全文获取类型
收费全文 | 106495篇 |
免费 | 1515篇 |
国内免费 | 1236篇 |
专业分类
电工技术 | 2167篇 |
综合类 | 148篇 |
化学工业 | 11303篇 |
金属工艺 | 5546篇 |
机械仪表 | 3266篇 |
建筑科学 | 2098篇 |
矿业工程 | 159篇 |
能源动力 | 3080篇 |
轻工业 | 6374篇 |
水利工程 | 714篇 |
石油天然气 | 670篇 |
武器工业 | 15篇 |
无线电 | 16266篇 |
一般工业技术 | 22349篇 |
冶金工业 | 26014篇 |
原子能技术 | 1490篇 |
自动化技术 | 7587篇 |
出版年
2022年 | 499篇 |
2021年 | 765篇 |
2020年 | 547篇 |
2019年 | 725篇 |
2018年 | 1179篇 |
2017年 | 1123篇 |
2016年 | 1225篇 |
2015年 | 982篇 |
2014年 | 1556篇 |
2013年 | 4820篇 |
2012年 | 2692篇 |
2011年 | 4009篇 |
2010年 | 3237篇 |
2009年 | 3846篇 |
2008年 | 4038篇 |
2007年 | 4205篇 |
2006年 | 3817篇 |
2005年 | 3410篇 |
2004年 | 3266篇 |
2003年 | 3137篇 |
2002年 | 2750篇 |
2001年 | 3063篇 |
2000年 | 2789篇 |
1999年 | 3175篇 |
1998年 | 9742篇 |
1997年 | 6366篇 |
1996年 | 4916篇 |
1995年 | 3266篇 |
1994年 | 2875篇 |
1993年 | 2809篇 |
1992年 | 1674篇 |
1991年 | 1633篇 |
1990年 | 1565篇 |
1989年 | 1370篇 |
1988年 | 1211篇 |
1987年 | 887篇 |
1986年 | 927篇 |
1985年 | 948篇 |
1984年 | 832篇 |
1983年 | 723篇 |
1982年 | 728篇 |
1981年 | 703篇 |
1980年 | 597篇 |
1979年 | 500篇 |
1978年 | 436篇 |
1977年 | 563篇 |
1976年 | 990篇 |
1975年 | 314篇 |
1974年 | 283篇 |
1973年 | 273篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
Service Load Effective Compression Flange Width in Fiber Reinforced Polymer Deck Systems Acting Compositely with Steel Stringers 总被引:1,自引:0,他引:1
This paper reports on the field study of a steel stringer-fiber reinforced polymer (FRP) deck composite bridge in Pennsylvania. The objective of the study is to assess the effective compression flange width in the FRP deck and floor systems when they act compositely with underlying steel girders at service conditions. The research results reported herein support the notion of employing a design approach, for both interior and exterior girders of a composite floor system, that is philosophically consistent with current practice related to steel girders acting compositely with concrete decking. It appears from the results presented herein that FRP decks and floors acting compositely with underlying steel girders exhibit an effective width that is close to the actual girder spacing for interior beams, and approximately one-half this value for exterior beams. 相似文献
994.
P. Kundu K.R. Justin Thomas J.T. Lin Y.‐T. Tao C.‐H. Chien 《Advanced functional materials》2003,13(6):445-452
A series of dicarbazolyl derivatives bridged by various aromatic spacers and decorated with peripheral diarylamines were synthesized using Ullmann and Pd‐catalyzed C–N coupling procedures. These derivatives emit blue light in solution. In general, they possess high glass‐transition temperatures (Tg > 125 °C) which vary with the bridging segment and methyl substitution on the peripheral amine. Double‐layer organic light‐emitting devices were successfully fabricated using these molecules as hole‐transporting and emitting materials. Devices of the configuration ITO/HTL/TPBI/Mg:Ag (ITO: indium tin oxide; HTL: hole‐transporting layer; TPBI: 1,3,5‐tris(N‐phenylbenzimidazol‐2‐yl)benzene) display blue emission from the HTL layer. The EL spectra of these devices appear slightly distorted due to the exciplex formation at the interfaces. However, for the devices of the configuration ITO/HTL/Alq3/Mg:Ag (Alq3 = tris(8‐hydroxyquinoline)aluminum) a bright green light from the Alq3 layer was observed. This clearly demonstrates the facile hole‐transporting property of the materials described here. 相似文献
995.
We address the problem of computing fundamental performance bounds for estimation of object boundaries from noisy measurements in inverse problems, when the boundaries are parameterized by a finite number of unknown variables. Our model applies to multiple unknown objects, each with its own unknown gray level, or color, and boundary parameterization, on an arbitrary known background. While such fundamental bounds on the performance of shape estimation algorithms can in principle be derived from the Cramer-Rao lower bounds, very few results have been reported due to the difficulty of computing the derivatives of a functional with respect to shape deformation. We provide a general formula for computing Cramer-Rao lower bounds in inverse problems where the observations are related to the object by a general linear transform, followed by a possibly nonlinear and noisy measurement system. As an illustration, we derive explicit formulas for computed tomography, Fourier imaging, and deconvolution problems. The bounds reveal that highly accurate parametric reconstructions are possible in these examples, using severely limited and noisy data. 相似文献
996.
997.
998.
999.
Yamaoka M. Maeda N. Shinozaki Y. Shimazaki Y. Nii K. Shimada S. Yanagisawa K. Kawahara T. 《Solid-State Circuits, IEEE Journal of》2006,41(3):705-711
The power consumption of a low-power system-on-a-chip (SoC) has a large impact on the battery life of mobile appliances. General SoCs have large on-chip SRAMs, which consume a large proportion of the whole LSI power. To achieve a low-power SoC, we have developed embedded SRAM modules, which use some low-power SRAM techniques. One technique involves expanding the write margin; another is a power-line-floating write technique, which enables low-voltage write operation. The power-line-floating write technique makes it possible to lower the minimum operating supply voltage by 100 mV. The other techniques involve using a process-variation-adaptive write replica circuit and reducing leakage current. These techniques reduce active power during write operations by 18% and reduce active leakage of the word-line driver by 64%. The prototype SRAM modules achieve 0.8-V operation, and a 512-kb SRAM module achieves 48.4-/spl mu/A active leakage and 7.8-/spl mu/A standby leakage with worst-leakage devices. 相似文献
1000.