全文获取类型
收费全文 | 746篇 |
免费 | 49篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 9篇 |
综合类 | 1篇 |
化学工业 | 189篇 |
金属工艺 | 10篇 |
机械仪表 | 27篇 |
建筑科学 | 87篇 |
矿业工程 | 2篇 |
能源动力 | 21篇 |
轻工业 | 84篇 |
水利工程 | 7篇 |
无线电 | 50篇 |
一般工业技术 | 156篇 |
冶金工业 | 17篇 |
原子能技术 | 2篇 |
自动化技术 | 135篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 25篇 |
2020年 | 19篇 |
2019年 | 23篇 |
2018年 | 19篇 |
2017年 | 25篇 |
2016年 | 34篇 |
2015年 | 31篇 |
2014年 | 34篇 |
2013年 | 59篇 |
2012年 | 41篇 |
2011年 | 43篇 |
2010年 | 40篇 |
2009年 | 31篇 |
2008年 | 46篇 |
2007年 | 39篇 |
2006年 | 31篇 |
2005年 | 33篇 |
2004年 | 23篇 |
2003年 | 17篇 |
2002年 | 23篇 |
2001年 | 7篇 |
2000年 | 19篇 |
1999年 | 16篇 |
1998年 | 21篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 4篇 |
排序方式: 共有797条查询结果,搜索用时 0 毫秒
681.
Harald Hetzner Jens Schaufler Stephan Tremmel Karsten Durst Sandro Wartzack 《Surface & coatings technology》2012
A diamond-like carbon (DLC) coating with a top layer of pure hydrogenated amorphous carbon (a-C:H) and an interlayer of tungsten-modified hydrogenated amorphous carbon (a-C:H:W) was deposited onto polished cylindrical specimens of a hardened and tempered cold work tool steel. On a load-scanning test rig, tribological–mechanical tests under dry conditions with DLC coated specimens sliding against identical, but uncoated specimens were performed. Additionally, comparative tests with DLC sliding against DLC and tool steel sliding against tool steel were carried out. During each test cycle, the normal load was gradually increased from 13 to 350 N, corresponding to a Hertzian contact pressure of 1.0 to 3.0 GPa. The coefficient of friction was monitored as a function of the normal load, with a significant increase in friction indicating failure of the coating. The tests were repeated and stopped at different total numbers of load cycles. After the tests, a FIB-assisted microscopical analysis in terms of wear and damage of the DLC coating was performed, revealing the (subsurface) failure mechanisms. For DLC sliding against steel, the coating fails within only few load cycles; first tribologically and after that mechanically. Failure is initiated by adherence and subsequent transfer of steel of the counter body. Below adhered steel flakes, tensile cracks form in the a-C:H top layer, with sharp crack edges removing even more steel from the counter body. In following load cycles, coating fragments are being pulled out at these spots, representing the final failure mode. In contrast, for DLC sliding against DLC, no coating failure and also no significant wear are observed, even after a considerably higher number of load cycles. 相似文献
682.
Induced chemical defense reactions are widespread in marine brown algae. Despite the evidence that the biosynthesis of defense
metabolites can be up-regulated upon herbivory, we do not know how this regulation of biosynthetic pathways to secondary metabolites
is achieved in brown algae. In higher plants, the phytohormone jasmonic acid (JA) is crucial for the mediation of induced
chemical defenses, and several findings of this metabolite from marine sources have been reported. We tested the hypothesis
that JA or related metabolites play a role in induced brown algal defense. Quantification of oxylipins with a detection limit
around 20 ng g−1 algal tissue did not reveal the presence of JA in the seven examined brown algal species Dictyota dichotoma, Colpomenia peregrina, Ectocarpus fasciculatus, Fucus vesiculosus, Himanthalia elongata, Saccharina latissima (formerly Laminaria saccharina), and Sargassum muticum. Moreover, treatment with ecologically relevant concentrations of JA and methyl jasmonate did not lead to a significant change
in the profile of medium- and non-polar metabolites of the tested algae. Only when high concentrations of ≥500 μg ml−1 medium of the phytohormones were applied that a metabolic response which could be attributed to unspecific stress was observed.
Bioassays with D. dichotoma that focused on medium- and non-polar compounds confirmed the lack of a biological role of JA and methyl jasmonate in the
induction of algal induced chemical defenses. The phytohormone-treated samples did not exhibit any increased defense potential
towards the amphipod Ampithoe longimana and the isopod Paracerceis caudata. JA and related phytohormones, known to be active in higher plants, thus appear to play no role in brown algae for induction
of the defense chemicals studied here. 相似文献
683.
Karsten Sammet Christoph Gastl Angelika Baro Sabine Laschat Peter Fischer Ina Fettig 《Advanced Synthesis \u0026amp; Catalysis》2010,352(13):2281-2290
Conjugate additions of Gilman cyanocuprates to (S)‐N‐amino‐2‐(methoxymethyl)pyrrolidine (SAMP)‐hydrazones 4 , 5 derived from cyclic and acyclic α,β‐unsaturated ketones were investigated. A protocol utilizing copper(II) sulfate/ammonium chloride was evolved, which allowed cleavage of SAMP (S)‐ 1 under the hydrolysis and work‐up conditions, followed by recovery of the auxiliary with ethylenediaminetetraacetic acid (EDTA). The enantioselectivity of cuprate additions was dominated for cyclic SAMP‐hydrazones 4 by the cuprate alkyl substituent and the ring size, in the case of acyclic arylidene SAMP‐hydrazones 5 , however, by the nature of the aryl substituent. Electron‐donating substituents gave poor enantiomeric excesses, whereas electron‐withdrawing groups provided excellent ee values of 98–99%. The configuration of the new stereocenter was determined to be (R). Moreover, a reaction sequence was developed which integrates a tandem 1,4‐addition/methylation and traceless hydrolytic cleavage of the auxiliary (S)‐ 1 in a one‐pot reaction, resulting in enantiomerically pure methyl ketones 11 – 13 , each of them with>99% ee. 相似文献
684.
685.
686.
Hild S Lück H Winkler W Strain K Grote H Smith J Malec M Hewitson M Willke B Hough J Danzmann K 《Applied optics》2006,45(28):7269-7272
Low-absorption optics made of OH-reduced fused silica are a key technology for future gravitational wave detectors such as the Advanced LIGO. We developed a sensitive method to measure the absorption inside the beam splitter of the GEO 600, taking advantage of the effect of thermal lensing. Using this method, we derived a bulk absorption of less than 0.25 ppm/cm for a piece of Suprasil 311 SV at a wavelength of 1064 nm. To the best of our knowledge, this is the lowest value of light absorption inside fused silica reported so far in the literature. 相似文献
687.
We present transport measurements of single-molecule junctions bridged by a molecule with three benzene rings connected by two double bonds and with thiol end-groups that allow chemical binding to gold electrodes. The I-V curves show switching behavior between two distinct states. By statistical analysis of the switching events, we show that a 300 meV mode mediates the transition between the two states. We propose that breaking and reformation of a S-H bond in the contact zone between molecule and electrode explains the observed bistability. 相似文献
688.
Ana Valvanuz Linares Fanny Vandevelde Jacques Pantigny Aude Falcimaigne‐Cordin Karsten Haupt 《Advanced functional materials》2009,19(8):1299-1303
Hierarchically nanostructured materials that combine two or more levels of structuring and that exhibit a combination of useful features have gained considerable interest over recent years. Here, the generation of surface‐bound nanofilaments with a high aspect ratio by nanomolding on a nanoporous template surface is described. The filaments, at the same time, carry molecularly imprinted binding sites. The dye fluorescein and the protein myoglobin are used as model templates for imprinting. The surfaces exhibit specific binding as revealed by fluorescence microscopy. The wetting properties of the surfaces depend on the dimensions of the nanofilaments and on the nature of the polymer. It is believed that these materials can potentially be useful for applications in biosensors and biochips. 相似文献
689.
Decision making in any complex system is a very difficult task. In Man, decisions are reached as a result of trying to satisfy both conscious and unconscious goals. To emulate this in a computer system we need to find a way of representing goals and modeling the decision making process. This paper describes a model for decision making in the context of the management of distributed computer systems, and discusses the implications for the representation of goals and other information used during the decision making process. The work described in this paper was performed in the ESPRIT II project DOMAINS. This project is concerned with developing an architecture for the integrated management of all resources in a networked system. The emphasis of this paper lies in modeling rather than implementation. 相似文献
690.
The learning of complex control behaviour of autonomous mobile robots is one of the actual research topics. In this article an intelligent control architecture is presented which integrates learning methods and available domain knowledge. This control architecture is based on Reinforcement Learning and allows continuous input and output parameters, hierarchical learning, multiple goals, self-organized topology of the used networks and online learning. As a testbed this architecture is applied to the six-legged walking machine LAURON to learn leg control and leg coordination. 相似文献