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   2181篇
  免费   61篇
电工技术   34篇
综合类   4篇
化学工业   502篇
金属工艺   65篇
机械仪表   48篇
建筑科学   92篇
矿业工程   23篇
能源动力   88篇
轻工业   92篇
水利工程   25篇
石油天然气   6篇
无线电   149篇
一般工业技术   368篇
冶金工业   433篇
原子能技术   29篇
自动化技术   284篇
  2021年   25篇
  2019年   21篇
  2018年   27篇
  2017年   18篇
  2016年   49篇
  2015年   27篇
  2014年   45篇
  2013年   173篇
  2012年   65篇
  2011年   106篇
  2010年   71篇
  2009年   88篇
  2008年   91篇
  2007年   87篇
  2006年   76篇
  2005年   86篇
  2004年   55篇
  2003年   54篇
  2002年   41篇
  2001年   36篇
  2000年   14篇
  1999年   35篇
  1998年   37篇
  1997年   40篇
  1996年   31篇
  1995年   35篇
  1994年   31篇
  1993年   28篇
  1992年   37篇
  1991年   19篇
  1990年   18篇
  1989年   29篇
  1988年   19篇
  1987年   25篇
  1986年   27篇
  1985年   38篇
  1984年   26篇
  1983年   33篇
  1982年   30篇
  1981年   31篇
  1980年   28篇
  1979年   33篇
  1978年   22篇
  1977年   24篇
  1976年   24篇
  1975年   28篇
  1974年   39篇
  1972年   17篇
  1969年   13篇
  1955年   17篇
排序方式: 共有2242条查询结果,搜索用时 15 毫秒
61.
62.
In this paper, we demonstrate that interleaved sampling techniques can be used to characterize the Hamiltonian of a qubit and its environmental decoherence rate. The technique offers a significant advantage in terms of the number of measurements that are required to characterize a qubit. When compared to the standard Nyquist?CShannon sampling rate, the saving in the total measurement time for the interleaved method is approximately proportional to the ratio of the sample rates.  相似文献   
63.
64.
Abstract

We consider pure continuous variable entanglement with nonequal correlations between orthogonal quadratures. We introduce a simple protocol which equates these correlations and in the process transforms the entanglement onto a state with the minimum allowed number of photons. As an example we show that our protocol transforms, through unitary local operations, a single squeezed beam split on a beam splitter into the same entanglement that is produced when two squeezed beams are mixed orthogonally. We demonstrate that this technique can in principle facilitate perfect teleportation utilizing only one squeezed beam.  相似文献   
65.
Most central cities must at present bargain with other units of their regions and the nation for the residents and industry they need; and their bargaining power is so weak as to threaten their viability unless aid from state and federal governments is supplied. Both in order to serve the disadvantaged residents they do attract, and to cultivate their attractiveness to other residents and to industry, cities must re-define “urban renewal” as consisting of large investments in the development of human, land, and transportation potentialities. Such investments must, as all investments, come from “surpluses” which are controlled by the states and the nation, not the cities.  相似文献   
66.
This paper examines the socially optimal (and also equilibrium) locations of two stores or libraries on a linear market of unit length. If each consumer has probability \(w\) of finding a desired product at each store, then the socially optimal locations are never completely centralized for full information, but are completely centralized for \(w \le 0.5\) when costly visit search is necessary. The Nash equilibrium locations of two stores, and various alternative models for the socially optimal locations of two stores, are also examined.  相似文献   
67.
What are batteries, fuel cells, and supercapacitors?   总被引:20,自引:0,他引:20  
Winter M  Brodd RJ 《Chemical reviews》2004,104(10):4245-4269
Electrochemical energy conversion devices are pervasive in our daily lives. Batteries, fuel cells and supercapacitors belong to the same family of energy conversion devices. They are all based on the fundamentals of electrochemical thermodynamics and kinetics. All three are needed to service the wide energy requirements of various devices and systems. Neither batteries, fuel cells nor electrochemical capacitors, by themselves, can serve all applications.  相似文献   
68.
Visual cryptography is an encryption technique that hides a secret image by distributing it between some shared images made up of seemingly random black‐and‐white pixels. Extended visual cryptography (EVC) goes further in that the shared images instead represent meaningful binary pictures. The original approach to EVC suffered from low contrast, so later papers considered how to improve the visual quality of the results by enhancing contrast of the shared images. This work further improves the appearance of the shared images by preserving edge structures within them using a framework of dithering followed by a detail recovery operation. We are also careful to suppress noise in smooth areas.  相似文献   
69.
The booklouse, Liposcelis bostrychophila, is an increasingly common pest of stored food products worldwide. We report here the cuticular lipid composition of this pest (the first report of the hydrocarbons of any member of the Order Psocoptera and the first report of fatty acid amides as cuticular components for any insect). No unsaturated hydrocarbons were present. A homologous series of n-alkanes (C21–C34), monomethyl alkanes (3-, 4-, 5-, 7-, 9-, 11-, 12-, 13- and 15-methyl-) with a carbon chain range of C28–C42, and dimethyl alkanes (3, 7-; 9, 13-; 11, 15-; 13, 17-; 9, 21-; 11, 19-; and 13, 21-); with a carbon number range of C31–C43 were identified. The relative abundances of these hydrocarbons were low, comprising approximately 0.0125% of total biomass. The amides were a homologous series (C16–C22 in chain length), with the major amide being stearoyl amide. In addition to the amides, free fatty acids (C16:1, C16:0, C18:2, C18:1, and C18:0 in chain length) and three straight chain aldehydes (C15, C16, and C17:1 in chain length) also occurred as cuticular components. These findings are discussed in terms of the chemical and physiological ecology of this species.  相似文献   
70.
Summary The preparation of epoxy fatty acid ester plasticizers has been reviewed. These plasticizers can be prepared by epoxidation reactions, utilizing a preformed peracid or anin-situ technique. A newin-situ epoxidation process, utilizing hydrogen peroxide and acetic acid in the presence of strong acid catalyst, has been described. Excellent conversions to epoxide have been achieved with a series of monounsaturated and polyunsaturated esters. Epoxy fatty acid esters are excellent plasticizers for vinyl resins. Their performance in a series of additional epoxy plasticizers of vegetable and marine origin is described. Novel epoxy plasticizers based upon mixed acetylated mono- and di-glyceride have been prepared and are found to have excellent plasticizer performance. Presented at the 28th fall meeting, American Oil Chemists’ Society, October 1954, Minneapolis, Minn.  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