全文获取类型
收费全文 | 1822篇 |
免费 | 24篇 |
国内免费 | 14篇 |
专业分类
化学 | 1212篇 |
晶体学 | 5篇 |
力学 | 24篇 |
综合类 | 1篇 |
数学 | 338篇 |
物理学 | 280篇 |
出版年
2022年 | 10篇 |
2021年 | 22篇 |
2020年 | 18篇 |
2019年 | 14篇 |
2018年 | 16篇 |
2017年 | 14篇 |
2016年 | 35篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 91篇 |
2012年 | 78篇 |
2011年 | 97篇 |
2010年 | 62篇 |
2009年 | 41篇 |
2008年 | 97篇 |
2007年 | 90篇 |
2006年 | 87篇 |
2005年 | 86篇 |
2004年 | 79篇 |
2003年 | 63篇 |
2002年 | 77篇 |
2001年 | 29篇 |
2000年 | 45篇 |
1999年 | 23篇 |
1998年 | 17篇 |
1997年 | 23篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 25篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 25篇 |
1984年 | 38篇 |
1983年 | 19篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1979年 | 28篇 |
1978年 | 32篇 |
1977年 | 23篇 |
1976年 | 24篇 |
1975年 | 25篇 |
1974年 | 20篇 |
1973年 | 24篇 |
1972年 | 13篇 |
排序方式: 共有1860条查询结果,搜索用时 15 毫秒
1.
An optimal control model of exhaustible resources is used to clarify the long run relationship between mineral rent and depletion cost at the industry level. A standard first order condition of the time rate of change of rents is reformulated to reveal that rent data may be used to help forecast the rise in extraction costs resulting from resource depletion. This application of the theory of exhaustible resources is illustrated using historical mineral industry rent and extraction cost data. A forecast of U.S. coal extraction costs, following the method proposed in this paper, suggests that future rates of extraction cost increases will be similar to rates experienced in the past. 相似文献
2.
R. Martínez-Snchez J. A. Matutes-Aquino O. Ayala-Valenzuela S. D. De la Torre 《Physica B: Condensed Matter》2002,320(1-4):285-287
An amorphous phase containing traces of non-transformed Co and Ti powders was obtained by mechanical alloying nominal compositions of Co67Ti33 and Co50Ti50 in a high-energy ball-mill. These alloys were prepared from elemental powders of Co and Ti. The heat treatment of Co67Ti33 at 573, 873 and 1173 K crystallized nanoparticles of Co2Ti and Co3Ti compounds, while the same treatments conducted on Co50Ti50 resulted in the formation of Co2Ti and CoTi nanoparticles. The saturation magnetizations reached a maximum value in the amorphous state and they decreased when the temperatures of the heat treatment rose. Demagnetizing interparticle interaction effects were estimated through hysteresis loops and initial magnetization curves using the Fourier technique. 相似文献
3.
4.
Starting with a partition of a rectangular box into subboxes, it is shown how to construct a natural tetrahedral (type-4) partition and associated trivariate C 1 quintic polynomial spline spaces with a variety of useful properties, including stable local bases and full approximation power. It is also shown how the spaces can be used to solve certain Hermite and Lagrange interpolation problems. 相似文献
5.
6.
Summary In this paper we show that the transverse mode evolution of a FEL operating with short pulses can be treated, in the small-signal
and low-gain regime, using a relatively simple mathematical technique leading to a potentially fast numerical algorithm. We
also point out that analytical solutions can be obtained for the cases where the slippage length is small compared to the
longitudinal bunch length. 相似文献
7.
Efficiencies of the maximum pseudolikelihood estimator and a number of related estimators for the case-cohort sampling design in the proportional hazards regression model are studied. The asymptotic information and lower bound for estimating the parametric regression parameter are calculated based on the effective score, which is obtained by determining the component of the parametric score orthogonal to the space generated by the infinite-dimensional nuisance parameter. The asymptotic distributions of the maximum pseudolikelihood and related estimators in an i.i.d. setting show that these estimators do not achieve the computed asymptotic lower bound. Simple guidelines are provided to determine in which instances such estimators are close enough to efficient for practical purposes. 相似文献
8.
9.
10.
Trivariate Cr macroelements defined in terms of polynomials of degree 8r + 1 on tetrahedra are analyzed. For r = 1,2, these spaces reduce
to well-known macroelement spaces used in data fitting and in the finite-element method.
We determine the dimension of these spaces, and describe stable local minimal determining sets and nodal minimal determining
sets. We also show that the spaces approximate smooth functions to optimal order. 相似文献