全文获取类型
收费全文 | 282159篇 |
免费 | 26621篇 |
国内免费 | 14188篇 |
专业分类
电工技术 | 20042篇 |
技术理论 | 34篇 |
综合类 | 28760篇 |
化学工业 | 37157篇 |
金属工艺 | 11902篇 |
机械仪表 | 16376篇 |
建筑科学 | 34824篇 |
矿业工程 | 14790篇 |
能源动力 | 13526篇 |
轻工业 | 18733篇 |
水利工程 | 17438篇 |
石油天然气 | 16905篇 |
武器工业 | 3889篇 |
无线电 | 16302篇 |
一般工业技术 | 21422篇 |
冶金工业 | 14882篇 |
原子能技术 | 3161篇 |
自动化技术 | 32825篇 |
出版年
2024年 | 1310篇 |
2023年 | 3844篇 |
2022年 | 7206篇 |
2021年 | 9277篇 |
2020年 | 9201篇 |
2019年 | 7170篇 |
2018年 | 6750篇 |
2017年 | 8549篇 |
2016年 | 10166篇 |
2015年 | 10797篇 |
2014年 | 18478篇 |
2013年 | 17320篇 |
2012年 | 19896篇 |
2011年 | 22238篇 |
2010年 | 16170篇 |
2009年 | 16675篇 |
2008年 | 15325篇 |
2007年 | 18670篇 |
2006年 | 17046篇 |
2005年 | 15005篇 |
2004年 | 12460篇 |
2003年 | 10892篇 |
2002年 | 8904篇 |
2001年 | 7388篇 |
2000年 | 6347篇 |
1999年 | 5074篇 |
1998年 | 3728篇 |
1997年 | 3284篇 |
1996年 | 2747篇 |
1995年 | 2313篇 |
1994年 | 1936篇 |
1993年 | 1419篇 |
1992年 | 1163篇 |
1991年 | 814篇 |
1990年 | 725篇 |
1989年 | 624篇 |
1988年 | 382篇 |
1987年 | 290篇 |
1986年 | 233篇 |
1985年 | 223篇 |
1984年 | 184篇 |
1983年 | 150篇 |
1982年 | 84篇 |
1981年 | 89篇 |
1980年 | 91篇 |
1979年 | 52篇 |
1978年 | 26篇 |
1977年 | 29篇 |
1959年 | 47篇 |
1951年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
152.
康山金矿地质地球化学特征及其成因 总被引:3,自引:1,他引:2
康山金矿产在豫西熊耳山古隆起区的结晶基底太华群和盖层中元古界熊耳群地层接触界面附近,矿体严格受构造破碎蚀变带控制。流体包裹体,稳定同位素等研究表明,成矿物质来自太华群变质岩,成矿流体的性质与变质热液截然不同,而与花岗岩浆热液相近似。该矿床的形成与燕山期发生的同构造-花岗岩浆期热液活动有关,金沉淀成矿阶段有大气水的混入。 相似文献
153.
Simulation of water and nitrogen dynamics in soils during wastewater applications by using a finite-element model 总被引:4,自引:0,他引:4
Vassilis Z. Antonopoulos 《Water Resources Management》1993,7(3):237-251
A mathematical model was developed to simulate water movement, mass transport, and nitrogen transformations in soils during wastewater applications. The model is one-dimensional and based on the Galerkin finite-element method. The submodel of mass transport of nitrogen incorporates the convection-dispersion processes of ammonium and nitrate nitrogen, nitrification, denitrification, ammonium exchange and uptake of ammonium and nitrate ions. The accuracy and validity of the proposed model was examined by comparison with an explicit-implicit finite-difference model results. The model was used for simulation of water and nitrogen dynamics during wastewater application in homogeneous and multi-layered soils under different N concentration, rate, duration and scheduling of application. 相似文献
154.
Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data. 相似文献
155.
Influence of Coherent Flow Structures on the Dynamics of Suspended Sediment Transport in Open-Channel Flow 总被引:1,自引:0,他引:1
The influence of suspended sediments on coherent flow structures has been studied by simultaneously measuring the longitudinal and vertical components of the instantaneous velocity vector and the instantaneous suspended particle concentration with an acoustic particle flux profiler. The measurements were carried out in clear water and in particle-laden open-channel flows. In both cases, they clearly show the predominance of ejection and sweep phases that are part of a burst cycle. The analysis further demonstrates the importance of the ejection and sweep phases in sediment resuspension and transport. Ejections pick up the sediment at the bed and carry it up through the water column close to the surface. It is shown that ejections and sweeps are in near equality in the near-bottom layer, whereas ejections clearly dominate in the remaining water column. The implications of these results for sediment transport dynamics are discussed. 相似文献
156.
This article presents a two-dimensional transient model for gas-solids flow and heat transfer through pipes using the coupled Computational Fluid Dynamics and Discrete Element Method approach. Numerical simulations have been conducted to examine the modification of fluid thermal structure due to the presence of particles in a pneumatic transport pipeline. Modeled results have demonstrated the key role of transversal motion of rebounding particles in the pipe cross section in altering fluid temperature. Further implementation of this modeling technique in air-drying processes is discussed and possible experimental methods for the measurement of in situ particle and fluid motion and temperature profile are cited. 相似文献
157.
J. C. Jones H. Rahmati T. D. H. Do 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,54(4):317-318
Wood shaving samples were heated in both cubic baskets and in a previously described system realising the conditions of the ‘infinite slab’ in thermal ignition. Results from the two sets of experiment were found to be totally consistent with each other. 相似文献
158.
本文采用粒子追踪理论对水平管中粒子流动状态进行了数值模拟.文中提出了一种新的粒子碰撞模型,并忽略粒子的旋转和扬力,仅考虑气流阻力和重力对粒子的影响,在输送量为9.13×10~3kg/s,混合比约0.3的条件下,通过数值计算得知:由于粒子间的碰撞,使得异径粒子的速度趋向平均化;粒子间的碰撞是粒子悬浮的原因之一;粒子的浓度沿管轴向是随时间而发生变化的. 相似文献
159.
In the first half of the paper, various types of processing pertaining to a polygon, using the 4×4 determinant theories are explained along with a new containment test algorithm of a point in a polygon. In the latter half of the paper, a general-purpose geometric processor, the POLYGON ENGINE, is presented which can deal with various types of interference problems, such as Boolean operations in solid modelling, hidden line and surface eliminations, ray tracing and so on. It is, a successor of the TRIANGLE PROCESSOR and is also based upon the 4×4 determinant theories [4–6]. While the TRIANGLE PROCESSOR processes a triangulated polygon on a triangle-by-triangle basis, the POLYGON ENGINE can treat a polygon without triangulation. The latter is expected to be more functional, more efficient and easier to use. 相似文献
160.
本文运用“软科学”一即通过建立数学模型,进行系统分析和系统优化,阐述对蒸汽管网优化运行的方法及原理,达到提高供热效率及节能降耗的目的. 相似文献