全文获取类型
收费全文 | 54886篇 |
免费 | 3064篇 |
国内免费 | 165篇 |
专业分类
电工技术 | 787篇 |
综合类 | 80篇 |
化学工业 | 11680篇 |
金属工艺 | 2339篇 |
机械仪表 | 3636篇 |
建筑科学 | 1228篇 |
矿业工程 | 28篇 |
能源动力 | 2336篇 |
轻工业 | 4304篇 |
水利工程 | 284篇 |
石油天然气 | 91篇 |
武器工业 | 2篇 |
无线电 | 8776篇 |
一般工业技术 | 11781篇 |
冶金工业 | 4251篇 |
原子能技术 | 761篇 |
自动化技术 | 5751篇 |
出版年
2024年 | 33篇 |
2023年 | 601篇 |
2022年 | 968篇 |
2021年 | 1649篇 |
2020年 | 1190篇 |
2019年 | 1330篇 |
2018年 | 1619篇 |
2017年 | 1594篇 |
2016年 | 1947篇 |
2015年 | 1459篇 |
2014年 | 2325篇 |
2013年 | 3371篇 |
2012年 | 3594篇 |
2011年 | 4312篇 |
2010年 | 3145篇 |
2009年 | 3302篇 |
2008年 | 3083篇 |
2007年 | 2413篇 |
2006年 | 2251篇 |
2005年 | 1926篇 |
2004年 | 1762篇 |
2003年 | 1652篇 |
2002年 | 1485篇 |
2001年 | 1236篇 |
2000年 | 1101篇 |
1999年 | 1034篇 |
1998年 | 1701篇 |
1997年 | 1095篇 |
1996年 | 892篇 |
1995年 | 643篇 |
1994年 | 522篇 |
1993年 | 436篇 |
1992年 | 327篇 |
1991年 | 299篇 |
1990年 | 288篇 |
1989年 | 266篇 |
1988年 | 227篇 |
1987年 | 185篇 |
1986年 | 139篇 |
1985年 | 124篇 |
1984年 | 96篇 |
1983年 | 67篇 |
1982年 | 42篇 |
1981年 | 43篇 |
1980年 | 35篇 |
1979年 | 33篇 |
1978年 | 31篇 |
1977年 | 45篇 |
1976年 | 68篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
Seong-Ku Kim Joon Kyu Lee Yong-Mo Kim Jae-Hyun Ahn 《Journal of Mechanical Science and Technology》2002,16(7):1009-1018
The Representative Interactive Flamelet (RIF) concept has been applied to numerically simulate the combustion processes and
pollutant formation in the direct injection diesel engine. Due to the ability for interactively describing the transient behaviors
of local flame structures with CFD solver, the RIF concept has the capabilities to predict the auto-ignition and subsequent
flame propagation in the diesel engine combustion chamber as well as to effectively account for the detailed mechanisms of
soot formation, NOX formation including thermal NO path, prompt and nitrous NOX formation, and reburning process. Special emphasis is given to the turbulent combustion model which properly accounts for
vaporization effects on the mixture fraction fluctuations and the pdf model. The results of numerical modeling using the RIF
concept are compared with experimental data and with numerical results of the commonly applied procedure which the low-temperature
and high-temperature oxidation processes are represented by the Shell ignition model and the eddy dissipation model, respectively.
Numerical results indicate that the RIF approach including the vaporization effect on turbulent spray combustion process successfully
predicts the ignition delay time and location as well as the pollutant formation. 相似文献
132.
The flow and heat transfer characteristics of a pair of embedded counter-rotating vortices are studied experimentally. In order to control the strength of longitudinal vortices, angle of attack of the vortex generators is varied from ±20° to ±45°, and the spacing between the vortex generators is 4 cm apart. The heat transfer measurements using thermo-chromatic liquid crystal are made to provide the local surface distributions of heat transfer coefficients. The following conclusions are obtained from the present experiment. For the common-flow-down cases, two maximum values in the local heat transfer distributions exist for the three angles of attack. With the common-flow-up cases, only one maximum value exists. The common-flow-down cases show better heat transfer characteristics than the common-flow-up cases. 相似文献
133.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
134.
The photoelectrochemical behaviors of RuL2(NCS)2 dye-sensitized SnO2/TiO2 coupled solar cell was studied and compared with TiO2 single system. The coupled system shows higher incident photon-to-current conversion efficiency (IPCE) value than the single system. A maximum IPCE value in the coupled system with 3.5 μm-thick SnO2 and 7 μm-thick TiO2 attained 82.4% at 530 nm wavelength. The higher IPCE value in the coupled system is attributed to the charge separation by fast electron transfer process from the excited RuL2(NCS)2 dye to TiO2 to SnO2 in the system with different energy level. 相似文献
135.
136.
Although the literature on the mechanics of cellular materials is vast, there is no theoretical model to account for the effects of axial yielding of struts aligned to the applied loading direction on the plastic yield surface under multiaxial loading conditions. An anisotropic hexagonal model having tapered strut morphology is developed to show these effects on the plastic yield surface under multiaxial tensile loading condition. This model covers several types of cellular structure such as two-dimensional (2D) hexagonal and square cellular materials, and three-dimensional (3D) hexagonal and rhombic cellular materials of rod-like columnar structure. A tetrahedral element with tapered strut morphology is also used for a foam model to illustrate these effects on the yield surface under axisymmetric loading condition. Plastic collapse due to bending moment in the inclined struts is a dominant mode. However, under multiaxial tensile loading, the collapse due to axial yielding of struts parallel to the loading direction is found to be an important mode. The shape of plastic yield surface was found to depend not only on relative density but also on the strut morphology. 相似文献
137.
Woo-Jin Han Eun-Kyoung Kim Yung-Hwan Oh 《Electronics letters》2002,38(6):292-294
A novel frame interpolation technique for two-band linear predictive coding (LPC) vocoders is proposed for maintaining natural speech quality at bit rates below 1 kbit/s. Experimental results show that the speech quality of the proposed vocoder is quite natural at bit rates 880 bit/s and comparable to that of 4.8 kbit/s CELP 相似文献
138.
Smart TDI readout circuit for long-wavelength IR detector 总被引:3,自引:0,他引:3
Byunghyuk Kim Hee Chul Lee 《Electronics letters》2002,38(16):854-855
A smart time delay and integration (TDI) readout circuit is suggested which performs background suppression, cell-to-cell non-uniformity compensation, and dead pixel correction. Using the smart TDI readout circuit, the integration capacitor area occupying almost the whole area of a unit-cell can be reduced to one-fifth and transimpedance gain can increase by five times. From measurement results, it is found that the skimming current error for a few hundred nA background current is < 1.25 nA corresponding to LSB/2 of ADC and the non-uniformity introduced by cell-to-cell background current variation is reduced to 1.02 nA 相似文献
139.
Hong Jeong Jeong‐Ho Park 《International Journal of Adaptive Control and Signal Processing》2002,16(1):1-23
Tracking targets of interest is one of the major research areas in radar surveillance systems. We formulate the problem as incomplete data estimation and apply EM to the MAP estimate. The resulting filter has a recursive structure analogous to the Kalman filter. The advantage is that the measurement‐update deals with multiple measurements in parallel and the parameter‐update estimates the system parameters on the fly. Experiments tracking separate targets in parallel show that tracking maintenance ratio of the proposed system is better than that of NNF and RMS position error is smaller than that of PDAF. Also, the system parameters are correctly obtained even from incorrect initial values. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
140.
Rotating-bending uniaxial fatigue tests and micro-fatigue crack initiation tests were carried out using a permanent mold cast
(PMC) and semi-solid die cast (SDC) with Al−7%Si−0.35%Mg composition in order to examine the relationship between solidification
structures and fatigue behaviors. The crack length was measured using a replication method. Fatigue strength was improved
in SDC, which was almost consistent with the predicted fatigue strength using the size of Si particle cluster. Resistance
to fatigue crack initiation and fatigue strength were improved in SDC owing to the finer Si cluster and to higher ultimate
tensile strength. Fatigue crack in PMC was preferentially initiated at pores. For SDC, the fatigue crack was initiated at
the Si particle/matrix interface, and then sucessively grew along eutectic cell boundaries. 相似文献