全文获取类型
收费全文 | 48840篇 |
免费 | 2166篇 |
国内免费 | 62篇 |
专业分类
电工技术 | 343篇 |
综合类 | 39篇 |
化学工业 | 10621篇 |
金属工艺 | 928篇 |
机械仪表 | 959篇 |
建筑科学 | 1465篇 |
矿业工程 | 99篇 |
能源动力 | 1292篇 |
轻工业 | 8314篇 |
水利工程 | 441篇 |
石油天然气 | 216篇 |
武器工业 | 7篇 |
无线电 | 1873篇 |
一般工业技术 | 7488篇 |
冶金工业 | 10244篇 |
原子能技术 | 273篇 |
自动化技术 | 6466篇 |
出版年
2024年 | 92篇 |
2023年 | 388篇 |
2022年 | 831篇 |
2021年 | 1301篇 |
2020年 | 925篇 |
2019年 | 1107篇 |
2018年 | 1624篇 |
2017年 | 1623篇 |
2016年 | 1725篇 |
2015年 | 1357篇 |
2014年 | 1726篇 |
2013年 | 3435篇 |
2012年 | 2693篇 |
2011年 | 2900篇 |
2010年 | 2266篇 |
2009年 | 2173篇 |
2008年 | 1999篇 |
2007年 | 1775篇 |
2006年 | 1370篇 |
2005年 | 1209篇 |
2004年 | 1114篇 |
2003年 | 993篇 |
2002年 | 927篇 |
2001年 | 664篇 |
2000年 | 661篇 |
1999年 | 711篇 |
1998年 | 3187篇 |
1997年 | 2160篇 |
1996年 | 1433篇 |
1995年 | 839篇 |
1994年 | 686篇 |
1993年 | 764篇 |
1992年 | 280篇 |
1991年 | 284篇 |
1990年 | 204篇 |
1989年 | 227篇 |
1988年 | 220篇 |
1987年 | 200篇 |
1986年 | 165篇 |
1985年 | 215篇 |
1984年 | 168篇 |
1983年 | 131篇 |
1982年 | 163篇 |
1981年 | 178篇 |
1980年 | 190篇 |
1979年 | 97篇 |
1978年 | 97篇 |
1977年 | 350篇 |
1976年 | 744篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 27 毫秒
71.
J Czeglédy T Major A Juhász G Répássy L Gergely 《Canadian Metallurgical Quarterly》1997,138(30):1891-1895
Human papillomavirus gene sequences have been detected in a number of malignant and benign tumours. Non-oncogenic types 6 and 11 are etiological factors of benign mucosal tumours. Types 16 and 18 can be detected in malignancies most often but their role in the etiopathogenesis of cancers is still unclear. In our study we examined formalin-fixed and paraffin-embedded archive laryngeal tissues containing squamous cell carcinoma, papilloma and precancerous lesions for the presence of human papillomavirus genes. As a control we also examined tissues harbouring laryngeal nodules which represented the normal larynx in our study. After DNA preparation from the paraffin blocks we performed polymerase chain reaction to detect the DNA of human papillomavirus types 6, 11, 16 and 18. In the squamous cell carcinomas, papillomas and precancerous lesions the presence of human papillomavirus gene sequences was significantly higher than in the control group. To verify the integrity of DNA we also amplified a sequence deriving from the cellular beta-globin gene. Based on the 100% positivity for this gene we declare that the combination of our DNA preparation and polymerase chain reaction is a reliable method for detecting DNA sequences from formalin-fixed and paraffin-embedded tissues. 相似文献
72.
I Contreras R San-Millán A Agustín-Barrasa J Pontón G Quindós 《Canadian Metallurgical Quarterly》1996,136(1):17-20
A clinical study was carried out in an attempt to assess the efficacy of a newly designed electric toothbrush compared to a conventional manual toothbrush using the American Dental Association's protocol for evaluating toothbrushes. An Oral-B 35 manual toothbrush, which served as the control, was compared to the Plaq & White125 electric toothbrush. Examinations were performed by two calibrated examiners at baseline, day 15 and day 30. Examinations included the gingival index, plaque index and bleeding index. Mean indices were calculated and compared between the two brushes using the repeated measures multiple analysis of variance. No statistically significant differences between the mean indices on the three examination days were observed following the use of the manual or the electric toothbrushes. The results of this study demonstrate that the electric toothbrush was numerically more effective than the manual toothbrush in reducing supragingival plaque levels, either before or after brushing, at each examination date compared to baseline plaque values. However, this difference was not statistically significant. This and other findings concluded that the Plaq & White toothbrush is comparable to the control ADA-accepted toothbrush. 相似文献
73.
74.
75.
76.
Characterisation of greywater was conducted in two different greywater streams in the Netherlands (Groningen and Sneek). The concentrations of macropollutants and nutrients measured were very different in both streams; in particular the COD was 425 mg/L in Groningen's water whereas in Sneek it was 1,583 mg/L. The aerobic treatment of greywater in a fed-batch reactor led to a 90% removal of COD at different organic loading rates. Anaerobically, the removal reached 40% COD removal on average, the possible reason being the high amount of surfactants present in the influent. 相似文献
77.
Bengt Sundén Tor Sköldheden 《International Communications in Heat and Mass Transfer》1985,12(5):559-566
An experimental investigation of heat transfer and pressure drop from a new type of corrugated channels is presented. The investigation has been carried out for Reynolds numbers in the range of for one corrugated and one smooth channel. It is found that the heat transfer from the corrugated channel is up to 3.5 times higher than for the smooth one. The pressure drop is however large (5 – 6 times the value of a smooth channel) and it is suggested that the corrugation height and length should be altered in order to balance the increases in heat transfer and pressure drop. 相似文献
78.
MJ González-Corbella MC López-Sabater AI Castellote-Bargalló C Campoy-Folgoso M Rivero-Urgell 《Canadian Metallurgical Quarterly》1998,52(11):813-818
OBJECTIVE: To assess the effect of long-chain polyunsaturated fatty acids (LCPUFA)- and vitamin E-supplemented formula feeding on erythrocyte and plasma alpha-tocopherol (VE), and plasma retinol (VA) concentrations in neonates and to compare these values with those found in infants feeding on infant formula without LCPUFA or breast milk SETTING: University Hospital of Granada, Spain. SUBJECTS: 49 full-term infants. DESIGN AND INTERVENTION: Subjects who chose not to breast feed were fed either (i) unsupplemented infant formula (F) or (ii) infant formula supplemented with LCPUFA and vitamin E (FL). Alpha-tocopherol and retinol were measured at 7 days, 1 month and 3 months. RESULTS: Plasma and erythrocyte VE concentrations and plasma VE/total lipids ratio increased significantly in all groups at 1 month of life (P < 0.05), but did not change significantly between 1 month and 3 months in any group (P > 0.05). Erythrocyte VE and VA retinol concentrations were higher in infants fed an infant formula than in breast milk-fed infants at 1 month of life (P < 0.05). Finally, there were no significant differences in plasma or erythrocyte VE levels, plasma VA or plasma VE/total lipid ratio between any groups at 3 months of life (P > 0.05). CONCLUSION: Infants fed on LCPUFA- and vitamin E-supplemented infant formula for 3 months have similar vitamin E and A status to infants fed on breast milk or infant formula without LCPUFA supplementation. 相似文献
79.
B Cukrowska I Trebichavsky P Rossmann Z Reháková J Sinkora K Haverson R Lodinová-Zádníková H Tlaskalová-Hogenová 《Canadian Metallurgical Quarterly》1998,6(3-4):171-178
We have recently reported that thymic B lymphocytes (TBL) are the first B-cell subpopulation undergoing isotype switching to IgG and IgA during embryonic life. The aim of this study is to analyze the influence of antigenic stimulation on TBL location and activity using a germ-free (GF) newborn pig model, in which maternal antibodies and antigens do not affect B-cell development. Immunohistological analysis showed that TBL were disseminated mainly in the thymic medulla. There were no differences in the distribution of TBL, both in GF newborn piglets before and after colonization with Escherichia coli and in older conventionally reared (CONV) piglets. The number of immunoglobulin (Ig)-secreting cells measured by the ELISPOT method was not influenced by microflora and food antigens. IgM-positive cells secreting IgM and CD45RC-positive cells spontaneously producing IgM, IgG, and IgA were detected in newborn thymus. Our findings suggest that TBL differentiation and Ig switching to IgG and IgA-secreting cells is not influenced by external antigens and that the thymic microenvironment plays an important role in this process. 相似文献
80.
J. L. Huertas A. Rueda D. Vázquez 《Analog Integrated Circuits and Signal Processing》1993,4(3):199-213
A design-for-test methodology for SC filters is presented, based on an architecture using some additional circuitry and providing extra capabilities for both off- and on-line tests. The approach uses a comparison (voting) mechanism to indicate whether or not two copies of a filter element (a biquad, for instance) have a similar response during their actual operation. The design and implementation of a few filter examples are included to assess the potential usefulness of this new approach. 相似文献