全文获取类型
收费全文 | 949篇 |
免费 | 38篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 13篇 |
综合类 | 1篇 |
化学工业 | 210篇 |
金属工艺 | 10篇 |
机械仪表 | 19篇 |
建筑科学 | 36篇 |
矿业工程 | 6篇 |
能源动力 | 20篇 |
轻工业 | 137篇 |
水利工程 | 7篇 |
石油天然气 | 2篇 |
无线电 | 54篇 |
一般工业技术 | 147篇 |
冶金工业 | 222篇 |
原子能技术 | 4篇 |
自动化技术 | 101篇 |
出版年
2023年 | 20篇 |
2022年 | 32篇 |
2021年 | 49篇 |
2020年 | 20篇 |
2019年 | 24篇 |
2018年 | 24篇 |
2017年 | 20篇 |
2016年 | 28篇 |
2015年 | 21篇 |
2014年 | 25篇 |
2013年 | 46篇 |
2012年 | 49篇 |
2011年 | 64篇 |
2010年 | 50篇 |
2009年 | 37篇 |
2008年 | 55篇 |
2007年 | 43篇 |
2006年 | 45篇 |
2005年 | 30篇 |
2004年 | 20篇 |
2003年 | 24篇 |
2002年 | 21篇 |
2001年 | 17篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 31篇 |
1997年 | 17篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有989条查询结果,搜索用时 15 毫秒
111.
Summary Phenylquinoxaline-arylene ester block copolymers were prepared from phenolic hydroxyl terminated oligomers of defined molecular weight using an oligomer/monomer(s) approach, in which generation of the ester linkage coupling the blocks occurred concomitantly with the growth of the polyester block. The molecular weight of the phenylquinoxaline block was held constant at 12,900, while the stoichiometry of the arylene ester monomers were adjusted to afford copolymers containing 15, 30, and 50 wt% poly(arylene ester). These copolymers represent the first example of PPQ-based block copolymers derived from well defined phenylquinoxaline oligomers. 相似文献
112.
G Hofer 《Canadian Metallurgical Quarterly》1976,71(37):1513-1519
113.
Assessed the effects of training in test-taking skills on kindergarten children's performance on a school readiness test with a sample of 131 Spanish-speaking children from low socioeconomic backgrounds. Half of the Ss were trained in content-free test-taking skills, and half were provided comparable time in nondirected paper/crayon activities. All Ss were tested in both Spanish and English, with order of administration balanced. Trained Ss performed better than untrained Ss in both languages. Males were more influenced by training than were females, but overall females outperformed males. Spanish administration scores were higher than English administration scores. Order of test administration was significant in that performance in English was improved when the test was taken first in Spanish; no influence of English on subsequent performance was found. Findings support the hypothesis that test-wiseness is an important influence on test performance of young children from nonmajority backgrounds and should be taken into account in readiness assessment programs. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
114.
Retardation of the recrystallization of tungsten wire in Ni- and NiCr-Matrix . Nickel and other metals like palladium, aluminium, manganese, platinum and iron are known to reduce the recrystallization temperature of doped tungsten and tungsten- 2 % thorium oxide. This effect and its retardation were investigated within the framework of a larger study of fiber reinforced materials. 相似文献
115.
Melanie Witzke 《电信纪事》2005,60(1-2):147-168
To suppress the co-antenna interference in multiple input multiple output (MIMO) systems, an iterative receiver with a linear detector for complex symbols is investigated. We show that the considered generalized MIMO system, i.e., a system that transmits complex conjugate repetitions in addition to the pure data, requires the application of a widely linear (wl) detector. Awl detector consists of four real filters which are represented by two complex filters for the received signal and its complex conjugate, respectively. Furthermore, we present approximations of the detector that significantly reduce computational complexity with only little loss in frame-error rate performance. Simulation results show that the proposed MIMO system achieves large gains over standard solutions. 相似文献
116.
RA Bruce T DeRouen DR Peterson JB Irving N Chinn B Blake V Hofer 《Canadian Metallurgical Quarterly》1977,39(6):833-840
In a follow-up study of 1,852 men with coronary heart disease, 195 deaths occurred within the first 3 years (33 +/- 13 months [mean +/- standard deviation]). Analysis of these cases indicated that the risk of sudden cardiac death in ambulatory men with clinical manifestations of coronary heart disease may be readily estimated from noninvasive clinical and exercise criteria. The important predictors are indexes of the severity of coronary heart disease and impairment of peak left ventricular function demonstrated with symptom-limited maximal exercise. The advantages of these predictors are that they may be elicited on the initial study as well as on follow-up noninvasive examinations of ambulatory patients. The appearance of nonelectrocardiographic predictors in serial examinations may provide an indication for invasive studies and be a more important finding than the ischemic S-T reponse to exertion. 相似文献
117.
Nuha M.K. Yousif Melanie Huch Tobias Schuster Gyu-Sung Cho Hamid A. Dirar Wilhelm H. Holzapfel Charles M.A.P. Franz 《Food microbiology》2010
The diversity of lactic acid bacteria associated with Hussuwa fermentation, a Sudanese fermented sorghum food, was studied using a polyphasic taxonomical approach. Predominant strains could be well characterised based on a combination of phenotypic tests and genotypic methods such as ARDRA, rep-PCR and RAPD-PCR, as well as 16S rRNA gene sequencing of representative strains. Thus, the majority (128 of 220, 58.3%) of strains exhibited phenotypic properties typical of heterofermentative lactobacilli and of these, 100 strains were characterised more closely using the genotyping methods. The majority (97/100) strains could be characterised as Lactobacillus fermentum strains. Seventy-two of 220 strains (32.7%) showed phenotypic properties that are characteristic of pediococci. Of 41 selected strains investigated by genotyping techniques, 38 (92.7%) could be characterised as Pediococcus acidilactici strains, while three (7.3%) could be characterised as Pediococcus pentosaceus strains. The Hussuwa fermentation thus appears to be dominated by L. fermentum strains and P. acidilactici strains. For this reason, we selected representative and predominant strains as potential starter cultures for Hussuwa fermentation. These strains, L. fermentum strains BFE 2442 and BFE 2282 and P. acidilactici strain BFE 2300, were shown on the basis of RAPD-PCR fingerprinting to predominate in a model fermentation when used as starter cultures inoculated at 1 × 106 CFU/g and to lower the pH of the fermentation to below pH 4.0 within 48 h. These cultures should be studied for further development as starter preparations in pilot scale studies in actual field fermentations. 相似文献
118.
ABSTRACT: Caffeine ranks as one of the top most commonly consumed dietary ingredients throughout the world. It is naturally found in coffee beans, cacao beans, kola nuts, guarana berries, and tea leaves including yerba mate. The total daily intake, as well as the major source of caffeine varies globally; however, coffee and tea are the 2 most prominent sources. Soft drinks are also a common source of caffeine as well as energy drinks, a category of functional beverages. Moderate caffeine consumption is considered safe and its use as a food ingredient has been approved, within certain limits, by numerous regulatory agencies around the world. Performance benefits attributed to caffeine include physical endurance, reduction of fatigue, and enhancing mental alertness and concentration. Caffeine has also been recently linked to weight loss and consequent reduction of the overall risks for developing the metabolic syndrome. However, the caloric contribution of caffeine-sweetened beverages needs to be considered in the overall energy balance. Despite all these benefits the potential negative effects of excessive caffeine intake should also be considered, particularly in children and pregnant women. 相似文献
119.
Andrea Wühr Melanie Deckert Monika Pischetsrieder 《Molecular nutrition & food research》2010,54(7):1021-1030
Coffee, a highly processed food, and Maillard mixtures are able to activate nuclear factor κB translocation in macrophages via generation of hydrogen peroxide. In this study, a substructure library was prepared and used to identify Maillard products that are responsible for this effect. Three different Maillard reaction products with aminoreductone substructure (C6‐aminoreductone, C4‐aminoreductone, and aminohexose reductone) strongly induce nuclear factor κB translocation in macrophages. The effect was almost completely blocked by co‐incubation with catalase, indicating that cellular activation was mediated by the ability of the test compounds to generate hydrogen peroxide. The cellular effect of a Maillard mixture, which was produced under conditions favoring aminoreductone formation, could be almost completely related to the presence of C6‐aminoreductone. 相似文献
120.
Antonio Pinto Ulrich Hoffmanns Dr. Melanie Ott Gert Fricker Prof. Dr. Nils Metzler‐Nolte Prof. Dr. 《Chembiochem : a European journal of chemical biology》2009,10(11):1852-1860
Enkephalin peptides are thought to be suitable vectors for the passage of the blood–brain barrier (BBB). Modifications that do not alter the amino acid sequence are often used to improve the permeation through living membrane systems. As a new type of modification we introduce organometallic compounds, in particular ferrocene carboxylic acid. Derivatives of [Leu5]enkephalin were synthesised and labelled with organometallic compounds by using solid‐phase synthesis techniques. All new metal–peptide bioconjugates were comprehensively characterised by HPLC, NMR spectroscopy and mass spectrometry and found to be at least 95 % pure. For the first time, permeation coefficients in a BBB model for organometal–peptide derivatives were determined in this work. The uptake and localisation of fluorescein‐labelled enkephalins was monitored by fluorescence microscopy on three cancer cell lines. Octanol/H2O partition coefficients of the compounds were measured by HPLC. The introduction of the organometallic moiety enhances the uptake into cells and the permeation coefficient of [Leu5]‐enkephalin. This could be due to an increase in lipophilicity caused by the organometallic label. The metal–peptide conjugates were found to be nontoxic up to mM concentrations. The low cytotoxicity encourages further experiments that could take advantage of the selectivity of enkephalin derivatives for opioid receptors. 相似文献