收费全文 | 309888篇 |
免费 | 9014篇 |
国内免费 | 4474篇 |
电工技术 | 9164篇 |
技术理论 | 5篇 |
综合类 | 4395篇 |
化学工业 | 45505篇 |
金属工艺 | 14997篇 |
机械仪表 | 10854篇 |
建筑科学 | 11707篇 |
矿业工程 | 1982篇 |
能源动力 | 8374篇 |
轻工业 | 28210篇 |
水利工程 | 2938篇 |
石油天然气 | 4513篇 |
武器工业 | 503篇 |
无线电 | 39340篇 |
一般工业技术 | 54199篇 |
冶金工业 | 53904篇 |
原子能技术 | 4730篇 |
自动化技术 | 28056篇 |
2022年 | 2588篇 |
2021年 | 4130篇 |
2020年 | 2896篇 |
2019年 | 2981篇 |
2018年 | 4144篇 |
2017年 | 4226篇 |
2016年 | 4258篇 |
2015年 | 4331篇 |
2014年 | 6120篇 |
2013年 | 14765篇 |
2012年 | 9484篇 |
2011年 | 12174篇 |
2010年 | 10227篇 |
2009年 | 10781篇 |
2008年 | 11431篇 |
2007年 | 11393篇 |
2006年 | 10753篇 |
2005年 | 9626篇 |
2004年 | 8530篇 |
2003年 | 8304篇 |
2002年 | 8367篇 |
2001年 | 8314篇 |
2000年 | 7519篇 |
1999年 | 8211篇 |
1998年 | 18226篇 |
1997年 | 12972篇 |
1996年 | 10248篇 |
1995年 | 7710篇 |
1994年 | 6723篇 |
1993年 | 6346篇 |
1992年 | 4579篇 |
1991年 | 4416篇 |
1990年 | 3882篇 |
1989年 | 3759篇 |
1988年 | 3639篇 |
1987年 | 3037篇 |
1986年 | 2943篇 |
1985年 | 3496篇 |
1984年 | 3110篇 |
1983年 | 2792篇 |
1982年 | 2596篇 |
1981年 | 2600篇 |
1980年 | 2462篇 |
1979年 | 2295篇 |
1978年 | 2251篇 |
1977年 | 2823篇 |
1976年 | 4179篇 |
1975年 | 1905篇 |
1974年 | 1807篇 |
1973年 | 1792篇 |
Large scale wireless sensor networks raise many challenges in the design of efficient and effective routing algorithm due to their complexity and hardware constraints. However, the scalability challenge may be mitigated from a macroscopic perspective. One example is the distributed De la Garza iteration (DDLGI) algorithm for global routing load-balancing, based on a set of partial differential equations iteratively solved by the De la Garza method. We theoretically analyze the parallelism of DDLGI and illustrate that the region of interest may impact the degree of parallelism and error. Furthermore, though DDLGI always converges, the slow convergence and long-range information exchange problems may lead to excess energy consumption in communication. Thus, we propose various enhanced De la Garza routing (E-DLGR) algorithms to alleviate the energy consumption problem by which nodes may exchange less information and only need to exchange information with closer nodes to complete each iteration. Our theoretical analysis and simulation results show that the proposed E-DLGR algorithms may have less transmission overhead, thus further reducing energy consumption, and converge faster while still maintaining adequate accuracy.
相似文献In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N2 gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 105 particles/cm3) corresponding to a volume fraction below 3 × 10–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.