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21.
Abstract— Intact leaves, previously adapted to darkness for a prolonged period of time, were suddenly illuminated with a strong, photosynthetically saturating, white light (ca 1500 μmol m−2 s_1 ), resulting in the rapid establishment of a large energy-dependent chlorophyll fluorescence quenching (qE ) as shown by in vivo fluorescence measurements with a pulse amplitude modulation technique. Two different photothermal methods, photoacoustic spectroscopy and photothermal deflection spectroscopy, were used to monitor thermal deactivation of excited pigments during the dark-light transitions. The in vivo photothermal signals measured with both techniques were shown to remain constant during induction of photosynthesis under high light conditions, suggesting that, in contrast to current hypotheses, energy-dependent quenching qE is not associated with significant changes in thermal dissipation of absorbed light energy in the chloroplasts. When photosynthesis was induced with a low-intensity modulated light, a noticeable decrease in the heat emission yield was observed resulting from the progressive activation of the competing photochemical processes. 相似文献
22.
The structures of Beccapoline and Beccapolinium, two new isoquinoline alkaloids from , Annonaceae, have been elucidated by spectroscopic analysis. They are the first examples of natural bisaporphines. 相似文献
23.
Bruno Hasiak Guy Ricart Didier Barbry Daniel Couturier Michel Hardy 《Journal of mass spectrometry : JMS》1981,16(1):17-20
The ammonia chemical ionization desorption spectra of N,N-dimethyl quaternary ammonium iodides in addition to high protonated molecular ion [M + H]+ intensity, show signals for an ion radical composed of N-methyl abstracted salt cation and ammonia [C + NH3? CH3]+˙. These ions corresponding to the cation +2 show increased importance in the chemical ionization mode, using the same reagent gas. The technique of chemical ionization desorption appears suitable for the analysis of salts, and thus for the determination of the molecular weight of both anion and cation. 相似文献
24.
H. Münzel F. Michel P. P. Coetzee V. Krivan 《Journal of Radioanalytical and Nuclear Chemistry》1977,37(1):267-273
The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the16O(n, p)16N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons.
It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam
current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen.
In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron
beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about
1010 n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced
fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent. 相似文献
25.
Under the action of nucleophile reagents such as water, hydrogen sulfide and sodium borohydride, the saturated azaheterocyclic spirochromenes are opened either on the azaheterocyclic side or on the benzopyran side or on both parts simultaneously. The merocyanines are either partially reduced or decomposed by the sodium borohydride. 相似文献
26.
S. Rezzoug G. Barci-Funel F. Fernex H. Michel G. Ardisson 《Journal of Radioanalytical and Nuclear Chemistry》2003,256(1):167-169
When a river flow rate is known on one point, it is possible to determine the one of upstream tributaries. This can be done by measuring the concentrations of a dissolved element (for example Ca2+), provided that no chemical precipitations have occurred in mixture waters. In this later case, the determination of flow rate is however possible by isotopic geochemistry, by knowing isotopic ratios of an element, for ex. 234U/238U, in each river considered and the ratio of the concentrations in dissolved 238U in two of them. A study of the Var and its tributary the Vésubie is performed: in January 31st, 2001, the flow rate D3, downstream the confluence was 35 m3/s. The ratio of the 238U concentrations in the Vésubie river and in the Var upstream (238U1/238U2) was 5.5. The isotopic ratios 234U/238U measured in the Var, downstream the confluence were R3 = 1.51, upstream R2 = 1.75, and in the Vésubie R1 = 1.08. We have calculated the Vésubie flow rate as D1 = 3.2 m3/s. 相似文献
27.
28.
Paul Ruelle Michel Buchmann Hô Nam-Tran Ulrich W. Kesselring 《Journal of computer-aided molecular design》1992,6(5):431-448
Summary The thermodynamics of mobile order is applied to predict the aqueous solubility of liquid and solid aliphatic and polycyclic aromatic hydrocarbons. The solubility values are mainly determined by the magnitude of the hydrophobic effect. However, contrary to the solubilities of the alkanes, the solubilities of polycyclic aromatic hydrocarbons in water predicted in absence of solute-solvent hydrogen (H) bonds are systematically too low. This shows the contribution of weak specific interactions between the OH groups and the electrons of the aromatic substances. According to the theory, these interactions are characterized by a stability bility constant Ko which can be derived from solubility data. At 25°C, this constant amounts to 80 cm3/mol, the order of magnitude of which can be explained by the competition of these intermolecular bonds with the rather weak self-association bonds in the secondary chains of water. 相似文献
29.
Michel Talagrand 《Inventiones Mathematicae》1992,107(1):1-40
Summary Forq>2, an operator fromC(K) toX is of cotypeq if and only if it factors through the Lorentz space
. Forq=2, ifX is a rearrangement invariant space on [0, 1], the injectionC([0, 1])X is of cotype 2 if and only if it factors through the Lorentz space
; but there is a cotype 2 operator C(K) that does not factor through
. If a Banach latticeX satisfies the Orlicz property, any bounded lattice operatorT:C(K)X is of cotype 2. We however construct a Banach lattice with the Orlicz property, but that fails to be of cotype 2.Oblatum 4-VII-1990 & 18-IV-1991Work partially supported by an NSF grant 相似文献
30.
Michel Talagrand 《Journal of Theoretical Probability》1992,5(2):327-331