全文获取类型
收费全文 | 4416篇 |
免费 | 117篇 |
国内免费 | 8篇 |
专业分类
化学 | 2707篇 |
晶体学 | 99篇 |
力学 | 133篇 |
数学 | 439篇 |
物理学 | 1163篇 |
出版年
2021年 | 32篇 |
2020年 | 64篇 |
2019年 | 41篇 |
2017年 | 32篇 |
2016年 | 94篇 |
2015年 | 91篇 |
2014年 | 86篇 |
2013年 | 140篇 |
2012年 | 161篇 |
2011年 | 210篇 |
2010年 | 137篇 |
2009年 | 135篇 |
2008年 | 185篇 |
2007年 | 162篇 |
2006年 | 174篇 |
2005年 | 146篇 |
2004年 | 151篇 |
2003年 | 139篇 |
2002年 | 112篇 |
2001年 | 93篇 |
2000年 | 94篇 |
1999年 | 64篇 |
1998年 | 64篇 |
1997年 | 54篇 |
1996年 | 82篇 |
1995年 | 72篇 |
1994年 | 52篇 |
1993年 | 60篇 |
1992年 | 69篇 |
1991年 | 58篇 |
1990年 | 49篇 |
1989年 | 59篇 |
1988年 | 62篇 |
1987年 | 60篇 |
1986年 | 54篇 |
1985年 | 45篇 |
1984年 | 30篇 |
1983年 | 52篇 |
1982年 | 37篇 |
1981年 | 65篇 |
1980年 | 46篇 |
1979年 | 59篇 |
1978年 | 62篇 |
1977年 | 47篇 |
1976年 | 51篇 |
1975年 | 31篇 |
1974年 | 37篇 |
1973年 | 38篇 |
1968年 | 28篇 |
1957年 | 30篇 |
排序方式: 共有4541条查询结果,搜索用时 0 毫秒
91.
92.
Rudolf F. X. Bauer Ikhlas A. Khan Hermann Lotter Hildebert Wagner Victor Wray 《Helvetica chimica acta》1985,68(8):2355-2358
The structure elucidation of four new constituents from the roots of Echinacea purpurea is described. They are shown to be cinnamoyl esters of sesquiterpene alcohols with a germacrane or a guaiane skeleton. First pharmacological results indicate immunological activities. 相似文献
93.
Zheng Y Cloutier P Hunting DJ Sanche L Wagner JR 《Journal of the American Chemical Society》2005,127(47):16592-16598
DNA damage by low-energy electrons (LEE) was examined using a novel system in which thin solid films of oligonucleotide tetramers (CGTA and GCAT) were irradiated with monoenergetic electrons (10 eV) under ultrahigh vacuum. The products of irradiation were examined by HPLC. These analyses permitted the quantitation of 16 nonmodified nucleobase, nucleoside, and nucleotide fragments of each tetramer resulting from the cleavage of phosphodiester and N-glycosidic bonds. The distribution of nonmodified products suggests a mechanism of damage involving initial electron attachment to nucleobase moieties, followed by electron transfer to the sugar-phosphate backbone, and subsequent dissociation of the phosphodiester bond. Moreover, virtually all the nonmodified fragments contained a terminal phosphate group at the site of cleavage. These results demonstrate that the phosphodiester bond breaks by a distinct pathway in which the negative charge localizes on the phosphodiester bond giving rise to nonmodified fragments with an intact phosphate group. Conversely, the radical must localize on the sugar moiety to give as yet unidentified modifications. In summary, the reaction of LEE with simple tetramers involved dissociative electron attachment leading to phosphodiester bond cleavage and the formation of nonmodified fragments. 相似文献
94.
Ulrike Gabriella Wagner Christoph Kratky Heinz Falk Heinz Flödl 《Monatshefte für Chemie / Chemical Monthly》1987,118(10):1185-1194
The crystal structure of the pentapyrrin1 was determined by X-ray diffraction methodes at two temperatures (298K and 97K). It is the first structure determination of a linear polypyrrole with more than four pyrrole rings. In the crystal, the molecule is located on a crystallographic two-fold axis, which passes through the central pyrrole ring. It assumes a helical overall-conformation, which is stabilized by intramolecular hydrogen bonding. The acidic proton at the nitrogen atom of the central pyrrolic ring is disordered, being observed with half occupancy at two symmetry-equivalent positions off the crystallographic diad. Attempts to remove the disorder by cooling to 97K were unsuccessful, since no indication for a phase transition was detected. 相似文献
95.
96.
The compounds Ce(10)Cl(4)Ga(5) and Ln(3)ClGa(4) (Ln = La, Ce) were synthesized from stoichiometric mixtures of Ln, LnCl(3), and Ga under Ar atmosphere in sealed Ta ampules at 910-1020 degrees C for 25-26 days. Ce(10)Cl(4)Ga(5) is isostructural to La(10)Cl(4)Ga(5) (space group I4/mcm, No. 140) with lattice constants a = 7.9546(11) A, c = 31.793(6) A. Ln(3)ClGa(4) represents a new structural type, also in the space group I4/mcm, with a = 8.1955(8) and 8.1123(11) A, c = 11.363(2) and 11.229(2) A, respectively, for Ln = La and Ce. Ce(10)Cl(4)Ga(5) features building blocks of Ga-centered Ce(6) trigonal prisms and distinctive two-dimensional intermetallic CuAl(2) and U(3)Si(2) type nets. Its electronic structure falls within the realm of reduced rare-earth halides. Ln(3)ClGa(4) also contains the intermetallic CuAl(2) type nets, but the interstitials are inverted: The building blocks are Cl-centered Ln(6) octahedra. Its electronic structure is characterized by strong peripheral Ln-Ga bonding stabilizing the Ln(6)Cl octahedron which normally would have its Ln-Ln antibonding orbitals filled with electrons from interstitials beyond chalcogen. Magnetic susceptibility and conductivity measurements confirm the metallic nature of all three compounds. 相似文献
97.
Clay A. Henry Mel Judy Barbara Dyer Martin Wagner James L. Matthews 《Photochemistry and photobiology》1995,61(4):410-413
Abstract— The phototoxicity of argon laser irradiation was studied in aqueous suspensions of Porphyromonas endodontalis (American Type Culture Collection [ATCC] 35406), Porphyromonas gingivalis (ATCC 33277), Prevotella denticola (ATCC 33184) and two strains of Prevotella intermedia (ATCC 15033 and 49046), all "black-pigmented bacteria," BPB, that accumulate cellular porphyrins. Several of these species have been implicated in the etiology of Periodontol disease. Non-black-pigmented bacteria were also studied to test the specificity of irradiation as a potential photodynamic treatment for Periodontol infections. Cell suspensions were irradiated with an argon laser at fluences of 20–200 J/cm2 . When cultured in hemin-supplemented media, ATCC 15033 was the most sensitive to irradiation. However, a second strain of the same species (ATCC 49046) was resistant. The photosensitivity of other species ranked ATCC 33277 > 35406 = 33184 = 35496. When hemin was replaced in media by hemoglobin, ATCC 33277 became resistant to irradiation. Protoporphyrin IX content in BPB cells was shown not to be a major factor determining photosensitivity. Oxygen was required during irradiation for BPB species to be affected. Non-black-pigmented bacteria were much less sensitive to irradiation than BPB. 相似文献
98.
Christian R. Noe M. Knollmüller G. Steinbauer E. Wagner H. Kürner P. Ettmayer H. Völlenkle 《Monatshefte für Chemie / Chemical Monthly》1991,122(4):299-317
Summary Enantiomerically pure 1,2-diols bearing optionallysyn oranti configurated secondary hydroxylic groups are synthesized from acetal-protected cyanohydrins. After resolution of the diastereomers the cyanohydrins are converted into -alkoxy-ketones by Grignard-reaction followed by reduction using common chelating or non-chelating agents. Among others syntheses of enantiomerically pure pheromones,endo-Brevicomin,exo-Brevicomin and Dispalure are given as examples.
Prof. Dr. Hans Berbalk zum 70. Geburtstag gewidmet 相似文献
99.
I. Wichterle J. Linek Z. Wagner J.-C. Fontaine K. Sosnkowska-Kehiaian et al. 《Transition Metal Chemistry》1991,16(5):546-547
Inorganic Chemistry Nomenclature
IUPAC Commission on Inorganic Chemistry Nomenclature; Newsletter 1990 相似文献100.