全文获取类型
收费全文 | 3642篇 |
免费 | 117篇 |
国内免费 | 19篇 |
专业分类
化学 | 2767篇 |
晶体学 | 10篇 |
力学 | 65篇 |
数学 | 510篇 |
物理学 | 426篇 |
出版年
2022年 | 17篇 |
2021年 | 36篇 |
2020年 | 40篇 |
2019年 | 50篇 |
2018年 | 31篇 |
2017年 | 21篇 |
2016年 | 79篇 |
2015年 | 102篇 |
2014年 | 75篇 |
2013年 | 136篇 |
2012年 | 182篇 |
2011年 | 222篇 |
2010年 | 160篇 |
2009年 | 109篇 |
2008年 | 216篇 |
2007年 | 198篇 |
2006年 | 199篇 |
2005年 | 196篇 |
2004年 | 134篇 |
2003年 | 108篇 |
2002年 | 115篇 |
2001年 | 60篇 |
2000年 | 69篇 |
1999年 | 64篇 |
1998年 | 57篇 |
1997年 | 66篇 |
1996年 | 59篇 |
1995年 | 55篇 |
1994年 | 51篇 |
1993年 | 64篇 |
1992年 | 56篇 |
1991年 | 25篇 |
1990年 | 32篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 39篇 |
1986年 | 33篇 |
1985年 | 56篇 |
1984年 | 24篇 |
1983年 | 30篇 |
1982年 | 43篇 |
1980年 | 37篇 |
1978年 | 27篇 |
1977年 | 37篇 |
1976年 | 17篇 |
1974年 | 18篇 |
1973年 | 19篇 |
1972年 | 19篇 |
1971年 | 19篇 |
1969年 | 20篇 |
排序方式: 共有3778条查询结果,搜索用时 15 毫秒
111.
112.
Bernhard Schrader 《Angewandte Chemie (International ed. in English)》1973,12(11):884-908
Raman spectorscopy is—like infrared spectroscopy—a method for the study of vibrations of molecules and crystals. The two methods are complementary: if a vibration results in a change of the polarizability of a molecule, it is Raman active; if a change in the molecular dipole moment results, it is infrared active Vibrations of nonpolar groups and totally symmetrical vibrations of molecules are often only Raman active. IR and Raman spectra together give information about the symmetries and structures of molecules and crystals and about the properties of chemical bonds and intermolecular interactions. Until about 10 years ago Raman spectra could only be recorded on relatively large amounts of essentially colorless substances. After the advent of laser light sources the situation changed completely. The amount of sample substance required is now in the region of milli- and micrograms. Gases, liquids and solid samples, especially air-sensitive and reactive substances, single crystals, crystal needles and filaments as well as aqueous solutions can be readily investigated. The identification of molecules and the elucidation of molecular structures, biochemical analysis, and control of evnivornmental pollution are important aplications of Raman spectroscopy. Raman spectroscopy now constitutes an additional powerful tool in instrumental analysis 相似文献
113.
Reinhard Schubert Achim Ansmann Paul Bleckmann Bernhard Schrader 《Journal of Molecular Structure》1975,26(2):429-438
By using the values of the vibrational frequencies of normal and deuterated cyclopropenone (II-d0 , II-d2 ) and 16 O-and 18 O-substituted dimethylcyclopropenone (III) as -well as the infrared and Raman intensities of II a consistent set of force constants has been derived for the cyclopropenone skeleton. The derived values show that the zwitterionic form makes a substantial contribution to the electronic ground state of the molecule. The combined frequency and intensity calculation - simulation of the infrared and the Raman spectrum - is shown to be a good method for making a proper assignment of calculated and observed vibrations and deriving realistic sets of force constants. 相似文献
114.
Bernhard S Barron JA Houston PL Abruña HD Ruglovksy JL Gao X Malliaras GG 《Journal of the American Chemical Society》2002,124(45):13624-13628
We have investigated the electrochemical, spectroscopic, and electroluminescent properties of a family of diimine complexes of Ru featuring various aliphatic side chains as well as a more extended pi-conjugated system. The performance of solid-state electroluminescent devices fabricated from these complexes using indium tin oxide (ITO) and gold contacts appears to be dominated by ionic space charge effects. Their electroluminescence efficiency was limited by the photoluminescence efficiency of the Ru films and not by charge injection from the contacts. The incorporation of di-tert-butyl side chains on the dipyridyl ligand was found to be the most beneficial substitution in terms of reducing self-quenching of luminescence. 相似文献
115.
Sesquialkoxides of Gallium and Indium Treatment of GaMe3 with one equivalent of HOcHex in toluene at 20 °C leads to [Me2GaOcHex]2 ( 4 ) under evolution of methane. The reaction of InMe3 with two equivalents of HOcHex leads under similar conditions not to [MeIn(OcHex)2]n but to the sesquialkoxide [In{Me2In(OcHex)2}3] ( 5 ). 5 can be described also as [{Me2InOcHex)}2{MeIn(OcHex)2}2]. The use of an excess of cyclohexanol in boiling toluene gives the same result. Under these reflux conditions, the reaction of GaMe3 with an excess of PhCH2OH leads exclusively to another type of sequialkoxides, [Ga{MeGa(OCH2Ph)3}3] ( 6 ). 4 — 6 were characterized by NMR, vibrational and MS spectra, as well as by X‐ray structure determinations. According to this, 4 forms centrosymmetrical and therefore planar Ga2O2 four‐membered rings. 5 and 6 possess basically the same structural motif, central M3+ ion ( 5 : In3+; 6 : Ga3+) coordinated by three metalate units ( 5 : [Me2In(OcHex)2]—; 6 : [MeGa(OCH2Ph)3]—). The central M3+ ions have always coordination number (CN) six while the three surrounding metal ions possess CN 4. Because of the spectroscopic findings 6 must exist in two isomers (1:1). The C3‐symmetrical isomer C3‐ 6 was characterized by X‐ray analysis, while the isomer C1‐ 6 could by described mainly by the complex NMR data. 相似文献
116.
Enantioselective Rhodium‐Catalyzed Dimerization of ω‐Allenyl Carboxylic Acids: Straightforward Synthesis of C2‐Symmetric Macrodiolides 下载免费PDF全文
Philip Steib Prof. Dr. Bernhard Breit 《Angewandte Chemie (International ed. in English)》2018,57(22):6572-6576
Herein, we report on the first enantioselective and atom‐efficient catalytic one‐step dimerization method to selectively transform ω‐allenyl carboxylic acids into C2‐symmetric 14‐ to 28‐membered bismacrolactones (macrodiolides). This convenient asymmetric access serves as an attractive route towards multiple naturally occuring homodimeric macrocyclic scaffolds and demonstrates excellent efficiency to construct the complex, symmetric core structures. By utilizing a rhodium catalyst with a modified chiral cyclopentylidene‐diop ligand, the desired diolides were obtained in good to high yields, high diastereoselectivity, and excellent enantioselectivity. 相似文献
117.
Thomas Pieper Martina Sommer Markus Galanski Bernhard K. Keppler Gerald Giester 《无机化学与普通化学杂志》2001,627(2):261-265
Indazolium (OC‐6‐11)‐tetrachlorobis(indazole) ruthenate(III), HInd (OC‐6‐11)‐[RuCl4ind2], exhibits excellent results in different tumor models in vitro and in vivo. Substitution reactions of this ruthenium(III) complex are of special interest for a deeper understanding of its interactions with biologically occurring targets and its mode of action. The indazolium complex salt can be transformed to the neutral, meridionally configurated trisindazole complex (OC‐6‐21)‐[RuCl3ind3] in solvents like tetrahydrofuran. The X‐ray crystal structure of this complex could be solved (monoclinic space group P2(1)/n, a = 12.441(3), b = 10.415(3), c = 21.635(4) Å, β = 105.02(1)°). In spite of the paramagnetic RuIII atom most of the coordinated indazole protons could be assigned with the help of two‐dimensional NMR experiments. Additionally, a reduced reaction product of HInd (OC‐6‐11)‐[RuCl4ind2] in the physiological solubilizer 2‐pyrrolidone could be isolated and the X‐ray crystal structure of this RuII complex, (OC‐6‐12)‐[RuCl2ind4], crystallized with two 2‐pyrrolidones, could be solved (monoclinic space group P2(1)/n, a = 12.139(2), b = 10.426(2), c = 14.426(3) Å, β = 100.06(3)°). 相似文献
118.
[Fc2B2(Br)(μ‐NPEt3)2]+Br– – a Ferrocenyl‐substituted Phosphoraneiminato Complex of Boron [Fc2B2(Br)(μ‐NPEt3)2]+Br– has been prepared from ferrocenylboron dibromide, [Fe(η5‐C5H5)(η5‐C5H4BBr2)], and the silylated phosphoraneimine Me3SiNPEt3 in dichloromethane solution to give orange‐red single crystals which were characterized by IR, NMR and 57Fe Mössbauer spectra, as well as by a crystal structure determination. [Fc2B2(Br)(μ‐NPEt3)2]+Br– · 3 CH2Cl2 ( 1 · 3 CH2Cl2): Space group P21/n, Z = 4, lattice dimensions at –50 °C: a = 1370.6(3), b = 2320.9(5), c = 1454.4(2), β = 95.38(1)°, R1 = 0.061. In the cation of 1 the ferrocenyl‐substituted boron atoms are connected by the nitrogen atoms of the [NPEt3]– groups to form a planar B2N2 four‐membered ring. One of the boron atoms having planar, the other tetrahedral coordination. 相似文献
119.
Lithium and Cesium Alkoxometalates The aluminium alkoxide, Al(OCH2Ph)3 ( 1 ), can be obtained from a direct synthesis of Al and PhCH2OH under HgCl2 catalysis. The formation of the metalate [{(Diglyme)Li}{Al(OtBu)4}] ( 2 ) from LiAlH4 and tBuOH in THF under evolution of hydrogen takes place, if the reaction product is heated under reflux with additional tBuOH in diglyme. The nucleophilic attack of F– ions leads during the treatment of CsF on a THF solution of Al(OcHex)3 after ligand redistribution to the coordination polymer [{Cs(THF)2}{Cs(THF)}{Al(OcHex)4}2]n ([3]n). 1 , 2 , and 3 were characterized by NMR, IR and MS techniques as well as by crystal structure analyses. According to them 1 is present as tetramer in solution and the solid state. The central structural motif of the metalate 2 is a heteronuclear and planar LiO2Al four‐membered ring with a penta‐coordinated Li+ ion. In the chainlike coordination polymer [ 3 ]n Cs+ ions with coordination number five and six occupy alternating positions. 相似文献
120.
Gottfried WAGNER Bernhard Traulich KarlM. Hartmann Dieter Oesterhelt 《Photochemistry and photobiology》1987,46(3):393-402
Quantitative action spectroscopy was performed in Halobacterium halobium. using four suited pigment mutants, namely the bacteriorhodopsin and halorhodopsin positive mutant strain M-l (BR+, HR+), the bacteriorhodopsin positive but halorhodopsin negative strain M-18 (BR+, HR-), the bacteriorhodopsin negative but halorhodopsin positive strain L-33 (BR-, HR+), and the bacteriorhodopsin and halorhodopsin negative strain L-07 (BR-, HR+). The approached questions were: First, photoenergetic synergism of halorhodopsin and bacteriorhodopsin in intact cells; second, photochromism and cellular function of the blue light-absorbing intermediates, i.e. M-412 and HR-410 in bacteriorhodopsin and in halorhodopsin, respectively. Dark-adapted cells of mutant strain M-l show wavelength-dependency of quantum yield of photo-phosphorylation, φATP. An 1.4-fold enhancement was found at 575 nm wavelength where the long wavelength absorbance bands of bacteriorhodopsin and halorhodopsin intersect. The enhancement vanished after a 30 min pulse of orange light (600 Wm-2 bandpass from 495 to 750 nm), but was restored after a 30 min pulse of blue light (100 Wm-2 bandpass from 325 to 480 nm). Photoreversibility of this enhancement probably reflects phototransformation of halorhodopsin from its ground state into its inactive intermediate, HR-410, and vice versa. The halorhodopsin-mediated enhancement with maximum quantum yield of photophosphorylation, φATP= 0.06, i.e. a quantum requirement of = 17 photons/ATP, is partly substituted by a rise in phosphate potential and explained in terms of a voltage-regulated gating effect on the H+-driven ATP-synthase, superimposed on the chemiosmotic mechanism of energy coupling. The blue-absorbing photochromic intermediate, M-412 of bacteriorhodopsin, dissipates light energy upon photoexcitation that is reflected by a spectral decline in quantum yield of photophosphorylation to a minimum value of = 0.01 at 415 nm, i.e. a quantum requirement of = 100 photons/ATP. 相似文献