全文获取类型
收费全文 | 2629篇 |
免费 | 41篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 249篇 |
金属工艺 | 28篇 |
机械仪表 | 24篇 |
建筑科学 | 79篇 |
矿业工程 | 14篇 |
能源动力 | 59篇 |
轻工业 | 137篇 |
水利工程 | 16篇 |
石油天然气 | 15篇 |
武器工业 | 3篇 |
无线电 | 253篇 |
一般工业技术 | 275篇 |
冶金工业 | 1196篇 |
原子能技术 | 26篇 |
自动化技术 | 285篇 |
出版年
2021年 | 18篇 |
2019年 | 14篇 |
2018年 | 24篇 |
2017年 | 15篇 |
2016年 | 26篇 |
2015年 | 21篇 |
2014年 | 27篇 |
2013年 | 104篇 |
2012年 | 43篇 |
2011年 | 74篇 |
2010年 | 38篇 |
2009年 | 42篇 |
2008年 | 67篇 |
2007年 | 57篇 |
2006年 | 58篇 |
2005年 | 48篇 |
2004年 | 36篇 |
2003年 | 47篇 |
2002年 | 44篇 |
2001年 | 31篇 |
2000年 | 39篇 |
1999年 | 69篇 |
1998年 | 328篇 |
1997年 | 213篇 |
1996年 | 154篇 |
1995年 | 97篇 |
1994年 | 89篇 |
1993年 | 95篇 |
1992年 | 43篇 |
1991年 | 29篇 |
1990年 | 48篇 |
1989年 | 47篇 |
1988年 | 37篇 |
1987年 | 30篇 |
1986年 | 29篇 |
1985年 | 40篇 |
1984年 | 33篇 |
1983年 | 27篇 |
1982年 | 19篇 |
1981年 | 23篇 |
1980年 | 32篇 |
1979年 | 18篇 |
1978年 | 21篇 |
1977年 | 50篇 |
1976年 | 92篇 |
1975年 | 17篇 |
1974年 | 11篇 |
1973年 | 21篇 |
1971年 | 14篇 |
1970年 | 10篇 |
排序方式: 共有2672条查询结果,搜索用时 31 毫秒
61.
ON GENERALIZED FRACTIONAL PROCESSES 总被引:3,自引:0,他引:3
Abstract. A class of stationary long-memory processes is proposed which is an extension of the fractional autoregressive moving-average (FARMA) model. The FARMA model is limited by the fact that it does not allow data with persistent cyclic (or seasonal) behavior to be considered. Our extension, which includes the FARMA model as a special case, makes use of the properties of the generating function of the Gegenbauer polynomials, and we refer to these models as Gegenbauer autoregressive moving-average (GARMA) models. While the FARMA model has a peak in the spectrum at f = 0, the GARMA process can model long-term periodic behavior for any frequency 0 f 0.5. Properties of the GARMA process are examined and techniques for generation of realizations, model identification and parameter estimation are proposed. The use of the GARMA model is illustrated through simulated examples as well as with classical sunspot data. 相似文献
62.
第一批人凝血因子Ⅶ浓制剂国家标准品协作标定 总被引:1,自引:0,他引:1
目的 协作标定第一批人凝血因子Ⅶ浓制剂国家标准品。方法 以 WHO 97/592批人凝血因子Ⅶ浓制剂国际标准品为对照,采用一期法标定我国首批人凝血因子Ⅶ因家标准品,并将标准品分别置4℃、22℃、37℃保存5个月,用加速破坏试验进行稳定性考查。结果 该批标准品效价为16.0IU/支,稳定性良好。其他项目均达到国家标准品要求。结论 已成功研制第一批人凝血因子Ⅶ浓制剂国家标准品。 相似文献
63.
Murray R. Gray 《加拿大化工杂志》2002,80(3):393-401
A number of coking processes use hot particles to heat liquid bitumen or petroleum residue to cause cracking reactions. These particles may be mineral or coke solids. Interactions of these particles, in fluid beds, moving beds and other types of contactors, are governed by the liquid films on the particle surfaces. This paper explores the analogy between granulation and coking, and suggests that the key relationships that will govern the behavior of wet particles in coking processes are the Stokes number of the particles, the thickness or the liquid films, and the diameter and surface roughness of the particles. The implications for distribution of liquid feed in the reactor, fouling, and defluidization or bogging are discussed. This analysis suggests experiments that can be performed under non‐reactive conditions with scaled variables in order to study phenomena that cannot be observed in situ in high‐temperature cracking processes. 相似文献
64.
Paul Gray 《Information Systems Management》2013,30(4):356-359
Abstract The research in this paper considers the complex and dynamic arrangements for potential and actual knowledge sharing in interorganizational networks. The essence of this stance is that “knowledge” relates to affirmative managerial action beyond the necessary collection of information facilitated through technology. The issue is to determine the nature and extent of the degree of organizational agreement that may be achieved as competitors either cooperate or continue to compete in the face of challenging and pervasive market conditions. The theory relating to network formulation is reviewed, findings from empirical analyses from the experiences from automobile distributors in a large USA city, and one scientific collaborators network are presented. A framework is proposed identifying the factors necessary to initially construct the network and then to further sustain it over time. A number of lessons learned are developed, which are believed to be of value to researchers and practitioners engaged in these processes. 相似文献
65.
Susan S. Gray Barbara J. Loud Carole P. Sokolowski 《Canadian Journal of Science, Mathematics, & Technology Education》2013,13(2):59-72
Abstract The ability to use and interpret algebraic variables as generalized numbers and changing quantities is fundamental to the learning of calculus. This study considers the use of variables in these advanced ways as a component of algebraic thinking. College introductory calculus students' (n = 174) written responses to algebra problems requiring the use and interpretation of variables as changing quantities were examined for evidence of algebraic and arithmetic thinking. A framework was developed to describe and categorize examples of algebraic, transitional, and arithmetic thinking reflected in these students' uses of variables. The extent to which students' responses showed evidence of algebraic or arithmetic thinking was quantified and related to their course grades. Only one third of the responses of these entering calculus students were identified as representative of algebraic thinking. This study extends previous research by showing that evidence of algebraic thinking in students' work was positively related to successful performance in calculus. 相似文献
66.
67.
J Permert J Larsson GT Westermark MK Herrington L Christmanson PM Pour P Westermark TE Adrian 《Canadian Metallurgical Quarterly》1994,330(5):313-318
Population-based psychiatric admission rates vary across geographic areas, but reasons for this variation are unknown. Insofar as Community Mental Health Centers (CMHCs) provide outpatient services that may deter the need for hospitalization, the presence and structural characteristics of CMHCs may have an impact on a population's psychiatric admission rates. This study uses small area analysis to examine how general hospital psychiatric admission rates are associated with CMHC characteristics. Based on a survey of all CMHCs in Iowa and corresponding small area variation data, it was found that population admission rates were higher in areas closer to the CMHC and lower in outlying catchment areas, adjusting for age, sex, and urban/rural differences in populations. There was little evidence that differences in staffing and service variables influenced admission rates, although greater CMHC staff coverage by social workers and psychiatric residents was associated with lower admission rates. The results suggest that CMHCs do not lower an area's hospitalization rate, and in fact, the presence of CMHCs may promote a "supplier-induced demand" phenomenon of higher admissions. 相似文献
68.
69.
The experience of being "in love" was studied in a sample of 186 early to middle adolescent males and 199 early to middle adolescent females. Results indicated that amount of dating experience of adolescents varied widely at each age. Being "in love" co-occurred with a reciprocal on-going relationship about half the time. Boys fell in love earlier and more often than girls, and both genders seemed to employ an increasingly narrow prototypical conception of being "in love". Qualitative analyses suggested that early and middle adolescents are actively reasoning about the nature and meaning of romantic feelings and experiences. Results are interpreted from the standpoint of psychosocial developmental theory, and implications for interventions with adolescents are discussed. 相似文献
70.
Neural network modules based on page-oriented dynamic digital photorefractive memory are described. The modules can implement two different interconnection organizations, fan-out and fan-in, depending on their target network applications. Neural network learning is realized by the real-time memory update of dynamic digital photorefractive memory. Physical separation of subvolumes in the page-oriented photorefractive memory architecture contributes to the low cross talk and high diffraction efficiency of the stored interconnection weights. Digitally encoded interconnection weights ensure high accuracy, providing superior neural network system scalability. Module scalability and feedforward throughput have been investigated based on photorefractive memory geometry and the photodetector power requirements. The following four approaches to extend module scalability are discussed: partial optical summation, semiparallel feedforward operation, time partitioning, and interconnection matrix partitioning. Learning capabilities of the system are investigated in terms of required interconnection primitives for implementing learning processes and three memory-update schemes. The experimental results of Perceptron learning network implementation with 900 input neurons with digital 6-bit accuracy are reported. 相似文献