全文获取类型
收费全文 | 732篇 |
免费 | 33篇 |
国内免费 | 3篇 |
专业分类
化学 | 483篇 |
晶体学 | 3篇 |
力学 | 16篇 |
数学 | 138篇 |
物理学 | 128篇 |
出版年
2023年 | 6篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 29篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 32篇 |
2012年 | 23篇 |
2011年 | 40篇 |
2010年 | 28篇 |
2009年 | 30篇 |
2008年 | 36篇 |
2007年 | 37篇 |
2006年 | 30篇 |
2005年 | 27篇 |
2004年 | 20篇 |
2003年 | 19篇 |
2002年 | 24篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1996年 | 6篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1959年 | 5篇 |
1932年 | 12篇 |
1931年 | 6篇 |
1930年 | 5篇 |
1928年 | 9篇 |
1927年 | 6篇 |
1926年 | 5篇 |
1901年 | 4篇 |
1900年 | 4篇 |
1898年 | 4篇 |
1896年 | 4篇 |
1895年 | 4篇 |
1893年 | 13篇 |
1892年 | 4篇 |
排序方式: 共有768条查询结果,搜索用时 31 毫秒
61.
Meade Bolton C. Kraus T. Leone Link Heraeus Flügge A. Pfeiffer E. Esmarch Carl Fränkel von Sehlen's M. Hochstetter G. Bischof Alex Köbrich O. Kasper Dupré Joseph Klein John Henry Smith J. W. Mallet's E. Reichardt Mayrhofer Leopold Spiegel Katharine J. Williams W. Ramsay A. B. Cooper Baeseler Nobbe Will W. Knop C. W. Heaton Thomas Stevenson Odling Tidy Crookes P. T. Austen Austen und Francis A. Wilber 《Fresenius' Journal of Analytical Chemistry》1888,27(1):77-84
Ohne Zusammenfassung 相似文献
62.
Leopold Löwenheim 《Mathematische Annalen》1918,79(3):223-236
Ohne Zusammenfassung 相似文献
63.
The spectroscopic, electronic, and DNA-binding characteristics of two novel ruthenium complexes based on the dialkynyl ligands 2,3-bis(phenylethynyl)-1,4,8,9-tetraaza-triphenylene (bptt, 1) and 2,3-bis(4-tert-butyl-phenylethynyl)-1,4,8,9-tetraaza-triphenylene (tbptt, 2) have been investigated. Electronic structure calculations of bptt reveal that the frontier molecular orbitals are localized on the pyrazine-dialkynyl portion of the free ligand, a property that is reflected in a red shift of the lowest energy electronic transition (1: λ(max) = 393 nm) upon substitution at the terminal phenyl groups (2: λ(max) = 398 nm). Upon coordination to ruthenium, the low-energy ligand-centered transitions of 1 and 2 are retained, and metal-to-ligand charge transfer transitions (MLCT) centered at λ(max) = 450 nm are observed for [Ru(phen)(2)bptt](2+)(3) and [Ru(phen)(2)tbptt](2+)(4). The photophysical characteristics of 3 and 4 in ethanol closely parallel those observed for [Ru(bpy)(3)](2+) and [Ru(phen)(3)](2+), indicating that the MLCT excited state is primarily localized within the [Ru(phen)(3)](2+) manifold of 3 and 4, and is only sparingly affected by the extended conjugation of the bptt framework. In an aqueous environment, 3 and 4 possess notably small luminescence quantum yields (3: ?(H(2)O) = 0.005, 4: ?(H(2)O) = 0.011) and biexponential decay kinetics (3: τ(1) = 40 ns, τ(2) = 230 ns; 4: τ(1) ~ 26 ns, τ(2) = 150 ns). Addition of CT-DNA to an aqueous solution of 3 causes a significant increase in the luminescence quantum yield (?(DNA) = 0.045), while the quantum yield of 4 is relatively unaffected (?(DNA) = 0.013). The differential behavior demonstrates that tert-butyl substitution on the terminal phenyl groups inhibits the ability of 4 to intercalate with DNA. Such changes in intrinsic luminescence demonstrate that 3 binds to DNA via intercalation (K(b) = 3.3 × 10(4) M(-1)). The origin of this light switch behavior involves two competing (3)MLCT states similar to that of the extensively studied light switch molecule [Ru(phen)(2)dppz](2+). The solvent- and temperature-dependence of the luminescence of 3 reveal that the extended ligand aromaticity lowers the energy of the (3)ππ* excited state into competition with the emitting (3)MLCT state. Interconversion between these two states plays a significant role in the observed photophysics and is responsible for the dual emission in aqueous environments. 相似文献
64.
Andrzej Rajca Prof. Velavan Kathirvelu Dr. Sandip K. Roy Dr. Maren Pink Dr. Suchada Rajca Dr. Santanu Sarkar Sandra S. Eaton Prof. Gareth R. Eaton Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(19):5778-5782
Site‐directed spin labeling and EPR spectroscopy offer accurate, sensitive tools for the characterization of structure and function of macromolecules and their assemblies. A new rigid spin label, spirocyclohexyl nitroxide α‐amino acid and its N‐(9‐fluorenylmethoxycarbonyl) derivative, have been synthesized, which exhibit slow enough spin‐echo dephasing to permit accurate distance measurements by pulsed EPR spectroscopy at temperatures up to 125 K in 1:1 water/glycerol and at higher temperatures in matrices with higher glass transition temperatures. Distance measurements in the liquid nitrogen temperature range are less expensive than those that require liquid helium, which will greatly facilitate applications of pulsed EPR spectroscopy to the study of structure and conformation of peptides and proteins. 相似文献
65.
Leopold Gegenbauer 《Monatshefte für Mathematik》1896,7(1):73-76
Ohne Zusammenfassung 相似文献
66.
Renk und Leopold Schulz 《Fresenius' Journal of Analytical Chemistry》1893,32(1):624-625
Ohne Zusammenfassung 相似文献
67.
Mohammadreza Shariatgorji Zdenek Spacil Gianluca Maddalo Lourdes B. Cardenas Leopold L. Ilag 《Rapid communications in mass spectrometry : RCM》2009,23(23):3655-3660
Quaternary protoberberine alkaloids belong to a pharmaceutically important class of isoquinoline alkaloids associated with bactericidal, fungicidal, insecticidal and antiviral activities. As traditional medicine gains wider acceptance, quick and robust analytical methods for the screening and analysis of plants containing these compounds attract considerable interest. Thin‐layer chromatography (TLC) combined with matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) is a powerful technique but suffers from dilution of the TLC bands resulting in decreased sensitivity and masking of signals in the low‐mass region both due to addition of matrix. This study integrates for the first time conventional silica gel TLC and laser desorption ionization mass spectrometry (LDI‐MS) thus eliminating the need for any external matrix. Successful separation of berberine (Rf = 0.56) and palmatine (Rf = 0.46) from Berberis barandana including their identification by MS are demonstrated. Furthermore, a robust electrospray ionization (ESI)‐MS method utilizing residual sample from TLC for quantification of berberine applying selected reaction monitoring and standard addition method is presented. The amount of berberine in the plant root prepared for the study was determined to be 0.70% (w/w). Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
68.
Ohne Zusammenfassung 相似文献
69.
Leopold Schmetterer 《Monatshefte für Mathematik》1948,52(2):162-178
Ohne Zusammenfassung 相似文献
70.