全文获取类型
收费全文 | 531263篇 |
免费 | 29941篇 |
国内免费 | 16296篇 |
专业分类
电工技术 | 24113篇 |
技术理论 | 45篇 |
综合类 | 25463篇 |
化学工业 | 87176篇 |
金属工艺 | 28199篇 |
机械仪表 | 27464篇 |
建筑科学 | 31948篇 |
矿业工程 | 12539篇 |
能源动力 | 14277篇 |
轻工业 | 40255篇 |
水利工程 | 8428篇 |
石油天然气 | 26500篇 |
武器工业 | 2797篇 |
无线电 | 58175篇 |
一般工业技术 | 71815篇 |
冶金工业 | 51359篇 |
原子能技术 | 7884篇 |
自动化技术 | 59063篇 |
出版年
2023年 | 5862篇 |
2022年 | 10600篇 |
2021年 | 15129篇 |
2020年 | 11298篇 |
2019年 | 9741篇 |
2018年 | 11863篇 |
2017年 | 13069篇 |
2016年 | 12223篇 |
2015年 | 15383篇 |
2014年 | 20071篇 |
2013年 | 28476篇 |
2012年 | 27088篇 |
2011年 | 31345篇 |
2010年 | 27101篇 |
2009年 | 26765篇 |
2008年 | 26332篇 |
2007年 | 25356篇 |
2006年 | 24945篇 |
2005年 | 22210篇 |
2004年 | 16327篇 |
2003年 | 14738篇 |
2002年 | 13922篇 |
2001年 | 12868篇 |
2000年 | 12598篇 |
1999年 | 13371篇 |
1998年 | 17452篇 |
1997年 | 13447篇 |
1996年 | 11395篇 |
1995年 | 9020篇 |
1994年 | 7466篇 |
1993年 | 6162篇 |
1992年 | 4648篇 |
1991年 | 4082篇 |
1990年 | 3629篇 |
1989年 | 3412篇 |
1988年 | 3192篇 |
1987年 | 2646篇 |
1986年 | 2471篇 |
1985年 | 2618篇 |
1984年 | 2383篇 |
1983年 | 2172篇 |
1982年 | 2004篇 |
1981年 | 2018篇 |
1980年 | 1891篇 |
1979年 | 1857篇 |
1978年 | 1793篇 |
1977年 | 2129篇 |
1976年 | 2714篇 |
1975年 | 1562篇 |
1973年 | 1615篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
82.
S. F. Edwards 《Polymer International》1985,17(2):122-125
Elasticity is discussed as an aspect of viscoelasticity, which is described by the tube model. The effects of both crosslinks and entanglements contribute to this model and a discussion of how these effects can be quantified is given. At high enough concentration, entanglements ensure the existence of elastic effects even without crosslinks, and a theory is presented on how this dynamical phase change comes about. 相似文献
83.
A simple apparatus for elongational test of molten polymers is presented. Its realiability is demonstrated by means of stress growth in constant stretching rate experiments and relaxation test on a low density polyethylene sample. 相似文献
84.
关于粒子加速器人身辐射安全联锁系统设计原则的建议 总被引:2,自引:2,他引:0
本文讨论了在粒子加速器上的联锁系统设计中应遵循的一些原则,其中建立隔离区、“失效导致安全(Fail-safe)”,使用“硬件”、“多重联锁”、设置急停开关等是最重要的。 相似文献
85.
86.
Statistics on the backscatter coefficient σ0 from the Ku -band Seasat-A Satellite Scatterometer (SASS) collected over the world's land surfaces are presented. This spaceborne scatterometer provided data on σ0 between latitude 80° S and 80° N at incidence angles up to 70°. The global statistics of vertical (V ) and horizontal (H ) polarization backscatter coefficients for 10° bands in latitude are presented for incidence angles between 20° and 70° and compared with the Skylab and ground spectrometer results. Global images of the time-averaged V polarization σ0 at a 45° incidence angle and its dependence on the incidence angle are presented and compared to a generalized map of the terrain type. Global images of the differences between the V an H polarization backscatter coefficients are presented and discussed. The most inhomogeneous region, which contains the deserts of North Africa and the Arabian Peninsula, is studied in greater detail and compared with the terrain type 相似文献
87.
介绍了基于策略的网络管理的概念和当前的研究状况,在策略定义、冲突检测和系统安全问题等方面进行了讨论,提出了一种适合基于策略的网络管理的结构方案,并分析了该方案的合理性。 相似文献
88.
1 前言 CONTOP~R工艺最初是由德国科隆的KHDHumboldt Wedag AG公司针对有色金属工业而开发的。两台迄今为止最大的CONTOP~R熔炼旋风炉建于美国德克萨斯的ASARCO公司,每台能力为32t/h铜精矿混和料。 1998年,奥钢联工程技术公司(VAI)获得了 相似文献
89.
Mingjun Li Kosuke Nagashio Ph.D. Kazuhiko Kuribayashi 《Metallurgical and Materials Transactions A》2002,33(8):2677-2683
A mullite (3Al2O3·2SiO2) sample has been levitated and undercooled in an aero-acoustic levitator, so as to investigate the solidification behavior
in a containerless condition. Crystal-growth velocities are measured as a function of melt undercoolings, which increase slowly
with melt undercoolings up to 380 K and then increase quickly when undercoolings exceed 400 K. In order to elucidate the crystal
growth and solidification behavior, the relationship of melt viscosities as a function of melt undercoolings is established
on the basis of the fact that molten mullite melts are fragile, from which the atomic diffusivity is calculated via the Einstein-Stokes equation. The interface kinetics is analyzed when considering atomic diffusivities. The crystal-growth
velocity vs melt undercooling is calculated based on the classical rate theory. Interestingly, two different microstructures are observed;
one exhibits a straight, faceted rod without any branching with melt undercoolings up to 400 K, and the other is a feathery
faceted dendrite when undercoolings exceed 400 K. The formation of these morphologies is discussed, taking into account the
contributions of constitutional and kinetic undercoolings at different bulk undercoolings. 相似文献
90.
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