全文获取类型
收费全文 | 28155篇 |
免费 | 2926篇 |
国内免费 | 1561篇 |
专业分类
电工技术 | 1671篇 |
综合类 | 3043篇 |
化学工业 | 3471篇 |
金属工艺 | 1181篇 |
机械仪表 | 1622篇 |
建筑科学 | 4934篇 |
矿业工程 | 1145篇 |
能源动力 | 1553篇 |
轻工业 | 1489篇 |
水利工程 | 912篇 |
石油天然气 | 2110篇 |
武器工业 | 279篇 |
无线电 | 2771篇 |
一般工业技术 | 2315篇 |
冶金工业 | 1521篇 |
原子能技术 | 537篇 |
自动化技术 | 2088篇 |
出版年
2024年 | 77篇 |
2023年 | 339篇 |
2022年 | 689篇 |
2021年 | 812篇 |
2020年 | 921篇 |
2019年 | 847篇 |
2018年 | 763篇 |
2017年 | 1007篇 |
2016年 | 1132篇 |
2015年 | 1179篇 |
2014年 | 1636篇 |
2013年 | 1792篇 |
2012年 | 2197篇 |
2011年 | 2276篇 |
2010年 | 1700篇 |
2009年 | 1633篇 |
2008年 | 1594篇 |
2007年 | 1970篇 |
2006年 | 1741篇 |
2005年 | 1397篇 |
2004年 | 1145篇 |
2003年 | 1018篇 |
2002年 | 841篇 |
2001年 | 704篇 |
2000年 | 579篇 |
1999年 | 493篇 |
1998年 | 345篇 |
1997年 | 345篇 |
1996年 | 279篇 |
1995年 | 251篇 |
1994年 | 222篇 |
1993年 | 143篇 |
1992年 | 139篇 |
1991年 | 91篇 |
1990年 | 73篇 |
1989年 | 71篇 |
1988年 | 43篇 |
1987年 | 32篇 |
1986年 | 18篇 |
1985年 | 27篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
单螺杆膨胀机作为有机朗肯循环系统中最适合的膨胀机类型之一,其性能对循环系统有重要影响。本文实验研究了有机朗肯循环系统中单螺杆膨胀机机壳及润滑油的散热损失及其在不同工况下对膨胀机性能的影响。实验结果表明,当进气温度由80℃升至123℃时,单螺杆膨胀机的散热损失增大,其中润滑油散热损失为主要散热损失,其散热量从0. 5 k W增至1. 05k W。随着膨胀比的增加,各散热损失占比逐渐减小。其中,当进气温度由80℃升至123℃时,机壳散热损失占比为5. 1%~2. 5%,润滑油散热损失占比为16. 1%~9. 5%。说明随着进气温度的增加,膨胀机性能逐渐改善,工质气体通过散热损失的能量比例逐渐减小,散热损失对膨胀机性能的影响逐渐减小。 相似文献
992.
993.
文章设计了一种具有可调增益功能的振动监测系统。首先从监测层和测量层两个方面提出了振动监测系统的整体框架,之后给出了硬件系统和软件系统的设计方法及软件实现代码,利用控制芯片和可调增益放大器,在监测系统中整合了一套可根据采集信号幅值大小调整增益的数据采集装置;利用模拟信号发生器对不加增益和设置可调增益之后的两种信号进行了对比分析,并在汽轮发电机组实际工况下进行了振动信号采集。结果表明,具备可调增益功能的振动监测系统可有效提高采集信号的信噪比,提高汽轮发电机组的振动监测能力。 相似文献
994.
Asymmetric bilayer membranes have been regarded as ideal wound dressings for skin regeneration. Our previous work reported the potential advantages of polydimethylsiloxane modified gelatin/silicone rubber (PGE/SR) asymmetric bilayer membrane as a wound dressing. However, it is still unknown whether the proportion of the two components of the bilayer membrane has a prominent influence on its relevant performance. Herein, various PGE/SR membranes with different PGE:SR weight ratios (100:25, 100:50 and 100:100) were fabricated through a self‐stratification method driven by surface tension gradients. Subsequently, the effects of the PGE:SR ratios on the relevant performance (i.e. porous structure, mechanical properties, degradability and biocompatibility) of PGE/SR membranes were systematically investigated. The current results demonstrate that the separating force between the PGE and SR components was reduced significantly on increasing the content of SR, and in particular the PGE/SR1 membrane (100:25) exhibited a well‐defined asymmetric bilayer structure with high porosity, appropriate toughness, water uptake, swelling ratio and water permeability. Concomitantly, the maximum weight loss for the PGE/SR1 membrane was ca 70.65% after 9 days of enzymatic degradation, which met the typical healing period of a normal skin wound. In addition, both the original and degraded PGE/SR1 membrane possessed favorable cytocompatibility in vitro, suggesting its potential application as a wound dressing. © 2019 Society of Chemical Industry 相似文献
995.
《Ceramics International》2021,47(18):26034-26041
The structure and spinnability of sol are essential for obtaining high-performance continuous alumina-based fibres. Herein, the surface electrostatic potential analysis and conventional experimental methods (X-ray diffraction, Fourier-transform infrared spectroscopy, 27Al nuclear magnetic resonance solution spectra and rheological methods) were combined to investigate and discuss the relationship between the structure and spinnability of aluminium carboxylate sols with different formic-acid-to-acetic-acid molar ratios. The results showed that the aluminium carboxylate sol structure changed with the formic-acid-to-acetic-acid molar ratio and greatly affected the sol's spinnability. The tetramer (AlO6 oligomer) products comprising two effective active carboxylate groups in the sol increased with the formic acid content, which helped form linear long-chain polymers. However, excess formic acid content led to a large increase of AlO6 monomer products that were unable to form linear long-chain polymers, which decreased the sol's spinnability. When the formic-acid-to-acetic-acid molar ratio was 1.15:0.85, the sol containing more AlO6 oligomer products had the best spinnability. Furthermore, α-Al2O3 ceramic fibres with good morphology, small grains and uniform diameter distribution were obtained after calcination at 1200 °C. 相似文献
996.
997.
Jose M Ayuso Shujah Rehman Mehtab Farooqui María Virumbrales-Muoz Vijayasaradhi Setaluri Melissa C Skala David J Beebe 《International journal of molecular sciences》2020,21(23)
Tumor-specific metabolic adaptations offer an interesting therapeutic opportunity to selectively destroy cancer cells. However, solid tumors also present gradients of nutrients and waste products across the tumor mass, forcing tumor cells to adapt their metabolism depending on nutrient availability in the surrounding microenvironment. Thus, solid tumors display a heterogenous metabolic phenotype across the tumor mass, which complicates the design of effective therapies that target all the tumor populations present. In this work, we used a microfluidic device to study tumor metabolic vulnerability to several metabolic inhibitors. The microdevice included a central chamber to culture tumor cells in a three-dimensional (3D) matrix, and a lumen in one of the chamber flanks. This design created an asymmetric nutrient distribution across the central chamber, generating gradients of cell viability. The results revealed that tumor cells located in a nutrient-enriched environment showed low to no sensitivity to metabolic inhibitors targeting glycolysis, fatty acid oxidation, or oxidative phosphorylation. Conversely, when cell density inside of the model was increased, compromising nutrient supply, the addition of these metabolic inhibitors disrupted cellular redox balance and led to tumor cell death. 相似文献
998.
Traditional optimization methods, which take a specific order of modal frequency as the design constraint, could fail to obtain the desired solution because of modal substitution. An improved optimization model with continuous sizing variables is established to solve this problem, in which the minimum weight and a given local modal frequency are considered as the objective and the constraint. To capture accurately the expected mode of vibration, a local mode identification technique is proposed based on the strain energy ratio between the local area and the whole structure. With that scheme, an optimization system is developed, in which the local mode can be effectively identified and the constraint can be updated with it in the iteration process. Two numerical examples, of a reinforced plate and a satellite structure, are applied to illustrate the effectiveness and efficacy of the proposed method. 相似文献
999.
Lithium‐sulfur batteries have attracted much research interest because of their high theoretical energy density and low‐cost raw materials. While the electrodes are composed of readily available materials, the processes that occur within the cell are complex, and the electrochemical performance of these batteries is very sensitive to a number of cell processing parameters. Herein, a simple electrochemical model will be used to predict, with quantitative agreement, the electrochemical properties of lithium‐sulfur cathodes with varying carbon to sulfur ratios. The discharge capacity and the polarization were very similar for the lowest sulfur loadings, while above 23.2 wt% sulfur the gravimetric capacity dropped significantly, and there was an increase in the cell polarization. In addition, a transition in the electrode morphology, from well dispersed to aggregated sulfur at the surface, will be reflected in the change in a critical model parameter demonstrating the sensitivity and functionality of even this simple model in predicting complex behavior in the lithium‐sulfur cells. 相似文献
1000.