全文获取类型
收费全文 | 78227篇 |
免费 | 4477篇 |
国内免费 | 2836篇 |
专业分类
化学 | 41403篇 |
晶体学 | 1044篇 |
力学 | 4564篇 |
综合类 | 275篇 |
数学 | 9686篇 |
物理学 | 28568篇 |
出版年
2023年 | 625篇 |
2022年 | 919篇 |
2021年 | 1190篇 |
2020年 | 1397篇 |
2019年 | 1364篇 |
2018年 | 2381篇 |
2017年 | 2340篇 |
2016年 | 2375篇 |
2015年 | 1847篇 |
2014年 | 2350篇 |
2013年 | 3791篇 |
2012年 | 4847篇 |
2011年 | 4940篇 |
2010年 | 3254篇 |
2009年 | 3322篇 |
2008年 | 3287篇 |
2007年 | 3156篇 |
2006年 | 2877篇 |
2005年 | 5447篇 |
2004年 | 5070篇 |
2003年 | 3370篇 |
2002年 | 1726篇 |
2001年 | 1877篇 |
2000年 | 1497篇 |
1999年 | 1436篇 |
1998年 | 1178篇 |
1997年 | 1139篇 |
1996年 | 1156篇 |
1995年 | 969篇 |
1994年 | 899篇 |
1993年 | 775篇 |
1992年 | 825篇 |
1991年 | 785篇 |
1990年 | 701篇 |
1989年 | 618篇 |
1988年 | 599篇 |
1987年 | 563篇 |
1986年 | 498篇 |
1985年 | 558篇 |
1984年 | 557篇 |
1983年 | 403篇 |
1982年 | 427篇 |
1981年 | 409篇 |
1979年 | 416篇 |
1978年 | 397篇 |
1977年 | 417篇 |
1976年 | 411篇 |
1975年 | 370篇 |
1974年 | 349篇 |
1973年 | 344篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
41.
Valiullina Z. R. Galeeva A. M. Miftakhov M. S. 《Russian Journal of Organic Chemistry》2021,57(9):1461-1465
Russian Journal of Organic Chemistry - The Reformatsky reaction of (3R,4R)-4-acetoxy-3-((1R)-1-{[tert-butyl(dimethyl)silyl]oxy}ethyl)azetidin-2-one with ethyl 4-bromo-3-oxopentanoate gave... 相似文献
42.
43.
44.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
45.
Nonlinear Dynamics - We generalize previously obtained solutions to the generalized nonlinear Schrödinger equation (NLSE) with cubic-quintic nonlinearity and distributed coefficients to obtain... 相似文献
46.
Dong Liangwei Qi Wei Peng Ping Wang Linxue Zhou Hui Huang Changming 《Nonlinear dynamics》2020,102(1):303-310
Nonlinear Dynamics - We address the nonlinear dynamics of binary Bose-Einstein condensates with mutually symmetric spinor components trapped in an optical lattice. The interaction between the... 相似文献
47.
Hejia Hu Linlin Wu Mei Li Cun Xue Guangcheng Wang Siying Chen Yong Huang Lin Zheng Aimin Wang Yueting Li Zipeng Gong 《Biomedical chromatography : BMC》2020,34(1):e4714
Eucommia ulmoides Oliv. (E. ulmoides) is a valuable and nourishing medicinal herb in China that has been used in the treatment of hypertension. Given the fact that most traditional Chinese medicine is mainly used to treat disease, investigating the pharmacokinetics of traditional Chinese medicines in the pathological state is more useful than that in the normal state. However, the differences in the absorption kinetics of active ingredients of E. ulmoides extract between pathological and physiological conditions have not been reported. Therefore, in this study, the rat intestinal in situ circulatory perfusion model was used to investigate the differences in absorption kinetics of seven active ingredients of E. ulmoides extract in normal and spontaneously hypertensive rats, namely, genipinic acid, protocatechuic acid, neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, (+)-pinoresinol di-O-β-D -glucopyranoside and (+)-pinoresinol 4′-O-β-D -glucopyranoside. Our results indicate that the pathological state of spontaneous hypertension may change the absorption of active components of E. ulmoides extracts, and these findings may provide a reference for improving the rational use of E. ulmoides in the clinic. 相似文献
48.
Xiao Sun Li Zhang Yu Cao Jinhua Li Atanas G. Atanasov Linfang Huang 《Biomedical chromatography : BMC》2020,34(12):e4949
Balanophora involucrata J. D. Hooker has been known to possess potential anti-inflammatory and antibacterial activities; however, its antiviral activity has not been evaluated so far. In order to find new neuraminidase inhibitors (NAIs), the neuraminidase (NA) inhibition activity of different B. involucrata extracts was evaluated. In this study, an in vitro NA inhibition assay was performed to identify which extract of B. involucrata exhibits (maximal) inhibitory activity against NA. Ultra high performance liquid chromatography/quadrupole time-of-flight–tandem mass spectroscopy (MS/MS) and molecular docking techniques were used to identify the specific compounds responsible for the anti-influenza activity of the extract, and to explore the potential natural NAIs. The ethyl acetate extract of B. involucrata exhibited significant inhibitory activity against NA with 50% inhibitory concentration (IC50) value of 159.5 μg/mL. Twenty compounds were identified according to the MS/MS spectra; among them two compounds (quercitrin and phloridzin) showed obvious inhibitory activity against NA, with IC50 of 311.76 and 347.32 μmol/L, respectively. This study suggested that B. involucrata can be a potential natural source of NAIs and may be useful in the fight against ferocious influenza viruses. 相似文献
49.
Here, we report a new strategy for rapid synthesis of branched peptide by side-chain hydrazide ligation at Asn. The hydrazide was converted to thioester at Asn side chain by NaNO2 and thiol reagent, and sequential ligation with an N-terminus Cys-peptide efficiently afforded the branched peptide. A branched cyclic peptide was successfully synthesized by side-chain ligation with a two-Cys-peptide and formation of a disulfide bond. This approach provides a new way for expeditious synthesis of branched peptides and facilitates the design of neopeptides as functional bio-mimics. 相似文献
50.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献