全文获取类型
收费全文 | 3964篇 |
免费 | 42篇 |
专业分类
电工技术 | 19篇 |
化学工业 | 157篇 |
金属工艺 | 16篇 |
机械仪表 | 24篇 |
建筑科学 | 50篇 |
矿业工程 | 4篇 |
能源动力 | 31篇 |
轻工业 | 159篇 |
水利工程 | 9篇 |
石油天然气 | 8篇 |
无线电 | 95篇 |
一般工业技术 | 229篇 |
冶金工业 | 3016篇 |
原子能技术 | 16篇 |
自动化技术 | 173篇 |
出版年
2022年 | 12篇 |
2021年 | 13篇 |
2018年 | 13篇 |
2017年 | 26篇 |
2016年 | 23篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 93篇 |
2012年 | 39篇 |
2011年 | 45篇 |
2010年 | 50篇 |
2009年 | 32篇 |
2008年 | 37篇 |
2007年 | 29篇 |
2006年 | 26篇 |
2005年 | 21篇 |
2004年 | 29篇 |
2003年 | 36篇 |
2002年 | 29篇 |
2001年 | 18篇 |
2000年 | 26篇 |
1999年 | 102篇 |
1998年 | 902篇 |
1997年 | 517篇 |
1996年 | 344篇 |
1995年 | 193篇 |
1994年 | 156篇 |
1993年 | 192篇 |
1992年 | 51篇 |
1991年 | 50篇 |
1990年 | 33篇 |
1989年 | 41篇 |
1988年 | 61篇 |
1987年 | 50篇 |
1986年 | 46篇 |
1985年 | 50篇 |
1984年 | 16篇 |
1983年 | 21篇 |
1982年 | 28篇 |
1981年 | 40篇 |
1980年 | 41篇 |
1979年 | 11篇 |
1978年 | 22篇 |
1977年 | 82篇 |
1976年 | 176篇 |
1975年 | 27篇 |
1974年 | 20篇 |
1973年 | 21篇 |
1972年 | 14篇 |
1971年 | 9篇 |
排序方式: 共有4006条查询结果,搜索用时 0 毫秒
91.
This article is a discussion of how to measure urban inequality using the results of large household samples. It has two aims. The first is to de-mystify the methods of measuring earnings inequality by discussing their logic and their results in plain language that is suitable for a non-specialist audience. The second is to persuade the reader that such surveys can be suitable for measuring income derived from all kinds of livelihood strategies, including informal sector activities. The results show persistently high levels of inequality over time among income earners on the Copperbelt. Disaggregation of the employed workforce by major occupational groups reveals increasingly more elementary and middle-income workers than higher income managers, professionals, and technicians. This pattern differs by gender, however, with only women experiencing a marked increase in low-skill, low-wage employment. 相似文献
92.
There are two approaches to mining text form online repositories. First, when the knowledge to be discovered is expressed directly in the documents to be mined, Information Extraction (IE) alone can serve as an effective tool for such text mining. Second, when the documents contain concrete data in unstructured form rather than abstract knowledge, Information Extraction (IE) can be used to first transform the unstructured data in the document corpus into a structured database, and then use some state-of-the-art data mining algorithms/tools to identify abstract patterns in this extracted data. This paper presents the review of several methods related to these two approaches. 相似文献
93.
Protein–polysaccharide complexes are used to improve protein stability and encapsulate high‐value ingredients, yet the influence of different salts on their formation has not been investigated. Using light scattering and turbidimetry, effects of chloride, sulphate and thiocyanate salts on β‐lactoglobulin and pectin complexes (protein/pectin ratio = 2:1 and 4:1) were determined in relation to effects of pH and ionic strength. Effects of anions on complex formation were significant at 25 mmol kg?1 added ionic strength. Cation effects were not significant. At 100 mmol kg?1 ionic strength, pH of complex formation increased with sulphate salts (pH 5.1) relative to chloride and thiocyanate salts (pH 4.9), while pH of coacervation increased with sulphate salts (pH 4.7) and decreased with thiocyanate salts (pH 4.4) relative to chloride salts (pH 4.6). Pure β‐lactoglobulin stability was otherwise reduced with thiocyanate salts below pH 5, implying a significant effect of pectin interactions. 相似文献
94.
Informal settlements have become dominant forms and processes of urban development in many cities, yet the task of helping students engage with design issues in such contexts is fraught with difficulties of access, safety, and complexity. Drawing on detailed fieldwork, this article explores ways in which informal settlement formation can be taught in design studio through the use of games that simulate incremental practices of room-by-room accretion and prospects for transformation. The pedagogical goals are to effect a blurring of authorship and authority, to undermine top-down thinking, and to nourish forms of design imagination that unite process and form. 相似文献
95.
The paper introduces and supports the contention that an idiographic methodology is appropriate to the post- hoc study and interpretation of individual construction project cash flows. A cash flow model based on the logit transformation is proposed to be consistent with this methodology. The model is based on historical data, and yields two parameters to describe each individual project. The model is tested using two samples totalling 72 projects. Goodness of fit for the model, using a measure of standard deviation from 1.0% to 4.6%, with a median of 2.5%, is found for individual projects. The experimental hypothesis (that there is substantial variation between projects) is supported by the graphical and statistical evidence of deviation, which is argued to be the result of the individual ontology of each project - systematic error - rather than random error from an ideal. The paper concludes that forecasts of individual cash flows are invalid when derived from analysis of grouped data. 相似文献
96.
The refractive index study of copoly(arylene-siloxane)s constructed with amide, ester, or ether linkage units was conducted to synthesize a step-growth polymer for application in flexible displays. The copoly(arylene-siloxane) based materials have potential use in optical applications due to their durability, flexibility, and possession of good optical clarity properties when compared to conventional silica-filled polydimethylsiloxane-based materials. Measurement of refractive index (RI) was used as the main mode of analysis due to its direct correlation to optical clarity and material flexibility. Synthesis and characterization, including RI compiled data, was performed for six series of step-growth polymers. Effects of different linkage units, namely amides, esters, and ethers, adjacent to at least one six-membered cyclic unit (aromatic or aliphatic) were evaluated. It was observed that the refractive index of these polymers was directly proportional to the aryl content; however, the influence on RI was not equal across all types of linkage units. The highest RI copolymer, poly(4,4-methylenediphenyl diisocyanate-co-carbinol-terminated polydimethylsiloxane) (MDI-SD1.0k), yielded refractive index 1.470 and molecular weight (Mn) 16,100 g/mol; however, the copolymer poly(toluene-2,4-diisocyanate-co-carbinol-terminated polydimethylsiloxane) (TDI-SD) had the highest RI (1.462) per phenyl content. The 4,4-methylenediphenyl diisocyanate (MDI), toluene-2,4-diisocyanate (TDI), and hydrogenated methylenediphenyl-4,4-diisocyanate (HMDI) amide containing linkages best improved the refractive indices of the materials studied. 相似文献
97.
98.
Isolation of Non-methylene Interrupted or Acetylenic Fatty Acids from Seed Oils Using Semi-preparative Supercritical Chromatography 下载免费PDF全文
Fernando Montañés Stephen Tallon Owen Catchpole 《Journal of the American Oil Chemists' Society》2017,94(7):981-991
Preparative scale supercritical fluid chromatography was used for isolating and purifying uncommon non-methylene interrupted or acetylenic polyunsaturated fatty acids ethyl esters from seed oils. Fractionation of Biota orientalis seed oil ethyl esters was performed by supercritical fluid chromatography to obtain juniperonic acid [(5Z,11Z,14Z,17Z)-eicosa-5,11,14,17-tetraenoic acid], a non-methylene interrupted polyunsaturated fatty acid. Fractionation of sandalwood seed oil ethyl esters yielded ximenynic acid [(E)-octadec-11-en-9-ynoic acid], an acetylenic polyunsaturated fatty acid. The effects of CO2 flow rate, column stationary phase and particle size were explored to optimize ximenynic and juniperonic ethyl ester recovery and purity from ethyl ester mixtures using online UV/Vis detection. Particle size, followed by the stationary phase, were found to be the most important parameters to achieving good separation. Under optimized conditions, ximenynic and juniperonic ethyl ester purities greater than 99 and 95%, respectively, were achieved in a one step process without co-solvent. The isolation and recovery of juniperonic acid from biota seed oil free fatty acids was also attempted. Using free fatty acids as the feed material, the non-methylene interrupted polyunsaturated sciadonic acid was also able to be separated from other compounds including juniperonic acid under some conditions, and gave an increase in concentration of more than 17 times. 相似文献
99.
100.
Kim Hyoun K.; Pears Katherine C.; Capaldi Deborah M.; Owen Lee D. 《Canadian Metallurgical Quarterly》2009,23(4):585
The role of emotion dysregulation in the intergenerational transmission of romantic relationship conflict was examined using multimethod and multiagent prospective longitudinal data across 21 years for 190 men and their mothers and fathers. As predicted, an individual’s emotion dysregulation was a key mediator in the transmission of relationship conflict, along with poor parenting skills. Parents’ emotion dysregulation was directly related to their son’s emotion dysregulation, which was in turn associated with the son’s later relationship conflict. Additionally, parents’ emotion dysregulation was significantly related to their poor discipline skills, which were linked to the son’s emotion dysregulation and eventual relationship conflict. Findings highlight emotion dysregulation as a significant mechanism explaining the continuity of romantic relationship conflict across generations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献