全文获取类型
收费全文 | 3721篇 |
免费 | 182篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 66篇 |
综合类 | 5篇 |
化学工业 | 1216篇 |
金属工艺 | 76篇 |
机械仪表 | 54篇 |
建筑科学 | 170篇 |
矿业工程 | 13篇 |
能源动力 | 76篇 |
轻工业 | 391篇 |
水利工程 | 20篇 |
石油天然气 | 7篇 |
无线电 | 268篇 |
一般工业技术 | 549篇 |
冶金工业 | 514篇 |
原子能技术 | 22篇 |
自动化技术 | 459篇 |
出版年
2023年 | 35篇 |
2022年 | 66篇 |
2021年 | 111篇 |
2020年 | 77篇 |
2019年 | 98篇 |
2018年 | 91篇 |
2017年 | 83篇 |
2016年 | 100篇 |
2015年 | 82篇 |
2014年 | 110篇 |
2013年 | 144篇 |
2012年 | 117篇 |
2011年 | 171篇 |
2010年 | 108篇 |
2009年 | 103篇 |
2008年 | 119篇 |
2007年 | 126篇 |
2006年 | 98篇 |
2005年 | 75篇 |
2004年 | 70篇 |
2003年 | 67篇 |
2002年 | 48篇 |
2001年 | 41篇 |
2000年 | 54篇 |
1999年 | 45篇 |
1998年 | 116篇 |
1997年 | 87篇 |
1996年 | 64篇 |
1995年 | 54篇 |
1994年 | 49篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 39篇 |
1990年 | 41篇 |
1989年 | 33篇 |
1987年 | 39篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 40篇 |
1980年 | 31篇 |
1978年 | 39篇 |
1977年 | 34篇 |
1976年 | 42篇 |
1974年 | 69篇 |
1973年 | 61篇 |
1972年 | 67篇 |
1971年 | 59篇 |
1970年 | 63篇 |
1969年 | 53篇 |
1968年 | 48篇 |
排序方式: 共有3906条查询结果,搜索用时 15 毫秒
91.
Long-lived renaming allows processes to repeatedly get distinct names from a small name space and release these names. This
paper presents two long-lived renaming algorithms in which the name a process gets is bounded above by the number of processes
currently occupying a name or performing one of these operations. The first algorithm is asynchronous, uses LL/SC objects, and has step complexity that is linear in the number of processes, c, currently getting or releasing a name. The second is synchronous, uses registers and counters, and has step complexity that
is polylogarithmic in c. Both tolerate any number of process crashes. 相似文献
92.
Martin Dietzfelbinger Jonathan E. Rowe Ingo Wegener Philipp Woelfel 《Algorithmica》2011,59(3):301-322
We investigate the effects of precision on the efficiency of various local search algorithms on 1-D unimodal functions. We
present a (1+1)-EA with adaptive step size which finds the optimum in O(log n) steps, where n is the number of points used. We then consider binary (base-2) and reflected Gray code representations with single bit mutations.
The standard binary method does not guarantee locating the optimum, whereas using the reflected Gray code does so in Θ((log n)2) steps. A(1+1)-EA with a fixed mutation probability distribution is then presented which also runs in O((log n)2). Moreover, a recent result shows that this is optimal (up to some constant scaling factor), in that there exist unimodal
functions for which a lower bound of Ω((log n)2) holds regardless of the choice of mutation distribution. For continuous multimodal functions, the algorithm also locates
the global optimum in O((log n)2). Finally, we show that it is not possible for a black box algorithm to efficiently optimise unimodal functions for two or
more dimensions (in terms of the precision used). 相似文献
93.
94.
Jan Birnstock Tobias Canzler Michael Hofmann Andrea Lux Sven Murano Philipp Wellmann Ansgar Werner 《Journal of the Society for Information Display》2008,16(2):221-229
Abstract— Currently, three issues are identified that decide upon the commercial success of organic light‐emitting diodes (OLEDs), both in display and lighting applications: power efficiency, lifetime, and price competitiveness. PIN OLEDs are widely seen as the preferred way to maximize power efficiency. Here, it is reported that this concept also delivers the world longest lifetimes. For a highly efficient deep‐red PIN OLED, a half‐lifetime of 25,000 hours for a starting brightness of 10,000 cd/m2 and a minimal voltage increase over lifetime is reported. This value corresponds to more than 1 × 106 hours at 1000 cd/m2 using an exponent of n = 1.7, which was measured by driving the OLEDs at different starting luminances. Because there is no initial luminance drop, these PIN OLEDs also exhibit a very high 80% lifetime (>300,000 hours at 1000 cd/m2). New record lifetime values for blue and green will be reported as well. Additionally, further topics that have impact on the production yield and cost such as the newly developed air‐stable organic n‐doping material NDN‐26 and top‐emitting structures will be discussed. 相似文献
95.
Analyzing the design of networks for visual information routing is an underconstrained problem due to insufficient anatomical and physiological data. We propose here optimality criteria for the design of routing networks. For a very general architecture, we derive the number of routing layers and the fanout that minimize the required neural circuitry. The optimal fanout l is independent of network size, while the number k of layers scales logarithmically (with a prefactor below 1), with the number n of visual resolution units to be routed independently. The results are found to agree with data of the primate visual system. 相似文献
96.
A precise calculation of the amount of intraalveolar fluid is the basis of a quantitative analysis of intraalveolar compounds. Different approaches have been made to cover this important problem. Here, we report a comparative study with five markers: 99mTc-DTPA, 51Cr-EDTA, inulin, urea, and methylene blue in animal experiments as well as in human experiments. The marker substances were added to the lavage fluid, and the "dilution" of the markers, i.e., the alveolar fluid, was calculated. The results showed that in animals with healthy lungs the tracer methods are able to calculate amounts of intraalveolar fluid that are comparable to morphologic findings. In animals as well as in humans, methylene blue and inulin were shown to be useless in determining alveolar fluid volume compared with the tracer methods. In humans, the calculations with the urea method and with Tc-DTPA were in the same magnitude, but there was no individual correlation. We conclude that, at present, the methods to quantitate alveolar fluid volume lack precision and add nothing to a deeper understanding of alveolar biology. 相似文献
97.
Rudolf Treleano Hans-Dieter Belitz Harald Jugel und Herbert Wieser 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1978,167(5):320-323
Zusammenfassung 1-Aminocycloalkan-l-carbonsäuren mit Ringgrößen von 4–11 (ohne 10) wurden synthetisiert und auf ihre Geschmackseigenschaften untersucht. Süßer Geschmack tritt vom 4-Ring bis zum 8-Ring auf, beim 6-Ring ist der Schwellenwert minimal (c
Ssü=1–3 mmol/l). Bitter sind die Verbindungen vom 5-Ring bis zum 9-Ring, das Minimum des Schwellenwertes liegt beim 8-Ring (c
sbi=2–5 mmol/l). Die größeren Ringe sind bis zu Konzentrationen von 20 mmol/l ohne Geschmack. Beim 6-Ring löscht eine 2-Methylgruppe jeden Geschmackseindruck, während die 3- und 4-Methylverbindungen süß und bitter sind. Die 4-Äthylverbindung ist bitter aber nicht süß, die 4-tert.-Butylverbindung ist ohne Geschmack. 1-Aminonorbornan-1-carbonsäure ist süß (c
Ssü 50 mmol/l) und bitter (c
sbi=5–7mmo1/1), wobei der Schwellenwert für bitter fast eine Zehnerpotenz kleiner ist. tert.-Leucin ist ohne Geschmack. Die Ergebnisse werden im Zusammenhang mit früheren Untersuchungen an offenkettigen Aminosäuren diskutiert und in Modelle über sterische Voraussetzungen für Geschmack eingeordnet.
Relationsships between structure and taste in amino acids with cyclic side chains
Summary 1-Aminocycloalkane-1-carboxylic acids with ring sizes of 4–11 (excluding 10) were synthesized and tested for their taste properties. The compounds with 4- to 8-membered rings are sweet, with threshold values going through a minimum for the 6-membered ring (c tsw = l-3 mM/l). The compounds with 5- to 9-membered rings are bitter. Here the threshold value reaches a minimum for the 8-membered ring (c tbi=2–5 mM/l). The larger rings are without taste up to concentrations of 20 mmol/l. With the 6-membered ring a 2-methyl group abolishes any taste impression, whereas the 3- and 4-methyl compounds are sweet and bitter. The 4-ethyl compound is bitter but not sweet, the 4-tert.-butyl compound has no taste. 1-Aminonorbornane-l-carboxylic acid is sweet (c tsw 50mM/l) and bitter (c tbi= 5–7 mM/l), withc tbi being significantly smaller thanc tsw. tert-Leucine is without taste. The results are discussed in relation to previous investigations into steric prerequisites for taste in the amino acid series.相似文献
98.
We have found experimentally that rf SQUID's working in a nonhysteretic mode with small critical currents give exactly at resonance and at very low rf bias a triangular pattern with a period equal to half of one elementary quantum of magnetic flux. We discuss a possible explanation of this peculiar result. 相似文献
99.
O'Sullivan B.J. Kaushik V.S. Ragnarsson L.-A. Onsia B. Van Hoornick N. Rohr E. DeGendt S. Heyns M. 《Electron Device Letters, IEEE》2006,27(7):546-548
A technique has been developed to fabricate transistors using a continuously scaled 0-2.5-nm SiO/sub 2/ interface layer between a silicon substrate and high-/spl kappa/ dielectric, on a single wafer. The transistor results are promising with good mobility values and drive current. The slant-etching process has no detrimental effect on the electrical characteristics of the Si/SiO/sub 2/ interface. This technique provides a powerful tool in examining the effect of the process variations on device performance. 相似文献
100.
Holahan Charles J.; Moos Rudolf H.; Holahan Carole K.; Brennan Penny L.; Schutte Kathleen K. 《Canadian Metallurgical Quarterly》2005,73(4):658
This study examined (a) the role of avoidance coping in prospectively generating both chronic and acute life stressors and (b) the stress-generating role of avoidance coping as a prospective link to future depressive symptoms. Participants were 1,211 late-middle-aged individuals (500 women and 711 men) assessed 3 times over a 10-year period. As predicted, baseline avoidance coping was prospectively associated with both more chronic and more acute life stressors 4 years later. Furthermore, as predicted, these intervening life stressors linked baseline avoidance coping and depressive symptoms 10 years later, controlling for the influence of initial depressive symptoms. These findings broaden knowledge about the stress-generation process and elucidate a key mechanism through which avoidance coping is linked to depressive symptoms. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献