全文获取类型
收费全文 | 60514篇 |
免费 | 5373篇 |
国内免费 | 3074篇 |
专业分类
电工技术 | 3920篇 |
技术理论 | 4篇 |
综合类 | 4322篇 |
化学工业 | 9787篇 |
金属工艺 | 3375篇 |
机械仪表 | 3927篇 |
建筑科学 | 4529篇 |
矿业工程 | 1312篇 |
能源动力 | 1698篇 |
轻工业 | 4374篇 |
水利工程 | 1188篇 |
石油天然气 | 2639篇 |
武器工业 | 484篇 |
无线电 | 7642篇 |
一般工业技术 | 7764篇 |
冶金工业 | 3105篇 |
原子能技术 | 761篇 |
自动化技术 | 8130篇 |
出版年
2024年 | 240篇 |
2023年 | 877篇 |
2022年 | 1679篇 |
2021年 | 2362篇 |
2020年 | 1707篇 |
2019年 | 1529篇 |
2018年 | 1622篇 |
2017年 | 1831篇 |
2016年 | 1840篇 |
2015年 | 2475篇 |
2014年 | 2974篇 |
2013年 | 3631篇 |
2012年 | 3890篇 |
2011年 | 4298篇 |
2010年 | 3880篇 |
2009年 | 3540篇 |
2008年 | 3568篇 |
2007年 | 3296篇 |
2006年 | 3277篇 |
2005年 | 2832篇 |
2004年 | 2093篇 |
2003年 | 1996篇 |
2002年 | 2270篇 |
2001年 | 1892篇 |
2000年 | 1519篇 |
1999年 | 1345篇 |
1998年 | 1276篇 |
1997年 | 1010篇 |
1996年 | 888篇 |
1995年 | 725篇 |
1994年 | 633篇 |
1993年 | 473篇 |
1992年 | 331篇 |
1991年 | 267篇 |
1990年 | 196篇 |
1989年 | 155篇 |
1988年 | 135篇 |
1987年 | 82篇 |
1986年 | 70篇 |
1985年 | 46篇 |
1984年 | 32篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 24篇 |
1980年 | 27篇 |
1979年 | 8篇 |
1977年 | 16篇 |
1976年 | 43篇 |
1975年 | 9篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
利用引进的制造技术和设备,制作出了 APT(STLRI)—1.78型系列化光纤连接器。 相似文献
22.
23.
Y. K. Cheung W. G. Jin O. C. Zienkiewicz 《International journal for numerical methods in engineering》1991,32(1):63-78
The application of the Trefftz method for calculating wave forces on offshore structures is presented. Indirect and direct formulations using complete and non-singular systems of Trefftz functions for the Helmholtz equation are posed in this paper. An effective technique using different interpolation functions for the velocity potential and wave force are suggested to improve the computational accuracy of the wave force. The numerical examples show that the present method is highly efficient and accurate. 相似文献
24.
25.
26.
27.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
28.
Jin‐Hong Kim 《Polymer Engineering and Science》2008,48(1):97-101
Polyetherimide (PEI) substrate for next‐generation high density optical data storage is fabricated and characterized. Cover‐layer incident or first‐surface recording configurations do not require optical properties of the substrate, which are the prerequisite conditions for the conventional material of polycarbonate (PC). Instead of the optical properties, good mechanical properties with a sufficient transcribability are required. Even though PEI has higher glass transition temperature than that of PC, a microscopic transcribability of PEI is comparable with PC by laminating a thermal insulation layer on the backside of a stamper to retard the heat flow. A macroscopic warpage of PEI substrate is smaller than that of PC substrates, which reduces tilt and servo burden. The lowest critical speed coupled with the flutter of PEI substrate is larger than that of PC substrate because of the mechanical properties of PEI. POLYM. ENG. SCI., 48:97–101, 2008. © 2007 Society of Plastics Engineers 相似文献
29.
Synthesis of 21R AlN polytypoids was investigated using Al and ultrafine SiO2 powder in a flowing nitrogen atmosphere by means of thermal gravity (TG), differential scanning calorimeter (DSC), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) linked with energy dispersive spectrometer (EDS). The results showed that the formation mechanism of AlN polytypoids was different from that in reaction sintering process using Si3N4, AlN, Al2O3 and other sintering additive as raw materials. It was suggested that firstly Al reduce SiO2 into Si and is also nitrided into AlN, then AlN, Al2O3 and SiO2 dissolve into silicon liquid until the AlN polytypoids precipitate in saturated liquid in a flowing nitrogen atmosphere at lower than 1700 °C. 相似文献
30.
Yawei Li Shaobai Sang Shengli Jin Chunyan Yang Nan Li 《Journal of Materials Science》2006,41(18):5815-5819
Synthesis of Mg-α-Sialon has been investigated by the mixture of silicon, aluminum and magnesia powders in a flowing nitrogen atmosphere in the range of 1300–1600 °C, when Mg-α-Sialon is designed with a chemical formulation of Mg
x
Si12−3x
Al3x
O
x
N16−x
in present work. The results showed that Mg-α-sialon initially occurred at 1400 °C and basically increased with elevated temperatures. For the samples of x = 0.6, 0.8 and 1.0 the products mainly consisted of Mg-α-Sialon with small amounts of Si, AlN and 21R AlN-polytypoid phases at 1600° C. However, in final products of x = 1.2, 1.4 and 1.6 only a little of Mg-α-Sialon formed and a great amount of Si remained in these samples at all the fired temperatures. Fortunately, the content of Mg-α-Sialon in these samples were obviously increased by adding a small amount of α-Si3N4 as seeds before nitridation. 相似文献