全文获取类型
收费全文 | 245792篇 |
免费 | 3525篇 |
国内免费 | 1242篇 |
专业分类
电工技术 | 4871篇 |
综合类 | 278篇 |
化学工业 | 35939篇 |
金属工艺 | 10947篇 |
机械仪表 | 7136篇 |
建筑科学 | 6499篇 |
矿业工程 | 505篇 |
能源动力 | 6376篇 |
轻工业 | 24282篇 |
水利工程 | 1861篇 |
石油天然气 | 1335篇 |
武器工业 | 3篇 |
无线电 | 31244篇 |
一般工业技术 | 45486篇 |
冶金工业 | 50235篇 |
原子能技术 | 3870篇 |
自动化技术 | 19692篇 |
出版年
2021年 | 1660篇 |
2019年 | 1519篇 |
2018年 | 2437篇 |
2017年 | 2307篇 |
2016年 | 2582篇 |
2015年 | 2033篇 |
2014年 | 3309篇 |
2013年 | 10999篇 |
2012年 | 5666篇 |
2011年 | 8041篇 |
2010年 | 6452篇 |
2009年 | 7118篇 |
2008年 | 7709篇 |
2007年 | 7818篇 |
2006年 | 7120篇 |
2005年 | 6597篇 |
2004年 | 6319篇 |
2003年 | 6309篇 |
2002年 | 6297篇 |
2001年 | 6399篇 |
2000年 | 5827篇 |
1999年 | 6447篇 |
1998年 | 16588篇 |
1997年 | 11632篇 |
1996年 | 8974篇 |
1995年 | 6708篇 |
1994年 | 5923篇 |
1993年 | 5743篇 |
1992年 | 4068篇 |
1991年 | 4007篇 |
1990年 | 3590篇 |
1989年 | 3507篇 |
1988年 | 3445篇 |
1987年 | 2910篇 |
1986年 | 2843篇 |
1985年 | 3421篇 |
1984年 | 3060篇 |
1983年 | 2752篇 |
1982年 | 2549篇 |
1981年 | 2572篇 |
1980年 | 2432篇 |
1979年 | 2274篇 |
1978年 | 2239篇 |
1977年 | 2812篇 |
1976年 | 4174篇 |
1975年 | 1903篇 |
1974年 | 1796篇 |
1973年 | 1785篇 |
1972年 | 1462篇 |
1971年 | 1317篇 |
排序方式: 共有10000条查询结果,搜索用时 973 毫秒
1.
2.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration. 相似文献
3.
Wireless Personal Communications - Besides anti-malware usage for the eradication of malicious attacks, researchers have developed epidemic models in order to gain more insights into the spread... 相似文献
4.
Optimization and Engineering - 相似文献
5.
A. Nakano T. Shimazaki M. Sekiya H. Shiozawa K. Ohtsuka A. Aoyagi T. Iwakiri Z. Mikami M. Sato Y. Sugino K. Kinoshita T. Matsuoka T. Imamura Y. Takayama K. Yamamoto 《International Journal of Hydrogen Energy》2021,46(29):15649-15659
Monitoring the temperature in liquid hydrogen (LH2) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa. 相似文献
6.
Anne-Margarethe Enge Florian Kaltner Christoph Gottschalk Albert Braeuning Stefanie Hessel-Pras 《International journal of molecular sciences》2021,22(8)
1,2-unsaturated pyrrolizidine alkaloids (PAs) are secondary plant metabolites occurring as food contaminants that can cause severe liver damage upon metabolic activation in hepatocytes. However, it is yet unknown how these contaminants enter the cells. The role of hepatic transporters is only at the beginning of being recognized as a key determinant of PA toxicity. Therefore, this study concentrated on assessing the general mode of action of PA transport in the human hepatoma cell line HepaRG using seven structurally different PAs. Furthermore, several hepatic uptake and efflux transporters were targeted with pharmacological inhibitors to identify their role in the uptake of the PAs retrorsine and senecionine and in the disposition of their N-oxides (PANO). For this purpose, PA and PANO content was measured in the supernatant using LC-MS/MS. Also, PA-mediated cytotoxicity was analyzed after transport inhibition. It was found that PAs are taken up into HepaRG cells in a predominantly active and structure-dependent manner. This pattern correlates with other experimental endpoints such as cytotoxicity. Pharmacological inhibition of the influx transporters Na+/taurocholate co-transporting polypeptide (SLC10A1) and organic cation transporter 1 (SLC22A1) led to a reduced uptake of retrorsine and senecionine into HepaRG cells, emphasizing the relevance of these transporters for PA toxicokinetics. 相似文献
7.
Abulyazied Dalia E. Alturki Asma M. Youness Rasha A. Abomostafa H. M. 《Journal of Inorganic and Organometallic Polymers and Materials》2021,31(10):4077-4092
Journal of Inorganic and Organometallic Polymers and Materials - In this work, a borosilicate glass sample (5SiO2–45B2O3–20Na2O–25CaO–5Ag2O) was added to nano-sized... 相似文献
8.
Dr. Thomas Le Bihan Dr. Cathryn H. S. Driver Dr. Thomas Ebenhan Dr. Nathalie Le Bris Dr. Jan Rijn Zeevaart Prof. Dr. Raphaël Tripier 《ChemMedChem》2021,16(5):809-821
An improved glucose-chelator-albumin bioconjugate (GluCAB) derivative, GluCAB-2Mal, has been synthesized and studied for in vivo 64Cu-PET/CT imaging in breast cancer mice models together with its first-generation analogue GluCAB-1Mal. The radioligand works on the principle of tumor targeting through the enhanced permeability and retention (EPR) effect with a supportive role played by glucose metabolism. [64Cu]Cu-GluCAB-2Mal (99 % RCP) exhibited high serum stability with immediate binding to serum proteins. In vivo experiments for comparison between tumor targeting of [64Cu]Cu-GluCAB-2Mal and previous-generation [64Cu]Cu-GluCAB-1Mal encompassed microPET/CT imaging and biodistribution analysis in an allograft E0771 breast cancer mouse model. Tumor uptake of [64Cu]Cu-GluCAB-2Mal was clearly evident with twice as much accumulation as compared to its predecessor and a tumor/muscle ratio of up to 5 after 24 h. Further comparison indicated a decrease in liver accumulation for [64Cu]Cu-Glu-CAB-2Mal. 相似文献
9.
During the service life of structural sealant glazing (SSG) facades, the load-bearing capacity of the silicone bonds needs to be guaranteed. Laboratory tests can assess the durability of SSG-systems based on mechanical characteristics of the bond after simultaneous exposure to both climatic and mechanical loads. This article studies how the material characteristics of two common structural sealants are affected by laboratory and field exposure. Dynamic mechanical analysis (DMA) confirms a reduction in the dynamic modulus of exposed silicone samples. Results from thermogravimetric analysis, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and small-angle X-ray scattering/wide-angle X-ray scattering show differences between the two sealants and indicate no/minor changes in the composition and morphology of the laboratory and field exposed sealants. Mechanical characterization methods, such as DMA, and tensile and shear testing of the structural bond, are shown to be sensitive toward the combined climatic and mechanical loadings, and are hence suitable for studying degradation mechanisms of structural sealants. 相似文献
10.