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41.
K. E. Collins M. L. M. M. Granja R. G. Pereira Filho T. A. Anazawa I. C. S. F. Jardim 《Chromatographia》1997,45(1):99-103
Summary Poly(methyloctylsiloxane) (PMOS), sorbed into the pores of HPLC silica particles by solvent evaporation, can function as a
useful stationary phase for reversed-phase chromatography. The present work addresses the question of how the PMOS is distributed
in the pores. Measurements of the surface area (BET, N2) of a series of partially loaded samples (0–40% PMOS, m/m) using a typical batch of HPLC silica (10 μm irregular particles
with 6 nm pores) show that the specific surface area of the samples decreases linearly with the specific loading (mass of
PMOS per gram of silica). This result is not consistent with a “film” model in which the PMOS is deposited uniformly on the
pore walls, but is consistent with a model in which long segmented “plugs” of PMOS are deposited within the pore system.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
42.
正丁烷氧化制顺酐流化床催化剂的性能 总被引:1,自引:0,他引:1
考察了前驱体制备过程中水合肼/五氧化二钒摩尔比(以下简记\r\n为n(N2H4)/n(V2O5))对催化剂性能的影响.由较高的n(N2H4)\r\n/n(V2O5)比制得的催化剂,其(VO)2P2O7相含量较多,正丁烷转化\r\n率较高.随着n(N2H4)/n(V2O5)比的减小,δ-VOPO4相的含量逐\r\n渐增多,正丁烷转化率随之升高;而顺酐选择性开始时升高,达到最大\r\n值后逐渐降低.在n(N2H4)/n(V2O5)=0.34时制备的催化剂最佳\r\n,在丁烷浓度为4.0%、空速为500h-1及反应温度为420℃的反应条件\r\n下,顺酐收率可达49.74%.本文中细粒床催化剂有较大的操作弹性. 相似文献
43.
Summary On-line coupled HPLC-GC has been used for the fractionation and analysis of polychlorobiphenyls (PCB) according to their planarity.
HPLC elution with porous graphitic carbon (PGC) as stationary phase, enables fractionation of PCB into classes according to
the amount ofortho-substitution, which is related to congener toxicity. This is a preliminary step before GC analysis, which enables complete
separation of PCB congeners according to vapour pressure. Conditions for HPLC-HRGC coupling were optimised, in particular
the appropriate proper HPLC solvent was selected, because it determines eluent strength and selectivity and the transfer conditions.
Different solvent were studied—n-hexane, dichloromethane, benzene, toluene, and their mixtures.
Samples containing PCB standards and the commercial mixtures Aroclor 1242 and 1254 were analysed. Dichloromethane-n-hexane, 1:1, was selected as mobile phase for separation of poly-ortho from mono-ortho PCB; benzene-dichloromethane 30:70 resulted in the best separation of the most retained non-ortho-substituted PCB. Under these conditions the co-solvent trapping procedure, performed by adding 4% ethylbenzene as co-solvent,
was used as transfer technique to overcome the drawback of losses of volatile congeners.
Appropriate analysis conditions were successfully used to fractionate the technical PCB formulations Aroclor 1242 and 1254. 相似文献
44.
用于流化床燃烧脱硫的石灰石的反应活性评价和测试研究 总被引:4,自引:1,他引:4
对用于燃煤流化床燃烧脱硫的脱硫剂石灰石的反应活性进行了研究,提出了易于进行数学处理的石灰石硫盐化模型,得出了评价石灰石反应活性的两个指标-最大转化率和反应速率常数。研究方法除采用了传统的热天平法和鼓泡流化床外,还根据循环流化床燃烧技术的特点,发展了提出了湍流床法和石英棉法,并进行了不同试验条件下的实验研究,对不同反应活性温度技术进行了试验比较。 相似文献
45.
N. Ibriş J. Mirza-Rosca A. Santana T. Vişan 《Journal of Solid State Electrochemistry》2002,6(2):119-125
The corrosion and passivation of Zn powder particles dispersed in a paste electrode immersed in 0.5 M Na2SO4 and 5×10–3 M Na2HPO4 solutions were studied mainly by electrochemical impedance spectroscopy. The role played by diffusion in the mechanism of
anodic oxidation of zinc powder particles has been shown. It was demonstrated that the anodic reactionof Zn powder in neutral
or near neutral media involves at least two adsorbed intermediates. By simulating the porous structure of the electrode, some
information about porous nature of zinc electrode could be extracted.
Electronic Publication 相似文献
46.
《中国化学快报》2020,31(4):988-991
Designing efficient electrocatalysts with low Pt loadings for hydrogen evolution reaction(HER) is urgently required for renewable and sustainable energy conversion.Here,we report a strategy that Pt nanoparticulates are spontaneously immobilized on porous MXene/MAX monolith as HER catalysts by utilizing the redox reaction between Ti_3C_2T_x MXene and [PtCl_4]~2 in H_2 PtCl_6 aqueous solution.By taking advantage of homogeneously distributed Pt nanoparticulates on highly electrically conductive porous Ti_3C_2T_x/Ti_3AlC_2 monolith,the as-prepared electrocatalysts show high catalytic performance for hydrogen evolution.Specifically,the binder-free electrocatalysts have Pt loadings as low as 8.9 μg/cm~2,with low overpotential of 43 mV at a curre nt density of 10 mA/cm~2 and low Tafel slope that three times lower than porous Ti_3C_2T_x/Ti_3AlC_2 without Pt loading.This strategy offers a new approach to constructing ultra-low Pt-loading HER catalysts on the basis of in situ redox reaction between noble metal ions and MXenes. 相似文献
47.
A simple theoretical model is described for deriving a 1-dimensional equation for the spreading of a tracer in a steady flow at the field scale. The originality of the model is to use a stochastic appoach not in the 3-dimensional space but in the 1-D space of the stream tubes. The simplicity of calculation comes from the local relationship between permeability and velocity in a 1-D flow. The spreading of a tracer front is due to local variations in the cross-sectional area of the stream tubes, which induces randomness in travel time. The derived transport equation is averaged in the main flow direction. It differs from the standard dispersion equation. The roles of time and space variables are exchanged. This result can be explained by using the statistical theory of Continuous Time Random Walk instead of a standard Random Walk. However, the two equations are very close, since their solutions have the same first and second moments. Dispersivity is found to be equal to the product of the correlation length by the variance of the logarithm of permeability, a result similar to Gelhar's macrodispersion.Nomenclature
A
total cross-section area of the sample
-
C
(resident) concentration of tracer
-
D,D
*
dispersion coefficient
-
F
flux of tracer
-
G
probability distribution function for permeability in the stream-tube segments
-
I
tracer intensity (mass crossing a surface per unit time)
-
K
permeability
-
L
length of the medium
-
M
number of stream tubes in the medium
-
N
number of segments along a stream tube
-
P
pressure
-
Q
total flow rate in the sample
-
a
length of an elementary stream-tube segment
-
g
probability distribution function for permeability in the space
-
i, j
indices, tube numbers
-
q
flow rate in each stream tube
-
s
variable cross-section area of a stream tube
-
t, t
time
-
u
front velocity
-
x
space variable in the flow direction
-
small local variation in time
-
,
t
longitudinal, transverse dispersivity
-
porosity of the porous medium
-
correlation length in the permeability field
-
viscosity of the fluid
-
time for filling an elementary stream tube segment
-
standard deviation of a stochastic variable
-
probability distribution of arrival times (Gaussian) 相似文献
48.
The purpose of this research was to select an activated carbon and alkaline solution blend that generated the best H2S adsorption on alkaline-activated carbon. RB2 (activated carbon) impregnated with NaOH solution was shown to have the optimum H2S removal efficiency. The optimum NaOH concentration was 50 mg per gram of carbon. H2S adsorption via RB2-NaOH50 was five times that of a corresponding fresh-activated carbon. The adsorption equivalent of H2S is nearly 1 (mol-H2S/mol-AOH), therefore, H2S + AOH AHS + H2O was the major reaction. The H2S adsorption isotherm corresponded to the Freundlich isotherm. 相似文献
49.
50.
Zanin Gisella M. Neitzel Ivo De Moraes Flavio F. 《Applied biochemistry and biotechnology》1993,(1):477-489
The axial dispersion of a liquid fluidized bed of controlled pore silica (CPS) particles has been determined by the pulse
tracer method. The CPS used was the same as for enzyme immobilization, having an average diameter of 0.436 mm and mean pore
size of 37.5 nm. The fluidization liquid is α-amylase liquefied manioc starch, 30% w/v, 45°C pH=4.5. Nominal bed porosities
tested were 0.7 and 0.8. The results show that the axial dispersion coefficient increases with greater superficial liquid
velocities. Various available correlations tested disagree with each other to a large extent and are unable to represent collected
experimental data. 相似文献