全文获取类型
收费全文 | 1663篇 |
免费 | 50篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 247篇 |
金属工艺 | 22篇 |
机械仪表 | 35篇 |
建筑科学 | 98篇 |
矿业工程 | 10篇 |
能源动力 | 27篇 |
轻工业 | 264篇 |
水利工程 | 8篇 |
石油天然气 | 3篇 |
无线电 | 87篇 |
一般工业技术 | 187篇 |
冶金工业 | 492篇 |
原子能技术 | 2篇 |
自动化技术 | 222篇 |
出版年
2022年 | 26篇 |
2021年 | 36篇 |
2020年 | 17篇 |
2019年 | 23篇 |
2018年 | 29篇 |
2017年 | 30篇 |
2016年 | 36篇 |
2015年 | 30篇 |
2014年 | 45篇 |
2013年 | 111篇 |
2012年 | 64篇 |
2011年 | 90篇 |
2010年 | 85篇 |
2009年 | 69篇 |
2008年 | 83篇 |
2007年 | 79篇 |
2006年 | 88篇 |
2005年 | 75篇 |
2004年 | 49篇 |
2003年 | 43篇 |
2002年 | 43篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 30篇 |
1998年 | 33篇 |
1997年 | 28篇 |
1996年 | 31篇 |
1995年 | 29篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 18篇 |
1988年 | 20篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 5篇 |
排序方式: 共有1714条查询结果,搜索用时 218 毫秒
991.
In rural areas, a lack of infrastructure often limits the promotion and implementation of community-based nutrition activities. Growth monitoring can potentially provide a platform for the promotion and implementation of community-based nutrition activities, provided that the growth-monitoring program has a high coverage. The aim of this study was to determine the acceptability of a community-based growth-monitoring project in terms of child attendance and maternal attitude. The study was done in a mountainous rural village that lacks health facilities in KwaZulu-Natal, South Africa. Attendance registers from 1996 to 2000 were used to determine the attendance ratio, coverage, adequacy of growth monitoring, and frequency distribution of the age of participating children. In 2001, focus group discussions were used for the qualitative assessment of maternal attitudes. The community-based growth-monitoring project had an estimated coverage of 90%, at least 60% of these children were covered adequately, and attendance was equally distributed over one-year-interval age categories for children aged five years and younger. Community-based growth monitoring can therefore provide a suitable platform for the promotion and implementation of community-based nutrition activities. 相似文献
992.
Bile salt/lecithin mixed micelles optimized for the solubilization of a poorly soluble steroid molecule using statistical experimental design 总被引:1,自引:0,他引:1
Bile salts and lecithin combine physiologically to form mixed micelles which aid the solubilization and absorption of dietary fats and drug molecules. In this series of experiments, we have shown how experimental design procedures aid the optimization of a formulation incorporating a bile salt, lecithin, and water with fluticasone propionate (FP) as the model poorly soluble drug. The initial inclusion of a categorical variable ruled out the use of classic response surface designs; therefore the experimental design was constructed using a d-optimal selection from a candidate set of all possible experimental combinations. A separate 2-factor central composite design was used to determine the optimum lecithin and bile salt concentrations over an extended range after the categorical variable had been eliminated. It has been demonstrated that an increase in either lecithin or cholic acid concentration produces an increase in solubility of FP, while sodium taurocholate appears to depress the solubility of FP compared with the other two bile salts. The increase in solubility associated with the increase in bile salt and lecithin is further demonstrated by a linear relationship between FP solubility and the total lipid in the formulation. The influence of molar ratio of lecithin to bile salt in the formulation is also significant. The physical properties of the mixed micellar system (solution turbidity and viscosity ranking) were used to further discriminate between formulations. The optimization showed that the dominant effect was the lecithin, which improves the solubilizing characteristics of the formulation with increasing concentration. The effect of salt concentration is less marked though slightly quadratic in nature. The overall increase in solubility demonstrated was from <1 microg/mL in water to 205 microg/mL in the optimized mixed micellar system. 相似文献
993.
Jane?Cleland-HuangEmail author Carl?K.?Chang Jeffrey?C.?Wise 《Requirements Engineering》2003,8(3):171-182
Current impact analysis techniques tend to focus on assessing the impact of change upon the system's functionality, whilst a consideration of performance related requirements is often deferred until after implementation. This tendency can lead to costly and time-consuming mistakes that frustrate customers and require frantic last-minute efforts to fix. This paper proposes a method for supporting performance-related impact analysis in a heterogeneous software engineering environment. An event-based approach is taken to establish dynamic traceability links, capable of propagating data values and commands between requirements and performance models. Quantitative values in performance related requirements are adjusted to reflect proposed changes, and impacted models are re-executed to measure the impact of the change. The resulting outputs are then automatically compared to relevant performance requirements and a system-wide report showing the impact of the proposed change upon performance is generated.
相似文献
Jane Cleland-HuangEmail: |
994.
In this study, the authors investigated the relationship between autobiographical memory and the onset and maintenance of distressing memories following cancer. In Study 1, participants recently diagnosed with head, neck, or lung cancer were assessed for acute stress disorder (ASD). Participants with ASD reported fewer specific memories than did participants without ASD. In Study 2, the same participants were assessed 6 months later for autobiographical memory and cancer-related posttraumatic stress disorder (PTSD). Deficits in the retrieval of specific memories in Study 1 were not predictive of subsequent PTSD. Increased hopelessness during the 6 months was associated with a decline in the retrieval of positive memories and an increase in the retrieval of negative memories. These findings accord with propositions that retrieval of distressing memories is guided by current self-image and attitude toward one's future. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
Semantic-level content analysis is a crucial issue in achieving efficient content retrieval and management. We propose a hierarchical
approach that models the statistical characteristics of audio events over a time series to accomplish semantic context detection.
Two stages, audio event and semantic context modeling, are devised to bridge the semantic gap between physical audio features
and semantic concepts. In this work, hidden Markov models (HMMs) are used to model four representative audio events, i.e.,
gunshot, explosion, engine, and car-braking, in action movies. At the semantic-context level, Gaussian mixture models (GMMs)
and ergodic HMMs are investigated to fuse the characteristics and correlations between various audio events. They provide
cues for detecting gunplay and car-chasing scenes, two semantic contexts we focus on in this work. The promising experimental
results demonstrate the effectiveness of the proposed approach and exhibit that the proposed framework provides a foundation
in semantic indexing and retrieval. Moreover, the two fusion schemes are compared, and the relations between audio event and
semantic context are studied. 相似文献
996.
997.
Pickett Theodore Jr.; Altmaier Elizabeth; Paulsen Jane S. 《Canadian Metallurgical Quarterly》2007,52(3):311
Objective: Huntington's disease (HD) is an autosomal dominant heritable disease characterized by progressive neuron death and subsequent degeneration of motor, cognitive, and emotional functioning. Caregiver research studies in HD are few. The purpose of the current study was to examine caregiver burden in HD. Method: The sample consisted of 62 pairs of caregivers and care receivers (persons with Huntington's disease; pHDs). Caregivers were assessed regarding their psychological functioning, subjective appraisal of burden, and appraisal of problem-solving ability as well as the general level of daily functioning of the pHD in their care; pHDs were queried regarding their psychological functioning. Results: Analyses showed that caregiver subjective burden, pHD depression, and caregiver problem-solving appraisal were significantly associated with caregiver depression. The results did not support caregiver burden as a mediator. Conclusions: Findings delineate impact of caregiving in HD and highlight the importance of mood assessment and treatment in all groups. Suggestions for future research and implications for clinical interventions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
The challenge problems for the Epistemic Uncertainty Workshop at Sandia National Laboratories provide common ground for comparing different mathematical theories of uncertainty, referred to as General Information Theories (GITs). These problems also present the opportunity to discuss the use of expert knowledge as an important constituent of uncertainty quantification. More specifically, how do the principles and methods of eliciting and analyzing expert knowledge apply to these problems and similar ones encountered in complex technical problem solving and decision making? We will address this question, demonstrating how the elicitation issues and the knowledge that experts provide can be used to assess the uncertainty in outputs that emerge from a black box model or computational code represented by the challenge problems. In our experience, the rich collection of GITs provides an opportunity to capture the experts' knowledge and associated uncertainties consistent with their thinking, problem solving, and problem representation. The elicitation process is rightly treated as part of an overall analytical approach, and the information elicited is not simply a source of data. In this paper, we detail how the elicitation process itself impacts the analyst's ability to represent, aggregate, and propagate uncertainty, as well as how to interpret uncertainties in outputs. While this approach does not advocate a specific GIT, answers under uncertainty do result from the elicitation. 相似文献
999.
Vladimir V. Ponkratov Josef Friedrich Jane M. Vanderkooi Alexander L. Burin Yuri A. Berlin 《Journal of Low Temperature Physics》2004,137(3-4):289-317
We present results of a hole burning study with thermal cycling and waiting time spectral diffusion experiments on a modified cytochrome - c protein in its native as well as in its denatured state. The experiments show features which seem to be characteristic for the protein state of matter and its associated dynamics at low temperature. The properties responsible for the observed patterns are organisation paired with randomness and, in addition, the finite size which gives rise to surface and solvent effects. We discuss some general model approaches which might serve as guide lines for understanding these features. 相似文献
1000.
Two studies investigated the ability to use contextual information in stories to infer the meanings of novel vocabulary by 9-10-year-olds with good and poor reading comprehension. Across studies, children with poor reading comprehension were impaired when the processing demands of the task were greatest. In Study 2, working memory capacity was related to performance, but short-term memory span and memory for the literal content of the text were not. Children with poor reading comprehension were not impaired in learning novel vocabulary taught through direct instruction, but children with both weak reading comprehension and vocabulary were. Implications for the relation between vocabulary development and text comprehension are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献