全文获取类型
收费全文 | 9838篇 |
免费 | 199篇 |
国内免费 | 68篇 |
专业分类
化学 | 6592篇 |
晶体学 | 85篇 |
力学 | 284篇 |
综合类 | 1篇 |
数学 | 1146篇 |
物理学 | 1997篇 |
出版年
2022年 | 55篇 |
2021年 | 59篇 |
2020年 | 103篇 |
2019年 | 100篇 |
2018年 | 68篇 |
2017年 | 77篇 |
2016年 | 188篇 |
2015年 | 161篇 |
2014年 | 183篇 |
2013年 | 503篇 |
2012年 | 417篇 |
2011年 | 589篇 |
2010年 | 256篇 |
2009年 | 242篇 |
2008年 | 506篇 |
2007年 | 527篇 |
2006年 | 494篇 |
2005年 | 495篇 |
2004年 | 434篇 |
2003年 | 390篇 |
2002年 | 359篇 |
2001年 | 194篇 |
2000年 | 206篇 |
1999年 | 136篇 |
1998年 | 111篇 |
1997年 | 120篇 |
1996年 | 185篇 |
1995年 | 120篇 |
1994年 | 125篇 |
1993年 | 145篇 |
1992年 | 136篇 |
1991年 | 127篇 |
1990年 | 107篇 |
1989年 | 85篇 |
1988年 | 121篇 |
1987年 | 93篇 |
1986年 | 90篇 |
1985年 | 136篇 |
1984年 | 130篇 |
1983年 | 77篇 |
1982年 | 124篇 |
1981年 | 120篇 |
1980年 | 110篇 |
1979年 | 116篇 |
1978年 | 101篇 |
1977年 | 116篇 |
1976年 | 95篇 |
1975年 | 100篇 |
1974年 | 92篇 |
1973年 | 79篇 |
排序方式: 共有10000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.
3.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive. 相似文献
4.
A practical Sonogashira alkynylation protocol for the preparation of 8-alkynylated adenosines and guanosines has been developed. Protection of the sugar hydroxyl substituents is not required; protection hinders the purification of these products. A preliminary fluorescent study is reported, which shows that the presence of a substituent on the phenylene ring influences the fluorescent properties considerably, an outcome that could be utilized in biological applications. 相似文献
5.
A parallel method for time discretization of parabolic equations based on Laplace transformation and quadrature 总被引:5,自引:0,他引:5
We consider the discretization in time of an inhomogeneous parabolicequation in a Banach space setting, using a representation ofthe solution as an integral along a smooth curve in the complexleft half-plane which, after transformation to a finite interval,is then evaluated to high accuracy by a quadrature rule. Thisreduces the problem to a finite set of elliptic equations withcomplex coefficients, which may be solved in parallel. The paperis a further development of earlier work by the authors, wherewe treated the homogeneous equation in a Hilbert space framework.Special attention is given here to the treatment of the forcingterm. The method is combined with finite-element discretizationin spatial variables. 相似文献
6.
The basic features of a chemical measurement 总被引:2,自引:0,他引:2
7.
8.
In this paper we prove the equivalence of various algebraically or geometrically defined assembly maps used in formulating the main conjectures in K- and L-theory, and C*-theory.Partially supported by NSERC grant A4000 and NSF grant DMS 9104026. The authors also wish to thank the SFB für Geometrie und Analysis, Münster, and the Max Planck Institut für Mathematik, Bonn, for their hospitality and support.Received: 7 May 2001 相似文献
9.
10.
D. Ohlberg J.J. Blackstock R. Ragan S. Kim R. Stanley Williams 《Applied Physics A: Materials Science & Processing》2005,80(6):1327-1334
A recently demonstrated [1] in-vacuo template-stripping process is applied to the study of platinum films stripped from ultra-flat silicon-oxide surfaces. Template-stripped (TS) Pt surfaces, prepared with a range of post-deposition annealing times prior to being stripped from the templating surface in an ultra-high vacuum (UHV) environment, are examined by UHV scanning tunneling microscopy (STM). These studies reveal that without post-deposition annealing, TS Pt surfaces are largely made up of poorly-ordered, granular nanostructures undesirable for many applications. The post-deposition annealing treatments explored in the study result in the emergence and continuous growth of large smooth crystallites. Issues with crystallite orientation relative to the TS surface and artefacts arising as a result of the epoxy used in the template-stripping process are presented and discussed in relation to optimizing the template-stripping procedure for specific applications such as self-assembled monolayer (SAM) formation for molecular electronics. PACS 68.37.Ef; 68.47.De; 68.55.Jk; 81.05.Bx; 81.15.Ef 相似文献