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排序方式: 共有2205条查询结果,搜索用时 265 毫秒
941.
Dr. Joon Soo An Dr. Hyunbin Lee Hyungyu Kim Seungyeon Woo Hyunsung Nam Jayho Lee Dr. Ji Yun Lee Prof. Sang-Jip Nam Prof. Sang Kook Lee Prof. Ki-Bong Oh Prof. Seokhee Kim Prof. Dong-Chan Oh 《Angewandte Chemie (International ed. in English)》2023,62(26):e202300998
Cihunamides A–D ( 1 – 4 ), novel antibacterial RiPPs, were isolated from volcanic-island-derived Streptomyces sp. The structures of 1 – 4 were elucidated by 1H, 13C, and 15N NMR, MS, and chemical derivatization; they contain a tetrapeptide core composed of WNIW, cyclized by a unique C−N linkage between two Trp units. Genome mining of the producer strain revealed two biosynthetic genes encoding a cytochrome P450 enzyme and a precursor peptide. Heterologous co-expression of the core genes demonstrated the biosynthesis of cihunamides through P450-mediated oxidative Trp-Trp cross-linking. Further bioinformatic analysis uncovered 252 homologous gene clusters, including that of tryptorubins, which possess a distinct Trp-Trp linkage. Cihunamides do not display the non-canonical atropisomerism shown in tryptorubins, which are the founding members of the “atropitide” family. Therefore, we propose to use a new RiPP family name, “bitryptides”, for cihunamides, tryptorubins, and their congeners, wherein the Trp-Trp linkages define the structural class rather than non-canonical atropisomerism. 相似文献
942.
943.
944.
945.
Kang DY Kim MJ Kim ST Oh KS Yuk SH Lee S 《Analytical and bioanalytical chemistry》2008,390(8):2183-2188
Asymmetrical flow field-flow fractionation (AsFlFFF) was used to determine the size distribution of drug-loaded core/shell
nanoparticles which have a lipid core of lecithin and a polymeric shell of a Pluronic. AsFlFFF provided separation of the
drug-loaded core/shell nanoparticles from smaller coreless polymeric micelles, thus allowing accurate size analysis of the
drug-loaded nanoparticles without interference by the coreless micelles. It was found from AsFlFFF that the drug-loaded nanoparticles
have broad size distributions ranging from 100 to 600 nm in diameter. It was also found that, after the nanoparticles had
been stored for 70 days, they disappeared as a result of self-degradation. Being a separation technique, AsFlFFF seems to
be more useful than transmission electron microscopy or dynamic light scattering for size analysis of core/shell nanoparticles,
which have broad and bimodal size distributions.
Figure Separation by AsFlFFF 相似文献
946.
Eun Mi Lee Hyun Woo Lee Jae Hyeung Park Young A. Han Byung Chul Ji Weontae Oh Yulin Deng Jeong Hyun Yeum 《Colloid and polymer science》2008,286(12):1379-1385
Poly(methyl methacrylate) (PMMA)/silver nanocomposite microspheres with unique multihollow structures were prepared by suspension
polymerization in the presence of dual dispersion agents. The addition of a lipophilic emulsifier, polyethylene glycol (30EO)
dipolyhydroxystearate (Arlacel P135), not only stabilized water-in-oil (W/O) emulsion, but also converted silver nanoparticles
from hydrophilic to lipophilic. When a suspension polymerization dispersion agent, poly(vinyl alcohol), was added to the above
W/O emulsion system, a water-in-oil-in-water suspension was formed with silver nanoparticles dispersed in the oil phase. The
suspension polymerization was carried out at low temperature with 2,2’-azobis(2,4-dimethylvaleronitrile) as the initiator.
When modified silver nanoparticles were added, the rate of polymerization increased slightly. High monomer conversion (about
85%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres
with various hollow structures were synthesized. The PMMA/silver microspheres with multihollow structure showed high antibacterial
ability. 相似文献
947.
The dinuclear Mn(II) complex, [Mn2(Hbida)2(H2O)2], was prepared using a tetradentate tripodal ligand, N-(benzimidazol-2-ylmethyl)iminodiacetic acid (H3bida) which has two carboxylate and one benzimidazole groups. The manganese ions are doubly bridged using μ,η1-bridging monodentate carboxylate oxygen atoms. The Mn–Mn bond distance of 3.446 Å in the complex is comparable to that observed in the active site of the native manganese arginase enzyme (3.30 Å). The geometry of the complex with four carboxylates in two different types of binding modes, non-bridging monodentate and μ,η1-type bridging monodentate, mimics the active site structure of manganese arginase. The magnetic properties of the complex show a coupling constant of J = −0.471(1) cm−1, which is consistent with weakly coupled antiferromagnetic MnII (S = 5/2) centers. The cyclic voltammograms of the Mn(II) complex in DMF show irreversible oxidation occurring around 570 mV (versus Ag/AgCl). 相似文献
948.
The transport efficiency of dried particles generated from an ultrasonic nebulizer (USN) was studied to improve the analytical performance of a lab-made, He-microchip plasma system, in which a quartz tube (~ 1 mm i.d.) was positioned inside the central channel of a poly(dimethylsiloxane) (PDMS) polymer chip. The polymer microchip plasma has the advantages of low cost, small size, easy handling and design, and self-ignition with long stabilization (> 24 h). However, direct introduction of aqueous solution into the microplasma for the detection of metals remains problematic due to plasma instability. In addition, the much smaller size of the system can cause signal suppression due to low transport efficiency. Therefore, knowledge of particle transport efficiency in this microplasma system is required to enhance the sensitivity and stability. The weight of transported particles in the range of 0.02 to 10 mg m− 3 was measured using a piezobalance with a precision of 0.4–17.8%, depending on the operating conditions. The significant effects of the USN operating conditions and the physical properties of the tubing, namely, length, inner diameter and surface characteristics, on the number of particles transported from the nebulizer to the microplasma were studied. When selected metals, such as Na, Mg and Pb, at a concentration of 5 mg L− 1 were nebulized, transported particles were obtained with a mass range of 0.5–5 mg m− 3, depending on atomic weights. For application of the He-rf-microplasma, the atomic emission system was optimized by changing both the radio frequency (rf) power (60–200 W) and cooling temperature of the USN (− 12–9 °C). The limits of detection obtained for K, Na and Cu were 0.26, 0.22, and 0.28 mg L− 1, respectively. These results confirmed the suitable stability and sensitivity of the He-rf-PDMS microchip plasma for application as an atomization source. 相似文献
949.
Shape Oscillation of a drop in ac electrowetting 总被引:2,自引:0,他引:2
A sessile drop oscillates when an ac voltage is applied in electrowetting. The oscillation results from the time-varying electrical force concentrated on the three-phase contact line. Little is known about the feature of drop oscillation in electrowetting. In the present work, the drop oscillations are observed systematically, and a theoretical model is developed to analyze the oscillation. It is revealed that resonance occurs at certain frequencies and the oscillation pattern is significantly dependent on the applied ac frequencies. The domain perturbation method is used to derive the shape-mode equations under the assumptions of a weak viscous effect and small drop deformation. The electrical force concentrated on the three-phase contact line is approximated as a delta function, which is decomposed and substituted into each shape-mode equation as a forcing term. The theoretical results for the shape and frequency responses are compared with experimental results, which shows qualitative agreement. 相似文献
950.
Jung Kwon Oh 《Journal of polymer science. Part A, Polymer chemistry》2008,46(21):6983-7001
Effective ways to conduct controlled/living radical polymerization (CRP) in emulsion systems are necessary for commercial latex production without significant modification of current industrial facilities. Conducting CRP in emulsion media is more complicated and more challenging than its application in homogeneous bulk. These challenges come from the intrinsic kinetics of emulsion polymerization. They include mass transport, slow chain growth mechanism, and exit of short radicals from polymeric particles. This review describes the recent developments of CRP in heterogeneous dispersion, including miniemulsion, microemulsion, dispersion, and especially emulsion. Various approaches for conducting emulsion CRP are detailed, including controlled seeded emulsion polymerization, nanoprecipitation, use of short oligomers as macroinitiators for in situ block copolymerization, and RAFT‐mediated self‐assembly. In addition many remaining challenges of the current methods barring wide spread industrial application of emulsion CRP are also suggested. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6983–7001, 2008 相似文献