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91.
Fernando Godoy Alejandra Gómez A. Hugo Klahn 《Journal of organometallic chemistry》2010,695(3):346-4353
The fulvene complexes [(η6-C5Me4CH2)Re(CO)2(R)] (1a, RI; 1b, RC6F5) react at the exocyclic methylene carbon with a vinylmagnesium bromide solution to produce the anionic species [(η5-C5Me4CH2CHCH2)Re(CO)2(R)]−. Protonation with HCl at 0 °C produces the hydride complexes [trans-(η5-C5Me4CH2CHCH2)Re(CO)2(R)(H)] (2a, RI; 2b, RC6F5). Thermolysis of an hexane solution of the iodo-hydride (2a) under a CO atmosphere yields the complex [(η5-C5Me4CH2CHCH2)Re(CO)3] (3) and [Re(CO)5I] as by-product. Thermolysis of 2b produced three new products, mainly the chelated complex [(η5:η2-C5Me4CH2CHCH2)Re(CO)2] (4) and complex 3, with a non-coordinated olefin group, in moderated yield, and traces of [Re(CO)5(C6F5)]. Thermolysis of an hexane solution of 2 in presence of an excess of PMe3, afforded the phosphine derivative [(η5-C5Me4CH2CHCH2)Re(CO)2(PMe3)] (5). All the complexes were characterized by IR, 1H, 13C and 31P NMR spectroscopies and mass spectrometry. The molecular structure of 4 has also been determined. The molecule exhibits a formal three-legged piano-stool structure, with two CO groups, and the third position corresponding to the η2-coordination of the propenyl side arm of the η5-C5Me4 ring. 相似文献
92.
ZHOU ShanShi HU XiaoGong WU Bin LIU Li QU WeiJing GUO Rui HE Feng CAO YueLing Wu XiaoLi ZHU LingFeng SHI Xin & TAN HongLi Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai China Graduate University of Chinese Academy of Sciences Beijing Beijing Global Information Application Development Center Beijing 《中国科学:物理学 力学 天文学(英文版)》2011,(6)
Aiming at regional services,the space segment of COMPASS (Phase I) satellite navigation system is a constellation of Geostationary Earth Orbit (GEO),Inclined Geostationary Earth Orbit (IGSO) and Medium Earth Orbit (MEO) satellites.Precise orbit determination (POD) for the satellites is limited by the geographic distribution of regional tracking stations.Independent time synchronization (TS) system is developed to supplement the regional tracking network,and satellite clock errors and orbit data may be obtai... 相似文献
93.
94.
The Miller–Tucker–Zemlin (MTZ) Subtour Elimination Constraints (SECs) and the improved version by Desrochers and Laporte (DL) have been and are still in regular use to model a variety of routing problems. This paper presents a systematic way of deriving inequalities that are more complicated than the MTZ and DL inequalities and that, in a certain way, “generalize” the underlying idea of the original inequalities. We present a polyhedral approach that studies and analyses the convex hull of feasible sets for small dimensions. This approach allows us to generate generalizations of the MTZ and DL inequalities, which are “good” in the sense that they define facets of these small polyhedra. It is well known that DL inequalities imply a subset of Dantzig–Fulkerson–Johnson (DFJ) SECs for two-node subsets. Through the approach presented, we describe a generalization of these inequalities which imply DFJ SECs for three-node subsets and show that generalizations for larger subsets are unlikely to exist. Our study presents a similar analysis with generalizations of MTZ inequalities and their relation with the lifted circuit inequalities for three node subsets. 相似文献
95.
A number of novel acid-sensitive Schiff bases derived from p-aminobenzyl alcohol and various benzaldehyde derivatives were synthesized and were subsequently shown to trigger benzyl elimination reactions. The kinetics of acid-catalyzed hydrolysis at pH 5.0 as well as stability at pH 7.4 were studied using fluorogenic model compounds. Two fluoro-substituted Schiff bases showed efficient hydrolysis at pH 5.0 combined with a long-term stability at pH 7.4 and are considered suitable candidates for the development of anticancer prodrugs. 相似文献
96.
Xiang Zhang 《International journal of quantum chemistry》2010,110(10):1880-1889
The density function theory (DFT) is to elucidate the electronic structure of bis(dinitrogen) Fe(0) complex, (CNC)Fe_2N2, and its N2 elimination mechanism. (CNC)Fe_2N2 has a low‐spin singlet (S = 0) ground state with a distorted square pyramidal structure. Fragment orbital interaction analysis yields total occupancy of π* orbitals (LUF(4)O and LUF(4)O−1) of apical N3 N4 is 0.188 while that of basal N1 N2 is 0.187 in S0(CNC)Fe_2N2, suggesting nearly the same activation extent for both basal and apical N2 ligands. The lowest‐lying triplet state T1 (3‐A′) has a repulsive potential energy surface along the Fe N3 bong length by PBE functional, while a minimum on T2 state (3‐A″) with higher energy is found by B3LYP functional. The nonadiabatic N2 elimination mechanism of (CNC)Fe_2N2 involves an S0‐T1 states crossing, which lowers the activation energy to 9.7 kcal/mol and produces high‐spin intermediate (CNC)Fe N2. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
97.
98.
The problem of solving large M-matrix linear systems with sparse coefficient matrix in block Hessenberg form is here addressed. In previous work of the authors a divide-and-conquer strategy was proposed and a backward error analysis of the resulting algorithm was presented showing its effectiveness for the solution of computational problems of queueing theory and Markov chains. In particular, it was shown that for block Hessenberg M-matrices the algorithm is weakly backward stable in the sense that the computed solution is the exact solution of a nearby linear system, where the norm of the perturbation is proportional to the condition number of the coefficient matrix. In this note a better error estimate is given by showing that for block Hessenberg M-matrices the algorithm is even backward stable. 相似文献
99.
基于多项式组主项解耦消元法 ,将几何定理的假设条件 (多项式组 PS)化为主项只含主变元的三角型多项式组 DTS,可得到定理命题成立的不含变元的非退化条件 ,即充分必要或更接近充分必要的非退化条件 .由于多项式主系数不含变元 ,已不存在 DTS多项式之间的约化问题 ,故方法有普遍意义 .文中例为西姆松定理的机器证明 . 相似文献
100.
Methyl (8R,13S)-8α,13:13,17-diepoxy-14,15-dinorlabdane-19-oate, easily prepared from communic acids, is a suitable intermediate for synthesizing pentacyclic quassinoids, because it enables the elaboration of the A ring and the further construction of the B-C-D ring system of these terpenoids. The cetal group is stable under the reaction conditions utilized during the elimination of the ester group and the introduction of the hydroxyl group on C-3. At the same time, it enables the regeneration of the methylketone and exocyclic double bond presented by methyl 13-oxo-14,15-dinorlabd-8(17)en-19-oate. The latter compound was previously used to construct the B-C-D-ring of these quassinoids. 相似文献