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91.
Romeiro NC Albuquerque MG de Alencastro RB Ravi M Hopfinger AJ 《Journal of computer-aided molecular design》2005,19(6):385-400
The p38-mitogen-activated protein kinase (p38-MAPK) plays a key role in lipopolysaccharide-induced tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) release during the inflammatory process, emerging as an attractive target for new anti-inflammatory agents. Four-dimensional quantitative structure-activity relationship (4D-QSAR) analysis [Hopfinger et al., J. Am. Chem. Soc., 119 (1997) 10509] was applied to a series of 33 (a training set of 28 and a test set of 5) pyridinyl-imidazole and pyrimidinyl-imidazole inhibitors of p38-MAPK, with IC50 ranging from 0.11 to 2100 nM [Liverton et al., J. Med. Chem., 42 (1999) 2180]. Five thousand conformations of each analogue were sampled from a molecular dynamics simulation (MDS) during 50 ps at a constant temperature of 303 K. Each conformation was placed in a 2 angstroms grid cell lattice for each of three trial alignments. 4D-QSAR models were constructed by genetic algorithm (GA) optimization and partial least squares (PLS) fitting, and evaluated by leave-one-out cross-validation technique. In the best models, with three to six terms, the adjusted cross-validated squared correlation coefficients, Q2adj, ranged from 0.67 to 0.85. Model D (Q2adj = 0.84) was identified as the most robust model from alignment 1, and it is representative of the other best models. This model encompasses new molecular regions as containing pharmacophore sites, such as the amino-benzyl moiety of pyrimidine analogs and the N1-substituent in the imidazole ring. These regions of the ligands should be further explored to identify better anti-inflammatory inhibitors of p38-MAPK. 相似文献
92.
Ana María Atria Ricardo Baggio María Teresa Garland Piedad Corts 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(7):m311-m314
The three title compounds, namely 4‐phenyl‐1H‐imidazolium hexa‐μ2‐chloro‐chloro‐μ4‐oxo‐tris(4‐phenyl‐1H‐imidazole‐κN1)tetracopper(II) monohydrate, (C9H9N2)[Cu4Cl7O(C9H8N2)3]·H2O, hexa‐μ2‐chloro‐μ4‐oxo‐tetrakis(pyridine N‐oxide‐κO)tetracopper(II), [Cu4Cl6O(C5H5NO)4], and hexa‐μ2‐chloro‐tetrakis(2‐methyl‐1H‐imidazole‐κN1)‐μ4‐oxo‐tetracopper(II) methanol trisolvate, [Cu4Cl6O(C4H6N2)4]·3CH4O, exhibit the same Cu4OCl6 framework, where the O atom at the centre of an almost regular tetrahedron bridges four copper cations at the corners. This group is in turn surrounded by a Cl6 octahedron, leading to a rather globular species. This special arrangement of the CuII cations results in a diversity of magnetic behaviours. 相似文献
93.
The electrophilic α-alkylation of ketones with alcohols is accomplished by a hydrogen autotransfer process catalyzed by RuCl2(DMSO)4. The reaction can produce either simple alkylated ketones or α,β-unsaturated ketones just by choosing the appropriate starting ketones (methyl ketones or bicyclic methylenic ketones, respectively), as well as quinolines (by using 2-aminobenzyl alcohol derivatives) or the corresponding alcohol derivatives by the addition of an extra equivalent of the initial alcohol. In the last case, after the above alkylation process reduction of the carbonyl compound takes place. A mechanistic study seems to indicate that the process goes through the oxidation of the alcohols with ruthenium (after a previous deprotonation) to yield the corresponding aldehyde and a ruthenium hydride intermediate. In turn, the aldehyde suffers a classical aldol reaction with the starting ketone to form the corresponding α,β-unsaturated ketone, which finally is reduced through a Michael-type addition by the aforementioned ruthenium hydride intermediate. 相似文献
94.
Adriano Francisco Barbosa Arnaldo César Pereira Lauro Tatsuo Kubota César Ricardo Teixeira Tarley 《Talanta》2007,71(4):1512-1519
The present paper proposes the application of multiwall carbon nanotubes (MWCNTs) as a solid sorbent for lead preconcentration using a flow system coupled to flame atomic absorption spectrometry. The method comprises the preconcentration of Pb (II) ions at a buffered solution (pH 4.7) onto 30 mg of MWCNTs previously oxidized with concentrated HNO3. The elution step is carried out with 1.0 mol L−1 HNO3. The effect of the experimental parameters, including sample pH, sampling flow rate, buffer and eluent concentrations were investigated by means of a 24 full factorial design, while for the final optimization a Doehlert design was employed. Under the best experimental conditions the preconcentration system provided detection and quantification limits of 2.6 and 8.6 μg L−1, respectively. A wide linear range varying from 8.6 up to 775 μg L−1 (r > 0.999) and the respective precision (relative standard deviation) of 7.7 and 1.4% for the 15 and 200 μg L−1 levels were obtained. The characteristics obtained for the performance of the flow preconcentration system were a preconcentration factor of 44.2, preconcentration efficiency of 11 min−1, consumptive index of 0.45 mL and sampling frequency estimated as 14 h−1. Preconcentration studies of Pb (II) ions in the presence of the majority foreign ions tested did not show interference, attesting the good performance of MWCNTs. The accuracy of the method was assessed from analysis of water samples (tap, mineral, physiological serum and synthetic seawater) and common medicinal herbs submitted to the acid decomposition (garlic and Ginkgo Biloba). The satisfactory recovery values obtained without using analyte addition method confirms the feasibility of this method for Pb (II) ions determination in different type of samples. 相似文献
95.
Surface-enhanced Raman scattering in the ultraviolet spectral region: UV-SERS on rhodium and ruthenium electrodes 总被引:3,自引:0,他引:3
Ren B Lin XF Yang ZL Liu GK Aroca RF Mao BW Tian ZQ 《Journal of the American Chemical Society》2003,125(32):9598-9599
We report the first observation of surface-enhanced Raman scattering (SERS) excited with ultraviolet (UV) light from transition metal electrodes. Adsorbed pyridine and SCN- on rough rhodium (Rh) and ruthenium (Ru) electrodes, respectively, have been studied using 325 nm laser excitation. In contrast, the best enhancers in the visible and near infrared, silver and gold, do not produce UV-SERS. The experimental data of UV-SERS are in agreement with our preliminary theoretical calculation based on the electromagnetic enhancement mechanism. The enhancement factor is about 2 orders of magnitude for the Rh and Ru electrodes when they are excited at 325 nm. 相似文献
96.
Ana María Atria María Angeles Mora María Teresa Garland Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):m490-m493
The polymeric title compounds, namely catena‐poly[[[di‐μ‐but‐2‐enoato‐κ3O:O,O′;κ3O,O′:O′‐bis[diaquadibut‐2‐enoato‐κO;κ2O,O′‐neodymium(III)]]‐μ‐4,4′‐bipyridyl N,N′‐dioxide‐κ2O:O′] 4,4′‐bipyridyl N,N′‐dioxide solvate] and the erbium(III) and yttrium(III) analogues, {[Ln2(C4H5O2)6(C10H8N2O2)(H2O)4]·C10H8N2O2}n (Ln = Nd, Er and Y), form from [Ln2(bt)6(H2O)4] dimers (bt is but‐2‐enoate) bridged by 4,4′‐bipyridyl dioxide (bno) spacers into sets of parallel chains; these linear arrays are interconnected by aqua‐mediated hydrogen bonds into broad two‐dimensional structures, which in turn interact with each other though the hydrogen‐bonded bridged bno solvent units. Both independent bno units in the structures are bisected by symmetry centres. 相似文献
97.
The title reactions were studied with a solid superacid, which was prepared by exposing Zr(OH)4 to 1 N H2SO4, followed by calcination at 650°C in air. Pentane and isopentane were converted into isopentane and isobutane, respectively, the selectivities being 84% under short contact conditions at 80°C.
, - Zr(OH)4 1 N- H2SO4 650°C . , , 84% 80°C.相似文献
98.
99.
Ricardo Bossio Stefano Marcaccini Valerio Parrini Roberto Pepino 《Journal of heterocyclic chemistry》1986,23(3):889-891
2-(2,6-Dimethylpyrimidin-4-ylaminobenzimidazole) (VIIa) and 2-(1,3,4-thiadiazol-2-ylamino)benzimidazole (VIIb) underwent a ring-closure reaction with phosgene giving 1,3-dimethyl-12H-benzirnidazo[1,2-a]pyrirnido[6,1][-d][1,3,5]triazin-12-one (IIa) and 5H-benzimidazo[1,2-a][1,3,4]thiadiazolo[2,3-d][1,3,5]triazin-5-one (IIb) two hitherto unknown heterocyclic systems. A convenient synthesis of 2,6-dimethyl-4-aminopyrimidine is described. 相似文献
100.
Summary Let (xini, y
i
be a sequence of independent identically distributed random variables, where x
i
R
p
and y
i
R, and let R
p
be an unknown vector such that y
i
=x
i
+u
i
(*), where u
i
is independent of x
i
and has distribution function F(u/), where >0 is an unknown parameter. This paper deals with a general class of M-estimates of regression and scale, (
*,*), defined as solutions of the system:
, where r= (y
i
–x
i
1*/)*, with R
p
×RR and RR. This class contains estimators of (, ) proposed by Huber, Mallows and Krasker and Welsch. The consistency and asymptotic normality of the general M-estimators are proved assuming general regularity conditions on and and assuming the joint distribution of (x
i
, y
i
) to fulfill the model (*) only approximately. 相似文献