全文获取类型
收费全文 | 104938篇 |
免费 | 8288篇 |
国内免费 | 4984篇 |
专业分类
电工技术 | 5632篇 |
技术理论 | 5篇 |
综合类 | 8420篇 |
化学工业 | 16894篇 |
金属工艺 | 5352篇 |
机械仪表 | 6100篇 |
建筑科学 | 6570篇 |
矿业工程 | 2358篇 |
能源动力 | 3056篇 |
轻工业 | 8474篇 |
水利工程 | 1882篇 |
石油天然气 | 3772篇 |
武器工业 | 690篇 |
无线电 | 13769篇 |
一般工业技术 | 12403篇 |
冶金工业 | 5716篇 |
原子能技术 | 1355篇 |
自动化技术 | 15762篇 |
出版年
2024年 | 319篇 |
2023年 | 1193篇 |
2022年 | 2297篇 |
2021年 | 3206篇 |
2020年 | 2519篇 |
2019年 | 2223篇 |
2018年 | 2429篇 |
2017年 | 2710篇 |
2016年 | 2613篇 |
2015年 | 3510篇 |
2014年 | 4703篇 |
2013年 | 6098篇 |
2012年 | 6720篇 |
2011年 | 7430篇 |
2010年 | 6678篇 |
2009年 | 6649篇 |
2008年 | 6695篇 |
2007年 | 6323篇 |
2006年 | 6062篇 |
2005年 | 5029篇 |
2004年 | 4225篇 |
2003年 | 3986篇 |
2002年 | 4739篇 |
2001年 | 4078篇 |
2000年 | 2803篇 |
1999年 | 2140篇 |
1998年 | 1897篇 |
1997年 | 1460篇 |
1996年 | 1272篇 |
1995年 | 1083篇 |
1994年 | 834篇 |
1993年 | 660篇 |
1992年 | 507篇 |
1991年 | 422篇 |
1990年 | 393篇 |
1989年 | 302篇 |
1988年 | 274篇 |
1987年 | 229篇 |
1986年 | 159篇 |
1985年 | 179篇 |
1984年 | 150篇 |
1983年 | 106篇 |
1982年 | 89篇 |
1981年 | 78篇 |
1980年 | 99篇 |
1979年 | 63篇 |
1978年 | 68篇 |
1977年 | 70篇 |
1976年 | 91篇 |
1975年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
高白度漂白商品浆的白度已从通常的88%~90%提高到更高的水平,达到92%.这种高白度的要求导致了纸厂使用高价格光学漂白剂,以及过量使用这种添加剂的环境风险. 相似文献
62.
Effect of Thickness of the p-AlGaN Electron Blocking Layer on the Improvement of ESD Characteristics in GaN-Based LEDs 总被引:1,自引:0,他引:1
Chung-Hsun Jang Sheu J.K. Tsai C.M. Shei S.C. Lai W.C. Chang S.J. 《Photonics Technology Letters, IEEE》2008,20(13):1142-1144
The following letter presents a study regarding GaN-based light-emitting diodes (LEDs) with p-type AlGaN electron blocking layers (EBLs) of different thicknesses. The study revealed that the LEDs could endure higher electrostatic discharge (ESD) levels as the thickness of the AlGaN EBL increased. The observed improvement in the ESD endurance ability could be attributed to the fact that the thickened p-AlGaN EBL may partly fill the dislocation-related pits that occur on the surface of the InGaN-GaN multiple-quantum well (MQW) and that are due to the strain and the low-temperature-growth process. If these dislocation-related pits are not partly suppressed, they will eventually result in numerous surface pits associated with threading dislocations that intersect the InGaN-GaN (MQW), thereby reducing the ESD endurance ability. The results of the experiment show that the ESD endurance voltages could increase from 1500 to 6000 V when the thickness of the p-AlGaN EBL in the GaN LEDs is increased from 32.5 to 130 nm, while the forward voltages and light output powers remained almost the same. 相似文献
63.
64.
65.
66.
In this paper we verified the submodeling technique applied in the thermomechanical reliability assessment of a flip-chip BGA under accelerated thermal cycling test conditions. Since the steady-state creep model was implemented for the solder bump to better represent its realistic mechanical behavior, submodeling procedures developed specifically for path-dependent thermomechanical problems were considered. A detailed global model for the flip-chip BGA was built up to verify submodeling solutions. This model also served as a benchmark to examine solution discrepancies caused by different simplifications of the global model. 相似文献
67.
68.
Hong Long Chen 《Canadian Metallurgical Quarterly》2007,23(4):171-181
The difficulty in applying the standard curve (S-curve) and cost-schedule integration (CSI) techniques for company-level cost flow forecasting in a project-based industry is the prerequisite of forecasting future unknown individual projects and contract classifications. By analyzing cost flows at the company level through a pool of macroeconomic and internal financial data, this paper proposes an innovative approach to firm-specific model estimation. First, a series of data transformations introduce linear relationships between cost, macroeconomic, and internal financial variables. Second, multivariate regression analysis is employed for initial model building. Third, for the purposes of model restructuring, a subsequent application of Yule–Walker estimates and incomplete principal component analysis is used. This paper uses a sample of four project-based construction firms to demonstrate model performance. Using this methodology, mean absolute percentage error (MAPE) values of the forecasting models range from 0.27 to 0.60%. As such, the transformed cost, macroeconomic, internal financial data could strongly predict company-level cost flow forecasting. While converting the predicted cumulative cost data to periodic cost flows, the MAPE values were augmented, ranging from 7.04 to 17.55%, thus, requiring future research. 相似文献
69.
Shuenn-Yih Chang 《Canadian Metallurgical Quarterly》2007,133(5):555-565
It was found that the discontinuity at the end of an impulse will lead to numerical inaccuracy as this discontinuity will result in an extra impulse and thus an extra displacement in the time history analysis. In addition, this extra impulse is proportional to the discontinuity value at the end of the impulse and the size of integration time step. To overcome this difficulty, an effective approach is proposed to reduce the extra impulse and hence the extra displacement. In fact, the novel approach proposed in this paper is to perform a single small time step immediately upon the termination of applied impulse, whereas other time steps can be conducted by using the step size determined from accuracy consideration in period. The feasibility of this approach is analytically explored. Further, analytical results are confirmed by numerical examples. Numerical studies also show that this approach can be applied to other step-by-step integration methods. It seems that to slightly complicate the programming of dynamic analysis codes is the only disadvantage of this approach. 相似文献
70.
官泓 《有色冶金设计与研究》2003,24(3):49-51
阐述水厂设计中对水厂规模、水源地、净水厂位置及净水工艺的确定过程,根据原水的特点,通过分析对无阀滤池进行改良。 相似文献