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991.
Aggarwal VK Grainger RS Newton GK Spargo PL Hobson AD Adams H 《Organic & biomolecular chemistry》2003,1(11):1884-1893
The C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide, was found to react with a range of 3-oxidopyridinium betaines (bearing different substituents on nitrogen) in high yield and with total diastereoselectivity. A 2.3:1 mixture of regioisomers was formed with all of the 3-oxidopyridinium betaines but the ratio was found to change over prolonged periods of time due to reversibility of the minor regioisomer. 3-Oxidopyridinium betaines bearing methyl substituents at either the 2- or 6-position were also tested in the cycloaddition process. Improved regioselectivity (8:1) and again high diastereoselectivity were observed with the betaine having an additional substituent at the 2-position, but with betaines having a substituent in the 6-position although high regioselectivity was observed (9.9:1), the major isomer was formed with low diastereoselectivity (5.5:4.4). The origin of the regio- and diastereo-selectivity with all the betaines is discussed. Finally, the C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide was reacted with an oxidopyrylium betaine in moderate yield. Good regioselectivity and moderate diastereoselectivity were observed. 相似文献
992.
Gonsalvi L Adams H Sunley GJ Ditzel E Haynes A 《Journal of the American Chemical Society》2002,124(45):13597-13612
Kinetic studies of the reactions of [M(CO)(L-L)I] [M = Rh, Ir; L-L = Ph(2)PCH(2)P(S)Ph(2) (dppms), Ph(2)PCH(2)CH(2)PPh(2) (dppe), and Ph(2)PCH(2)P(O)Ph(2) (dppmo)] with methyl iodide have been undertaken. All the chelate ligands promote oxidative addition of methyl iodide to the square planar M(I) centers, by factors of between 30 and 50 compared to the respective [M(CO)(2)I(2)](-) complexes, due to their good donor properties. Migratory CO insertion in [Rh(CO)(L-L)I(2)Me] leads to acetyl complexes [Rh(L-L)I(2)(COMe)] for which X-ray crystal structures were obtained for L-L = dppms (3a) and dppe (3b). Against the expectations of simple bonding arguments, methyl migration is faster by a factor of ca. 1500 for [Rh(CO)(dppms)I(2)Me] (2a) than for [Rh(CO)(dppe)I(2)Me] (2b). For M = Ir, alkyl iodide oxidative addition gives stable alkyl complexes [Ir(CO)(L-L)I(2)R]. Migratory insertion (induced at high temperature by CO pressure) was faster for [Ir(CO)(dppms)I(2)Me] (5a) than for its dppe analogue (5b). Reaction of methyl triflate with [Ir(CO)(dppms)I] (4a) yielded the dimer [[Ir(CO)(dppms)(mu-I)Me](2)](2+) (7), which was characterized crystallographically along with 5a and [Ir(CO)(dppms)I(2)Et] (6). Analysis of the X-ray crystal structures showed that the dppms ligand adopts a conformation which creates a sterically crowded pocket around the alkyl ligands of 5a, 6, and 7. It is proposed that this steric strain can be relieved by migratory insertion, to give a five-coordinate acetyl product in which the sterically crowded quadrants flank a vacant coordination site, exemplified by the crystal structure of 3a. Conformational analysis indicates similarity between M(dppms) and M(2)(mu-dppm) chelate structures, which have less flexibility than M(dppe) systems and therefore generate greater steric strain with the "axial" ligands in octahedral complexes. Ab initio calculations suggest an additional electronic contribution to the migratory insertion barrier, whereby a sulfur atom trans to CO stabilizes the transition state compared to systems with phosphorus trans to CO. The results represent a rare example of the quantification of ligand effects on individual steps from catalytic cycles, and are discussed in the context of catalytic methanol carbonylation. Implications for other catalytic reactions utilizing chelating diphosphines (e.g., CO/alkene copolymerization and alkene hydroformylation) are considered. 相似文献
993.
J. H. Adams J. E. Goodrich 《Journal of polymer science. Part A, Polymer chemistry》1970,8(5):1269-1277
The nonvolatile products of polypropylene that has been process degraded in the melt by a Brabender torque rheometer have been quantitatively identified by infrared analysis and chemical reactions carried out on molded sheets. The molecular weight changes with degradation have been determined by gel-permeation chromatography (GPC). It was determined that there is only one functional group per chain scission instead of the two groups previously found for thermal oxidation in the solid state. The molecular weight distribution is similar, but the functional groups and the general scheme of oxidation differ slightly from those previously found for polyolefin oxidation carried out below the melting point. The functional group distribution differs from that determined in a process-degraded polyethylene sample. 相似文献
994.
The reaction of Fe2(CO)6(μ-S2),1 withbis(dibenzylideneacetone)-palladium, Pd(dba)2, in the presence of 2,2′-bipyridine yielded the new compound Fe2(CO)6(μ 3-S)2Pd(bipy),2 in good yield (66%). Compound2 was characterized by IR,1H NMR and single-crystal X-ray diffraction analyses. Compound2 contains a Pd(bipy) group that has been inserted into the S-S bond of1. Crystal data for2: space group P21/n,a=10.019(2) Å,b=25.414(5) Å,c=7.714(2) Å,β=90.26(2)°,Z=4, 1436 reflections,R=0.023. 相似文献
995.
From the reaction of [Ru5(C)(CO)14]2– with Pt(COD)Cl2, COD=1, 5 cyclooctadiene, the new platinum-ruthenium carbido cluster complex PtRu5 (C)(CO)14(COD),1, was obtained in 41% yield. When1 was allowed to react with carbon monoxide (25°C/1 atm), the new complex PtRu5(C)(CO)16,2, was obtained almost quantitatively (97% yield). Compound2 was characterized by IR and single-crystal X-ray diffraction analysis. The six metal atoms are arranged in the form of an octahedron with the carbide ligand located in the center. Compound1 is believed to have a similar structure to2 except for a COD ligand coordinated to the platinum atom. When activated by treatment with Me3NO, compound2 reacts with Pt(COD)2 at 25°C to yield two higher nuclearity cluster complexes, Pt2Ru5C(CO)13(COD)2.3, and Pt3Ru5C(CO)14(COD)2,4. The structure of3 is similar to that of1, but contains a Pt(COD) grouping capping one Ru3 triangle of the PtRu5 octahedron. The structure of4 consists of a PtRu5 octahedron with two Pt(COD) capping groups, one on an Ru3 triangle and the other on a PtRu2 triangle of the octahedron. Crystal data: for2, space group=P21/n,a=9.341 (2) Å,b=14.957 (3) Å,c=36.80 (1) Å, =90.38 (2) °,Z=8, 4034 reflections,R=0.030, for3, space group=P21/c,a=14.998 (3) Å,b=10.288 (3) Å,c=26.581 (7) Å, =102.75 (2) °,Z=4, 2917 reflections,R=0.028. for4, space group=P21/n,a=13.412 (4) Å,b=16.252 (4) Å,c=20.107 (4) Å, =106.13 (2) °,Z=4, 2745 reflections,R=0.032. 相似文献
996.
Chris J. Adams Michael I. Bruce Brian W. Skelton Allan H. White 《Journal of Cluster Science》1992,3(2):219-227
The reaction between Ru5(5-C2PPh2)(-PPh2)(CO)13 and Au(C2Ph)(PPh3) afforded AuRu5(5-C2PPh2)(-C2Ph)(-PPh2)(CO)13 (PPh3), in which the Ru5 cluster has a scorpion geometry; the Au(PPh3) group bridges one of the Ru-Ru bonds of the Ru3 triangle, while the C2Ph group bridges one of the tail Ru-Ru vectors.For Part 84, see Ref. 1. 相似文献
997.
D. A. Lightner J.-S. Ma T. C. Adams R. W. Franklin G. L. Landen 《Journal of heterocyclic chemistry》1984,21(1):139-144
Xanthobilirubic acid, 5-[1,5-didehydro-3-ethyl-4-methyl-5-oxo-2H-pyrrol-2-ylidene)methyl]-2,4-dimethyl-1H-pyrrol-3-propanoic acid, its methyl ester, amide, N-methylamide and dimethylamide, and kryptopyrromethenone have been synthesized and characterized spectroscopically. In d6-DMSO solution all pyrromethenones were monomeric, with lactam and pyrrole N-Hs H-bonded to solvent. In deuteriochloroform, the pyrromethenones preferred a dimeric form, with intramolecular H-bonding between the lactam C = 0 of one unit and the lactam and pyrrole N-Hs of the second. 相似文献
998.
Brown CN Cooper WE Finley DA Jonckheere AM Jostlein H Kaplan DM Lederman LM Smith SR Luk KB Gray R Plaag RE Rutherfoord JP Straub PB Young KK Hemmi Y Imai K Miyake K Sakai Y Sasao N Tamura N Yoshida T Maki A Crittenden JA Hsiung YB Adams MR Glass HD Jaffe DE McCarthy RL Hubbard JR Mangeot P 《Physical review letters》1986,57(17):2101-2104
999.
1000.