全文获取类型
收费全文 | 16807篇 |
免费 | 1084篇 |
国内免费 | 841篇 |
专业分类
电工技术 | 1057篇 |
综合类 | 787篇 |
化学工业 | 5339篇 |
金属工艺 | 1628篇 |
机械仪表 | 614篇 |
建筑科学 | 926篇 |
矿业工程 | 175篇 |
能源动力 | 250篇 |
轻工业 | 946篇 |
水利工程 | 58篇 |
石油天然气 | 475篇 |
武器工业 | 108篇 |
无线电 | 1473篇 |
一般工业技术 | 1964篇 |
冶金工业 | 536篇 |
原子能技术 | 243篇 |
自动化技术 | 2153篇 |
出版年
2024年 | 58篇 |
2023年 | 240篇 |
2022年 | 557篇 |
2021年 | 599篇 |
2020年 | 445篇 |
2019年 | 397篇 |
2018年 | 320篇 |
2017年 | 401篇 |
2016年 | 518篇 |
2015年 | 531篇 |
2014年 | 760篇 |
2013年 | 953篇 |
2012年 | 990篇 |
2011年 | 1258篇 |
2010年 | 989篇 |
2009年 | 1060篇 |
2008年 | 963篇 |
2007年 | 1135篇 |
2006年 | 1074篇 |
2005年 | 828篇 |
2004年 | 681篇 |
2003年 | 606篇 |
2002年 | 532篇 |
2001年 | 411篇 |
2000年 | 355篇 |
1999年 | 287篇 |
1998年 | 229篇 |
1997年 | 181篇 |
1996年 | 164篇 |
1995年 | 109篇 |
1994年 | 94篇 |
1993年 | 108篇 |
1992年 | 85篇 |
1991年 | 74篇 |
1990年 | 64篇 |
1989年 | 64篇 |
1988年 | 45篇 |
1987年 | 41篇 |
1986年 | 54篇 |
1985年 | 56篇 |
1984年 | 46篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1978年 | 35篇 |
1977年 | 39篇 |
1976年 | 43篇 |
1975年 | 48篇 |
1974年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Polyamide (PA6) and polycarbonate (PC) were prepared by a Brabender mixer ( PLV- 151) at 240℃ with 30 rpm for duration of 8 and 6 minutes respectively. The epoxy resin (E) addition can lead to substantial microstructural changes in the PA6/PC blends. Scanning electron microscope (SEM) was used to observe the mixtures characterized by the domains of clearly segregated homophases and voids between the two polymers. PA6/PC of polyamide 6 and polycarbonate with epoxy resin addition under the composition ratio of 20/80, 20/80/1, 40/60/1 and 40/60, were tested to verify the key role of epoxy in promoting the compatibility of PA6 with PC during blending. 相似文献
52.
53.
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
54.
Journal of Electronic Materials - Low pressure chemical vapor deposition (LPCVD) of tungsten (W) by SiH4 reduction of WF6 on Si(100) surfaces was studied in a single-wafer, cold-wall reactor over a... 相似文献
55.
56.
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
57.
58.
59.
60.
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