全文获取类型
收费全文 | 8883篇 |
免费 | 882篇 |
国内免费 | 486篇 |
专业分类
电工技术 | 674篇 |
综合类 | 545篇 |
化学工业 | 1364篇 |
金属工艺 | 447篇 |
机械仪表 | 488篇 |
建筑科学 | 630篇 |
矿业工程 | 238篇 |
能源动力 | 259篇 |
轻工业 | 611篇 |
水利工程 | 224篇 |
石油天然气 | 292篇 |
武器工业 | 97篇 |
无线电 | 1133篇 |
一般工业技术 | 1155篇 |
冶金工业 | 776篇 |
原子能技术 | 118篇 |
自动化技术 | 1200篇 |
出版年
2024年 | 41篇 |
2023年 | 154篇 |
2022年 | 291篇 |
2021年 | 389篇 |
2020年 | 334篇 |
2019年 | 277篇 |
2018年 | 270篇 |
2017年 | 320篇 |
2016年 | 325篇 |
2015年 | 387篇 |
2014年 | 503篇 |
2013年 | 651篇 |
2012年 | 635篇 |
2011年 | 617篇 |
2010年 | 524篇 |
2009年 | 500篇 |
2008年 | 477篇 |
2007年 | 444篇 |
2006年 | 385篇 |
2005年 | 336篇 |
2004年 | 238篇 |
2003年 | 224篇 |
2002年 | 253篇 |
2001年 | 219篇 |
2000年 | 135篇 |
1999年 | 126篇 |
1998年 | 203篇 |
1997年 | 141篇 |
1996年 | 119篇 |
1995年 | 85篇 |
1994年 | 66篇 |
1993年 | 70篇 |
1992年 | 53篇 |
1991年 | 54篇 |
1990年 | 38篇 |
1989年 | 32篇 |
1988年 | 26篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 21篇 |
1978年 | 10篇 |
1977年 | 36篇 |
1976年 | 61篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
The effect of charge on the dihydrogen storage capacity of Sc2–C6H6 has been investigated at B3LYP-D3/6-311G(d,p) level. The neutral system Sc2–C6H6 can store 8H2 with gravimetric density of 8.76 wt %, and one H2 dissociates and bonds atomically on the scandium atom. The adsorption of 8H2 on Sc2–C6H6 is energetically favorable below 155 K. The atom-centered density matrix propagation (ADMP) molecular dynamics simulations show that Sc2–C6H6 can adsorb 3H2 within 1000 fs at 300K. Compared with Sc2–C6H6, the charged systems can adsorb more hydrogen molecules with higher gravimetric density, and all the H2 are adsorbed in the molecular form. The gravimetric densities of Sc2–C6H6+ and Sc2–C6H62+ are 9.75 and 10.71 wt%. Moreover, the maximum adsorption of charged systems are favorable in wider temperature range. Most importantly, the ADMP-MD simulations indicate that Sc2–C6H62+ can adsorb 6 hydrogen molecules within 1000 fs at 300K. It can be found that the gravimetric density (6.72 wt%) of Sc2–C6H62+ still exceeds the target of US Department of Energy (DOE) under ambient conditions. 相似文献
4.
Yang Yueyi Wang Lide Chen Huang Wang Chong 《Analog Integrated Circuits and Signal Processing》2021,107(3):605-616
Analog Integrated Circuits and Signal Processing - Fault diagnosis of analog circuit is critical to improve safety and reliability in electrical systems and reduce losses. Traditional fault... 相似文献
5.
Lai-Ying Leong Teck-Soon Hew Keng-Boon Ooi Alain Yee Loong Chong Voon-Hsien Lee 《Information & Management》2021,58(2):103416
This paper examines what influences trust in mobile social commerce environment. Drawing on trust-based acceptance model (i.e. cognitive and emotional trust) and online review features (i.e. profile photo, linguistic style, and reported experience), we examine how these factors affect trust in mobile social commerce. Hypotheses were tested using survey data. The results of our model showed that there are significant influences of profile photo, reported experience, cognitive, and emotional trust towards trust in ms-commerce. This work contributes to existing literature by examining the roles of previous trust in mobile payments and online reviews on trust in mobile social commerce. 相似文献
6.
Chong D. Y. R. Lim B. K. Rebibis K. J. Pan S. J. Sivalingam K. Kapoor R. Sun A. Y. S. Tan H. B. 《Advanced Packaging, IEEE Transactions on》2006,29(4):674-682
The recent advancement in high- performance semiconductor packages has been driven by the need for higher pin count and superior heat dissipation. A one-piece cavity lid flip chip ball grid array (BGA) package with high pin count and targeted reliability has emerged as a popular choice. The flip chip technology can accommodate an I/O count of more than five hundreds500, and the die junction temperature can be reduced to a minimum level by a metal heat spreader attachment. None the less, greater expectations on these high-performance packages arose such as better substrate real estate utilization for multiple chips, ease in handling for thinner core substrates, and improved board- level solder joint reliability. A new design of the flip chip BGA package has been looked into for meeting such requirements. By encapsulating the flip chip with molding compound leaving the die top exposed, a planar top surface can be formed. A, and a flat lid can then be mounted on the planar mold/die top surface. In this manner the direct interaction of the metal lid with the substrate can be removed. The new package is thus less rigid under thermal loading and solder joint reliability enhancement is expected. This paper discusses the process development of the new package and its advantages for improved solder joint fatigue life, and being a multichip package and thin core substrate options. Finite-element simulations have been employed for the study of its structural integrity, thermal, and electrical performances. Detailed package and board-level reliability test results will also be reported 相似文献
7.
8.
The accurate prediction of the propagation of a wetting front in an unsaturated soil subjected to surficial infiltration is of practical importance to many geotechnical and geoenvironmental problems. The finite element method is the most common solution technique as the hydraulic soil properties are highly nonlinear. Two important issues are often found to create difficulties in such analyses. First, numerical oscillations are usually observed in the calculated pore pressures at the wetting front. Second, when a reasonable mesh size and time step are used, the elevation of the wetting front may be seriously overpredicted. This paper is focused on the second issue. The under-relaxation (UR) technique used in the iterative process within each time step is found to have a serious impact on rate of convergence with refinement in mesh size and time step. Two different techniques are typically used; the first evaluates the hydraulic conductivity using an average of heads calculated from the preceding time node and the most recent iteration of the current time node (UR1), and the second evaluates the hydraulic conductivity using the average of heads calculated from the two most recent iterations of the current time nodes (UR2). The study shows that UR1, which is adopted in programs such as SEEP/W, ensures that the solution converges rapidly to a stable solution within a time step, but may converge to the wrong wetting front at a given elapsed time unless a sufficiently refined mesh is used. UR2 converges much more slowly within a time step, but the error in the wetting front is smaller than that generated by UR1. 相似文献
9.
Petroleum asphaltenes have been precipitated in solvent mixtures of n-heptane and toluene at various temperatures, likewise n-heptane asphaltenes have been dissolved in under similar conditions. This give added evidence to apparent hysteresis phenomenon between the two processes. The Asphaltenes have been characterized showing that although data is scattered convergence to certain structural parameters as incipient flocculation is approached. The asphaltenes are seen to consist of an associating and a non-associating part. The solubility of asphaltenes has been correlated/modelled using the Flory-Huggins equation using two different terms for the Flory parameter. A process for evaluation of best choice of solubility parameter and molar volume for the asphaltenes is proposed. Dissolution processes are seen to be best fitted by the equations. Based on these findings the asphaltenes are proposed to be formed by a colloidal and a true solution part. 相似文献
10.
Delay-dependent state estimation for delayed neural networks 总被引:3,自引:0,他引:3
Yong He Qing-Guo Wang Min Wu Chong Lin 《Neural Networks, IEEE Transactions on》2006,17(4):1077-1081
In this letter, the delay-dependent state estimation problem for neural networks with time-varying delay is investigated. A delay-dependent criterion is established to estimate the neuron states through available output measurements such that the dynamics of the estimation error is globally exponentially stable. The proposed method is based on the free-weighting matrix approach and is applicable to the case that the derivative of a time-varying delay takes any value. An algorithm is presented to compute the state estimator. Finally, a numerical example is given to demonstrate the effectiveness of this approach and the improvement over existing ones. 相似文献