全文获取类型
收费全文 | 307038篇 |
免费 | 4411篇 |
国内免费 | 1157篇 |
专业分类
电工技术 | 5267篇 |
综合类 | 2651篇 |
化学工业 | 42540篇 |
金属工艺 | 12859篇 |
机械仪表 | 9050篇 |
建筑科学 | 6978篇 |
矿业工程 | 1432篇 |
能源动力 | 6253篇 |
轻工业 | 21788篇 |
水利工程 | 3119篇 |
石油天然气 | 3314篇 |
武器工业 | 17篇 |
无线电 | 37834篇 |
一般工业技术 | 58066篇 |
冶金工业 | 54469篇 |
原子能技术 | 3971篇 |
自动化技术 | 42998篇 |
出版年
2021年 | 1917篇 |
2020年 | 1446篇 |
2019年 | 1720篇 |
2018年 | 16998篇 |
2017年 | 15853篇 |
2016年 | 12753篇 |
2015年 | 2888篇 |
2014年 | 3772篇 |
2013年 | 9847篇 |
2012年 | 8803篇 |
2011年 | 16521篇 |
2010年 | 14105篇 |
2009年 | 12182篇 |
2008年 | 13880篇 |
2007年 | 14801篇 |
2006年 | 6595篇 |
2005年 | 7154篇 |
2004年 | 6841篇 |
2003年 | 6669篇 |
2002年 | 5837篇 |
2001年 | 5742篇 |
2000年 | 5397篇 |
1999年 | 5923篇 |
1998年 | 17628篇 |
1997年 | 11542篇 |
1996年 | 8824篇 |
1995年 | 6343篇 |
1994年 | 5465篇 |
1993年 | 5428篇 |
1992年 | 3567篇 |
1991年 | 3446篇 |
1990年 | 3362篇 |
1989年 | 3205篇 |
1988年 | 2937篇 |
1987年 | 2384篇 |
1986年 | 2435篇 |
1985年 | 2826篇 |
1984年 | 2493篇 |
1983年 | 2236篇 |
1982年 | 2026篇 |
1981年 | 2211篇 |
1980年 | 1954篇 |
1979年 | 1779篇 |
1978年 | 1757篇 |
1977年 | 2227篇 |
1976年 | 3178篇 |
1975年 | 1513篇 |
1974年 | 1452篇 |
1973年 | 1428篇 |
1972年 | 1170篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
231.
232.
M. Loidl E. Leblanc T. Branger H. Rotzinger T. Daniyarov M. Linck A. Fleischmann C. Enss 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):73-75
We report on a feasibility study on precise determination of mass-specific activity of low-energy emitting radioisotopes. Conventional methods of activity measurement suffer from source self-absorption and a strong decrease in detection efficiency for low-energy electrons and photons. We propose a new method based on metallic magnetic microcalorimeters with the source embedded in the detector target in a 4π geometry. First results with a 55Fe source show that electrons and photons are detected with a detection efficiency close to unity and with little loss of energy for electrons. The aim of this study is to provide standards of activity with very low uncertainties in the framework of radiation metrology. 相似文献
233.
B. A. Young J. R. Williams S. W. Deiker S. T. Ruggiero B. Cabrera 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):307-310
We summarize a continuing investigation into using ion implantation to alter the transition temperature of superconducting thin films. The primary motivation for the work presented here was to study the feasibility of using magnetic ion doping to replace the bi-layer Tc control process currently used for certain cryogenic detector applications at National Institute for Standards and Technology. The results from work with various ion species implanted into aluminum, molybdenum, titanium and tungsten host films are presented. 相似文献
234.
S. Zh. Davrenbekov E. S. Mustafin B. K. Kasenov S. T. Edil'baeva Sh. B. Kasenova E. K. Zhumadilov Zh. I. Sagintaeva 《Inorganic Materials》2004,40(9):976-978
NdMCr2O5 (M = Na, K, Cs) and NdMgCr2O5.5 are prepared by solid-state reactions between appropriate oxides and carbonates and are shown to have a tetragonal structure. The heat capacity of these chromites, measured from 298.15 to 673 K, exhibits sharp changes attributable to second-order phase transitions. The C
p
0(T) data are represented by quadratic best fit equations. The electrical resistivity of the chromites is measured between 303 and 493 K. The results attest to semiconducting behavior of the materials in certain temperature ranges. 相似文献
235.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property. 相似文献
236.
The phase relations of the ternary system Cu-In-Se were studied at 750° C by quenching experiments. Special attention was given to the region CuInSe2In2Se3-In4Se3. Only four ternary phases with extended homogeneity ranges were found to exist. They were characterized by X-ray powder diffraction, electron microprobe analysis (EK8PA)' end optical microscopy. Differential thermal analysis (DTA) investigations allowed us to construct theT-x diagram of the Cu2Se-In2Se3. out between 47 and 100 mol% In2Se3. Besides, it was also possible to give a tentative diagram of the solid-liquid equilibria at 750° C and to get some information on the sub-solid existence fields beside the Cu2Se-In2Se3 cut. 相似文献
237.
238.
Peak-to-average power reduction in space division multiplexing based OFDM systems through spatial shifting 总被引:2,自引:0,他引:2
A new method to reduce the peak-to-average power ratio (PAPR) in space division multiplexing systems applying orthogonal frequency division multiplexing is proposed. The method applies spatial shifting to partial transmit sequences to achieve a decreased PAPR on all transmit branches. 相似文献
239.
Alinur Büyükaksoy 《电信纪事》1985,40(7-8):402-410
An asymptotic solution to the problem of the diffraction of high-frequency waves by the edge of a cylindrically curved surface whose convex and concave faces present soft and hard boundary conditions is obtained. The results permit us to define new diffraction coefficients related to this kind of mixed boundary conditions. When the radius of the curvature becomes infinitely large, the edgediffraction coefficient reduces to this known for the softhard half-plane. 相似文献
240.