全文获取类型
收费全文 | 44922篇 |
免费 | 1664篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 432篇 |
综合类 | 26篇 |
化学工业 | 9361篇 |
金属工艺 | 815篇 |
机械仪表 | 798篇 |
建筑科学 | 1664篇 |
矿业工程 | 372篇 |
能源动力 | 936篇 |
轻工业 | 5128篇 |
水利工程 | 443篇 |
石油天然气 | 313篇 |
武器工业 | 2篇 |
无线电 | 2481篇 |
一般工业技术 | 6970篇 |
冶金工业 | 10556篇 |
原子能技术 | 335篇 |
自动化技术 | 6002篇 |
出版年
2023年 | 254篇 |
2022年 | 409篇 |
2021年 | 812篇 |
2020年 | 656篇 |
2019年 | 772篇 |
2018年 | 1200篇 |
2017年 | 1105篇 |
2016年 | 1222篇 |
2015年 | 974篇 |
2014年 | 1343篇 |
2013年 | 3063篇 |
2012年 | 2054篇 |
2011年 | 2138篇 |
2010年 | 1718篇 |
2009年 | 1697篇 |
2008年 | 1890篇 |
2007年 | 1773篇 |
2006年 | 1419篇 |
2005年 | 1226篇 |
2004年 | 1117篇 |
2003年 | 1037篇 |
2002年 | 1004篇 |
2001年 | 696篇 |
2000年 | 579篇 |
1999年 | 707篇 |
1998年 | 1903篇 |
1997年 | 1371篇 |
1996年 | 1061篇 |
1995年 | 744篇 |
1994年 | 696篇 |
1993年 | 720篇 |
1992年 | 520篇 |
1991年 | 351篇 |
1990年 | 485篇 |
1989年 | 464篇 |
1988年 | 413篇 |
1987年 | 467篇 |
1986年 | 413篇 |
1985年 | 523篇 |
1984年 | 510篇 |
1983年 | 436篇 |
1982年 | 429篇 |
1981年 | 362篇 |
1980年 | 351篇 |
1979年 | 381篇 |
1978年 | 324篇 |
1977年 | 336篇 |
1976年 | 408篇 |
1975年 | 260篇 |
1973年 | 237篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Robert Greetham 《Landscape Research》1992,17(1):10-19
An account of the use of landscape as subject-matter as a basis for the exploration of personal concerns and the search for self by various 20th Century photographers. Particular reference is made to the landscape photography of Eugene Atget, Edward Weston and Bill Brandt. 相似文献
43.
44.
45.
46.
47.
The RNAse A mismatch cleavage method was used to analyze genomic variability in RNA and DNA systems. However, there is no method which relates the digestion patterns observed to the extent of genetic variation. Here we report computer simulations which provide a simple estimator of genetic distances from the comparison of RNAse A digestion patterns. The results show that the number of non-shared fragments is proportional to the number of mutations between each pair of sequences compared. This prediction is supported by the comparison of the RNAse A mismatch patterns and the nucleotide sequences of a set of influenza A (H3N2) hemagglutinin genes. The procedure allows a quantitative and reliable use of the RNAse A mismatch cleavage method. 相似文献
48.
Spontaneous mutation for a quantitative trait in Drosophila melanogaster. II. Distribution of mutant effects on the trait and fitness 总被引:7,自引:0,他引:7
Exposure of the Chinese hamster ovarian AuxB1 cell line in vitro to fractionated X-irradiation generated sublines designated DXR-10, which proved resistant to multiple drugs and overexpressed P-glycoprotein (Pgp), as judged by Western blotting using the C219 monoclonal antibody. Further characterization of these irradiated DXR-10 sublines has provided evidence for: (i) the expression of cross-resistance to gramacidin D, taxol, puromycin and Navelbine, but not to daunomycin or mitoxantrone; (ii) overexpression of the class I Pgp, as judged by Western blotting using the C494 monoclonal antibody; (iii) decreased accumulation of 3H-vincristine, which could be enhanced by verapamil addition; (iv) unaltered accumulation and subcellular distribution of adriamycin; (v) significantly increased rhodamine 123 accumulation in the presence of verapamil; (vi) plasma-membrane ultrastructural modifications resulting in a significantly increased surface area; (vii) numerous clonal karyotypic alterations, with abnormalities involving the long arm of chromosome 1 being consistently identified; (viii) a lack of overexpression of sorcin; (ix) increased total glutathione levels and overexpression of glutathione S-transferase pi. The fact that only certain of these features are considered characteristic of the 'classic' multidrug-resistant CHRC5 cell line supports our earlier proposal that exposure to fractionated X-irradiation results in the expression of a unique drug-resistance phenotype. 相似文献
49.
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
50.
Robert M. Wirtshafter 《Energy Policy》1985,13(2):143-155
Utility conservation programmes are designed to benefit both participants and non-participants. This article outlines the issues involved in designing conservation programmes for utilities and determining the appropriate amount of incentives that can be provided to participants without harming non-participants. More importantly, the article discusses the issue of access to the programmes by utility customers. It concludes that it is the existing restrictions to participation, and not the level of compensation, that are of greatest concern to non-participants. A number of utility programmes designed to eliminate the problem of non-participation are reviewed. 相似文献