全文获取类型
收费全文 | 304084篇 |
免费 | 7000篇 |
国内免费 | 2905篇 |
专业分类
电工技术 | 7537篇 |
技术理论 | 3篇 |
综合类 | 3411篇 |
化学工业 | 44651篇 |
金属工艺 | 12468篇 |
机械仪表 | 11321篇 |
建筑科学 | 9666篇 |
矿业工程 | 2278篇 |
能源动力 | 7783篇 |
轻工业 | 25306篇 |
水利工程 | 3334篇 |
石油天然气 | 6978篇 |
武器工业 | 412篇 |
无线电 | 39799篇 |
一般工业技术 | 55388篇 |
冶金工业 | 48475篇 |
原子能技术 | 5966篇 |
自动化技术 | 29213篇 |
出版年
2022年 | 2408篇 |
2021年 | 3685篇 |
2020年 | 2780篇 |
2019年 | 3158篇 |
2018年 | 4680篇 |
2017年 | 4927篇 |
2016年 | 4984篇 |
2015年 | 3876篇 |
2014年 | 6099篇 |
2013年 | 13722篇 |
2012年 | 9078篇 |
2011年 | 11680篇 |
2010年 | 9415篇 |
2009年 | 10170篇 |
2008年 | 11023篇 |
2007年 | 10827篇 |
2006年 | 10160篇 |
2005年 | 9109篇 |
2004年 | 8328篇 |
2003年 | 8374篇 |
2002年 | 8274篇 |
2001年 | 8119篇 |
2000年 | 7473篇 |
1999年 | 7635篇 |
1998年 | 15222篇 |
1997年 | 11120篇 |
1996年 | 8965篇 |
1995年 | 7078篇 |
1994年 | 6287篇 |
1993年 | 6019篇 |
1992年 | 4854篇 |
1991年 | 4432篇 |
1990年 | 4218篇 |
1989年 | 3931篇 |
1988年 | 3780篇 |
1987年 | 3263篇 |
1986年 | 3119篇 |
1985年 | 3646篇 |
1984年 | 3407篇 |
1983年 | 3049篇 |
1982年 | 2872篇 |
1981年 | 2964篇 |
1980年 | 2770篇 |
1979年 | 2658篇 |
1978年 | 2499篇 |
1977年 | 2945篇 |
1976年 | 3555篇 |
1975年 | 2316篇 |
1974年 | 2312篇 |
1973年 | 2318篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
J. C. Jones H. Rahmati T. D. H. Do 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,54(4):317-318
Wood shaving samples were heated in both cubic baskets and in a previously described system realising the conditions of the ‘infinite slab’ in thermal ignition. Results from the two sets of experiment were found to be totally consistent with each other. 相似文献
992.
993.
994.
995.
The improved understanding of adsorption chemistry which has arisen from the development of new surface analytical techniques during the last twenty years has had a major effect on the understanding of catalytic reaction mechanisms. However, there are many other areas of technology where Interfacial chemistry has a determining role but where the understanding is much less developed. In this paper examples are presented of the role of interfacial chemistry in adhesion. In particular, It Is shown that modification of a surface to the extent of just a few atomic layers in depth can have dramatic effects on the performance of adhesive bonds, particularly when exposed to hostile environmental conditions. These examples will be used to highlight a need for greater fundamental understanding of the interfacial chemistry of adhesion and also other technologies where interface effects are dominant. 相似文献
996.
R.I.R. Blyth S.S. Dhesi P.A. Gravil K. Newstead R. Cosso R.J. Cole A.J. Patchett T. Mitrelias N.P. Prince S.D. Barrett 《Journal of Alloys and Compounds》1992,180(1-2):259-263
Angle-resolved UV photoemission has been used to investigate the electronic structure of the (0001) surfaces of scandium, yttrium, praseodymium and gadolinium. Off-normal emission spectra were recorded with high angular resolution, enabling detailed mapping of the dispersion of valence band features. Yttrium and gadolinium show similar results to published data from Ho(0001), suggesting minimal 4f influence in the lanthanide bandstructures. Differences seen on praseodymium and scandium may be due to 4f derived states and surface states respectively. 相似文献
997.
A Veldman G J Borggreve E J Mulders D van de Lagemaat 《Food Additives & Contaminants》1992,9(6):647-655
The mycotoxin contamination of feed components used by the Dutch cooperative feed industry was surveyed to estimate the risk for animal production losses. Of 89 randomly and 6 selectively taken samples of raw materials harvested in 1988 and 1989 27% were contaminated with ochratoxin A (OCHRA), 31% with zearalenone (ZEA) and 20% with deoxynivalenol (DON). The mean content (microgram/kg) of all positive randomly taken samples was 18 (OCHRA), 62 (ZEA) and 630 (DON). The highest level (microgram/kg) for all samples was 120 (OCHRA) in barley, 3100 (ZEA) in corn cob mix and 1900 (DON) in maizegluten feed. The results of this survey show that feed components are often contaminated with mycotoxins. However, the contamination level could only sporadically cause production losses in animal husbandry. 相似文献
998.
M J Scotter S A Thorpe S L Reynolds L A Wilson D J Lewis 《Food Additives & Contaminants》1992,9(3):237-242
Retail samples of livers from calf (23), ox (18), lamb (17), pig (15), chicken (16) and turkey (1) were analysed to determine levels of vitamin A (all trans-retinol) and to aid assessment of the effects of using vitamin supplemented compound feedingstuffs for livestock. For comparison, 22 liver samples from lambs reared on diets not containing vitamin-supplemented compound feedingstuffs and four samples of liver from ox which had received supplemented feed but not during the last four months prior to slaughter were also analysed. The chosen method of analysis utilized saponification, solvent extraction and normal-phase high performance liquid chromatography with fluorescence detection. For all species analysed, the levels of vitamin A ranged from 10 to 1100 mg/kg, with all but seven at or below 400 mg/kg. For lamb and ox livers, the mean levels were 310 mg/kg and 200 mg/kg respectively for retail samples. The mean levels were 220 mg/kg (lamb) and 120 mg/kg (ox) in liver samples from animals fed controlled diets. The results are of the same order as those reported over recent years. 相似文献
999.
Parameters affecting the frequencies of transformation and co-transformation with synthetic oligonucleotides in yeast. 总被引:7,自引:0,他引:7
T Yamamoto R P Moerschell L P Wakem D Ferguson F Sherman 《Yeast (Chichester, England)》1992,8(11):935-948
Factors influencing the direct transformation of the yeast Saccharomyces cerevisiae with synthetic oligonucleotides were investigated by selecting for cyc1 transformants that contained at least partially functional iso-1-cytochrome c. Approximately 3 x 10(4) transformants, constituting 0.1% of the cells, were obtained by using 1 mg of oligonucleotide in the reaction mixture. Carrier, such as heterogeneous oligonucleotides, enhanced transformation frequencies. Transformation frequencies were dramatically reduced if the oligonucleotides had a large number of mismatches or had terminally located mismatches. Transformation with oligonucleotides, but not with linearized double-strand plasmid, was efficient in a rad52- strain, suggesting that the pathway for transformation with oligonucleotides is different from that with linearized double-strand plasmid. We describe a procedure of co-transformation with two oligonucleotides, one correcting the cyc1 defect of the target allele in the host strain, and the other producing a desired amino acid alteration elsewhere in the iso-1-cytochrome c molecule; approximately 20% of the transformants obtained by co-transformation contained these desired second alterations. 相似文献
1000.
T. RONALD A. MAGEE CAROLE P.D. WILKINSON 《International Journal of Food Science & Technology》1992,27(5):541-549
Investigation of the effects of varying air velocity, slice thickness, and pre-treatment with sodium chloride solutions and surface active agents on drying potato slices indicated that the drying occurred entirely in the falling rate period and was controlled by the mechanism of liquid diffusion. The rate of drying, and therefore the diffusion coefficients, increased with the addition of sodium chloride and surface active agents. Diffusion coefficients were also influenced by air velocity and slice thickness, suggesting that the rate of drying of potato slices is controlled by a combination of internal and external resistances. 相似文献