全文获取类型
收费全文 | 392587篇 |
免费 | 5512篇 |
国内免费 | 2226篇 |
专业分类
电工技术 | 7479篇 |
技术理论 | 5篇 |
综合类 | 3468篇 |
化学工业 | 58494篇 |
金属工艺 | 20398篇 |
机械仪表 | 15590篇 |
建筑科学 | 9511篇 |
矿业工程 | 2822篇 |
能源动力 | 7209篇 |
轻工业 | 29525篇 |
水利工程 | 4754篇 |
石油天然气 | 7519篇 |
武器工业 | 243篇 |
无线电 | 41468篇 |
一般工业技术 | 78731篇 |
冶金工业 | 54349篇 |
原子能技术 | 6779篇 |
自动化技术 | 51981篇 |
出版年
2021年 | 2506篇 |
2019年 | 2157篇 |
2018年 | 22748篇 |
2017年 | 22283篇 |
2016年 | 16013篇 |
2015年 | 3789篇 |
2014年 | 4882篇 |
2013年 | 11636篇 |
2012年 | 12438篇 |
2011年 | 24907篇 |
2010年 | 21559篇 |
2009年 | 19062篇 |
2008年 | 20498篇 |
2007年 | 23023篇 |
2006年 | 8654篇 |
2005年 | 11575篇 |
2004年 | 9263篇 |
2003年 | 8616篇 |
2002年 | 7238篇 |
2001年 | 6481篇 |
2000年 | 6196篇 |
1999年 | 5968篇 |
1998年 | 12928篇 |
1997年 | 9592篇 |
1996年 | 7354篇 |
1995年 | 5564篇 |
1994年 | 5141篇 |
1993年 | 4996篇 |
1992年 | 3985篇 |
1991年 | 3808篇 |
1990年 | 3840篇 |
1989年 | 3792篇 |
1988年 | 3552篇 |
1987年 | 3030篇 |
1986年 | 3057篇 |
1985年 | 3423篇 |
1984年 | 3333篇 |
1983年 | 3095篇 |
1982年 | 2709篇 |
1981年 | 2915篇 |
1980年 | 2651篇 |
1979年 | 2861篇 |
1978年 | 2750篇 |
1977年 | 2857篇 |
1976年 | 3700篇 |
1975年 | 2463篇 |
1974年 | 2296篇 |
1973年 | 2327篇 |
1972年 | 1988篇 |
1971年 | 1786篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before. 相似文献
52.
Jasmin Kuhn Philipp M. Klein Nader Al Danaf Joel Z. Nordin Sren Reinhard Dominik M. Loy Miriam Hhn Samir El Andaloussi Don C. Lamb Ernst Wagner Yoshitsugu Aoki Taavi Lehto Ulrich Lchelt 《Advanced functional materials》2019,29(48)
Phosphorodiamidate morpholino oligomers (PMOs) are oligonucleotide analogs that can be used for therapeutic modulation of pre‐mRNA splicing. Similar to other classes of nucleic acid‐based therapeutics, PMOs require delivery systems for efficient transport to the intracellular target sites. Here, artificial peptides based on the oligo(ethylenamino) acid succinyl‐tetraethylenpentamine (Stp), hydrophobic modifications, and an azide group are presented, which are used for strain‐promoted azide‐alkyne cycloaddition conjugation with splice‐switching PMOs. By systematically varying the lead structure and formulation, it is determined that the type of contained fatty acid and supramolecular assembly have a critical impact on the delivery efficacy. A compound containing linolenic acid with three cis double bonds exhibits the highest splice‐switching activity and significantly increases functional protein expression in pLuc/705 reporter cells in vitro and after local administration in vivo. Structural and mechanistic studies reveal that the lipopeptide PMO conjugates form nanoparticles, which accelerate cellular uptake and that the content of unsaturated fatty acids enhances endosomal escape. In an in vitro Duchenne muscular dystrophy exon skipping model using H2K‐mdx52 dystrophic skeletal myotubes, the highly potent PMO conjugates mediate significant splice‐switching at very low nanomolar concentrations. The presented aminoethylene‐lipopeptides are thus a promising platform for the generation of PMO‐therapeutics with a favorable activity/toxicity profile. 相似文献
53.
54.
Joo H. Kang Eujin Um Alexander Diaz Harry Driscoll Melissa J. Rodas Karel Domansky Alexander L. Watters Michael Super Howard A. Stone Donald E. Ingber 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(42):5657-5666
Magnetic nanoparticles have been employed to capture pathogens for many biological applications; however, optimal particle sizes have been determined empirically in specific capturing protocols. Here, a theoretical model that simulates capture of bacteria is described and used to calculate bacterial collision frequencies and magnetophoretic properties for a range of particle sizes. The model predicts that particles with a diameter of 460 nm should produce optimal separation of bacteria in buffer flowing at 1 L h−1. Validating the predictive power of the model, Staphylococcus aureus is separated from buffer and blood flowing through magnetic capture devices using six different sizes of magnetic particles. Experimental magnetic separation in buffer conditions confirms that particles with a diameter closest to the predicted optimal particle size provide the most effective capture. Modeling the capturing process in plasma and blood by introducing empirical constants (ce), which integrate the interfering effects of biological components on the binding kinetics of magnetic beads to bacteria, smaller beads with 50 nm diameters are predicted that exhibit maximum magnetic separation of bacteria from blood and experimentally validated this trend. The predictive power of the model suggests its utility for the future design of magnetic separation for diagnostic and therapeutic applications. 相似文献
55.
56.
High‐intensity sweeteners in espresso coffee: ideal and equivalent sweetness and time–intensity analysis 下载免费PDF全文
Bruna M. Azevedo Flávio L. Schmidt Helena M. A. Bolini 《International Journal of Food Science & Technology》2015,50(6):1374-1381
The efficient substitution of sucrose by a sweetener in beverages requires the application of some sensory techniques. First, one must determine the concentrations of the sweeteners under study, equivalent in sweetness to the ideal sucrose concentration. In addition, it is fundamental to determine which is most similar to sucrose. The objectives of this study were to determine the ideal sweetness for espresso coffee and the equivalent concentrations in sweetness of different sweeteners, as well as characterise the time–intensity profile of each sweetener in relation to sweetness. The sweeteners evaluated were sucralose, aspartame, neotame, a cyclamate/saccharin mixture (2:1) and stevia. The sucrose concentration considered ideal by consumers was 12.5% (w/v), and the equivalent concentrations of the sweeteners were 0.0159% for sucralose, 0.0549% for aspartame, 0.0016% for neotame, 0.0359% for the cyclamate/saccharin mixture and 0.0998% for stevia. The time–intensity analysis indicated that possibly the sweeteners neotame, aspartame and sucralose would be the best substitutes for sucrose. 相似文献
57.
58.
A. V. Kozlov I. A. Portnykh V. I. Pastukhov 《The Physics of Metals and Metallography》2018,119(4):396-401
The influence of the temperature gradient over the thickness of the cladding of a fuel element of a fast-neutron reactor on the migration of point defects formed in the cladding material due to neutron irradiation has been studied. It has been shown that, under the action of the temperature gradient, the flux of vacancies onto the inner surface of the cladding is higher than the flux of interstitial atoms, which leads to the formation of a specific concentration profile in the cladding with a vacancy-depleted zone near the inner surface. The experimental results on the spatial distribution of pores over the cladding thickness have been presented with which the data on the concentration profiles and vacancy fluxes have been compared. 相似文献
59.
The Raman spectrum of water adsorbed on a metallic silver surface reveals an anomalously large shift of the vibrational frequency as compared to that in the bulk. The results are compared to data reported by other researchers, and possible interpretations of the observed phenomenon are discussed. 相似文献
60.
S. A. Pul’nev A. I. Pryadko A. V. Chikiryaka V. I. Nikolaev 《Technical Physics Letters》2018,44(11):992-994
The behavior of a superelastic Cu?14.2% Al?4%Ni single crystal in the case of high reversible strains under a longitudinal bending force was investigated. The effect of strain confinement along the crystal length was revealed and studied. The highest reversible strains (up to 10%) were shown to be confined within the central part of the bent crystal. 相似文献