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981.
Honscheid K. Schubert K. R. Waldi R. 《Zeitschrift fur Physik C Particles and Fields》1994,63(1):117-120
Consequences of the interference between spectator amplitudes for the lifetimes and semileptonic decay fractions ofB
0 andB
+ mesons are discussed. Extracting these amplitudes from a fit to 11 exclusive hadronicB decay fractions we finda
1=1.05±0.03±0.10,a
2=+0.227±0.012±0.022, an inclusive semileptonic decay fraction of (11.2±0.5±1.7)%, and a lifetime ratio (B
+)/(B
0)=0.83±0.01±0.01.Supported under DOE grant number DE-FG02-91-ER40690 相似文献
982.
983.
Hermann M. Niemeyer 《Tetrahedron》1977,33(7):775-778
CNDO/2 MO studies have been carried out on CH4, C2H6, CHCL3 CH3CN, CH3NO2, CH3CHO, CH3COCH3, and their corresponding anions, both in the gas phase and in “aqueous solution” The results closely parallel related experimental studies. 相似文献
984.
Schmidt K Böker A Zettl H Schubert F Hänsel H Fischer F Weiss TM Abetz V Zvelindovsky AV Sevink GJ Krausch G 《Langmuir : the ACS journal of surfaces and colloids》2005,21(25):11974-11980
We investigate the mechanism of microdomain orientation in concentrated block copolymer solutions exposed to a dc electric field by in situ synchrotron small-angle X-ray scattering (SAXS). As a model system, we use concentrated solutions of a lamellar polystyrene-b-polyisoprene block copolymer in toluene. We find that both the microscopic mechanism of reorientation and the kinetics of the process strongly depend on the initial degree of order in the system. In a highly ordered lamellar system with the lamellae being aligned perpendicular to the electric field vector, only nucleation and growth of domains is possible as a pathway to reorientation and the process proceeds rather slowly. In less ordered samples, grain rotation becomes possible as an alternative pathway, and the process proceeds considerably faster. The interpretation of our finding is strongly corroborated by dynamic self-consistent field simulations. 相似文献
985.
A series of lanthanide(III) complexes formulated as M[Ln(Hdo3ap)].xH(2)O (M = Li or H and Ln = Tb, Dy, Er, Lu, and Y) with the monophosphonate analogue of H(4)dota, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-methylphosphonic acid (H(5)do3ap), was prepared in the solid state and studied using X-ray crystallography. All of the structures show that the (Hdo3ap)(4-) anion is octadentate coordinated to a lanthanide(III) ion similarly to the other H(4)dota-like ligands, i.e., forming O(4) and N(4) planes that are parallel and have mutual angle smaller than 3 degrees . The lanthanide(III) ions lie between these planes, closer to the O(4) base than to the N(4) plane. All of the structures present the lanthanide(III) complexes in their twisted-square-antiprismatic (TSA) configuration. Twist angles of the pendants vary in the range between -24 and -30 degrees, and for each complex, they lie in a very narrow region of 1 degree. The coordinated phosphonate oxygen is located slightly above (0.02-0.19 Angstroms) the O(3) plane formed with the coordinated acetates. A water molecule was found to be coordinated only in the terbium(III) and neodymium(III) complexes. The bond distance Tb-O(w) is unusually long (2.678 Angstroms). The O-Ln-O angles decrease from 140 degrees [Nd(III)] to 121 degrees [Lu(III)], thus confirming the increasing steric crowding around the water binding site. A comparison of a number of structures of Ln(III) complexes with DOTA-like ligands shows that the TSA arrangement is flexible. On the other hand, the SA arrangement is rigid, and the derived structural parameters are almost identical for different ligands and lanthanide(III) ions. 相似文献
986.
Helmut Werner Hans-Juergen Kraus Ulrich Schubert Klaus Ackermann Peter Hofmann 《Journal of organometallic chemistry》1983,250(1):517-536
The complexes (η5-C5H5)Pd(η1-C5H5)PR3 which are prepared from [Cl(PR3)-Pd]2(μ-OCOCH3)2 and TlC5H5 are fluxional in solution. According to the 1H and 13C NMR spectra at various temperatures, two dynamic processes occur. The process with the higher activation energy is a π/σ (η5/η1) exchange of the two different cyclopentadienyl ligands, whereas the second one with the lower activation energy presumably is a metallotropic rearrangement (1,2-shift). The coalescence temperature for the η5/η1 exchange depends on the size of the phosphine. The X-ray structural analysis of (C5H5)2PdPPri3 proves that it exists as a “frozen” η5 + η1 structure in the crystal with the palladium approximately in a square-planar coordination. The η5-bonded cyclopentadienyl ring shows some unusual bonding patterns which are obviously electronic in nature. EHT-MO calculations for (η5-C5H5)PdCH3(PH3) indicate that in this model system alternating CC distances in the ring and a stronger bond of the metal to one of the five carbon atoms of the C5H5 ligand are to be expected. The calculations suggest that in similar complexes possessing a six-electron donor ligand like C5H5? and a metal fragment which is isolobal to PdCH3(PH3)+, analogous distortions should be observed. Some reactions of the compounds (η5-C5H5)Pd(η1-C5H5)PR3 are described. 相似文献
987.
RNA molecules are the only known molecules which possess the double property of being depository of genetic information, like DNA, and of displaying catalytic activities, like protein enzymes. RNA molecules intervene in all steps of gene expression and in many other biological activities. Like proteins, RNAs achieve those biological functions by adopting intricate three-dimensional folds and architectures. Further, as in protein sequences, RNA sequences contain signatures specific for three-dimensional motifs which participate in recognition and binding. In regulatory pathways, RNA molecules exist in equilibria between transient structures differentially stabilized by effectors such as proteins or cofactors. Therefore, RNA molecules display their potential as drug targets on different levels, namely in three-dimensional folds, in structural equilibria and in RNA-protein interfaces. Several examples will be described together with the already available techniques for combinatorial synthesis and high-throughput screening of potential drug and target RNA molecules. 相似文献
988.
Helmut Bode Klaus -Joachim Tusche und Hermann -Franz Wahrhausen 《Fresenius' Journal of Analytical Chemistry》1962,190(1):48-60
Zusammenfassung Es wurden die Na- bzw. Ca-Salze folgender Dithiocarbamidsäuren hergestellt: N-Methyl-N-glucityl-DTCH, -Carboxy-N-N-cyclotetramethylen-DTCH, N-Carboxymethyl-DTCH, N-Nitrilo-DTCH. Ihre Haltbarkeit in wäßrigen Lösungen unterschiedlichen pH-Wertes wurde untersucht. Die Verbindungen bilden mit einer großen Zahl von Kationen Komplexe, die zum weit überwiegenden Teil in Wasser leicht löslich sind. Diese Komplexbildungsreaktionen können zur Grundlage photometrischer und maßanalytischer Bestimmungsverfahren gemacht werden. In einer Reihe von Fällen lassen sie sich auch als Hilfskomplexbildner zur Maskierung bestimmter Ionen verwenden.Zur Abkürzung werden im folgenden verwendet DTCH
Dithiocarbamidsäure
- DTC
Anion einer Dithiocarbamidsäure oder auch allgemein Dithiocarbamidat
Herrn Prof. Dr. W. Fischer zum 60. Geburtstag gewidmet.VIII. Mitteilung, diese Z. 172, 1 (1960).Unsere Arbeiten wurden durch die Deutsche Forschungsgemeinschaft und den Verband der Chemischen Industrie, Fonds der Chemie, durch Sachbeihilfen gefördert, wofür auch an dieser Stelle gedankt sei. 相似文献
989.
The biosynthesis of adenosylcobalamin (vitamin B12) 总被引:9,自引:0,他引:9
990.
Summary The complex [Rh2Cl2(-CO)(-vdpp)2] (1) (vdpp=H2C=C(PPh2)2) was prepared by reaction of [Rh2(CO)4-(-Cl)2] with vdpp. When (1) is allowed to stand overnight under an atmosphere of CO without stirringtrans-[Rh2Cl2(CO)2(-vdpp)2] is formed as a red precipitate in low yields. On rapid addition of CO the tricarbonyl complex [Rh2(CO)2(-CO)(-Cl)(-vdpp)2]-Cl is formed instead. The chemical behaviour of the vdpp-substituted complex (1) is very similar to that of the corresponding dppm-substituted complex [Rh2(Cl2-(-CO)(-dppm)2] (dppm=H2C(PPh2)2). this similarity also extends to the molecular structures of both compounds. Unit cell parameters of (1): space group Pben (Z=8),a=2344.7(5),b=1506.9(7),c=3021.6(9)pm. Rh-Rh 267.4(1) pm. 相似文献