全文获取类型
收费全文 | 1399篇 |
免费 | 66篇 |
国内免费 | 5篇 |
专业分类
化学 | 966篇 |
晶体学 | 7篇 |
力学 | 35篇 |
综合类 | 1篇 |
数学 | 155篇 |
物理学 | 306篇 |
出版年
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 27篇 |
2015年 | 36篇 |
2014年 | 26篇 |
2013年 | 51篇 |
2012年 | 81篇 |
2011年 | 92篇 |
2010年 | 45篇 |
2009年 | 31篇 |
2008年 | 75篇 |
2007年 | 106篇 |
2006年 | 97篇 |
2005年 | 87篇 |
2004年 | 81篇 |
2003年 | 58篇 |
2002年 | 47篇 |
2001年 | 34篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 17篇 |
1995年 | 24篇 |
1994年 | 19篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 14篇 |
1974年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有1470条查询结果,搜索用时 15 毫秒
31.
Balthazar José Manoel Mook Dean T. Weber Hans Ingo Brasil Reyolando M.L.R.F. Fenili A. Belato D. Felix J.L.P. 《Meccanica》2003,38(6):613-621
We analyze the dynamical coupling between energy sources and structural response that must not be ignored in real engineering problems, since real motors have limited output power. 相似文献
32.
Ronald G. Cavell Christo M. Angelov Dean A. Mazzuca 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):625-628
Abstract: Chlorophosphines react with trivalent (silylamino)phosphines via a direct oxidative addition process with elimination of trimethyl silyl chloride to produce phosphino-phosphoranimines with concomitant formation of a P-P bond. Oxidation of the phosphine center with sulfur and an exchange transformation of the phosphine are discussed. 相似文献
33.
Jiamin Gu Reihong Feng Zhiyuan Wu Shuguang Guan Jiling Guo Chunru Cheng Pingping Xu Jingxian Zhang Yang Wang Hua Qu Wei Man Wenbo Yu Yajun Cui Shuhong Guan Dean Guo 《Journal of separation science》2013,36(14):2366-2372
A rapid and convenient method was established to preparatively isolate the three ellagic acid types of compounds, which were the main polyphenols in Euphorbia pekinensis, by flexibly applying solvent extraction combined with counter‐current chromatography (CCC). The total extract (extracted using 95% ethanol) of E. pekinensis was pretreated by two simple steps before CCC isolation, following the procedure: the total extract was extracted by classical solvent extraction using petroleum ether and ethyl acetate, respectively, and then the ethyl acetate extract was suspended using 95% ethanol, after being allowed to stand overnight, the sediment was obtained. Partial sediment (100 mg) was then directly separated by CCC with a two‐phase solvent system composed of chloroform‐95% ethanol‐water‐85% formic acid (50:50:50:5, v/v/v/v). About 22 mg of 3,3′‐dimethoxy ellagic acid (1), 12 mg of 3,3′‐di‐O‐methyl‐4‐O‐(β‐d ‐xylopyranosyl)ellagic acid (2), and 35 mg of ellagic acid (3) with purities of 96.0, 95.2, and 95.4% were obtained respectively in one step within 4 h. After being purified by washing with methanol, the purities of the three compounds obtained were all above 98%. The purities were determined by HPLC and their chemical structures were further identified by 1H and 13C NMR spectroscopy. The recoveries were calculated as 84.6, 85.7, and 89.5%, respectively. The result demonstrated that the present isolation method was rapid, economical and efficient for the preparative separation of polyphenols from E. pekinensis. 相似文献
34.
35.
36.
37.
Anna S. Gardberg Brian S. Potter Rex A. Palmer Garry J. McIntyre Dean A. A. Myles 《Journal of chemical crystallography》2011,41(4):470-480
Abstract
Single-crystal neutron diffraction data were collected at 20 K to a resolution of 1.05 ? on a crystal of the inverse formyl peptide receptor agonist cyclosporin H, CsH, (crystal form II, CsH-II) on the Laue diffractometer VIVALDI at the Institut Laue-Langevin (Grenoble). The solvent structure and hydrogen bonding network of CsH-II have been unambiguously determined by single-crystal neutron diffraction; the agreement factor R(F 2) is 13.5% for all 2726 reflections. All hydrogen atom positions, including methyl-group orientations, have been determined by crystallographic refinement. The neutron structure of cyclosporin provides unique and complementary insights into methyl orientation, hydrogen-bonding, and solvent interactions that are not available from X-ray analysis alone. 相似文献38.
39.
40.
Chris Capaccio Nikolay S. Stoykov Raji Sundararajan David A. Dean 《Journal of Electrostatics》2009,67(4):652-662
The application of appropriate electric fields to cells and tissues, termed electroporation, can result in efficient and safe gene transfer. We have shown previously that this approach results in high level gene transfer to and expression in the vasculature of living animals. This paper presents the results of an electric field distribution study of a rat mesenteric vasculature model using the Finite-Element Time-Domain (FETD) technique. A novelty of this work is the use of Debye dispersive dielectric parameters, as the electrical response of biological tissues is inherently frequency-dependent. The results compare fairly well with experimental findings. 相似文献