全文获取类型
收费全文 | 24746篇 |
免费 | 1972篇 |
国内免费 | 851篇 |
学科分类
工业技术 | 27569篇 |
出版年
2024年 | 44篇 |
2023年 | 389篇 |
2022年 | 520篇 |
2021年 | 983篇 |
2020年 | 707篇 |
2019年 | 655篇 |
2018年 | 686篇 |
2017年 | 794篇 |
2016年 | 749篇 |
2015年 | 920篇 |
2014年 | 1232篇 |
2013年 | 1574篇 |
2012年 | 1576篇 |
2011年 | 1721篇 |
2010年 | 1398篇 |
2009年 | 1440篇 |
2008年 | 1340篇 |
2007年 | 1241篇 |
2006年 | 1349篇 |
2005年 | 1164篇 |
2004年 | 843篇 |
2003年 | 760篇 |
2002年 | 760篇 |
2001年 | 542篇 |
2000年 | 522篇 |
1999年 | 599篇 |
1998年 | 573篇 |
1997年 | 461篇 |
1996年 | 430篇 |
1995年 | 343篇 |
1994年 | 276篇 |
1993年 | 189篇 |
1992年 | 172篇 |
1991年 | 115篇 |
1990年 | 90篇 |
1989年 | 71篇 |
1988年 | 87篇 |
1987年 | 47篇 |
1986年 | 43篇 |
1985年 | 21篇 |
1984年 | 29篇 |
1983年 | 13篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1965年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
941.
纯铜双层辉光离子渗镍研究 总被引:5,自引:0,他引:5
介绍了采用双层辉光离子渗金属技术在纯铜表面制备Cu-Ni合金层的新方法,讨论了Cu-Ni合金层的组织、成分和性能特点,分析了辉光放电条件、源极溅射率及表面金属势对Cu-Ni合金层形成过程的影响.试验结果表明渗层厚度及渗层质量与辉光放电条件有关,在保证渗金属温度的前提下,应尽可能提高源极电压,降低试件电压.此外,该工艺还具有渗速快、效率高、无污染等优点. 相似文献
942.
943.
Mechanical alloying (MA) and rapid solidification (RS) are two important routes to obtain amorphous alloys. An Fe-Ni based metal-metalloid alloy (Fe50Ni30P14Si6) prepared by these two different processing routes was studied by differential scanning calorimetry, scanning electron microscopy with microanalysis, inductive coupled plasma, X-ray diffraction (XRD) and transmission Mössbauer spectroscopy (TMS). The results were compared with that obtained from other Fe-Ni based alloys of similar compositions. The structural analyses show that the materials obtained by mechanical alloying are not completely disordered after 40 h of milling whereas fully amorphous alloys were obtained by rapid solidification. TMS analyses show that, independent of the composition, after milling for 40 h, about 7% of the Fe remains unreacted. Furthermore, the thermal stability of mechanically alloyed samples is lower than that of the analogous material prepared by rapid solidification. In the MA alloys, a broad exothermic process associated to structural relaxation begins at low temperature. XRD patterns of crystallized alloys indicate that the crystallization products are bcc(Fe,Ni), fcc(Ni,Fe), and (Fe,Ni)-phosphides and -silicides. 相似文献
944.
945.
The preparation and characterization of a new cyclometalated iridium complex with 2-(1-naphthalene) pyridine ligand were reported. An electrophosphorescent device was fabricated by using this new iridium complex as guest and poly-(cyano-paraphenylene) as host. Red electrophosphorescence was observed with an emission peak at approximately 600 nm. An external quantum efficiency of 1.3% was achieved in this electrophosphorescent polymer light-emitting devices. 相似文献
946.
947.
948.
YanluHuang GongyingLiang JunyiSu 《北京科技大学学报(英文版)》2004,11(1):13-17
A 3-D transient mathematical model for laser cladding by powder feeding was developed to examine the macroscopic heat and momentum transport during the process, based on which a novel method for determining the configuration and thickness of cladding layer was presented. By using Lambert-Beer theorem and Mie‘s theory, the interaction between powder stream and laser beam was treated to evoke their subtle effects on heat transfer and fluid flow in laser molten pool. The numerical study was performed in a co-ordinate system moving with the laser at a constant scanning speed. A fixed grid enthalpy-porosity approach was used,which predicted the evolutionary development of the laser molten pool. The commercial software PHOENICS, to which several modules were appended, was used to accomplish the simulation. The results obtained by the simulation were coincident with those measured in experiment basically. 相似文献
949.
Experiment research on grain drying process in the heat pump assisted fluidized beds 总被引:5,自引:0,他引:5
Jing Yang Li Wang Fi Xiang Lige Tong and Hua SuMechanical Engineering School University of Science Technology Beijing Beijing China 《北京科技大学学报(英文版)》2004,11(4)
A heat pump assisted fluidized bed grain drying experimental system was developed. Based on this system, a serial of experiments was performed under four kinds of air cycle conditions. According to the experimental analysis, an appropriate drying medium-air cycle for the heat pump assisted fluidized bed drying equipment was decided, which is different from the commonly used heat pump assisted drying system. The experimental results concerning the drying operation performance of the new system show that the averaged coefficient of performance (COP) can reach more than 2.5. The economical evaluation was performed and the power consumption for removing a kilogram water from grains was about 0.485 kW·2222h/kg (H2O), which shows its reasonable commercial efficiency and great application potentiality in future market. 相似文献
950.
SUHao WUShun-hua YANHai-yang 《武汉理工大学学报(材料科学英文版)》2004,19(4):62-64
The dielectric ceramics with a main crystal phase of MGTiO3 and additional crystal phase of CaTiO3 were prepared by the conventional electronic ceramics technology .the strucures of MgTiO3 are ilmenitetype,and belong to hexagonal syngony.the ratio of MgTiO3 to Ca TiO3 doping on the dielectric properties of MGTiO3-CaTiO3(MCT)ceranics were inrestigated.the addition of B2O3 decreases the sintering temperatnre and results in rapid desification without obrious negative effect on the Q values of the system(Q=1/tan ).B2O3 exists as liquid phase in the sintering process,promoting the reactions as a singering agent. 相似文献