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991.
用新分离的巨大芽孢杆菌对映选择性水解缩水甘油苯基醚 总被引:1,自引:0,他引:1
Microbial epoxide hydrolases from bacterial and fungal sources?1? are hi ghly versatile catalysts for the asymmetric hydrolysis of chiral epoxides which are extensively employed as useful building blocks for the synthesis of various biologically active products in the pharmaceutical and agrochemical industries. Microorganism means allows an unlimited supply of these enzymes for preparative -scale applications. Phenyl glycidyl ether (PGE), an aryl epoxide, is a potenti ally useful compound in the synthesis of chiral amino alcohols and bioactive com pounds such as ?blockers. No suitable biocatalyst with sufficiently high enan tioselectivity (E?20) for the kinetic resolution of this compound was previ ously found among bacteria and fungi. This prompted us to screen epoxide hydrola se-producing microorganisms with higher enantioselectivity toward phenyl glycid yl ether from soil samples. 相似文献
992.
优化得到了碱基腺嘌呤、胸腺嘧啶、尿嘧啶、鸟嘌呤及胞嘧啶与甘氨酸二肽分子形成的28个氢键复合物的稳定结构并计算了结合能, 探讨了五种碱基与甘氨酸二肽分子间氢键作用的最佳位点. 本文研究发现: 每种碱基均可以通过不同位点与二肽分子形成氢键复合物, 腺嘌呤、胸腺嘧啶、尿嘧啶、鸟嘌呤及胞嘧啶分别最倾向使用A3、T1、U1、G3及C1位点与甘氨酸二肽分子形成氢键复合物; 碱基分子某位点的质子化反应焓变越负所形成的氢键复合物越稳定, 去质子化反应焓变越小所形成的氢键复合物越稳定; 由氢键复合物的结合能计算得到的稳定性次序与由碱基分子质子化和去质子化反应焓变推得的稳定性次序一致. 相似文献
993.
综述了近十年来,金鸡纳碱、硫脲、手性离子液体、季铵盐、脯氨酸和葡萄糖类衍生物等有机小分子在催化查尔酮的不对称Michael加成反应中的应用.有机小分子催化的机理大部分都是通过氢键、离子键等与底物相互作用而使其有较好的对映选择性. 相似文献
994.
995.
Varvara A. Drozd Roman V. Ottenbacher Konstantin P. Bryliakov 《Molecules (Basel, Switzerland)》2022,27(8)
Asymmetric epoxidation of a series of olefinic substrates with sodium percarbonate oxidant in the presence of homogeneous catalysts based on Mn complexes with bis-amino-bis-pyridine ligands is reported. Sodium percarbonate is a readily available and environmentally benign oxidant that is studied in these reactions for the first time. The epoxidation proceeded with good to high yields (up to 100%) and high enantioselectivities (up to 99% ee) using as low as 0.2 mol. % catalyst loadings. The epoxidation protocol is suitable for various types of substrates, including unfunctionalized alkenes, α,β-unsaturated ketones, esters (cis- and trans-), and amides (cis- and trans-). The reaction mechanism is discussed. 相似文献
996.
Lihi Habaz Korey Bedard Mitchell Smith Liqin Du Alexander Kornienko Tomas Hudlicky 《Molecules (Basel, Switzerland)》2022,27(12)
A 15-step chemoenzymatic total synthesis of C-1 methoxycarbonyl narciclasine (10) was accomplished. The synthesis began with the toluene dioxygenase-mediated dihydroxylation of ortho-dibromobenzene to provide the corresponding cis-dihydrodiol (12) as a single enantiomer. Further key steps included a nitroso Diels–Alder reaction and an intramolecular Heck cyclization. The C-1 homolog 10 was tested and evaluated for antiproliferative activity against natural narciclasine (1) as the positive control. Experimental and spectral data are reported for all novel compounds. 相似文献
997.
二溴对甲基偶氮羧质子化及其离解 总被引:1,自引:0,他引:1
用萃取法对二溴对甲基偶氮羧进行了纯化,并用分光光度法研究了二溴对甲基偶氮羧的质子化和五级离解作用,测定了其质子化常数和逐级离解常数,获得满意的效果。 相似文献
998.
A. Z. Kreindlin P. V. Petrovskii I. G. Barakovskaya L. M. Epstein E. S. Shubina M. I. Rybinskaya 《Russian Chemical Bulletin》1999,48(1):179-182
Previously unknown μ-acyl osmium clusters containing simultaneously permethyl-metallocenyl and Os3 cluster fragments were synthesized. The IR, UV, NMR (1H and13C), and FAB-MS spectra were examined. Protonation of the clusters proceeds at the metal atom of the metallocenyl fragment.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 180–183, January, 1999. 相似文献
999.
N. D. Strekal' V. F. Oskirko G. A. Gachko L. N. Kivach S. A. Maskevich 《Journal of Applied Spectroscopy》1999,66(5):701-707
An investigation of giant RS spectra of a thiamine (vitamin B1) molecule adsorbed on the surface of an anodized silver electrode from weak-concentration aqueous solutions is made. The
dependences of the spectral bands sensitive to the ionic state of the adsorbed molecule on the pH and the electrode potential
are discussed. It is shown that the rate constant of thiamine protonation in the adsorbed layer depends on the electrode potential
and is substantially lower than the corresponding value for the solution. In conformity with the important role of short-range
mechanisms of enhancement of electrochemical GRS in the excitation wavelength range investigated, models of the structural-conformational
states of the molecule in the adsorbed state are constructed and a conclusion is drawn about the possibility of monitoring
the acid-base equilibrium of these states for a molecular layer of thiamine under the conditions of an electrochemical cell.
To whom correspondence should be addressed.
Ya. Kupala Grodno State University, 22, Ozheshko Str., Grodno, 230023, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 66, No. 5, pp. 622–626, September–October, 1999. 相似文献
1000.
A new class of chiral pyrrolidine ligands have been successfully synthesized and their chiral induction abilities have been examined in the homogeneous catalytic enantioselective cyclo-propanation of styrene. 15-30% enantiomeric excess ( ee) has been achieved. 相似文献