全文获取类型
收费全文 | 76912篇 |
免费 | 6268篇 |
国内免费 | 3272篇 |
专业分类
电工技术 | 4264篇 |
技术理论 | 13篇 |
综合类 | 4464篇 |
化学工业 | 13170篇 |
金属工艺 | 4260篇 |
机械仪表 | 4915篇 |
建筑科学 | 6545篇 |
矿业工程 | 2229篇 |
能源动力 | 2263篇 |
轻工业 | 4641篇 |
水利工程 | 1243篇 |
石油天然气 | 4921篇 |
武器工业 | 645篇 |
无线电 | 8997篇 |
一般工业技术 | 9613篇 |
冶金工业 | 3941篇 |
原子能技术 | 899篇 |
自动化技术 | 9429篇 |
出版年
2024年 | 302篇 |
2023年 | 1262篇 |
2022年 | 2160篇 |
2021年 | 2926篇 |
2020年 | 2326篇 |
2019年 | 1961篇 |
2018年 | 2135篇 |
2017年 | 2489篇 |
2016年 | 2220篇 |
2015年 | 2961篇 |
2014年 | 3689篇 |
2013年 | 4345篇 |
2012年 | 4809篇 |
2011年 | 5059篇 |
2010年 | 4429篇 |
2009年 | 4145篇 |
2008年 | 4045篇 |
2007年 | 4052篇 |
2006年 | 4250篇 |
2005年 | 3684篇 |
2004年 | 2545篇 |
2003年 | 2216篇 |
2002年 | 2096篇 |
2001年 | 1903篇 |
2000年 | 1882篇 |
1999年 | 2180篇 |
1998年 | 1903篇 |
1997年 | 1579篇 |
1996年 | 1501篇 |
1995年 | 1163篇 |
1994年 | 1096篇 |
1993年 | 744篇 |
1992年 | 574篇 |
1991年 | 450篇 |
1990年 | 337篇 |
1989年 | 270篇 |
1988年 | 248篇 |
1987年 | 155篇 |
1986年 | 112篇 |
1985年 | 81篇 |
1984年 | 40篇 |
1983年 | 38篇 |
1982年 | 40篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1959年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A new basic electrolyte with two cationic plating additives,polydiaminourea and polyaminosulfone,was investigated for the electrochemical deposition of the bismuth telluride film on a nickel-plated copper foil.Tellurium starts to deposit at a higher potential(-0.35 V) than bismuth(-0.5 V) in this electrolyte.The tellurium-to-bismuth ratio increases while the deposition potential declines from-1 to-1.25 V, indicating a kinetically quicker bismuth deposition at higher potentials.The as-deposited film featu... 相似文献
992.
993.
根据构式语法,典型SVOC结构(即NP2后是名词短语和形容词短语)的构式义是致使变化。而SVOC结构研究中争议较大之处是如何看待和界定NP2后是非限定结构的情况。根据语义分析,这类情况中有些是属于非典型SVOC结构,其意义仍然是致使变化,而另外一些则应视为其它句式,如SVO。不同的学者从不同的角度出发往往得出不同的结论,这种情况从原型范畴理论的角度来看是完全可以理解并且是非常正常的。 相似文献
994.
995.
A series of new polyamides 3a–d containing aryl-azo, ether and sulfone groups in the main chain were synthesized from bis[4-(4-aminophenoxy)phenyl sulfone]
1 and several azo aromatic diacyl chlorides 2a–d by the low temperature solution polycondensation technique. FTIR spectroscopy, nuclear magnetic resonance (NMR) and elemental
analyses confirmed the structure of these polymers. Owing to the aryl and amide groups in the main chain, these polymers exhibit
photochromic properties as well as excellent thermal stabilities. The transition temperatures (T
g) are between 242 and 265 °C, and the char yields at 800 °C in nitrogen atmosphere were above 39%. Based on incorporation
of flexible ether linkages and polar sulfone groups, the polyamides show desirable solubility in organic solvents such as
DMAc, N,N-dimethylformamide (DMF), N-methyl-2-pyrroidinone (NMP) and dimethylsulfoxide (DMSO). And it is exemplified that
polyamide containing 2 and 2′ substitutes performed better solubility.
Funded by the National Natural Science Foundation of China (No. 50572081) 相似文献
996.
Evolution of carbides and carbon content in matrix of an ultra-high carbon sintered steel during heat treatment process 总被引:2,自引:0,他引:2
Yuan-zhi Zhu ) Zhe Zhu) Zhi-min Yin) Zhi-dong Xiang) ) Key Laboratory of the Ministry of Education of China for Ferrous Metallurgy Resources Utilization Wuhan University of Science Technology Wuhan China ) School of Materials Metallurgy China ) School of Material Science & Engineering Central South University Changsha China 《北京科技大学学报(英文版)》2009,16(3):299-303
DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quench-ing temperature in the range of 840-900℃ and remains constant in the range of 900 to 1100℃. It decreases rapidly when the tem-perature is higher than 1100℃. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840℃ is 0.38, but when the quenching temperature is increased to 1150℃, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840℃. When the quenching temperature is increased to 1150℃, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel. 相似文献
997.
Failure mode and strength anisotropic characteristic of stratified rock mass under uniaxial compressive situation 总被引:1,自引:1,他引:0
A stratified rock mass model was founded by FLAC3D. The failure mode and anisotropic characteristic of strength for stratified rock mass were analyzed. The analysis results
show that the numerical simulation can visually reflect the failure modes of rock samples under different inclination angles
β of structural plane. The stiffness of rock sample before peak strength changes in the compressive procedure. With the increase
of β, the compressive strength σ
c of rock sample decreases firstly and then increases; when β is in the range of 20°–30° and 80°–90°, σ
c has the largest sensitivity to β; while β falls in the range of 30°–70°, σ
c varies little. When ϕ
j
<β<90° (β
j
is friction angle of structure plane), the results obtained from numerical simulation and theoretical analysis are in almost
the same values; while β⩽ ϕ
j
or β=90°, they are in great different values. The results obtained from theoretical analysis are obvious larger than those from
numerical simulation; and the results from numerical simulation can reflect the difference of compressive strength of rock
samples for the two situations of β⩾ ϕ
j
and β=90°, which is in more accordance with the real situation.
Foundation item: Project (50099620) supported by the National Natural Science Foundation of China 相似文献
998.
To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement
of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on
the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer
containing 33.3%(mass fraction) fly ash by steam curing at 80 °C for 6 d is improved by 35.5%. The 3-day compressive strength,
flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the
shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy
(SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects
and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.
Foundation item: Project(2006AA06Z225) supported by the National High-Tech Research and Development Program of China 相似文献
999.
文章研究了攻击型无人机鲁棒导引系统,采用对干扰和摄动具有自适应能力的滑动模态变结构控制方法设计了攻击型无人机滑模导引规律.针对用于消除颤振的伪滑动模态不能实现精确跟踪的缺陷,对滑模导引规律中颤振消除进行了优化设计,引入系统运动状态轨迹接近角变量,使消除颤振的伪滑动模态边界层宽度随着系统状态到达滑动模态而逐渐减小为零,从而达到了既能消除颤振又能实现精确跟踪的设计目标.通过仿真验证了该导引规律具有攻击弹道平缓、抗目标机动扰动能力强、鲁棒性好、制导精度高的优点. 相似文献
1000.
文章介绍了一个新的服务发现模型ICSD模型,解决了传统服务发现技术中服务的功能与非功能特性较难控制的问题.文中第1节定义了模型中用到理论的9个相关概念.第2节具体介绍了模型的实现原理,给出了模型的一个原理图及模型中用到的一个相似度计算算法.文中第3节介绍了一个基于ICSD模型开发的原型系统,并引入了一套测试方案对系统进行了验证.试验证明随着服务数量的增加,系统的精确率稳定到0.8. 相似文献