全文获取类型
收费全文 | 234712篇 |
免费 | 15766篇 |
国内免费 | 7955篇 |
专业分类
电工技术 | 11934篇 |
技术理论 | 10篇 |
综合类 | 12915篇 |
化学工业 | 34279篇 |
金属工艺 | 13464篇 |
机械仪表 | 12302篇 |
建筑科学 | 14163篇 |
矿业工程 | 4611篇 |
能源动力 | 5672篇 |
轻工业 | 14433篇 |
水利工程 | 4613篇 |
石油天然气 | 7315篇 |
武器工业 | 1453篇 |
无线电 | 28380篇 |
一般工业技术 | 34135篇 |
冶金工业 | 9669篇 |
原子能技术 | 2146篇 |
自动化技术 | 46939篇 |
出版年
2024年 | 607篇 |
2023年 | 2449篇 |
2022年 | 4920篇 |
2021年 | 6955篇 |
2020年 | 4980篇 |
2019年 | 3993篇 |
2018年 | 18455篇 |
2017年 | 17983篇 |
2016年 | 14243篇 |
2015年 | 7084篇 |
2014年 | 8395篇 |
2013年 | 10274篇 |
2012年 | 14141篇 |
2011年 | 21244篇 |
2010年 | 18439篇 |
2009年 | 15281篇 |
2008年 | 16294篇 |
2007年 | 16674篇 |
2006年 | 8763篇 |
2005年 | 8275篇 |
2004年 | 5882篇 |
2003年 | 4903篇 |
2002年 | 4179篇 |
2001年 | 3146篇 |
2000年 | 3060篇 |
1999年 | 2875篇 |
1998年 | 2530篇 |
1997年 | 2126篇 |
1996年 | 1989篇 |
1995年 | 1575篇 |
1994年 | 1259篇 |
1993年 | 1004篇 |
1992年 | 815篇 |
1991年 | 597篇 |
1990年 | 480篇 |
1989年 | 375篇 |
1988年 | 332篇 |
1987年 | 218篇 |
1986年 | 179篇 |
1985年 | 161篇 |
1984年 | 107篇 |
1983年 | 79篇 |
1982年 | 79篇 |
1981年 | 68篇 |
1980年 | 61篇 |
1976年 | 62篇 |
1968年 | 50篇 |
1959年 | 48篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
971.
从北京地区公众成年人~(232)Th 的膳食日食入量,空气日吸入量,以及骨中~(232)Th 的沉积量出发,利用 ICRP 30号报告中参考人的代谢参数和内照射的库室模型,估算了北京地区公众成年人膳食摄入~(232)Th 后经胃肠道向体液转移份额 f_1值。结果表明,对于公众中成年人0.005是 f_1值的合适代表值,是 ICRP 30号报告推荐值 f_1=0.0002的25倍。虽然 ICRP 推荐值并不用于公众,但可以对群体有所了解;而北京地区从实测数据资料出发导出的 f_1值可能是更适于公众的。 相似文献
972.
Lead zirconate titanates (Pb (Zrx Ti1–x )O3 or PZT) are well-known materials with useful ferroelectric properties for nonvolatile memory applications. The device applications usually require processes which form the ferroelectric perovskite phase at low temperatures. Understanding the various aspects of structure development of PZT films is the key to develop low-temperature processes. An effective, versatile, and nondestructive optical method was developed for the study of the structure development in PZT films. Also, models for the structure development were proposed and were verified by this optical method. Using this method, the characteristic temperatures at which both pyrochlore phase and perovskite phase are initiated and completed were identified. The pyrochloreperovskite transformation was initiated at lower temperature and completed faster for the films on the titanium-rich side than those on the zirconium-rich side. In addition, the volume fractions of the perovskite phase were obtained as a function of annealing temperature by this optical method. 相似文献
973.
The unity gain buffer will be good to design high frequency SCF if its resistiveeffects can be eliminated,and therefore the whole parasitic sensitivities will greatly be reduced.On the basis of this concept,a novel parasitic tolerant SC DTE(differential transconductanceelement)is proposed.SC floating inductor and integrator fit for high frequency applications areformed by the DTE.The computer simulation and experiment on a third order elliptic LP filterverify its validity. 相似文献
974.
Pole-Shang Lin Ching-Yuan Wu 《Electron Devices, IEEE Transactions on》1991,38(6):1376-1383
A new simplified two-dimensional model for the threshold voltage of MOSFETs is derived in terms of simple characteristic functions. These characteristic functions are transformed from the exact series solution of the two-dimensional Poisson's equation, in which the effects of a nonuniformly doped substrate and a finite graded source-drain junction depth are included. In this model, charge-screening effects are proposed to account for the weak dependence of the threshold voltage on the substrate bias for short-channel MOSFETs, and exact source and drain boundary potentials can be approximated by their equivalent power functions. The accuracy of the simplified 2-D model is verified by 2-D numerical analysis. Moreover, comparisons between the simplified 2-D model and the experimental results are made, and good agreement is obtained for wide ranges of channel lengths, applied substrate, and drain biases 相似文献
975.
976.
977.
978.
979.
Co-evolution as a computational and cognitive model of design 总被引:6,自引:0,他引:6
Co-evolutionary design has been developed as a computational model that assumes two parallel search spaces: the problem space
and the solution space. The design process iteratively searches each space using the other space as the basis for a fitness
function when evaluating the alternatives. Co-evolutionary design can also be developed as a cognitive model of design by
characterizing the way in which designers iteratively search for a design solution, making revisions to the problem specification.
This paper presents the computational model of co-evolutionary design and then describes a protocol study of human designers
looking for evidence of co-evolution of problem specifications and design solutions. The study shows that co-evolutionary
design is a good cognitive model of design and highlights the similarities and differences between the computational model
and the cognitive model. The results show that the two kinds of co-evolutionary design complement each other, having strengths
in different aspects of the design process.
Electronic Publication 相似文献
980.
He G.S. Helgeson R. Lin T.-C. Qingdong Zheng Wudl F. Prasad P.N. 《Quantum Electronics, IEEE Journal of》2003,39(8):1003-1008
We report the observation of one-, two-, and three-photon pumped lasing in the same medium, a novel liquid dye salt system when excited by pulsed 0.532-, 1.06-, and /spl sim/1.49-/spl mu/m coherent radiation pulses, respectively. Since the gain medium is a liquid and not a solution, it contains a significantly higher effective dye concentration and, therefore, is highly suitable for multiphoton pumped lasing and optical power limiting applications. The lasing spectra, temporal waveforms, near- and far-field intensity distributions, and output/input efficiency were measured under the conditions of one-, two-, and three-photon pump configurations. 相似文献