全文获取类型
收费全文 | 188178篇 |
免费 | 15468篇 |
国内免费 | 8344篇 |
学科分类
工业技术 | 211990篇 |
出版年
2024年 | 763篇 |
2023年 | 2879篇 |
2022年 | 5306篇 |
2021年 | 7343篇 |
2020年 | 5505篇 |
2019年 | 4560篇 |
2018年 | 5202篇 |
2017年 | 5823篇 |
2016年 | 5150篇 |
2015年 | 7117篇 |
2014年 | 8744篇 |
2013年 | 11023篇 |
2012年 | 11758篇 |
2011年 | 12710篇 |
2010年 | 11184篇 |
2009年 | 10956篇 |
2008年 | 10945篇 |
2007年 | 10277篇 |
2006年 | 10386篇 |
2005年 | 9033篇 |
2004年 | 6394篇 |
2003年 | 5465篇 |
2002年 | 5256篇 |
2001年 | 4876篇 |
2000年 | 4627篇 |
1999年 | 4971篇 |
1998年 | 4211篇 |
1997年 | 3634篇 |
1996年 | 3168篇 |
1995年 | 2670篇 |
1994年 | 2105篇 |
1993年 | 1674篇 |
1992年 | 1331篇 |
1991年 | 1034篇 |
1990年 | 805篇 |
1989年 | 696篇 |
1988年 | 545篇 |
1987年 | 390篇 |
1986年 | 297篇 |
1985年 | 254篇 |
1984年 | 142篇 |
1983年 | 109篇 |
1982年 | 127篇 |
1981年 | 93篇 |
1980年 | 75篇 |
1979年 | 56篇 |
1978年 | 35篇 |
1977年 | 42篇 |
1976年 | 59篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
Interfacial segregation of Ti in the brazing of diamond grits onto a steel substrate using a Cu-Sn-Ti brazing alloy 总被引:1,自引:0,他引:1
Wen-Chung Li Shun-Tian Lin Cheng Liang 《Metallurgical and Materials Transactions A》2002,33(7):2163-2172
Diamond grits were brazed onto a steel substrate using a prealloyed Cu-10Sn-15Ti (wt pct) brazing alloy at 925 °C and 1050
°C. Due to the relatively high concentration of Ti in the brazing alloy, the braze matrix exhibited a composite structure,
composed of β-(Cu,Sn), a Cu-based solid solution, and various intermetallic compounds with different morphologies. The reaction of Ti with
diamond yielded a continuous TiC layer on the surfaces of the diamond grits. On top of the TiC growth front, an intermetallic
compound, composed of Sn and Ti, nucleated and grew into a randomly interwoven fine lacey structure. An interfacial structure
developed as the interwoven fine lacey phase was semicoherently bonded to the TiC layer, with the Cu-based braze matrix filling
its interstices. The thickness of such a composite layer was increased linearly with the square root of isothermal holding
time at 925 °C, complying with the law of a diffusion-controlled process. However, at 1050 °C, the segregation behavior of
Ti and Sn to the interfaces between the TiC layer and the braze matrix diminished, due to the increased solubility of Ti in
the Cu-based liquid phase. The enhanced dissolution of Ti in the Cu-based liquid phase at 1050 °C also caused the precipitation
of rod-like CuTi with an average diameter of about 0.2 μm during cooling. SnTi3 was the predominant intermetallic compound and existed in three different forms in the braze matrix. It existed as interconnected
grains of large size which either floated to the surface of the braze matrix or grew into faceted grains. It also exhibited
a nail-like structure with a mean diameter of about 1 μm for the rod section and a lamellar structure arising from a eutectic reaction during cooling. 相似文献
84.
新型高k栅介质材料研究进展 总被引:5,自引:0,他引:5
随着半导体技术的不断发展,MOSFET(metal-oxide-semiconductor field effect transistor)的特征尺寸不断缩小,栅介质等效氧化物厚度已小至nm数量级。这时电子的直接隧穿效应将非常显著,将严重影响器件的稳定性和可靠性。因此需要寻找新型高k介质材料,能够在保持和增大栅极电容的同时,使介质层仍保持足够的物理厚度来限制隧穿效应的影响。本文综述了研究高k栅介质材料的意义;MOS栅介质的要求;主要新型高k栅介质材料的最新研究动态;展望了高k介质材料今后发展的主要趋势和需要解决的问题。 相似文献
85.
86.
87.
本文是对市场上几款高级便携式打印机主要性能特点的比较考察报告,包括:佳能生产的CanonBJC-70型便携式彩色喷墨打印机,惠普生产的HPDeskJet340型便携式彩色喷墨打印机和Pentax生产的Pentax PocketJet便携式打印机,后者必须使用热敏纸。 相似文献
88.
The formula and program for calculating the total and negative first harmonic interaction impedance from the data of “large
perturbation measurement” are given. This program is a part of the programs for CCTWT design. 相似文献
89.
以有机锡(Fascat4102)作催化剂,苯酐和辛醇(2-乙基己醇)酯化反应生成邻苯二甲酸二辛酯(DOP),其最佳工艺条件为:酯化温度215~225℃,催化剂加入量2.0‰,过量醇含量17%,脱醇真空为20KPa(绝压),脱醇温度为155℃,活性炭加入量为1‰,省却中和水洗和汽提工序,产品质量可以达到优级品. 相似文献
90.
The Synthesis of Sulfated Titanium Oxide Nanotubes 总被引:1,自引:0,他引:1
Chiu-Hsun Lin Shu-Hua Chien Jiunn-Hsing Chao Chyi-Yang Sheu Yu-Cheng Cheng Ya-Jean Huang Chih-Hsiang Tsai 《Catalysis Letters》2002,80(3-4):153-159
TiO2 nanotubes can be prepared in gram quantities by treating anatase TiO2 powder with concentrated NaOH solution. These TiO2 nanotubes acquired strong acidity after being impregnated with sulfuric acid solution and calcined at 300 °C. The anatase TiO2 powder used to prepare the nanotube did not catalyze the esterification between cyclohexanol and acetic acid, while sulfated TiO2 nanotubes were very reactive toward the esterification reaction. 相似文献