全文获取类型
收费全文 | 10960篇 |
免费 | 688篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 156篇 |
综合类 | 46篇 |
化学工业 | 2952篇 |
金属工艺 | 259篇 |
机械仪表 | 226篇 |
建筑科学 | 727篇 |
矿业工程 | 54篇 |
能源动力 | 334篇 |
轻工业 | 1084篇 |
水利工程 | 99篇 |
石油天然气 | 43篇 |
武器工业 | 1篇 |
无线电 | 824篇 |
一般工业技术 | 1903篇 |
冶金工业 | 679篇 |
原子能技术 | 68篇 |
自动化技术 | 2206篇 |
出版年
2023年 | 127篇 |
2022年 | 271篇 |
2021年 | 442篇 |
2020年 | 262篇 |
2019年 | 266篇 |
2018年 | 358篇 |
2017年 | 320篇 |
2016年 | 423篇 |
2015年 | 340篇 |
2014年 | 477篇 |
2013年 | 772篇 |
2012年 | 627篇 |
2011年 | 779篇 |
2010年 | 521篇 |
2009年 | 607篇 |
2008年 | 564篇 |
2007年 | 496篇 |
2006年 | 413篇 |
2005年 | 362篇 |
2004年 | 322篇 |
2003年 | 304篇 |
2002年 | 228篇 |
2001年 | 158篇 |
2000年 | 162篇 |
1999年 | 137篇 |
1998年 | 158篇 |
1997年 | 155篇 |
1996年 | 120篇 |
1995年 | 105篇 |
1994年 | 92篇 |
1993年 | 97篇 |
1992年 | 66篇 |
1991年 | 68篇 |
1990年 | 69篇 |
1989年 | 77篇 |
1988年 | 57篇 |
1987年 | 58篇 |
1986年 | 62篇 |
1985年 | 60篇 |
1984年 | 72篇 |
1983年 | 54篇 |
1982年 | 45篇 |
1981年 | 45篇 |
1980年 | 47篇 |
1979年 | 38篇 |
1978年 | 39篇 |
1976年 | 43篇 |
1975年 | 43篇 |
1974年 | 38篇 |
1973年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Gianni S Calosci N Aelen JM Vuister GW Brunori M Travaglini-Allocatelli C 《Protein engineering, design & selection : PEDS》2005,18(8):389-395
PDZ domains represent a large family of protein-interaction modules associated with a variety of unrelated proteins with different functions. We report a complete characterization of the kinetic folding mechanism of a fluorescent variant of PDZ2 from PTP-BL, investigated under a variety of different experimental conditions. For this purpose, we engineered a fluorescent variant of this protein Y43W (called pseudo-wild-type, pWT43). The results suggest the presence of a high-energy intermediate in the folding of PDZ2, as revealed by a pronounced non-linear dependence of the unfolding rate constant on denaturant concentration. Such an intermediate may or may not be detectable depending on the experimental conditions, giving rise to apparent two-state folding under stabilizing conditions (e.g. in the presence of sodium sulfate). Interestingly, even under these conditions, three-state folding can be restored by selectively destabilizing the native-like rate-limiting barrier by one specific mutation (V44A). Finally, we show that data taken on pWT43 under different experimental conditions (e.g. different pH values from 2.1 to 8.0 or in the presence of a stabilizing salt) and also data on a site-directed conservative mutant can be rationalized in terms of a simple reaction scheme involving a single set of intermediates and transition states. 相似文献
172.
The pheromone of the eastern tent caterpillar,Malacosoma americanum (F.) (lepidoptera,Lasiocampidae)
Jan Kochansky Ada Hill John W. Neal Jr. Jo-Ann Bentz Wendell Roelofs 《Journal of chemical ecology》1996,22(12):2251-2261
The pheromone system of the eastern tent caterpillar,M. americanum, has been identified as a mixture of (E,Z)-5,7-dodecadienal and the corresponding alcohol. Field data on the attractiveness of the aldehyde alone were not consistent, but mixtures of aldehyde and alcohol in varying proportions were attractive to males. Addition of small amounts ofE,Z acetate toE,Z aldehyde had no effect on male response, but larger amounts reduced trap catch. Traps baited withZ,E, E,E, orZ,Z aldehydes were not more attractive than blank traps. Pherocon IC traps fortified with extra adhesive and baited with lures consisting of 500 µg (E,Z)-5,7-dodecadienal with either 250 or 100 µg of the corresponding alcohol trapped as many as 100 males/trap/night with means of 15–20. Lures prepared from purified (94%E,Z) aldehyde and alcohol were more attractive than those prepared from unpurified (58%E,Z) materials.DeceasedMention of a company name or proprietary product does not constitute an endorsement by the U.S. Department of Agriculture. 相似文献
173.
A recent article [C. Zhang, H. He, K. Tanaka, Catal. Commun. 6 (2005) 211] investigates the use of a Pt/TiO2 catalyst for the oxidation of formaldehyde. The findings demonstrate nearly complete oxidation at ambient temperature (25 °C) for values of the surface velocity in the range 5–10 × 104 h−1 and a 45% destruction when using a surface velocity of 20 × 104 h−1.In the present communication, this oxidation was assessed by theoretical considerations of the reaction kinetics. The destruction efficiency was predicted using a first-order reaction rate expression, combined with different theoretical or semi-empirical equations for the intrinsic reaction rate constant. Predicted and experimental data are in fair agreement, thus validating the theoretical approach and confirming the experimental results. 相似文献
174.
One of today's grand societal challenges is to replace the current ‘take‐make‐waste’ economic model with a circular economic model that allows a gradual decoupling of economic activities from the consumption of finite virgin resources. While circular economy (CE) scholars have long lauded digital technologies such as sensors, distributed ledgers, or platforms as key enablers, our own community has not fully explored the potentials of information systems (IS) for a CE. Considering recent technological advances in software and hardware and our history of helping address wicked challenges, we believe the time is ripe to mobilise IS scholarship for a CE. Our findings from an interdisciplinary literature review show that research has primarily examined IS potentials for increasing efficiency of isolated intra‐organisational processes while neglecting the larger sustainability potential of IS to establish circular material flows—that is, slow down and close material loops across entire product lifecycles. In response, we propose directions for IS research that develop our knowledge of how IS can help understand and enact circular material flows to intensify and extend use of products and components and recycle waste materials. Our directions offer pathways to building and evaluating the problem‐solution pairing that could characterise a prolific CE‐IS relationship. 相似文献
175.
Jan Brinker Halil Ibrahim Gündüz 《The International Journal of Advanced Manufacturing Technology》2016,87(5-8):2259-2268
The determining of efficient packaging sizes is a key factor in saving material and transportation costs and also in reducing packaging waste. By analyzing the range of items and their contribution to sales-relevant order structures of a globally operating mail order company, a simplified packing algorithm is proposed. In combination with well-known methodologies, this heuristic provides near optimal solutions improving current packaging of eCommerce companies. It is shown that simple, practical heuristics are sufficient to achieve average material savings of more than 10 %. In order to find efficient packaging sizes, a set of them is generated by discretization of packaging dimensions. Given the set of orders and the set of packaging sizes, a p-median approach is applied to find a specified number of optimal, demand-related packaging sizes. 相似文献
176.
Muhammad Khafidh Natalia Valentina Rodriguez Marc Arthur Masen Dirk Jan Schipper 《Tribology - Materials, Surfaces & Interfaces》2016,10(2):70-73
The friction in tribo-systems that contain viscoelastic materials, such as elastomers, is relevant for a large number of applications. Examples include tyres, hoses, transmission and conveyor belts. To quantify the friction in these applications, one must first understand the contact behaviour of such viscoelastic materials, both in static and in dynamic situations. This work discusses an experimental study into the change of the contact area with the sliding velocity and relates the change in contact area with the mechanical properties of the elastomer. The results show that for a tribo-system containing an elastomer, there is a threshold velocity, above which the size of the contact area significantly reduces. 相似文献
177.
Peter E. Neerincx Martin Hofmann Oleksandr Gorodetskyi Kirill Feldman Jan Vermant Han E. H. Meijer 《Polymer Engineering and Science》2021,61(4):1257-1269
Relatively recently, we advanced a route to create, in a controlled fashion, combined horizontal and vertical stratified structures by simple and energy-efficient processing operations employing static mixing elements. While in state-of-the-art static mixing the focus is on layer multiplication, here the aim is to create hierarchical fractal structures. Therefore, the main question addressed in this article is how structures, rather than layers, can be multiplied. The key aspect is the addition of layers on the sides or in the midplane of the flow during the process; every addition step increases the hierarchy by one level. This article derives the general formalism for forming fractal structures with controlled hierarchy, and we develop the language required to design and construct the dies. The main part of the article addresses this main topic and is based on the splitting serpentine static mixer geometry that can be easily made on the parting surfaces of a mold on both the micro- and the macroscale. The second part of the article addresses the strategy to minimize the number of mirroring steps, eventually avoiding mirroring completely, and is based on the rotation-free multiflux static mixer geometry. With the design language derived, complex hierarchical fractal structures can be generated simply by changing the number and sequence of operators within extrusion dies or molds, providing a one-step solution to produce material structures for potential use in diverse applications ranging from advanced mechanical systems to photovoltaic devices, where controlled assembly of dissimilar materials, and the realization of huge interfaces and genuine cocontinuity throughout the cross section, is critical. 相似文献
178.
Đurović Gordana Van Neerbos Francine A. C. Bossaert Sofie Herrera-Malaver Beatriz Steensels Jan Arnó Judit Wäckers Felix Sobhy Islam S. Verstrepen Kevin J. Jacquemyn Hans Lievens Bart 《Journal of chemical ecology》2021,47(8-9):788-798
Journal of Chemical Ecology - There is increasing evidence that microorganisms, particularly fungi and bacteria, emit volatile compounds that mediate the foraging behaviour of insects and therefore... 相似文献
179.
Effect of artificial aging on intergranular corrosion of extruded AlMgSi alloy with small Cu content
The effect of artificial aging parameters on the corrosion performance of air cooled AlMgSi(Cu) model alloy extrusions was investigated. Accelerated corrosion test revealed that the extrusions were highly susceptible to intergranular corrosion (IGC) in the naturally aged condition. However, IGC susceptibility was reduced, and finally eliminated, by artificial aging. Overaging introduced slight pitting susceptibility. EDS X-ray mapping in FE-TEM revealed Mg2Si and Q-phase (Al4Cu2Mg8Si7) grain boundary precipitates and a continuous Cu-enriched grain boundary film. IGC susceptibility was related to the Cu-enriched grain boundary film. Increased IGC resistance was caused by coarsening of the grain boundary film by aging. Pitting susceptibility by over aging evolved due to coarsening of the Q-phase particles in the grain bodies. 相似文献
180.
Cathodic disbonding and charge transport through paint films were studied as a function of polarization potential, temperature, dry-film thickness and cation type in the electrolyte. It was found that both the disbonding rate and the charge transport were linearly related to the polarization potential. The activation energy for the disbonding process and the charge transport were quite different. The disbonding rate was linearly related to the dry-film thickness and was dependent on the cation type in the electrolyte. This was not the case for the charge transport. The results indicate a rate controlling factor for the disbonding process involving transport of cations through the film where the film is already disbonded. A fundamental difference in the conductive properties of the paint film on either side of the disbonding front is also proposed. 相似文献