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81.
Damien Mahaut Dr. Aurélien Chardon Loïc Mineur Prof. Guillaume Berionni Prof. Benoît Champagne 《Chemphyschem》2021,22(19):1958-1966
The activation or heterolytic splitting of methane, a challenging substrate usually restricted to transition metals, has so far proven elusive in experimental frustrated Lewis pair (FLP) chemistry. In this article, we demonstrate, using density functional theory (DFT), that 1-aza-9-boratriptycene is a conceptually simple intramolecular FLP for the activation of methane. Systematic comparison with other FLP systems allows to gain insight into their reactivity with methane. The thermodynamics and kinetics of methane activation are interpreted by referring to the analysis of the natural charges and by employing the distortion-interaction/activation strain (DIAS) model. These showed that the nature of the Lewis base influences the selectivity over the reaction pathway, with N Lewis bases favoring the deprotonation mechanism and P bases the hydride abstraction one. The lower barrier of activation for 1-aza-9-boratriptycene and the higher products stability are due to a better interaction energy than its counterparts, itself due to electrostatic interactions with the methane moiety, favorable orbital overlaps allowed by the side-attack, and space proximity between the B and N atoms. 相似文献
82.
Dr. Antoine Nitelet Dr. Damien Thevenet Dr. Bruno Schiavi Dr. Christophe Hardouin Dr. Jean Fournier Dr. Rodolphe Tamion Prof. Dr. Xavier Pannecoucke Prof. Dr. Philippe Jubault Prof. Dr. Thomas Poisson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3262-3266
The copper-photocatalyzed borylation of aryl, heteroaryl, vinyl and alkyl halides (I and Br) was reported. The reaction proceeded using a new heteroleptic Cu complex under irradiation with blue LEDs, giving the corresponding boronic-acid esters in good to excellent yields. The reaction was extended to continuous-flow conditions to allow an easy scale-up. The mechanism of the reaction was studied and a mechanism based on a reductive quenching (CuI/CuI*/Cu0) was suggested. 相似文献
83.
Nathan J. Downs Damien P. Igoe Alfio V. Parisi Olivia Taylor Shari L. Lazzaroni Alex Rawlings Daniel R. Garzn‐Chavez Simone L. Harrison 《Photochemistry and photobiology》2019,95(4):1083-1093
The risk of keratinocyte skin cancer, malignant melanoma and ultraviolet radiation (UVR)‐induced eye disease is disproportionately higher in Australia and New Zealand compared to equivalent northern hemisphere latitudes. While many teachers are aware of the importance of reinforcing sun safety messages to students, many may not be aware of the considerable personal exposure risk while performing outdoor duties in locations experiencing high to extreme ambient UVR year‐round. Personal erythemally effective exposure of classroom teachers in tropical Townsville (19.3°S) was measured to establish seasonal extremes in exposure behavior. Mean daily personal exposure was higher in winter (91.2 J m‐2, 0.91 Standard Erythema Dose [SED]) than summer (63.3 J m?2, 0.63 SED). The range of exposures represents personal exposures that approximate current national guidelines for Australian workers at the study latitude of approximately 1.2 SED (30 J m?2 effective to the International Commission on Non‐Ionizing Radiation Protection). Similar proportions of teachers spent more than 1 h outdoors per day in winter (28.6%) and summer (23.6%) as part of their teaching duties with seasonal differences having little effect on the time of exposure. Personal exposures for teachers peaked during both seasons near school meal break times at 11:00 am and 1:00 pm, respectively. 相似文献
84.
85.
The total and bioaccessible concentration of 16 polycyclic aromatic hydrocarbons (PAHs) in soil from a former industrial site was investigated. Typical total concentrations across the sampling sites ranged from 1.5 mg kg−1 for acenaphthylene up to 243 mg kg−1 for fluoranthene. The oral bioaccessibility of PAHs in soil was assessed using an in vitro gastrointestinal extraction (Fed Organic Estimation human Simulation Test, FOREhST method). The oral bioaccessibility data indicated that fluorene, phenanthrene, chrysene, indeno(1,2,3-cd)pyrene and dibenzo(a,h)anthracene had the highest % bioaccessible fraction (based on their upper 75th percentile values being >60%) while the other PAHs had lower % bioaccessible fractions (means ranging between 35 and 59%). Significantly lower bioaccessibilities were determined for naphthalene. With respect to method validation and inter-laboratory comparison, the total and bioaccessible concentrations of benzo(a)anthracene, benzo(b)anthracene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene and dibenzo(a,h)anthracene was compared to published data derived using the same samples. The total PAH concentrations at the site were compared with generic assessment criteria (GAC) using the residential land use scenario (with plant uptake at 6% soil organic matter). Concentrations of 7 of the PAHs investigated within the soils could lead to an unacceptable risk to human health at this site. 相似文献
86.
A new and easy protocol for the formation of substituted 4,5-dihydro-1,2,4-triazin-6(1H)-ones was developed on solid support. The heterocyclic compounds were formed by nucleophilic reaction of hydrazine on thioamide esters. As cyclization was concomitant with cleavage from the support, substituted 4,5-dihydrotriazinones were obtained in high purity. 相似文献
87.
88.
François Couty François Durrat Gwilherm Evano Damien Prim 《Tetrahedron letters》2004,45(40):7525-7528
A synthesis of stereodefined enantiomerically pure 2-alkenyl azetidines is described using Wittig olefination as key step. The quaternary triflate ammonium salts of these heterocycles were prepared in a stereoselective way and treatment of these azetidinium salts with a base (KHMDS or PhLi) induced a regioselective Stevens rearrangement leading to a 3-alkenyl pyrrolidine. An unprecedented SN2′ reaction involving phenyllithium as nucleophile and an ammonium as leaving group was observed in one case. 相似文献
89.
Braekers D Peters C Bogdan A Rudzevich Y Böhmer V Desreux JF 《The Journal of organic chemistry》2008,73(2):701-706
Calix[4]arenes substituted by four urea functions are self-complementary molecules that spontaneously combine in apolar solvents in the presence of an ammonium salt to form dimeric capsules held together by a belt of hydrogen bonds. In the presence of tetraethylammonium salts, the Et4N+ cation is included as a guest. The sorting between dimeric capsules formed in a mixture of calix[4]arenes directly depends on the steric crowding of the substituents grafted on the urea groups whether aromatic derivatives or aliphatic chains linking urea functions in mono-, di-, or tetraloop structures. Simple rules allow one to anticipate which capsules will be exclusively formed when calix[4]arenes are mixed in different proportions. The stabilization of the dimeric structures by hydrogen bonds is thwarted by the overlaps of aliphatic loops and/or by bulky groups that cannot pass through these loops. Despite the structural similarity of the calixarenes, the exclusive formation of dimers of well-defined compositions and clear titration breaks are observed by electrospray mass spectrometry. This technique yields reliable information on stoichiometries and composition despite measurements in the gas phase rather than in solution and it does not suffer from excessive peak overlaps in contrast with NMR. 相似文献
90.
Ji Min Kim Loc Nguyen Mary Frances Barr Michael Morabito Damien Stringer J. Helen Fitton Kelly A. Mowery 《Analytica chimica acta》2015
The use of polyanion and polycation-sensitive membrane electrodes to detect five different preparations of fucoidan is described. Unlike linear polyanionic molecules previously measured with polymer membrane-based electrochemical sensors, fucoidans from marine brown algae are all highly branched, sulfated polysaccharides with varying charge densities and structures, depending on the species of seaweed, method of extraction used and extent of purification. When tridodecylmethylammonium (TDMA) was used as the ion-exchanger, a large, non-equilibrium EMF response was observed over a concentration range of 0.5–50 μg mL−1 fucoidan. Fucoidan was also measured by titration with polycationic protamine, using a dinonylnaphthalene sulfonate (DNNS)-doped membrane electrode as the potentiometric endpoint detector. Potentiometric titration was used to determine the binding ratio between protamine and fucoidan at the neutralization endpoint for each fucoidan preparation. This binding ratio was then used to successfully determine the fucoidan content of commercially available nutritional supplements. Fucoidan was also measured in undiluted blood serum, demonstrating that this method may be applicable for measuring fucoidan for clinical applications. 相似文献