全文获取类型
收费全文 | 1405篇 |
免费 | 66篇 |
国内免费 | 5篇 |
专业分类
化学 | 998篇 |
晶体学 | 7篇 |
力学 | 35篇 |
综合类 | 1篇 |
数学 | 156篇 |
物理学 | 279篇 |
出版年
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 20篇 |
2017年 | 14篇 |
2016年 | 27篇 |
2015年 | 36篇 |
2014年 | 26篇 |
2013年 | 52篇 |
2012年 | 81篇 |
2011年 | 91篇 |
2010年 | 45篇 |
2009年 | 31篇 |
2008年 | 75篇 |
2007年 | 100篇 |
2006年 | 95篇 |
2005年 | 82篇 |
2004年 | 80篇 |
2003年 | 57篇 |
2002年 | 54篇 |
2001年 | 30篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 12篇 |
1996年 | 18篇 |
1995年 | 24篇 |
1994年 | 20篇 |
1993年 | 11篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 12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1476条查询结果,搜索用时 46 毫秒
21.
Summary In this paper a database of atomic residual charges has been constructed for all the molecular fragments defined previously in a combinatorial search of the Cambridge Structural Database. The charges generated for the atoms in each fragment are compared with charges calculated for whole molecules containing those fragments. The fragment atomic charges lie within 1 S.D. of the mean for 68%, and within 2 S.D. for 91%, of the atoms whose charges were computed for whole molecules. The actual charges on any atom are strongly influenced by the adjacent connected atoms. There is a large spread of atomic residual charge within the fragments database. 相似文献
22.
Siya Ram William Evans Dean S. Wise Leroy B. Townsend John W. Mccall 《Journal of heterocyclic chemistry》1989,26(4):1053-1059
A series of methyl 2-substituted purine 8-carbamates was prepared and evaluated for antifilarial activity. These purines were synthesized as aza congeners of benzimidazole carbamates which have shown significant anthelmintic activity to determine the effect that this modification might have on anthelmintic activity. The compounds were tested against the filarial infection, B. pahangi, in jirds. None of the compounds prepared in this study demonstrated antifilarial activity. 相似文献
23.
Addition of a benzyl substituent to the macrocyclic ring of DOTA has a substantial impact on the conformational ring flipping motion of the macrocycle in the resulting LnDOTA complexes. The p-NO2-benzyl substituent in the Ln(p-NO2-Bn-DOTA)- complexes lies in an equatorial position and effectively "locks" the conformation of the ring into the deltadeltadeltadelta configuration. The presence of the p-NO2-benzyl group also increases the population of the square antiprismatic (SAP) coordination isomer for all Ln(p-NO2-Bn-DOTA)- complexes relative to that seen for the respective LnDOTA- complexes. Despite this increase in SAP isomer population, the rate of water exchange in these complexes remains comparatively fast. The kinetic and thermodynamic stabilities of the Ln(p-NO2-Bn-DOTA)- complexes are also slightly lower than the corresponding LnDOTA- complexes but appear to be sufficiently high for in vivo use. 相似文献
24.
A novel approach to the fabrication of metal ring-disk (RD) microelectrodes is presented that employs flexible chemical vapor deposition (CVD) and electrode modification techniques. Specifically, the development of a copper ring-disk microelectrode is described utilizing a combination of CVD coating, electroetching, and electroplating. Initially, a 25 μm diameter tungsten wire is concentrically coated by CVD with an insulating layer of silica, a layer of tungsten metal, and finally, a second outer layer of silica. The copper surface was prepared by first creating micrometer cavities by electrochemical etching the tungsten in hydroxide solutions followed by electrodeposition of copper from aqueous solutions of Cu(II). Each step of the process was characterized by scanning electron microscopy, optical microscopy, and cyclic voltammetry, demonstrating the preparation of a viable metal-based dual ring-disk microelectrode system. For the purpose of demonstrating the concept of introducing specific selectivity into the device, amperometric detection of galactose in 0.1 M NaOH was performed at +0.60 V in bulk solution and after flow injection analysis in a capillary column. 相似文献
25.
The adverse effects of injection solvent strength on microbore packed column SFC band broadening are demonstrated and a solventless injection system that eliminates these effects is introduced. The injection system removes solvent in a GC-like manner using a retention gap and an on-column capillary GC syringe. The analyte is delivered to the analytical column in a solvent-free plug of supercritical fluid mobile phase. 相似文献
26.
Potter CV Thomas S Dean JL Kybett AP Kidd R James M Saxton H 《Chemical communications (Cambridge, England)》2004,(24):2781-2786
In January 2004, the Royal Society of Chemistry launched Organic & Biomolecular Chemistry (OBC) - a journal promising to provide high quality research from all aspects of synthetic, physical and biomolecular organic chemistry. The journal was set to build upon the foundations laid down by its predecessor publications (J. Chem. Soc., Perkin Trans. 1 and J. Chem. Soc., Perkin Trans. 2) as well as complement the subject coverage already published in prestigious general chemistry journals such as Chemical Communications and Chemical Society Reviews. Nearly two years on, just how is the programme developing and what can the community expect to see from the Royal Society of Chemistry (RSC)? 相似文献
27.
Friedman LA You F Sabat M Harman WD 《Journal of the American Chemical Society》2003,125(49):14980-14981
The rhenium furan complexes TpRe(CO)(MeIm)(eta2-2-methylfuran) (1) and TpRe(CO)(MeIm)(eta2-2,5-dmethylfuran) (2) undergo Lewis acid-promoted cyclopentannulation reactions with enones and enals to generate 3-acetylcyclopentene complexes. During the reaction, a rearrangement occurs such that the alpha and beta carbons of the enone are incorporated into the new carbocycle. Treatment of these complexes with an oxidant (H2O2 or silver triflate) liberates the acetylcyclopentene. When a resolved form of the rhenium complex is used, the acetylcyclopentenes can be obtained enantioselectively. 相似文献
28.
W. K. Dean 《Journal of organometallic chemistry》1980,190(4):353-361
Bis(dimethylthiocarbamoyl)sulfide, (Me2NCS)2S, reacts with (PH3P)2MCOCl complexes giving ionic species [Ph3PM(η2-CSNMe2)(S2CNMe2)CO]X (M = Rh, Ir; X = Cl, PF6) as kinetic products. On standing solution, [Ph3PRh(η2-CSNMe2)(S2CNMe2)CO]Cl is slowly transformed into the thermodynamic product Ph3PRh(η2-CSNMe2)S2CNMe2)Cl. The known reactions of Vaska-type complexes with Me2NCSCl to give [trans-(Ph3P)2Ir(η2-CSNMe2)COCl]Cl and trans-(Ph3P)2Rh(η2-CSNMe2)Cl2 probably follow a similar course. (PH3P)RuNOCl reacts with (Me2NCS)2S and Me2NCSCl in the same way as (Ph3P)2IrCOCl, but reacts with (Me2NCS)2NPh to give [trans-(Ph3P)2Ru(η2-CSNMe2)NOCl]PF6. The mechanism and stereochemistry of these reactions are discussed. Reactions were monitored by NMR spectroscopy in an attempt to identify intermediate η1-thiocarboxamido complexes, but no such species could be detected. 相似文献
29.
Trost BM Shen HC Horne DB Toste FD Steinmetz BG Koradin C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2577-2590
The Ru-catalyzed intramolecular [5+2] cycloaddition of cyclopropylenynes is investigated with respect to the regio- and diastereoselectivity as well as the functional group compatibility of the reaction. Evidence for the mechanism as occurring through a ruthenacyclopentene intermediate is elucidated from 1) the study of the diastereoselectivity of the cycloaddition; 2) the effect of variation of substituents on the regioselectivity of cyclopropyl bond cleavage in 1,2-trans- and 1,2-cis-disubstituted cyclopropanes and 3) examples that clearly do not involve ruthenacyclohexene as intermediates as products still incorporate the cyclopropyl moiety. The scope and limitations of the Ru-catalyzed cycloaddition are discussed and compared with the Rh-catalyzed reaction. The potential power of this methodology towards natural product total synthesis is demonstrated by the formation of several polycyclic systems with the chosen reaction conditions and readily available cyclopropylenyne substrates. 相似文献
30.
用原子吸收光谱法测下了“东北水三七”根、茎、叶的21种化学元素,结果表明,不同部位的元素含量有一定差别。 相似文献