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21.
The influences of fluorines in chemistry have emerged as a breakthrough in various arenas of bio-organic and medicinal chemistry. But its incorporation in β-turn design and its implications for supramolecular chemistry remains in a rudimentary stage. Inspired by the diversity displayed by the isomers of mono-fluorinated phenylalanine in biological sciences, here our effort is to modulate the solid state conformational analysis of three terminally protected synthetic tripeptides Boc-(Y)-F-Phe-Aib-Xaa-OMe, where (Y is (2)-F-Phe, Xaa; Leu in peptide I, (3)-F-Phe, Xaa; Leu in peptide II and (4)-F-Phe, Xaa; Ile in peptide III). Interestingly, all the three peptides display a conformational preference for β-turns, stabilized by 4→1 intramolecular hydrogen bonding. Our investigation further demonstrates that mere interchange of positions of fluorines in mono-fluorinated phenylalanine in peptides I–III introduces significant diversity in supramolecular chemistry. X-ray crystallography sheds some light at atomic resolution. Furthermore, this supramolecular heterogeneous behavior is evident from the morphologies obtained from the materials of all the three peptides grown from acetone to petroleum ether solution, studied by field emission scanning electron microscopy. Thus, these monofluorinated peptides I–III may serve as prominent candidates in understanding the structure and function of misfolded disease causing peptides like prion and Alzheimer's amyloid. 相似文献
22.
Shailesh K. Goswami Lyall R. Hanton C. John McAdam Stephen C. Moratti Jim Simpson 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(4):407-411
The title compounds, C11H11BrO3, (I), and C11H11NO5, (II), respectively, are derivatives of 6‐hydroxy‐5,7,8‐trimethylchroman‐2‐one substituted at the 5‐position by a Br atom in (I) and by a nitro group in (II). The pyranone rings in both molecules adopt half‐chair conformations, and intramolecular O—H...Br [in (I)] and O—H...Onitro [in (II)] hydrogen bonds affect the dispositions of the hydroxy groups. Classical intermolecular O—H...O hydrogen bonds are found in both molecules but play quite dissimilar roles in the crystal structures. In (I), O—H...O hydrogen bonds form zigzag C(9) chains of molecules along the a axis. Because of the tetragonal symmetry, similar chains also form along b. In (II), however, similar contacts involving an O atom of the nitro group form inversion dimers and generate R22(12) rings. These also result in a close intermolecular O...O contact of 2.686 (4) Å. For (I), four additional C—H...O hydrogen bonds combine with π–π stacking interactions between the benzene rings to build an extensive three‐dimensional network with molecules stacked along the c axis. The packing in (II) is much simpler and centres on the inversion dimers formed through O—H...O contacts. These dimers are stacked through additional C—H...O hydrogen bonds, and further weak C—H...O interactions generate a three‐dimensional network of dimer stacks. 相似文献
23.
Papori Goswami 《合成通讯》2013,43(13):2271-2278
A wide range of substituted coumarin derivatives were synthesized by refluxing in acetonitrile, ethyl acetoacetate, and ethyl benzoyl acetate with a wide range of structurally diverse phenol derivatives within a short reaction time with a catalytic combination of pyridine dicarboxylic acid as organocatalyst and nanocrystalline ZnO. 相似文献
24.
Dr. Manivannan Ethirajan Dr. Ping Chen Dr. Tymish Y. Ohulchanskyy Dr. Lalit N. Goswami Dr. Anurag Gupta Dr. Avinash Srivatsan Dr. Mahabeer P. Dobhal Joseph R. Missert Prof. Paras N. Prasad Prof. Karl M. Kadish Prof. Ravindra K. Pandey 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(21):6670-6684
We report herein a simple and efficient approach to the synthesis of a variety of meso‐substituted purpurinimides. The reaction of meso ‐ substituted purpurinimide with N‐bromosuccinimide regioselectively introduced a bromo functionality at the 20‐position, which on further reaction with a variety of boronic acids under Suzuki reaction conditions yielded the corresponding meso‐substituted analogues. Interestingly, the free base and the metalated analogues showed remarkable differences in photosensitizing efficacy (PDT) and tumor‐imaging ability. For example, the free‐base conjugate showed significant in vitro PDT efficacy, but limited tumor avidity in mice bearing tumors, whereas the corresponding NiII derivative did not produce any cell kill, but showed excellent tumor‐imaging ability at a dose of 0.3 μmol kg?1 at 24, 48, and 72 h post‐injection. The limited PDT efficacy of the NiII analogue could be due to its inability to produce singlet oxygen, a key cytotoxic agent required for cell kill in PDT. Based on electrochemical and spectroelectrochemical data in DMSO, the first one‐electron oxidation (0.52 V vs. SCE) and the first one‐electron reduction (?0.57–0.67 V vs. SCE) of both the free base and the corresponding NiII conjugates are centered on the cyanine dye, whereas the second one‐electron reduction (?0.81 V vs. SCE) of the two conjugates is assigned to the purpurinimide part of the molecule. Reduction of the cyanine dye unit is facile and occurs prior to reduction of the purpurinimide group, which suggests that the cyanine dye unit as an oxidant could be the driving force for quenching of the excited triplet state of the molecules. An interaction between the cyanine dye and the purpurinimide group is clearly observed in the free‐base conjugate, which compares with a negligible interaction between the two functional groups in the NiII conjugate. As a result, the larger HOMO–LUMO gap of the free‐base conjugate and the corresponding smaller quenching constant is a reason to decrease the intramolecular quenching process and increase the production of singlet oxygen to some degree. 相似文献
25.
We have developed a FRET-based ratiometric fluorescent probe for the detection of CN− using a fluorescein–Zn–naphthalene ensemble (NFH·Zn2+). The sensing mechanism was ascribed by displacement approach. The chemosensor exhibits high selectivity and sensibility for CN−. The speculation was supported by fluorescence emission spectra, UV–vis spectrum, 1H NMR titration experiments, and mass spectra. The interconversion of probe NFH and NFH·Zn2+ via the complexation/decomplexation by the modulation of Zn2+/CN− mimics INHIBIT gate. In addition, it also shows an excellent performance in ‘dip stick’ method. 相似文献
26.
Anik Goswami Gunjan Verma P. A. Hassan Vinod K. Aswal 《Journal of Dispersion Science and Technology》2014,35(12):1717-1726
The adsorption behavior of binary mixtures comprising nonionic surfactants at the air–water interface has been studied by bubble pressure tensiometry at concentrations above and below their critical micelle concentrations. Surfactants with the same hydrocarbon chains but different degree of ethoxylations were chosen as the components to understand their mixing behavior at equilibrium and dynamic conditions. At short times, the adsorption is found to be diffusion limited for individual components as well as for the mixtures, as predicted by the Ward and Tordai model. The effective diffusion coefficient of the monomers in the mixed state displays a dynamic synergism, consistent with the molecular thermodynamic model for dynamic surface tension. However, the equilibrium surface tension and micellar diffusion coefficient of the mixtures exhibit ideal behavior. 相似文献
27.
J. S. Samantray Sunil Goswami V. K. Sharma Jayashree Biswal H. J. Pant 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(2):979-982
A radiotracer investigation was carried out in a diesel hydrotreater (DHDT) unit in a refinery for leak detection in a breech-lock heat exchanger system. The main objectives of the study were to identify the leaking heat exchanger in a system with six heat exchangers and estimate the leak rate. Bromine-82 as dibromobiphenyl was selected and used as radiotracer for the investigation. The radiotracer was instantaneously injected into the suction end of the feed pump line to the heat exchanger of the DHDT unit. The movement of the tracer was measured at strategically selected locations using NaI(Tl) scintillation detectors. Based upon the results of the radiotracer investigation, it was found that out of six heat exchangers, exchanger E-1F was leaking. 相似文献
28.
Haladhara Naik Ashok Goswami Guinyun Kim Kwangsoo Kim Sung-Chul Yang Muhammad Sahid Muhammad Zaman Manwoo Lee Sung-Gyun Shin Moo-Hyun Cho 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(3):1335-1343
The independent isomeric-yield ratios of 89m,gNb for the 93Nb(γ, 4n) 89m,gNb reaction with bremsstrahlung energies of 45-, 50-, 55-, 60-, and 70-MeV were measured by the activation and the off-line γ-ray spectrometric technique at 100 MeV electron linac of the Pohang accelerator laboratory. The isomeric-yield ratios of 89m,gNb for the natZr(p, xn) 89m,gNb and the 89Y(α, 4n) 89m,gNb reactions were measured by using a stacked-foil activation technique with the proton energies of 19–45 MeV and alpha energies of 38.9-, 40.5-, and 42.5-MeV at the MC-50 cyclotron of Korea Institute of Radiological and Medical Sciences. The measured isomeric-yield ratio of 89m,gNb from the 93Nb(γ, 4n), natZr(p, xn), and 89Y(α, 4n) reactions were compared with the similar literature data in the 89Y(3He, 3n) reaction. It was found that the isomeric yield ratio of 89m,gNb increases with projectile energy, which indicate the effect of excitation energy. However, for the similar compound nucleus with the same excitation energy, the isomeric-yield ratios of 89m,gNb in the 89Y(α, 4n) and 89Y(3He, 3n) reactions are higher than those in the 93Nb(γ, 4n) and natZr(p, xn) reactions, which indicates the role of input angular momentum. The isomeric-yield ratios of 89m,gNb in the 93Nb(γ, 4n), natZr(p, xn), 89Y(α, 4n), and 89Y(3He, 3n) reactions were also calculated theoretically using computer code TALYS 1.4. The theoretical isomeric-yield ratios of 89m,gNb from four reactions increase with excitation energy. However, the theoretical value are significantly higher than the experimental data in the 93Nb(γ, 4n) and natZr(p, xn) reactions but slightly lower or comparable in the 89Y(α, 4n) rand 89Y(3He, 3n) reactions. 相似文献
29.
Dr. Bhupendra Goswami Dr. Thomas J. Feuerstein Dr. Ravi Yadav Dr. Ralf Köppe Dr. Sergei Lebedkin Prof. Dr. Manfred M. Kappes Prof. Dr. Peter W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(13):4401-4411
The synthesis of calcium complexes ligated by three different chiral iminophosphonamide ligands, L- H ( L =[Ph2P{N(R)CH(CH3)Ph}2]), L′ -H ( L′ =[Ph2P{NDipp}{N(R)CH(CH3)Ph}]), (Dipp=2,6-iPr2C6H3), and L′′ -H ( L′′ =[Ph2P{N(R)CH(CH3)naph}2]), (naph=naphthyl) is presented. The resulting structures [ L 2Ca], [ L′ 2Ca], and [ L′′ 2Ca] represent the first examples of enantiopure homoleptic calcium complexes based on this type of ligands. The calcium complexes show blue–green photoluminescence (PL) in the solid state, which is especially bright at low temperatures. Whereas the emission of [ L′′ 2Ca] is assigned to the fluorescence of naphthyl groups, the PL of [ L 2Ca] and [ L′ 2Ca] is contributed by long-lived phosphorescence and thermally activated delayed fluorescence (TADF), with a strong variation of the PL lifetimes over the temperature range of 5–295 K. Furthermore, an excellent catalytic activity was found for these complexes in hydroboration of ketones at room temperature, although no enantioselectivity was achieved. 相似文献
30.
Dr. Yong Zhang Dr. Devrishi Goswami Dr. Danling Wang Dr. Tsung‐Shing Andrew Wang Shiladitya Sen Dr. Thomas J. Magliery Dr. Patrick R. Griffin Dr. Feng Wang Dr. Peter G. Schultz 《Angewandte Chemie (International ed. in English)》2014,53(1):132-135
The X‐ray crystal structure of a bovine antibody (BLV1H12) revealed a unique structure in its ultralong heavy chain complementarity determining region 3 (CDR3H) that folds into a solvent‐exposed β‐strand “stalk” fused to a disulfide crosslinked “knob” domain. We have substituted an antiparallel heterodimeric coiled‐coil motif for the β‐strand stalk in this antibody. The resulting antibody (Ab‐coil) expresses in mammalian cells and has a stability similar to that of the parent bovine antibody. MS analysis of H–D exchange supports the coiled‐coil structure of the substituted peptides. Substitution of the knob‐domain of Ab‐coil with bovine granulocyte colony‐stimulating factor (bGCSF) results in a stably expressed chimeric antibody, which proliferates mouse NFS‐60 cells with a potency comparable to that of bGCSF. This work demonstrates the utility of this novel coiled‐coil CDR3 motif as a means for generating stable, potent antibody fusion proteins with useful pharmacological properties. 相似文献