全文获取类型
收费全文 | 403773篇 |
免费 | 15570篇 |
国内免费 | 7828篇 |
专业分类
电工技术 | 13038篇 |
综合类 | 9906篇 |
化学工业 | 57732篇 |
金属工艺 | 17639篇 |
机械仪表 | 14811篇 |
建筑科学 | 13539篇 |
矿业工程 | 5467篇 |
能源动力 | 10195篇 |
轻工业 | 37921篇 |
水利工程 | 6324篇 |
石油天然气 | 8936篇 |
武器工业 | 1613篇 |
无线电 | 43492篇 |
一般工业技术 | 69396篇 |
冶金工业 | 68644篇 |
原子能技术 | 9036篇 |
自动化技术 | 39482篇 |
出版年
2022年 | 5357篇 |
2021年 | 7556篇 |
2020年 | 5591篇 |
2019年 | 4910篇 |
2018年 | 7295篇 |
2017年 | 7691篇 |
2016年 | 7741篇 |
2015年 | 7437篇 |
2014年 | 10482篇 |
2013年 | 20123篇 |
2012年 | 16360篇 |
2011年 | 19208篇 |
2010年 | 16292篇 |
2009年 | 16701篇 |
2008年 | 17407篇 |
2007年 | 17044篇 |
2006年 | 14444篇 |
2005年 | 12456篇 |
2004年 | 11210篇 |
2003年 | 9877篇 |
2002年 | 9277篇 |
2001年 | 8978篇 |
2000年 | 8299篇 |
1999年 | 7949篇 |
1998年 | 20985篇 |
1997年 | 14362篇 |
1996年 | 10743篇 |
1995年 | 7892篇 |
1994年 | 6924篇 |
1993年 | 7011篇 |
1992年 | 4670篇 |
1991年 | 4472篇 |
1990年 | 4373篇 |
1989年 | 4333篇 |
1988年 | 4000篇 |
1987年 | 3596篇 |
1986年 | 3594篇 |
1985年 | 3955篇 |
1984年 | 3619篇 |
1983年 | 3339篇 |
1982年 | 3191篇 |
1981年 | 3229篇 |
1980年 | 3229篇 |
1979年 | 2949篇 |
1978年 | 2975篇 |
1977年 | 3451篇 |
1976年 | 4701篇 |
1975年 | 2499篇 |
1974年 | 2440篇 |
1973年 | 2459篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The authors describe a scalable neural system, HyperNet, based on a probabilistic RAM-based architecture and using a custom VLSI IC. A system using five HyperNet VLSI ICs and capable of realising up to 10240 neurons has been designed, manufactured and demonstrated to have the potential to learn more than three orders of magnitude faster than simulations on current workstations 相似文献
992.
Blumenthal D.J. Prucnal P.R. Sauer J.R. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1994,82(11):1650-1667
Photonic packet switches offer high speed, data rate and format transparency, and flexibility required by future computer communications and cell-based telecommunications networks. In this paper, we review experimental progress in state-of-the-art photonic packet switches with an emphasis on all-optical guided-wave systems. The term all-optical implies that the data portion of a packet remains in optical format from the source to the destination. While the data remain all-optical, both optical and optoelectronic techniques have been used to process packet routing functions based on extremely simple routing protocols. An overview of the design issues for all-optical photonic packet switching is given and contrasted with electronic packet switch implementations. Low-level functions that have been experimentally implemented include routing, contention resolution, synchronization, and header regeneration. System level demonstrations, including centralized photonic switching and distributed all-optical multihop networks, will be reviewed 相似文献
993.
A computer method for the calculation of the phase shift due to optically injected carriers in an InP avalanche transit time diode has been suggested using the numerically simulated negative resistance profiles in the depletion layer of the diode. The results show that the phase shift due to hole injection is larger than that due to electron injection which explains the pronounced effect of photogenerated hole leakage current in modulating the microwave properties of InP diodes 相似文献
994.
Cadiou J.F. Guena J. Penard E. Legaud P. Minot C. Palmier J.F. Le Person H. Harmand J.E. 《Electronics letters》1994,30(20):1690-1691
For the first time, a direct optically injection-locked oscillator based on the Esaki-Tsu effect in superlattices is reported. The microwave output power is -7 dBm at 20 GHz with an optical input power of -10 dBm at a wavelength of 1.3 μm 相似文献
995.
Characterization of a diffusion-bonded Al-Mg alloy/SiC interface by high resolution and analytical electron microscopy 总被引:6,自引:0,他引:6
The interfacial structure of a diffusion-bonded Al-4.55 at. pct Mg/SiC interface was examined by conventional and high-resolution
transmission electron microscopy. Formation of Mg2Si, MgO, and Al2MgO4 was observed. The monoclinic Mg2Si phase formed at the Al/SiC interface, while the oxides MgO and Al2MgO4 formed at the monoclinic Mg2Si/Al interface. It is shown that the formation of these phases can be predicted using simple thermodynamic criteria such
as the relative bond strengths between Al, Si, C, O, and Mg. In addition, precipitation of some equilibrium Al8Mg5 precipitate was also observed at the interface. The interfacial structure observed in the Al-Mg/SiC system is contrasted
with that observed in the pure Al/SiC system. 相似文献
996.
997.
Solving the experimental difficulties associated with measurement of the electrical impedance of living tissues gives access to valuable tissue compartment parameters which are sensed within seconds using minimally invasive, simple metallic electrodes. Extracellular conductivity and cell membrane capacitance can be followed over time under conditions of metabolic toxicity, perfusion loss and thermal stress in liver, brain cortex, and muscle, respectively. Application of this technique in burns therapy allows an accurate estimation of the severity of thermal injury to skeletal muscle, supporting predictions on tissue survival. 相似文献
998.
SH Braat B Leclercq R Itti A Lahiri B Sridhara P Rigo 《Canadian Metallurgical Quarterly》1994,35(10):1581-1585
There is no evidence of myocardial redistribution after tetrofosmin injection, therefore, two separate injections are needed to differentiate scar from ischemia with this tracer. The injections can be given on the same day (one-day protocol) or on separate days (two-day protocol). As part of a Phase II clinical study, a one-day protocol was compared with a two-day protocol. METHODS: Fifty-five patients with suspected coronary artery disease were studied according to the following protocol: on the first day at rest, anterior, left lateral, left anterior oblique 40 degrees and 70 degrees images were acquired 30 min after injection of 8 mCi of tetrofosmin for 5 min each. Two days later, exercise and rest images were acquired on the same day. At peak exercise, 8 mCi of tetrofosmin were injected and 30 min later the same four standard planar images were recorded as on Day one. Four hours after the exercise injection, 24 mCi of tetrofosmin were injected at rest and imaging was repeated 30 min later. Qualitative comparisons between the one- and two-day protocols were performed in 50 patients in whom all data were available following blinded evaluation of images by three readers. RESULTS: All three readers reported identical results for the 26 patients. A difference in extent or location between the observers was found in seven patients, differences between normal and abnormal in eight patients, while discrepancies between ischemia and necrosis were noted in four patients. In five patients, an ischemic area was found according to the one-day protocol, but according to the data of the two-day protocol, this area was judged to be necrotic. One observer reported the opposite in one patient. These discrepancies between the reversibility of defects were restricted to the inferior wall. Comparison with 201Tl data showed no systematic pattern of variation. CONCLUSION: Tetrofosmin can be used in a one-day protocol. However, in planar imaging, the inferior wall should be reported with caution. 相似文献
999.
1000.
Preparative isoelectric focusing in multicompartment electrolyzers is based on the production of isoelectric membranes of precise isoelectric point, able to buffer at their pI value and to titrate proteins tangent to or crossing the membranes. Up to the present, such membranes have been based on polyacrylamide chemistry; acrylamide, however, is neither stable in acidic nor basic environments. We describe here novel membranes, produced with a unique monomer, N-acryloylaminoethoxyethanol (AAEE). Poly(AAEE) membranes are extremely stable to alkaline hydrolysis (500 times more stable than polyacrylamide) and even more hydrophilic than the latter matrix. This allows production of highly reproducible membranes (these do not change their pI with time, since no acrylic acid is produced by hydrolysis upon storage) which do not adsorb proteins by hydrophobic interaction. 相似文献