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991.
992.
993.
Young-Suk Noh Kwanpyo Lee Junghun Suh 《Journal of polymer science. Part A, Polymer chemistry》1999,37(21):3936-3942
The formation constant (Kf) for the uranyl complex of 2,2′-dihydroxyazobenzene (DHAB) was measured with DHAB attached to poly(ethylenimine) (DHAB-PEI) at pH 7.7 to 9.4. The value of Kf was estimated from the equilibrium constant for extraction of uranyl ion from the uranyl complex of DHAB-PEI (UO2DHAB-PEI) with carbonate ion, which in turn was measured from the absorbance change observed on addition of bicarbonate ion to the solution of UO2DHAB-PEI. At pH 8.0, the uranyl-binding ability of DHAB was enhanced by about 104 times on attachment of DHAB to PEI. The major origin of the increased ability of uranyl ion complexation is the basic local microenvironment of PEI, which encourages ionization of the phenol groups of DHAB. Various other possible origins are discussed also. The log Kf for DHAB-PEI at pH 8.0 indicates that DHAB moieties of DHAB-PEI are mostly occupied, whereas DHAB unattached to PEI is mostly unoccupied by uranyl ion under conditions of seawater when only the pH and concentrations of bicarbonate and uranyl ions of seawater are considered. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3936–3942, 1999 相似文献
994.
Dong Seok Kim Sang Chul Shim 《Journal of polymer science. Part A, Polymer chemistry》1999,37(13):2263-2273
Polymerization of o-, m-, and p-(dimethylsilyl)phenylacetylene by chloroplatinic acid-catalyzed hydrosilylation gave the corresponding poly(dimethylsilylenephenylenevinylene)s. The monomer reactivity and polymer structure were very much dependent upon the substituent position. Interesting optical behavior and thermal properties were observed which suggested the polymers to be useful as preceramic materials. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2263–2273, 1999 相似文献
995.
996.
Vinyl pivalate (VPi) was polymerized in bulk by ultraviolet-ray initiation at low temperatures using 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) and 2,2'-azobis(isobutyronitrile) (AIBN) as photoinitiators. High molecular weight (HMW) poly(vinyl pivalate) (PVPi), having a number-average degree of polymerization (Pn) of 13,000–28,000, was obtained at conversions below 30% and converted by saponification to a syndiotacticity-rich HMW poly(vinyl alcohol) (PVA) microfibrillar fiber with Pn of 7300–18,300, syndiotactic diad (S-diad) and triad contents of ∼ 64% and ∼ 39%, respectively, and crystal melting temperature (Tm) of ∼ 249°C. ADMVN gave higher Pn than AIBN. On the other hand, conversion was smaller with the former than with the latter, and it was found that the initiation rate of ADMVN was lower than that of AIBN. Pn of PVA was constant while Pn of the precursor PVPi increased with increasing conversion. The syndiotacticity, Tm and thermal stability of PVA obtained from PVPi were much superior to those of PVA derived from poly(vinyl acetate) prepared under the same polymerization conditions. Polymerization of VPi at lower temperatures gave PVA with higher syndiotacticity. © 1997 John Wiley & Sons, Inc. 相似文献
997.
Insup Noh Krishnan Chittur Steven L. Goodman Jeffrey A. Hubbell 《Journal of polymer science. Part A, Polymer chemistry》1997,35(8):1499-1514
Poly(tetrafluoroethylene) (PTFE) films were surface modified in a solution of benzophenone and sodium hydride in dry dimethylformamide by ultraviolet (UV) light irradiation. The extent of surface modification was characterized after durations of UV light irradiation from 5–20 min at temperatures from 19–60°C. The modified films were analyzed by electron spectroscopy for chemical analysis, diffuse reflectance ultraviolet-visible light spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, dynamic contact angle measurement, and low-voltage scanning electron microscopy. PTFE surfaces produced by this modification demonstrated extensive defluorination, oxygen incorporation, surface unsaturation, and reduction in both advancing and receding dynamic water contact angles in a manner that was more extensive at long durations of irradiation and at high temperatures. Morphological damage depended upon treatment conditions, but extensive surface modification could be obtained without substantial morphological damage to PTFE films. Control experiments indicated that the surface modification proceeded by photoexcitation of either diphenyl ketyl radical anion or benzhydrol anion, the products of reaction of benzophenone with sodium hydride. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1499–1514, 1997 相似文献
998.
Hong Ma Jingdong Luo Seok Ho Kang Sharon Wong Jae Wook Kang Alex K.‐Y. Jen Rick Barto Curtis W. Frank 《Macromolecular rapid communications》2004,25(19):1667-1673
Summary: A novel crosslinkable dendritic polymer has been synthesized by the thermal polymerization of peripheral aryl trifluorovinyl ether moieties of a highly fluorinated dendrimer. The resulting perfluorocyclobutane(PFCB)‐containing dendritic polymer exhibited excellent processability, low optical loss (0.36 dB · cm−1 at 1 310 nm with 1% dye doping), high thermal stability, and good solvent resistance for waveguide‐based photonic applications.
Structure of the crosslinkable fluorinated dendrimer synthesized. 相似文献
999.
Dong Seok Kim Min Chul Suh Sang Chul Shim 《Journal of polymer science. Part A, Polymer chemistry》1998,36(13):2275-2282
Poly[(methylsilylene)ethynylene] ( 1 ) and poly[2,5-thiophenediyl(methylsilylene)] ( 2 ) are prepared in good yields. Thermogravimetric analysis and differential scanning calorimetry indicate the Si H group to increase the pyrolysis residue yields. Gelation was achieved from polymer 1 to get improved preceramic materials. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2275–2282, 1998 相似文献
1000.
Monodisperse hydrogel beads composed of calcium alginate and crosslinked polyNIPAAm (N-isopropylacrylamide) were synthesized based on a simultaneous interpenetrating network process. With increasing the temperature above the phase transition temperature of polyNIPAAm, a core-shell type of hydrogel beads was developed; polyNIPAAm-enriched core region and Ca-alginate-enriched outer shell layer were observed. The thermally reversible formation of the core-shell double structure in the IPN hydrogel beads was applied for the temperature modulated drug release using indomethacin as a model drug. 相似文献