全文获取类型
收费全文 | 17117篇 |
免费 | 1488篇 |
国内免费 | 1628篇 |
专业分类
化学 | 3829篇 |
晶体学 | 135篇 |
力学 | 1125篇 |
综合类 | 329篇 |
数学 | 11159篇 |
物理学 | 3656篇 |
出版年
2024年 | 21篇 |
2023年 | 117篇 |
2022年 | 272篇 |
2021年 | 317篇 |
2020年 | 419篇 |
2019年 | 412篇 |
2018年 | 425篇 |
2017年 | 495篇 |
2016年 | 617篇 |
2015年 | 430篇 |
2014年 | 760篇 |
2013年 | 1396篇 |
2012年 | 822篇 |
2011年 | 929篇 |
2010年 | 846篇 |
2009年 | 1105篇 |
2008年 | 1127篇 |
2007年 | 1196篇 |
2006年 | 957篇 |
2005年 | 846篇 |
2004年 | 803篇 |
2003年 | 818篇 |
2002年 | 660篇 |
2001年 | 536篇 |
2000年 | 516篇 |
1999年 | 472篇 |
1998年 | 431篇 |
1997年 | 385篇 |
1996年 | 339篇 |
1995年 | 240篇 |
1994年 | 231篇 |
1993年 | 166篇 |
1992年 | 143篇 |
1991年 | 124篇 |
1990年 | 109篇 |
1989年 | 83篇 |
1988年 | 81篇 |
1987年 | 63篇 |
1986年 | 44篇 |
1985年 | 78篇 |
1984年 | 53篇 |
1983年 | 39篇 |
1982年 | 60篇 |
1981年 | 49篇 |
1980年 | 29篇 |
1979年 | 42篇 |
1978年 | 35篇 |
1977年 | 34篇 |
1976年 | 25篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
201.
气体放电击穿过程的物理和数值研究 总被引:1,自引:0,他引:1
胡希伟 《核聚变与等离子体物理》1994,14(1):44-50
本文对低气压(10^-2Pa)热阴极气体放电的击穿过程给出了物理描述和相应的双流体数学型,并发展了一种选择和调整未知初始条件的有效算法,可以通过伴随试射法得到对初始条件十分敏感的非线性两点边值常微分方程组的数值解,从而给出这类气体放电中击穿过程的定量描述。 相似文献
202.
Non-Markovian Brownian motion in a periodic potential is studied by means of an electronic analogue simulator. Velocity spectra, the Fourier transforms of velocity autocorrelation functions, are obtained for three types of random force, that is, a white noise, an Ornstein—Uhlenbeck process, and a quasimonochromatic noise. The analogue results are in good agreement both with theoretical ones calculated with the use of a matrix-continued-fraction method, and with the results of digital simulations. An unexpected extra peak in the velocity spectrum is observed for Ornstein-Uhlenbeck noise with large correlation time. The peak is attributed to a slow oscillatory motion of the Brownian particle as it moves back and forth over several lattice spaces. Its relationship to an approximate Langevin equation is discussed. 相似文献
203.
S. Sarkar A. D. Thakur C. V. Tomy G. Balakrishnan D. McK Paul S. Ramakrishnan A. K. Grover 《Pramana》2006,66(1):193-207
New experimental data are presented on the scan rate dependence of the magnetization hysteresis width ΔM(H) (∞ critical current densityJ
c(H)) in isothermalMH scans in a weakly pinned single crystal of Ca3Rh4Sn13, which displays second magnetization peak (SMP) anomaly as distinct from the peak effect (PE). We observe an interesting
modulation in the field dependence of a parameter which purports to measure the dynamical annealing of the disordered bundles
of vortices injected through the sample edges towards the destined equilibrium vortex state at a givenH. These data, in conjunction with the earlier observations made while studying the thermomagnetic history dependence inJ
c(H) in the tracing of the minor hysteresis loops, imply that the partially disordered state heals towards the more ordered state
between the peak field of the SMP anomaly and the onset field of the PE. The vortex phase diagram in the given crystal of
Ca3Rh4Sn13 has been updated in the context of the notion of the phase coexistence of the ordered and disordered regions between the
onset field of the SMP anomaly and the spinodal line located just prior to the irreversibility line. A multi-critical point
and a critical point in the (H,T) region of the Bragg glass phase have been marked in this phase diagram and the observed behavior is discussed in the light
of recent data on multi-critical point in the vortex phase diagram in a single crystal of Nb. 相似文献
204.
Alignment of photon-induced L3 vacancies is studied in rare earth and highZ elements at energies of experimental interest, near thresholds to 60 keV, under nonrelativistic dipole approximation. Numerical
calculations of the matrix element are undertaken to produce theoretical data for comparison with the experimental findings.
The A2 values being s>0.1 at photoelectron energies <20 keV are certainly higher than 5–8% uncertainties quoted in experimental
results. Present findings are from a very basic model, hydrogen-like and can further be treated as reference to observe the
impact of screening, relativistic, multipole and retardation corrections to the model 相似文献
205.
We study infinite-dimensional systems of ordinary differential equations having applications in some popular and important physical problems. The appearance of infinite-dimensional space–time chaos is considered, namely, the bifurcations and critical phenomena that occur in the phase space of the systems and explain some physical problems are described. 相似文献
206.
Suppose there is a Poisson process of points X
i
on the line. Starting at time zero, a grain begins to grow from each point X
i
, growing at rate A
i
to the left and rate B
i
to the right, with the pairs (A
i
, B
i
) being i.i.d. A grain stops growing as soon as it touches another grain. When all growth stops, the line consists of covered intervals (made up of contiguous grains) separated by gaps. We show (i) a fraction 1/e of the line remains uncovered, (ii) the fraction of covered intervals which contain exactly k grains is (k–1)/k!, (iii) the length of a covered interval containing k grains has a gamma(k–1) distribution, (iv) the distribution of the grain sizes depends only on the distribution of the total growth rate A
i
+B
i
, and other results. Similar theorems are obtained for growth processes on a circle; in this case we need only assume the pairs (A
i
, B
i
) are exchangeable. These results extend those of Daley, et al. (2000) who studied the case where A
i
=B
i
=1. Simulation results are given to illustrate the various theorems. 相似文献
207.
In contrast to stochastic differential equation models used for the calculation of the term structure of interest rates, we
develop an approach based on linear dynamical systems under non-stochastic uncertainty with perturbations. The uncertainty
is described in terms of known feasible sets of varying parameters. Observations are used in order to estimate these parameters
by minimizing the maximum of the absolute value of measurement errors, which leads to a linear or nonlinear semi-infinite
programming problem. A regularized logarithmic barrier method for solving (ill-posed) convex semi-infinite programming problems
is suggested. In this method a multi-step proximal regularization is coupled with an adaptive discretization strategy in the
framework of an interior point approach. A special deleting rule permits one to use only a part of the constraints of the
discretized problems. Convergence of the method and its stability with respect to data perturbations in the cone of convexC
1-functions are studied. On the basis of the solutions of the semi-infinite programming problems a technical trading system
for future contracts of the German DAX is suggested and developed.
Supported by the Stiftung Rheinland/Pfalz für Innovation, No. 8312-386261/307. 相似文献
208.
A method has been developed to determine the boiling point distribution of sulfur compounds in light cycle oils (LCO'S). The method chosen for this analysis was GC with a flame photometric detector (FPD) and pyrolyzer. Tests were carried out to evaluate the recovery efficiency, repeatability, and accuracy of the method. Repeatabilities within 2% were obtained. The recovery of benzothiophenes and dibenzothiophenes was close to 100%; this was important because these are the major sulfur components in LCO's. No hydrocarbon or solvent interferences were observed with the use of the pyrolyzer, even for a 95% solvent level. Comparison with results from other techniques showed that the method accurately determined the levels of sulfur compounds in the LCO boiling point range. 相似文献
209.
Steven J. Sepanski 《Journal of Theoretical Probability》1997,10(4):1053-1063
For independent identically distributed random vectors belonging to the generalized Domain of Attraction of the multivariate normal law, we define two partial sum processes analogous to that of Donsker's Theorem. We prove that each converges in distribution to a Brownian Motion in the space of continuous functions. One process uses nonrandom operator normalization, and the other is a studentization of the first, using normalization by the empirical covariance operator. 相似文献
210.
It was shown by G. A. Jones and the first author in [8] that underlying any map on a compact orientable surface S there is a natural complex structure making S into a Riemann surface. In this paper we consider regular maps and enquire about the Weierstrass points on the underlying Riemann surface. We are particularly interested to know when these are geometric, i.e. whether they lie at vertices, face-centres or edge-centres of the map. 相似文献