全文获取类型
收费全文 | 289篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 220篇 |
晶体学 | 4篇 |
力学 | 1篇 |
数学 | 35篇 |
物理学 | 45篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 5篇 |
2012年 | 21篇 |
2011年 | 18篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 14篇 |
2007年 | 6篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1971年 | 3篇 |
1962年 | 2篇 |
1960年 | 2篇 |
1955年 | 4篇 |
1954年 | 2篇 |
1948年 | 2篇 |
1947年 | 2篇 |
1941年 | 5篇 |
1939年 | 3篇 |
1937年 | 5篇 |
1935年 | 5篇 |
1934年 | 3篇 |
1929年 | 2篇 |
1925年 | 6篇 |
1914年 | 2篇 |
1912年 | 2篇 |
排序方式: 共有305条查询结果,搜索用时 15 毫秒
51.
Wenger D Gerecke AC Heeb NV Naegeli H Zenobi R 《Analytical and bioanalytical chemistry》2008,390(8):2021-2029
An in vitro reporter gene assay based on human breast cancer T47D cells (ER-CALUX) was applied to examine the ability of diesel exhaust to induce or inhibit estrogen receptor (ER)-mediated gene expression. Exhaust from a heavy-duty diesel engine was either treated by iron- or copper/iron-catalyzed diesel particulate filters (DPFs) or studied as unfiltered exhaust. Collected samples included particle-bound and semivolatile constituents of diesel exhaust. Our findings show that all of the samples contained compounds that were able to induce ER-mediated gene expression as well as compounds that suppressed the activity of the endogenous hormone 17beta-estradiol (E2). Estrogenic activity prevailed over antiestrogenic activity. We found an overall ER-mediated activity of 1.63 +/- 0.31 ng E2 CALUX equivalents (E2-CEQs) per m(3) of unfiltered exhaust. In filtered exhaust, we measured 0.74 +/- 0.07 (iron-catalyzed DPF) and 0.55 +/- 0.09 ng E2-CEQ m(-3) (copper/iron-catalyzed DPF), corresponding to reductions in estrogenic activity of 55 and 66%, respectively. Our study demonstrates that both catalytic DPFs lowered the ER-mediated endocrine-disrupting potential of diesel exhaust. 相似文献
52.
The synthesis and photophysical properties of a series of chromophore-quencher complexes are reported. They are all comprised of a luminescent rhenium(I) tricarbonyl diimine complex that is covalently attached to anthracene or phenanthrene moieties via rigid rod-like p-xylene bridges of variable lengths. Rhenium-to-anthracene energy transfer is strongly exergonic (-DeltaG0 approximately 0.9 eV) and causes very efficient rhenium MLCT luminescence quenching. By contrast, rhenium-to-phenanthrene energy transfer is only observed when complexes with sufficiently high MLCT energies are used because for these dyads, the driving force for energy transfer is low (-DeltaG0 approximately 0.1 eV). For a approximately 15 angstroms donor-acceptor distance, the rate constants of the weakly and the strongly exergonic energy transfer processes differ by more than 3 orders of magnitude. 相似文献
53.
Dr. Narayan Sinha Polina Yaltseva Prof. Dr. Oliver S. Wenger 《Angewandte Chemie (International ed. in English)》2023,62(30):e202303864
The expansion of d-orbitals as a result of metal-ligand bond covalence, the so-called nephelauxetic effect, is a well-established concept of coordination chemistry, yet its importance for the design of new photoactive complexes based on first-row transition metals is only beginning to be recognized. Until recently, much focus has been on optimizing the ligand field strength, coordination geometries, and molecular rigidity, but now it becomes evident that the nephelauxetic effect can be a game changer regarding the photophysical properties of 3d metal complexes in solution at room temperature. In CrIII and MnIV complexes with the d3 valence electron configuration, the nephelauxetic effect was exploited to shift the well-known ruby-like red luminescence to the near-infrared spectral region. In FeII and CoIII complexes with the low-spin d6 electron configuration, charge-transfer excited states were stabilized with respect to detrimental metal-centered excited states, to improve their properties and to enhance their application potential. In isoelectronic (3d6) isocyanide complexes of Cr0 and MnI, the nephelauxetic effect is likely at play as well, enabling luminescence and other favorable photoreactivity. This minireview illustrates the broad applicability of the nephelauxetic effect in tailoring the photophysical and photochemical properties of new coordination compounds made from abundant first-row transition metals. 相似文献
54.
Durola F Russo L Sauvage JP Rissanen K Wenger OS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(31):8749-8753
3,3'-biisoquinoline ligands (biiq) L, bearing aromatic substituents on their 8 and 8' positions, have been used to generate interwoven systems consisting of three crescent-shaped ligands disposed around an octahedral metal centre. Mono-ligand complexes of the type [ReL(CO)3py]+ (py: pyridine) have also been prepared, leading to sterically non-hindering complexes in spite of the endotopic nature of the chelate used. The three-component entanglements have been prepared by using either FeII or RuII as gathering metal centre. The synthetic procedure is simple and efficient, affording fully characterised complexes as their PF6 or SbCl6 salts. X-ray crystallography clearly shows that the crescent-shaped ligands do not repel each other in the tris-chelate complexes. In an analogous way, the ReI complexes show open structures with no steric repulsion between the L ligand and the ancillary CO or py groups. The FeL3 or RuL3 compounds are very unusual in the sense that, contrary to all the other tris-bidentate chelate complexes made till now, the three organic components are tangled up, in a situation which will be very favourable to the formation of new non trivial topologies of the catenane type. 相似文献
55.
Insertion of the glycosylidene carbenes derived from the diazirines 1 , 14 , and 15 into the B−alkyl bond of the B‐alkyl‐9‐oxa‐10‐borabicyclo[3.3.2]decanes 5 , 6 , and 7 yielded the stable glycosylborinates 8 / 9 (55%, 55 : 45), 10 / 11 (31%, 65 : 35), 12 / 13 (47%, 60 : 40), 16 / 17 (55%, 55 : 45), 18 / 19 (47%, 45 : 55), and 20 / 21 (31%, 30 : 70). Crystal‐structure analysis of 17 and NOEs of 9 and 19 show that 17 , 9 , and 19 adopt similar conformations. The glycosylborinates are stable under acidic, basic and thermal conditions. The unprotected glycosylborinate 25 was obtained in 80% by hydrogenolysis of 12 . Insertion of the glycosylidene carbene derived from the diazirine 1 into a B−C bond of BEt3, BBu3, and BPh3 led to unstable glycosylboranes that were oxidised to yield the hemiacetals 29 (55%), 31 (45%), and 33 (48%), respectively, besides the glucals 30 (13%), 32 (20%), and 34 (20%), respectively. Insertion of the glycosylidene carbenes derived from 14 and 15 into a B−C bond of BEt3 led exclusively to hemiacetals; only 15 yielding traces of the glucal 40 besides the hemiacetal 39 . The glycosylidene carbene derived from 1 reacted with Al(iBu)3 and AlMe3 to generate reactive glycosylalanes that were hydrolysed, yielding the C‐glycosides 46 (21%) and 49 (30%), respectively, besides the glucals 48 (26%) and 51 (30%); deuteriolysis instead of protonolysis led to the monodeuterio analogues of 46 and 49 , respectively, which possess an equatorial 2H‐atom at the anomeric center. 相似文献
56.
Dr. Tao Jin Dorothee Wagner Prof. Dr. Oliver S. Wenger 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(10):e202314475
Ruthenium(II) complexes with chelating polypyridine ligands are among the most frequently investigated compounds in photophysics and photochemistry, owing to their favorable luminescence and photoredox properties. Equally good photoluminescence performance and attractive photocatalytic behavior is now achievable with isoelectronic molybdenum(0) complexes. The zero-valent oxidation state of molybdenum is stabilized by carbonyl or isocyanide ligands, and metal-to-ligand charge transfer (MLCT) excited states analogous to those in ruthenium(II) complexes can be established. Microsecond MLCT excited-state lifetimes and photoluminescence quantum yields up to 0.2 have been achieved in solution at room temperature, and the emission wavelength has become tunable over a large range. The molybdenum(0) complexes are stronger photoreductants than ruthenium(II) polypyridines and can therefore perform more challenging chemical reductions. The triplet nature of their luminescent MLCT states allows sensitization of photon upconversion via triplet-triplet annihilation, to convert low-energy input radiation into higher-energy output fluorescence. This review summarizes the current state of the art concerning luminescent molybdenum(0) complexes and highlights their application potential. Molybdenum is roughly 140 times more abundant and far cheaper than ruthenium, hence this research is relevant in the greater context of finding more sustainable alternatives to using precious and rare transition metals in photophysics and photochemistry. 相似文献
57.
Single crystals of CdAl2S4 and CdAl2Se4 showing high transparency were grown by the chemical vapour transport method. Their composition was proven by microprobe analysis. Structural investigations were done by Rietveld refinements and are in good agreement with known structure data. From transmittance and reflectance measurements the energy of the band gap WBS estimated. Assuming a direct nature of the corresponding optical transition the following values were obtained: Eg = 3.82 eV (RT), Eg = 3.94 eV (85 K) for CdAl2S4 and Eg = 2.95 eV (RT), Eg = 3.07 eV (85 K) for CdAl2Se4 respectively. 相似文献
58.
Jonathan T. Ferguson Craig D. Wenger William W. Metcalf Neil L. Kelleher 《Journal of the American Society for Mass Spectrometry》2009,20(9):1743-1750
Combining our previous work with current platforms presented here that identified 99 new proteins (Supplemental Table 1), a total of 200 protein identities in M. acetivorans have been confirmed. Of these, five proteins were unannotated, 15 were mispredicted, two exhibited variable removal of the start methionine, and one was a proteolysis fragment from the identical C-terminus of two possible proteins. The incorporation of LC-MS/MS and offline automation speeds up the processing of samples through automation of the top-down process. For five data files that were automatically processed and iteratively searched, 2 h were required to complete analysis. In these, a total of 835 identifications were detected by the search algorithm in this time period. The expanded use of top-down will use both online and offline strategies, with increasingly sophisticated data acquisition strategies tailored for the challenges of top-down fragmentation [[16], [18], [19], [32] and [33]]. 相似文献
59.
The central part of the cover picture shows that the rates for long‐range charge transfer across covalent phenylene bridges can be very sensitive to the chemical substituents attached to the individual bridging units. The peripheral parts of the picture illustrate the flash–quench technique employed to investigate intramolecular charge transfer between a phenothiazine donor and a photochemically generated ruthenium(III) complex. On page 1203 , M. E. Walther and O. S. Wenger explain their experimental findings in terms of donor‐bridge energy matching for hole transfer.
60.
Kuang D Ito S Wenger B Klein C Moser JE Humphry-Baker R Zakeeruddin SM Grätzel M 《Journal of the American Chemical Society》2006,128(12):4146-4154
Two novel heteroleptic sensitizers, Ru((4,4-dicarboxylic acid-2,2'-bipyridine)(4,4'-bis(p-hexyloxystyryl)-2,2-bipyridine)(NCS)2 and Ru((4,4-dicarboxylic acid-2,2'-bipyridine)(4,4'-bis(p-methoxystyryl)-2,2'-bipyridine) (NCS)2, coded as K-19 and K-73, respectively, have been synthesized and characterized by 1H NMR, FTIR, UV-vis absorption, and emission spectroscopy and excited-state lifetime and spectroelectrochemical measurements. The introduction of the alkoxystyryl group extends the conjugation of the bipyridine donor ligand increasing markedly their molar extinction coefficient and solar light harvesting capacity. The dynamics of photoinduced charge separation following electronic excitation of the K-19 dye was scrutinized by time-resolved laser spectroscopy. The electron transfer from K-19 to the conduction band of TiO2 is completed within 20 fs while charge recombination has a half-life time of 800 s. The high extinction coefficients of these sensitizers enable realization of a new generation of a thin film dye sensitized solar cell (DSC) yielding high conversion efficiency at full sunlight even with viscous electrolytes based on ionic liquids or nonvolatile solvents. An unprecedented yield of over 9% was obtained under standard reporting conditions (simulated global air mass 1.5 sunlight at 1000 W/m2 intensity) when the K-73 sensitizer was combined with a nonvolatile "robust" electrolyte. The K-19 dye gave a conversion yield of 7.1% when used in conjunction with the binary ionic liquid electrolyte. These devices exhibit excellent stability under light soaking at 60 degrees C. The effect of the mesoscopic TiO2 film thickness on photovoltaic performance has been analyzed by electrochemical impedance spectroscopy (EIS). 相似文献