全文获取类型
收费全文 | 57960篇 |
免费 | 7035篇 |
国内免费 | 4182篇 |
专业分类
电工技术 | 5502篇 |
技术理论 | 4篇 |
综合类 | 5963篇 |
化学工业 | 9575篇 |
金属工艺 | 2478篇 |
机械仪表 | 4604篇 |
建筑科学 | 3885篇 |
矿业工程 | 1919篇 |
能源动力 | 5343篇 |
轻工业 | 1504篇 |
水利工程 | 6114篇 |
石油天然气 | 4282篇 |
武器工业 | 669篇 |
无线电 | 1920篇 |
一般工业技术 | 5179篇 |
冶金工业 | 3141篇 |
原子能技术 | 1492篇 |
自动化技术 | 5603篇 |
出版年
2024年 | 284篇 |
2023年 | 869篇 |
2022年 | 1724篇 |
2021年 | 1956篇 |
2020年 | 2026篇 |
2019年 | 1742篇 |
2018年 | 1632篇 |
2017年 | 2056篇 |
2016年 | 2292篇 |
2015年 | 2346篇 |
2014年 | 3275篇 |
2013年 | 3890篇 |
2012年 | 3862篇 |
2011年 | 4475篇 |
2010年 | 3101篇 |
2009年 | 3393篇 |
2008年 | 3191篇 |
2007年 | 3755篇 |
2006年 | 3478篇 |
2005年 | 3133篇 |
2004年 | 2555篇 |
2003年 | 2327篇 |
2002年 | 1891篇 |
2001年 | 1566篇 |
2000年 | 1369篇 |
1999年 | 1166篇 |
1998年 | 964篇 |
1997年 | 828篇 |
1996年 | 767篇 |
1995年 | 690篇 |
1994年 | 581篇 |
1993年 | 436篇 |
1992年 | 366篇 |
1991年 | 244篇 |
1990年 | 239篇 |
1989年 | 172篇 |
1988年 | 134篇 |
1987年 | 92篇 |
1986年 | 62篇 |
1985年 | 36篇 |
1984年 | 52篇 |
1983年 | 39篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 18篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1959年 | 24篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
建立了水驱强度影响下的水驱油渗流数学模型,在获得数学模型解的基础上,计算了考虑井筒储存、表皮效应以及水驱强度影响下油井的压力及压力导数典型曲线,分析了压力动态特征,通过这些研究为水驱油藏的试井分析提供了理论基础,为水驱油藏的识别提供了一种新的手段。 相似文献
102.
103.
In the present study a continuum model for one-dimensional plane Couette-Poiseuille flow is implemented to turbomolecular pumps in different flow regimes. Pumping performance of various turbomolecular pumps including 6 single rotors, a rotor-stator row, a rotor-stator-rotor row, and a multi-row with 13 alternative rotor-stator rows is considered here. The obtained results show that the model provides good quantitative values for pumping performance of turbomolecular pumps over the whole regimes ranging from molecular flow to transition to slip flow. 相似文献
104.
105.
Yen-Cho ChenJ.N. Chung 《Computers & Fluids》2003,32(6):795-822
This study intends to provide an increased understanding of the laminar-turbulent transition phenomena for the buoyancy-assisted heated vertical channel flow during the early transient stage. The spectral method with weak formulation is applied in the direct numerical simulation. Initial disturbances consist of the finite-amplitude two-dimensional TS wave and a pair of three-dimensional oblique waves for the K-type disturbances. The results from the harmonic energy competitions of different wave modes show that for the buoyancy-assisted heated flow, the (kx=1, kz=1) or (1,1) and (1,0) modes would gain energy immediately and start to rise at almost the same rate. This phenomenon is different from that of the buoyancy-opposed flow, where the (1,1) mode decays slowly in the beginning until other modes gain enough energy and then it begins to grow quickly and overtakes the (1,0) mode after a short time period. These different transition patterns match with the experimental results that the flow transition is supercritical and subcritical for the buoyancy-assisted and -opposed flows, respectively. Buoyancy-assisted heated flow transition follows the general trend of an isothermal flow in the beginning, but the thermal-buoyant force is crucial in accelerating the instability and also causing notable differences during the subsequent transition process. All of the results for the vortex structures development, kinetic energy budget of the disturbances, flow visualization by tagged fluid particles, and the local temperature fluctuations are consistent in pointing to a clear pattern for the buoyancy-assisted heated flow transition. 相似文献
106.
Differential pressure fluctuation time series were obtained at different locations in a two-dimensional spout-fluid bed with a cross section of 300 × 30 mm and height 2000 mm. Shannon entropy analysis of differential pressure fluctuations was developed to characterize the dynamic behavior. Effects of two important operating parameters (spouting gas velocity and fluidizing gas flow rate) on the Shannon entropy were examined. It was demonstrated that a spout-fluid bed at a high spouting gas velocity or fluidizing gas flow rate was a deterministic chaos system since the Shannon entropies at all bed locations increased sharply and asymmetric unstable flows occurred. Shannon entropies were found to be significantly different at various bed locations. Shannon entropies of different flow regimes were distinct, so they were used to identify the flow regimes. The results show that the Shannon entropy helps to grasp the complex characteristics of dynamic behavior in spout-fluid beds. 相似文献
107.
介绍了天铁炼钢厂中间包水模实验原理和过程,分析了斜、直、圆三种型式挡渣墙模拟结果,提出了合理的挡渣控流方案,在生产实践中使用效果良好。 相似文献
108.
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
109.
An increasing amount of laser beam welded T‐joints (e.g. skin‐stringer) of aluminium alloys are now in use in advanced fuselage applications designed as ‘integral structures’ for weight and cost savings. It is known that weld joints generally show lower strength (undermatching) than base metal in both laser beam and friction stir welded joints of 6xxx series Al‐alloys. Damage tolerance considerations in terms of the residual strength of such joints require limit load solutions to be used in engineering fitness‐for‐service (FFS) analysis. The paper, therefore, provides an upper bound limit load solution in closed form for welded T‐joints (idealized) with strength undermatching and subject to a bending moment. In addition to the necessary requirements of the upper bound theorem, the kinematically admissible velocity field chosen leads to a stress field, which satisfies the equilibrium equations and some stress boundary conditions in the plastic zone. This is an advantage of the solution and, therefore, it is expected that the upper bound obtained is close to the exact limit load of such joints. 相似文献
110.
Sushil K. Singh 《Canadian Metallurgical Quarterly》2007,133(2):155-161
A semianalytical model is developed for computing drawdowns in and around a partially penetrating large diameter well. The new model can take into account an unsteady pumping discharge and thus drawdowns during recovery can be computed. This model can also yield the unsteady contributions from well and aquifer storages to the pumped discharge. While developing the model, the flow from the bottom of the well is also accounted. 相似文献