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51.
The cyclization of geranylgeranyl diphosphate (GGDP) to taxadiene catalyzed by taxadiene synthase has been suggested to proceed in stages, involving a transient bicyclic verticillyl carbocation intermediate, which also has been proposed in the biosynthetic pathway leading to phomactatriene by marine fungi of Phoma sp. On incubation with des-7-methylGGDP, which would be expected to decrease the stability of a carbocation produced by hydride migration, taxadiene synthase produced phomactatrienes as major products. This indicates that the verticillyl carbocation was indeed formed but underwent further skeletal rearrangements, diverging from the usual pathway taken by GGDP en route to taxadiene. Products were identified using GC-MS, one- and two-dimensional NMR, and X-ray crystallography. 相似文献
52.
Heterodialkylation of [Pt2(μ‐S)2(dppp)2] (dppp=Ph2P(CH2)3PPh2) was achieved under high pressure (10 kbar). This enabled the synthesis of rare diplatinum complexes with structurally diverse thiolate bridges, such as [Pt2(μ‐SC5H10CO2CH2CH3)(μ‐SC3H7)‐(dppp)2](PF6)2, which was crystallographically identified. Complete homodialkylation was also achieved under similar conditions (6 kbar at room temperature), thus permitting the isolation of [Pt2(μ‐SC2H4CO2CH2CH3)2(dppp)2]‐(PF6)2. The isolation of these complexes extends the applications of high‐pressure chemistry to thiolato homo‐ and heterobridged complexes that are otherwise not accessible. 相似文献
53.
On ultraviolet irradiation of the cyclopent-2-enyl methyl ketones 1a – c at ?54° ? t ? 139°, photo-CIDNP. effects of the starting ketones, the 1,3-acetyl shifted isomers (2) , and radical disproportionation and combination products (4 – 7) were observed. These effects show a unique dependence of the polarization phase on temperature which is a novel feature in photo-CIDNP. studies. The results of the investigation, which also included experiments using triplet quenchers, triplet sensitizers and radical scavengers, are rationalized in terms of Schemes 2 and 3. α-Cleavage is a major excited-state reaction of 1a – c on direct irradiation. Temperature-activated α-cleavage (k(t)) to the radical pair R · · R ′1 and intersystem crossing (kisc) to the T2 state are among the competing S1 deactivation processes. The T2 state in turn cleaves (k) to R · · R ′3 A ‘low-temperature range’ with kisc ? k(t) and a ‘high-temperature range’ with k(t) ? kisc exhibiting preferential reactivity from the T2 and S1 states, respectively, can be defined for all three β,γ-unsaturated ketones 1a – c . 相似文献
54.
Sixteen notched concrete beams with
, 0.5, 0.7 were tested in three-point bending—eight in strain control and eight in load control. The time to peak load was
kept approximately the same for both cases for a given notch depth. The load-displacement traces were very similar and equivalent
energy values agreed well in most cases. However the fracture-energy values based on the RILEM proposed specification were
affected by the type of response control used.
Paper was presented at the 1986 SEM Spring Conference on Experimental Mechanics held in New Orleans, LA on June 8–13. 相似文献
55.
Lai Khai Siew Larry A. Winger Julia A. Spoors John L. Dessi Lyn Jennens Colin H. Self 《International journal of environmental analytical chemistry》2013,93(5):417-426
Although polyclonal antisera have been used for immunodiagnostic measurement of aldicarb, both as components of commercial kits and as stand-alone products, no monoclonal antibody (MAb) reactive to this carbamate pesticide has yet been described. We have generated two MAbs with specificity to aldicarb, which function in our prototypic field immunoassays to identify this chemical in water samples. Further exploitation of these inherently stable immunoreagents should be valuable for point-of-need testing for the presence of aldicarb. 相似文献
56.
Sie Tiong Ha Lay Khoon Ong Siew Ling Lee Hong Cheu Lin Yip Foo Win Siew Teng Ong 《中国化学快报》2010,21(6):637-640
<正>A homologous series of Schiff base esters,4-chlorobenzylidene-4'-n-alkanoyloxyanilines,containing even number of carbons at the end groups of the molecules(C_(n-1)H_(2n-1)COO-,n=4,6,8,10,12,14,16) were synthesized.The mesomorphic properties were investigated by differential scanning calorimetry(DSC) and polarizing optical microscopy(POM).It was found that the end groups of the molecules had an effect on the mesomorphic properties.n-Butanoyloxy was found non-mesogenic,whilst n-hexanoyloxy exhibited monotropic smectic phase.The higher members in this homologous series were enantiotropic smectogens. 相似文献
57.
Transition metal (TM) embedded two-dimensional phthalocyanine (Pc) sheets have been recently synthesized in experiments [M. Abel, S. Clair, O. Ourdjini, M. Mossoyan, and L. Porte, J. Am. Chem. Soc. 133, 1203 (2010)], where the transition metal ions are uniformly distributed in porous structures, providing the possibility of capturing gas molecules. Using first principles and grand canonical Monte Carlo simulations, TMPc sheets (TM = Sc, Ti, and Fe) are studied for pre-combustion CO(2) capture by considering the adsorptions of H(2)/CO(2) gas mixtures. It is found that ScPc sheet shows a good selectivity for CO(2), and the excess uptake capacity of single-component CO(2) on ScPc sheet at 298 K and 50 bar is found to be 2949 mg/g, larger than that of any other reported porous materials. Furthermore, electrostatic potential and natural bond orbital analyses are performed to reveal the underlying interaction mechanisms, showing that electrostatic interactions as well as the donation and back donation of electrons between the transition metal ions and the CO(2) molecules play a key role in the capture. 相似文献
58.
The influence of the underlying interface on adsorption of cobalt (Co) is investigated by comparing the nucleation and growth of Co at room temperature on three carbon (C) surfaces, i.e. highly oriented pyrolytic graphite (HOPG), epitaxial graphene/SiC(0001) (hereafter abbreviated as EG) and precursor of EG i.e. C-rich (6√3 × 6√3)R30°/SiC(0001) (hereafter abbreviated as 6√3). On all three surfaces, Co adopts Volmer–Weber growth mode via formation of three-dimensional dome-shaped nanoclusters. Co clusters formed on 6√3 surface are smaller but denser than Co/HOPG or Co/EG. Scaling analysis reveals a critical nucleus size, i* = 1 (atom) and the smallest stable cluster (i* + 1) would be a dimer. Co/HOPG and Co/EG have the same order of magnitude for their cluster densities and sizes. Scaling analyses however show that the i* for Co/EG (i* = 3) is larger than Co/HOPG (i* = 0) and in this respect the smallest stable cluster would be tetramer and monomer respectively. This difference is attributed to the influence of an interface situated between graphene and SiC bulk. It appears that EG is more inert than HOPG towards the adsorption of Co and may act as a better substrate to host Co clusters. 相似文献
59.
Khalil MI Sulaiman SA Alam N Moniruzzaman M Bai'e S Man CN Jamalullail SM Gan SH 《Molecules (Basel, Switzerland)》2012,17(1):674-687
This study was conducted to evaluate the effects of evaporation, gamma irradiation and temperature on the total polyphenols, flavonoids and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activities of Tualang honey samples (n = 14) following storage over three, six or twelve months. The mean polyphenol concentrations of the six gamma irradiated honey samples at three, six and twelve months, respectively, were 96.13%, 98.01% and 102.03% higher than the corresponding values of the eight non-gamma irradiated samples. Similarly, the mean values for flavonoids at three, six and twelve months were 111.52%, 114.81% and 110.04% higher, respectively, for the gamma irradiated samples. The mean values for DPPH radical-scavenging activities at three, six and twelve months were also 67.09%, 65.26% and 44.65% higher, respectively, for the gamma irradiated samples. These data indicate that all gamma irradiated honey samples had higher antioxidant potential following gamma irradiation, while evaporation and temperature had minor effects on antioxidant potential. 相似文献
60.
SL Jothy A Torey I Darah YS Choong D Saravanan Y Chen LY Latha S Deivanai S Sasidharan 《Molecules (Basel, Switzerland)》2012,17(9):10292-10305
The genus Cassia, comprising about 600 species widely distributed worldwide is well known for its diverse biological and pharmacological properties. Cassia spectabilis (sin Senna spectabilis) (DC) Irwin et Barn (Fabaceae) is widely grown as an ornamental plant in tropical and subtropical areas. C. spectabilis has been commonly used in traditional medicine for many years. Information in the biomedical literature has indicated the presence of a variety of medicinally-important chemical constituents in C. spectabilis. Pharmacological studies by various groups of investigators have shown that C. spectabilis possesses significant biological activity, such as antibacterial, antibiofilm, antifungal and antioxidant properties. Beside this, toxicity studies of this plant have revealed no toxic effect on mice. In view of the immense medicinal importance of C. spectabilis, this review aimed at compiling all currently available information on C. spectabilis's botany, phytochemistry, pharmacology, and mechanism of actions, toxicology and its ethnomedicinal uses. 相似文献