全文获取类型
收费全文 | 2418篇 |
免费 | 129篇 |
国内免费 | 12篇 |
专业分类
化学 | 1839篇 |
晶体学 | 11篇 |
力学 | 38篇 |
数学 | 310篇 |
物理学 | 361篇 |
出版年
2023年 | 16篇 |
2021年 | 27篇 |
2020年 | 77篇 |
2019年 | 59篇 |
2018年 | 32篇 |
2017年 | 15篇 |
2016年 | 55篇 |
2015年 | 68篇 |
2014年 | 70篇 |
2013年 | 98篇 |
2012年 | 93篇 |
2011年 | 130篇 |
2010年 | 60篇 |
2009年 | 68篇 |
2008年 | 109篇 |
2007年 | 98篇 |
2006年 | 89篇 |
2005年 | 125篇 |
2004年 | 100篇 |
2003年 | 84篇 |
2002年 | 67篇 |
2001年 | 70篇 |
2000年 | 47篇 |
1999年 | 33篇 |
1998年 | 36篇 |
1997年 | 37篇 |
1996年 | 33篇 |
1995年 | 34篇 |
1994年 | 27篇 |
1993年 | 33篇 |
1992年 | 29篇 |
1991年 | 29篇 |
1990年 | 38篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 29篇 |
1983年 | 15篇 |
1982年 | 17篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 23篇 |
1977年 | 24篇 |
1976年 | 25篇 |
1974年 | 17篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有2559条查询结果,搜索用时 15 毫秒
61.
62.
Ohne Zusammenfassung 相似文献
63.
Clorobiocin (clo) and novobiocin (nov) are potent inhibitors of bacterial DNA gyrase. The two substances differ in the substitution pattern at C-8' of the aminocoumarin ring, carrying a chlorine atom or a methyl group, respectively. By gene inactivation, clo-hal was identified as the gene of the halogenase responsible for the introduction of the chlorine atom of clorobiocin. Inactivation of cloZ did not affect clorobiocin formation, showing that this ORF is not essential for clorobiocin biosynthesis. Expression of the methyltransferase gene novO in the clo-hal(-) mutant led to the very efficient formation of a hybrid antibiotic containing a methyl group instead of a chlorine atom at C-8'. Comparison of the antibacterial activity of clorobiocin analogs with -Cl, -H, or -CH(3) at C-8' showed that chlorine leads to 8-fold higher activity than hydrogen and to 2-fold higher activity than a methyl group. 相似文献
64.
H. Madeheim R. Hippler H. O. Lutz 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,15(4):327-331
The integral alignmentA 20 was investigated for H(2p) excitation in H-He, Ne, Ar collisions at incident energies of 1–25 keV. The experimental results are compared with theoretical calculations based on different theoretical models. Calculations which do not account for the quasi-molecular aspect of the collision process are at variance with the experimental data below incident energies of 10 keV. Above 15 keV, fair agreement is obtained with calculations which include simultaneous excitation of both projectile and target. 相似文献
65.
In the case of the formation of thiospinels (MnCr2S4, ZnCr2S4 and CdCr2S4) a simple method for the determination of the activation energy of solid state reactions in polycrystalline samples by means of conductivity measurements is shown. The maxima and minima of conductivity (glow curve maxima and -minima) in the σ vs T-curves got by annealing with linearly increasing temperature are shifted towards higher temperatures with increasing rate of heating(q). By plotting ln (q/T) vs 1/Tσmax a straight line results. The activation energy of the reaction may be deduced from the slope of this straight line in analogy to the determination of the trap depth of electrons from glow curves observed in thermoluminescence. 相似文献
66.
The present work discusses the grafting by electron beam irradiation of poly(ethylene oxide) (PEO) star-shaped polymers onto porous expanded polytetrafluoroethylene (EXPTFE) surfaces. The resulting materials are intended to combine the good biocompatible properties of PEO with the outstanding mechanical properties of PTFE. The star-shaped PEOs were synthesized via anionic polymerization. 3 Mev electron beam irradiation was applied to graft these PEO stars onto porous EXPTFE surfaces. The hydrophobic EXPTFE surface had to be pre-modified with N-vinylpyrrolidone. ESCA was used to quantify the amount of grafted star-shaped PEO. Unmodified EXPTFE surfaces are well known, when implanted in a body, to be rapidly covered by a layer of cells and fibrin. The EXPTFE coated with PEO were implanted in the peritoneal cavity of rats (or under the back skin). This implantation did not induce any inflammation reactions and SEM analysis had attested the absence of adsorbed cells and fibrin. The glucose diffusion properties of these membranes were studied by a lag time analysis method and compared to those of pure PEO hydrogels. As expected, glucose diffuses through the hydrogel coated membrane and diffusion is not affected by the presence of the EXPTFE membrane. 相似文献
67.
C. Segebade G. J. Lutz H. -P. Weise H. -U. Fusban 《Journal of Radioanalytical and Nuclear Chemistry》1981,67(1):205-214
Interferences of different types (competing reactions, overlapping photons emission energies etc.) occur more frequently during
activation analysis with high energy exciting radiation that in conventional thermal neutron activation. Three main types
of interference in high energy photon activation analysis (PAA) have been determined quantitatively, using experimentally
obtained data exclusively. Based on the results presented, it is possible in many critical cases to improve significantly
the accuracy of analysis results obtained by PAA. 相似文献
68.
R. Bailey D. G. Bardsley E. Belau T. Böhringer M. Bosman M. Cerrada V. Chabaud C. Damerell C. Dauin G. De Rijk H. Dijkstra A. Dwurazny A. Gillman R. Gilmore L. Görlich Z. Hajduk C. Hardwick W. Hoogland B. D. Hyams R. Klanner G. Lütjens G. Lutz J. Malos W. Männer G. Polok M. Rozanska K. Rybicki H. J. Seebrunner W. Spierenburg U. Stierlin R. J. Tappel H. G. Tiecke M. Turala J. Vermeulen G. Waltermann P. Weilhammer F. Wickens L. W. Wiggers A. Wylie T. Zeludziewicz ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1984,24(2):111-118
The reactions \(K^ - Be \to {}^(\bar K^) *^0 (890)X,\pi ^ - Be \to {}^(\bar K^) *^0 (890)X\) , have been studied in a 175 GeV unseparated hadron beam in the kinematic range 0<x F <1.0 andp T 2 <5 GeV2. Integrated cross-sections and the dependence of the cross-sections on the longitudinal and transverse momentum are presented, together with quark counting rules predictions. The nuclear dependence ofK ? fragmentation intoK *0(890) with respect to Feynmanx is investigated from hydrogen to beryllium. 相似文献
69.
Zusammenfassung Es wurde eine einfache, quantitative Trennung von Mikrogrammmengen Gallium von der bis zum Tausendfachen betragenden Menge Eisen durch Ionenaustausch-Chromatographie am stark basischen Anionenaustauscher Amberlite I. R. A.-400 ausgearbeitet. Die Methode beruht auf der unterschiedlichen Stabilität und Wanderungsgeschwindigkeit der Bhodanidkomplexe dieser Elemente bei ihrer Elution mit 0,1-n Salzsäure, wobei das Gallium vor dem Eisen ins Eluat übergeht.
Herrn Prof. Dr.Robert Strebinger zum 70. Geburtstag gewidmet. 相似文献
Summary A new method was developed for a simple quantitative separation of microgram quantities of gallium from amounts of iron a thousand times as great. The method is based on ion exchange chromatography on strongly basic anion exchanger Amberlite I. R. A.-400. The basis of the method is the divergent stability and migration velocity of the thiocyanate complexes of these elements when eluted with 0.1 N hydrochloric acid. The gallium precedes the iron in the eluate.
Résumé Mise au point d'une séparation simple et quantitative de masses de gallium de l'ordre de grandeur du microgramme de masses de fer pouvant être mille fois plus élevées, par chromatographie par échange d'ions. On emploie à cette fin un échangeur d'anions fortement basique: l'amberlite I. R. A.-400. Le principe de la méthode repose sur les différences de stabilité et de vitesse de migration des suifocyanures complexes de ces éléments lors de leur élution par l'acide chlorhydrique 0, l N: le gallium passe en effet dans l'éluat avant le fer.
Herrn Prof. Dr.Robert Strebinger zum 70. Geburtstag gewidmet. 相似文献
70.
Lattice Vibration Spectra. LXIII. Be(IO3)2 · 4 H2O, a Hydrate with Unusual Bonding and Lattice Dynamics The IR and Raman spectra (4000–50 cm?1) of Be(IO3)2 · 4 H2O and of deuterated specimens are recorded at 90 and 300 K and discussed in terms of the unusual relations of the masses of the atoms involved and the large polarization power of the beryllium ions. Thus, the translatory modes of the Be2+ ions (BeO4 skeleton vibrations), the librations of the H2O molecules, and the internal vibrations of the IO3? ions in the spectral regions of 300–400 and 600–1000 cm?1 couple and coincide producing unusual vH/vD isotopic ratios of partly < 1. The H-bond donor strengths of the water molecules is so much increased (due to the very large ionic potential of Be2+ ions, viz. 49 e nm?1) (synergetic effect) that the H-bonds formed are similar in strength as those in hydrates of hydroxides with the very strong H-bond acceptor group OH? (vOD of matrix isolated HDO molecules 2 074 and 2 244 (H2O I) and 2 206 and 2 349 cm?1 (H2O II)) 相似文献