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51.
Mohamed Boumerzoug Marcel Boudreau Peter Mascher 《Plasma Chemistry and Plasma Processing》1997,17(2):181-192
Real-time optical emission spectroscopy (OES) was used to monitor the deposition of TiN both from mixtures of tetrakis(dimethylamino)titanium
(TDMATi)-N2 and TiCl4-H2-N2 in an electron cyclotron resonance chemical vapor deposition system. The accurate control of the ratio of the emission intensities
of ionized nitrogen at 391.4 nm and molecular nitrogen at 357.7 nm (N
2
+
/N2) led to low temperature deposition of stoichiometric TiN (Ti/N ≈ 1) and very low resistivity in both cases. It was found
that high ion density plasmas are crucial for a considerable reduction of the deposition temperature while maintaining good
film quality. OES shows that the abundance of certain excited plasma species is not only dependent on the gas mixture and
the deposition parameters, such as total pressure and microwave power, but also is strongly affected by the magnetic field
configuration. The deposition rate and the film resistivity can be related to the emission intensity ratio, I(N
2
+
)/I(N2). Finally, the two processes are compared in terms of the quality of as-deposited and heat-treated films. The comparison
shows that the films obtained with TDMATi exhibit lower resistivity and are thermally more stable than with TiCl4. 相似文献
52.
Brian K. Nicholson 《Journal of organometallic chemistry》1992,440(3):411-418
The specific additions of one, three or four Ph3PAu groups to [M(CO)5]− (M=Mn, Re) are described. Thus [M(CO)5] − in THF reacts with [(Ph3PAu)3O]BF4 to give [(Ph3PAu)4Mn(CO)4]BF4. An X-ray crystal structure of the M = Mn example shows the cation to have a trigonal bipyramidal Au4Mn core with the Mn in an equatorial site. The previously known neutral (Ph3PAu)3M(CO)4 clusters are formed by addition of two Ph3PAu groups, using the mixed reagent [(Ph3PAu) 3O]BF4/[ppn][Co(CO)4], to Ph3PAuM(CO)5, which itself is readily prepared from [M(CO)5]− and Ph3PAuCl. 相似文献
53.
54.
Michael I. Bruce Omar bin Shawkataly Brian K. Nicholson 《Journal of organometallic chemistry》1985,286(3):427-437
H2Ru3(μ3-S)(CO)9 is deprotonated by K[HBBus3] to give cluster anions which react with [O{Au(PPh3)}3]+ or with AuCl(PPh3)/T1+ to give HRu3Au(μ3-S)(CO)9(PPh3) (1) and Ru3Au2(μ3-S)(CO)9(PPh3)2 (3). A similar sequence with HRu3(μ3-SBut)(CO)9 leads to Ru3Au(μ3-SBut)(CO)9(PPh3) (2) as the main product although some 1 also forms, indicating SC cleavage competes with deprotonation of HRu3(μ3-SBut)(CO)9 by [HBBus3]?. The X-ray crystal structures of 1, 2 and 3 are described; (1) and (2) have “butterfly” AuRu3 cores with markedly different hinge angles of 119 and 148° respectively, while 3 has a trigonal-bipyramidal Au2Ru3 skeleton. All three clusters have the sulphur atom symmetrically bridging the Ru3 triangular face. 相似文献
55.
《Chemical physics letters》2006,417(1-3):246-250
Ionic fragmentation of core-excited α-alanine in gas phase was observed. The most dominant ionic species is COOH+ for all core-ionizations at C 1s, N 1s, and O 1s. An increase in COO+ and a decrease in COOH+, which were observed as core-hole atom selectivity for the O 1s ionization, are explained by the enhancement of O–H bond scission. Further state-selective O–H bond scission, observed at the O 1s second peak, is attributed to the OOH1s → 3s/σ* transition. 相似文献
56.
Tleugabulova D Duft AM Zhang Z Chen Y Brook MA Brennan JD 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5924-5932
At present, there is no direct experimental evidence that primary silica particles, which exist only transiently for a few seconds during the St?ber silica synthesis, can be stable in aqueous solutions. In the present work, we show that primary silica particles are formed spontaneously after the dissolution of diglycerylsilane (DGS) in aqueous solutions and remain stable for prolonged periods of time. By using time-resolved fluorescence anisotropy (TRFA), we demonstrate that this unique property of DGS is ascribed to the slow kinetics of silica particle growth in diluted sols at pH approximately 9.0. The anisotropy decay of the cationic dye rhodamine 6G (R6G), which strongly adsorbs to silica oligomers and nanoparticles in DGS sols, could be fit to three components: a fast (picosecond) scale component associated with free R6G, a slower (nanosecond) rotational component associated with R6G bound to primary silica particles, and a residual (nondecaying) anisotropy component associated with R6G that was bound to secondary or larger particles that were unable to rotate on the time scale of the R6G emission lifetime (4 ns). The data show that, under conditions where fast hydrolysis is obtained, the initial size of the nuclei depends on the silica concentration, with larger nuclei being present in more concentrated sols, while the rate of growth of primary particles depends on both silica concentration and solution pH. At low silica concentrations and high pHs, it was possible to observe the growth of stable, nonaggregating primary silica particles by a mechanism involving rapid nucleation followed by monomer addition. The presence of stable primary particles was confirmed by atomic force microscopy (AFM) imaging. At higher silica concentrations and lower pHs, there was an increase in the initial size of the nuclei formed, which subsequently grew to a larger radius (> 4.5 nm) or aggregated with time, and in such cases, nucleation and aggregation occurred simultaneously in the early stage of silica formation. The data clearly show the power of time-resolved fluorescence anisotropy decay measurements for probing the growth of silica colloids and show that this method is useful for elucidating the mechanism of particle formation and growth in situ. 相似文献
57.
J. Choma H. Jankowska J. Piotrowska M. Jaroniec 《Monatshefte für Chemie / Chemical Monthly》1987,118(3):315-321
A simple isotherm equation for describing gas adsorption on solids showing heterogeneity of microporous structure is proposed. It is shown that this equation gives a good representation of the experimental data of argon, nitrogen and benzene adsorption on different types of activated carbons. Its parameters may be used to characterize heterogeneity of microporous structure of the solids.
Eine einfache Isotherme zur Beschreibung der Gas-Adsorption an heterogenen mikroporösen Feststoffen
Zusammenfassung Es wird eine einfache Isotherme zur Beschreibung der Gasadsorption an Feststoffen mit heterogener mikroporöser Struktur vorgeschlagen. Es wird gezeigt, daß diese Gleichung die experimentellen Daten für die Adsorption von Argon, Stickstoff und Benzol an verschiedenen Typen von Aktivkohle gut beschreibt. Die Parameter der Isotherme können zur Charakterisierung der Heterogenität der mikroporösen Struktur von Festkörpern herangezogen werden.相似文献
58.
The VSEPR model is a consequence of the correlation of same-spin electrons resulting from the operation of the Pauli exclusion principle. Although the VSEPR rules can be interpreted in terms of an orbital model they do not provide the physical basis for the model. 相似文献
59.
Jane?Jin John?C.?Achenbach Shiping?ZhuEmail author Yingfu?Li 《Colloid and polymer science》2005,283(11):1197-1205
The influences of polymer-related properties such as molecular weight, charge density, counter ion, and hydrophilic block
on the complexation of polyelectrolytes and a fluorescein-labeled oligonucleotide (ON) were investigated. A series of well-defined
and well-controlled 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) polymers and block copolymers were prepared using living anionic and radical polymerization
methods. Fluorescence measurement was used to reveal the effects of polymer molecular weight, charge density, and counter
ion type on the complexation. PolyDMAEMA samples having double molecular weights of the chosen oligonucleotide gave the optimal
complexation performance. Kinetic studies showed that high-molecular weight/high-charge density polymer samples produced very
stable complexes. The fully charged polyDMAEMA displayed the strongest binding with the ON. These complexes were therefore
less sensitive to the changes in the environment. PolyDMAEMA–DMSQ samples had slightly higher complexation ability than polyDMAEMA–MCQ
(DMSQ: dimethylsulfate quat; MCQ: methylchloride quat). Both poly(DMAEMA-b-HEMA) and poly(DMAEMA–MCQ-b-PEG) block copolymers
showed good complexation ability and steric stability [HEMA: 2-hydroxyethyl methacrylate; PEG: poly(ethylene glycol)]. PEG,
but not HEMA block, enhanced the effectiveness of polyDMAEMA–MCQ binding with the ON. 相似文献
60.
Band structure calculations at the level of LMTO-ASA provide insight into the electronic structure of BaV10O15 and the origin of the structural phase transition. A crystal orbital Hamiltonian population/integrated crystal orbital Hamiltonian population analysis provides evidence that the crystallographic phase transition is driven by V-V bond formation. As well, the energy bands near the Fermi level are very narrow, <1 eV, consistent with the fact that the observed insulating behavior can be due to electron localization via either Mott-Hubbard correlation and/or Anderson disorder. The partial solid solution, BaV10−xTixO15, was examined to study the effect of Ti-doping at the V sites on the structure and electronic transport properties. In spite of the non-existence of “BaTi10O15”, the limiting x=8, as indicated by a monotonic increase in the cell volume and systematic changes in properties. This limit may be due to the difficulty of stabilizing Ti2+ in this structure. For x=0.5 both the first order structural phase transition and the magnetic transition at 40 K are quenched. The samples obey the Curie-Weiss law to x=3 with nearly spin only effective moments along with θ values which range from −1090 K (x=0.5) to −1629 K (x=3). For x>3 a very large, ∼2×10−3 emu/mol, temperature independent (TIP) contribution dominates. Conductivity measurements on sintered, polycrystalline samples show semiconducting behavior for all compositions. Activation energies for Mott hopping derived from high temperature data range from ∼0.1 eV for x=0-1 and fall to a plateau of 0.06 eV for x=3-7. Low temperature data for x=3, 5 and 7 show evidence for Mott variable range hoping (VRH) with a T1/4 law and in one case between 5 and 17 K, a Efros-Shklovskii correlated hopping, T1/2 law, was seen, in sharp contrast to BaV10O15 where only the E-S law was observed up to 75 K. Seebeck coefficients are small (<35 μV/K), positive, roughly TIP and increase with increasing x up to x=5. This may point to a Heikes hopping of holes but a simple single carrier model is impossible. The compositions for x>3 are remarkable in that local moment behavior is lost, yet a metallic state is not reached. The failure of this system to be driven metallic even at such high doping levels is not fully understood but it seems clear that disorder induced carrier localization plays a major role. 相似文献