全文获取类型
收费全文 | 3812篇 |
免费 | 468篇 |
国内免费 | 314篇 |
专业分类
电工技术 | 308篇 |
综合类 | 425篇 |
化学工业 | 229篇 |
金属工艺 | 77篇 |
机械仪表 | 213篇 |
建筑科学 | 776篇 |
矿业工程 | 92篇 |
能源动力 | 345篇 |
轻工业 | 64篇 |
水利工程 | 610篇 |
石油天然气 | 37篇 |
武器工业 | 19篇 |
无线电 | 585篇 |
一般工业技术 | 396篇 |
冶金工业 | 81篇 |
原子能技术 | 19篇 |
自动化技术 | 318篇 |
出版年
2024年 | 16篇 |
2023年 | 86篇 |
2022年 | 121篇 |
2021年 | 169篇 |
2020年 | 177篇 |
2019年 | 135篇 |
2018年 | 101篇 |
2017年 | 141篇 |
2016年 | 158篇 |
2015年 | 167篇 |
2014年 | 242篇 |
2013年 | 263篇 |
2012年 | 311篇 |
2011年 | 335篇 |
2010年 | 249篇 |
2009年 | 228篇 |
2008年 | 196篇 |
2007年 | 259篇 |
2006年 | 212篇 |
2005年 | 167篇 |
2004年 | 128篇 |
2003年 | 137篇 |
2002年 | 111篇 |
2001年 | 76篇 |
2000年 | 74篇 |
1999年 | 61篇 |
1998年 | 61篇 |
1997年 | 41篇 |
1996年 | 35篇 |
1995年 | 29篇 |
1994年 | 28篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1982年 | 2篇 |
1980年 | 7篇 |
1951年 | 1篇 |
排序方式: 共有4594条查询结果,搜索用时 15 毫秒
1.
Numerical dissipation acts as artificial viscosity to make smoke viscous. Reducing numerical dissipation is able to recover visual details smeared out by the numerical dissipation. Great efforts have been devoted to suppress the numerical dissipation in smoke simulation in the past few years. In this paper we investigate methods of combating the numerical dissipation. We describe visual consequences of the numerical dissipation and explore sources that introduce the numerical dissipation into course of smoke simulation. Methods are investigated from various aspects including grid variation, high-order advection, sub-grid compensation, invariant conservation, and particle-based improvement, followed by discussion and comparison in terms of visual quality, computational overhead, ease of implementation, adaptivity, and scalability, which leads to their different applicability to various application scenarios. 相似文献
2.
新型的芯片间互连用CMOS/BiCMOS驱动器 总被引:5,自引:2,他引:3
从改善不同类型 IC芯片之间的电平匹配和驱动能力出发 ,设计了几例芯片间接口 (互连 )用 CMOS/Bi CMOS驱动电路 ,并提出了采用 0 .5 μm Bi CMOS工艺 ,制备所设计驱动器的技术要点和元器件参数。实验结果表明所设计驱动器既具有双极型电路快速、大电流驱动能力的特点 ,又具备 CMOS电路低压、低功耗的长处 ,因而它们特别适用于低电源电压、低功耗高速数字通信电路和信息处理系统。 相似文献
3.
4.
本文回顾了PCB制造常用的环氧树脂及其增强材料的性能和用途。同时,还介绍了代用树脂材料和代用增强材料的最新进展,如改性环氧树脂、无卤树脂、Thermount、PTFE、氰酸酯等,并就其性能进行了探讨。 相似文献
5.
6.
D. SHERMAN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(1):32-40
Fracture experiments with silicon specimens in recent years have shown the need for a new approach to the analysis of rapidly propagating cracks in single crystals. Behaviour and phenomena have been revealed that fracture in these materials is rather different from the fracture of both amorphous and polycrystalline materials. We show that continuum mechanics is insufficient for analyzing crack propagation in single crystals since it is unable to consider atomistic‐scale phenomena. Accordingly, we describe basic phenomena associated with rapid crack propagation in silicon : (i) anisotropic velocity‐dependent R‐curve behaviour, as a key phenomenon dictating atomistic scale behaviour, (ii) crack deflection from one cleavage plane to another as a mesoscopic scale phenomenon in single‐crystal fracture, (iii) the Rayleigh surface wave speed as the limiting crack tip velocity is re‐examined, (vi) the lowest crack velocity in brittle crystals is examined, and finally (v) the interaction between crack path and preferred cleavage planes in single crystals is depicted. 相似文献
7.
Rahul Sarpeshkar Richard F. Lyon Carver Mead 《Analog Integrated Circuits and Signal Processing》1998,16(3):245-274
Low-power wide-dynamic-range systems are extremely hard to build. The biological cochlea is one of the most awesome examples of such a system: It can sense sounds over 12 orders of magnitude in intensity, with an estimated power dissipation of only a few tens of microwatts. In this paper, we describe an analog electronic cochlea that processes sounds over 6 orders of magnitude in intensity, and that dissipates 0.5 mW. This 117-stage, 100 Hz to 10 KHz cochlea has the widest dynamic range of any artificial cochlea built to date. The wide dynamic range is attained through the use of a wide-linear-range transconductance amplifier, of a low-noise filter topology, of dynamic gain control (AGC) at each cochlear stage, and of an architecture that we refer to as overlapping cochlear cascades. The operation of the cochlea is made robust through the use of automatic offset-compensation circuitry. A BiCMOS circuit approach helps us to attain nearly scale-invariant behavior and good matching at all frequencies. The synthesis and analysis of our artificial cochlea yields insight into why the human cochlea uses an active traveling-wave mechanism to sense sounds, instead of using bandpass filters. The low power, wide dynamic range, and biological realism make our cochlea well suited as a front end for cochlear implants. 相似文献
8.
本文介绍红外热象技术在工程热物理研究中某些应用的探索。作为实例,通过热象技术,实验研究了具有水平凸台离散热源的倾斜板的散热,在研究它的自然对流换热部份结合利用激光全息干涉技术。此间着重于分析倾斜角对散热的影响。 相似文献
9.
Dmitri E. Nikonov George I. Bourianoff Paolo A. Gargini 《Journal of Superconductivity and Novel Magnetism》2006,19(6):497-513
Quantum limits of power dissipation in spintronic computing are estimated. A computing element composed of a single electron
in a quantum dot is considered. Dynamics of its spin due to external magnetic field and interaction with adjacent dots are
described via the Bloch equations. Spin relaxation due to magnetic noise from various sources is described as coupling to
a reservoir. Resulting dissipation of energy is calculated and is shown to be much less than the thermal limit, ∼kT per bit,
if the rate of spin relaxation is much slower than the switching rate. Clues on how to engineer an energy efficient spintronic
device are provided. 相似文献
10.
A. G. ATKINS Z. CHEN B. COTTERELL 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(1):67-77
In this paper, energy dissipation rate D vs. Δa curves in ductile fracture are predicted using a ‘conversion’ between loads, load‐point displacements and crack lengths predicted by NLEFM and those found in real ELPL propagation. The NLEFM/ELPL link was recently discovered for the DCB testpiece, and we believe it applies to other cracked geometries. The predictions for D agree with experimental results. The model permits a crack tip toughness R(Δa) which rises from Jc and saturates out when (if) steady state propagation is reached after a transient stage in which all tunnelling, crack tip necking and shear lip formation is established. JR is always greater than the crack tip R(Δa) and continues to rise even after R(Δa) levels off. The analysis is capable of predicting the usual D vs. Δa curves in the literature which have high initial values and fall monotonically to a plateau at large Δa. It also predicts that D curves for CCT testpieces should be higher than those for SENB/CT, as found in practice. The possibility that D curves at some intermediate Δa may dip to a minimum below the levelled‐off value at large Δa is predicted and confirmed by experiment. Recently reported D curves that have smaller initial D than the D‐values after extensive propagation can also be predicted. The testpiece geometry and crack tip R(Δa) conditions required to produce these different‐shaped D vs. Δa curves are established and confirmed by comparison with experiment. The energy dissipation rate D vs. Δa is not a transferable property as it depends on geometry. The material characteristic R(Δa) may be the ‘transferable property’ for scaling problems in ELPL fracture. How it can be deduced from D vs. Δa curves (and by implication, JR vs. Δa curves) is established. 相似文献