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251.
252.
Elżbieta Lipiec Grzegorz Siara Katarzyna Bierla Laurent Ouerdane Joanna Szpunar 《Analytical and bioanalytical chemistry》2010,397(2):731-741
A method for the simultaneous determination of selenomethionine (SeMet), selenocysteine (SeCys), and selenite [Se(IV)] in
chicken eggs was developed. A sample preparation protocol including defatting, protein denaturation, and carbamidomethylation
was optimized in order to achieve complete protein digestion and to avoid SeCys losses. Quantification was carried out by
reversed-phase HPLC–inductively coupled plasma mass spectrometry (ICP MS) after quantitative isolation of the selenium-containing
fraction by size-exclusion liquid chromatography. The detection limits were 0.06, 0.003, and 0.01 μg g−1 (dry weight) for SeCys, Se(IV) and SeMet, respectively, and the precision was 5–10%. The end products of carbamidomethylation
of the different selenium species were identified for the first time by electrospray QTOF MS after custom-designed 2D HPLC
purification. Differences in selenium speciation in egg yolk and white were highlighted, the yolk containing more SeCys and
the white more SeMet. An insight into selenium bioaccessibility in eggs was obtained by digestion with simulated gastric and
gastrointestinal juices and size-exclusion HPLC-ICP MS. 相似文献
253.
A predictive reactivity of Cp2An(IV)Me2 (with An = uranium [U], neptunium [Np] and plutonium [Pu]) with pyridine N-oxide has been studied at the theoretical level. The predictive reaction, which consists in the formation of a formaldehyde complex, begins after the initial formation of a cyclometalated complex produced by a C-H activation of the pyridine N-oxide. A difference of reactivity between U/Pu and Np has been observed and has been attributed to the presence of a more covalent bond between Np and the carbene group in the transition state of formation of a transient carbene intermediate. 相似文献
254.
Laurent Bultel Malena Landoni Eric Grand Alicia S. Couto José Kovensky 《Journal of the American Society for Mass Spectrometry》2010,21(1):178-190
Nitrous acid degradation of heparin followed by high-performance anion-exchange chromatography (HPAEC) separation and ultraviolet
matrix assisted laser desorption/ionization time-of-flight (UV-MALDI-TOF) analysis led to the structural determination of
six sulfated oligosaccharides. Three different matrices (α-cyano-4-hydroxycinnamic acid (CHCA), nor-harmane, and dihydroxybenzoic
acid (DHB)) have been used, and the complementary results obtained allowed in most cases to assign the position of sulfate
groups. Based on the different cleavages produced on the purified oligosaccharides in source during the MS analysis by the
use of the different matrices, this approach provides a new tool for structural analysis. 相似文献
255.
Recent development in nanotechnology has provided new tools for cancer therapy and diagnostics. Because of their small size, nanoscale devices readily interact with biomolecules both on the cell surface and inside the cell. Nanomaterials, such as fullerenes and their derivatives, are effective in terms of interactions with the immune system and have great potential as anticancer drugs. Comparatively, other nanomaterials are able to load active drugs to cancer cells by selectively using the unique tumor environment, such as their enhanced permeability, retention effect and the specific acidic microenvironment. Multifunctional and multiplexed nanoparticles, as the next generation of nanoparticles, are now being extensively investigated and are promising tools to achieve personalized and tailored cancer treatments. 相似文献
256.
Bruno Therrien Julien Freudenreich Sergey S. Shapovalov Laurent Plasseraud 《Journal of organometallic chemistry》2010,695(3):409-1919
A series of neutral, anionic and cationic arene ruthenium complexes containing the trichlorostannyl ligand have been synthesised from SnCl2 and the corresponding arene ruthenium dichloride dimers [(η6-arene)Ru(μ2-Cl)Cl]2 (arene = C6H6, PriC6H4Me). While the reaction with triphenylphosphine and stannous chloride only gives the neutral mono(trichlorostannyl) complexes [(η6-C6H6)Ru(PPh3)(SnCl3)Cl] (1) and [(η6-PriC6H4Me)Ru(PPh3)(SnCl3)Cl] (2), the neutral di(trichlorostannyl) complex [(η6-PriC6H4Me)Ru(NCPh)(SnCl3)2] (3) could be obtained for the para-cymene derivative with benzonitrile as additional ligand. By contrast, the analogous reaction with the benzene derivative leads to a salt composed of the cationic mono(trichlorostannyl) complex [(η6-C6H6)Ru(NCPh)2(SnCl3)]+ (5) and of the anionic tris(trichlorostannyl) complex [(η6-C6H6)Ru(SnCl3)3]− (6). On the other hand, [(η6-PriC6H4Me)Ru(μ2-Cl)Cl]2 reacts with SnCl2 and hexamethylenetetramine hydrochloride or 18-crown-6 to give the anionic di(trichlorostannyl) complex [(η6-PriC6H4Me)Ru(SnCl3)2Cl]− (4), isolated as the hexamethylenetetrammonium salt or the chloro-tin 18-crown-6 salt. The single-crystal X-ray structure analyses of 1, 2, [(CH2)6N4H][4], [(18-crown-6)SnCl][4] and [5][6] reveal for all complexes a pseudo-tetrahedral piano-stool geometry with ruthenium-tin bonds ranging from 2.56 (anionic complexes) to 2.60 Å (cationic complex). 相似文献
257.
Ahmed Yahia Polly L. Arnold Prof. Dr. Jason B. Love Dr. Laurent Maron Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(16):4881-4888
A theoretical investigation of the reductive oxo‐group silylation reaction of the uranyl dication held in a Pacman macrocylic environment has been carried out. The effect of the modeling of the Pacman ligand on the reaction profiles is found to be important, with the dipotassiation of a single oxo group identified as a key component in promoting the reaction between the Si? X and uranium–oxo bonds. This reductive silylation reaction is also proposed to occur in an aqueous environment but was found not to operate on bare ions; in this latter case, substitution of a ligand in the equatorial plane was the most likely reaction. These results demonstrate the importance of the presence but not the identity of the equatorial ligands upon the silylation of the uranyl U? O bond. 相似文献
258.
When a test sound consisting of pure tones with equal intensities is preceded by a precursor sound identical to the test sound except for a reduction in the intensity of one tone, an auditory "enhancement" phenomenon occurs: In the test sound, the tone which was previously softer stands out perceptually. Here, enhancement was investigated using inharmonic sounds made up of five pure tones well resolved in the auditory periphery. It was found that enhancement can be elicited not only by increases in intensity but also by shifts in frequency. In both cases, when the precursor and test sounds are separated by a 500-ms delay, inserting a burst of pink noise during the delay has little effect on enhancement. Presenting the precursor and test sounds to opposite ears rather than to the same ear significantly reduces the enhancement resulting from increases in intensity, but not the enhancement resulting from shifts in frequency. This difference suggests that the mechanisms of enhancement are not identical for the two types of change. For frequency shifts, enhancement may be partly based on the existence of automatic "frequency-shift detectors" [Demany and Ramos, J. Acoust. Soc. Am. 117, 833-841 (2005)]. 相似文献
259.
Laurent Galbrun 《Applied Acoustics》2011,(4):205-209
This paper examines space averaging methods applied to structural level differences measured in lightweight building structures (two beam junction and single plate and beam junction). The methods studied include the averaging assuming a constant input force, the averaging based on a constant vibration level across the source element, and the arithmetic averaging of level differences. Tests indicate that a fairly steady input force can be easily produced when using an impulsive source such as a hammer; the constant input force method is then appropriate and can be used to space average level differences (the two beam structure showing a standard deviation of 0.1 dB from the averaging based on levels normalised to the force). On the other hand, acceleration levels can exhibit significant variations with position due to the low mode count and modal overlap of some lightweight elements such as timber beams. Variations in the vibration level across the source element can then be responsible for large inaccuracies in the level difference calculated from the constant level assumption, the two beams’ results showing errors greater than 5 dB at several 1/3 octave band frequencies. The latter averaging method is then inappropriate and should not be used. 相似文献
260.
Parthey CG Matveev A Alnis J Bernhardt B Beyer A Holzwarth R Maistrou A Pohl R Predehl K Udem T Wilken T Kolachevsky N Abgrall M Rovera D Salomon C Laurent P Hänsch TW 《Physical review letters》2011,107(20):203001
We have measured the 1S-2S transition frequency in atomic hydrogen via two-photon spectroscopy on a 5.8 K atomic beam. We obtain f(1S-2S) = 2,466,061,413,187,035 (10) Hz for the hyperfine centroid, in agreement with, but 3.3 times better than the previous result [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)]. The improvement to a fractional frequency uncertainty of 4.2 × 10(-15) arises mainly from an improved stability of the spectroscopy laser, and a better determination of the main systematic uncertainties, namely, the second order Doppler and ac and dc Stark shifts. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb. 相似文献