全文获取类型
收费全文 | 926篇 |
免费 | 34篇 |
国内免费 | 71篇 |
专业分类
电工技术 | 7篇 |
综合类 | 37篇 |
化学工业 | 263篇 |
金属工艺 | 42篇 |
机械仪表 | 29篇 |
建筑科学 | 2篇 |
矿业工程 | 5篇 |
能源动力 | 42篇 |
轻工业 | 16篇 |
水利工程 | 1篇 |
石油天然气 | 8篇 |
无线电 | 198篇 |
一般工业技术 | 268篇 |
冶金工业 | 12篇 |
原子能技术 | 9篇 |
自动化技术 | 92篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 11篇 |
2018年 | 3篇 |
2017年 | 33篇 |
2016年 | 49篇 |
2015年 | 23篇 |
2014年 | 23篇 |
2013年 | 36篇 |
2012年 | 33篇 |
2011年 | 55篇 |
2010年 | 31篇 |
2009年 | 50篇 |
2008年 | 58篇 |
2007年 | 94篇 |
2006年 | 83篇 |
2005年 | 38篇 |
2004年 | 54篇 |
2003年 | 33篇 |
2002年 | 30篇 |
2001年 | 30篇 |
2000年 | 52篇 |
1999年 | 38篇 |
1998年 | 29篇 |
1997年 | 29篇 |
1996年 | 25篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 17篇 |
1992年 | 12篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1031条查询结果,搜索用时 0 毫秒
1.
Li Xi Zuoyan Peng Wei Fan Kui Guo Gu Jianmin Muyu Zhao Wu Guoqiang 《Materials Science and Engineering: B》1996,40(2-3):147-152
SrMgxTi1 - xO3 nanocrystals (x = 0.1–0.6) were synthesized by the stearic acid gel method. Powder samples were characterized by X-ray diffraction and X-ray photoelectron (XP) spectroscopy. The results showed that the lattice parameter a and the O 1s XP spectrum changed not only with the Mg content x but also with the grain size d of the samples. The conductivity of a thick film specimen fabricated on an aluminium oxide wafer was investigated in a nitrogen—oxygen atmosphere. 相似文献
2.
3.
Feng-En Teng Benwei Yang Yuming Wang 《Metallurgical and Materials Transactions A》1992,23(10):2859-2861
Making use of the data obtained already in our laboratory on elongated, quenched samples of austenitic steel lCrl8Ni9, such
as the effective domain size Deff, the average dislocation density-ρ, the average dislocation configuration parameter, -M, the range of strain field -Re, the elastic energy density 〈E/V〉,etc., some exact and clear expressions for the relation of intrinsic stack-ing fault (SF) density α′, extrinsic SF density α″,
twin fault density β, SF energy γ, true particle size D0, minimum value of the fault width Tmin, and maximum particle size Dmax are given. 相似文献
4.
Investigation of the reaction mechanism of chloromethane on ZSM5 is a new topic. In this work an in situ FTIR technique was employed to study the conversion processes of chloromethane, the active sites on HZSM5, and the desorption state of surface species. The catalytic conversion of chloromethane to higher hydrocarbons was also studied. It is demonstrated that chloromethane can be reversibly adsorbed on acidic sites of HZSM5 at room temperature. At 100°C chloromethane is irreversibly and dissociatively adsorbed on the strong acidic sites of HZSM5, on which surface methoxyl is formed as proved by infrared characteristic C-H stretchings of-CH3 at 2960 and 2870 cm–1. Alkoxyls are produced and adsorbed on the catalyst surface as characterized by the infrared absorption bands of -CH2-groups at 1460 and 2930 cm–1. At 100°C the adsorbed methoxyl and alkoxyls are the main surface species, and a small amount of aromatics might exist as detected by a characteristic absorption band at 1510 cm–1. Between 100 and 200°C the adsorbed surface methoxyl and alkoxyls are converted to aromatics, and the occupied OH groups partially appear. At temperature higher than 300°C the adsorbed aromatics are thermally desorbed into the gas phase. Aromatics and alkanes are the main products in catalytic conversion. These results reveal that the formation of aromatics from methoxyl and alkoxyls is easier than the desorption of aromatics from HZSM5 catalyst. An alkoxyl mechanism is proposed for the conversion of chloromethane on HZSM5 based upon the experimental results and the three assumptions: (a) The primary C-C bond is formed from surface methoxyl groups via the methoxyl group polarization and C-H bond weakening, (b) The adsorbed alkoxyls are converted to aromatics via hydrogen transfer and bond rearrangement similar to the conventional carbenium ion mechanism for the aromatization of olefins and alkanes on HZSM5. The hydrogen atoms from the aromatization stimulate the desorption of alkoxyls to alkanes. (c) At temperature higher than 300°C surface reactions and desorption of adsorbed species take place simultaneously, determining the product distribution in the catalytic conversion. 相似文献
5.
Ren X Xue Y Liu J Zhang K Zheng J Luo G Guo C Mu Y Shen J 《Chembiochem : a European journal of chemical biology》2002,3(4):356-363
A novel dicyclodextrinyl ditelluride (2-TeCD) compound was devised as a functional mimic of the glutathione peroxidase (GPX) enzymes that normally remove hydroperoxides from the cell. The GPX activity of the mimic was found to be 46.7 U microM(-1), which is 46 times as active as Ebselen, a well-known GPX mimic. A detailed steady-state kinetic study was undertaken to probe the reason for the high catalytic efficiency of 2-TeCD. This high efficiency can be explained based on both the binding of the substrate to the cyclodextrin and the catalytic mechanism of 2-TeCD, which is different from that of diselenide compounds. 2-TeCD exhibits good water solubility and is chemically and biologically stable. The biological effect of 2-TeCD was evaluated by its ability to protect mitochondria from oxidative damage. 2-TeCD exhibited excellent antioxidant capacity in comparison with Ebselen. 相似文献
6.
By means of the molecular dynamics (MD) simulation, the crystallization mechanism of 22,8-polyurethane which contains hydrogen-bond units is investigated and the results show that the crystallization process at a fixed temperature can be characterized by three stages: (1) The extended chain collapses to a globular random coil; (2) The random coil reorganizes into an ordered lamellar structure; (3) Accompanied with the segments clustering due to the hydrogen-bond formation, the lamellar develops with local defects. Two kinds of hydrogen-bond, which are formed between NH group and CO group (N-H?OC), and between NH group and urethane alkoxy oxygen (N-H?O), respectively, are found to play an important role in the crystallization process of 22,8-polyurethane. Furthermore, the effect of temperature on the crystallization is also studied by selecting three temperatures 200, 300 and 400 K. The lower the crystal temperature is, the slower the crystallization rate is and the stronger the hydrogen-bonding interactions are presented. This is in harmony with the experimental results. 相似文献
7.
Minhao Jiang Xiangyu Yan Yibo Wang Fang Pu Huiling Liu Yumei Li Chunfeng Yang Jiawei Zhu Xuemeng Liu Jinsong Ren Xiaogang Qu 《Advanced functional materials》2023,33(24):2300091
Hydrogen-bond organic frameworks (HOFs) with excellent structural and luminescent properties have emerged as a promising material for the construction of fluorescence sensors. However, designing a facile, universal and high throughput sensor with multiplex detection capacity still remains challenging. Herein, a one-component sensor array is constructed that mimics natural gustatory system for accurate and high-throughput discrimination and identification of versatile analytes. HOF as a single sensing element greatly simplifies the probe preparation in sensor array and detection procedure. Metal ions, proteins and bacteria as the model targets are rapid and accurately discriminated, presenting the universality of the system. Particularly, the system is successfully used for the classification of antibiotic mechanisms. The study expands the application scope of HOFs and provides a facile and universal system for sensing applications. 相似文献
8.
提出一个由不完备投影数据重建图象的有理逼近方法。该方法首先引入图象象素间连接的假设,然后导出满足最优解的线性方程组,再通过在此方程组中引入一个人工参数将其变形,并用摄动展开方法解新形成的线性方程组,再利用向量值函数的有理逼近来构造原线性方程组的解。该方法还避免了原方程组直接求解计算量非常大的问题,因为使用该有理逼近方法,只需展开几项,便可获得较满意的重建图象。 相似文献
9.
将嗜热菌Geobacillus Kaustophilus HTA426中的磷酸三酯酶基因转入毕赤酵母GS115中,整合到染色体DNA基因组上,并进行诱导表达.SDS-PAGE和Western-blot试验结果显示,重组蛋白是一个分子量约为50KD的磷酸三酯酶二聚体.酶活检测证明重组蛋白具有较高的磷酸三酯酶活性,其最适温度为70℃,最适pH为10.0. 相似文献
10.
《Optical Materials》2005,27(2):315-321
The one-photon absorption and two-photon absorption (TPA) properties of a series of pyrazoline derivatives have been theoretically investigated by means of density functional theory and ZINDO-SOS method. On the basis of optimized geometry and UV–vis spectrum, the position and strength of the TPA for molecules are reported. The theoretical findings are consistent with the experimental observations. It is found that a most crucial role in increasing TPA cross-section is played by the conjugated length and the introduction of donors. The calculated maximum TPA cross-section values are in the range of 360–1760 × 10−50 cm4 s/photon. The TPA response will be as another possible application for derived pyrazoline. 相似文献