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41.
Vinod K. Ahluwalia Manjula Khanna Rishi P. Singh 《Monatshefte für Chemie / Chemical Monthly》1983,114(1):71-77
Condensation of orcinol with 2-methylbuta-1,3-diene (isoprene) has been achieved in the presence of orthophosphoric acid as catalyst leading to the exclusive formation of 2,2-dimethylchromans in one step. A novel route for the synthesis of 5-methylxanthyletin derivatives is described. 相似文献
42.
Kalpana Sharma Rishi Pal Chahal Suman Mahendia Anil Kumar Tomar Shyam Kumar 《辐射效应与固体损伤》2013,168(5):378-384
Polyvinyl alcohol films were irradiated to 90 MeV O 6+ and 150 MeV Si 14+ ions at fluence ranging from 1010 to 1012 ions/cm2. The observed changes in optical energy gap of this polymer have been investigated and results are tried to be explained in terms of energy transferred by the incident ions. It has been noticed that the value of optical energy gap decreases with increasing energy loss during the ion–polymer interaction process. 相似文献
43.
Estimation of relative order tensors, and reconstruction of vectors in space using unassigned RDC data and its application 总被引:1,自引:1,他引:0
Miao X Mukhopadhyay R Valafar H 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,194(2):202-211
Advances in NMR instrumentation and pulse sequence design have resulted in easier acquisition of Residual Dipolar Coupling (RDC) data. However, computational and theoretical analysis of this type of data has continued to challenge the international community of investigators because of their complexity and rich information content. Contemporary use of RDC data has required a-priori assignment, which significantly increases the overall cost of structural analysis. This article introduces a novel algorithm that utilizes unassigned RDC data acquired from multiple alignment media (nD-RDC, n 3) for simultaneous extraction of the relative order tensor matrices and reconstruction of the interacting vectors in space.Estimation of the relative order tensors and reconstruction of the interacting vectors can be invaluable in a number of endeavors. An example application has been presented where the reconstructed vectors have been used to quantify the fitness of a template protein structure to the unknown protein structure. This work has other important direct applications such as verification of the novelty of an unknown protein and validation of the accuracy of an available protein structure model in drug design. More importantly, the presented work has the potential to bridge the gap between experimental and computational methods of structure determination. 相似文献
44.
Vimlesh Chandra Rishi SrivastavaS. Sundar Manoharan 《Journal of magnetism and magnetic materials》2008
A series of nano-crystalline CoxAg100−x solid solutions have been prepared by NaBH4 reduction of the corresponding metal salts at room temperature in Ar gas flow. Alloys heat-treated at 600 °C in Ar/H2 (5%) show the evolution of metastable fcc Co precipitates in Ag. Magnetic studies indicate that all the compositions are ferromagnetic with Curie temperatures >400 K. For a nominal composition of Co60Ag40, heat-treated at 600 °C, an effective negative magneto-resistance (MR) ratio of the order of ∼21% at 350 K, at 2 T is observed. This could arise from the influence of magnetic field on the electron–phonon scattering effects near to Tc and to the spin-mixing scattering by magnons. 相似文献
45.
ABSTRACTModified coupled-cluster (CC) methods such as linearized coupled-cluster doubles (LinCCD), approximate coupled pair (ACP D14), 2CC (from nCC family), parameterized CCSD (pCCSD) and distinguishable cluster (DCSD) can have their advantages over general CC methods. Though these methods include connected clusters of single and double excitations at most, distinguishable cluster, parameterized CC and approximate coupled pair methods, in particular, have been shown to produce quantitatively correct results in benchmark studies. To put these methods on a stronger foothold, it is essential to understand the rationale for their success: mimicking the effect of connected triple excitations. We exploit the relation between CC and many body perturbation theory (MBPT) in general, and between CCSD and MBPT(4)/MP4 in particular, to take a step towards bringing clarity to this persisting conundrum. Our aim here is to look for numerical signs of ‘addition by subtraction’ or ‘inclusion by deletion’ effect that is likely behind the success of these modified CCD or CCSD methods. We achieve this by revisiting well-studied examples of single and multiple bond dissociation and comparing the performance of these modified CCSD methods with higher-level CC methods. Though our results are qualitative in nature, we hope this would lead to more rigorous analysis in future studies. 相似文献
46.
Rex A. Palmer A. I. El-Shora Harkishan Singh Dharam Paul 《Journal of chemical crystallography》1989,19(4):629-640
The crystal structure of 4,17a-di(2-hydroxyethyl)-4,17a-diaza-d-homo-5-androstane, C22N2O2H40 (HS461), the tertiary amine related to HS781, a potential bisquaternary neuromuscular blocking agent, has been determined by direct methods and refined by full-matrix least squares toR=0.0867 for 2049 reflections (R=0.0597), CuK radiation 65°. The space group is P212121
a=20.295(4),b=7.278(6),c=14.052(4) Å,Z=4. The rings in the modified steroid nucleus are alltrans connected symmetrical chairs. Hydroxyethyl side groups at N(4) and N(17a) both have an equatorial disposition, and the side chains assumetrans conformations. 相似文献
47.
Miller BT Singh RP Klauda JB Hodoscek M Brooks BR Woodcock HL 《Journal of chemical information and modeling》2008,48(9):1920-1929
A new web portal for the CHARMM macromolecular modeling package, CHARMMing (CHARMM interface and graphics, http://www.charmming.org), is presented. This tool provides a user-friendly interface for the preparation, submission, monitoring, and visualization of molecular simulations (i.e., energy minimization, solvation, and dynamics). The infrastructure used to implement the web application is described. Two additional programs have been developed and integrated with CHARMMing: GENRTF, which is employed to define structural features not supported by the standard CHARMM force field, and a job broker, which is used to provide a portable method for using grid and cluster computing with CHARMMing. The use of the program is described with three proteins: 1YJP , 1O1O , and 1UFY . Source code is provided allowing CHARMMing to be downloaded, installed, and used by supercomputing centers and research groups that have a CHARMM license. Although no software can replace a scientist's own judgment and experience, CHARMMing eases the introduction of newcomers to the molecular modeling discipline by providing a graphical method for running simulations. 相似文献
48.
49.
M. Oddone P. Márton G. Bigazzi K. T. Biró 《Journal of Radioanalytical and Nuclear Chemistry》1999,242(1):147-153
Obsidian samples from the Tokaj Mountains (Hungary) and from the neighbouring Zemplin Hills (Slovakia) were analysed by instrumental
and epithermal neutron activation analysis for obtaining a “fingerprint” for discrimination of potential natural sources of
raw material that would permit tracing the origin of archaeological obsidian artefacts. These techniques fully discriminate
the Zemplin Hills sources (Carpathian I, eastern Slovakia) and the Tokaj Mountain sources (Carpathian II, north-eastern Hungary)
as well as these Central European sources from those already studied of the Mediterranean basin and adjacent regions. 相似文献
50.
Dielectric relaxation studies of binary (jk) polar mixtures of tetrahydrofuran with N-methyl acetamide, N,N-dimethyl acetamide, N-methyl formamide and N,N-dimethyl formamide dissolved in benzene(i) for different weight fractions (w j k ’s) of the polar solutes and mole fractions (x j ’s) of tetrahydrofuran at 25 °C are attempted by measuring the conductivity of the solution under 9.90 GHz electric field using Debye theory. The estimated relaxation time (τ j k ’s) and dipole moment (μ j k ’s) agree well with the reported values signifying the validity of the proposed methods. Structural and associational aspects are predicted from the plot of τ j k and μ j k against x j of tetrahydrofuran to arrive at solute–solute (dimer) molecular association upto x j =0.3 of tetrahydrofuran and thereafter solute–solvent (monomer) molecular association upto x j =1.0 for all systems except tetrahydrofuran + N,N-dimethyl acetamide. 相似文献