全文获取类型
收费全文 | 21970篇 |
免费 | 1382篇 |
国内免费 | 1033篇 |
专业分类
电工技术 | 1250篇 |
综合类 | 1092篇 |
化学工业 | 6316篇 |
金属工艺 | 1901篇 |
机械仪表 | 826篇 |
建筑科学 | 1130篇 |
矿业工程 | 212篇 |
能源动力 | 371篇 |
轻工业 | 1216篇 |
水利工程 | 120篇 |
石油天然气 | 552篇 |
武器工业 | 129篇 |
无线电 | 1979篇 |
一般工业技术 | 2950篇 |
冶金工业 | 641篇 |
原子能技术 | 330篇 |
自动化技术 | 3370篇 |
出版年
2024年 | 61篇 |
2023年 | 279篇 |
2022年 | 624篇 |
2021年 | 668篇 |
2020年 | 526篇 |
2019年 | 483篇 |
2018年 | 419篇 |
2017年 | 528篇 |
2016年 | 620篇 |
2015年 | 637篇 |
2014年 | 951篇 |
2013年 | 1186篇 |
2012年 | 1232篇 |
2011年 | 1620篇 |
2010年 | 1266篇 |
2009年 | 1365篇 |
2008年 | 1318篇 |
2007年 | 1513篇 |
2006年 | 1409篇 |
2005年 | 1121篇 |
2004年 | 925篇 |
2003年 | 829篇 |
2002年 | 682篇 |
2001年 | 583篇 |
2000年 | 610篇 |
1999年 | 407篇 |
1998年 | 311篇 |
1997年 | 251篇 |
1996年 | 234篇 |
1995年 | 184篇 |
1994年 | 178篇 |
1993年 | 173篇 |
1992年 | 141篇 |
1991年 | 116篇 |
1990年 | 104篇 |
1989年 | 94篇 |
1988年 | 68篇 |
1987年 | 64篇 |
1986年 | 78篇 |
1985年 | 74篇 |
1984年 | 53篇 |
1983年 | 41篇 |
1982年 | 43篇 |
1981年 | 43篇 |
1980年 | 35篇 |
1978年 | 36篇 |
1977年 | 41篇 |
1976年 | 44篇 |
1975年 | 49篇 |
1974年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
Witt Ellen; Frank Rainer; Hengstenberg Wolfgang 《Protein engineering, design & selection : PEDS》1993,6(8):913-920
The 6-phospho-ß-galactosidase of Staphylococcus aureus,Lactococcus lactis and Lactobacillus casei and 6-phospho-ßglucosidaseB of Escherichia coli build a subfamily inside a greater enzymefamily, named the glycosal hydrolase family 1, which, hi addition,contains nine ß-glycosidases of different origins.Kinetic and immunological evidence is provided in this reportwhich strengthens the relationship of the four 6-phospho-ß-glycosidases.It is shown that the 6-phospho-ß-galactosidases and6-phospho-ß-glucosidase B are able to split aromaticß-galactoside phosphates and ß-glucosidephosphates. The turnover numbers of hydrolysis of substrateswith different epimerization at C-4 of the glycon vary up to15-fold only. Two polydonal antisera, one derived against thenative 6-phospho-ß-galactosidase from S.aureus andthe other derived against the 6-phospho-ß-glucosidaseB, cross-reacted with both enzymes. Peptides of the proteinswere separated by reverse phase HPLC. The cross-reacting peptideswere sequenced and shown to be localized at almost the sameposition in the aligned primary structures of both enzymes.An insertion of nine amino adds near these antigenic domainsis unique for the 6-phospho-ß-glycosidases and missingwithin the sequences of the ß-glycoside-specific membersof the family. The lacG gene of a 6-phospho-ß-galactosidasenegative S.aureus mutant was doned into E.coli and sequenced.In the totally inactive mutant protein only the glycine at position332 was changed to an arginine. This amino acid is part of thesequence insertion near the antigenic domain reacting with bothantisera. These data support the assumption that the regionis of great importance for the function of the enzymes and thatit is possible it determines the specificity of the phosphorylatedform of the substrates. In addition, the 6-phospho-ß-galactosidaseof S.aureus was modified by sitedirected mutagenesis of thecorresponding lacG gene hi order to replace residues Glul60and Glu375, which were suspected of being involved hi the generalacid catalysis of substrate hydrolysis, with glutamine residues.The mutant protein 160EQ retained some catalytic activity whilethe protein 375EQ was totally inactive. Glu375 is the activesite nudeophile of the 6-phospho-ß-galactosidase ofS.aureus. It is located in the sequence motif ENG where Glu358was identified as the catalytkally active nudeophile hi theß-glucosidase of Agrobacterium. 相似文献
43.
F. H. Sam Froes 《Powder Metallurgy and Metal Ceramics》2007,46(5-6):303-310
The approaches to production of titanium powder injection molded parts are reviewed. Historically, oxygen levels have been
too high for structural use (particularly with the Ti-6Al-4V alloy). However, recent advances in starting powders, binders
and sintering facilities now allow oxygen levels in the Ti-6Al-4V alloy to be controlled to about 0.2 wt.% oxygen. This should
result in significant expansion of the titanium PIM market place into aerospace, automobiles, surgical instruments, dentistry,
communication devices (such as computers and cell phones), knives and guns.
__________
Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 118–125, 2007. 相似文献
44.
45.
46.
计算机网络的发展日新月异。下一代计算机网络(NGN)的探讨、研究已经成为当前的潮流。下一代网络是目前电信、互联网运营商和设备厂商都在讨论的热点技术,国内外许多网络运营商都在探讨,并正在或考虑建设试验网进行更深入的研究。本文介绍了NGN的定义、主要特点、分层结构和关键技术。 相似文献
47.
When a fault occurs on transmission or distribution systems due to lightning or overvoltage, often an arc discharge occurs at the fault point. The arc discharge, which is caused by a fault current, has a high current, high temperature, strong light emission, etc., thus it sometimes causes heavy damages to electric power equipment. The arc discharge is influenced by the conditions around the arcs, i.e., gas, insulation materials, gap length, weather, etc. Also, the arc voltage along the arc column indicates the characteristics of the arc. If the voltage waveforms of the arcs caused by the fault on transmission or distribution systems are classified, it is possible to find the location and the equipment where the fault occurred. In this paper, the arc voltage data in 6-kV class XLPE cables and 6-kV class overhead lines are analyzed and an artificial neural network method is applied to classify the arc voltage waveforms. The results obtained from the six artificial neural networks developed show that the artificial neural network method is effective for classification of arc voltage waveforms if adequate input parameters are selected. 相似文献
48.
焊前处理方式对LF6铝合金扩散焊的影响 总被引:4,自引:0,他引:4
利用Gleeble-1500热/力模拟试验机,研究了LF6铝合金的扩散焊工艺,通过对焊接温度、压力、时间的调整和选用不同的料前处理方法,确定了最佳的扩散规范,研究结果表明:在一定的温度和时间范围内,LF65铝合金扩散焊接头的剪切哟度随焊接温度和时间的增加而提高;化学浸蚀法比机械打磨法能更有效的去除铝合金表面的氧化膜;在现有试验条件下,得到LF6铝合金扩散焊的最佳规范参数,搭接试扩散焊接头的剪切强度 相似文献
49.
孔婷 《计算机与数字工程》2012,40(5):121-123
IPv6组播技术作为下一代互联网的核心技术之一,相对于IPv4组播技术具有更大的优越性。文章首先对PIM-SM组播协议在IPv6上实现PIM-SM涉及的问题进行了论述,然后在OPNET网络仿真模型中实现了对IPv6和IPv4混合网络场景的配置,进行组播的仿真实验比较单播与组播网络的性能,系统地分析了PIM-SM协议在OPNET中的实现。 相似文献
50.