全文获取类型
收费全文 | 356242篇 |
免费 | 2761篇 |
国内免费 | 613篇 |
专业分类
化学 | 173764篇 |
晶体学 | 5914篇 |
力学 | 17385篇 |
综合类 | 12篇 |
数学 | 49554篇 |
物理学 | 112987篇 |
出版年
2021年 | 2175篇 |
2020年 | 2559篇 |
2019年 | 2845篇 |
2018年 | 11337篇 |
2017年 | 12134篇 |
2016年 | 8939篇 |
2015年 | 3803篇 |
2014年 | 5165篇 |
2013年 | 12072篇 |
2012年 | 12899篇 |
2011年 | 22080篇 |
2010年 | 14243篇 |
2009年 | 14351篇 |
2008年 | 19209篇 |
2007年 | 22314篇 |
2006年 | 9233篇 |
2005年 | 14075篇 |
2004年 | 10461篇 |
2003年 | 9989篇 |
2002年 | 8014篇 |
2001年 | 8210篇 |
2000年 | 6320篇 |
1999年 | 4634篇 |
1998年 | 3758篇 |
1997年 | 3634篇 |
1996年 | 3524篇 |
1995年 | 3238篇 |
1994年 | 3135篇 |
1993年 | 2971篇 |
1992年 | 3652篇 |
1991年 | 3587篇 |
1990年 | 3505篇 |
1989年 | 3547篇 |
1988年 | 3501篇 |
1987年 | 3450篇 |
1986年 | 3286篇 |
1985年 | 4142篇 |
1984年 | 4246篇 |
1983年 | 3411篇 |
1982年 | 3522篇 |
1981年 | 3502篇 |
1980年 | 3236篇 |
1979年 | 3627篇 |
1978年 | 3707篇 |
1977年 | 3771篇 |
1976年 | 3547篇 |
1975年 | 3249篇 |
1974年 | 3239篇 |
1973年 | 3212篇 |
1972年 | 2228篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Summary In the present paper we study truncated projections for the fanbeam geometry in computerized tomography. First we derive consistency conditions for the divergent beam transform. Then we study a singular value decomposition for the case where only the interior rays in the fan are provided, as for example in region-of-interest tomography. We show that the high angular frequency components of the searched-for densities are well determined and we present reconstructions from real data where the missing information is approximated based on the singular value decomposition.The work of the authors was supported by the Deutsche Forschungsgemeinschaft under grant Lo 310/2-4 相似文献
993.
Roger M. Hill 《The Journal of the Operational Research Society》1989,40(11):983-992
The context is that of a retail chain where stock is purchased into a central warehouse from which branch stocks are replenished. This paper considers possible methods of allocating limited warehouse stock to branches, and uses simulation to quantify the resulting benefits. 相似文献
994.
Using the symbolic computation program MAPLE, we compute several terms of an asymptotic expansion for the distribution function of the logistic midrange. 相似文献
995.
Summary We consider a class of infinite delay equations of neutral type which includes Volterrra type integral und integrodifferential equations. Using abstract approximation results (cf. Trotter-Kato-type) for strongly continuous semigroups we develop an approximation scheme which is based on approximation of the system state by Laguerre (and Legendre) polynomials. Numerical examples demonstrate the feasibility of the scheme and show infinite order convergence for smooth data.Supported in part by the Air Force Office of Scientific Research under Contracts AFORS-84-0398 and AFORS-85-0303 and the National Aeronautics and Space Administration under NASA Grant NAG-1-517 and by NSF under Grant UINT-8521208Supported in part by the Air Force Office of Scientific Research under Contract AFORS-84-0398 and in part by the Fonds zur Förderung der wissenschaftlichen Forschung, Austria, under project No. S3206 相似文献
996.
997.
O. V. Gusev V. V. Krivykh P. V. Petrovskii M. I. Rybinskaya 《Russian Chemical Bulletin》1987,36(7):1532-1534
Conclusions The allyl ligand in neutral molybdenum and cobalt complexes is readily exchanged by dienes in the presence of a strong protic acid with the formation of cationic complexes. This exchange is facilitated by an increase in the basicity of the starting compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1655–1657, July, 1987. 相似文献
998.
999.
O. V. Bakbardina I. Yu. Pukhnyarskaya M. A. Gazalieva S. D. Fazylov E. M. Makarov 《Russian Journal of Applied Chemistry》2006,79(10):1726-1728
S-Amino derivatives of O-alkyldithiocarbonic acid were prepared by oxidative condensation of certain alkaloids with sodium xanthates. Some of the compounds synthesized exhibit fungicidal activity. 相似文献
1000.
A. P. Avdeenko S. A. Konovalova O. N. Ludchenko 《Russian Journal of Organic Chemistry》2006,42(5):683-688
Reactions of halogens with N-arylsulfonyl-1,4-benzoquinone monoimines occur with the formation of a halogenonium ion that either transforms into a carbocation where the first halogen atom adds to the carbon in the ortho-position relative to the carbonyl carbon, or the halogenonium ion adds directly the second halogen atom. 相似文献