全文获取类型
收费全文 | 211115篇 |
免费 | 3284篇 |
国内免费 | 943篇 |
专业分类
电工技术 | 4091篇 |
综合类 | 875篇 |
化学工业 | 31206篇 |
金属工艺 | 7187篇 |
机械仪表 | 6351篇 |
建筑科学 | 5725篇 |
矿业工程 | 821篇 |
能源动力 | 4865篇 |
轻工业 | 20799篇 |
水利工程 | 1911篇 |
石油天然气 | 843篇 |
武器工业 | 10篇 |
无线电 | 24506篇 |
一般工业技术 | 35537篇 |
冶金工业 | 47695篇 |
原子能技术 | 2868篇 |
自动化技术 | 20052篇 |
出版年
2019年 | 1023篇 |
2018年 | 1736篇 |
2017年 | 2002篇 |
2016年 | 2540篇 |
2015年 | 1990篇 |
2014年 | 2478篇 |
2013年 | 7734篇 |
2012年 | 5692篇 |
2011年 | 7649篇 |
2010年 | 4722篇 |
2009年 | 5426篇 |
2008年 | 5863篇 |
2007年 | 6148篇 |
2006年 | 5440篇 |
2005年 | 7977篇 |
2004年 | 7020篇 |
2003年 | 6442篇 |
2002年 | 5336篇 |
2001年 | 5253篇 |
2000年 | 4534篇 |
1999年 | 4762篇 |
1998年 | 13841篇 |
1997年 | 9744篇 |
1996年 | 7511篇 |
1995年 | 5573篇 |
1994年 | 4813篇 |
1993年 | 4729篇 |
1992年 | 3304篇 |
1991年 | 3235篇 |
1990年 | 3162篇 |
1989年 | 3133篇 |
1988年 | 2945篇 |
1987年 | 2579篇 |
1986年 | 2485篇 |
1985年 | 2933篇 |
1984年 | 2564篇 |
1983年 | 2436篇 |
1982年 | 2344篇 |
1981年 | 2318篇 |
1980年 | 2204篇 |
1979年 | 2066篇 |
1978年 | 1999篇 |
1977年 | 2875篇 |
1976年 | 4049篇 |
1975年 | 1779篇 |
1974年 | 1559篇 |
1973年 | 1597篇 |
1972年 | 1319篇 |
1971年 | 1220篇 |
1970年 | 1051篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Copper films with (1 1 1) texture are of crucial importance in integrated circuit interconnects. We have deposited strongly (1 1 1)-textured thin films of copper by atomic layer deposition (ALD) using [2,2,6,6-tetramethyl-3,5-heptadionato] Cu(II), Cu(thd)2, as the precursor. The dependence of the microstructure of the films on ALD conditions, such as the number of ALD cycles and the deposition temperature was studied by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy. Analysis of (1 1 1)-textured films shows the presence of twin planes in the copper grains throughout the films. SEM shows a labyrinthine structure of highly connected, large grains developing as film thickness increases. This leads to low resistivity and suggests high resistance to electromigration. 相似文献
152.
J. B. Quinn G. E. Schumacher L. W. Schultheis 《Journal of Failure Analysis and Prevention》2004,4(1):41-46
Several days after heart surgery, a patient discovered his upper right canine tooth had broken at the root. Such tooth damage,
recognized post-operatively, is usually assumed to be caused by blunt mechanical force from an instrument used by the anesthesiologist
during placement of a breathing tube at the start of surgery.
In this case, the patient had saved the crown portion of the broken tooth, and it was possible to examine the root fracture
characteristics. The curvature and direction of the crack path and natural tooth situation suggested that failure could be
described through a cantilever beam model. This was confirmed when a whole extracted sample tooth was embedded and broken
by a measured force in a manner consistent with the model. The resulting fracture surface matched that of the patient’s broken
canine tooth. However, the high load and force direction necessary to fracture the root was inconsistent with forces applied
during the anesthesia procedure. The failure analysis and further investigation indicated tooth clenching on the breathing
tube during recovery was the likely cause of fracture.
This paper presents an alternate explanation for intubation-related dental injury, demonstrates the practicality of fractographic
analysis of biological materials, and introduces a methodology for simulating in vitro tooth settings for mechanical testing. 相似文献
153.
We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ?4 ps long pulses of 565 nm laser light with 2×1013 photons/cm2 per pulse and repetition rate of 76 MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (<4 ps). We suggest that the transient IRAV absorption is due to secondary polarons formation following exciton dissociation. 相似文献
154.
155.
156.
Heng Zhang Jack Gromek Gayath W. Fernando Harris L. Marcus Sam Boorse 《Journal of Phase Equilibria》2002,23(3):246-248
The thermal equilibrium decomposition properties of the PdO-Pd system under oxygen partial pressures ranging from 0.1 to 1.0 atm in a total combined pressure of oxygen and nitrogen of 1.0 atm were investigated by means of thermal-gravimetric analyses. The phase diagram of Pd-PdO over the range of oxygen/nitrogen gas concentration was established. The decomposition temperature of PdO to Pd was found to increase with the partial pressure of oxygen. 相似文献
157.
H. W. Brinks V. A. Yartys B. C. Hauback H. Fjellvg B. Ouladdiaf 《Journal of Alloys and Compounds》2002,340(1-2):62-66
TbNiSiD1.78 has been studied by powder neutron diffraction below 100 K. The compound takes the hexagonal room temperature structure at 100 and 50 K (P63/mmc). At 2 K, below the antiferromagnetic ordering temperature of 10 K, there is a small orthorhombic distortion of the lattice. The refined unit-cell dimensions at 2 K (space group Pnma) are a=7.9505(2), b=4.02502(14), c=6.9823(2) Å. The magnetic moments of Tb are 8.71(6) μB, and are ordered antiferromagnetically along a. 相似文献
158.
Younan N.H. Cox B.I. Taylor C.D. Prather W.D. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):394-398
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz 相似文献
159.
160.
Carroll R.D. Merritt S.W. Branciforte E.J. Tanski W.J. Cullen D.E. Sacks R.N. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(3):416-418
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal 相似文献