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91.
Transient propagation of weak pressure perturbations in a homogeneous, isotropic, fluid saturated aquifer has been studied. A damped wave equation for the pressure in the aquifer is derived using the macroscopic, volume averaged, mass conservation and momentum equations. The equation is applied to the case of a well in a closed aquifer and analytical solutions are obtained to two different flow cases. It is shown that the radius of influence propagates with a finite velocity. The results show that the effect of fluid inertia could be of importance where transient flow in porous media is studied.List of symbols
b
Thickness of the aquifer, m
-
c
0
Wave velocity, m/s
-
k
Permeability of the porous medium, m2
-
n
Porosity of the porous medium
-
p(
,t)
Pressure, N/m2
-
Q
Volume flux, m3/s
-
r
Radial coordinate, m
-
r
w
Radius of the well, m
-
s
Transform variable
-
S
Storativity of the aquifer
-
S
d(r, t)
Drawdown, m
-
t
Time, s
-
T
Transmissivity of the aquifer, m2/s
-
(
,t)
Velocity of the fluid, m/s
-
Coordinate vector, m
-
z
Vertical coordinate, m
-
Coefficient of compressibility, m2/N
-
Coefficient of fluid compressibility, m2/N
-
Relaxation time, s
-
(r, t)
Hydraulic potential, m
-
Dynamic viscosity of the fluid, Ns/m2
-
Dimensionless radius
-
Density of the fluid, Ns2/m4
-
(, )
Dimensionless drawdown
-
Dimensionless time
-
, x
Dummy variables
-
0,
1
Auxilary functions 相似文献
92.
On the basis of copper sulphate pentahydrate thermal dissociation, for analyzed reactions I to IV, 6 thermokinetic equations was discussed. Arrhenius law parameters were determined and the isokinetic effect (IE) and Kissinger law appearing was analyzed. It was found that only dependence resulting from isokinetic effect, in the form k
m=q/T
m, relates to the suitable thermokinetic Eq. (2) and Kissinger law in modified form (14). The confirmation was made that the possibility of determining the averaged activation energy from thermokinetic equations using suitable correction coefficients exists.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
93.
From conductance and viscosities measurements on Pr4NCl, Et4NBr, and AgNO3 in acetonitrile and Et3NBr in nitrobenzene, the Walden products of the anion at infinite dilution were determined in presence of various concentrations of substituted benzoic acids. From these data it was possible to compute the values of the Walden products of the once complexed anions and to estimate the order of magnitude of the Walden products of twice complexed anions. Stokes' law is not obeyed, and the Walden products are not proportional to the third root of the molar volume of the complexed ions, as a consequence of their lack of sphericity. The assumption that the drag force which acts on the ions is proportional to the volume of the substituents results in a linear expression between the reciprocals of the Walden products and the molar volume of the ligands. The experimental results fit this expression within the limits of the experimental errors, and the slopes of the lines are nearly the same for all the anions and for the two solvents studied here, namely, 2.5×10–4 ohm-cm–5 mole-cP–1. 相似文献
94.
Mavroudis A Demertzis 《Analytica chimica acta》2004,505(1):73-76
An efficient, more sensitive and accurate spectrophotometric process is possible and can be used to obtain qualitative or quantitative results for analytes at limiting concentrations lower than usual. Transmission measurements (incident light power, P0, or transmitted, P) are performed with a fluorescence spectrometer. One cell only is used to measure standards or unknown solutions, placed between the standard holder cuvette and the emission monochromator of the instrument. The source of the radiant power (P0) is not the xenon lamp but the fluorescence or scattered radiation from the holder cuvette filled with an appropriate solution. The analyte concentration is found from a calibration graph, based upon Beer’s law or the approximate formula P0−P=2.303P0εbc, which is valid for dilute solutions. Determination of iron in a reference material, using 1,10-phenanthroline as the chromogenic reagent, was chosen as an example to demonstrate the suitability of the proposed method and clarify several important statistical questions. Also discussed is why and to what extent molecular fluorescence methods are more sensitive than molecular absorption methods. 相似文献
95.
Measurement of rheological properties of corn stover suspensions 总被引:1,自引:0,他引:1
Corn stover is currently being evaluated as a feedstock for ethanol production. The corn stover suspensions fed to reactors
typically range between 10 and 40% solids. To simulate and design bioreactors for processing highly loaded corn stover suspensions,
the rheologic properties of the suspension must be measured. In systems with suspended solids, rheologic measurements are
difficult to perform owing to settling in the measurement devices. In this study, viscosities of corn stover suspensions were
measured using a helical ribbon impeller viscometer. A calibration procedure is required for the impeller method in order
to obtain the shear rate constant, k, which is dependent on the geometry of the measurement system. The corn stover suspensions are described using a power law
flow model. 相似文献
96.
Mathematical apparatus, which makes it possible to perform calculations of the current-voltage characteristics of cathodes of fuel cells with a solid polymer electrolyte in conditions where there are present extraneous diffusion restrictions is proposed. In so doing, the partial pressure of oxygen and the absolute pressure of gas in the gas chamber may assume any values. First of all presented are the results of calculations of the current-voltage characteristics intrinsic to active layers of the air and oxygen cathodes, which are performed under the assumption that the extraneous diffusion restrictions are absent altogether. Thereafter, in the same conditions (at the same parameters that characterize the active layer of a cathode), obtained are results of a calculation of the current-voltage characteristics inherent in the air and oxygen cathodes in the presence of extraneous diffusion restrictions. Afterward there is performed an analysis of the way a gas-diffusion layer restricts the process of generation of current in a cathode and of what measures should be taken in order for the extraneous diffusion restrictions to become less significant. 相似文献
97.
Earlier studies of electric field assisted LC (EF-LC) have shown that the effect on charged analytes of the application of an electric field over a capillary LC column is relatively small. Charged analytes can only be affected by the electric field while present in the mobile phase, which makes the effective time for influence of the electric field t(0) independent of retention time. Because the charged analytes only can be affected for a short time the electric field strength ought to be high in order to increase the impact of the electric field on the separation. We have, however, found that only a relatively low electric field strength can be used in EF-LC when pressure is used as main driving force. The useful field strength was limited by a dramatic increase in the current. This increase in current was found to origin from an increased concentration of buffer ions that have an electrophoretic mobility towards the pumped flow. 相似文献
98.
Influence
of heating rate on kinetic quantities of solid phase thermal decomposition 总被引:1,自引:0,他引:1
Thermogravimetric
analyses of thermal decomposition (pyrolysis, thermal dissociation and combustion)
of 9 different samples were carried out in dynamic conditions at different
heating rates. The kinetic parameters (E, A and km)
of thermal decomposition were determined and interrelations between the parameters
and heating rate q were analyzed. There
were also relations between Arrhenius and Eyring equations analyzed for thermal
decomposition of solid phase. It was concluded that Eyring theory is an element,
which interconnects used thermokinetic equations containing Arrhenius law
and suggests considering kinetic quantities in way relative to 3 kinetic constants
(E, A
and km). Analysis
of quantities other than km (i.e. E, A, Δ+H, Δ+S) in relation to heating rate is an incomplete method
and does not lead to unambiguous conclusions. It was ascertained that in ideal
case, assuming constant values of kinetic parameters (E
and A) towards heating rate and satisfying
both Kissinger equations, reaction rate constant km
should take on values intermediate between constants (km)1
and (km)2
determined from these equations. Whereas behavior of parameters E and A towards q were not subjected to any rule, then plotting relation km vs. q in the background of (km)1
and (km)2
made possible classification of differences between thermal decomposition
processes taking place in oxidizing and oxygen-free atmosphere. 相似文献
99.
Vapor-liquid equilibria have been investigated experimentally for the nitrogen-isobutane system at temperatures from 120 K
to 220 K and at pressures up to 150 bar. Below 126.5 K, two liquid phases were observed as pressure was increased to near
the vapor pressure of pure nitrogen. The equilibrium ratio of nitrogen in the binary system and the Henry’s law constants
for nitrogen in isobutane were determined from experimental data. The experimental phase equilibrium data were correlated
by means of the Peng-Robinson equation of state. 相似文献
100.
Ward Whitt 《Queueing Systems》1991,9(3):235-268
A fundamental principle of queueing theory isL=W (Little's law), which states that the time-average or expected time-stationary number of customers in a system is equal to the product of the arrival rate and the customer-average or expected customer-stationary time each customer spends in the system. This principle is now well known and frequently applied. However, in recent years there have been extensions, such as H=G and the continuous, distributional, ordinal and central-limit-theorem versions, which show that theL=W relation, when viewed properly, has much more power than was previously realized. Moreover, connections have been established between H=G and other fundamental relations, such as the rate conservation law and PASTA (Poisson arrivals see time averages), which show that there is a much greater unity in the overall theory than was previously realized. This paper provides a review.This paper is dedicated to the memory of our colleague Professor Peter Franken (1937–1989), who contributed greatly to the subject of this paper and to queueing theory more generally. 相似文献