全文获取类型
收费全文 | 232934篇 |
免费 | 20953篇 |
国内免费 | 11122篇 |
专业分类
电工技术 | 14321篇 |
技术理论 | 31篇 |
综合类 | 23585篇 |
化学工业 | 30150篇 |
金属工艺 | 11267篇 |
机械仪表 | 12051篇 |
建筑科学 | 31123篇 |
矿业工程 | 12717篇 |
能源动力 | 8562篇 |
轻工业 | 17561篇 |
水利工程 | 10728篇 |
石油天然气 | 11898篇 |
武器工业 | 3320篇 |
无线电 | 15380篇 |
一般工业技术 | 20665篇 |
冶金工业 | 11857篇 |
原子能技术 | 1898篇 |
自动化技术 | 27895篇 |
出版年
2024年 | 878篇 |
2023年 | 2976篇 |
2022年 | 5756篇 |
2021年 | 7802篇 |
2020年 | 7308篇 |
2019年 | 5678篇 |
2018年 | 5273篇 |
2017年 | 6608篇 |
2016年 | 8137篇 |
2015年 | 8806篇 |
2014年 | 15779篇 |
2013年 | 14205篇 |
2012年 | 16638篇 |
2011年 | 18653篇 |
2010年 | 13729篇 |
2009年 | 14005篇 |
2008年 | 12886篇 |
2007年 | 15476篇 |
2006年 | 13997篇 |
2005年 | 12233篇 |
2004年 | 10279篇 |
2003年 | 8865篇 |
2002年 | 7266篇 |
2001年 | 5966篇 |
2000年 | 5177篇 |
1999年 | 4035篇 |
1998年 | 2942篇 |
1997年 | 2588篇 |
1996年 | 2115篇 |
1995年 | 1760篇 |
1994年 | 1492篇 |
1993年 | 1089篇 |
1992年 | 925篇 |
1991年 | 682篇 |
1990年 | 596篇 |
1989年 | 521篇 |
1988年 | 312篇 |
1987年 | 222篇 |
1986年 | 197篇 |
1985年 | 232篇 |
1984年 | 191篇 |
1983年 | 143篇 |
1982年 | 84篇 |
1981年 | 95篇 |
1980年 | 91篇 |
1979年 | 45篇 |
1978年 | 29篇 |
1977年 | 35篇 |
1975年 | 23篇 |
1959年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 640 毫秒
51.
This paper investigates the relationship between economic growth, carbon dioxide (CO2) emissions, and energy consumption with an aim to test the validity of the Environmental Kuznets Curve (EKC) hypothesis in five ASEAN (Association of South East Asian Nations) countries (Indonesia, Malaysia, Philippines, Singapore, and Thailand) by applying the panel smooth transition regression (PSTR) model as a new econometric technique. The PSTR model is more flexible and appropriate for describing cross-country heterogeneity and time instability. Our empirical results strongly rejected the null hypothesis of linearity, and the test for no remaining nonlinearity indicated a model with one transition function and two threshold parameters. The first regime (levels of GDP per capita below 4686 USD) showed that environmental degradation increases with economic growth while the trend was reversed in the second regime (GDP per capita above 4686 USD). The results also showed that energy consumption with either the first or the second regime lead to increase CO2. The overall results support the validity of the EKC hypothesis in the ASEAN countries. 相似文献
52.
This study proposes that a novel integrated circuit (IC) and system design for renewable energy inverters can harvest renewable energy to power direct current (DC) and alternating current (AC) loads. In addition, an intelligent synthesis and management tool is developed to design the proposed system and to judge the system’s operational maintenance decisions. Finally, a renewable energy inverter’s information is posted to an online system. Users can obtain the proposed system’s information at any time and place. The accurate and superior performance of the proposed IC and system is confirmed by computer simulations and experimental results. 相似文献
53.
54.
《Food Control》2015
The aim of the study was to investigate annual and regional differences in the level of aflatoxin B1 (AFB1) in grains and dairy cattle feed. Maize (n = 972), wheat (n = 201), barley (n = 147), oat (n = 136), grain mixtures (n = 168), and dairy cattle feed (n = 325) were sampled from 2009 to 2013 on different farms and in different farm factories situated in four Croatian regions. The samples were analysed for AFB1 using the validated ELISA immunoassay. AFB1 was determined in 16.4% of all investigated samples, among which maize was proven to be the most contaminated, with 21.7% of the samples recovered during 2013 harbouring AFB1 in concentrations over the permissible ones. Levels higher than permitted were observed in 17.9% and 12.3% of grain mixtures and dairy cattle feed, respectively, whereas concentrations of AFB1 determined in other crops throughout the investigated period met the stipulated requirements. The results revealed the AFB1 occurrence to be significantly (p < 0.05) dependent on the cultivation region, with the highest levels generally found in maize harvested in 2013 and consequently in grain mixtures and cattle feed that can most likely be associated with climatic conditions as the most critical factor for mould formation, and thus also AFB1 production. 相似文献
55.
为检查工程质量,查找输水系统可能存在的问题并消除隐患,保障电站安全运行,福建仙游抽水蓄能电站在投产发电前,要对输水发电系统进行充水试验与放空排水试验,在试验过程中监测输水系统的应力、应变与渗漏水情况。本文以尾水系统为例,介绍了试验所应具备的工程条件、工作程序及技术要求、试验成果分析和存在问题处理等。试验表明,仙游抽水蓄能电站尾水系统设计合理,施工质量优良,结构可靠,可供同类工程参考与借鉴。 相似文献
56.
氢工质在新能源与动力、航天推进、化工材料等领域有着广泛应用。通过开展高温氢工质热力学与输运性质研究,建立了原子态氢、分子态氢、热解平衡态氢的热物理性质计算模型,开发了热物性计算程序Prop_H_H2,适用范围为温度100~3 500 K、压力104~5×107 Pa 。验证表明,Prop_H_H2在适用范围内计算氢工质的物性参数合理可靠,在温度200~3 000 K、压力104~107 Pa范围内,程序预测值更加准确,相对偏差在±5%左右。本研究可为氢工质相关的航天推进、应用物理学、能源动力等行业的科研和应用提供支持借鉴。 相似文献
57.
58.
59.
Dr. Tomasz Ratajczyk Prof. Dr. Gerd Buntkowsky Dr. Torsten Gutmann Dr. Bartłomiej Fedorczyk Dr. Adam Mames Dr. Mariusz Pietrzak Zuzanna Puzio Piotr Grzegorz Szkudlarek 《Chembiochem : a European journal of chemical biology》2021,22(5):855-860
The biorelevant PyFALGEA oligopeptide ligand, which is selective towards the epidermal growth factor receptor (EGFR), has been successfully employed as a substrate in magnetic resonance signal amplification by reversible exchange (SABRE) experiments. It is demonstrated that PyFALGEA and the iridium catalyst IMes form a PyFALGEA:IMes molecular complex. The interaction between PyFALGEA:IMes and H2 results in a ternary SABRE complex. Selective 1D EXSY experiments reveal that this complex is labile, which is an essential condition for successful hyperpolarization by SABRE. Polarization transfer from parahydrogen to PyFALGEA is observed leading to significant enhancement of the 1H NMR signals of PyFALGEA. Different iridium catalysts and peptides are inspected to discuss the influence of their molecular structures on the efficiency of hyperpolarization. It is observed that PyFALGEA oligopeptide hyperpolarization is more efficient when an iridium catalyst with a sterically less demanding NHC ligand system such as IMesBn is employed. Experiments with shorter analogues of PyFALGEA, that is, PyLGEA and PyEA, show that the bulky phenylalanine from the PyFALGEA oligopeptide causes steric hindrance in the SABRE complex, which hampers hyperpolarization with IMes. Finally, a single-scan 1H NMR SABRE experiment of PyFALGEA with IMesBn revealed a unique pattern of NMR lines in the hydride region, which can be treated as a fingerprint of this important oligopeptide. 相似文献
60.
Reliability based criteria are quite popular for optimal sensor network design. We present a modified definition of system reliability for sensor network design for two applications: reliable estimation of variables in a steady state linear flow process, and reliable fault detection and diagnosis for any process. Unlike the weakest-link based definition of system reliability in the literature, the proposed definition considers the entire system and is consistent with the reliability concept used in classical reliability literature. For each application, dual approaches for defining system reliability are proposed, and their analogy with the reliability problem in the classical reliability literature is established. Using examples and stochastic simulations, the advantage of using the proposed system reliability in contrast to the existing definition is illustrated. Part II of this series of articles presents methods for efficient generation of the system reliability function and its use in optimization-based approaches for designing optimal sensor networks. 相似文献