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891.
The unique diazafluoranthene alkaloid eupolauridine (1) was synthesized by a three-step route utilizing as the initial step the thermal rearrangement of the oxime O-crotyl ether 12, which afforded onychine (2). Bracher pyridine synthesis procedure subsequently converted 2 into 1. On the other hand, Friedländer reaction was employed for the synthesis of 3, which is a benzo-annulated derivative of eupolauridine (1). 相似文献
892.
Reactions of [Ru]Cl ([Ru]={Cp(PPh3)2Ru}; Cp=cyclopentadienyl) with three alkynyl compounds, 1 , 5 , and 8 , each containing a cyclobutyl group, are explored. For 1 , the reaction gives the vinylidene complex 2 , with a cyclobutylidene group, through dehydration at CδH and CγOH. With an additional methylene group, compound 5 reacts with [Ru]Cl to afford the cyclic oxacarbene complex 6 . The reaction proceeds via a vinylidene intermediate followed by an intramolecular cyclization reaction through nucleophilic addition of the hydroxy group onto Cα of the vinylidene ligand. Deprotonation of 2 with NaOMe produces the acetylide complex 3 and alkylations of 3 by allyl iodide, methyl iodide, and ethyl iodoacetate generate 4 a – c , respectively, each with a stable cyclobutyl group. Dehydration of 1 is catalyzed by the cationic ruthenium acetonitrile complex at 70 °C to form the 1,3‐enyne 7 . The epoxidation reaction of the double bond of 7 yields oxirane 8 . Ring expansion of the cyclobutyl group of 8 is readily induced by the acidic salt NH4PF6 to afford the 2‐ethynyl‐substituted cyclopentanone 9 . The same ring expansion is also seen in the reaction of [Ru]Cl with 8 in CH2Cl2, affording the vinylidene complex 10 , which can also be obtained from 9 and [Ru]Cl. However, in MeOH, the same reaction of [Ru]Cl with 8 affords the bicyclic oxacarbene complex 12 a through an additional cyclization reaction. Transformation of 10 into 12 a is readily achieved in MeOH/HBF4, but, in MeOH alone, acetylide complex 11 is produced from 10 . In the absence of MeOH, cyclization of 10 , induced by HBF4, is followed by fluorination to afford complex 13 . Crystal structures of 6 and 12 a ′ were determined by single‐crystal diffraction analysis. 相似文献
893.
Optimal Consecutive-k-out-of-(2k+1): G Cycle 总被引:1,自引:0,他引:1
We present a complete proof for the invariant optimal assignment for consecutive-k-out-of-(2k+1): G cycle, which was proposed by Zuo and Kao in 1990 with an incomplete proof, pointed out recently by Jalali, Hawkes, Cui and Hwang. 相似文献
894.
Kang Ying LI Zheng Hong ZHOU Chi Hung YEUNG Chu Chi TANG* State Key Laboratory of Elemento-Organic Chemistry Nankai University Tianjin Laboratory of Chiral Technology Department of Applied Biology Chemical Technology The Hong Ko 《中国化学快报》2001,(10)
The suitable chiral derivatizing agent (CDA) is the essential factor for the determination of the optical purity of the enantiomeric substances by NMR method. Among different kinds of CDAs, the chiral phosphorous derivatizing agents1 have become very popular. In this paper, we report a simple and highly efficient 31P NMR method for the ee determination of chiral alcohols and amines, based on the phosphorous CDA 12. R1R2XH+X=O, NH+123A3BOOPClXR1R2HOOPOOPXR1R2H The po… 相似文献
895.
The anatase-rutile phase transformation of TiO(2) bulk material is investigated using a density functional theory (DFT) approach in this study. According to the calculations employing the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional with the Vanderbilt ultrasoft pseudopotential, it is suggested that the anatase phase is more energetically stable than rutile, which is in variance with the experimental observations. Consequently, the DFT?+?U method is employed in order to predict the correct structural stability in titania from electronic-structure-based total energy calculations. The Hubbard U term is determined by examining the band structure of rutile with various values of U from 3 to 10?eV. At U?=?5?eV, a theoretical bandgap for rutile is obtained as 3.12?eV, which is in very good agreement with the reported experimental bandgap. Hence, we choose the DFT?+?U method (with U?=?5?eV) to investigate the transformation pathway using the newly-developed solid-state nudged elastic band (ss-NEB) method, and consequently obtain an intermediate transition structure that is 9.794?eV per four-TiO(2) above the anatase phase. When the Ti-O bonds in the transition state are examined using charge density analysis, seven Ti-O bonds (out of 24 bonds in the anatase unit cell) are broken, and this result is in excellent agreement with a previous experimental study (Penn and Banfield 1999 Am. Miner. 84 871-6). 相似文献
896.
897.
Hue Minh Thi Nguyen Tien Van Pham Hung Van Hoang Pham Tho Hoan Ngo Tuan Cuong 《国际化学动力学杂志》2020,52(2):84-91
Gas-phase mechanism and kinetics of the reactions of the 2-propargyl radical (H2CCCH), an important intermediate in combustion processes, with ammonia were investigated using ab initio molecular orbital theory at the coupled-cluster CCSD(T)//B3LYP/6-311++G(3df,2p) method in conjunction with transition state theory (TST), variational transition state theory (VTST), and Rice–Ramsperger–Kassel–Macus (RRKM) calculations for rate constants. The potential energy surface (PES) constructed shows that the C3H3 + NH3 reaction has four main entrances, including two H-abstraction and two addition channels in which the former are energetically more favorable. The H-abstraction channels occur via energy barriers of 24 (T0/P2) and 26 kcal/mol (T0/P3) forming loose van de Waals complexes, COM_1 (12 kcal/mol) and COM_2 (14 kcal/mol), respectively. These complexes can easily be decomposed via barrier-less processes resulting HCCCH3 + NH2 (P2, 14 kcal/mol) and HCCCH3 + NH2 (P3, 15 kcal/mol), respectively. The additional channels occur initially by formation of two intermediate states, H2CCCHNH3 (35 kcal/mol) and H2CC(NH3)CH (37 kcal/mol) via energy barriers of 37 and 40 kcal/mol at T0/1 and T0/5, respectively, followed by isomerization and decomposition yielding 21 different products. These processes are fully depicted in an as-complete-as-possible PES. The rate constants and product branching ratios for the low-energy channels calculated show that the C3H3 + NH3 reaction is almost pressure-independent. For the temperature range of 300–2000 K, the HCCCH3 + NH2 is the major product, whereas the minor one, HCCCH3 + NH2, has more contribution when temperature increases. Theoretical results on the mechanism and kinetics of the reaction considered may be helpful for future experiments as well as for understanding the role of the propargyl radical in combustion chemistry. 相似文献
898.
899.
Tang-Chia Chung Wung-Pung Su Hwang-Shang Kou Yu-Ting Lin Min-Yuan Hung Hsin-Lung Wu 《Journal of fluorescence》2010,20(1):421-424
trans, trans-Muconic acid (MA) is a polar metabolite of benzene and used as a biomarker for monitoring human exposure to benzene. Because
MA is a trace metabolite, sensitive method is required for its detection. In addition, MA is a highly polar compound with
dicarboxyl functions that could incur unfavorable adsorption on silica-based stationary phase usually used for separation.
To address these problems, we planned to derivatize MA with a fluorescent reagent 2-(2-naphthoxy)ethyl-2-(piperidino)ethanesulfonate
to give a naphthoxy derivative of MA for improving detection sensitivity and chromatographic properties. Surprisingly, the
resulting derivative shows no fluorescent activity (λex: 226 nm; λem: 350 nm). The negative results could be used as an instructive example for discussing on fluorescence quenching. 相似文献
900.
Li‐Ting Huang Hung‐Ju Yen Cha‐Wen Chang Guey‐Sheng Liou 《Journal of polymer science. Part A, Polymer chemistry》2010,48(21):4747-4757
A series of novel poly(amine–amide–imide)s (PAAIs) based on tetraphenyl‐p‐phenylenediamine (TPPA) units showing anodically/cathodically electrochromic characteristic with three primary colors [red, green, and blue (RGB)] were prepared from the direct polycondensation of the TPPA‐based diamine monomer with various aromatic bis(trimellitimide)s. These multicolored electrochromic polymers were readily soluble in polar organic solvents and showed excellent thermal stability associated with high glass‐transition temperatures (288–314 °C) and high‐char yield (higher than 60% at 800 °C in nitrogen). The PAAI films revealed electrochemical oxidation and reduction accompanied with high contrast of optical transmittance color changes from the pale yellow neutral state to the green/blue oxidized state and red reduced state, respectively. The electrochromic films had high‐coloration efficiency (CE = 178 and 242 cm2/C at the first and the second stages, respectively), low‐switching time, and good redox stability, which still retained a high electroactivity after long‐term redox cycles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献