全文获取类型
收费全文 | 951篇 |
免费 | 103篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 221篇 |
金属工艺 | 9篇 |
机械仪表 | 10篇 |
建筑科学 | 54篇 |
矿业工程 | 1篇 |
能源动力 | 20篇 |
轻工业 | 138篇 |
水利工程 | 27篇 |
石油天然气 | 3篇 |
无线电 | 60篇 |
一般工业技术 | 173篇 |
冶金工业 | 227篇 |
原子能技术 | 3篇 |
自动化技术 | 105篇 |
出版年
2024年 | 4篇 |
2023年 | 22篇 |
2022年 | 34篇 |
2021年 | 51篇 |
2020年 | 38篇 |
2019年 | 38篇 |
2018年 | 62篇 |
2017年 | 42篇 |
2016年 | 49篇 |
2015年 | 30篇 |
2014年 | 29篇 |
2013年 | 38篇 |
2012年 | 54篇 |
2011年 | 85篇 |
2010年 | 72篇 |
2009年 | 42篇 |
2008年 | 63篇 |
2007年 | 50篇 |
2006年 | 46篇 |
2005年 | 34篇 |
2004年 | 25篇 |
2003年 | 26篇 |
2002年 | 14篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 8篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1970年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1955年 | 1篇 |
1929年 | 1篇 |
1926年 | 4篇 |
1925年 | 11篇 |
排序方式: 共有1054条查询结果,搜索用时 15 毫秒
91.
Emily Jackson Levitt David L. Pelletier Charlotte Dufour Alice N. Pell 《Food Security》2011,3(3):363-381
Coordination across sectors to address undernutrition with its varied underlying causes remains a challenge in developing
countries. In Afghanistan, harmonization of health and agriculture policies and actions to reduce endemic undernutrition occurred
during 2002-2007. This qualitative case study explores the forms of harmonization, enabling features and constraints in the
policy process. We interviewed 57 stakeholders (39 central level, 18 provincial) involved in public nutrition or food security
issues. Forms of harmonization included written policies, reseach, training and advocacy. Important features of the policy
process included: policy entrepreneurs with operational and strategic capacity, consensus-building using a shared causal framework,
working groups and strategic alliances. This case presents an interesting alternative to a national nutrition coordinating
body, an approach that has met with mixed results, often due to the lack of authority, budget, and operational capacity of
such a body to oversee ministries and enforce national nutrition objectives. Mid-level professionals mobilized into task forces
achieved much with the support of national and international partners. This study highlights the importance of building capacity
for sustaining change through local institutions. 相似文献
92.
Terpenes and alkaloids are ever-growing classes of natural products that provide new molecular structures that inspire chemists and possess a broad range of biological activity. Terpenoid-alkaloids originate from the same prenyl units that construct terpene skeletons. However, during biosynthesis, a nitrogen atom (or atoms) is introduced in the form of β-aminoethanol, ethylamine, or methylamine. Nitrogen incorporation can occur either before, during, or after the cyclase phase. The outcome of this unique biosynthesis is the formation of natural products containing unprecedented structures. These complex structural motifs expose current limitations in organic chemistry, thus providing opportunities for invention. This review focuses on total syntheses of terpenoid-alkaloids and unique issues presented by this class of natural products. More specifically, it examines how these syntheses relate to the way terpenoid-alkaloids are made in Nature. Developments in chemistry that have facilitated these syntheses are emphasized, as well as chemical technology needed to conquer those that evade synthesis. 相似文献
93.
Ditre Joseph W.; Brandon Thomas H.; Zale Emily L.; Meagher Mary M. 《Canadian Metallurgical Quarterly》2011,137(6):1065
Tobacco addiction and chronic pain represent 2 highly prevalent and comorbid conditions that engender substantial burdens upon individuals and systems. Interrelations between pain and smoking have been of clinical and empirical interest for decades, and research in this area has increased dramatically over the past 5 years. We conceptualize the interaction of pain and smoking as a prototypical example of the biopsychosocial model. Accordingly, we extrapolated from behavioral, cognitive, affective, biomedical, and social perspectives to propose causal mechanisms that may contribute to the observed comorbidity between these 2 conditions. The extant literature was 1st dichotomized into investigations of either effects of smoking on pain or effects of pain on smoking. We then integrated these findings to present a reciprocal model of pain and smoking that is hypothesized to interact in the manner of a positive feedback loop, resulting in greater pain and increased smoking. Finally, we proposed directions for future research and discussed clinical implications for smokers with comorbid pain disorders. We observed modest evidence that smoking may be a risk factor in the multifactorial etiology of some chronically painful conditions and that pain may come to serve as a potent motivator of smoking. We also found that whereas animal studies yielded consistent support for direct pain-inhibitory effects of nicotine and tobacco, results from human studies were much less consistent. Future research in the emerging area of pain and smoking has the potential to inform theoretical and clinical applications with respect to tobacco smoking, chronic pain, and their comorbid presentation. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
94.
While the quality control procedures for multistage has been considerably studied, multistage process capability analysis has not been explored much at all. Fostering on the recent development of the multistage process variation transmission model, a multistage process capability analysis algorithm is developed to prioritize process improvement efforts. The application of algorithm is demonstrated with two 2-stage industrial process examples and a 4-stage process example for its expandability. 相似文献
95.
This article details permeation tests that were performed on sheet samples of elastomers, over a wide range of pressures and temperatures, to study their effects on gas diffusion and solubility. It also explains how ageing is affected by gas permeation, and how the permeation test results can be used as input data for finite element analysis to aid the design of elastomeric components. 相似文献
96.
Nonlinear models of chatter in drilling processes 总被引:2,自引:0,他引:2
We develop a nonlinear model of chatter in drilling that incorporates friction of the material on the cutting tool and its interaction with the axial-torsional mode of vibration seen in twist drills. Stability criteria are determined for both regenerative and non-regenerative chatter, and the effect of tool parameters and the friction law itself on the results is analysed. Our analysis shows that the exact form of the friction law is not critical in the stability calculation, only the size of the friction coefficient for steady cutting, and the slope of the friction law at the steady cutting state. However, its interaction with the geometry of the vibration is crucial. In the laboratory, drilling vibrational instabilities can occur at frequencies less than the natural frequency of the excited mode of the drill, and we find this result depends critically on the shape of the vibration mode projected onto the cutting edge of the drill. 相似文献
97.
This article argues that the devaluation of options with missing information, found in previous research, is a specific example of ambiguity avoidance in choice. H. J. Einhorn and R. M. Hogarth's (see record 1986-13621-001) ambiguity model was used to make predictions concerning responses to missing information in an employee-selection context. A within-subjects design was used to test the hypothesis that decision makers would avoid options with missing information when they were anticipating gain, but they would prefer such options when they were anticipating loss. Degree of ambiguity was expected to interact with this effect. The results supported the hypothesized effect of decision-maker perspective on choice. However, although there was a significant interaction between decision-maker perspective and degree of ambiguity, it was not of the nature that was predicted by the Einhorn-Hogarth model. Generalized pessimism was negatively correlated with preferences for missing-information options. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
98.
People's motivational states--their wishes and preferences--influence their processing of visual stimuli. In 5 studies, participants shown an ambiguous figure (e.g., one that could be seen either as the letter B or the number 13) tended to report seeing the interpretation that assigned them to outcomes they favored. This finding was affirmed by unobtrusive and implicit measures of perception (e.g., eye tracking, lexical decision tasks) and by experimental procedures demonstrating that participants were aware only of the single (usually favored) interpretation they saw at the time they viewed the stimulus. These studies suggest that the impact of motivation on information processing extends down into preconscious processing of stimuli in the visual environment and thus guides what the visual system presents to conscious awareness. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
99.
We employ first-principles density functional calculations to explore atomic-level interactions and predict the ideal work of adhesion at the SiO2 /nickel and ZrO2 /SiO2 interfaces. We find that chemical bonding at the interface serves to strengthen significantly interfaces formed with SiO2 , which exhibits significant covalent bonding character, relative to those formed using more ionic oxides, such as Al2 O3 , in place of SiO2 . The improved strength of these interfaces due to local bonding interactions may hold materials design implications for practical applications that require optimal adhesion between metal-ceramic layered structures, including thermal barrier coatings. 相似文献
100.
Personality traits related to neuroticism and disinhibition have been consistently associated with substance use disorders (SUDs). It is unclear, however, whether different personality traits predict distinct forms of substance dependence. Additionally, it is unclear whether personality traits continue to predict alcohol, drug, and tobacco dependence after controlling for comorbid antisociality and other SUDs. The current study addresses these questions by characterizing relations between personality traits and substance dependence symptoms in a longitudinal sample of 3,720 college students. Results revealed that antisociality and certain core personality traits predicted multiple types of substance pathology. In addition, several personality traits were differentially associated with alcohol, drug, and tobacco symptomatology. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献