全文获取类型
收费全文 | 29441篇 |
免费 | 2386篇 |
国内免费 | 1246篇 |
专业分类
电工技术 | 2290篇 |
技术理论 | 1篇 |
综合类 | 2569篇 |
化学工业 | 3205篇 |
金属工艺 | 1050篇 |
机械仪表 | 1414篇 |
建筑科学 | 4978篇 |
矿业工程 | 2501篇 |
能源动力 | 1121篇 |
轻工业 | 1764篇 |
水利工程 | 1878篇 |
石油天然气 | 1906篇 |
武器工业 | 125篇 |
无线电 | 1208篇 |
一般工业技术 | 1470篇 |
冶金工业 | 2172篇 |
原子能技术 | 504篇 |
自动化技术 | 2917篇 |
出版年
2024年 | 92篇 |
2023年 | 271篇 |
2022年 | 700篇 |
2021年 | 788篇 |
2020年 | 810篇 |
2019年 | 633篇 |
2018年 | 593篇 |
2017年 | 767篇 |
2016年 | 925篇 |
2015年 | 1000篇 |
2014年 | 1827篇 |
2013年 | 1898篇 |
2012年 | 2085篇 |
2011年 | 2194篇 |
2010年 | 1684篇 |
2009年 | 1689篇 |
2008年 | 1571篇 |
2007年 | 1925篇 |
2006年 | 1810篇 |
2005年 | 1458篇 |
2004年 | 1388篇 |
2003年 | 1200篇 |
2002年 | 1072篇 |
2001年 | 957篇 |
2000年 | 706篇 |
1999年 | 615篇 |
1998年 | 435篇 |
1997年 | 362篇 |
1996年 | 338篇 |
1995年 | 293篇 |
1994年 | 231篇 |
1993年 | 149篇 |
1992年 | 126篇 |
1991年 | 111篇 |
1990年 | 83篇 |
1989年 | 70篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 24篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1964年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
This study presents a new database of land use categories in Brazil at a spatial resolution of 30 arc-second (about 1 km2). The spatial representation of current major land uses formally combines agricultural statistics from Brazil's latest census of the year 2006 at micro-region level and the Food and Agriculture Organization 2010 forest statistics with spatial land cover data sets. Spatial allocation (“downscaling”) algorithms were applied to obtain a spatial distribution of seven major land use categories. Remaining shares in each grid-cell were termed residual land, and were categorized according to legal protection status, biodiversity value, and whether they belong to the territory of the Amazon biome. We found a total of 84 Mha residual land of which 37 Mha occurred outside the territory of the Amazon biome and was neither legally protected nor categorized as highly biodiverse land. The 37 Mha “available residual land” equates to 4.4% of Brazil's geographical area and to 50% of its current cultivated land area. We assessed land quality using the Agro-ecological Zones modelling framework provides land suitability and productivity estimates of the available residual land. Nearly one-third of land emerged of prime quality and is therefore promising for biofuel feedstock production. Analysis of potential food-fuel competition suggests that until 2030 productivity improvements on current pastures could accommodate land demand for Brazil's increasing cattle herd and expanding croplands. If these productivity increases could be achieved on current agricultural land, residual land could provide areas for the sustainable expansion of biofuel feedstock production. 相似文献
982.
Regardless of the different theoretical positions held at present, we can probably agree that an abusive and problematic use of the Internet exists. We present an instrumental study whose objective is to develop a brief, valid, and reliable questionnaire to measure this abuse in epidemiological contexts. The Internet Abusive Use Questionnaire (IAUQ) consists of 12 items to respond to according to the Likert scale. A total of 908 respondents participated, 48% males, with ages ranging between 17 and 70 years. The IAUQ showed a single factor structure. This model presents a good adjustment, with CFI, GFI, and NFI fit index over .90. Internal consistency was found to be .90. The IAUQ showed direct correlations with the Internet abusive use self-assessment, anxiety and depression, and inverse correlations with quality of life. All correlations were significant (p < .001), which demonstrated convergent validity. Significant differences were also found in the IAUQ scores among groups with different age, cultural level, and other addictions, which evidenced discriminant validity. In conclusion, the obtained results demonstrate structural validity and adequate indices of convergent validity and discriminative capacity. These psychometric characteristics —combined with the fact that the IAUQ evaluates harmful use of Internet briefly and simply— fulfill our goal. 相似文献
983.
There is growing evidence that social media addiction is an evolving problem, particularly among adolescents. However, the absence of an instrument measuring social media addiction hinders further development of the research field. The present study, therefore, aimed to test the reliability and validity of a short and easy to administer Social Media Disorder (SMD) Scale that contains a clear diagnostic cut-off point to distinguish between disordered (i.e. addicted) and high-engaging non-disordered social media users.Three online surveys were conducted among a total of 2198 Dutch adolescents aged 10 to 17. The 9-item scale showed solid structural validity, appropriate internal consistency, good convergent and criterion validity, sufficient test-retest reliability, and satisfactory sensitivity and specificity. In sum, this study generated evidence that the short 9-item scale is a psychometrically sound and valid instruments to measure SMD. 相似文献
984.
As the smartphone becomes an integral part of our lives, its value as a rich data source reaches an increasing potential. Several previous studies have used smartphone-derived data to discover relationships between user characteristics and different types of smartphone use. However, none tried to use smartphone data to capture an individual's social behavior into one profile, aimed at providing additional information for the diagnostic evaluation of social deficits. This study presents a novel way of combining different modalities of smartphone data for the creation of sociability profiles using a scoring mechanism that allows for easy addition and removal of data sources. Following installation of the smartphone application, data is being sampled in the background to allow for the assessment of spontaneous smartphone use. Sociability scores were based on the integration of social communication and social exploration scores derived from smartphone use and environmental data sampling (e.g., GPS and external Bluetooth signals). Finally, we have applied our Sociability model to create social profiles of ten test subjects as a baseline for future studies. This pilot study provided insight in the usability of the individual sociability scores for future smartphone application to provide longitudinal objective measures of normal and atypical human social behavioral profiles in their natural environment. 相似文献
985.
Viswanath Venkatesh Tracy Ann Sykes Srinivasan Venkatraman 《Information Systems Journal》2014,24(3):249-269
Electronic government (e‐Government) is one of the most important ways to bridge the digital divide in developing countries. We develop a model of e‐Government portal use. We use various individual characteristics, namely demographics and personality, as predictors of e‐Government portal use. Specifically, our predictors were (1) gender, age, income and education; (2) the Big Five personality characteristics, i.e. extraversion, neuroticism, conscientiousness, agreeableness and openness to experience; and (3) personal innovativeness with information technology. We conducted a field study in a village in India. We collected data from over 300 heads of household. We found support for our model, with most variables being significant and explaining 40% of the variance in e‐Government portal use. 相似文献
986.
《石油化工》2016,45(11):1369
针对石脑油的组成特点,对分子同系物(MTHS)矩阵进行简化,以C_3~C_(12)的正构烷烃、异构烷烃、环烷烃和芳烃构成的分子矩阵来表示石脑油的分子水平组成;建立了通过工业中常用的石脑油物性数据(如蒸馏曲线、密度)等计算石脑油分子水平组成的方法。以各项物理性质的实测值与预测值的残差平方和构建目标函数,并在原模型的基础上加以有效的约束,进行优化求解,得到石脑油分子水平组成数据。选择两组已知组成的石脑油作为样本,由Aspen Plus模拟软件计算其蒸馏曲线、密度等整体性质,根据上述方法对两组样本进行计算。两组样本的预测结果与真实组成的对比表明,该方法可用来预测石脑油分子水平组成,且准确度较原模型有提升。 相似文献
987.
The development of business applications with game features has given rise to a new trend called gamification and challenged e-banking to introduce new game elements, such as mechanics and social cues, to its traditional applications. Yet, there has been a lack of empirical evidence regarding the intention to use, these type of applications and their possible impacts on business. Here, we explore the role of gamification, socialness, and other four well-known variables (ease-of-use, usefulness, enjoyment, and intention to use) in a gamified business application and corresponding business. We proposed and evaluated a model based on the Technology Acceptance Model to better analyze and understand the adoption of gamified business applications. To test this model, we developed a study using a sample of 183 bank customers, and we found that gamification significantly improved the customer’s sense of social interaction, which, in turn, strongly influenced the customer’s intention to use the applications. We argue that this intention to use could provide a strong benefit to the business, in term of increased customer engagement. This paper presents a new conceptual model to predict behavioral intention in regards to gamification in e-banking, illustrating seven variables that affect the adoption of e-banking by bank customers. Our findings contribute overall to a better understanding of gamification in e-banking (with the extension of Technology Acceptance Model theories, and the new variable gamification), providing important practical implications for software development and marketing practices. 相似文献
988.
The recent trend of aging population, not to mention the unprecedented pandemic, draws great attention from the general public about health concerns. Since healthcare information technology is different from non-healthcare information technology, additional contexts should be properly incorporated into technology acceptance research to accurately identify influential factors affecting the acceptance of wearable healthcare technology. Thus, we selectively reconfigured factors from health, privacy, and socio-demographic contexts to formulate a health-aware acceptance model. Then, it was empirically analyzed using structural equation modeling. Based on the results, whereas privacy concerns were directly associated with intention to use wearable healthcare technology, health concerns were not. Moreover, age had a moderating effect on social influence and facilitating conditions. These findings suggest valuable insights that the adoption rate of healthcare technology is increased by 1) keeping personal information securely, 2) facilitating social interaction among users, and 3) offering intuitive user experience for elderly people. 相似文献
989.
Mass customisation systems have been well-established in the fashion industry. Some fashion brands offer the mass customisation system for their selected seasonal products, and allow unconditional returns and full refund for any unsatisfied customers. Motivated by the above mentioned observed industrial practice and based on the growing importance of responsive supply, we explore in this paper the value of quick response supply in fashion mass customisation systems with consumer returns. We focus on investigating how the consumer returns rate affects (i) the optimal inventory decision of the fashion brand, (ii) the achievability of Pareto improvement in implementing quick response supply, (iii) the respective values of quick response for the fashion brand, the fashion supplier and also the fashion supply chain, and (iv) the impact of quick response supply on the environment. We interestingly find that consumer returns enhance the value of quick response supply to the fashion supplier. Quick response supply is also found to be helpful in reducing the environmental cost under the fashion mass customisation system with consumer returns. 相似文献
990.
针对步进式加热炉炉底出渣较困难的情况,分析氧化铁皮渣产生的原因,开发了一种新型提渣装置,以解决炉底地坑内堆积炉渣的清理问题,实现了无需用天车即可将炉底氧化铁皮渣运至地面以上。通过以上工作,承钢成功研制了一种步进式加热炉炉底提渣专利装置。 相似文献