全文获取类型
收费全文 | 2472篇 |
免费 | 10篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 66篇 |
金属工艺 | 53篇 |
机械仪表 | 8篇 |
建筑科学 | 4篇 |
能源动力 | 10篇 |
轻工业 | 41篇 |
水利工程 | 1篇 |
石油天然气 | 2篇 |
无线电 | 56篇 |
一般工业技术 | 142篇 |
冶金工业 | 1983篇 |
原子能技术 | 54篇 |
自动化技术 | 61篇 |
出版年
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 6篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 28篇 |
2012年 | 33篇 |
2011年 | 28篇 |
2010年 | 31篇 |
2009年 | 34篇 |
2008年 | 31篇 |
2007年 | 18篇 |
2006年 | 28篇 |
2005年 | 16篇 |
2004年 | 15篇 |
2003年 | 14篇 |
2002年 | 13篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 58篇 |
1998年 | 600篇 |
1997年 | 320篇 |
1996年 | 249篇 |
1995年 | 154篇 |
1994年 | 118篇 |
1993年 | 108篇 |
1992年 | 26篇 |
1991年 | 43篇 |
1990年 | 40篇 |
1989年 | 22篇 |
1988年 | 31篇 |
1987年 | 32篇 |
1986年 | 28篇 |
1985年 | 39篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 34篇 |
1976年 | 110篇 |
1975年 | 11篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1968年 | 3篇 |
排序方式: 共有2486条查询结果,搜索用时 17 毫秒
1.
Wireless Personal Communications - Multiple-input–multiple-output orthogonal frequency division multiplexing (MIMO–OFDM) is a promising 4G technology to increase data rate and capacity... 相似文献
2.
Inam Ridha Ali Basiri Sudhakar Godeshala Md Zubair Ebne Rafique Deepanjan Ghosh Jason Williams Nikhilesh Chawla Jung Keun Lee Jacquelyn Kilbourne Yu Yao Kaushal Rege 《Advanced functional materials》2021,31(6):2007811
Poor strength, infection, leakage, long procedure times, and inflammation limit the efficacy of common tissue sealing devices in surgeries and trauma. Light-activated sealing is attractive for tissue sealing and repair, and can be facilitated by the generation of local heat following absorption of nonionizing laser energy by chromophores. Here, the inherent ability of biomaterials is exploited to absorb nonionizing, mid-infrared (midIR) light in order to engender rapid photothermal sealing and repair of soft tissue wounds. In this approach, the biomaterial simultaneously acts as a photothermal convertor as well as a biosealant, which dispenses the need for exogeneous light-absorbing nanoparticles or dyes. Biomechanical recovery, mathematical modeling, histopathology analyses, tissue strain mapping using digital imaging correlation, and visualization of the biosealant-tissue interface using hyperspectral imaging indicate superior performance of midIR sealing in live mice compared to conventional sutures and glue. The midIR-biosealant approach demonstrates rapid sealing of soft tissues, improves cosmesis, lowers potential for scarring, obviates safety concerns because of the nonionizing light used, and allows adoption of a wide diversity of biomaterials. Taken together, the studies demonstrate a novel advance both in biomaterials for surgical sealing along with the use of nonionizing midIR light, with high potential for clinical translation. 相似文献
3.
4.
5.
6.
Numerical and semi-analytical results of the propagation of high-power ultra-short near IR laser pulses propagating in ionizing air are presented. 相似文献
7.
8.
Cerium (Ce)-containing Sn-3.9Ag-0.7Cu alloy exhibits desirable attributes of microstructural refinement, increased ductility, and mechanical shock performance, while possessing better oxidation resistance than other rare-earth-containing solders. In addition to the beneficial mechanical properties, it is imperative to study the reliability performance of novel solder alloys in the form of electromigration experiments, in comparison with Sn-3.9Ag-0.7Cu. In this study, electromigration tests were conducted on solder joints at elevated temperature with a constant current using a V-groove testing methodology. The microstructural change of solder joints during electromigration was investigated by scanning electron microscopy, and the void growth was monitored utilizing the three-dimensional (3D) x-ray microtomography imaging technique. The current density inside the solder matrix was determined by 3D microstructure-based finite-element modeling. Finally, the product of diffusivity and effective charge number of solder joints during electromigration was calculated from both marker displacement and 3D void growth. It was found that electromigration-induced Cu diffusion in Sn-3.9Ag-0.7Cu-0.5Ce alloy was greatly accelerated, and void formation at the cathode side was retarded as a result of finer microstructure and existence of CeSn3 intermetallic particles. 相似文献
9.
S.S. Singh R. Sarkar H.-X. Xie C. Mayer J. Rajagopalan N. Chawla 《Journal of Electronic Materials》2014,43(4):978-982
The growth of metallic (predominantly Sn) whiskers from pure metallic platings has been studied for over 50 years. While the phenomenon of Sn whiskering has been studied for decades, very little is known about the mechanical properties of these materials. This can be attributed to the difficulty in handling, gripping, and testing such fine-diameter and high-aspect-ratio whiskers. We report on the stress–strain behavior of Sn whiskers inside a dual-beam focused ion beam (FIB) with a scanning electron microscope (SEM). Lift-out of the whiskers was conducted in situ in the FIB, and the whiskers were tested using a microelectromechanical system tensile testing stage. Using this technique, the whiskers had minimum exposure to ambient air and were not handled by hand. SEM images after fracture enabled reliable calculation of the whisker cross-sectional area. Tests on two different whiskers revealed relatively high tensile strengths of 720 MPa and 880 MPa, respectively, and a limited strain to failure of ~2% to 3%. For both whiskers, the Young’s modulus was between 42 GPa and 45 GPa. It is interesting to note that the whiskers were quite strong and had limited ductility. These findings are intriguing and provide a basis for further work to understand the effect of Sn whisker mechanical properties on short circuits in electronics. 相似文献
10.
Bhanu K. Patibandla Akshita Narra Ranil DeSilva Varun Chawla Yael Vin Robert S. Brown Alexander S. Goldfarb‐Rumyantzev 《Hemodialysis international. International Symposium on Home Hemodialysis》2014,18(1):118-126
The benefits of an arteriovenous fistula (AVF) as the preferred vascular access for hemodialysis have been clearly demonstrated. However, only about 20% of patients in the United States initiate hemodialysis with an AVF. In this study, we assessed whether disparities exist in the type of first hemodialysis access placed prior to dialysis start (rather than that used at dialysis initiation), to detect whether certain disadvantaged groups might have lower likelihood of AVF placement. Study cohort of 118,767 incident hemodialysis patients ≥67 years of age (1/2005–12/2008) derived from the United States Renal Data System was linked with Medicare claims data to identify the type of initial access placed predialysis. We used logistic regression model with outcome being the initial predialysis placement of an AVF as opposed to an arteriovenous graft or a central venous catheter. Increasing age, female sex, black race, lower body mass index, urban location, certain comorbidities, and shorter pre–end‐stage renal disease nephrology care are all associated with a significantly lower likelihood of AVF placement as initial access predialysis. Our study suggests the presence of significant disparities in the placement of an AVF as initial hemodialysis vascular access. We suggest that additional attention should be paid to these patient groups to improve disparities by patient education, earlier referral, and close follow‐up. 相似文献