全文获取类型
收费全文 | 1120篇 |
免费 | 82篇 |
国内免费 | 45篇 |
专业分类
电工技术 | 36篇 |
综合类 | 45篇 |
化学工业 | 168篇 |
金属工艺 | 10篇 |
机械仪表 | 32篇 |
建筑科学 | 110篇 |
矿业工程 | 9篇 |
能源动力 | 7篇 |
轻工业 | 165篇 |
水利工程 | 13篇 |
石油天然气 | 39篇 |
武器工业 | 10篇 |
无线电 | 76篇 |
一般工业技术 | 87篇 |
冶金工业 | 198篇 |
原子能技术 | 2篇 |
自动化技术 | 240篇 |
出版年
2024年 | 5篇 |
2023年 | 12篇 |
2022年 | 70篇 |
2021年 | 77篇 |
2020年 | 35篇 |
2019年 | 44篇 |
2018年 | 52篇 |
2017年 | 29篇 |
2016年 | 43篇 |
2015年 | 23篇 |
2014年 | 76篇 |
2013年 | 84篇 |
2012年 | 68篇 |
2011年 | 78篇 |
2010年 | 49篇 |
2009年 | 49篇 |
2008年 | 53篇 |
2007年 | 64篇 |
2006年 | 45篇 |
2005年 | 37篇 |
2004年 | 36篇 |
2003年 | 28篇 |
2002年 | 33篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1986年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1968年 | 2篇 |
1966年 | 2篇 |
1965年 | 5篇 |
1964年 | 8篇 |
1963年 | 5篇 |
1962年 | 3篇 |
1961年 | 5篇 |
1960年 | 10篇 |
1959年 | 5篇 |
1958年 | 3篇 |
1957年 | 3篇 |
1956年 | 9篇 |
1955年 | 4篇 |
1954年 | 4篇 |
排序方式: 共有1247条查询结果,搜索用时 31 毫秒
991.
Yi Liu Cong Zhang Yi Liu Jiayong Zhu Hui Qu Siqi Zhou Ming Chen Dan Xu Liaobin Chen Hui Wang 《International journal of molecular sciences》2022,23(23)
Clinical and animal studies suggest that paternal exposure to adverse environments (bad living habits and chronic stress, etc.) has profound impacts on offspring development; however, the mechanism of paternal disease has not been clarified. In this study, a meta-analysis was first performed to suggest that paternal exposure to nicotine, ethanol, or caffeine is a high-risk factor for adverse pregnancy outcomes. Next, we created a rat model of paternal nicotine/ethanol/caffeine mixed exposure (PME), whereby male Wistar rats were exposed to nicotine (0.1 mg/kg/d), ethanol (0.5 g/kg/d), and caffeine (7.5 mg/kg/d) for 8 weeks continuously, then mated with normal female rats to obtain a fetus (n = 12 for control group, n = 10 for PME group). Then, we analyzed the changes in paternal hypothalamic–pituitary–adrenal (HPA) axis activity, testicular function, pregnancy outcomes, fetal serum metabolic indicators, and multiple organ functions to explore the mechanism from the perspective of chronic stress. Our results demonstrated that PME led to enhanced paternal HPA axis activity, decreased sperm quality, and adverse pregnancy outcomes (stillbirth and absorption, decreased fetal weight and body length, and intrauterine growth retardation), abnormal fetal serum metabolic indicators (corticosterone, glucolipid metabolism, and sex hormones), and fetal multi-organ dysfunction (including hippocampus, adrenal, liver, ossification, and gonads). Furthermore, correlation analysis showed that the increased paternal corticosterone level was closely related to decreased sperm quality, adverse pregnancy outcomes, and abnormal offspring multi-organ function development. Among them, the decreased activity of the glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis may be the main mechanism of offspring development and multi-organ dysfunction caused by PME. This study explored the impact of common paternal lifestyle in daily life on offspring development, and proposed the GC-IGF1 programming mechanisms of paternal chronic stress-induced offspring dysplasia, which provides a novel insight for exploring the important role of paternal chronic stress in offspring development and guiding a healthy lifestyle for men. 相似文献
992.
20世纪30年代,德国学者劳伯梅耶和前苏联学者索柯洛夫创造了气测法,揭开了油气化探发展的序幕。至今,已经形成了一系列方法指标,用于检测地表环境中与烃类微渗漏有关的各种物理、化学、生物学变化,检测地表微量油气信息的化探实验测试技术得到了长足的发展,根据地表化探异常评价深部含油气性的可靠性也大大提高。尽管地表地球化学勘探技术尚无法准确评价油气藏的含油气层系、埋藏深度及其规模,然而国内外勘探实践结果证明,油气地表地球化学勘探在区域含油气性评价、检测圈闭构造中的直接油气信息、钻探靶区优选等方面均取得良好效果,是一种有效的油气勘探手段,对石油地质和地球物理等常规油气勘探方法具有重要的辅助作用。从现有研究和应用成果来看,无论在陆地还是海洋,油气化探技术与常规油气勘探方法相结合在油气勘探开发全过程均能发挥一定的作用。由于地表地球化学勘探技术具有廉价、快速、直接等特点和优势,随着研究的不断深入和方法技术的不断创新,其在我国未来几十年油气勘探中将发挥越来越大的作用。 相似文献
993.
基于一次产品成功FPC(First Product Correct)的原理,研究了凸轮公差优化分配的数学模型及其公差优化设计算法,开发了一套凸轮机构公差优化设计的软件,并进行了实例分析计算;结果表明,该方法保证了凸轮机构公差设计一次达到最优,从而实现了一次产品成功。 相似文献
994.
The present study investigates the success factors (SFs) for implementing wearable sensing devices (WSDs) for safety and health monitoring within the construction industry. A questionnaire survey was designed and administered to stakeholders in the Architectural, Engineering, and Construction (AEC) industry in the United States. A total of 416 valid responses were received from practitioners with experience using WSDs on a construction project. The relative importance and criticality of 25 SFs for WSDs implementation were examined, and survey responses were grouped into general success factors, which were then tested for distinctions across four contingency variables: type of corporation, organization size, levels of Internet of Things (IoT) maturity, and organization experience using WSDs. The results of the statistical analysis revealed the most important SFs for WSDs implementation. The findings of the overall investigation indicate that the critical success factors (CSFs) typically differs depending on the contingency. However, educating and training workers, promoting personalized WSDs, and conducting detailed and continuous assessments of WSDs were identified as key strategies to improve the implementation of WSDs regardless of contingency. Overall, the present study provides a richer understanding of the essential elements required to successfully implement WSDs for safety and health monitoring in construction. Moreover, the present study provides vital information that should inform the development of research frameworks, guidelines, and strategies for improving WSDs integration into construction work processes. 相似文献
995.
The in-line milk analysis system (IMAS) is an automated biosensor technology that samples and quantifies milk progesterone concentrations (P4c) at frequent intervals starting early postpartum until pregnancy. The objective was to validate the use of pregnancy notifications (PregN) generated by an IMAS based on P4c profiles after artificial insemination (AI) to determine pregnancy and nonpregnancy status in dairy cows. Records of 1,821 AI events from 715 Holstein cows that had milk P4c (ng/mL) measured every 2.2 ± 1.9 d (mean ± standard deviation) between 24.5 ± 8.2 and 173.4 ± 49.3 d in milk through a real-time IMAS (Herd Navigator, DeLaval International, Tumba, Sweden) were evaluated. Based on variations in adjusted milk P4c (< vs. ≥ the 5.0 ng/mL threshold), the system determined the sampling frequency, onset and cessation of luteal phases, and pregnancy. If a luteal phase initiated (P4c increased to ≥5.0 ng/mL) after AI and remained uninterrupted, a PregN was generated starting at (mean ± standard deviation) 31.0 ± 4.3 d until 53.4 ± 7.9 d after AI, when sampling stopped, unless a decline in P4c (to <5.0 ng/mL) occurred indicating nonpregnancy and imminent estrus. The assessment of IMAS PregN at 4 weekly intervals was tested, and a confirmed calving occurrence between 262 and 296 d after AI, with no other subsequent AI recorded, was the gold standard for pregnancy. In total, 14.1 (256/1,821), 41.0 (746/1,821), and 50.7% (924/1,821) of AI events were followed by a decline in P4c before 19, 23, and 30 d after AI, respectively. Frequency of the last 3 sampling events preceding P4c decline was greater if P4c decline occurred between 18 and 25 d after AI (1.4 ± 0.5 samples per day) compared with before 17 or beyond 26 d after AI (1.0 ± 0.5 samples per day). At 30 ± 3 (27 to 33) d after AI, PregN occurred in 46.8% (853/1,821) of AI events, of which 15.2% (130/853) had a decline in P4c between 30 and 55 d after AI and 17.1% (146/853) was later confirmed nonpregnant based on the gold standard. A total of 40.7% (742/1,821) of AI events was confirmed pregnant by the gold standard, which was no different than the proportion of PregN at 51 ± 3 (48 to 54) d (40.9%; 744/1,821). At any time point between 27 and 54 d after AI, sensitivity and negative predictive values for PregN were greater than 95.0 and 96.0%, respectively, whereas specificity values were less than 90.0% for PregN before 40 d but greater than 94.0% for PregN beyond 41 d after AI. In conclusion, IMAS is able to diagnose pregnancy based on P4c profiles with high precision and determine early nonpregnancy based on the spontaneous cessation of the luteal phase. However, for accuracy greater than 95.0%, pregnancy declaration based on IMAS notifications alone should occur no earlier than 41 d after AI. 相似文献
996.
Nathan Cofnas 《Critical reviews in food science and nutrition》2019,59(13):2052-2060
According to the Academy of Nutrition and Dietetics' influential position statement on vegetarianism, meat and seafood can be replaced with milk, soy/legumes, and eggs without any negative effects in children. The United States Department of Agriculture endorses a similar view. The present paper argues that the Academy of Nutrition and Dietetics ignores or gives short shrift to direct and indirect evidence that vegetarianism may be associated with serious risks for brain and body development in fetuses and children. Regular supplementation with iron, zinc, and B12 will not mitigate all of these risks. Consequently, we cannot say decisively that vegetarianism or veganism is safe for children. 相似文献
997.
Magorzata Szczuko Justyna Kikut Dominika Maciejewska Danuta Kulpa Zbigniew Celewicz Maciej Zitek 《International journal of molecular sciences》2020,21(23)
Short-chain fatty acids (SCFAs) mediate the transmission of signals between the microbiome and the immune system and are responsible for maintaining balance in the anti-inflammatory reaction. Pregnancy stages alter the gut microbiota community structure, which also synthesizes SCFAs. The study involved 90 pregnant women, divided into two groups: 48 overweight/obese pregnant women (OW) and 42 pregnant women with normal BMI (CG). The blood samples for glucose, insulin, and HBA1c were analyzed as well as stool samples for SCFA isolation (C2:0; C3:0; C4:0i; C4:0n; C5:0i; C5:0n; C6:0i; C6:0n) using gas chromatography. The SCFA profile in the analyzed groups differed significantly. A significant positive correlation between C2:0, C3:0, C4:0n and anthropometric measurements, and between C2:0, C3:0, C4:0n, and C5:0n and parameters of carbohydrate metabolism was found. SCFA levels fluctuate during pregnancy and the course of pregnancy and participate in the change in carbohydrate metabolism as well. The influence of C2:0 during pregnancy on anthropometric parameters was visible in both groups (normal weight and obese). Butyrate and propionate regulate glucose metabolism by stimulating the process of intestinal gluconeogenesis. The level of propionic acid decreases with the course of pregnancy, while its increase is characteristic of obese women, which is associated with many metabolic adaptations. Propionic and linear caproic acid levels can be an important critical point in maintaining lower anthropometric parameters during pregnancy. 相似文献
998.
This paper pioneers the investigation of the significant factors that influence corporate decisions on the use of social media for supply chain social sustainability, and it highlights a crucial research area that is currently understudied in supply chain management literature. A theoretical framework was developed in this study based upon the Technology–Organization–Environment (TOE) and Human–Organization–Technology (HOT) theories to obtain the significant critical success factors (CSFs) which influence the use of social media for supply chain social sustainability in freight logistics firms in Nigeria. The Best-Worst Method was applied to analyse and rank the CSFs using their determined relative importance level. The research findings indicate that customer satisfaction, sufficient security and privacy, affordability and competitive pressure are the highest ranked CSFs to achieve supply chain social sustainability using of social media. This research has important implications for policy makers and practitioners to gain perspectives on how to foster the use of social media in the freight logistics sector for supply chain social sustainability. 相似文献
999.
This study aims to examine the relationship and alignment between business and project strategy and their impact on the success of information and communications technology (ICT) projects. The proposed conceptual model was tested through structural equation modelling (SEM), with an analysis of SmartPLS based on survey data from 144 firms. The results indicate that project success is positively influenced by project strategy, while business strategy shows no impact on project success. In addition, alignment between business strategy and project strategy affects project success positively. 相似文献
1000.
Muhammad Saeed Muhammad Naveed Jannat BiBi Asghar Ali Kamboh Lucas Phil 《Critical reviews in food science and nutrition》2019,59(20):3293-3319
AbstractCoffee is a composite mixture of more than a thousand diverse phytochemicals like alkaloids, phenolic compounds, vitamins, carbohydrates, lipids, minerals and nitrogenous compounds. Coffee has multifunctional properties as a food additive and nutraceutical. As a nutraceutical, coffee has anti-inflammatory, anti-oxidant, antidyslipidemic, anti-obesity, type-2 diabetes mellitus (DM), and cardiovascular diseases (CVD), which can serve for the treatment and prevention of metabolic syndrome and associated disorders. On the other hand, as a food additive, coffee has antimicrobial activity against a wide range of microorganisms, inhibits lipid peroxidation (LPO), and can function as a prebiotic. The outcomes of different studies also revealed that coffee intake may reduce the incidence of numerous chronic diseases, like liver disease, mental health, and it also overcomes the all-cause mortality, and suicidal risks. In some studies, high intake of coffee is linked to increase CVD risk factors, like cholesterol, plasma homocysteine and blood pressure (BP). There is also a little evidence that associated the coffee consumption with increased risk of lung tumors in smokers. Among adults who consume the moderate amount of coffee, there is slight indication of health hazards with strong indicators of health benefits. Moreover, existing literature suggests that it may be cautious for pregnant women to eliminate the chances of miscarriages and impaired fetal growth. The primary purpose of this narrative review is to provide an overview of the findings of the positive impacts and risks of coffee consumption on human health. In conclusion, to date, the best available evidence from research indicates that drinking coffee up to 3–4 cups/day provides health benefits for most people. 相似文献