全文获取类型
收费全文 | 1201篇 |
免费 | 62篇 |
国内免费 | 4篇 |
学科分类
工业技术 | 1267篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 20篇 |
2020年 | 19篇 |
2019年 | 16篇 |
2018年 | 34篇 |
2017年 | 22篇 |
2016年 | 26篇 |
2015年 | 30篇 |
2014年 | 39篇 |
2013年 | 76篇 |
2012年 | 76篇 |
2011年 | 84篇 |
2010年 | 75篇 |
2009年 | 49篇 |
2008年 | 64篇 |
2007年 | 66篇 |
2006年 | 46篇 |
2005年 | 40篇 |
2004年 | 49篇 |
2003年 | 35篇 |
2002年 | 26篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 20篇 |
1998年 | 47篇 |
1997年 | 35篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 22篇 |
1993年 | 21篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1976年 | 9篇 |
1974年 | 8篇 |
1972年 | 3篇 |
1969年 | 3篇 |
1968年 | 3篇 |
排序方式: 共有1267条查询结果,搜索用时 675 毫秒
1.
2.
BF Habbick JL Nanson RE Snyder RE Casey AL Schulman 《Canadian Metallurgical Quarterly》1996,87(3):204-207
Ethers and thioethers of monosaccharides have been synthesised which show potent toxicity to mouse (LD50 > or = 4 g.kg-1 O.W. and 0.2 to 1.5 g.kg-1 I.P.W.). A study of calcium antagonist activity for the full series of compounds indicated that the activity was similar for both O- and S- ethers and maximum activities were observed for monoacetoneglucose ethers possessing carbon chain close to 8 carbons. 相似文献
3.
Phil Spruce 《电子产品世界》2002,(19):63-64
大多数电信企业为获得3G许可证投入了巨额资金,现在他们还需要进行基础设施投资,以为这一企盼已久的技术提供支持。总的成本将会达数十亿英磅,因此电信商面临很大的压力,需要尽快偿还债务并快速获得赢利,达到这一目标的最快速的方法还是尽快启动3G的消费市场。对于价格竞争激烈的多媒体功能等服务,赢得消费者和商业客户青睐并迅速收回投资的关键是提供价格合理的手机。包括发射器和接收器在内的手机内部电路在手机成本中占了相当大的部分。为降低3G手机射频解决方案的总体成本,必须满足三个主要目标:即降低芯片成本、减少外部器件… 相似文献
4.
The World Solar Challenge is a 3000 km race for solar powered cars across the Australian continent from Darwin to Adelaide. Each car is powered by a panel of photovoltaic cells which convert sunlight into electrical power. The power can be used directly to drive the car or stored in a battery for later use. Previous papers (P. Howlett, P. Pudney, T. Tarnopolskaya, and D. Gates, IMA Journal of Mathematics Applied in Business and Industry vol. 8, pp. 59–81, 1997; P.G. Howlett and P.J. Pudney, Dynamics of Continuous, Discrete and Impulsive Systems vol. 4, pp. 553–567, 1998) using a simplified model of the battery, have shown that the optimal strategy is essentially a speedholding strategy. In this paper, with a more realistic model of the battery, we show that the optimal driving strategy is a critical speed strategy. For an optimal journey with no beginning and no ending the solar car must always travel at the critical speed. For an optimal journey of finite length the speed must be close to the critical speed for most of the journey. The critical speed depends on the solar power and will normally vary slowly with time. 相似文献
5.
With the increasing interest in yardstick regulation, there is a need to understand the most appropriate method for realigning tariffs at the outset. Benchmarking is the tool used for such realignment and is therefore a necessary first-step in the implementation of yardstick competition. A number of concerns have been raised about the application of benchmarking, making some practitioners reluctant to move towards yardstick based regimes. We assess five of the key concerns often discussed and find that, in general, these are not as great as perceived. The assessment is based on economic principles and experiences with applying benchmarking to regulated sectors, e.g. in the electricity and water industries in the UK, The Netherlands, Austria and Germany in recent years. The aim is to demonstrate that clarity on the role of benchmarking reduces the concern about its application in different regulatory regimes. We find that benchmarking can be used in regulatory settlements, although the range of possible benchmarking approaches that are appropriate will be small for any individual regulatory question. Benchmarking is feasible as total cost measures and environmental factors are better defined in practice than is commonly appreciated and collusion is unlikely to occur in environments with more than 2 or 3 firms (where shareholders have a role in monitoring and rewarding performance). Furthermore, any concern about companies under-recovering costs is a matter to be determined through the regulatory settlement and does not affect the case for using benchmarking as part of that settlement. 相似文献
6.
Abstract. Certification is one criterion that employers seek when hiring network professionals. Many employers assume a certified network professional is better able to manage networked resources than is a non-certified counterpart. Therefore, employers often offer a monetary premium to attract certified network professionals. By measuring end-user perceptions, the current study empirically assesses the popular industry assumption that certified network professionals are more adept managers of network resources than those individuals who are not certified network professionals. Analyses of a data derived from 299 end-users of 11 separate local area networks indicate no statistically significant difference exists between the capabilities of certified network professionals and non-certified network professionals. 相似文献
7.
Y Xu DC Gaudette JD Boynton A Frankel XJ Fang A Sharma J Hurteau G Casey A Goodbody A Mellors 《Canadian Metallurgical Quarterly》1995,1(10):1223-1232
Ascites from ovarian cancer patients contain potent growth-promoting activity toward human ovarian cancer cells both in vitro and in vivo. This activity is associated with rapid increases in cytosolic free calcium ([Ca2+]i) as a consequence of phosphoinositide hydrolysis. In this study, we describe the purification, characterization, and identification of an ovarian cancer activating factor (OCAF) from ascites of ovarian cancer patients. We have isolated OCAF by a combination of solvent extraction, silica gel chromatography, and TLC. Mass spectral analysis, phospholipase sensitivity, and gas chromatographic behavior of purified OCAF indicate that OCAF is composed of various species of lysophosphatidic acid (LPA), including LPAs with polyunsaturated fatty acyl chains (linoleic, arachidonic, and docosahexaenoic acids). However, OCAF is more potent than sn-1 palmitoyl, oleoyl, or stearoyl LPA in increasing [Ca2+]i in ovarian cancer cells. The ability of OCAF to alter [Ca2+]i is sensitive to the effects of lipoxidase, whereas the activity of sn-1 oleoyl, stearoyl, or palmitoyl LPA is not, suggesting that polyunsaturated bonds in the fatty acyl chain of OCAF may account for its increased ability to activate ovarian cancer cells. Furthermore, a sn-2 linoleoyl LPA generated by phospholipase A1 treatment of synthetic phosphatidic acid is much more active than are sn-1 palmitoyl, stearoyl, or oleoyl LPA in increasing [Ca2+]i in ovarian cancer cells. Taken together, these data suggest that the ability of OCAF to increase cellular calcium may reside in the structure and/or location of the fatty acyl chain of LPA. Purified OCAF, at concentrations similar to those present in ascites from ovarian cancer patients, was sufficient to induce proliferation of ovarian cancer cells, as indicated by thymidine incorporation, reduction of 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, or colony formation. However, even at optimal concentrations of OCAF, proliferation was lower than that induced by FCS or ascites from ovarian cancer patients, indicating that, although OCAF may be a major regulator of ovarian cancer cells in vivo, it is not the sole mediator present in ascites, and it likely functions in concert with other growth factor activities. 相似文献
8.
Krueger Robert F.; Schmutte Pamela S.; Caspi Avshalom; Moffitt Terrie E.; Campbell Kathleen; Silva Phil A. 《Canadian Metallurgical Quarterly》1994,103(2):328
Is there a relationship between personality and criminal behavior? We addressed this question in a representative birth cohort of 862 male and female 18-yr-olds. Personality was assessed with the Multidimensional Personality Questionnaire (MPQ). The MPQ measures 10 relatively independent personality traits and was not designed to identify offenders. Delinquency was assessed via 3 data sources: self-reports, informant reports, and official records. Variable-centered analyses revealed that MPQ scales indexing negative emotionality and behavioral constraint were consistent predictors of delinquency across the 3 data sources. Person-centered analyses revealed that youths abstaining from delinquency were uniquely characterized by low interpersonal potency. Youths involved in extensive delinquency were uniquely characterized by feelings of alienation, lack of social closeness and risk taking. Advances in understanding criminal behavior can be made through research that places the personality-delinquency link in a developmental context. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
10.