全文获取类型
收费全文 | 1044篇 |
免费 | 37篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 22篇 |
综合类 | 2篇 |
化学工业 | 243篇 |
金属工艺 | 27篇 |
机械仪表 | 25篇 |
建筑科学 | 7篇 |
能源动力 | 20篇 |
轻工业 | 55篇 |
无线电 | 89篇 |
一般工业技术 | 193篇 |
冶金工业 | 317篇 |
原子能技术 | 26篇 |
自动化技术 | 57篇 |
出版年
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 19篇 |
2013年 | 52篇 |
2012年 | 24篇 |
2011年 | 31篇 |
2010年 | 26篇 |
2009年 | 39篇 |
2008年 | 35篇 |
2007年 | 27篇 |
2006年 | 26篇 |
2005年 | 29篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 21篇 |
2001年 | 23篇 |
2000年 | 26篇 |
1999年 | 35篇 |
1998年 | 133篇 |
1997年 | 74篇 |
1996年 | 39篇 |
1995年 | 34篇 |
1994年 | 28篇 |
1993年 | 35篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 16篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 5篇 |
排序方式: 共有1083条查询结果,搜索用时 0 毫秒
11.
Watanabe Y. Hing Wong Kirihata T. Kato D. DeBrosse J.K. Hara T. Yoshida M. Mukai H. Quader K.N. Nagai T. Poechmueller P. Pfefferl P. Wordeman M.R. Fujii S. 《Solid-State Circuits, IEEE Journal of》1996,31(4):567-574
This paper describes a 256 Mb DRAM chip architecture which provides up to ×32 wide organization. In order to minimize the die size, three new techniques: an exchangeable hierarchical data line structure, an irregular sense amp layout, and a split address bus with local redrive scheme in the both-ends DQ were introduced. A chip has been developed based on the architecture with 0.25 μm CMOS technology. The chip measures 13.25 mm×21.55 mm, which is the smallest 256 Mb DRAM ever reported. A row address strobe (RAS) access time of 26 ns was obtained under 2.8 V power supply and 85°C. In addition, a 100 MHz×32 page mode operation, namely 400 M byte/s data rate, in the standard extended data output (EDO) cycle has been successfully demonstrated 相似文献
12.
Cobalt molybdenum (Co-Mo) carbides were prepared by the carburization of Co-Mo oxides at temperatures of 723–973 K in a stream of CH4/H2 gas. The carburized catalysts were evaluated using a single-stack fuel cell and three-electrode cell. The results showed high activities for the anodic electrooxidation of hydrogen over the Co-Mo catalysts carburized at 873 and 923 K. The 873 K carburized Co-Mo catalyst had the highest activity and achieved 10.9% of the performance of a commercial Pt/C catalyst in a single-stack fuel cell. The XRD, TPC, TPR and XPS results showed that the Co-Mo oxycarbide in the bulk and on the surface are the active species for the hydrogen oxidation reaction. 相似文献
13.
Hiroyuki Yamada Atsushi Tsurumaki‐Fukuchi Masaki Kobayashi Takuro Nagai Yoshikiyo Toyosaki Hiroshi Kumigashira Akihito Sawa 《Advanced functional materials》2015,25(18):2708-2714
Tunnel electroresistance in ferroelectric tunnel junctions (FTJs) has attracted considerable interest, because of a promising application to nonvolatile memories. Development of ferroelectric thin‐film devices requires atomic‐scale band‐structure engineering based on depolarization‐field effects at interfaces. By using FTJs consisting of ultrathin layers of the prototypical ferroelectric BaTiO3, it is demonstrated that the surface termination of the ferroelectric in contact with a simple‐metal electrode critically affects properties of electroresistance. BaTiO3 barrier‐layers with TiO2 or BaO terminations show opposing relationships between the polarization direction and the resistance state. The resistance‐switching ratio in the junctions can be remarkably enhanced up to 105% at room temperature, by artificially controlling the fraction of BaO termination. These results are explained in terms of the termination dependence of the depolarization field that is generated by a dead layer and imperfect charge screening. The findings on the mechanism of tunnel electroresistance should lead to performance improvements in the devices based on nanoscale ferroelectrics. 相似文献
14.
Osteoclastic features of multinucleated giant cells responding to synthetic hydroxyapatite implanted in rat jaw bone. 总被引:2,自引:0,他引:2
N Takeshita T Akagi M Yamasaki T Ozeki T Nojima Y Hiramatsu N Nagai 《Journal of electron microscopy》1992,41(3):141-146
Multinucleated giant cells (MGCs) that responded to synthetic hydroxyapatite (HAP) implanted in rat mandibles were studied with electron microscopy. HAP used in this study sintered at 200 degrees C (HAP200) and at 125 degrees C (HAP1250) after the synthesis by a wet method. One to three weeks after the intraosseous implantation of HAP, MGCs responding to HAP200 had not only well-developed ruffled border and the clear zone but well-developed perinuclear Golgi complex, many mitochondria and vesicles in their cytoplasms. MGCs responding to HAP1250 had the clear zone, but not the ruffled border although they showed similar cytoplasmic features to those of MGCs responding to HAP200. They merely extended short slender cytoplasmic processes to HAP1250. These results suggest that although osteoclast-like MGCs respond to HAP implanted in the bone, the development of the ruffled border-clear zone system depends on physicochemical properties of HAP. 相似文献
15.
Nagai H. Hishii M. Shibayama K. Nagai A. Akiba T. 《Quantum Electronics, IEEE Journal of》1982,18(3):416-422
Discharge stabilization, long-term operation, output power characteristics, and efficiency of the high-pressure CW CO2 laser have been investigated under sealed conditions. A comparison is made with low-pressure CW CO2 lasers. Two types of electrode structures suitable for operations in the pressure range 100-760 torr are presented. Effects of O2 and CO on the discharge stability and unsaturated gain are described. By using molecular sieve3A as an adsorbent of water vapor, which was the most detrimental impurity, sealed operation with no decrease in output power was achieved at 0.5-1.5 kW for more than 150 h elapsed time including about 30 h of discharge time. It has been demonstrated that high efficiency can be obtained in spite of high-pressure and sealed operation. The efficiency was improved by reducing the cavity loss due to the absorption of intracavity radiation by CO2 molecules in the unexcited region, and by finding the optimum of gas mixture. A maximum efficiency of 19 percent was obtained at a 1 kW power level for a 100 torr gas mixture of either CO2 -CO-N2 -He = 2-1-19-19 or CO2 -CO-N2 -He-Ar = 2-1-18-10-10. The effects of Ar and N2 proportion on the unsaturated gain and saturation parameter are discussed. 相似文献
16.
A novel InP/InGaAsP buried heterostructure laser diode on p-type InP substrate has been developed. The laser has achieved a threshold current as low as 20 mA DC with high power output of 50 mW under CW operation in the fundamental transverse mode. 相似文献
17.
The ideal low- and high-frequency capacitance-voltage curves of a semiconductor(2)-insulator-semiconductor(1) (SIS) structure were first calculated with the insulator thickness, conductivity types and doping concentrations in semiconductor(1) and semiconductor(2) as parameters. The effects of fixed oxide charge and interface trap charge on the low and high frequency capacitance-voltage curves were also calculated. It was found that the fixed oxide sheet charge density with its centroid and the order estimation of the interface trap charge density with its effective type in addition to the insulator thickness, conductivity types and doping concentrations in semiconductor(1) and semiconductor(2) could be estimated from measured low and high frequency capacitance-voltage curves of an SIS structure. 相似文献
18.
Jintong Li Kenichi Tachihara Kazukiyo Nagai Tsutomu Nakagawa Shichang Wang 《应用聚合物科学杂志》1996,60(10):1645-1654
Several sulfolanes such as 3-methylsulfolane, sulfolane, and 3-sulfolene were tested as modifiers in poly(trimethylsilyl methyl methacrylate) (PTMSMMA) and poly(trimethylsilyl propyne) (PMSP) to improve the selectivity of CO2. The gas permeabilities for the PTMSMMA-blend membranes containing high 3-methylsulfolane content were determined on a nonvacuum system in which the membranes started to be measured at their steady states at 30°C; those for all the other membranes were determined in a vacuum system in which those membranes were measured after they reached their unsteady states at 30°C. The PTMSMMA-blend membrane containing 40% 3-methylsulfolane was found to give the best separation of CO2 under the conditions in this study compared to all the PTMSMMA-blend membranes and the others prepared in our work; its ideal separation factors for CO2 over N2 were above 40 and its permeability coefficients of CO2 increased to above 250 Barrer. The modifications of PMSP membranes by impregnating with sulfolane and blending with sulfolene were found to be effective in improving the selectivity for CO2 over N2 for the PMSP membrane. The ideal separation factors for CO2 over N2 for the modified PMSP membranes impregnated with 30% sulfolane and blended with 25% 3-sulfolene were improved to above 10 and 13, respectively. © 1996 John Wiley & Sons, Inc. 相似文献
19.
α-Synuclein (αSyn) plays a major role in the pathogenesis of Parkinson’s disease (PD), which is the second most common neurodegenerative disease after Alzheimer’s disease. The accumulation of αSyn is a pathological hallmark of PD, and mutations in the SNCA gene encoding αSyn cause familial forms of PD. Moreover, the ectopic expression of αSyn has been demonstrated to mimic several key aspects of PD in experimental model systems. Among the various model systems, Drosophila melanogaster has several advantages for modeling human neurodegenerative diseases. Drosophila has a well-defined nervous system, and numerous tools have been established for its genetic analyses. The rapid generation cycle and short lifespan of Drosophila renders them suitable for high-throughput analyses. PD model flies expressing αSyn have contributed to our understanding of the roles of various disease-associated factors, including genetic and nongenetic factors, in the pathogenesis of PD. In this review, we summarize the molecular pathomechanisms revealed to date using αSyn-expressing Drosophila models of PD, and discuss the possibilities of using these models to demonstrate the biological significance of disease-associated factors. 相似文献
20.
Shinji Kanehashi Yuko Tomita Hiroshi Kawakita Shuichi Sato Tetsuo Miyakoshi Kazukiyo Nagai 《应用聚合物科学杂志》2013,129(4):2036-2045
Poly[methacryloxypropylheptacyclopentyl‐T8‐silsesquioxane (MAPOSS)‐co‐3‐methacryloxypropyltris(trimethylsiloxy)silane (SiMA)] was synthesized through free radical polymerization. The physical and carbon dioxide (CO2) sorption properties of the copolymer membranes were investigated in terms of the MAPOSS content. As the MAPOSS content increases, the membrane density increased, suggesting a decrease in the fractional free volume. In addition, the thermal stability was improved with increasing the MAPOSS content. These are because of the polyhedraloligomericilsesquioxane (POSS) units that restrict the high mobility of poly(SiMA) segments. The glass transition temperature, Tg of the copolymers was single Tg based on the differential scanning calorimetry, suggesting that the copolymers were random and not phase separation. Based on the CO2 sorption measurement, the POSS units play a role in reducing Henry's dissolution by suppressing the mobility of the poly(SiMA) component, while POSS units increase the nonequilibrium excess free volume, which contributes to the Langmuir dissolution. Based on these results, the introduction of MAPOSS unit is one of the effective ways to improved the thermal stability and CO2 sorption property due to the enhancement of the polymer rigidity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献