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71.
Masahiko Maekawa Megumu Munakata Takayoshi Kuroda-Sowa Koji Hachiya 《Inorganica chimica acta》1995,230(1-2):249-252
A novel hexanickel(II) complex [Ni6(NCCHCH2CH2CHCN)6] (2) with 1,4-dicyanobutane-1,4-diyl (L) which was produced by the metal-induced dimerization of acrylonitrile (AN) has been isolated and the structure has been determined crystallographically. Complex 2 is triclinic, space group . Each nickel atom is coordinated by two carbon atoms of L and two nitrogen atoms of the cyano group of two other L, providing a square-plenar geometry. The six nickel atoms are bridged by the cyano group and carbon atom to form the slightly distorted octahedral Ni6 core. 相似文献
72.
Sylviane Olive Catherine Dubois †Melitta Schachner Geneviève Rougon 《Journal of neurochemistry》1995,65(5):2307-2317
Abstract: The F3 molecule is a member of the immunoglobulin superfamily anchored to plasma membranes by a glycosylphosphatidylinositol group. In adult mouse cerebellum, F3 is predominantly expressed on a subset of axons, the parallel fibers, and at their synapses. In vitro studies established that it is a plurifunctional molecule that, depending on the cellular context and the ligand with which it interacts, either mediates repulsive interactions or promotes neurite outgrowth. In the present study, we report the isolation of two fractions of F3-containing microdomains from adult cerebellum on the basis of their resistance to solubilization by Triton X-100 at 4°C. Both fractions were composed of vesicles, ranging from 100 to 200 nm in diameter. Lipid composition analysis indicated that the lighter fraction was enriched in cerebrosides and sulfatides. F3 sensitivity to phosphatidylinositol phospholipase C differed between the two fractions, possibly reflecting structural differences in the lipid anchor of the F3 molecule. Both fractions were highly enriched in other glycosylphosphatidylinositol-anchored proteins such as NCAM 120 and Thy-1. It is interesting that these vesicles were devoid of the transmembrane forms (NCAM 180 and NCAM 140), which were recovered in Triton X-100-soluble fractions, but contained the L1 transmembrane adhesion molecule that is coexpressed with F3 on parallel fibers and the fyn tyrosine kinase. Immunoprecipitation experiments indicated that F3, but not NCAM 120 or Thy-1, was physically associated in a complex with both L1 and fyn tyrosine kinase. This strongly suggests that the interaction between L1 and F3, already described to occur with isolated molecules, is present in neural tissue. More important is that our study provides information on the molecular machinery likely to be involved in F3 signaling. 相似文献
73.
De Andrade Antônio V. M. Da Costa Nivan B. Longo Ricardo L. Malta Oscar L. Simas Alfredo M. De Sá Gilberto F. 《Molecular Engineering》1997,7(3-4):293-308
Theoretical techniques have been developed and/or improved to predict the molecular structure of lanthanide complexes which
were used to calculate their electronic properties, in particular, their electronic spectra and energy levels necessary to
calculate the rates of energy transfer from the ligands to the metal ion. The molecular structure has been obtained by the
SMLC/AM1 (Sparkle Model for the Calculation of Lanthanide Complexes – Austin Model 1) model where the lanthanide ion is simulated
by a sparkle implemented into the AM1 Hamiltonian used to perform a HF-SCF (Hartree-Fock Self-Consistent Field) calculation.
The previous implementation of the SMLC/AM1 model (sparkle/1) involving only two parameters has been generalized to be consistent
with the AM1 Hamiltonian and the new model (sparkle/2) significantly improved the prediction of molecular structures of Eu(III)
complexes. For the electronic spectra and energy level calculations of the lanthanide complexes the model replaces the metal
ion by a point charge with the ligands held in their positions as determined by the SMLC/AM1 model, and uses a INDO/S-CI (intermediate
neglect of differential overlap/spectroscopic-configuration interaction) model. A preliminary study of the solvent effects
on the absorption spectra of the free ligand is also presented. For the ligand-lanthanide ion energy transfer Fermi's golden
rule is used with the multipolar and exchange mechanisms being implemented and tested for several complexes. These theoretical
techniques have been applied to several complexes yielding very good results when compared to experimental data as well as
predictions for the molecular and electronic structures and the relative contributions of the mechanisms for the energy transfer
rates.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
74.
Crystal structures of bovine chymotrypsin and trypsin complexed to the inhibitor domain of Alzheimer's amyloid beta-protein precursor (APPI) and basic pancreatic trypsin inhibitor (BPTI): engineering of inhibitors with altered specificities. 总被引:1,自引:0,他引:1 下载免费PDF全文
A. J. Scheidig T. R. Hynes L. A. Pelletier J. A. Wells A. A. Kossiakoff 《Protein science : a publication of the Protein Society》1997,6(9):1806-1824
The crystal structures of the inhibitor domain of Alzheimer's amyloid beta-protein precursor (APPI) complexed to bovine chymotrypsin (C-APPI) and trypsin (T-APPI) and basic pancreatic trypsin inhibitor (BPTI) bound to chymotrypsin (C-BPTI) have been solved and analyzed at 2.1 A, 1.8 A, and 2.6 A resolution, respectively. APPI and BPTI belong to the Kunitz family of inhibitors, which is characterized by a distinctive tertiary fold with three conserved disulfide bonds. At the specificity-determining site of these inhibitors (P1), residue 15(I)4 is an arginine in APPI and a lysine in BPTI, residue types that are counter to the chymotryptic hydrophobic specificity. In the chymotrypsin complexes, the Arg and Lys P1 side chains of the inhibitors adopt conformations that bend away from the bottom of the binding pocket to interact productively with elements of the binding pocket other than those observed for specificity-matched P1 side chains. The stereochemistry of the nucleophilic hydroxyl of Ser 195 in chymotrypsin relative to the scissile P1 bond of the inhibitors is identical to that observed for these groups in the trypsin-APPI complex, where Arg 15(I) is an optimal side chain for tryptic specificity. To further evaluate the diversity of sequences that can be accommodated by one of these inhibitors, APPI, we used phage display to randomly mutate residues 11, 13, 15, 17, and 19, which are major binding determinants. Inhibitors variants were selected that bound to either trypsin or chymotrypsin. As expected, trypsin specificity was principally directed by having a basic side chain at P1 (position 15); however, the P1 residues that were selected for chymotrypsin binding were His and Asn, rather than the expected large hydrophobic types. This can be rationalized by modeling these hydrophilic side chains to have similar H-bonding interactions to those observed in the structures of the described complexes. The specificity, or lack thereof, for the other individual subsites is discussed in the context of the "allowed" residues determined from a phage display mutagenesis selection experiment. 相似文献
75.
Roman Bo?a Peter Baran L'ubor Dlháň Hartmut Fuess Wolfgang Haase Franz Renz Wolfgang Linert Ingrid Svoboda Rüdiger Werner 《Inorganica chimica acta》1997,260(2):4119-136
The structure of the [Fe(bzimpy)2](ClO4)2·xH2O system (x = 0.25) was determined by single crystal X-ray structure analysis. The Fe(II) ion is hexacoordinated by six donor nitrogen atoms. The magnetic properties of the complex were investigated by powder magnetic susceptibility measurements and ESR. The freshly prepared sample does not show any traces of iron(III) impurities but these are formed as a function of time. After 1 year the sample contains 8.2% iron(III) as shown by UV spectroscopy and indicated by geff = 4.3 and 2.0 in its ESR spectrum. This explains the recorded ξ versus T behaviour at low temperature: with increasing temperature the ξ value decreases according to the Curie-Weiss law for a S = 5/2 system having an effective g = 4.3. Above 220 K a continuous increase in the ξ value is observed and a spin crossover applies. The spin transition is not complete at room temperature. A pronounced hysteresis is observed upon heating/cooling the sample between 220 and 414 K on the basis of magnetic data and infrared spectra. 相似文献
76.
Maurizio Zandomeneghi 《Chirality》1995,7(6):446-451
Complexation of 2-(3′-benzoylphenyl)propionic acid (ketoprofen), 1 , to bovine serum albumin (BSA) results in an intense negative circular dichroism in the ketonic n → π* band of the benzoylphenyl moiety. This high CD contrasts with the weak CD of 1 -enantiomers dissolved in common solvents. Furthermore, a number of chiral and achiral molecules containing the benzophenone moiety are easily complexed to BSA: all these complexes show an intense CD at the same transition. To account for the observed CD intensities of the above molecules, it appears that BSA complexation markedly shifts the equilibrium between strongly asymmetric, antipodic conformers. Dissymmetry of these conformers is connected to the instability of a structure with phenyl rings coplanar to the carbonyl chromophore, as also indicated by molecular mechanics calculations. The magnification of the Cotton effects of the 1 -antipodes, due to the protein, can be used to measure the optical purity of 1 -samples with excellent precision. In contrast with BSA, human SA is unable to recognize the chirality of 1 -antipodes; oleic acid cocomplexation modifies this fact as well as other features of the binding. © 1995 Wiley-Liss, Inc. 相似文献
77.
Solubilities and transfer chemical potentials of carboplatin, cisplatin, iproplatin, and several related platinum complexes have been determined in methanol-water mixtures. the range of solvation behaviour is discussed in relation to possible oral administration of complexes of this type. 相似文献
78.
Bo Lönnerdal Barbara O. Schneeman Carl L. Keen Lucille S. Hurley 《Biological trace element research》1980,2(3):149-158
Rat bile and pancreatic fluid were examined for the presence of low molecular weight zinc complexes. Fluids were collected
separately by cannulation, and zinc distribution in collected samples was analyzed by gel filtration on Sephadex G-50. Most
of the zinc in bile was associated with low molecular weight zinc complexes; only a small amount of zinc was present in the
high molecular weight fraction. In contrast, pancreatic secretions did not contain low molecular weight zinc complexes, but
there were considerable amounts of zinc bound to high molecular weight compounds. The addition of zinc to bile resulted in
an increased amount of zinc in the low molecular weight fraction, while the addition of zinc to pancreatic fluid resulted
primarily in an increase in zinc bound to the high molecular weight components. Like pancreatic fluid, homogenates of pancreatic
tissue had no low molecular weight zinc complex. In rats whose bile and pancreatic fluid were removed and not returned into
the intestine, the amount of zinc bound to low molecular weight complexes in intestinal homogenates was reduced. This alteration
of the molecular distribution of zinc in intestinal homogenates by removal of bile and pancreatic fluid suggests the potential
importance of low molecular weight zinc complexes for zinc homeostasis. 相似文献
79.
The dissociation products of isolated phycobilisomes of Mastigocladus laminosus were separated and analyzed by ultracentrifugation and, in part, by isoelectric focusing. With the exception of the allophycocyanin core, the sedimentation constants of peripheral phycocyanin- and phycoerythrocyanin-phycocyanin complexes lay in the range of 6 to 17S. The latter was represented by a 17S aggregate of two hexameric phycocyanins (dodecamer, dipartite unit). A complex with an absorption maximum at 610 nm (phycocyanin) and a shoulder at 580 nm (phycoerythrocyanin), a fluorescence emission maximum at 645 nm and a sedimentation constant of 11 S is described as a heterogeneously composed hexamer of ()3-phycoerythrocyanin-()3-phycocyanin. It was stable under extended dissociation in the cold and under isoelectric focusing. An aggregate of 14 S with an absorption maximum at 576 nm and a shoulder in the fluorescence emission spectrum at 625 nm (phycoerythrocyanin) in addition to the maximum at 645 nm (phycocyanin) is interpreted as a polar phycoerythrocyanin/ phycoerythrocyanin-phycocyanin complex. Combining these complexes with phycocyanin dodecamers creates peripheral rods of the phycobilisome. A proposal of the phycobiliprotein distribution within the phycobilisome of M. laminosus is presented.Abbreviations APC
allophycocyanin
- PC
phycocyanin
- PE
phycoerythrin
- PEC
phycoerythrocyanin 相似文献
80.
B. H. Li M. Kwasniewski J. Kirchner R. Bockrath 《Molecular & general genetics : MGG》1992,231(3):480-484
Summary Expression of the lacZ gene in Escherichia coli is inactivated by exposure to ultraviolet light (UV). Inactivation is exceptionally effective when cells contain amplified levels of DNA photolyase (which forms complexes with pyrimidine dimers in the absence of light for actual photoreversal) and a prophage. Without amplified photolyase, the prophage or both, inactivation rates are similar and much lower. UV-inactivation of lacZ gene expression in the presence of both amplified photolyase and is even more effective if cI857 is used in place of the wildtype prophage but is wholly unexceptional if the prophage carries defects in the genes rexA or rexB. When Rex AB proteins are provided by expression from a plasmid and the cell also contains amplified photolyase, exceptional inactivation rates again obtain; in fact inactivation is most effective under these conditions. The data are considered to reveal a role for Rex AB proteins, which mediate superinfection exclusion, in the exceptional inactivation of gene expression by photolyase bound to pyrimidine dimers in DNA. Photolyase-dimer complexes may mimic the structure of certain complexes that arise during phage development and thus influence Rex A and/or B proteins, thereby shutting down cell metabolism. 相似文献