全文获取类型
收费全文 | 1523篇 |
免费 | 51篇 |
国内免费 | 4篇 |
专业分类
化学 | 1194篇 |
晶体学 | 21篇 |
力学 | 4篇 |
数学 | 32篇 |
物理学 | 327篇 |
出版年
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 28篇 |
2015年 | 25篇 |
2014年 | 39篇 |
2013年 | 84篇 |
2012年 | 64篇 |
2011年 | 70篇 |
2010年 | 39篇 |
2009年 | 43篇 |
2008年 | 71篇 |
2007年 | 96篇 |
2006年 | 76篇 |
2005年 | 94篇 |
2004年 | 69篇 |
2003年 | 68篇 |
2002年 | 69篇 |
2001年 | 42篇 |
2000年 | 45篇 |
1999年 | 21篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 8篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 26篇 |
1991年 | 14篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 30篇 |
1984年 | 22篇 |
1983年 | 10篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1976年 | 8篇 |
1975年 | 13篇 |
1974年 | 17篇 |
1973年 | 11篇 |
1968年 | 5篇 |
排序方式: 共有1578条查询结果,搜索用时 15 毫秒
71.
Duanjun Xu Kunio Miki Yasushi Kai Nobutami Kasai Masanori Wada 《Journal of organometallic chemistry》1985,287(2):265-273
The structure of a nickel(II) complex, trans-[Ni(C6Cl5)(PMe2Ph)2{C(OMe)Me}]BF4, containing the simplest alkyl(alkoxy)carbene ligand has been determined by X-ray crystallography (R = 0.091). The geometry around the nickel atom is square-planar. The comparatively short NiC(1) bond length of 1.843(10) Å showed the presence of π-bonding in the nickel-carbene bond. 相似文献
72.
Hattori S Wada Y Yanagida S Fukuzumi S 《Journal of the American Chemical Society》2005,127(26):9648-9654
The electron self-exchange rate constants of blue copper model complexes, [(-)-sparteine-N,N'](maleonitriledithiolato-S,S')copper ([Cu(SP)(mmt)])(0/)(-), bis(2,9-dimethy-1,10-phenanthroline)copper ([Cu(dmp)(2)](2+/+)), and bis(1,10-phenanthroline)copper ([Cu(phen)(2)](2+/+)) have been determined from the rate constants of electron transfer from a homologous series of ferrocene derivatives to the copper(II) complexes in light of the Marcus theory of electron transfer. The resulting electron self-exchange rate constant increases in the order: [Cu(phen)(2)](2+/+) < [Cu(SP)(mmt)](0/)(-) < [Cu(dmp)(2)](2+/+), in agreement with the order of the smaller structural change between the copper(II) and copper(I) complexes due to the distorted tetragonal geometry. The dye-sensitized solar cells (DSSC) were constructed using the copper complexes as redox couples to compare the photoelectrochemical responses with those using the conventional I(3)(-)/I(-) couple. The light energy conversion efficiency (eta) values under illumination of simulated solar light irradiation (100 mW/cm(2)) of DSSCs using [Cu(phen)(2)](2+/+), [Cu(dmp)(2)](2+/+), and [Cu(SP)(mmt)](0/)(-) were recorded as 0.1%, 1.4%, and 1.3%, respectively. The maximum eta value (2.2%) was obtained for a DSSC using the [Cu(dmp)(2)](2+/+) redox couple under the light irradiation of 20 mW/cm(2) intensity, where a higher open-circuit voltage of the cell was attained as compared to that of the conventional I(3)(-)/I(-) couple. 相似文献
73.
Summary Several polystyrene gels of different pore sizes were packed into a 500 mm×2.1 mm I.D. column. Semi-micro size-exclusion chromatography
(SEC) using these columns was carried out with a system consisting of a triple piston pump, a micro loop injector and a flow
cell with 1.0-μl cell volume constructed for semi-micro HPLC, because the dead volume of the injector and the cell volume
of flow cell for conventional HPLC caused a significant loss in column efficiency.
The effects of sample amount, injection volume and mobile phase flow rate on column efficiency and retention volume were examined
and the optimized operational variables of the sample amount (below 500 μg), the injection volume (less than 15 μl) and the
flow rate range (30–70 μl/min) determiend for semi-micro SEC.
Oligostyrene, epoxy resin, phenol-formaldehyde resin and phthalates were analyzed by the optimized semi-micro SEC system under
the given conditions. In addition, molecular weight distribution of four different poly(ethylene terephthalate) films was
successfully measured by using a mixture of chloroform and hexafluoroisopropanol as the eluent. 相似文献
74.
Secondary structural changes of chymotrypsinogen A,-chymotrypsin, and their isolated polypeptides Cys1-Leu13, Ile16-Tyr146, and Ala149-Asn245were examined in aqueous solutions of sodium dodecyl sulfate (SDS), urea, and guanidine hydrochloride (residue numbers from chymotrypsinogen). After the fragmentation by the cleavage of disulfide bridges in-chymotrypsin, the helical structure was formed in the isolated polypeptide 16–146 where the helical segments do not exist in the protein state. The polypeptide 149–245, where the helical segments of the parent protein are originally located, contained no helices. The polypeptide 1–13 was almost disordered. The three polypeptides, chymotrypsinogen,-chymotrypsin and the polypeptide 16–146, clearly showed differences in the stabilities of helical structures in solutions of urea and guanidine hydrochloride. The addition of SDS accelerated the formation of helical structures in each polypeptide except for 1–13. 相似文献
75.
Wada A Ogo S Nagatomo S Kitagawa T Watanabe Y Jitsukawa K Masuda H 《Inorganic chemistry》2002,41(4):616-618
The first isolation and spectroscopic characterization of the mononuclear hydroperoxo-iron(III) complex [Fe(H(2)bppa)(OOH)](2+) (2) and the stoichiometric oxidation of substrates by the mononuclear iron-oxo intermediate generated by its decomposition have been described. The purple species 2 obtained from reaction of [Fe(H(2)bppa)(HCOO)](ClO(4))(2) with H(2)O(2) in acetone at -50 degrees C gave characteristic UV-vis (lambda(max) = 568 nm, epsilon = 1200 M(-1) cm(-1)), ESR (g = 7.54, 5.78, and 4.25, S = (5)/(2)), and ESI mass spectra (m/z 288.5 corresponding to the ion, [Fe(bppa)(OOH)](2+)), which revealed that 2 is a high-spin mononuclear iron(III) complex with a hydroperoxide in an end-on fashion. The resonance Raman spectrum of 2 in d(6)-acetone revealed two intense bands at 621 and 830 cm(-1), which shifted to 599 and 813 cm(-1), respectively, when reacted with (18)O-labeled H(2)O(2). Reactions of the isolated (bppa)Fe(III)-OOH (2) with various substrates (single turnover oxidations) exhibited that the iron-oxo intermediate generated by decomposition of 2 is a nucleophilic species formulated as [(H(2)bppa)Fe(III)-O*]. 相似文献
76.
Nishiyama Y Kaneda M Saito R Mori T Wada T Inoue Y 《Journal of the American Chemical Society》2004,126(21):6568-6569
In the enantiodifferentiating photoaddition of ROH (R = Me, Et, i-Pr) to 1,1-diphenylpropene sensitized by fructosyl 1,4-naphthalenedicarboxylate in supercritical carbon dioxide, the enantiomeric excess of photoadduct increased with increasing bulkiness of the alcohol at all pressures used, with an accompanying sudden jump at the critical density, for which the enhanced clustering of alcohol, particularly in the subcritical pressure region, was revealed to be responsible from the fluorescence spectral examinations. 相似文献
77.
4-Thiouridine, 6-thioguanosine, and 6-thioinosine 3',5'-bisphosphates (9, 20, and 28) were synthesized in good yields by considerably improved methods. In the former two compounds, uridine and 2-N-phenylacetylguanosine were converted via transient O-trimethylsilylation to the corresponding 4- and 6-O-benzenesulfonyl intermediates (2 and 13), which, in turn, were allowed to react with 2-cyanoethanethiol in the presence of N-methylpyrrolidine to give 4-thiouridine (3) and 2-N-phenylacetyl-6-thioguanosine derivatives (14), respectively. In situ dimethoxytritylation of these thionucleoside derivatives gave the 5'-masked products 4 and 15 in high overall yields from 1 and 11. 6-S-(2-Cyanoethyl)-5'-O-(4,4'-dimethoxytrityl)-6-thioinosine (23) was synthesized via substitution of the 5'-O-tritylated 6-chloropurine riboside derivative 22 with 2-cyanoethanethiol. These S-(2-cyanoethyl)thionucleosides were converted to the 2'-O-(tert-butyldimethylsilyl)ribonucleoside 3'-phosphoramidite derivatives 7, 18, and 26 or 3',5'-bisphosphate derivatives 8, 19, and 27. Treatment of 8, 19, and 27 with DBU gave thionucleoside 3',5'-bisphosphate derivatives 9, 20, and 28, which were found to be substrates of T4 RNA ligase. These thionucleoside 3',5'-bisphosphates were examined as donors for ligation with m3(2,2,7) G5'pppAmUmA, i.e., the 5'-terminal tetranucleotide fragment of U1 snRNA, The 4-thiouridine 3',5'-bisphosphate derivative 9 was found to serve as the most active substrate of T4 RNA ligase with a reaction efficiency of 96%. 相似文献
78.
The adsolubilization behaviors of 2-naphthol, biphenyl, and their binary solutes in the hexadecyltrimethyl ammonium bromide (HTAB) adsorbed layer formed on silica have been studied with solution pH. Two feed concentrations of HTAB are employed: 1.5 and 3.0 mmol dm(-3). At the feed concentration of 1.5 mmol dm(-3) HTAB, most of HTAB are adsorbed on the silica as a monolayer, while a bilayer formation occurs at the feed concentration of 3.0 mmol dm(-3). It is found that the adsolubilized amounts of respective single solutes increase with increasing solution pH except acidic region for biphenyl under a constant feed concentration of 2-naphthol (0.4 mmol dm(-3)) and biphenyl (0.047 mmol dm(-3)). The adsolubilization of binary solutes depends on the feed concentration of HTAB; at the low HTAB feed concentration, competitive adsolubilization between 2-naphthol and biphenyl occurs above pH 4.5, while at the high HTAB feed concentration the adsolubilization of biphenyl is enhanced by the incorporation of 2-naphthol over a whole pH region. These behaviors in the adsolubilization are discussed from the surfactant structure of HTAB adsorbed as well as the admicellar partitioning coefficients. 相似文献
79.
Eight modes of the guest-host cells (GH-cells), in which types of dye, liquid crystal and their alignments are adequately combined, are surveyed, and the color contrast of each mode is calculated. Three modes among them are of positive type display, that is, colored patterns on the colorless background contrary to the initially proposed fundamental GH-cell. Another three modes are the GH-cells without polarizer, by which bright display can be obtained. Light stability of dyes are also discussed and lifetimes of various dyes are estimated by accelerated life test. As a result, it is found that diazo-and axomethine-dayes without thiazole groups as well as anthraqunone-dyes have satisfying lifetimes as long as they are used indoors. 相似文献
80.