全文获取类型
收费全文 | 2650篇 |
免费 | 75篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 46篇 |
综合类 | 4篇 |
化学工业 | 466篇 |
金属工艺 | 31篇 |
机械仪表 | 39篇 |
建筑科学 | 87篇 |
矿业工程 | 4篇 |
能源动力 | 49篇 |
轻工业 | 219篇 |
水利工程 | 19篇 |
石油天然气 | 5篇 |
无线电 | 358篇 |
一般工业技术 | 384篇 |
冶金工业 | 479篇 |
原子能技术 | 18篇 |
自动化技术 | 519篇 |
出版年
2022年 | 18篇 |
2021年 | 40篇 |
2020年 | 20篇 |
2019年 | 28篇 |
2018年 | 34篇 |
2017年 | 49篇 |
2016年 | 51篇 |
2015年 | 50篇 |
2014年 | 68篇 |
2013年 | 121篇 |
2012年 | 114篇 |
2011年 | 131篇 |
2010年 | 101篇 |
2009年 | 112篇 |
2008年 | 128篇 |
2007年 | 106篇 |
2006年 | 118篇 |
2005年 | 101篇 |
2004年 | 97篇 |
2003年 | 90篇 |
2002年 | 69篇 |
2001年 | 46篇 |
2000年 | 50篇 |
1999年 | 58篇 |
1998年 | 118篇 |
1997年 | 66篇 |
1996年 | 74篇 |
1995年 | 50篇 |
1994年 | 41篇 |
1993年 | 46篇 |
1992年 | 32篇 |
1991年 | 26篇 |
1990年 | 26篇 |
1989年 | 18篇 |
1988年 | 28篇 |
1987年 | 33篇 |
1986年 | 27篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 21篇 |
1979年 | 20篇 |
1977年 | 19篇 |
1976年 | 33篇 |
1975年 | 14篇 |
1974年 | 16篇 |
1973年 | 17篇 |
1972年 | 12篇 |
排序方式: 共有2727条查询结果,搜索用时 15 毫秒
51.
About 20 years ago, Markus and Robey noted that most research on IT impacts had been guided by deterministic perspectives and had neglected to use an emergent perspective, which could account for contradictory findings. They further observed that most research in this area had been carried out using variance theories at the expense of process theories. Finally, they suggested that more emphasis on multilevel theory building would likely improve empirical reliability. In this paper, we reiterate the observations and suggestions made by Markus and Robey on the causal structure of IT impact theories and carry out an analysis of empirical research published in four major IS journals, Management Information Systems Quarterly (MISQ), Information Systems Research (ISR), the European Journal of Information Systems (EJIS), and Information and Organization (I&O), to assess compliance with those recommendations. Our final sample consisted of 161 theory-driven articles, accounting for approximately 21% of all the empirical articles published in these journals. Our results first reveal that 91% of the studies in MISQ, ISR, and EJIS focused on deterministic theories, while 63% of those in I&O adopted an emergent perspective. Furthermore, 91% of the articles in MISQ, ISR, and EJIS adopted a variance model; this compares with 71% from I&O that applied a process model. Lastly, mixed levels of analysis were found in 14% of all the surveyed articles. Implications of these findings for future research are discussed. 相似文献
52.
Megumi Shinozaki Masato Kusanagi Kazunori Umeda Guy Godin Marc Rioux 《Computer Vision and Image Understanding》2009,113(11):1170-1179
Most active optical range sensors record, simultaneously with the range image, the amount of light reflected at each measured surface location: this information forms what is called a range intensity image, also known as a reflectance image. This paper proposes a method that uses this type of image for the correction of the color information of a textured 3D model. This color information is usually obtained from color images acquired using a digital camera. The lighting condition for the color images are usually not controlled, thus this color information may not be accurate. On the other hand, the illumination condition for the range intensity image is known since it is obtained from a controlled lighting and observation configuration, as required for the purpose of active optical range measurement. The paper describes a method for combining the two sources of information, towards the goal of compensating for a reference range intensity image is first obtained by considering factors such as sensor properties, or distance and relative surface orientation of the measured surface. The color image of the corresponding surface portion is then corrected using this reference range intensity image. A B-spline interpolation technique is applied to reduce the noise of range intensity images. Finally, a method for the estimation of the illumination color is applied to compensate for the light source color. Experiments show the effectiveness of the correction method using range intensity images. 相似文献
53.
Ronen Gradwohl Moni Naor Benny Pinkas Guy N. Rothblum 《Theory of Computing Systems》2009,44(2):245-268
We consider cryptographic and physical zero-knowledge proof schemes for Sudoku, a popular combinatorial puzzle. We discuss
methods that allow one party, the prover, to convince another party, the verifier, that the prover has solved a Sudoku puzzle,
without revealing the solution to the verifier. The question of interest is how a prover can show: (i) that there is a solution
to the given puzzle, and (ii) that he knows the solution, while not giving away any information about the solution to the
verifier.
In this paper we consider several protocols that achieve these goals. Broadly speaking, the protocols are either cryptographic
or physical. By a cryptographic protocol we mean one in the usual model found in the foundations of cryptography literature.
In this model, two machines exchange messages, and the security of the protocol relies on computational hardness. By a physical
protocol we mean one that is implementable by humans using common objects, and preferably without the aid of computers. In
particular, our physical protocols utilize items such as scratch-off cards, similar to those used in lotteries, or even just
simple playing cards.
The cryptographic protocols are direct and efficient, and do not involve a reduction to other problems. The physical protocols
are meant to be understood by “lay-people” and implementable without the use of computers.
Research of R. Gradwohl was supported by US-Israel Binational Science Foundation Grant 2002246.
Research of M. Naor was supported in part by a grant from the Israel Science Foundation.
Research of B. Pinkas was supported in part by the Israel Science Foundation (grant number 860/06).
Research of G.N. Rothblum was supported by NSF grant CNS-0430450 and NSF grant CFF-0635297. 相似文献
54.
Ernest B. Cady Ann Lorek Yakito Takei John S. Wyatt Juliet M. Penrice A. David Edwards Donald Peebles Marzena Wylezinska Huw Owen-Reece Vincent Kirkbride Christopher E. Cooper Richard F. Aldridge Simon C. Roth Guy Brown David T. Delpy E. Osmund R. Reynolds 《Magma (New York, N.Y.)》1994,2(3):437-439
The aim of this study was to reproduce the delayed (secondary) cerebral energy failure previously described in birth-asphyxiated newborn infants and to investigate relationships between primary insult severity and the extent of the delayed energy failure. Phosphorus (31P) magnetic resonance spectroscopy (MRS) at 7 T was used to study the brains of 12 newborn piglets during an acute, reversible, cerebral hypoxic-ischemic episode which continued until nucleotide triphosphates (NTP) were depleted. After reperfusion and reoxygenation, spectroscopy was continued for 48 h. High-energy metabolite concentrations returned to near normal levels after the insult, but later they fell as delayed energy failure developed. The time integral of NTP depletion in the primary insult correlated strongly with the minimum [phosphocreatine (PCr)]/[inorganic orthophosphate (Pi)] observed 24–48 h after the insult. (Linear regression analysis gave slope –8.04 h–1; ordinate intercept=1.23;r=0.92;P<0.0001.) This model is currently being used to investigate the therapeutic potential of various cerebroprotective strategies including hypothermia. 相似文献
55.
Patrice Le Boudec François Sanchez Pierre-Luc FranÇois Jean-François Bayon Guy Michel StÉphan 《电信纪事》1994,49(3-4):178-192
The dynamics of the erbium doped fiber laser is analysed both experimentally and theoretically. This laser operates spontaneously in self-pulsing, in sinusoidal or in CW regime. Experiments have allowed to determine the control parameters : the cavity losses, the pumping rate and the ion pairs concentration. An antiphase dynamics is observed when the laser operates simultaneously at 1.55 µn and 1.536 µm. The self-pulsing behavior is attributed to a fast energy transfer which occurs between two neighboring ions (pair induced quenching). A simple model considering the active medium as a mixture of isolated ions and ions pairs is developped and leads to a good qualitative agreement with the experimental results. 相似文献
56.
Nima Taghipour Mariona Dalmases Guy L. Whitworth Miguel Dosil Andreas Othonos Sotirios Christodoulou Shanti Maria Liga Gerasimos Konstantatos 《Advanced materials (Deerfield Beach, Fla.)》2023,35(1):2207678
The use of colloidal quantum dots (CQDs) as a gain medium in infrared laser devices has been underpinned by the need for high pumping intensities, very short gain lifetimes, and low gain coefficients. Here, PbS/PbSSe core/alloyed-shell CQDs are employed as an infrared gain medium that results in highly suppressed Auger recombination with a lifetime of 485 ps, lowering the amplified spontaneous emission (ASE) threshold down to 300 µJ cm−2, and showing a record high net modal gain coefficient of 2180 cm−1. By doping these engineered core/shell CQDs up to nearly filling the first excited state, a significant reduction of optical gain threshold is demonstrated, measured by transient absorption, to an average-exciton population-per-dot 〈Nth〉g of 0.45 due to bleaching of the ground state absorption. This in turn have led to a fivefold reduction in ASE threshold at 〈Nth〉ASE = 0.70 excitons-per-dot, associated with a gain lifetime of 280 ps. Finally, these heterostructured QDs are used to achieve near-infrared lasing at 1670 nm at a pump fluences corresponding to sub-single-exciton-per-dot threshold (〈Nth〉Las = 0.87). This work brings infrared CQD lasing thresholds on par to their visible counterparts, and paves the way toward solution-processed infrared laser diodes. 相似文献
57.
The caterpillars of Gloveria sp. mark trails with a pheromone they deposit by dragging the ventral surface of the tip of the abdomen along branch pathways as they move between their communal nest and distance feeding sites. The threshold sensitivity of the caterpillar for an extract prepared from the secretory site was approximately 0.5 × 10–3 caterpillar equivalents/cm of trail. Bioassays show that Gloveria follows neither authentic trails of Malacosoma americanum nor artificial trails prepared from 5-cholestane-3-one, a chemical previously reported to elicit trail following from other social caterpillars. Although our observations show that fed caterpillars mark heavily as they return to their nest, we found no evidence that individual caterpillars are able to recruit hungry nestmates to new food finds. In this species, recruitment to food occurs only after many caterpillars have reinforced a trail to a newly discovered food source. In contrast, hungry caterpillars of the confamilial species M. americanum, tested under identical conditions, responded strongly to the postprandial trails of individual caterpillars and rapidly abandoned depleted sites in favor of new food finds. We postulate that the difference in the efficiency with which these two species recruit nestmates to food evolved in response to differences in the spatial distribution of their food supplies. 相似文献
58.
59.
Selecting the incorrect control during the operation of underground bolting and drilling equipment causes serious injuries. Shape coding and the layout of dual control banks are two aspects of control design which require further examination. The aims of this research were: (i) to determine whether arbitrary shape coding was effective in reducing selection error rates in a virtual analogy of roof-bolting; and (ii) to determine whether any advantages exist for mirror or place layouts for dual control situations in this situation. Two experiments were conducted to address these questions. No benefits of arbitrary shape coding were evident while control location remained constant. When control location was altered, shape coding did provide a significant reduction in selection error rate. No differences between mirror or place arrangements were detected and this question remains open. 相似文献
60.
Daniel F. Macedo Aldri L. dos Santos Luiz H.A. Correia José M. Nogueira Guy Pujolle 《Computer Networks》2010,54(17):2979-2990
Wireless networks can vary both the transmission power and modulation of links. Existing routing protocols do not take transmission power control (TPC) and modulation adaptation (also known as rate adaptation – RA) into account at the same time, even though the performance of wireless networks can be significantly improved when routing algorithms use link characteristics to build their routes. This article proposes and evaluates extensions to routing protocols to cope with TPC and RA. The enhancements can be applied to any link state or distance vector routing protocols. An evaluation considering node density, node mobility and link error show that TPC- and RA-aware routing algorithms improve the average latency and the end-to-end throughput, while consuming less energy than traditional protocols. 相似文献