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991.
Three new purine derivatives, namely, 4-caryboxy-5,6-dihydro-4H,8H-pyrimido[1,2,3-cd]purine-8,10(9H)-dione (1), 7,9-dihydro-1-(3-oxobutyl)-1H-purine-6,8-dione (2), and 7-hydro-9-(3-oxobutyl)-1H-purine-6,8-dione (3) together with six known purine and pyrimidine derivatives were isolated from the EtOH/CH(2)Cl(2) extracts of the South China Sea gorgonian Subergorgia suberosa. The structures of 1-3 were determined on the bases of extensive spectroscopic analysis, including 1D and 2D NMR data. 相似文献
992.
Jing‐Yi JIN Shou‐Feng WANG Wei XUAN Ji‐Wen SHENG Si‐Hong WANG Guan‐Rong TIAN 《中国化学》2008,26(1):153-157
Both enantiomers of 2‐benzyl‐5‐bromo‐4‐oxopentanoic acid were prepared utilizing the diazo ketones as the key intermediates. The compounds were assayed for inhibitory activity against carboxypeptidase A (CPA, EC 3.4.17.1). The (R)‐form is 260‐fold more potent than the corresponding (S)‐form. The finding that (R)‐form, which belongs to the L‐series, is mostly responsible for the inhibitory activity accords with the substrate specificity of CPA. For comparison, both the optical forms of 2‐benzyl‐4‐oxopentanoic acid were also synthesized and evaluated as the inhibitors against CPA. These results reveal that the introduction of a bromo group at the α‐position of ketones can significantly enhance the electrophilicity of the carbonyl group. Further molecular docking study suggested that the gem‐diol form of the α‐bromo ketone, which mimics the transition state in the CPA catalytic process, could chelate the zinc ion in the active site of CPA and thus result in the strong inhibition. 相似文献
993.
994.
Xiang Wen Kong a Yi Hua Zhang a Li Dai b Hui Ji b Yi Sheng Lai a Si Xun Peng a a Center of Drug Discovery China Pharmaceutical University Nanjing China b Department of Pharmacology China Pharmaceutical University Nanjing China 《中国化学快报》2008,19(2):149-152
A series of novel nitric oxide-donating sixalkoxyl biphenyl derivatives (14a-1) were synthesized by coupling furoxan with alkoxyl biphenyl skeleton using amino acids as the spacers, and their cytotoxicity against HepG2 cells in vitro were evaluated by MTT method. It was found that 14c, 14d, 14f, 14i, 14j and 14k showed more potent cytotoxic activities than control 5-fluorouracil. NO release assay of target compounds indicated that the maximum amount of NO released by most active compounds 14c and 14j was about 6 × 10^-2 μmol/L, whereas 14a and 14h with very weak activity only released NO of 1 × 10^-2 μmol/L. 相似文献
995.
Si Guo Yuan Shao Hui Zhang Wei Hua Zou Yong Hao Zhou Xiao Hui Zhou 《中国化学快报》2008,19(5):611-614
A kind of pseudo-hypercrosslinked polymer resin was firstly synthesized via a continuous Friedel-Crafts alkylation poly- merization of benzene, diphenyl and their dichloromethyl derivatives. And the micromorphology and adsorption properties of these resins were investigated. The results demonstrated that the novel resins have high-specific surface area (581.26-974.88 m^2/g), high- pore volume (0.56-1.65 mL/g), small average porous radius (1.93-3.67 nm) and excellent adsorption properties for small non-polar organic molecules. 相似文献
996.
α-{3-[2-hydroxy-3-(N-methyl-N-hydroxyethylamino)propoxy]propyl}-ω-butylpolydimethylsiloxanes Ⅲ with various moleculax weights were prepared by epoxy addition of α-[3-(2,3-epoxy-propoxy)propyl]-ω-butylpolydimethylsiloxanes Ⅱ and Nmethylmonoethanolamine.At each step.the outcome compounds were characterized through FT-IR and NMR spectra,the results showed that each step was successfully carried out and objective products were achieved. 相似文献
997.
Tun Hai Xu Gang Lv Tong Hua Liu Ya Juan Xu Yun Shan Si Sheng Xu Xie Hong Feng Zhao Dong Han Dong Ming Xu 《中国化学快报》2008,19(7):817-820
A new tdterpenoid glycoside, 3-β-O-β-D-glucopyranosyl presenegenin 28-O-α-L-arabipyranosyl(1 → 3)-6-β- xylopyranosyl(1 → 4)-[β-D-apiofuranosyl(1 → 3)]-Ct-L-rhamnopyranosyl(1 → 2)-[α-L-rhamnopyranosyl(1 → 3)]-β-D-fucopyranosyl ester (1) was isolated from the Polygala tenuifolia Willd., together with two known saponins, including polygalasaponinXXIV (2) and polygalasaponinXXVIII (3). The structure of new compound was elucidated by spectroscopic methods. 相似文献
998.
A poset is order-scattered if it does not embed the chain η of the rational numbers. We prove that there are eleven posets such that N(P), the MacNeille completion of P, is order-scattered if and only if P embeds none of these posets. Moreover these posets are pairwise non-embeddable in each other. This result completes a previous characterisation due to Duffus, Pouzet, Rival [4]. The proof is based on the “bracket relation”:
a famous result of F. Galvin.Dedicated to the memory of Ivan Rival.Received June 16, 2004; accepted in final form October 3, 2004.This revised version was published online in August 2005 with a corrected cover date. 相似文献
999.
Nanostructured scandium hydrous oxides were hydrothermally synthesized at 180 degrees C for 18 h, using NaOH, NH(4)OH, and KOH as the bases. They were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption, thermogravimetry and differential thermal analysis (TG-DTA), infrared and Raman spectroscopy, and pyridine adsorption. XRD and TEM measurements showed that the nature and concentration of the bases played key roles in determining the phasic composition, texture behavior (shape and size), and surface chemistry of the hydrothermal products. In addition, the shape evolution of the crystalline products seemed to be closely connected with their crystal structures. As the basicity value was raised from pH 10 to 5 mol L(-1) NaOH (or KOH), alpha-ScOOH nanorods, alpha-ScOOH nanosized hexagonal-like plates, and cubic Sc(OH)3 cubes/cuboids in micrometer size were produced in turn; while within pH 10-12 using NH4OH, gamma-ScOOH nanosized lozenge-like plates were mainly obtained. According to XRD, TEM, and TG-DTA results, all the as-prepared nanostructured ScOOH and micrometric Sc(OH)3 could be converted to cubic Sc2O3 with sustained crystalline shape via calcination at 500 degrees C. Pyridine adsorption revealed the existence of Lewis acid sites on the surfaces of the nanostructured alpha-ScOOH samples and some of their Sc2O3 counterparts calcined at 700 degrees C. The alpha-ScOOH nanorod sample displayed the strongest Lewis acidity among all the samples tested, due to its highest surface area as determined by N2 adsorption. Finally, an olation-oxolation process based on a dissolution/recrystallization mechanism accounts for the formation of various ScOOH polymorphs and Sc(OH)3 with different shapes. 相似文献
1000.
Ubiquitin (Ub) chain isopeptide bond mimics are useful molecules for biochemical and biophysical studies. Herein, we report the semi-synthesis of the disulfide-linked K11/K48-branched tri-Ub (Ub311/48(S–S)), the first example of an isopeptide mimic for the branched Ub chains, which have recently emerged as an interesting category of Ub modifications. Our strategy comprised the E1-dependent synthesis of the Ub conjugate of aminoethanethiol, followed by disulfide formation with Ub(K11C, K48C). The structure of the synthetic isopeptide bond mimics was verified by the crystal structure of Ub311/48(S–S). Deubiquitination and pulldown assays indicated that the synthetic Ub311/48(S–S) could be hydrolyzed by linkage-specific deubiquitinases (K11-specific Cezanne and K48-specific OTUB1), and recognized by proteasomal ubiquitin receptor S5a. 相似文献