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321.
The complex [{Re(CO)5}2(μ,η1:η1-C2O4)] 1 undergoes thermal decarbonylation to give [Re2(CO)6(C2O4)]n, which reacts with triphenylphosphine and trans-1,2-bis(diphenylphosphino)ethylene (dppene) to give anti-[Re2(PPh3)2(CO)6(μ,η2:η2-C2O4)] 2 and [Re2(μ-dppene)(CO)6(μ,η2:η2-C2O4)] 4, respectively. Complex 2 is oxidized on prolonged exposure to air (1 week) to form anti-[Re2(OPPh3)2(CO)6(μ,η2:η2-C2O4)] 3. In the presence of excess dppene, the complex [Re2(μ-dppene)2(CO)6(μ,η1:η1-C2O4)] 5 is also formed alongside 4. With the chelating diphosphine 1,3-bis(diphenylphosphino)propane (dppp), the complex [(η2-dppp)Re(CO)3(μ,η1:η1-C2O4)Re(CO)3(η2-dppp)] 6 is formed. The structures of 3 and 4 have been determined by X-ray crystallography. The dppene ligand in complex 4 adopts an unusual “syn” conformation wherein the two phosphorus lone pairs of electrons are eclipsed, thus forming an “A-frame” type of bridge. 相似文献
322.
New chlorophosphonates bearing a 1,3,2-dioxaphosphorinane ring which are useful for the stereospecific synthesis of 5-chlorofurfuryl substituted olefins and chloro-substituted dienes have been obtained by an easy, inexpensive route. The utility of some of these in the synthesis of ferrocenyl- and anthracenyl-substituted unsymmetrical acetylenes has been explored. The structures of the phosphonates (OCH(2)CMe(2)CH(2)O)P(O)CH(2)(C(4)H(2)ClO) (4) and (OCH(2)CMe(2)CH(2)O)P(O)(CH=CHCH(Cl)Ph (7) have been determined; in addition, the stereochemistry of (5-chlorofurfuryl)CH=CH(4-ClC(6)H(4)) (13b) and 2, 4-Cl(2)C(6)H(3)-CH=CH-CH=C(Ph)Cl (14a) is unambiguously proved by the X-ray structure determination. 相似文献
323.
Kumar Biradha Valerie M. Hansen Weng Kee Leong Roland K. Pomeroy Michael J. Zaworotko 《Journal of Cluster Science》2000,11(2):285-306
The structures of Os3(CO)11(PR3) with R=F, OPh, Et, p-C6H4Me, o-C6H4Me, p-C6H4(CF3) and C6H11, and with PR3=P(OCH2)3CMe have been determined. The Os–Os bond lengths in these compounds are compared to the Os–Os lengths for the other structures of Os3(CO)11(PR3) clusters reported in the literature. In most cases, the Os–Os bond length remote from the P ligand [range, 2.8666(4)–2.9044(4) Å] and that in the pseudo-trans position [range, 2.8712(5)–2.900(1) Å] show little variation as the steric and electronic properties of the P ligand are varied. The Os–Os length cis to PR3 shows more variation [range, 2.879(1)–2.9429(4) Å] and is sensitive to both the size and the -donor/-acceptor properties of the PR3 ligand: larger or better donor PR3 ligands cause an increase in the Os–Os bond length. The Os–P distances [range, 2.15(2)–2.478(1) Å] show a similar dependence on the steric and electronic properties of the PR3 ligand. 相似文献
324.
The performance of graphite-tube electrothermal atomizers is evaluated for laser-excited atomic-fluorescence spectrometry for several elements. Three pulsed laser systems are used to pump tunable dye lasers which subsequently are used to excite Pb, Ga, In, Fe, Ir, and Tl atoms in the hot graphite tube. The dye laser systems used are pumped by nitrogen, copper vapour and Nd:YAG lasers. Detection limits in the femtogram and subfemtogram range are typically obtained for all elements. A commercial graphite-tube furnace is important for the successful utilization of the laser-based method when the determination of trace elements is intended, especially when complicated matrices may be present. 相似文献
325.
A series of new polypseudorotaxanes were synthesized in high yields when the middle poly(ethylene oxide) (PEO) block of poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) triblock copolymers was selectively recognized and included by alpha-cyclodextrin (alpha-CD) to form crystalline inclusion complexes (ICs), although the middle PEO block was flanked by two thicker PPO blocks, and a PPO chain had been previously thought to be impenetrable to alpha-CD. X-ray diffraction studies demonstrated that the IC domains of the polypseudorotaxanes assumed a channel-type structure similar to the necklace-like ICs formed by alpha-CD and PEO homopolymers. Solid-state CP/MAS (13)C NMR studies showed that the alpha-CD molecules in the polypseudorotaxanes adopted a symmetrical conformation due to the formation of ICs. The compositions and stoichiometry of the polypseudorotaxanes were studied using (1)H NMR, and a 2:1 (ethylene oxide unit to alpha-CD) stoichiometry was found for all polypseudorotaxanes although the PPO-PEO-PPO triblock copolymers had different compositions and block lengths, suggesting that only the PEO block was closely included by alpha-CD molecules, whereas the PPO blocks were uncovered. The hypothesis was further supported by the differential scanning calorimetry (DSC) studies of the polypseudorotaxanes. The glass transitions of the PPO blocks in the polypseudorotaxanes were clearly observed because they were uncovered by alpha-CD and remained amorphous, whereas the glass-transition temperatures increased, because the molecular motion of the PPO blocks was restricted by the hard crystalline phases of the IC domains formed by alpha-CD and the PEO blocks. The thermogravimetric analysis (TGA) revealed that the polypseudorotaxanes had better thermal stability than their free components due to the inclusion complexation. Finally, the kinetics of the threading process of alpha-CD onto the copolymers was also studied. The findings reported in this article suggested interesting possibilities in designing other cyclodextrin ICs and polypseudorotaxanes with block structures. 相似文献
326.
Tan H Wong L Lai MY Kiruba GS Leong WK Wong MW Fan WY 《The journal of physical chemistry. B》2005,109(42):19657-19663
A transition metal carbonyl species, Cr(CO)(4)dpp, has been successfully attached to bare silver nanoparticles prepared by laser ablation of a metal foil in ethanol. Transmission electron microscopy (TEM) images have shown that at least a portion of the silver nanoparticles have been capped by the chromium species, and ligand shells corresponding to Cr(CO)(4)dpp multilayer adsorption onto the silver nanoparticles of 30-50 nm diameter have been observed. The detection of the strongest Raman-active nu(CO) band of Cr(CO)(4)dpp at 2004 cm(-1) revealed that the species has been adsorbed without decomposition. The time-of-flight secondary ion mass spectrometry (TOF-SIMS) signals recorded of the chromium-capped silver nanoparticles were also consistent with the nondecomposition adsorption process. Density functional calculations have been used to reproduce the Raman spectrum using Ag(7)(+) as a model surface. A large binding energy of about 122 kJ/mol has also been computed between silver and nitrogen atoms thus lending support to Cr(CO)(4)dpp being chemisorbed onto the silver surface. 相似文献
327.
The problem of differentiating spectral data to yield the third and fourth derivatives is converted into one of solving an integral equation of the first kind. This equation is solved by Tikhonov regularization. The method of General Cross Validation is used to guide the choice of the regularization parameter that keeps noise amplification under control. The performance of this route to third and fourth derivative spectra is demonstrated by applying it to a number of published spectra. A computational problem associated with General Cross Validation has been identified. 相似文献
328.
Hamilton RJ Leong CG Bigam G Miskolzie M Bergens SH 《Journal of the American Chemical Society》2005,127(12):4152-4153
The compound fac-[Ru((R)-BINAP)(H)(2-PrOH)3]+ (6) (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) reacts with (R,R)-dpen (dpen = 1,2-diphenylethylenediamine) under H2 at -60 degrees C in 2-PrOH-d8/CD2Cl2 to generate the cationic dihydrogen putative intermediate trans-[Ru((R)-BINAP)(H)(eta2-H2)((R,R)-dpen)]+ (2') without H-D exchange between the hydrogen ligands and the solvent. A 1H NMR study concludes that the dihydrogen ligand in 2' does not protonate 2-PrOH to a catalytically significant extent, and that 2' requires an added base or hydride source to be an active catalyst. 相似文献
329.
Y.J. Chen T.L. HuangJ.Z. Shi J. DengJ. Ding W.M. LiS.H. Leong B.Y. ZongHnin Yu Yu Ko S.B. HuJ.M. Zhao 《Journal of magnetism and magnetic materials》2012,324(3):264-268
The switching of single bit magnetic islands in bit patterned media (BPM) for two cases with 10 times difference in coercivity, as well as the switching field distribution (SFD) of the islands, has been studied using magnetic force microscopy (MFM) measurements. The intrinsic SFD is measured to be ∼9-11% of the remanence coercivity (Hcr), which contributes only ∼20-50% of the total SFD broadening (∼23-41% of Hcr). High resolution MFM observations clearly showed the influence of surrounding islands on the switching behaviour and switching fields of individual bit islands, resulting in significant contributions in SFD broadening due to non-intrinsic dipolar interactions. It was further observed that single magnetic islands could be switched within a very narrow switching field range as small as 4 Oe, which indicates very sharp and uniform switching for each individual island of BPM. 相似文献
330.
Boon Leong Lan 《International Journal of Theoretical Physics》2009,48(3):642-644
As another counterexample to prevalent conventional belief, a realistic theory, which is local and reproduces all the probabilistic
predictions of quantum theory, is presented for Mermin’s version of the Einstein-Podolsky-Rosen (EPR) experiment. 相似文献