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排序方式: 共有239条查询结果,搜索用时 31 毫秒
91.
92.
Samira M. Abozeid Didar Asik Gregory E. Sokolow Jonathan F. Lovell Alexander Y. Nazarenko Janet R. Morrow 《Angewandte Chemie (International ed. in English)》2020,59(29):12093-12097
Three paramagnetic CoII macrocyclic complexes containing 2‐hydroxypropyl pendant groups, 1,1′,1′′,1′′′‐(1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetrakis‐ (propan‐2‐ol) ([Co(L1)]2+, 1,1′‐(4,11‐dibenzyl‐1,4,8,11‐tetraazacyclotetradecane‐1,8‐diyl)bis(propan‐2‐ol) ([Co(L2)]2+), and 1,1′‐(4,11‐dibenzyl‐1,4,8,11‐tetraazacyclotetradecane‐1,8‐diyl)bis(octadecan‐2‐ol) ([Co(L3)]2+) were synthesized to prepare transition metal liposomal chemical exchange saturation transfer (lipoCEST) agents. In solution, ([Co(L1)]2+) forms two isomers as shown by 1H NMR spectroscopy. X‐ray crystallographic studies show one isomer with 1,8‐pendants in cis‐configuration and a second isomer with 1,4‐pendants in trans‐configuration. The [Co(L2)]2+ complex has 1,8‐pendants in a cis‐configuration. Remarkably, the paramagnetic‐induced shift of water 1H NMR resonances in the presence of the [Co(L1)]2+ complex is as large as that observed for one of the most effective LnIII water proton shift agents. Incorporation of [Co(L1)]2+ into the liposome aqueous core, followed by dialysis against a solution of 300 mOsm L?1 produces a CEST peak at 3.5 ppm. Incorporation of the amphiphilic [Co(L3)]2+ complex into the liposome bilayer produces a more highly shifted CEST peak at ?13 ppm. Taken together, these data demonstrate the feasibility of preparing CoII lipoCEST agents. 相似文献
93.
The yields of secondary photons, i.e. photons emitted from sputtered excited states, have been described variously as being proportional to either P(?i) bfi or P(?i) vfiAfi. Here P( the function giving the probability of a sputtered particle having excitation energy ?i, bfi is the branching ratio, vfi is the photon frequency, and Afi is the transition probability. In an attempt to clarify the role of Afi we have compared experimental yields from bombarded Li, Zn, Cd, Sc, and Ti with tabulated plasma yields and obtained results which suggest that Afi does not enter, in the case of secondary photons, as a simple multiplier of P(?i). This is not really surprising, as secondary photons are emitted by isolated atoms whereas the use of the factor A(fi) assumes thermodynamic equilibrium during decay, as in a plasma. In further experiments, yields were measured versus distance in front of the target. Introducing the decay rate constant, γi = ΣAfi, one finds that for γi exceeding 0.4 × 108 s?1 the signals fall by a factor of 10 within 1.5 mm, for γi of (0.02?0.2) × 108 s?1 they fall by such a factor within 3–10 mm, and for γi of (0.0004–0.004) × 108 s?1 significant decay occurs beyond the reach of the detector. This shows that Afi does indeed play a role in describing photon yields whenever γi is sufficiently small, namely in the somewhat complicated relation describing the spatial distribution of the photon emission. Nevertheless, in most situations the use of Afi is unjustified. 相似文献
94.
R. H. Compton K. T. V. Grattan T. Morrow 《Applied Physics A: Materials Science & Processing》1980,22(3):307-311
The fundamental photophysical parameters of the organic scintillators, anthracene, 9, 10 dimethyl antracene (DMA), 9, 10 diphenyl
anthracene (DPA), 2-(1-napthyl)-5-phenyloxazole (α-NPO) and 2, 2′-p-phenyl bis (5-phenyloxazole) (POPOP), were investigated
in the liquid and vapour phases. Their ground state, triplet-triplet and fluorescence spectra were determined and accurate
extinction coefficients obtained. Photodecomposition of POPOP vapour under 337 nm excitation was investigated in detail and
a photodecomposition quantum yield of 1.1×10−2 obtained at 568 K. The POPOP triplet state in the vapour phase is quenched by the addition of 1, 3, 5, 7 cyclo-octatetraene
and a quenching rate constant of 2.9×1010 M−1 s−1 was determined. 相似文献
95.
J. C. Morrow 《Journal of chemical crystallography》1974,4(4):243-252
The crystal and molecular structure of dichlorobis(pyridine-1-oxide) copper(II), C10H10N2O2Cl2Cu, has been determined from 3931 reflections measured on a Picker four-circle diffractometer, using the /2 scan technique and MoK radiation. The crystals are monoclinic, space groupP21/c,a = 6.900(4),b = 15.065(7),c = 12.065(5) Å, = 97.00(4) ° andZ = 4. The structure was solved by Fourier methods and refined by full-matrix least-squares. The final conventionalR-factor was 0.033. The compound is dimeric, and the units of the dimer are held together by oxygen bridges. The coordination polyhedron for Cu is a tetragonal pyramid, with two bridging oxygens and two chlorines in the basal plane. The apical position is occupied by oxygen in the non-bridging ligand. The Cu–Cu distance in the dimer is 3.306(1) Å. 相似文献
96.
Robert A. Craig Robin K. Harris Robert J. Morrow 《Magnetic resonance in chemistry : MRC》1980,13(3):229-231
A procedure for doubly selective irradiation of an AX NMR spin system so as to achieve complete magnetization transfer from X to A is described. In combination with suitably gated decoupling this sequence will give substantial savings of time in determinations of T1 for low-sensitivity spin-½ nuclei, particularly those with negative magnetogyric ratios. 相似文献
97.
Hamuro Y Coales SJ Molnar KS Tuske SJ Morrow JA 《Rapid communications in mass spectrometry : RCM》2008,22(7):1041-1046
Statistical analysis of data from 39 proteins (13 766 amino acid residues) digested with immobilized porcine pepsin under conditions compatible with hydrogen/deuterium (H/D) exchange (<1 degrees C, <30 s) was performed to examine pepsin cleavage specificity. The cleavage of pepsin was most influenced by the amino acid residue at position P1. Phe and Leu are favored residues each with a cleavage probability greater than 40%. His, Lys, Arg, or Pro residues prohibit cleavage when found at the P1 position. Pro also cannot be at position P2 (cleavage probability <0.3%). Occupation of the P3 position by His, Lys, or Arg, or occupation of the P2' position by Pro, also leads to very little cleavage (cleavage probability <1.7%). The average cleavage probability over the entire data set was 13.6%, which is slightly lower than the value previously obtained by Powers et al. (14.8%). This is due, in part, to the larger protein sizes used in the current study. While the specificity of pepsin was similar to that previously observed, higher selectivity was observed in the present study due to less experimental variation in the conditions used to generate our database. 相似文献
98.
Swarnagowri Nayak Santosh L. Gaonkar Ebraheem Abdu Musad Abdullah Mohammed AL Dawsar 《Journal of Saudi Chemical Society》2021,25(8):101284
Chemotherapy is an important therapeutic approach for the treatment of cancer. Currently, many anticancer drugs are available in the market that plays an important role in cancer treatment, but concerns such as, drug resistance and side effects create an urgent need for the development of new anti-tumor drugs with high potency and less side effects. Heterocycles are of great interest due to their fascinating anticancer activity. Among them, 1,3,4-oxadiazoles showed attracting anti-tumor activity and its derivatives are under clinical trials for the treatment of cancer. Hybridization of 1,3,4-oxadiazole moiety with other heterocyclic pharmacophoresis a promising approach to overcome various disadvantages of current anticancer drugs such as drug resistance, toxicity, and other side effects. Thus, 1,3,4-oxadiazole-heterocycle hybrids occupy a significant position in the discovery of anti-tumor drugs. Among the reported oxadiazole-based hybrids reviewed here, compounds 45i, 59j, and 62x showed the highest anticancer activity with IC50 values in the nanomolar range. This review summarizes the recent developments in the anticancer potential, structure–activity relationships, and mechanisms of actions of 1,3,4-oxadiazole-heterocycle hybrids. 相似文献
99.
Dylan Heuer Chelsey Morrow Ben Noteboom Sara Solhjem Jessica Striker Corey Vorland 《Discrete Mathematics》2017,340(12):2732-2752
We define and enumerate two new two-parameter permutation families, namely, placements of a maximum number of non-attacking rooks on chained-together chessboards, in either a circular or linear configuration. The linear case with corresponds to standard permutations of , and the circular case with and corresponds to a three-person chessboard. We give bijections of these rook placements to matrix form, one-line notation, and matchings on certain graphs. Finally, we define chained linear and circular alternating sign matrices, enumerate them for certain values of and , and give bijections to analogues of monotone triangles, square ice configurations, and fully-packed loop configurations. 相似文献
100.
Mathews RA Rossiter CS Morrow JR Richard JP 《Dalton transactions (Cambridge, England : 2003)》2007,(34):3804-3811
Mononuclear complexes between Zn(2+) and the following four macrocycles were prepared: 1,4,7,10-tetraazacyclododecane (1), 1-oxa-4,7,10-triazacyclododecane (2), 1,5,9-triazacyclododecane (3) and 1-hydroxyethyl-1,4,7-triazacyclononane (4). The pH rate profiles of values of the observed second-order rate constant log (k(Zn))(app) for Zn(X)(OH(2))-catalyzed cleavage (X = 1, 2, 3 and 4) of 2-hydroxypropyl-4-nitrophenyl phosphate (HpPNP) show downward breaks centered at the pK(a) for ionization of the respective zinc bound water. At low pH, where the rate acceleration for the catalyzed reaction is largest, the stabilizing interaction between the catalyst and the bound transition state is 5.7, 7.4, 7.4 and 5.9 kcal mol(-1) for the reactions catalyzed by Zn(1)(OH(2)), Zn(2)(OH(2)), Zn(3)(OH(2)) and Zn(4)(OH(2)), respectively. The interactions between the metal cation and the macrocycle cause either a modest increase or reduction in transition state stabilization compared with 6.6 kcal mol(-1) stabilization for catalysis by Zn(OH(2))(6). The best Zn(II)-macrocycle catalysts are those for which the interactions between the metal ion and macrocycle are the weakest. Inhibition studies show that each of the four catalysts form complexes with phosphate and oxalate dianions with a much higher affinity than diethyl phosphate monoanion, consistent with stronger interaction of the catalysts with the transition state dianion compared with the substrate monoanion HpPNP. The pH-dependence of methyl phosphate inhibition of Zn(2) catalyzed cleavage of HpPNP shows that only the Zn(2)(OH(2)) species binds the inhibitor. This result is consistent with a mechanism that has Zn(2)(OH(2)) as the active catalytic species. 相似文献