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11.
Richard Ley D. Hagena D. Weil G. Werth W. Arnold H. Schneider 《Hyperfine Interactions》1994,89(1):327-341
Electric dipole transitions in the microwave range have been induced between the fine-structure levels of positronium in the excited staten=2. As an indication of the transitions, we used the increase in Lyman- radiation when the metastable 23S1-level is depopulated. The results for the transitions 23S123P0,1,2 are
0=18499.65±1.20±4.00 MHz,
1=13012.42 ±0.65±1.54 MHz and
2=8624.38±0.54±1.40 MHz. The first error is statistical and the second systematic. The precision of the present measurement has improved by a factor of 3, compared to previous data. Recent bound state QED-calculations have been extended to the orderR
t8
4ln
–1. The not yet completely calculated orderR
t8
4 is estimated to contribute less than 1 MHz. Our experimental results are in good agreement with theory. By applying a weak magnetic field, we were able to observe the transition 23S121P1 which is strictly forbidden byC-invariance in zero field. Our result, corrected for Zeeman- and motional Starkeffect, is
3=11180.0±5.0±4.0 MHz. An upper limit for theC-violating matrix element of
MHz could be deduced. Our experiment used moderated slow positrons from the bremsstrahlung and pair production of a pulsed electron linear accelerator (TEPOS facility at the university of Giessen). 相似文献
12.
Two pyrene-labeled hydroxylamines, 5-Bn and 5-Bz, O-protected with the benzyl and the benzoyl group, respectively, have been prepared for the generation of siderophore-based new chelators incorporating both the pyrene chromophore and the hydroxamic acid functionality. 5-Bz formed the starting point toward the synthesis of the tripod-shaped trishydroxamate, 1. That trichromophoric ligand displays remarkable fluorescence emission properties (dual emission: "monomer" and excimer type) which are markedly and selectively modified by binding Fe(NO(3))(3) and Ga(NO(3))(3). Ferric ions induce a quasi total quenching of the pyrene fluorescence, whereas the nonquenching Ga(III) cations are observed to affect the value of the excimer-to-monomer fluorescence intensity ratio. Ethylenediaminetetraacetic acid (EDTA) competition reactions yielded an estimated value of 3.8 for log K of the complex LFe in methanol/water (80/20 v/v), where K = ([LFe][H(+)](3))/([LH(3)][Fe(3+)]) and L is the ligand in its totally deprotonated form. Compound 1 is the prototype of a new class of photoresponsive molecular systems which could act as sensitive probes for metal cation detection and recognition. 相似文献
13.
Ingo Hartenbach Falk Lissner Tanja Nikelski Steffen F. Meier Helge Müller‐Bunz Thomas Schleid 《无机化学与普通化学杂志》2005,631(12):2377-2382
About Lanthanide Oxotantalates with the Formula MTaO4 (M = La – Nd, Sm – Lu) Besides being a by‐product of solid state syntheses in tantalum ampoules the lanthanide(III) oxotantalates of the formula MTaO4 can be easily prepared by sintering lanthanide sesquioxide M2O3 and tantalum(V) oxide Ta2O5 with sodium chloride as flux. Under these conditions two structure types emerge depending upon the M3+ cationic radius. For M = La – Pr the MTaO4‐type tantalates crystallize in the space group P21/c with lattice constants of a = 762(±1), b = 553(±4), c = 777(±4) pm, β = 101(±1)° and four formula units per unit cell. With M = Nd, Sm – Lu, the monoclinic cell dimensions (space group P2/c) shrink to the lattice constants like a = 516(±9), b = 551(±9), c = 534(±9) pm, β = 96.5(±0.3)° and there are only two formula units present. Both structures show a coordination sphere of eight oxygen atoms for the lanthanide trications shaped as distorted square antiprism for the structure with the larger lanthanides (in the following referred to as A‐type) and as trigonal dodecahedron for the structure with the smaller ones (called as B‐type in the following). The coordination environment about the Ta5+ cations can be described as a slightly distorted octahedron (CN = 6) for the A‐type structure of MTaO4 and a heavily distorted one (CN = 6) for the B‐type. The difference between the two types results from the interconnection of these [TaO6]7? octahedra. Whereas they are connected via four vertices to form corrugated layers according to parallel the bc‐plane in the A‐type, the octahedra of the B‐type MTaO4 structure share edges to built up zig‐zag chains along the c axis. 相似文献
14.
Matthias Weil 《无机化学与普通化学杂志》2004,630(7):1048-1053
Single crystals of HgII(H4TeVIO6) (colourless to light‐yellow, rectangular plates) and HgI2(H4TeVIO6)(H6TeVIO6)·2H2O (colourless, irregular) were grown from concentrated solutions of orthotelluric acid, H6TeO6, and respective solutions of Hg(NO3)2 and Hg2(NO3)2. The crystal structures were solved and refined from single crystal diffractometer data sets (HgII(H4TeVIO6): space group Pna21, Z = 4, a =10.5491(17), b = 6.0706(9), c = 8.0654(13)Å, 1430 structure factors, 87 parameters, R[F2 > 2σ(F2)] = 0.0180; HgI2(H4TeVIO6)(H6TeVIO6)·2H2O: space group P1¯, Z = 1, a = 5.7522(6), b = 6.8941(10), c = 8.5785(10)Å, α = 90.394(8), β = 103.532(11), γ = 93.289(8)°, 2875 structure factors, 108 parameters, R[F2 > 2σ(F2)] = 0.0184). The structure of HgII(H4TeVIO6) is composed of ribbons parallel to the b axis which are built of [H4TeO6]2— anions and Hg2+ cations held together by two short Hg—O bonds with a mean distance of 2.037Å. Interpolyhedral hydrogen bonding between neighbouring [H4TeO6]2— groups, as well as longer Hg—O bonds between Hg atoms of one ribbon to O atoms of adjacent ribbons lead, to an additional stabilization of the framework structure. HgI2(H4TeVIO6)(H6TeVIO6)·2H2O is characterized by a distorted hexagonal array made up of [H4TeO6]2— and [H6TeO6] octahedra which spread parallel to the bc plane. Interpolyhedral hydrogen bonding between both building units stabilizes this arrangement. Adjacent planes are stacked along the a axis and are connected by Hg22+ dumbbells (d(Hg—Hg) = 2.5043(4)Å) situated in‐between the planes. Additional stabilization of the three‐dimensional network is provided by extensive hydrogen bonding between interstitial water molecules and O and OH‐groups of the [H4TeO6]2— and [H6TeO6] octahedra. Upon heating HgI2(H4TeVIO6)(H6TeVIO6)·2H2O decomposes into TeO2 under formation of the intermediate phases HgII3TeVIO6 and the mixed‐valent HgIITeIV/VI2O6. 相似文献
15.
Wolfgang Weil 《manuscripta mathematica》1981,36(1):1-18
It is shown that there exists a distribution T on n ( unit sphere of Euclidean n-space) such that the mixed volume V(K1,...,Kn) equals
for all convex bodies Ki, where
is the support function of ki and denotes the tensor product. As a consequence, mixed volumes are approximated uniformly by n-fold integrals of the corresponding support functions. 相似文献
16.
Omar Ouadoudi Tanja Kaehler Michael Bolte Hans-Wolfram Lerner Matthias Wagner 《Chemical science》2021,12(16):5898
The isoelectronic replacement of C C bonds with −B N+ bonds in polycyclic aromatic hydrocarbons (PAHs) is a widely used tool to prepare novel optoelectronic materials. Far less well explored are corresponding B,O-doped PAHs, although they have a similarly high application potential. We herein report on the modular synthesis of B,N- and B,O-doped PAHs through the [Au(PPh3)NTf2]-catalyzed 6-endo-dig cyclization of BN–H and BO–H bonds across suitably positioned C C bonds in the key step. Readily available, easy-to-handle o-alkynylaryl boronic and borinic acids serve as starting materials, which are either cyclized directly or first converted into the corresponding aminoboranes and then cyclized. The reaction even tolerates bulky mesityl substituents on boron, which later kinetically protect the formed B,N/O-PAHs from hydrolysis or oxidation. Our approach is also applicable for the synthesis of rare doubly B,N/O-doped PAHs. Specifically, we prepared 1,2-B,E-naphthalenes and -anthracenes, 1,5-B2-2,6-E2-anthracenes (E = N, O) as well as B,O2-containing and unprecedented B,N,O-containing phenalenyls. Selected examples of these compounds have been structurally characterized by X-ray crystallography; their optoelectronic properties have been studied by cyclic voltammetry, electron spectroscopy, and quantum-chemical calculations. Using a new unsubstituted (B,O)2-perylene as the substrate for late-stage functionalization, we finally show that the introduction of two pinacolatoboryl (Bpin) substituents is possible in high yield and with perfect regioselectivity via an Ir-catalyzed C–H borylation approach.Singly and doubly B,E-doped PAHs were synthesized using a protocol that starts from easy-to-handle boronic and borinic acids and offers the possibility to choose between the preparation of B,O- and B,N-PAHs in the final reaction step. 相似文献
17.
Matthias Weil 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):i37-i39
The crystal structure of Hg3AlF6O2H, trimercury(II) aluminium hydrogen hexafluoride dioxide, can be derived from a slightly distorted cubic close‐packed (ccp) arrangement of the metal atoms, where three quarters of the positions are occupied by Hg atoms and one quarter by Al atoms. The F and O atoms are considerably dislocated from the tetrahedral voids of this arrangement, thus forming [HgO2F6] polyhedra, with two short Hg—O distances, two intermediate Hg—F distances and four longer Hg—F distances, and nearly ideal [AlF6] octahedra. The H atoms are presumably located close to the inversion centre. Their positions were derived from crystal chemical arguments, and they take part in the formation of O—H?O hydrogen bonds between two O atoms, with an O?O distance of 2.562 (9) Å. 相似文献
18.
Matthias Weil Franz Werner Frank Kubel 《Monatshefte für Chemie / Chemical Monthly》2002,133(3):267-275
Summary. Single crystals of MgAl2F8(H2O)2 have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF3 and MgAlF5(H2O)2 in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F
2 > 2σ (F
2)) = 0.0282, wR(F
2 all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting
the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF6 octahedra with an overall composition of AlF4
− which are connected via common fluorine atoms of [MgF4/2(H2O)2/1] octahedra. Group-subgroup relations of MgAl2F8(H2O)2 to WO3(H2O)0.33 and to other M(II)M(III)2 F8(H2O)2 structures are briefly discussed. Above 570°C, MgAl2F8(H2O)2 decomposes under elimination of water into α-AlF3, β-AlF3, and MgF2.
Received October 29, 2001. Accepted (revised) December 6, 2001 相似文献
19.
20.
Prof. Dr. Heinz Langhals Dr. Bernd Böck M. Sc. Tanja Schmid Alexey Marchuk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(41):13188-13194
Benzoperylene derivatives with two angularly attached dicarboxylic imide rings, which were prepared by the Diels–Alder‐Reaction, exhibit strong fluorescence and their free peri positions allow either control of the UV/Vis spectra through their substituents or form anchor positions for the attachment of functional units. The angular chromophore 3 may be used both for fluorescent labeling such as for primary amines or enzymes or as building blocks for more complex assemblies where they may act as energy donors for FRET or electron acceptors in PET such as for photovoltaic solar cells. 相似文献