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991.
Fan Zhang 《Tetrahedron》2009,65(1):83-8937
The carbonyl allylation of methyl trifluoropyruvate (MeTFP) with activated alkenes has been investigated in detail using organic bases as catalysts. Organic bases, such as DMAP, Et3N, DABCO, NMM, Et2NH, and quinine, could deprotonate the allylic hydrogen of activated alkenes and furnish nucleophilic species to undergo the addition reaction with methyl trifluoropyruvate and afford versatile homoallylic alcohols with CF3 group in excellent yields. The 19F NMR monitoring indicated that the isomerization induced by base gave two separable diastereoisomers in an equilibrium ratio of 1:3. The relative configuration of hydroxy and the neighboring alkyl group in the major diastereoisomer was determined as syn-configuration by X-ray diffraction analysis. 相似文献
992.
993.
双水相手性萃取拆分扁桃酸外消旋体 总被引:2,自引:0,他引:2
研究了扁桃酸(MA)对映体在含β-环糊精(β-CD)手性选择剂的聚乙二醇(PEG)/(NH_4)_2SO_4双水相体系中的萃取分配行为.考察了pH、PEG和(NH_4)_2SO_4的质量分数、β-CD的浓度、MA的浓度与萃取温度等因素对拆分效果的影响.实验结果表明:双水相手性萃取具有很强的手性分离能力,β-CD对L-MA对映体的识别能力大于对D-MA对映体的识别能力;当温度为30℃、pH=1.0、PEG2000质量分数为30%、(NH_4)_2SO_4质量分数为20%、β-CD的浓度为0.008 mol/L、扁桃酸的浓度为0.05 mol/L时,分离因子(α)达到2.46,上、下相对映体过剩值(e.e.%)分别为42.13%和40.43%. 相似文献
994.
Peng Liu Xiaoli Sun Wei He Ru Jiang Pingan Wang Yan Zhao Shengyong Zhang 《Journal of separation science》2009,32(1):125-134
This paper describes an improved access to mono‐6A‐aminoethylamino‐β‐CD (β‐CDen), a very efficient cationic chiral selector for CZE in the separation of eight chiral aromatic vicinal diols. The β‐CDen concentration has a strong influence on the efficiency of enantioseparation. The effects of the pH and concentration of the BGE, the capillary temperature, and the applied voltage on the resolution and separation selectivity have been studied. Excellent chiral resolution was achieved under the optimal conditions of β‐CDen 10 mM, pH 10, 200 mM borate buffer at 15 kV and 20°C within 20 min. Moreover, the developed method was successfully applied to the determination of the enantiomeric purity of the catalytic asymmetric dihydroxylation (AD) reaction products. 相似文献
995.
Emmanuelle Lipka Julie Charton Marie‐Pierre Vaccher Marcia Folly‐Klan Jean‐Paul Bonte Claude Vaccher 《Journal of separation science》2009,32(11):1907-1915
Baseline separation of 18 new substituted benzimidazole derivatives, potent AMP‐activated protein kinase (AMPK) activators, with one chiral center, was achieved by CD‐EKC using sulfated and highly sulfated CDs (SCDs and HS‐CDs) as chiral selectors. The influence of the type and concentration of the chiral selectors on the enantioseparations was investigated. The SCDs exhibit a very high enantioselectivity power since they allow excellent enantiomeric resolutions compared to those obtained with the neutral CDs. The enantiomers were resolved with analysis times around 6 min using 25 mM phosphate buffer at pH 2.5 containing either β‐S‐CD, HS‐β‐CD, HS‐γ‐CD (3 or 4% w/v) at 25°C, with a voltage of 20 kV. The apparent association constants of the inclusion complexes were calculated. The study of the solute structure‐enantioseparation relationships seems to show the high contribution of the interactions between the solutes phenyl ring and the CDs to the enantiorecognition process. The optimized method was briefly validated (LOD less than 1%) and the purity of enantiomers of compound 3 was determined. The enantiomer migration shows reversal order depending on the kind of CD. 相似文献
996.
Shabi Abbas Zaidi Kyoung Moon Han Sung Soon Kim Dong Guk Hwang Won Jo Cheong 《Journal of separation science》2009,32(7):996-1001
An open tubular molecule imprinted polymer (OT‐MIP) capillary column has been prepared for chiral separation of ofloxacin enantiomers in CEC. The S‐ofloxacin imprinted OT column was fabricated by thermally initiated non‐covalent polymerization procedure inside a pretreated and silanized fused silica capillary. The template molecule was incorporated with methacrylic acid (MAA), ethylene glycol dimethacrylate (EDMA) and 4‐styrenesulfonic acid (4‐SSA) and dissolved in a porogen mixture of ACN/2‐propanol (9:1). The separation efficiency of the 4‐SSA MIP column was found quite better than that of the MIP column without 4‐SSA. It has been demonstrated that our OT‐MIP column can separate ofloxacin enantiomers with excellent chiral separation efficiency after tuning the various chromatographic conditions. The optimized chromatographic eluent was 85:15, v/v%, ACN/60 mM sodium acetate at pH 7. The separation efficiency and selectivity of chiral separation of this study were far better than those obtained by previous methods for chiral separation of R‐ and S‐ofloxacin. 相似文献
997.
A rapid and effective method was developed for the chiral separation of raltitrexed (RD) enantiomers by carboxymethyl-beta-cyclodextrin
(CM-β-CD)-modified micellar electrokinetic chromatography (MEKC). Optimization of conditions including the type and concentration
of the chiral selector, concentration of sodium dodecyl sulfate (SDS), pH and concentration of the background electrolyte
(BGE), capillary temperature, and applied voltage was investigated. The enantiomers of raltitrexed could be separated with
satisfactory resolution and linear response by using 75 mM Tris-phosphate at pH 8.0 containing 30 mM SDS and 8 mM CM-β-CD
as buffer system. Furthermore, the usefulness of this method was demonstrated in a purity test of a real synthetic drug sample.
Figure Chiral separation of raltitrexed by CM-β-CD MEKC was optimized and applied to test the purity of a synthetic drug sample 相似文献
998.
Modeling of retention of adrenoreceptor agonists and antagonists on polar stationary phases in hydrophilic interaction chromatography: a review 总被引:1,自引:0,他引:1
Retention prediction models for reversed-phase liquid chromatography (RPLC) have been extensively studied owing to the fact
that RPLC remains the most widely used chromatographic technique especially in the field of pharmaceutical and biomedical
analyses. However, RPLC is not always the method of choice for the analysis of some compounds that have high polarity. Hydrophilic
interaction chromatography (HILIC) has been gaining interest in the last few years as an alternative option to RPLC for the
analysis of polar and hydrophilic analytes. HILIC is a variant of normal-phase liquid chromatography, but utilizes water in
a water-miscible organic solvent as the eluent in conjunction with a hydrophilic stationary phase. The present review aims
to summarize recent contributions on the development of retention prediction models for a group of basic analytes, namely,
the adrenoreceptor agonists and antagonists, on different polar stationary phases. The use of multiple linear regression and
artificial neural networks in model building is highlighted. 相似文献
999.
Ruthenium acts as a good catalyst for the racemization reaction of secondary alcohols and amines. Ruthenium-catalyzed racemization is coupled with enzymatic kinetic resolution to prepare chiral compounds in 100% theoretical yield. Ten ruthenium complexes (1–10) act as a good catalyst the for racemization reaction and are also compatible with DKR process. Two other ruthenium complexes [RuCl2(PPh3)3] and [Cp*RuCl(COD)] are active for racemization reaction but their successful compatibility with DKR has not yet been reported. Ru/γ-Al2O3 and Ru–HAP are the heterogeneous catalysts used for the racemization reaction. They have also not been employed for DKR process. Polymer supported ruthenium is employed as a reusable racemization catalyst for aerobic DKR of alcohols. 相似文献
1000.
We wished to prepare planar chiral compounds by the lithiation of acetal 2-ferrocenyl-(4S,5S)-bis(methoxymethyl)-1,3-dioxolane (1) with butyllithium followed by the reaction with an electrophile. However, the desired products were not observed and two unexpected products, 1-ferrocenyl-1-pentanol (4) of the nucleophilic attack product and 2-ferrocenyl-4,5-dimethylene-1,3-dioxolane (5) of the proton abstraction product, were isolated. Because the nucleophilic attack on acetal carbon is rarely reported so far and both products 4 and 5 may have some potential uses in organic synthesis, these unexpected reactions are investigated in detail. The mechanisms of these reactions are discussed. 相似文献