全文获取类型
收费全文 | 3912篇 |
免费 | 59篇 |
国内免费 | 66篇 |
专业分类
化学 | 2548篇 |
晶体学 | 8篇 |
力学 | 19篇 |
综合类 | 4篇 |
数学 | 65篇 |
物理学 | 1009篇 |
无线电 | 384篇 |
出版年
2023年 | 12篇 |
2022年 | 14篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 38篇 |
2013年 | 19篇 |
2012年 | 246篇 |
2011年 | 374篇 |
2010年 | 82篇 |
2009年 | 27篇 |
2008年 | 320篇 |
2007年 | 331篇 |
2006年 | 332篇 |
2005年 | 328篇 |
2004年 | 275篇 |
2003年 | 236篇 |
2002年 | 192篇 |
2001年 | 126篇 |
2000年 | 159篇 |
1999年 | 58篇 |
1998年 | 32篇 |
1997年 | 20篇 |
1996年 | 70篇 |
1995年 | 48篇 |
1994年 | 84篇 |
1993年 | 96篇 |
1992年 | 82篇 |
1991年 | 51篇 |
1990年 | 29篇 |
1989年 | 34篇 |
1988年 | 30篇 |
1987年 | 31篇 |
1986年 | 41篇 |
1985年 | 32篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1972年 | 8篇 |
1971年 | 9篇 |
1969年 | 4篇 |
1968年 | 5篇 |
1967年 | 7篇 |
1966年 | 6篇 |
1957年 | 7篇 |
1948年 | 10篇 |
排序方式: 共有4037条查询结果,搜索用时 109 毫秒
921.
A flowthrough theophylline fluoroimmunosensor with an antibody covalently immobilised on a solid support has been developed. The immobilisation technique proposed in this paper used Protein-A on control pore glass (Protein A-CPG) in an immunoreactor and dimethylsuberimidate as a cross-linking agent. Several supports and cross-linking reagents were tested in order to obtain oriented immobilisation and thus efficiency of the immunological reaction and reusability of the immunosensor. The immunosensor performance characteristics were established. The precision expressed as RSD, was 1.6%; the detection limit was 3 mug l(-1); the immunoreactor lifetime was established in 80 assays and there were no interferences with structurally similar compounds such as aminophylline, dihydroxypropyltheophylline and caffeine in the determination of the analyte. This fluoroimmunosensor was applied to determine theophylline in human serum samples from patients of the Puerta de Hierro Hospital in Madrid. The results obtained show that there are no significant differences between the proposed immunosensor and the high-pressure liquid chromatographic method with UV detection used by the Hospital, thus demonstrating the validity of the method. 相似文献
922.
Pashley RM Rzechowicz M Pashley LR Francis MJ 《The journal of physical chemistry. B》2005,109(3):1231-1238
It is demonstrated that de-gassed water is more effective at dispersing hydrophobic "dirt", such as liquid hydrocarbons or oils. This effect appears to be due to the reduction of natural cavitation, which would otherwise oppose the dispersion of hydrophobic liquid droplets into water. De-gassing of the oil enhances this effect still further, and this has led to a proposal for a novel cleaning process, based on using a combination of a de-gassed (hydrophobic) solvent followed by rinsing in de-gassed water. This method might be useful as an effective, detergent-free cleaning process. Also reported are some initial studies which suggest that the effect of "inert" dissolved gases on the electrical conductivity of water may need to be reconsidered. 相似文献
923.
Nicolaou KC Mitchell HJ Fylaktakidou KC Rodríguez RM Suzuki H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(17):3116-3148
The stereoselective synthesis of everninomicin's 13,384-1 (1) FGHA2 fragment (2) in a suitable form for incorporation into the final target (1) is described. The construction of the FG 1,1'-disaccharide linkage relied on a new method based on tin-acetal chemistry, while for the GH orthoester bridge, a number of approaches were explored. Final success for the latter construction came when a novel 1,2-phenylseleno migration reaction was applied to couple rings G and H, followed by ketene acetal and orthoester formation. 相似文献
924.
化学通报第十五卷第一期刊有北京市中等化学教师教研会所写‘对东北版初高中化学教科书的讨论(一)’一文,对该教科书初中课本第一、二两章,高中第一章中所存在的一些不妥当的地方予以必要的修改,并对教法及课堂时间的利用提出了具体的意见,这对中等化学教师在提高教学质量上的帮助是很大的,不过在阅读后对该文有下列几点意见提出来供读者参考,并希望加以批评。一、该文中说:‘第8页:实验1.用碱式碳酸铜粉末做实验这种碱式碳酸铜不易得到,(虽然可用 CuSO_4+Na_2CO_3制取)。实验不易有结 相似文献
925.
Cosman PC Tseng C Gray RM Olshen RA Moses LE Davidson HC Bergin CJ Riskin EA 《IEEE transactions on medical imaging》1993,12(4):727-739
The authors apply a lossy compression algorithm to medical images, and quantify the quality of the images by the diagnostic performance of radiologists, as well as by traditional signal-to-noise ratios and subjective ratings. The authors' study is unlike previous studies of the effects of lossy compression in that they consider nonbinary detection tasks, simulate actual diagnostic practice instead of using paired tests or confidence rankings, use statistical methods that are more appropriate for nonbinary clinical data than are the popular receiver operating characteristic curves, and use low-complexity predictive tree-structured vector quantization for compression rather than DCT-based transform codes combined with entropy coding. The authors' diagnostic tasks are the identification of nodules (tumors) in the lungs and lymphadenopathy in the mediastinum from computerized tomography (CT) chest scans. Radiologists read both uncompressed and lossy compressed versions of images. For the image modality, compression algorithm, and diagnostic tasks the authors consider, the original 12 bit per pixel (bpp) CT image can be compressed to between 1 bpp and 2 bpp with no significant changes in diagnostic accuracy. The techniques presented here for evaluating image quality do not depend on the specific compression algorithm and are useful new methods for evaluating the benefits of any lossy image processing technique. 相似文献
926.
927.
928.
929.
930.