全文获取类型
收费全文 | 1980篇 |
免费 | 57篇 |
国内免费 | 10篇 |
专业分类
化学 | 1048篇 |
晶体学 | 54篇 |
力学 | 35篇 |
数学 | 205篇 |
物理学 | 705篇 |
出版年
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 27篇 |
2017年 | 13篇 |
2016年 | 40篇 |
2015年 | 42篇 |
2014年 | 32篇 |
2013年 | 57篇 |
2012年 | 74篇 |
2011年 | 83篇 |
2010年 | 39篇 |
2009年 | 54篇 |
2008年 | 74篇 |
2007年 | 80篇 |
2006年 | 62篇 |
2005年 | 63篇 |
2004年 | 75篇 |
2003年 | 34篇 |
2002年 | 73篇 |
2001年 | 41篇 |
2000年 | 39篇 |
1999年 | 36篇 |
1998年 | 28篇 |
1997年 | 35篇 |
1996年 | 37篇 |
1995年 | 30篇 |
1994年 | 39篇 |
1993年 | 31篇 |
1992年 | 24篇 |
1991年 | 34篇 |
1990年 | 36篇 |
1989年 | 17篇 |
1988年 | 41篇 |
1987年 | 45篇 |
1986年 | 17篇 |
1985年 | 41篇 |
1984年 | 29篇 |
1983年 | 30篇 |
1982年 | 24篇 |
1981年 | 40篇 |
1980年 | 31篇 |
1979年 | 29篇 |
1978年 | 24篇 |
1977年 | 15篇 |
1976年 | 21篇 |
1975年 | 24篇 |
1974年 | 18篇 |
1973年 | 19篇 |
1972年 | 11篇 |
1938年 | 9篇 |
排序方式: 共有2047条查询结果,搜索用时 46 毫秒
91.
92.
J. Adam Jr. J. Mareš O. Richter M. Sotona S. Frullani 《Czechoslovak Journal of Physics》1992,42(11):1167-1196
Formalism for the electroproduction of strange particles based on the one photon exchange approximation and the Feynman diagrams representation of hadron current is reviewed. Different photoproduction models are compared with available photo and electroproduction data. New experiments are proposed that may resolve existing uncertainties and inconsistencies. The formation of hypernuclei via kaon electroproduction is investigated theoretically and compared with other reactions involving purely hadronic processes. 相似文献
93.
G. Hermann G. Lasnitschka J. Richter A. Scharmann 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1988,10(1):27-33
Level-crossing spectroscopy with pulsed two-photon excitation is used to determine life-times and for the first time to determine hyperfine splittings. The experiments have been performed on thalliumnP 3/2 states (n=8, 9 andn=8–11 respectively). By appropriate choice of the polarization and direction of incident light — and, thereby, of the two-photon transition operator — the signal ratio of neighbouring Δm=2 crossings is altered. Thus, in the case of overlapping crossings improved resolution can be obtained without further efforts. 相似文献
94.
Preparation, Raman Spectra, and Crystal Structures of V2O3(SO4)2, K[VO(SO4)2], and NH4[VO(SO4)2] The oxo-sulfato-vanadates(V) V2O3(SO4)2, K[VO(SO4)2], and NH4[VO(SO4)2] have been prepared as crystals suitable for X-ray structure determination. In all structures sulfate acts as an unidentate ligand only toward a single vanadium atom. The structure of V2O3(SO4)2 consists of a threedimensional network of pairs of cornershared VO6 octahedra with one terminal oxygen atom each, and SO4 tetrahedra. All oxygen atoms of the sulfate ions are coordinated. NH4[VO(SO4)2] and K[VO(SO4)2] are isostructural. VO6 octahedra with one terminal oxygen atom and pairs of sulfate tetrahedra form infinite chains by corner sharing. The chains are weakly interlinked to layers. The sulfate ions are distorted towards planar SO3 molecules and single oxygen atoms attached to vanadium. This structural detail gives an explanation for the mechanism of the reversible reaction K[VO(SO4)2] ? K[VO2(SO4)] + SO3 at 400°C. Raman spectra of the compounds have been recorded and interpreted with respect to their structures. Crystal data: V2O3(SO4)2, monoclinic, space group P21/a, a = 947.2(4), b = 891.3(3), c? 989.1(4) pm, β = 104.56(3)°, Z = 4, 878 unique data, R(Rw) = 0.039(0,033); K[VO(SO4)2], orthorhombic, space group P212121, a = 495.3(2), b = 869.6(9), c = 1 627(1)pm, Z = 4, 642 unique data, R(Rw) = 0,11(0,10); NH4[VO(SO4)2], orthorhombic, space group P212121, a = 495.3(1), b = 870.0(2), c = 1 676.7(4)pm, Z = 4, 768 unique data, R(Rw) = 0.088(0.083). 相似文献
95.
Köhler K Förster G Hauser A Dobner B Heiser UF Ziethe F Richter W Steiniger F Drechsler M Stettin H Blume A 《Journal of the American Chemical Society》2004,126(51):16804-16813
The temperature-dependent self-assembly of the single-chain bolaamphiphile dotriacontan-1,1'-diyl-bis[2-(trimethylammonio)ethyl phosphate] (PC-C32-PC) was investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), X-ray scattering, rheological measurements, and dynamic light scattering (DLS). At room temperature this compound, in which two phosphocholine headgroups are connected by a C(32) alkyl chain, proved to be capable of gelling water very efficiently by forming a dense network of nanofibers (Kohler et al. Angew. Chem., Int. Ed. 2004, 43, 245). A specific feature of this self-assembly process is that it is not driven by hydrogen bonds but solely by hydrophobic interactions of the long alkyl chains. The nanofibers have a thickness of roughly the molecular length and show a helical superstructure. A model for the molecular structure of the fibrils which considers the extreme constitution of the bolaamphiphile is proposed. Upon heating the suspensions three different phase transitions can be detected. Above 49 degrees C, the temperature of the main transition where the alkyl chains become "fluid", a clear low-viscosity solution is obtained due to a breakdown of the fibrils into smaller aggregates. Through mechanical stress the gel structure can be destroyed as well, indicating a low stability of these fibers. The gel formation is reversible, but as a drastic rearrangement of the molecules takes place, metastable states occur. 相似文献
96.
Joachim G. Liehr Gareth A. Brenton John H. Beynon James A. McCloskey Wolfgang Blum Wilhelm J. Richter 《Helvetica chimica acta》1981,64(3):835-843
In isobutane chemical ionization mass spectrometry benzyl alcohol exhibits ions at m/z 147 (‘M + 39’) that arise by a loss of H2O from [M + C4H9]+, i.e. ‘M + 57’ complex ions. Electrophilic aromatic substitution of a proton at an ortho-position of neutral C6H5CH2OH with [t-C4H9]+ and, alternatively, nucleophilic substitution of H2O at the benzylic carbon in \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C_6 H_5 CH_2}\mathop {\rm O}\limits^+ {\rm H}_2 $\end{document} with CH2?C (CH3)2 are discussed as possible pathways. Evidence in favor of the latter is derived from the analysis of C6D5CH2OH and C6H5CD2OH for the origin of the H-atoms lost in H2O. The inferred ion structure of m/z 147 is verified by mass-analyzed ion kinetic energy (MIKE.) measurements of its collision-activated (CA.) decomposition. MIKE./CA. spectra of mass-selected m/z 147 ions, once generated by (CI(i-C4H10) from benzyl alcohol and, once, from 2-methyl-4-phenyl-2-butanol match closely and, thus, reflect identical ion structures. With reference to the simple genesis of this ion from the latter precursor, the structure in question can be concluded to be \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C_6 H_5 CH_2 CH_2}\mathop {\rm C}\limits^+ ({\rm CH}_3)_2 $\end{document} . 相似文献
97.
Sarah Eichenberger Moritz Hnig Matthieu J. R. Richter Renana Gershoni-Poranne Erick M. Carreira 《Chemical science》2020,11(20):5294
A novel Lewis acid-catalyzed cycloisomerization of alkylidenecyclopropane acylsilanes is disclosed. The readily available starting materials participate in tandem Prins addition/ring expansion/1,2-silyl shift to grant access to bicyclo[4.2.0]octanes and bicyclo[3.2.0]heptanes, which are common motifs in terpenoid natural products. Notably, the transformation relies on the ability of acylsilanes to act sequentially as acceptors and donors on the same carbon atom.A novel Lewis acid-catalyzed cycloisomerization of alkylidenecyclopropane acylsilanes is disclosed that involves tandem Prins addition/ring expansion/1,2-silyl shift to grant access to bicyclo[4.2.0]octanes and bicyclo[3.2.0]heptanes. 相似文献
98.
Jorge Angulo Cornejo Ketty Ayala Rainer Richter Heinz Bhlig Lothar Hennig Lothar Beyer 《无机化学与普通化学杂志》2005,631(15):3040-3045
Hydrogen Bonds in 1,1‐Bis(2‐hydroxyethyl)‐3‐benzoylthiourea and its Nickel(II)‐ and Copper(II)‐Chelate Complexes The ligand 1,1‐bis(2‐hydroxyethyl)‐3‐benzoylthiourea HL, ( 1 ), yields with nickel(II) and copper(II) ions neutral complexes [NiL2], ( 2 ), and [CuL2], ( 3 ). By X‐ray structure analysis and IR spectroscopy different intramolecular hydrogen bonds (OH…O) and (OH…N) could be identified in both equally coordinated ligands of the [NiL2] molecule. For comparison X‐ray and IR data were also estimated for 1 and 3 . 相似文献
99.
100.
H. Spieler H. J. K?rner K. E. Rehm M. Richter H. P. Rother 《Zeitschrift für Physik A Hadrons and Nuclei》1976,53(5):241-250
The reactions120Sn+72 MeV18O and122Sn+74 MeV16O were investigated with time of-flightE-E-telescopes. Data are presented for all quasi-elastic reaction channels. The two neutron stripping and pickup reactions (18O,16O), (18O,20O) and (16O,18O) are analyzed in detail. It is shown that these heavy ion induced two neutron transfer reactions proceed with essentially the same type of selectivity as the corresponding light ion induced reactions. The differential cross sections for transfer reactions leaving the120, 122Sn nuclei in their 2+ first excited states are shown to be influenced by interference effects due to additional inelastic excitations. 相似文献