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511.
Conclusions 1. Peregrinol and two new diterpenoids—marrubiol and vulgarol—have been isolated from the plantMarrubium vulgare L. for the first time.2. The structure of marrubiol (I), which is possibly a biogenetic precursor of marrubiin, has been demonstrated.Khimiya Prirodnykh Soedinenii, Vol. 4, No. 6, pp. 345–348, 1968 相似文献
512.
Temperature-dependent c-axis resistivity measurements on stages 1–7 potassium-graphite compounds show a crossover from metallic to activated behaviour between stages 4 and 5, as well as the onset of a new type of anomaly for stage ≥4. KC8 shows in addition a tendency toward a metal-insulator transition below 40K. The high-stage transport process is discussed in terms of weak depletion of the interior layers by interlayer screening. We suggest that the high stage anomalies reflect an instability in the c-axis charge distribution. 相似文献
513.
A new cassane diterpenoid, caesaldecan, was isolated from Caesalpinia decapetala with eight known compounds, spathulenol, 4,5-epoxy-8(14)-caryophyllene, squalene, lupeol, trans-resveratrol, quercetin, astragalin, and stigmasterol. The (1)H- and (13)C-NMR spectra of the new compound were completely assigned by using a combination of 2D NMR techniques, namely, (1)H-(1)H COSY, HMQC, HMBC, and ROESY. 相似文献
514.
Andrzej Rykowski Danuta Branowska Mieczyslaw Makosza Phan Van Ly 《Journal of heterocyclic chemistry》1996,33(6):1567-1571
An efficient procedure for the preparation of 1,2,4-triazin-5-ylcarbaldehyde oximes 2a-f from 1,2,4-triazines 1a-f and nitromethide ion is described. The oximes 2c-d were converted into corresponding 5-cyano-1,2,4-triazines 6c-d . The latter compounds react easily with various nucleophiles to afford 5-substituted 1,2,4-triazines 7a-i and with 1-pyrrolidino-1-cyclohexene to form cyano derivative of 5,6,7,8-tetrahydroisoquinoline 9 . 相似文献
515.
516.
A novel class of 2-fluoro-6-O-propargyl-11,12-carbamate ketolide derivatives of erythromycin has been synthesized for antibacterial SAR studies. Replacement of the C2-hydrogen by a fluorine atom allows the synthesis of 6-O-propargylic ketones and electron-deficient 6-O-propargylic aromatic derivatives by preventing intramolecular C2-enolate Michael cyclization. 相似文献
517.
Hanessian S Papeo G Fettis K Therrien E Viet MT 《The Journal of organic chemistry》2004,69(15):4891-4899
A bicyclic indolizidinone carboxylic acid and a tricyclic constrained analogue of l-proline were synthesized and evaluated for their ability to induce helix formation as l-Ala tetrapeptides. Variable-temperature NMR, DMSO titration, CD spectra, and X-ray structure analyses, in conjunction with molecular modeling, confirmed the existence of 3(10)-helical motifs with di- and tetrapeptides of l-Ala. 相似文献
518.
The tris(tetra-n-butylammonium) salt of thiopyrophosphate 5 was prepared from trimethyl phosphate in four steps. Treatment of geranyl bromide with 5 gave an 80% yield of geranyl S-thiolodiphosphate (6). Thiolodiphosphate 6 is substantially less reactive than geranyl diphosphate (7) in the prenyl transfer reaction catalyzed by farnesyl diphosphate synthase and is a good inhibitor of the enzyme. 相似文献
519.
Thiolo thiophosphate analogues of isopentenyl diphosphate (IPP), dimethylallyl diphosphate (DMAPP), geranyl diphosphate (GPP), farnesyl diphosphate (FPP), and geranylgeranyl diphosphate (GGPP) were synthesized. Inorganic thiopyrophosphate (SPP(i)) was prepared from trimethyl phosphate in four steps. The tris(tetra-n-butylammonium) salt was then used to convert isopentenyl tosylate to (S)-isopentenyl thiodiphosphate (ISPP). (S)-Dimethylallyl (DMASPP), (S)-geranyl (GSPP), (S)-farnesyl (FSPP), and (S)-geranylgeranyl thiodiphosphate (GGSPP) were prepared from the corresponding bromides in a similar manner. ISPP and GSPP were substrates for avian farnesyl diphosphate synthase (FPPase). Incubation of the enzyme with ISPP and GPP gave FSPP, whereas incubation with IPP and GSPP gave FPP. GSPP was a substantially less reactive than GPP in the chain elongation reaction and was an excellent competitive inhibitor, K(I)(GSPP) = 24.8 microM, of the enzyme. Thus, when ISPP and DMAPP were incubated with FPPase, GSPP accumulated and was only slowly converted to FSPP. 相似文献
520.
Trong Nghia Ngo Nu Dan Phuong Nguyen Ngoc Thien Ly Nguyen Nguyen Kim Tuyen Pham Nhat Minh Phan Trong Dat Bui 《Natural product research》2020,34(13):1820-1826
AbstractFrom the leaves of Markhamia stipulata var. canaense V.S. Dang, one new phytosphingolipid, named markhasphingolipid A (6) together with five known compounds, 4’,7-O-dimethylapigenin (1), narigenin (2), tectoquinone (3), mollic acid (4), 1-hexadecanoyl-sn-glycerol (5) were classified by various chromatographic methods. Their structures were designated by IR, UV, HR-ESI-MS, HR-ESI-MS/MS and NMR experiments. All compounds were recognized for the first time from this species. The cytotoxicity of all n-hexane fractions and isolated compounds (5 & 6) against three human cancer cell lines (HeLa, HepG2, and MCF-7) were evaluated by SRB assay. All n-hexane fractions expressed cytotoxic effect on three tested cancer cell lines (at the concentration of 100?μg/mL, percent of cytotoxicity ranged from 55.81% to 95.83%) as well as compound 5 (IC50 ranged from 48.51 to 63.30?μM) whereas fraction H.I and compound 6 did not show activity. 相似文献