science》1985,12(2):117-123
The method for the detection and possible quantification of the unusual amino acid 3-methyl-l-histidine has been refined and elucidated. This is an essential prerequisite for the determination of its value as a robust unequivocal index of lean meat protein.  相似文献   
35.
Summary This paper deals with discounted Markov decision processes, Markov with respect to a finite statespaceI, where for eachiI, and each decision epocht, there is a finite action space K(i, t). The paper is concerned with problems which are formulated in terms of the discounted rewards in several ways. In order to ensure that optimal, or near optimal, policies are obtained, the state spaceI is extended to augmented state-spaces A(n), or A(), including the accumulated discounted rewards. Specimen problems are formulated and some computational aspects examined.
Zusammenfassung Es werden diskontierte Markovsche Entscheidungsprozesse behandelt mit endlichem Zustandsraum I, wobei die Mengen der zulässigen Entscheidungen K(i, t) vom Zustandi I und vom Zeitpunktt abhängen können. Es werden verschiedene Zielfunktionen betrachtet, die jeweils als Funktion des diskontierten Gesamtgewinns (nicht dessen Erwartungswerts) formuliert werden. Um optimale oder fast-optimale Politiken zu erhalten ohne die gesamte Vorgeschichte zu registrieren, wird der Zustandsraum um die akkumulierten diskontierten Auszahlungen erweitert. Eine Auswahl solcher Probleme wird exemplarisch diskutiert einschließlich einiger Aspekte der numerischen Behandlung.
  相似文献   
36.
A variety of different imaging techniques produce data which naturally lie in stratified spaces. These spaces consist of smooth regions of maximal dimension glued together along lower dimensional boundaries. Diffusion processes are important as they can be used to represent noise in statistical models on spaces for which standard parametric probability distributions do not exist. We consider particles undergoing Brownian motion in some low dimensional stratified spaces, and obtain analytic solutions to the heat equation specifying the distribution of particles. These solutions play the role of prototypical distributions for studying behaviour near singularities. While probabilistic reasoning can be used to solve the heat equation in some straightforward cases, more generally we construct solutions from eigenfunctions of the Laplacian. Specifically, we solve the heat equation on: open books; two-dimensional cones; the Petersen graph with unit edge length; and the cone of this graph which corresponds to a space of evolutionary trees.  相似文献   
37.
Adsorption and desorption of hydrogen and coadsorption of H2 with H2O and CO over Ru(00l) surface have been studied under UHV conditions using the technique of TDS. Surface hydrogen interacts with adsorbed water resulting in an additional desorption state at 510 K which is not easily displaced by CO, but the total number of adsorption sites for hydrogen adsorption is independent of the amount of H2O predosed at room temperature. Hydrogen adsorption is blocked easily by CO dose (more than 0.5 L) or a small amount of O(a) formed from dissociative adsorption of water, and adsorbed hydrogen formed in the absence of significant water is easily displaced by CO dose at even room temperature.  相似文献   
38.
The high-resolution structure of several specific DNA-bindingproteins have been determined, and they display a common structuralmotif which mediates their binding to DNA. This motif consistsof two -helices connected by a sharp turn, and its amino acidsequence has several distinguishing features. A computer searchof the proteins coded by the genome of bacteriophage T7 hasbeen performed in an attempt to identify those proteins thatpotentially contain this motif. Eight proteins were found tohave regions similar to that of the motif. Of these, three arerelatively small, have no known function and are good candidatesfor being DNA-binding regulatory proteins. The methods describeduse commonly available computer programs and databases, andare therefore easy to implement.  相似文献   
39.
Petroleum pitch (Ashland A240) has been subjected to thermal treatment and solvent fractionation to produce refined pitches to be evaluated as impregnants for C-C composites. The solvent fractions were obtained by sequential Soxhlet extraction with solvents such as hexane, benzene, and pyridine. Thermal treatment to 408 °C produced a mesophase pitch (≈50% mesophase); an appreciable portion of the mesophase was soluble in strong solvents. There were substantial differences in chemical composition and in pyrolysis behaviour of the fractions. As the depth of fraction increased, the pyrolysis yield and bloating increased, and the microstructure of the coke became finer until glassy microconstituents were formed in the deepest fractions.  相似文献   
40.
An experimental investigation of the rheological properties of glass fiber-reinforced polycarbonate melts and the extrusion of such compounds through capillary and slit dies is presented. The viscosity–shear rate function seems independent of instrument for cone-plate and capillary investigations. The presence of fibers increases the level of the viscosity. Normal stresses at fixed shear stress are also increased by the presence of fibers. The extrudate swell is decreased by the presence of fibers and surface roughness is increased. Fiber orientation increases and surface roughness decreases with increasing extrusion rate.  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