全文获取类型
收费全文 | 1134篇 |
免费 | 109篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 1篇 |
综合类 | 8篇 |
化学工业 | 377篇 |
金属工艺 | 132篇 |
机械仪表 | 24篇 |
建筑科学 | 7篇 |
矿业工程 | 4篇 |
能源动力 | 170篇 |
轻工业 | 5篇 |
无线电 | 125篇 |
一般工业技术 | 315篇 |
冶金工业 | 64篇 |
原子能技术 | 14篇 |
自动化技术 | 25篇 |
出版年
2024年 | 3篇 |
2023年 | 144篇 |
2022年 | 61篇 |
2021年 | 59篇 |
2020年 | 87篇 |
2019年 | 73篇 |
2018年 | 39篇 |
2017年 | 75篇 |
2016年 | 55篇 |
2015年 | 107篇 |
2014年 | 87篇 |
2013年 | 69篇 |
2012年 | 41篇 |
2011年 | 44篇 |
2010年 | 35篇 |
2009年 | 21篇 |
2008年 | 10篇 |
2007年 | 25篇 |
2006年 | 26篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 24篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 2篇 |
1996年 | 3篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1271条查询结果,搜索用时 16 毫秒
31.
The high pressure phase equilibria of ethyl esters (ethyl decanoate/caprate, ethyl dodecanoate/laurate, ethyl tetradecanoate/myristate and ethyl hexadecanoate/palmitate) in supercritical ethane and propane have been measured in the temperature ranges 311–358 K (TR = 1.02–1.17) and 376–409 K (TR = 1.02–1.11), respectively. The measurements were conducted in a high pressure view cell for ethyl ester mass fractions between 0.015 and 0.65. The results show a generally linear relationship between the phase transition temperature and pressure. No temperature inversions or three phase regions were observed. An increase in hydrocarbon backbone length leads to an increase in phase transition pressure. For ethane as supercritical solvent, this increase is linear. For propane as supercritical solvent, the nature of the increase was not quantified as the magnitude of the increase would be significantly influenced by the experimental measurement error as the observed increase is not very large. Comparison of the phase behaviour of ethyl esters with methyl esters shows very little difference, yet the phase transition pressure of ethyl esters in supercritical ethane and propane is significantly lower than those of the corresponding acids. The phase transition pressure of ethyl esters in ethane and propane is also lower than those in carbon dioxide. 相似文献
32.
33.
Yan Han Yijing Wang Li Li Yaping Wang Lifang Jiao Huatang Yuan Shuangxi Liu 《Electrochimica acta》2011,(9):9821
Flower-like hematite (α-Fe2O3) has been successfully prepared by heat-treatment from the iron(III)-oxyhydroxide precursor, which is obtained by the hydrolysis of FeCl3 solution in the presence of NaClO. In this process, no templates or catalysts are required. SEM and TEM characterizations confirm that micro-flowers are composed of several dozen self-assembled nanopetals with the thickness of about 20 nm. On the basis of the morphology investigations in time-dependent experiments, the possible growth mechanism of the flower-like α-Fe2O3 is proposed, which is similar to a two-stage growth process. Furthermore, as an anode electrode material for rechargeable lithium-ion batteries, the flower-like α-Fe2O3 exhibits excellent electrochemical performance, which can be attributed to the high surface area induced by the flower-like structure, the short lithium diffusion length and the restriction of volume change of the Li+ insertion/extraction. 相似文献
34.
35.
Zheng Xie Xiangxuan Liu Weipeng Wang Can Liu Zhengcao Li Zhengjun Zhang 《Nanoscale research letters》2014,9(1):105
Nanostructured titanium nitride (TiN) films with varying porosity were prepared by the oblique angle deposition technique (OAD). The porosity of films increases as the deposition angle becomes larger. The film obtained at an incident angle of 85° exhibits the best catalytic activity and sensitivity to hydrogen peroxide (H2O2). This could be attributed to its largest contact area with the electrolyte. An effective approach is thus proposed to fabricate TiN nanostructure as H2O2 sensor by OAD. 相似文献
36.
Iodinated polyurethanes (IPUs) with radiopaque property were prepared using poly(oxytetramethylene) glycol, 4,4′‐diphenylmethane diisocyanate, and a novel chain extender. The chain extender, described as N‐(1,3‐dihydroxypropan‐2‐yl)‐2,3,5‐triiodobenzamide, was synthesized in two steps from 2‐aminopropane‐1,3‐diol and 2,3,5‐triiodobenzoic acid with a high yield. A thorough study on the chemical structure, mechanical properties, radiopacity, and physiological properties of the IPUs was conducted. It is revealed that with increasing content of chain extender, the molecular weights of IPUs decreased slightly while the tensile modulus and breaking strength of IPUs increased significantly, illustrating an excellent comprehensive performance. With iodine content high to about 16 wt %, the IPU sample is equal to the aluminum plate with the same thickness in X‐ray radiopacity, meaning that the synthesized polyurethanes are promising as radiopaque materials. The oxidative degradation and cytotoxicity tests illustrated a good performance of stability and biocompatibility for the IPUs. It confirmed that the as‐synthesized IPUs are promising for biomedicine applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42693. 相似文献
37.
Preparation of conductive polyphenylene sulfide/polyamide 6/multiwalled carbon nanotube composites using the slow migration rate of multiwalled carbon nanotubes from polyphenylene sulfide to polyamide 6 下载免费PDF全文
Conductive polyphenylene sulfide (PPS)/polyamide 6 (PA6)/multiwalled carbon nanotube (MWCNT) composites having 10–30 wt % PA6 and 1 wt % MWCNTs are prepared by melt mixing at 300°C for 8 min using a high concentration PPS/MWCNT masterbatch approach, and the migration kinetics of MWCNTs from thermodynamically unfavored PPS to favored PA6 was investigated. The morphology of the composites was investigated by field emission scanning electron microscopy and transmission electron microscopy, showing the localization of most MWCNTs in the PPS phase and at the interface, being different from the case of direct melt mixing where non‐conductive materials were obtained with most MWCNTs found in the PA6 phase and at the interface. The electrical resistivity and morphology of the materials as a function of time were investigated, showing that the conductive materials can be prepared within a mixing time of 4–16 min because of the slow migration rate of MWCNTs from PPS toward PA6, and MWCNTs can eventually migrate into the PA6 phase after a long mixing time of 30 min. The slow migration rate of MWCNTs was attributed to the high viscosity ratio of the two phases. This article shows a good example where the migration of MWCNTs was slow enough to control and can be used to prepare conductive polymer blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42353. 相似文献
38.
《Carbon》2015
We perform classical molecular dynamics simulations to investigate the mechanical compression effect on the thermal conductivity of the single-walled carbon nanotube (SWCNT) forest, in which SWCNTs are closely aligned and parallel with each other. We find that the thermal conductivity can be linearly enhanced by increasing compression before the buckling of SWCNT forests, but the thermal conductivity decreases quickly with further increasing compression after the forest is buckled. Our phonon mode analysis reveals that, before buckling, the smoothness of the inter-tube interface is maintained during compression, and the inter-tube van der Waals interaction is strengthened by the compression. Consequently, the twisting-like mode (good heat carrier) is well preserved and its group velocity is increased by increasing compression, resulting in the enhancement of the thermal conductivity. The buckling phenomenon changes the circular cross section of the SWCNT into ellipse, which causes effective roughness at the inter-tube interface for the twisting motion. As a result, in ellipse SWCNTs, the radial breathing mode (poor heat carrier) becomes the most favorable motion instead of the twisting-like mode and the group velocity of the twisting-like mode drops considerably, both of which lead to the quick decrease of the thermal conductivity with further increasing compression after buckling. 相似文献
39.
Aramid based on poly (p-phenylene terephthalamide) (PPTA) is widely concerned as high-performance materials. Herein, copolymerized aramid nanofibers (CANFs) were prepared for the first time by a direct bottom-up polymerization method without additives. Three kinds of third monomers of m-phenylenediamine, 4,4′-diaminodiphenyl ether, and 2,5-dichloro-1,4-phenylenediamine were separately copolymerized in PPTA and transformed into nanofiber dispersions in water medium. The characterization results revealed the relationship between the morphology of products and the structure as well as dosages of the different kinds of monomers, which was explained by the influence on conjugate regularities of the PPTA molecules. Furthermore, CANFs were used to build aramid paper blended in pure PPTA nanofibers, and the mechanical and insulation properties of composite paper were improved significantly, which would be of potential use as the new building block for aramid composite materials. 相似文献
40.
氨是纺织、制药、化肥等领域重要的化工原料,也是一种清洁的能源载体,需求量大。目前氨的工业生产主要为Haber-Bosch法,反应条件严苛,能源消耗大且碳排放较高。电催化氮气还原(NRR)合成氨是一种在常温常压下进行的反应,工作电位低,且电能可通过清洁能源提供,是一种很有潜力的合成氨新工艺。但目前电催化NRR材料的产氨速率和法拉第效率低、工作稳定性不够高、溶液中痕量氨的定量检测困难及检测标准不统一等都为其发展带来了巨大挑战。本文首先介绍了电催化NRR的反应机理和常用研究方法,然后重点梳理了2019年以来NRR催化材料的最新研究进展,最后对该领域研究面临的挑战和机遇进行了展望。 相似文献