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911.
Sugiura K Kato A Iwasaki K Miyasaka H Yamashita M Hino S Arnold DP 《Chemical communications (Cambridge, England)》2007,(20):2046-2047
The reaction of Hg(CF3CO2)2 with metalloporphyrins produces mercurated porphyrins regioselectively, the reaction, surprisingly occurring at the most hindered betaB-position; this behavior is in marked contrast to the usual electrophilic substitution reactions of porphyrins, whose reactions produce meso-substituted porphyrins; the obtained mercurated porphyrins are active to transition metal-catalyzed coupling reactions, such as the Mizoroki-Heck reaction. 相似文献
912.
We show that the ability to control the architecture/orientation of vancomycin on the surface of magnetic nanoparticles has a drastic effect on the ability of the nanoparticles to magnetically confine vancomycin-antibody modified polystyrene microbeads. 相似文献
913.
The problem of determining limiting distributions for sums of records has been studied by several authors who have considered
a variety of assumptions sufficient to ensure that sums of records properly normalized will converge to a non-degenerate distribution.
As a parallel to these endeavors, it is of interest to establish conditions under which the sum of Pfeifer records, properly
normalized, converges. Pfeifer records are defined under the assumption that initial observations are i.i.d. with common survival
function and following the (n−1)-th record value the observations are assumed to have survival function ,n=1,2,.... The study of the asymptotic behavior of sums of Pfeifer records constitutes a natural generalization of work on
sums of classical records. The present paper introduces conditions under which the limit distribution of sums of Pfeifer records
is non-degenerate.
相似文献
914.
Deena M. Butryn Michael S. Gross Lai-Har Chi Arnold Schecter James R. Olson Diana S. Aga 《Analytica chimica acta》2015
The presence of polybrominated diphenyl ethers (PBDEs) and their hydroxylated (OH-BDE) and methoxylated (MeO-BDE) analogs in humans is an area of high interest to scientists and the public due to their neurotoxic and endocrine disrupting effects. Consequently, there is a rise in the investigation of the occurrence of these three classes of compounds together in environmental matrices and in humans in order to understand their bioaccumulation patterns. Analysis of PBDEs, OH-BDEs, and MeO-BDEs using liquid chromatography-mass spectrometry (LC-MS) can be accomplished simultaneously, but detection limits for PBDEs and MeO-BDEs in LC-MS is insufficient for trace level quantification. Therefore, fractionation steps of the phenolic (OH-BDEs) and neutral (PBDEs and MeO-BDEs) compounds during sample preparation are typically performed so that different analytical techniques can be used to achieve the needed sensitivities. However, this approach involves multiple injections, ultimately increasing analysis time. In this study, an analytical method was developed for a “one-shot” analysis of 12 PBDEs, 12 OH-BDEs, and 13 MeO-BDEs using gas chromatography with tandem mass spectrometry (GC-MS/MS). This overall method includes simultaneous extraction of all analytes via pressurized liquid extraction followed by lipid removal steps to reduce matrix interferences. The OH-BDEs were derivatized using N-(t-butyldimethylsilyl)-N-methyltrifluoroacetamide (TBDMS-MTFA), producing OH-TBDMS derivatives that can be analyzed together with PBDEs and MeO-BDEs by GC-MS/MS in “one shot” within a 25-min run time. The overall recoveries were generally higher than 65%, and the limits of detection ranged from 2 to 14 pg in both breast milk and serum matrices. The applicability of the method was successfully validated on four paired human breast milk and serum samples. The mean concentrations of total PBDEs, OH-BDEs, and MeO-BDEs in breast milk were 59, 2.2, and 0.57 ng g−1 lipid, respectively. In serum, the mean total concentrations were 79, 38, and 0.96 ng g−1 lipid, respectively, exhibiting different distribution profiles from the levels detected in breast milk. This “one-shot” GC-MS/MS method will prove useful and cost-effective in large-scale studies needed to further understand the partitioning behavior, and ultimately the adverse health effects, of these important classes of brominated flame retardants in humans. 相似文献
915.
Dr. Susanne Bähr Dr. Sabine Brinkmann-Chen Dr. Marc Garcia-Borràs Dr. John M. Roberts Dr. Dimitris E. Katsoulis Prof. K. N. Houk Prof. Frances H. Arnold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(36):15637-15641
Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild-type cytochrome P450 monooxygenase (P450BM3 from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this non-native activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves C−H bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native C−H hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire. 相似文献
916.
We report on an experimental study of turbulent vortex rings injected with velocity U v0 into a grid-generated turbulent flow (with RMS streamwise velocity u *) and followed relative to the mean flow. The initial Reynolds number of the vortices varies from 4500 to 11,500. The turbulence was characterised by an intensity It =u */U v0, which varied over the range 0<It <0.03. A mathematical model based on a stochastic model of the vortex core is developed to explain and interpret the results. The vortex radius grows diffusively in time with the rate of increase of the square of the vortex radius increasing linearly with It . As the vortices grow, they slow down sufficiently rapidly in a manner that they penetrate a finite distance into the turbulence. The vortex velocity, averaged over many experiments, showed an initial t ?1 decay, consistent with Maxworthy’s experiments. The analysis and experiments show that such vortices ultimately only move a finite distance from their point of generation and this distance varies inversely with It . 相似文献
917.
G. W. Arnold 《辐射效应与固体损伤》2013,168(1-4):17-30
Abstract Ion implantation can be used to introduce network damage and to alter the chemical composition in glasses. Structural changes can be inferred from IR measurements near 1000 cm?1 and by optical absorption near 2150 Å. Implantation-induced damage decreases the implanted volume in fused silica with consequent changes in the refractive index, the near-surface hardness, and the tensile surface stress. Prior work in these areas is reviewed. Implantation into alkali silicate glasses depletes the alkali content in the implanted region. These changes allow preferential surface crystallization in Li2O-2SiO2 glasses. Crystallization of amorphous SiO2 can be induced by implantation of Li. Insight into the crystallization process is obtained by following the associated ion movement by elastic recoil detection (ERD) and optical techniques. Implantation of 20keV H shows that saturation of implanted H-sites in fused silica occurs at about 2.2 × 1021 H/cm3 in agreement with free volume estimates of the maximum number of available interstitial sites. Details of H and D interactions in fused silica were studied as a function of fluence and temperature. Results are of interest in studies of corrosion in glasses considered for nuclear waste encapsulation and for components in fusion reactors. IV Summary 相似文献
918.
Mehrdad Pourayoubi James A. Golen Mahnaz Rostami Chaijan Vladimir Divjakovic Monireh Negari Arnold L. Rheingold 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(5):m160-m164
In the new tin(IV) and copper(II) complexes, cis‐dichlorido‐trans‐dimethyl‐cis‐bis(N,N′,N′′‐tricyclohexylphosphoric triamide‐κO)tin(IV), [Sn(CH3)2Cl2(C18H36N3OP)2], (I), and trans‐diaquabis(N,N′,N′′‐tricyclohexylphosphoric triamide‐κO)copper(II) dinitrate–N,N′,N′′‐tricyclohexylphosphoric triamide (1/2), [Cu(C18H36N3OP)2(H2O)2](NO3)2·2C18H36N3OP, (II), the N,N′,N′′‐tricyclohexylphosphoric triamide (PTA) ligands exist as hydrogen‐bonded dimers via P=O...H—N interactions around the metal center. The asymmetric unit in (I) consists of one complete complex molecule located on a general position. The SnIV coordination geometry is octahedral with two cis hydrogen‐bonded PTA ligands, two cis chloride ligands and two trans methyl groups. The asymmetric unit in (II) contains one half of a [Cu(PTA)2(H2O)2]2+ dication on a special position (site symmetry for the Cu atom), one nitrate anion and one free PTA molecule, both on general positions. The complex adopts a square‐planar trans‐[CuO2O2] coordination geometry, with the CuII ion coordinated by two PTA ligands and two water molecules. Each of the noncoordinated PTA molecules is hydrogen bonded to a neighboring coordinated PTA molecule and an adjacent water molecule; the phosphoryl O atom acts as a double‐H‐atom acceptor. The P atoms in the PTA ligands of both complexes and in the noncoordinated hydrogen‐bonded molecules in (II) adopt a slightly distorted tetrahedral environment. 相似文献
919.
The reaction of meso-tetraphenylporphyrinatomanganese(II) (MnTPP) and N,7,7-tricyanoquinomethanimine (TCQMI) forms {[Mn(III)TPP](+)}(2)[TCQMI](2)(2-), which possesses a one-dimensional chain with μ(1,3)-NCN linkages. The reduced [TCQMI](?-) dimerizes as [TCQMI](2)(2-) with a long, central 1.611(8) ? C-C bond and leads to a honeycomb, two-dimensionally layered structure with 24-membered rings. The μ(1,3)-NCN linkage stabilizes a canted antiferromagnetic (weak ferromagnetic) behavior with T(c) of 3.7 K. 相似文献
920.
Arnold M Bittermann H Kalbfuss-Zimmermann B Neumann T Schmidt K Sekul R Hilbrig F Ludolph H Freitag R 《Journal of chromatography. A》2011,1218(29):4649-4659
Libraries of small molecules were searched for Fc-fragment selective binders to a recombinant human antibody ("MDJ8″, IgG(1)-subtype, κ-light chain) via SPR-based screening of chemical microarrays. Identified hit structures were immobilised on NHS-activated Sepharose for the determination of MDJ8 binding and selectivity versus typical proteineous impurities represented by the spend cell culture supernatant. Columns were packed and the most promising ligands further characterized in terms of binding constants, binding kinetics, as well as dynamic and equilibrium binding capacities. The performance of the best ligand, 2A10, was compared to standard Protein A chromatography. Using ligand 2A10 antibody capture from unprocessed cell culture supernatants was possible at similar recovery yield (>90%), purity (>80%), and eluting concentration (approximately 1 g/L) as with Protein A. Affinity constants (K(d)) of 2A10 were an order of magnitude higher than for the Protein A material, but still in the nM-range, while maximum binding capacities and binding kinetics were in the same order of magnitude. Ligand 2A10 was also able to capture a murine monoclonal antibody, again with similar efficiency as Protein A, as well as a number of humanised therapeutic antibodies. Antibody elution from the 2A10 column was possible using the Protein A standard protocol, i.e. 100mM glycine HCl pH 3.0, but also at near physiological pH, when some organic solvent or modifiers were present. Ligand 2A10 thus constitutes a cheaper, more robust alternative to Protein A as possible generic antibody binder. Moreover, the outlined approach to ligand selection could in principle by used to create suitable affinity ligands for other high value biotech products. 相似文献