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61.
62.
Takezawa Y Tanaka K Yori M Tashiro S Shiro M Shionoya M 《The Journal of organic chemistry》2008,73(16):6092-6098
Metal-mediated base pairing with artificial ligand-bearing nucleosides allows site-selective metal incorporation inside DNA duplexes. In particular, this strategy has provided a general way of discrete, heterogeneous metal arrays in a programmable manner. To increase the kind of metallo-building blocks, we have newly synthesized two artificial nucleosides which have an O, S-donor ligand as the nucleobase moiety, mercaptopyridone ( M) and hydroxypyridinethione ( S). These nucleosides were found to efficiently form metal-mediated base pairs with soft transition metal ions such as Pd (2+) and Pt (2+). 相似文献
63.
Taki M Desaki M Ojida A Iyoshi S Hirayama T Hamachi I Yamamoto Y 《Journal of the American Chemical Society》2008,130(38):12564-12565
We described here a coumarin-based dual-excitation ratiometric probe for cadmium, CadMQ. This fluorescence sensor has high quantum yields of 0.59 and 0.70 in the metal-free and Cd2+-bound forms, respectively, and has a dissociation constant of 0.16 nM for Cd2+. CadMQ is cell permeable and locates within the acidic compartments of the cells. We further show that CadMQ is a useful tool to ratiometrically probe the change in the intracellular Cd2+ levels with the use of two excited wavelengths. 相似文献
64.
Recent studies suggest the dominant role of main-chain H-bond formation in specifying beta-sheet topology. Its essentially sequence-independent nature implies a large degree of freedom in designing beta-sheet-based nanomaterials. Here we show rational design of beta-sheet face inversions by incremental deletions of beta-strands from the single-layer beta-sheet of Borrelia outer surface protein A. We show that a beta-sheet structure can be maintained when a large number of native contacts are removed and that one can design large-scale conformational transitions of a beta-sheet such as face inversion by exploiting the promiscuity of strand-strand interactions. High-resolution X-ray crystal structures confirmed the success of the design and supported the importance of main-chain H-bonds in determining beta-sheet topology. This work suggests a simple but effective strategy for designing and controlling nanomaterials based on beta-rich peptide self-assemblies. 相似文献
65.
66.
New triazine-type dehydrocondensing reagents, such as ROMP-Trz-Cl and ROMP(OH)-Trz-Cl, were synthesized by a ring opening metathesis polymerization (ROMP) method, and these showed higher loading than conventional polymer-supported condensing reagents. These polymers effect the formation of amides in good yields by addition of a mixture of carboxylic acid, amine and NMM. ROMP(OH)-Trz-Cl, which contains hydroxyl groups in the polymer chain, gave amides in good yields even in MeOH. 相似文献
67.
Shohei Inoue 《Journal of polymer science. Part A, Polymer chemistry》2000,38(16):2861-2871
The story of the outset of the concept of immortal polymerization is presented. Immortal polymerization is the polymerization that gives polymers with a narrow molecular distribution, even in the presence of a chain transfer reaction, because of its reversibility, which leads to the revival of the polymers once dead, that is, the immortal nature of the polymers. As a result, immortal polymerization can afford polymers with a controlled molecular weight, the number of polymer molecules being more than that of the initiator. The compound that plays a leading role is metalloporphyrin, in which the metal‐axial ligand bond has an unusually high reactivity. Immortal polymerization can be carried out in the ring‐opening polymerizations of epoxides, episulfides, and lactones by the selection of an appropriate metalloporphyrin as the initiator and a protic compound as the chain transfer agent. Immortal polymerization is an effective method for synthesizing end‐functional polymers and oligomers with narrow molecular weight distributions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2861–2871, 2000 相似文献
68.
69.
Nakahata T Fujimura S Kuwahara S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(17):4584-4593
Pteridic acid A (1) is a spirocyclic octaketide produced by the phytoepiphytic actinomycete Streptomyces hygroscopicus TP-A0451 and possesses potent plant-growth-promoting activity comparable to that of indole-3-acetic acid. The enantioselective total synthesis of this natural product was achieved by employing the Sn(OTf)(2)-mediated Evans aldol reaction and the Fukuyama acetylenic coupling reaction as the key C--C bond-forming steps producing 1 through a 14-step sequence in 22 % overall yield from a known oxazolidinone derivative. MgBr(2)-mediated equilibration of an anomerically favored spirocyclic intermediate used for the synthesis of 1 brought about partial epimerization of the spirocenter to give the corresponding anomerically disfavored epimer, which was converted into pteridic acid B (11-epi-1), another plant-growth promoter of the same microbial origin. 相似文献
70.
Nakahara H Nakamura S Hiranita T Kawasaki H Lee S Sugihara G Shibata O 《Langmuir : the ACS journal of surfaces and colloids》2006,22(3):1182-1192
Surface pressure (pi)-, surface potential (deltaV)-, and dipole moment (mu(perpendicular))-area (A) isotherms and morphological behavior were examined for monolayers of a newly designed 18-mer amphiphilic alpha-helical peptide (Hel 13-5), DPPC, and DPPC/egg-PC (1:1) and their combinations by the Wilhelmy method, ionizing electrode method, fluorescence microscopy (FM), and atomic force microscopy (AFM). The newly designed Hel 13-5 showed rapid adsorption into the air-liquid interface to form interfacial films such as a SP-B function. Regardless of the composition and constituents in their multicomponent system of DPPC/egg-PC, the collapse pressure (pi(c); approximately 42 mN m(-1)) was constant, implying that Hel 13-5 with the fluid composition of egg-PC is squeezed out of Hel 13-5/DPPC/egg-PC monolayers accompanying a two- to three-dimensional phase transformation. FM showed that adding a small amount of Hel 13-5 to DPPC induced a dispersed pattern of ordered domains with a "moth-eaten" appearance, whereas shrinkage of ordered domains in size occurred for the DPPC/egg-PC mixture with Hel 13-5. Furthermore, AFM indicated that (i) the intermediate phase was formed in pure Hel 13-5 systems between monolayer states and excluded nanoparticles, (ii) protrusions necessarily located on DPPC monolayers, and (iii) beyond the collapse pressure of Hel 13-5, Hel 13-5 was squeezed out of the system into the aqueous subphase. Furthermore, hysteresis curves of these systems nicely resemble those of the DPPC/SP-B and DPPC/SP-C mixtures reported before. 相似文献