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71.
The Liebeskind-Srogl coupling/intramolecular Diels-Alder (IMDA) reaction cascade that stereoselectively affords a tricarbocyclic compound with a trans–trans-cis fused ring system including an all-carbon quaternary stereogenic center at the ring junction is described. The cascade reactions proceed quickly and stereoselectively afford the products within 2?h at room temperature in the presence of a suitable thioester. The developed protocol as well as the prepared chiral compounds are useful for the enantioselective total synthesis of terpenoids with the trans–trans-cis fused ring system. 相似文献
72.
Nanami Hara Shu Fujisawa Mizuki Fujita Mikako Miyazawa Kazuma Ochiai Satoshi Katsuda Tetsuya Fujimoto 《Tetrahedron》2018,74(2):296-302
Kinetic resolution of secondary alcohols by benzoylation using a phosphinite derivative of (1S,2R)-1-amino-2-indanol as the catalyst was investigated. The aminophosphinite catalyst is effective for the kinetic resolution of aryl cycloalkyl carbinols with a small number of examples for organocatalytic kinetic resolution to achieve resolution with s = up to 44. Although the benzoylation of phenylalkanols proceeded with a low selectivity, 1-arylalkanols bearing at least one substituent at the ortho position on the benzene ring or a branched alkyl group on the carbinol carbon were resolved with acceptable selectivity. 相似文献
73.
The complexes [NaphAu(PPh(3))], and [mu-Naph{Au(PPh(3))}(2)]ClO(4), having the Au-C (aromatic) bond have been synthesized and characterized. The unique structure of with two gold atoms bridged by a naphthyl group has been determined by X-ray crystallography. The intramolecular Au-Au separation in is 2.7731(4) A. Upon excitation at 266 nm, both complexes display intraligand phosphorescence at room temperature in solution and in solid state. 相似文献
74.
A novel extraction procedure for stir bar sorptive extraction (SBSE) termed sequential SBSE was developed. Compared to conventional SBSE, sequential SBSE provides more uniform enrichment over the entire polarity/volatility range for organic pollutants at ultra-trace levels in water. Sequential SBSE consists of a SBSE performed sequentially on a 5-mL sample first without modifier using one stir bar, then on the same sample after addition of 30% NaCl using a second stir bar. The first extraction with unmodified sample is mainly targeting solutes with high Kow (logKow>4.0), the second extraction with modified sample solution (containing 30% NaCl) is targeting solutes with low and medium Kow (logKow<4.0). After extraction the two stir bars are placed in a single glass desorption liner and are simultaneously desorbed. The desorbed compounds were analyzed by thermal desorption and gas chromatography-mass spectrometry (TD-GC-MS). Recovery of model compounds consisting of 80 pesticides (organochlorine, carbamate, organophosphorus, pyrethroid, and others) for sequential SBSE was evaluated as a function of logKow (1.70-8.35). The recovery using sequential SBSE was compared with those of conventional SBSE with or without salt addition (30% NaCl). The sequential approach provided very good recovery in the range of 82-113% for most of the solutes, and recovery less than 80% for only five solutes with low Kow (logKow<2.5), while conventional approaches (with or without salt addition) showed less than 80% recovery for 23 and 41 solutes, respectively. The method showed good linearity (r2>0.9900) and high sensitivity (limit of detection: <10ngL(-1)) for most of the model compounds even with the scan mode in the MS. The method was successfully applied to screening of pesticides at ngL(-1) level in river water samples. 相似文献
75.
Nagata M Kondo M Suemori Y Ochiai T Dewa T Ohtsuka T Nango M 《Colloids and surfaces. B, Biointerfaces》2008,64(1):16-21
Dialkyl disulfide-linked naphthoquinone, (NQ-Cn-S)2, and anthraquinone, (AQ-Cn-S)2, derivatives with different spacer alkyl chains (Cn: n = 2, 6, 12) were synthesized and these quinone derivatives were self-assembled on a gold electrode. The formation of self-assembled monolayers (SAMs) of these derivatives on a gold electrode was confirmed by infrared reflection-absorption spectroscopy (IR-RAS). Electron transfer between the derivatives and the gold electrode was studied by cyclic voltammetry. On the cyclic voltammogram a reversible redox reaction between quinone (Q) and hydroquinone (QH2) was clearly observed under an aqueous condition. The formal potentials for NQ and AQ derivatives were −0.48 and −0.58 V, respectively, that did not depend on the spacer length. The oxidation and reduction peak currents were strongly dependent on the spacer alkyl chain length. The redox behavior of quinone derivatives depended on the pH condition of the buffer solution. The pH dependence was in agreement with a theoretical value of E1/2 (mV) = E′ − 59pH for 2H+/2e− process in the pH range 3–11. In the range higher than pH 11, the value was estimated with E1/2 (mV) = E′ − 30pH , which may correspond to H+/2e− process. The tunneling barrier coefficients (β) for NQ and AQ SAMs were determined to be 0.12 and 0.73 per methylene group (CH2), respectively. Comparison of the structures and the alkyl chain length of quinones derivatives on these electron transfers on the electrode is made. 相似文献
76.
Cyclopolymerization of a bis-methacrylate monomer derived from trans-cyclohexanediol and 2-methacryloyloxyethyl isocyanate proceeded through 19-membered ring formation. The unusual large ring formation originated from the designed steric regulation by the cyclohexane ring and the hydrogen bonds. The RAFT polymerization employing cumyl dithiobenzoate attained controlled polymerization, which supported the quantitative cyclization. 相似文献
77.
A Tin Analogue of Carbenoid: Isolation and Reactivity of a Lithium Bis(imidazolin‐2‐imino)stannylenoid
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Tatsumi Ochiai Dr. Daniel Franz Dr. Xiao‐Nan Wu Dr. Elisabeth Irran Prof. Dr. Shigeyoshi Inoue 《Angewandte Chemie (International ed. in English)》2016,55(24):6983-6987
The lithium bis(imino)stannylenoid (NIPr)2Sn(Li)Cl ( 1 ; NIPr=bis(2,6‐diisopropylphenyl)imidazolin‐2‐imino) was prepared by the reaction of LiNIPr with 0.5 equiv of SnCl2?diox (diox=1,4‐dioxane) and the ambiphilic character of the compound was demonstrated by investigations into its reactivity. Treatment of 1 with I2 or MeI yielded the oxidative addition products (NIPr)2SnI2 and (NIPr)2Sn(Me)I, respectively. In contrast, the reaction of 1 with one equivalent of Me3SiCl resulted in the formation of Me3SiNIPr and the chlorostannylene dimer [NIPrSnCl]2. Moreover, the substitution reaction of compound 1 with MeLi led to the formation of the methyl‐substituted stannate (NIPr)2Sn(Li)Me. 相似文献
78.
The mixed catalyst system, Pd(CH3CN)2Cl2/P(t-Bu)3/[Ru(2,2'-bipyridine)3].2PF6, promotes the copper-free Sonogashira coupling reaction of aryl bromides at room temperature under irradiation of visible light. 相似文献
79.
4-(Difluoroiodo)toluene-induced domino lambda(3)-iodanation-1,4-halogen shift-ring enlargement-fluorination reaction of 5-halopentynes with a four-, five-, or six-membered carbocycle afforded the ring-expanded (E)-delta-fluoro-beta-halovinyl-lambda3-iodanes stereoselectively in high yields, probably via the intermediacy of five-membered halonium ions. Use of internal alkynes makes it possible to synthesize tetrasubstituted beta-halovinyl-lambda(3)-iodanes with defined stereochemistry. 相似文献
80.
In this work, we first formulate the Tsallis entropy in the context of complex networks. We then propose a network construction whose topology maximizes the Tsallis entropy. The growing network model has two main ingredients: copy process and random attachment mechanism (C-R model). We show that the resulting degree distribution exactly agrees with the required degree distribution that maximizes the Tsallis entropy. We also provide another example of network model using a combination of preferential and random attachment mechanisms (P-R model) and compare it with the distribution of the Tsallis entropy. In this case, we show that by adequately identifying the exponent factor q, the degree distribution can also be written in the q-exponential form. Taken together, our findings suggest that both mechanisms, copy process and preferential attachment, play a key role for the realization of networks with maximum Tsallis entropy. Finally, we discuss the interpretation of q parameter of the Tsallis entropy in the context of complex networks. 相似文献