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61.
Costa AM Jimeno C Gavenonis J Carroll PJ Walsh PJ 《Journal of the American Chemical Society》2002,124(24):6929-6941
The optimization of asymmetric catalysts for enantioselective synthesis has conventionally revolved around the synthesis and screening of enantiopure ligands. In contrast, we have optimized an asymmetric reaction by modification of a series of achiral ligands. Thus, employing (S)-3,3'-diphenyl BINOL [(S)-Ph(2)-BINOL] and a series of achiral diimine and diamine activators in the asymmetric addition of alkyl groups to benzaldehyde, we have observed enantiomeric excesses between 96% (R) and 75% (S) of 1-phenyl-1-propanol. Some of the ligands examined have low-energy chiral conformations that can contribute to the chiral environment of the catalyst. These include achiral diimine ligands with meso backbones that adopt chiral conformations, achiral diimine ligands with backbones that become axially chiral on coordination to metal centers, achiral diamine ligands that form stereocenters on coordination to metal centers, and achiral diamine ligands with pendant groups that have axially chiral conformations. Additionally, we have structurally characterized (Ph(2)-BINOLate)Zn(diimine) and (Ph(2)-BINOLate)Zn(diamine) complexes and studied their solution behavior. 相似文献
62.
63.
Dr. Gábor London Kuang‐Yen Chen Dr. Gregory T. Carroll Prof. Dr. Ben L. Feringa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10690-10697
We report the synthesis of altitudinal molecular motors that contain functional groups in their rotor part. In an approach to achieve dynamic control over the properties of solid surfaces, a hydrophobic perfluorobutyl chain and a relatively hydrophilic cyano group were introduced to the rotor part of the motors. Molecular motors were attached to quartz surfaces by using interfacial 1,3‐dipolar cycloadditions. To test the effect of the functional groups on the rotary motion, photochemical and thermal isomerization studies of the motors were performed both in solution and when attached to the surface. We found that the substituents have no significant effect on the thermal and photochemical processes, and the functionalized motors preserved their rotary function both in solution and on a quartz surface. Preliminary results on the influence of the functional groups on surface wettability are also described. 相似文献
64.
In the present work, quantitative calculations were carried out for production and depletion of the 93m Mo isomer in a relatively simple experiment using 91Zr beam ions. Such studies could be arranged at existing and operating accelerator facilities, e.g. at GSI or in JINR. The 93m Mo nuclei produced in a He gas target due to the 4He(91Zr, 2n) reaction will recoil into a gas stopper with a high velocity, being then depleted due to NEEC in highly-ionized species. 相似文献
65.
Molecular electronics is, relatively speaking, a young field. Even so, there have been many significant advances and a much greater understanding of the types of materials that will be useful in molecular electronics, and their properties. The purpose of this review is to provide a broad basis for understanding the areas where new advances might arise, and to provide introduction to the subdisciplines of molecular electronics. This review is divided into two major parts; an historical examination of the development of conventional electronics, which should provide some understanding of the push towards molecular electronics. The problems associated with continuing to shrink conventional systems are presented, along with references to some of the efforts to solve them. This section is followed by an in-depth look at the most important research into the types of behaviors that molecular systems have been found to display. 相似文献
66.
[reaction:see text] During the total synthesis of the novel cyclic depsipeptide callipeltin A (1), the unit (3S,4R)-3,4-dimethylglutamine, was successfully synthesized by asymmetric Michael addition and subsequent electrophilic azidation. The key feature of this approach is the generation of three adjacent stereogenic centers using the same camphorsultam chiral auxiliary. 相似文献
67.
M.A. Nasser M.M. Gazzaly J.V. Geaga B. Höistad G. Igo J.B. McClelland A.L. Sagle H. Spinka J.B. Carroll V. Perez-Mendez E.T.B. Whipple 《Nuclear Physics A》1978,312(3):209-216
The p-4He elastic differential cross section has been measured at a kinetic energy of 2.68 GeV. The momentum transfer region studied is t = 0.15–0.66 (GeV/c)2. The cross section displays a shallow first minimum and shape very similar to recent data at 1 GeV. 相似文献
68.
P.J. Bussey C. Raine J.G. Rutherglen P.S.L. Booth L.J. Carroll G.R. Court P.R. Daniel A.W. Edwards R. Gamet C.J. Hardwick P.J. Hayman J.R. Holt J.N. Jackson W.H. Range F.H. Combley W. Galbraith V.H. Rajaratnam C. Sutton 《Nuclear Physics B》1979,154(3):492-502
The polarisation parameters Σ, P and T have been measured for the process γp→π0p in the photon energy range 1300–2100 MeV and c.m. angles between 30° and 110°, in an experiment with a polarised beam and polarised target. The results are compared with a recent theoretical analysis which fits data from threshold to 16 GeV. The new data are in general agreement with the analysis, but with some significant discrepancies in detail. 相似文献
69.
70.
R. Daniel Little George W. Muller Manuel G. Venegas Gary L. Carroll Ahmed Bukhari Larry Patton Keith Stone 《Tetrahedron》1981,37(25):4371-4383
A comparison of the inter- and intramolecular diyl trapping routes to linearly fused tricyclopentanoids is presented. In addition, several of the factors which are responsible for the stereoselectivity which is associated with the intramolecular process are examined and it is concluded that conformational rather than electronic (secondary orbital) factors play the dominant role. It is shown that gem methyl groups located on the acyclic chain which joins the diyl and diylophile (in reference to 32 and 35, but not to 47) have no practical effect upon the outcome of the trapping reaction. The intramolecular process is stereospecific with respect to diylophile geometry, and highly stereoselective with respect to the ring junction stereochemistry. Finally, an abortive attempt to synthesize the marine natural product Δ9(12)-capnellene (19) as well as a successful synthesis of the mold metabolite d,l- hirsutene (18) is presented. 相似文献