全文获取类型
收费全文 | 2418篇 |
免费 | 98篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 51篇 |
综合类 | 4篇 |
化学工业 | 636篇 |
金属工艺 | 33篇 |
机械仪表 | 48篇 |
建筑科学 | 84篇 |
能源动力 | 67篇 |
轻工业 | 192篇 |
水利工程 | 9篇 |
石油天然气 | 10篇 |
无线电 | 233篇 |
一般工业技术 | 483篇 |
冶金工业 | 174篇 |
原子能技术 | 16篇 |
自动化技术 | 479篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 39篇 |
2021年 | 71篇 |
2020年 | 31篇 |
2019年 | 53篇 |
2018年 | 64篇 |
2017年 | 61篇 |
2016年 | 67篇 |
2015年 | 74篇 |
2014年 | 92篇 |
2013年 | 126篇 |
2012年 | 141篇 |
2011年 | 195篇 |
2010年 | 133篇 |
2009年 | 129篇 |
2008年 | 137篇 |
2007年 | 113篇 |
2006年 | 124篇 |
2005年 | 100篇 |
2004年 | 98篇 |
2003年 | 58篇 |
2002年 | 71篇 |
2001年 | 54篇 |
2000年 | 35篇 |
1999年 | 41篇 |
1998年 | 78篇 |
1997年 | 53篇 |
1996年 | 41篇 |
1995年 | 35篇 |
1994年 | 24篇 |
1993年 | 21篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1966年 | 2篇 |
1948年 | 2篇 |
排序方式: 共有2519条查询结果,搜索用时 12 毫秒
1.
Dr. Laurent David Dr. Mark Wenlock Dr. Patrick Barton Dr. Andreas Ritzén 《ChemMedChem》2021,16(17):2669-2685
Chameleonic properties, i. e., the capacity of a molecule to hide polarity in non-polar environments and expose it in water, help achieving sufficient permeability and solubility for drug molecules with high MW. We present models of experimental measures of polarity for a set of 24 FDA approved drugs (MW 405-1113) and one PROTAC (MW 1034). Conformational ensembles in aqueous and non-polar environments were generated using molecular dynamics. A linear regression model that predicts chromatographic apparent polarity (EPSA) with a mean unsigned error of 10 Å2 was derived based on separate terms for donor, acceptor, and total molecular SASA. A good correlation (R2=0.92) with an experimental measure of hydrogen bond donor potential, Δlog Poct-tol, was found for the mean hydrogen bond donor SASA of the conformational ensemble scaled with Abraham's A hydrogen bond acidity. Two quantitative measures of chameleonic behaviour, the chameleonic efficiency indices, are introduced. We envision that the methods presented herein will be useful to triage designed molecules and prioritize those with the best chance of achieving acceptable permeability and solubility. 相似文献
2.
A first‐principles‐based effective Hamiltonian is developed and employed to investigate finite‐temperature structural properties of a prototype of perovskite halides, that is CsPbI3. Such simulations, when using first‐principles‐extracted coefficients, successfully reproduce the existence of an orthorhombic Pnma state and its iodine octahedral tilting angles around room temperature. However, they also yield a direct transformation from Pnma to cubic upon heating, unlike measurements that reported the occurrence of an intermediate long‐range‐tilted tetragonal P4/mbm phase in‐between the orthorhombic and cubic phases. Such disagreement, which may cast some doubts about the extent to which first‐principle methods can be trusted to mimic hybrid perovskites, can be resolved by “only” changing one short‐range tilting parameter in the whole set of effective Hamiltonian coefficients. In such a case, some reasonable values of this specific parameter result in the predictions that i) the intermediate P4/mbm state originates from fluctuations over many different tilted states; and ii) the cubic phase is highly locally distorted and develops strong transverse antiphase correlation between first‐nearest neighbor iodine octahedral tiltings, before undergoing a phase transition to P4/mbm under cooling. 相似文献
3.
Two proprietary biocides were compounded and extruded at three concentrations, respectively, into high density polyethylene-maple wood flour lumber (HDPE-MWL) and evaluated for their efficacy to control fungal colonization and discoloration using the ASTM Standard G 21-96. Although the silver biocide used in this study did not control fungal colonization and discoloration of HDPE-MWL, statistically significant difference was observed between the highest silver biocide concentration and those of the two lower silver biocide concentrations. The latter exhibited no significant difference with the controls. In contrast, the three levels of zinc biocides showed significant difference from each other with respect to their efficacy against fungal colonization and discoloration of HDPE-MWL. Overall, only the zinc biocide was efficacious against fungal colonization and discoloration. The biocide containing zinc as an active biocidal agent was most efficacious at 1% (by weight) concentration. 相似文献
4.
5.
The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H2S and SO2 in humid air at 25 °C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 °C or with ammonia/steam at 800 °C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption-regeneration cycles showed important differences between oxidative retention of H2S and SO2 and the subsequent catalyst/support regeneration process. 相似文献
6.
7.
8.
Auguste Commeyras Hlne Collet Laurent Boiteau Jacques Taillades Odile Vandenabeele‐Trambouze Herv Cottet Jean‐Philippe Biron Raphaël Plasson Louis Mion Olivier Lagrille Herv Martin Franck Selsis Michel Dobrijevic 《Polymer International》2002,51(7):661-665
Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry. 相似文献
9.
An optical nondestructive strain measurement technique was performed to analyze the mechanical deformation induced by an electrical field within the insulating materials. Poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) films were then subjected to constant electrical fields right up to their electrical breakdown. The experimental technique made it possible to follow the various stages of the mechanical behavior of PEN in real time. The final breakdown occurred in the observation zone and the related mechanical deformation was captured. A “margarita” structure was observed with a hole at the center. The experimental results indicated that the level of the induced‐mechanical deformations depended on the local environment. We defined two different zones representing the inside and the outside of the damaged area. The induced‐deformations were larger in the damaged zone. It was also observed that deformations increased when the sample had a lower degree of crystallinity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
10.