全文获取类型
收费全文 | 392篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 297篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 54篇 |
物理学 | 45篇 |
出版年
2022年 | 3篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 12篇 |
2012年 | 6篇 |
2011年 | 12篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 15篇 |
2006年 | 16篇 |
2005年 | 23篇 |
2004年 | 20篇 |
2003年 | 10篇 |
2002年 | 18篇 |
2001年 | 4篇 |
1999年 | 8篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 17篇 |
1973年 | 11篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1955年 | 4篇 |
1930年 | 3篇 |
1925年 | 4篇 |
1911年 | 2篇 |
1910年 | 2篇 |
1908年 | 2篇 |
1902年 | 2篇 |
排序方式: 共有398条查询结果,搜索用时 62 毫秒
61.
Stannyl and silyl alkylselenides have been efficiently transformed to the corresponding alkylselenolates on reaction with butyllithiums. Other conditions proved to be limited. 相似文献
63.
2,4-Disubstituted benzo[b][1,5]thiazepines represent nonfluorescent intense yellow chromophores and are readily synthesized
from acid chlorides, terminal alkynes, and ortho-amino thiophenols by a consecutive one-pot three-component Sonogashira coupling–Michael addition–cyclocondensation sequence
under mild conditions in good yields. 相似文献
64.
E. Matlis proved that if R is an integral domain with quotient field Q and K is the R-module Q/R, then all torsion R-modules decompose into a direct sum of local submodules if and only if K decomposes into a direct sum of local submodules. Thus K is a test module to determine whether torsion modules decompose. We generalize this result to commutative rings. If R is a commutative ring and a torsion theory of R is given by a Gabriel topology , then form the ring of quotients R and let K be the cokernel of the canonical ring homomorphism from R to R. In some special cases, every -torsion R-module decomposes into a direct sum of local submodules if and only if K decomposes. However, there is an example where this is not the case. The principal result is: given R, and K, there is a related filter K of ideals of R, which is a subset of , such that all K-pretorsion R-modules decompose into a direct sum of local submodules if and only if K decomposes. The relationship between and K is investigated. 相似文献
65.
Niklas Rinn Dr. Jens P. Eußner Willy Kaschuba Dr. Xiulan Xie Prof. Dr. Stefanie Dehnen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):3094-3104
Reactions of R1SnCl3 (R1=CMe2CH2C(O)Me) with (SiMe3)2Se yield a series of organo‐functionalized tin selenide clusters, [(SnR1)2SeCl4] ( 1 ), [(SnR1)2Se2Cl2] ( 2 ), [(SnR1)3Se4Cl] ( 3 ), and [(SnR1)4Se6] ( 4 ), depending on the solvent and ratio of the reactants used. NMR experiments clearly suggest a stepwise formation of 1 through 4 by subsequent condensation steps with the concomitant release of Me3SiCl. Furthermore, addition of hydrazines to the keto‐functionalized clusters leads to the formation of hydrazone derivatives, [(Sn2(μ‐R3)(μ‐Se)Cl4] ( 5 , R3=[CMe2CH2CMe(NH)]2), [(SnR2)3Se4Cl] ( 6 , R2=CMe2CH2C(NNH2)Me), [(SnR4)3Se4][SnCl3] ( 7 , R4=CMe2CH2C(NNHPh)Me), [(SnR2)4Se6] ( 8 ), and [(SnR4)4Se6] ( 9 ). Upon treatment of 4 with [Cu(PPh3)3Cl] and excess (SiMe3)2Se, the cluster fragments to form [(R1Sn)2Se2(CuPPh3)2Se2] ( 10 ), the first discrete Sn/Se/Cu cluster compound reported in the literature. The derivatization reactions indicate fundamental differences between organotin sulfide and organotin selenide chemistry. 相似文献
66.
The optimization of a liquid chromatographic separation of four anthracyclines (doxorubicin, epirubicin, daunorubicin and idarubicin) and their respective 13-S-dihydro metabolites (doxorubicinol, epirubicinol, daunorubicinol and idarubicinol) is described. Inclusion of epidaunorubicin in the assay allows internal standardization. Potential chromatographic interference of aglycones (doxorubicinone, daunorubicinone, idarubicinone, doxorubicinolone, daunorubicinolone and idarubicinolone) was investigated and tackled. The analyses were performed on a C18 RP column and gradient elutions were performed with a mixture of 0.1% formic acid in water and 0.1% formic acid in ACN. The analytes were measured by fluorescence detection with an excitation wavelength of 480 nm and emission wavelength of 555 nm, respectively. The separation will potentially allow a broad field of applications, ranging from therapeutic drug monitoring and kinetic studies in cancer patients to monitoring hospital personnel and effluents. 相似文献
67.
A simple, rapid and accurate method for the simultaneous determination of four purine and pyrimidine bases (cytosine, 5-methylcytosine, adenine and N6-methyladenine) has been developed. The quantitative determination of these bases was accomplished by ion chromatography (IC) with direct conductivity detection (CD) based on their ionization in acidic medium without chemical suppression. The recovery of cytosine, 5-methylcytosine, and adenine in calf thymus DNA was more than 98% (n=3) and the relative standard deviation (RSD, n=5) less than 2.4%. In a single chromatographic run, the four bases could be separated and determined in less than 10 min. The detection limits were found to be 0.05 microg/mL for cytosine, 0.08 microg/mL for 5-methylcytosine, 0.07 microg/mL for adenine, and 0.07 microg/mL for N6-methyladenine. Linear ranges were 0.2-95.1 microg/mL for cytosine (r2=0.9996), 0.3-196.6 microg/mL for 5-methylcytosine (r2=0.9994), 0.3-105.5 microg/mL for adenine (r2=0.9998), and 0.3-159.1 microg/mL for N6-methyladenine (r2=0.9999). With the proposed method, purine and pyrimidine bases could be successfully detected in calf thymus DNA. We also determined these bases in calf thymus DNA using RP-HPLC. Compared to RP-HPLC, the IC method offers advantages such as high selectivity and simple mobile phase. 相似文献
68.
Gómez-González Y Surratt JD Cuyckens F Szmigielski R Vermeylen R Jaoui M Lewandowski M Offenberg JH Kleindienst TE Edney EO Blockhuys F Van Alsenoy C Maenhaut W Claeys M 《Journal of mass spectrometry : JMS》2008,43(3):371-382
In the present study, we have characterized in detail the MS(2) and MS(3) fragmentation behaviors, using electrospray ionization (ESI) in the negative ion mode, of previously identified sulfated isoprene secondary organic aerosol compounds, including 2-methyltetrols, 2-methylglyceric acid, 2-methyltetrol mononitrate derivatives, glyoxal and methylglyoxal. A major fragmentation pathway for the deprotonated molecules of the sulfate esters of 2-methyltetrols and 2-methylglyceric acid and of the sulfate derivatives of glyoxal and methylglyoxal is the formation of the bisulfate [HSO(4)](-) anion, while the deprotonated sulfate esters of 2-methyltetrol mononitrate derivatives preferentially fragment through loss of nitric acid. Rational interpretation of MS(2), MS(3) and accurate mass data led to the structural characterization of unknown polar compounds in K-puszta fine aerosol as organosulfate derivatives of photooxidation products of unsaturated fatty acids, i.e. 2-hydroxy-1,4-butanedialdehyde, 4,5- and 2,3-dihydroxypentanoic acids, and 2-hydroxyglutaric acid, and of alpha-pinene, i.e. 3-hydroxyglutaric acid. The deprotonated molecules of the sulfated hydroxyacids, 2-methylglyceric acid, 4,5- and 2,3-dihydroxypentanoic acid, and 2- and 3-hydroxyglutaric acids, showed in addition to the [HSO(4)](-) ion (m/z 97) neutral losses of water, CO(2) and/or SO(3), features that are characteristic of humic-like substances. The polar organosulfates characterized in the present work are of climatic relevance because they may contribute to the hydrophilic properties of fine ambient aerosol. In addition, these compounds probably serve as ambient tracer compounds for the occurrence of secondary organic aerosol formation under acidic conditions. 相似文献
69.
70.
Suci PA Berglund DL Liepold L Brumfield S Pitts B Davison W Oltrogge L Hoyt KO Codd S Stewart PS Young M Douglas T 《Chemistry & biology》2007,14(4):387-398
Nanomedicine directed at diagnosis and treatment of infections can benefit from innovations that have substantially increased the variety of available multifunctional nanoplatforms. Here, we targeted a spherical, icosahedral viral nanoplatform to a pathogenic, biofilm-forming bacterium, Staphylococcus aureus. Density of binding mediated through specific protein-ligand interactions exceeded the density expected for a planar, hexagonally close-packed array. A multifunctionalized viral protein cage was used to load imaging agents (fluorophore and MRI contrast agent) onto cells. The fluorescence-imaging capability allowed for direct observation of penetration of the nanoplatform into an S. aureus biofilm. These results demonstrate that multifunctional nanoplatforms based on protein cage architectures have significant potential as tools for both diagnosis and targeted treatment of recalcitrant bacterial infections. 相似文献