全文获取类型
收费全文 | 496534篇 |
免费 | 36803篇 |
国内免费 | 20145篇 |
专业分类
电工技术 | 27335篇 |
技术理论 | 46篇 |
综合类 | 32612篇 |
化学工业 | 78464篇 |
金属工艺 | 29234篇 |
机械仪表 | 29712篇 |
建筑科学 | 34620篇 |
矿业工程 | 14189篇 |
能源动力 | 12759篇 |
轻工业 | 31656篇 |
水利工程 | 9707篇 |
石油天然气 | 26565篇 |
武器工业 | 3743篇 |
无线电 | 54902篇 |
一般工业技术 | 60356篇 |
冶金工业 | 23883篇 |
原子能技术 | 4673篇 |
自动化技术 | 79026篇 |
出版年
2024年 | 1697篇 |
2023年 | 6255篇 |
2022年 | 11476篇 |
2021年 | 16113篇 |
2020年 | 12189篇 |
2019年 | 9867篇 |
2018年 | 24120篇 |
2017年 | 24848篇 |
2016年 | 20918篇 |
2015年 | 17003篇 |
2014年 | 21090篇 |
2013年 | 25023篇 |
2012年 | 30630篇 |
2011年 | 39153篇 |
2010年 | 34899篇 |
2009年 | 31005篇 |
2008年 | 31763篇 |
2007年 | 31627篇 |
2006年 | 24393篇 |
2005年 | 22233篇 |
2004年 | 15711篇 |
2003年 | 14256篇 |
2002年 | 13024篇 |
2001年 | 11184篇 |
2000年 | 10297篇 |
1999年 | 10364篇 |
1998年 | 7708篇 |
1997年 | 6602篇 |
1996年 | 6203篇 |
1995年 | 5069篇 |
1994年 | 4113篇 |
1993年 | 2782篇 |
1992年 | 2189篇 |
1991年 | 1676篇 |
1990年 | 1307篇 |
1989年 | 1051篇 |
1988年 | 872篇 |
1987年 | 558篇 |
1986年 | 433篇 |
1985年 | 265篇 |
1984年 | 217篇 |
1983年 | 174篇 |
1982年 | 137篇 |
1981年 | 84篇 |
1980年 | 102篇 |
1979年 | 48篇 |
1968年 | 46篇 |
1959年 | 46篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
李得天 《真空科学与技术学报》2003,23(4):289-294
在真空技术应用中 ,高精度气体微流量计用于连续膨胀法校准系统压力的产生、漏孔漏率的测量以及真空泵抽速的测定。PTB先后研制了三代气体微流量计 ,第一代为手动型 ,第二代为半自动型 ,第三代为全自动型。本文详细介绍了PTB研制的气体微流量计的性能和特点 ,并介绍了气体微流量计在真空漏孔的漏率测量方面的应用。另外 ,还介绍了PTB最近研制的大气压力下漏孔漏率测量系统的性能和特点 相似文献
992.
储运罐区计算机监测系统的开发与应用 总被引:3,自引:1,他引:2
储运罐区计算机监测系统是石化企业自动控制的薄弱环节。中国石油集团公司抚顺石油一厂使用ZYG-101型电子智能液位仪,以及使用FIX组态软件完成该系统的数据库组态、工艺流程显示、实时和历史趋势显示、报警和报表等处理过程,通过二次表的串行口与计算机进行通信,由计算机实时监测每个罐的各种重要参数。运行证明:该系统测量误差小,数据实时性好.易于存储及远程传送,较理想地达到储运罐区的自动检测功能。 相似文献
993.
This paper considers the axisymmetric steady flow driven by exact counter rotation of two co-axial disks of finite radius.
At the edges of the rotating disks one of three conditions is (typically) imposed: (i) zero velocity, corresponding to a stationary,
impermeable, cylindrical shroud (ii) zero normal velocity and zero tangential fluid traction, corresponding to a (confined)
free surface and (iii) an edge constraint that is consistent with a similarity solution of von Kármán form. The similarity
solution is valid in an infinite geometry and possesses a pitchfork bifurcation that breaks the midplane symmetry at a critical
Reynolds number. In this paper, similar bifurcations of the global (finite-domain) flow are sought and comparisons are made
between the resulting bifurcation structure and that found for the similarity solution. The aim is to assess the validity
of the nonlinear similarity solutions in finite domains and to explore the sensitivity of the solution structure to edge conditions
that are implicitly neglected when assuming a self-similar flow. It is found that, whilst the symmetric similarity solution
can be quantitatively useful for a range of boundary conditions, the bifurcated structure of the finite-domain flow is rather
different for each boundary condition and bears little resemblance to the self-similar flow. 相似文献
994.
A new technique for the preparation of CuI nanoparticles from CuSO4 and KI ethanol solutions has been developed. Preparation conditions were optimized through a series of experiments. Under
these conditions, the yield of CuI reached 95.39%. The product was characterized and the reaction kinetics was studied. The
results show that the product takes a roughly spherical shape with an average particle size of less then 50 nm. The activation
energy of the formation of CuI is found to be E
a = 0.58 × 102 kJ/mol, and the preexponential factor in the Arrhenius equation is k
0 = 7.43 × 1016 mol/(l s).
The text was submitted by the authors in English. 相似文献
995.
用溶胶-凝胶法制备了平均粒径为2~3μm的小颗粒、高亮度的Li(2-x)(MoO4)2:Eu系列钼酸盐红色荧光体。用XRD、SEM、粒度分析和分子荧光光度计对荧光体进行了表征和研究。常规的固相反应合成Li(2-x)(MoO4)2:Eux系列红色荧光粉需要在900℃以上的高温才能够形成均一的固溶体,而采用溶胶-凝胶法制取,在700℃就可以形成均一的单相Li(2-x)(MoO4)2:Eux,在750℃就可得到发光亮度最高的荧光体。其亮度是常规固相反应于900℃制得的荧光体的124%。采用溶胶-凝胶法制取Li(2-x)(MoO4)2:Eux系列,可以在相当宽的实验条件范围内得到小粒径、窄分布和高亮度的荧光体,具有良好的颗粒形貌。 相似文献
996.
997.
Solidification time and heat treatment are known to have a large effect on the microstructure of cast aluminum alloys. This
study was conducted to quantify how the fatigue properties of a 319-type aluminum alloy are affected by solidification time
and heat treatment. Both porosity-containing (non-hot isostatically pressed (HIP)) and porosity-free (HIP) samples in the
T6 (“peak aged”) or T7 (“overaged”) heattreated conditions were tested. As the solidification time increased, the average
initiating pore diameter increased and stress-controlled fatigue life decreased. Heat treatment was observed to have a large
effect on fatigue properties of the HIP samples. However, in the non-HIP fatigue samples, heat treatment did not significantly
change the fatigue life or fatigue strength of the cast 319-type alloy. The absence of an influence of heat treatment on fatigue
response is attributed to the predominance of the microporosity in fatigue crack initiation in cast aluminum. 相似文献
998.
端电压比较法直接寻找无刷直流电动机换相点及其斩波调速 总被引:4,自引:0,他引:4
提供了一种利用端电压比较结合软件算法直接寻找直流无刷无位置传感器电动机换相点的方案,解决了直流无刷无位置传感器电动机控制的关键问题-转子位置检测,并以单片机PIC16C72为核心构成先进的数字控制系统,实现了软件斩波调速。 相似文献
999.
Central to cost-based competition is the capability to accurately predict the cost of delivering a project. Most literature on cost estimation focuses on specific estimation methods as generic techniques and little attention has been paid to the unique requirements at each project stage. This note attempts to identify the critical factors for effective estimation at various stages of typical construction projects. Drawing from organization control theory and cost estimating literature, this note develops a theoretical framework that identifies the critical factors for effective cost estimation during each project phase of a conventional construction project. The underlying logic is that as a cost estimating effort progresses, both task programmability and output measurability improve. As a result, control effort will shift from input-oriented control to a combination of output and behavior control. 相似文献
1000.
Nicolas Clauvelin Basile Audoly Sébastien Neukirch 《Scientific Modeling and Simulation》2007,14(1):95-101
The DNA molecule is modeled as an elastic rod with bending and twisting rigidities, subjected to external tension and twist applied at one end, the other end being clamped. We study the plectonemic equilibrium of such a rod, taking into account the impenetrability constraint. Numerical solutions of this boundary value problem have previously shown that purely elastic models can reproduce the supercoiling response of the DNA molecule. Using a variational approach, we derive analytical formulae for the elastic response of the filament, and extend former numerical results. 相似文献