全文获取类型
收费全文 | 56918篇 |
免费 | 3642篇 |
国内免费 | 76篇 |
专业分类
电工技术 | 401篇 |
综合类 | 134篇 |
化学工业 | 12364篇 |
金属工艺 | 1077篇 |
机械仪表 | 1179篇 |
建筑科学 | 1711篇 |
矿业工程 | 137篇 |
能源动力 | 1308篇 |
轻工业 | 10209篇 |
水利工程 | 562篇 |
石油天然气 | 295篇 |
武器工业 | 7篇 |
无线电 | 2310篇 |
一般工业技术 | 9209篇 |
冶金工业 | 11645篇 |
原子能技术 | 248篇 |
自动化技术 | 7840篇 |
出版年
2024年 | 96篇 |
2023年 | 488篇 |
2022年 | 864篇 |
2021年 | 1691篇 |
2020年 | 1234篇 |
2019年 | 1391篇 |
2018年 | 2214篇 |
2017年 | 2193篇 |
2016年 | 2311篇 |
2015年 | 1695篇 |
2014年 | 2179篇 |
2013年 | 4508篇 |
2012年 | 3490篇 |
2011年 | 3365篇 |
2010年 | 2726篇 |
2009年 | 2480篇 |
2008年 | 2356篇 |
2007年 | 2112篇 |
2006年 | 1557篇 |
2005年 | 1305篇 |
2004年 | 1161篇 |
2003年 | 1148篇 |
2002年 | 988篇 |
2001年 | 770篇 |
2000年 | 700篇 |
1999年 | 763篇 |
1998年 | 3692篇 |
1997年 | 2455篇 |
1996年 | 1612篇 |
1995年 | 954篇 |
1994年 | 740篇 |
1993年 | 790篇 |
1992年 | 305篇 |
1991年 | 281篇 |
1990年 | 217篇 |
1989年 | 232篇 |
1988年 | 242篇 |
1987年 | 213篇 |
1986年 | 176篇 |
1985年 | 210篇 |
1984年 | 188篇 |
1983年 | 134篇 |
1982年 | 170篇 |
1981年 | 196篇 |
1980年 | 216篇 |
1979年 | 103篇 |
1978年 | 103篇 |
1977年 | 351篇 |
1976年 | 747篇 |
1973年 | 94篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
131.
132.
G Armengol M Tarkkanen M Virolainen A Forus J Valle T B?hling S Asko-Seljavaara C Blomqvist I Elomaa E Karaharju AH Kivioja MA Siimes E Tukiainen MR Caballín O Myklebost S Knuutila 《Canadian Metallurgical Quarterly》1997,75(10):1403-1409
Comparative genomic hybridization (CGH) was used to detect copy number changes of DNA sequences in the Ewing family of tumours (ET). We analysed 20 samples from 17 patients. Fifteen tumours (75%) showed copy number changes. Gains of DNA sequences were much more frequent than losses, the majority of the gains affecting whole chromosomes or whole chromosome arms. Recurrent findings included copy number increases for chromosomes 8 (seven out of 20 samples; 35%), 1q (five samples; 25%) and 12 (five samples; 25%). The minimal common regions of these gains were the whole chromosomes 8 and 12, and 1q21-22. High-level amplifications affected 8q13-24, 1q and 1q21-22, each once. Southern blot analysis of the specimen with high-level amplification at 1q21-22 showed an amplification of FLG and SPRR3, both mapped to this region. All cases with a gain of chromosome 12 simultaneously showed a gain of chromosome 8. Comparison of CGH findings with cytogenetic analysis of the same tumours and previous cytogenetic reports of ET showed, in general, concordant results. In conclusion, our findings confirm that secondary changes, which may have prognostic significance in ET, are trisomy 8, trisomy 12 and a gain of DNA sequences in 1q. 相似文献
133.
AI Quintero Del Río 《Canadian Metallurgical Quarterly》1997,89(1-3):12-14
Motor vehicle accidents are the main cause of death and disability between 1 and 4 years of age. Since 1980 the Academy of Pediatrics has been promoting the correct use of car seats. The major reason that car seats are not fulfilling their full potential is their incorrect or lack of use. In order to evaluate parental knowledge about car seat use for children and their actual use in the population visiting HURRA, a survey was performed which demonstrated that only 57.6% of the parents interviewed had infant car seats and that only 83.3% of owners actually use it. As many as 94.4% had correct knowledge about car seat use, but the majority of correct information was not provided by the medical staff. The majority of parents use seat belts for their own protection but a significantly smaller percentage use car seats for their own children. 相似文献
134.
135.
J Nesvera M Pátek J Hochmannová Z Abrhámová V Becvárová M Jelínkova J Vohradsky 《Canadian Metallurgical Quarterly》1997,179(5):1525-1532
The complete nucleotide sequence (4,826 bp) of the cryptic plasmid pGA1 from Corynebacterium glutamicum was determined. DNA sequence analysis revealed four putative coding regions (open reading frame A [ORFA], ORFA2, ORFB, and ORFC). ORFC was identified as a rep gene coding for an initiator of plasmid replication (Rep) according to the high level of homology of its deduced amino acid sequence with the Rep proteins of plasmids pSR1 (from C. glutamicum) and pNG2 (from Corynebacterium diphtheriae). This function was confirmed by deletion mapping of the minimal replicon of pGA1 (1.7 kb) which contains only ORFC. Deletion derivatives of pGA1 devoid of ORFA exhibited significant decreases in the copy number in C. glutamicum cells and displayed segregational instability. Introduction of ORFA in trans into the cells harboring these deletion plasmids dramatically increased their copy number and segregational stability. The ORFA gene product thus positively influences plasmid copy number. This is the first report on such activity associated with a nonintegrating bacterial plasmid. The related plasmids pGA1, pSR1, and pNG2 lacking significant homology with any other plasmid seem to be representatives of a new group of plasmids replicating in the rolling-circle mode. 相似文献
136.
137.
The neuronal cytoskeleton is one of the most profoundly altered organelles in late life neuro-degenerative disorders that are characterized by progressive impairments in cognitive abilities. The elucidation of the protein building blocks of these organelles as well as advances in understanding how these proteins become altered in Alzheimer's disease (AD) and other less common dementing illnesses, i.e., diffuse Lewy body disease (DLBD) or the Lewy body variant of AD (LBVAD), will provide insights into the molecular basis of these disorders. Within, we review evidence that normal adult human tau is abnormally phosphorylated and converted into the subunits of AD paired helical filaments (PHFs), and that Lewy bodies (LBs) represent accumulation of altered neurofilament (NF) triplet subunits. Although the precise biological consequences of PHF and LB formation in neurons is unknown, growing evidence suggests that the formation of PHFs and LBs from normal neuronal cytoskeletal proteins could have deleterious effects on neuronal function and survival. Finally, insights into the composition of PHFs and LBs could lead to the development of novel strategies for the timely and accurate diagnosis of AD, DLBD and the LBVAD. 相似文献
138.
139.
140.