全文获取类型
收费全文 | 2427篇 |
免费 | 87篇 |
国内免费 | 2篇 |
专业分类
化学 | 1969篇 |
晶体学 | 28篇 |
力学 | 27篇 |
数学 | 96篇 |
物理学 | 396篇 |
出版年
2023年 | 12篇 |
2022年 | 16篇 |
2021年 | 38篇 |
2020年 | 24篇 |
2019年 | 35篇 |
2018年 | 27篇 |
2017年 | 21篇 |
2016年 | 56篇 |
2015年 | 50篇 |
2014年 | 53篇 |
2013年 | 124篇 |
2012年 | 117篇 |
2011年 | 162篇 |
2010年 | 75篇 |
2009年 | 77篇 |
2008年 | 172篇 |
2007年 | 149篇 |
2006年 | 144篇 |
2005年 | 178篇 |
2004年 | 133篇 |
2003年 | 105篇 |
2002年 | 103篇 |
2001年 | 48篇 |
2000年 | 36篇 |
1999年 | 24篇 |
1998年 | 29篇 |
1997年 | 28篇 |
1996年 | 34篇 |
1995年 | 23篇 |
1994年 | 27篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1985年 | 25篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 27篇 |
1981年 | 19篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1978年 | 23篇 |
1977年 | 15篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1974年 | 12篇 |
1973年 | 10篇 |
排序方式: 共有2516条查询结果,搜索用时 15 毫秒
71.
Cordonier CE Satake K Atarashi M Kawamoto Y Okamoto H Kimura M 《The Journal of organic chemistry》2005,70(9):3425-3436
[reaction: see text] The reaction of 2-methoxy-3H-azepines, in the presence or absence of a nucleophile, with N-bromosuccinimide (NBS) gave a regioselective 1,4-adduct from which the corresponding 2H-azepine derivatives were formed via base-promoted hydrogen bromide elimination, generally in moderate to quantitative yield. Competitive formation of 4-bromo-2-methoxy-3H-azepine by electrophilic substitutuion or 3H-azepin-2-yl 2H-azepin-2-yl ether by transetherification was minimized at lower reaction temperatures. Quantitative substitution of 2-(2',4',6'-trichlorophenoxy)-2H-azepine derivatives, formed in moderate yield from the respective 3H-azepine and NBS in the presence of 2,4,6-trichlorophenol (TCP), by various nucleophiles gave the corresponding 2-substituted 2H-azepine. Among these nucleophiles were alkanethiol and alkylamine that are not tolerated in the reaction of 3H-azepine and NBS. 相似文献
72.
Treatment of 1,4‐disubstituted 1,2,3‐triazoles with aryl chlorides in the presence of potassium carbonate under palladium catalysis and microwave irradiation at 250 °C for 15 min leads to arylation of the triazole at the 5‐position. A variety of functional groups, including ester and hydroxy groups, are compatible. The procedure is suitable for the regioselective preparation of trisubstituted triazoles. Microwave irradiation accelerates the reaction, thus allowing the rapid synthesis of trisubstituted triazoles, which are difficult to synthesize selectively. 相似文献
73.
Allylation of acetals with allylsilanes is catalyzed by iodotrimethylsilane to give the corresponding homoallyl ethers, with regiospecific transposition of the allyl group. 相似文献
74.
Kazuhiro Matsuo 《Journal of statistical physics》1978,18(6):535-555
A projection operator method is presented, which provides the most efficient way for calculating the stationary behavior of nonlinear Brownian motion. A continued-fraction expansion of the Fourier-Laplace transform of the displacement correlation function or the spectral density is used. This method utilizes a successive optimization procedure on the nonlinear terms and includes the method of statistical linearization as the lowest order approximation. A systematic way to calculate the continued fraction numerically up to sufficient order for convergence is developed, which enables us to obtain the spectral density of a system previously uncomputable.Numerical computations of the spectral density of a nonlinear oscillator with a double-well potential are presented and compared with the results obtained by statistical linearization.This work was supported in part by the National Science Foundation under Grant CHE 75-20624. 相似文献
75.
Wang ZS Hara K Dan-oh Y Kasada C Shinpo A Suga S Arakawa H Sugihara H 《The journal of physical chemistry. B》2005,109(9):3907-3914
A new coumarin dye, cyano-{5,5-dimethyl-3-[2-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)vinyl]cyclohex-2-enylidene}-acetic acid (NKX-2753), was prepared and characterized with respect to photophysical and electrochemical properties. It was employed as a dye sensitizer in dye-sensitized solar cells and showed efficient photon-to-electron conversion properties. The photocurrent action spectrum exhibited a broad feature with a maximum incident photon-to-electron conversion efficiency (IPCE) of 84% at 540 nm, which is comparable to that for the famous red dye RuL2(NCS)2 (known as N3), where L stands for 2,2'-bipyridyl-4,4'-dicarboxylic acid. The sandwich-type solar cell with NKX-2753, under illumination of full sun (AM1.5, 100 mW cm(-2)), produced 16.1 mA cm(-2) of short-circuit photocurrent, 0.60 V of open-circuit photovoltage, and 0.69 of fill factor, corresponding to 6.7% of overall energy conversion efficiency using 0.1 M LiI, 0.05 M I2, 0.1 M guanidinium thiocyanate, and 0.6 M 1,2-dimethyl-3-n-propyl-imidazolium iodide in dry acetonitrile as redox electrolyte. In comparison with its analogue NKX-2586 (Langmuir 2004, 20, 4205), NKX-2753 with an extra side ring on the alkene chain produced much higher IPCE values at the same conditions. The side ring acted as a spacer to efficiently prevent dye aggregation when adsorbed on the TiO2 surface, resulting in significant improvements of short-circuit photocurrent, open-circuit photovoltage, and fill factor compared with NKX-2586 that aggregated on the TiO2 surface. 相似文献
76.
Matsuo Nonoyama 《Journal of organometallic chemistry》1984,262(3):407-412
2-(1-Pyrrolyl)pyridine (Hplp) is cyclometallated with lithium tetrachloropalladate(II) and hexahalogenotetrakis(tri-n-butylphosphine)dirhodium(III) to give [PdCl(plp)]2 and [RhX2(plp(PBu3)2] (X = Cl, Br; PBu3 = tri-n-butylphosphine), respectively, where deprotonated plp is coordinated via the pyridine-N and pyrrole-2C atoms forming a five-membered metallacycle. [PdCl(plp)]2 reacts with pyridine (py) and with PBu3 to form the adducts [PdCl(plp)L] (L = py, PBu3) and with acetylacetone (Hacac) to afford the complex [Pd(plp)(acac)]. Metathesis of [RhCl2(plp)(PBu3)2] with excess lithium iodide gives a mixed halogeno complex [RhClI(plp)(PBu3)2]. These complexes are characterized spectroscopically. 相似文献
77.
Tamás Veszprémi Yoshiya Harada Koichi Ohno Hideki Mutoh 《Journal of organometallic chemistry》1983,252(2):121-125
Penning ionization electron spectroscopy and CNDO/S calculations have been successfully applied to the analyses of the UV photoelectron spectra of 2- and 2,5-bistrimethylsilylthiophene and 2-t-butylthiophene. The relative intensities of the π type bands are greatly enhanced in the Penning spectra compared with those of the UV photoelectron spectra. 相似文献
78.
Osako T Terada S Tosha T Nagatomo S Furutachi H Fujinami S Kitagawa T Suzuki M Itoh S 《Dalton transactions (Cambridge, England : 2003)》2005,(21):3514-3521
The structure and dioxygen-reactivity of copper(I) complexes R supported by N,N-bis(6-methylpyridin-2-ylmethyl)amine tridentate ligands L2R[R (N-alkyl substituent)=-CH2Ph (Bn), -CH2CH2Ph (Phe) and -CH2CHPh2(PhePh)] have been examined and compared with those of copper(I) complex (Phe) of N,N-bis[2-(pyridin-2-yl)ethyl]amine tridentate ligand L1(Phe) and copper(I) complex (Phe) of N,N-bis(pyridin-2-ylmethyl)amine tridentate ligand L3(Phe). Copper(I) complexes (Phe) and (PhePh) exhibited a distorted trigonal pyramidal structure involving a d-pi interaction with an eta1-binding mode between the metal ion and one of the ortho-carbon atoms of the phenyl group of the N-alkyl substituent [-CH2CH2Ph (Phe) and -CH2CHPh2(PhePh)]. The strength of the d-pi interaction in (Phe) and (PhePh) was weaker than that of the d-pi interaction with an eta2-binding mode in (Phe) but stronger than that of the eta1 d-pi interaction in (Phe). Existence of a weak d-pi interaction in (Bn) in solution was also explored, but its binding mode was not clear. Redox potentials of the copper(I) complexes (E1/2) were also affected by the supporting ligand; the order of E1/2 was Phe>R>Phe. Thus, the order of electron-donor ability of the ligand is L1Phe相似文献
79.
Komuro T Matsuo T Kawaguchi H Tatsumi K 《Dalton transactions (Cambridge, England : 2003)》2004,(10):1618-1625
Treatment of cyclotrisilathiane (Me2SiS)3 with 3 equiv. of RLi (R = Me, But) in hexane-Et2O afforded the lithium silanethiolates LiSSiMe2R, and the tmeda adduct [(tmeda)LiSSiMe2But]2 1 (tmeda =N,N,N',N'-tetramethylethylenediamine) was isolated in the case of R = But. Reaction of Fe(CH3CN)2(CF3SO3)2, CoCl2, and [Cu(CH3CN)4](PF6) with 1 gave rise to the silanethiolato complexes M(SSiMe2But)2(tmeda)(M = Fe 2, Co 3), and [Cu(SSiMe2But)]4 4, respectively. Complexes (C5H5)2Ti(SSiMe2R)2(R = Me 5, But 6) and Ni(SSiMe2R)2(dppe)[R = Me 7, But 8; dppe = 1,2-bis(diphenylphosphino)ethane] were prepared from treatments of (C5H5)2TiCl2 and NiCl2(dppe) with the corresponding lithium silanethiolates. Complex 7 readily reacted with (C5H5)TiCl3 to produce the Ti-Ni heterobimetallic compound (C5H5)TiCl(mu-S)2Ni(dppe) 9, in which silicon-sulfur bond cleavage took place. Characterization of all compounds through spectroscopic techniques and elemental analyses are also described. X-Ray structural data for compounds 1 and 3-9 are reported. 相似文献
80.
Spectrophotometric determinations of palladium(II) and tartaric acid were respectively investigated by using the color reactions between 2(5-nitro-2-pyridylazo)-5-(N-propyl-N-3-sulfopropylamino)phenol(5-NO2.PAPS) and palladium(II) in strong acidic media, and between 5-NO2.PAPS, niobium(V) tartaric acid in weak acidic media. The calibration graphs were linear in the range of 0–25 μg/10 ml palladium(II), with an apparent molecular coefficient () of 6.2×104 l mol−1 cm−1 at 612 nm, and 0–23 μg/10 ml tartaric acid with =1.08×106 l mol−1 cm−1 at 612 nm, respectively. The proposed methods were selective and sensitive in comparison with other chelating pyridylazo dyes–palladium(II) or metavanadic acid–tartaric acid method, and the effect of foreign ions such as copper(II) was negligible for the assay of palladium(II) with 5-NO2.PAPS. 相似文献