全文获取类型
收费全文 | 7172篇 |
免费 | 315篇 |
国内免费 | 80篇 |
专业分类
化学 | 4273篇 |
晶体学 | 221篇 |
力学 | 193篇 |
综合类 | 4篇 |
数学 | 1046篇 |
物理学 | 1830篇 |
出版年
2022年 | 72篇 |
2021年 | 69篇 |
2020年 | 93篇 |
2019年 | 141篇 |
2018年 | 100篇 |
2017年 | 98篇 |
2016年 | 142篇 |
2015年 | 122篇 |
2014年 | 187篇 |
2013年 | 562篇 |
2012年 | 312篇 |
2011年 | 354篇 |
2010年 | 239篇 |
2009年 | 212篇 |
2008年 | 248篇 |
2007年 | 253篇 |
2006年 | 219篇 |
2005年 | 176篇 |
2004年 | 173篇 |
2003年 | 202篇 |
2002年 | 171篇 |
2001年 | 100篇 |
2000年 | 94篇 |
1999年 | 66篇 |
1997年 | 70篇 |
1996年 | 79篇 |
1995年 | 86篇 |
1994年 | 82篇 |
1993年 | 84篇 |
1992年 | 98篇 |
1991年 | 88篇 |
1990年 | 76篇 |
1989年 | 110篇 |
1988年 | 76篇 |
1987年 | 70篇 |
1986年 | 81篇 |
1985年 | 126篇 |
1984年 | 119篇 |
1983年 | 93篇 |
1982年 | 98篇 |
1981年 | 101篇 |
1980年 | 85篇 |
1979年 | 98篇 |
1978年 | 74篇 |
1977年 | 101篇 |
1976年 | 79篇 |
1975年 | 86篇 |
1974年 | 92篇 |
1973年 | 97篇 |
1972年 | 57篇 |
排序方式: 共有7567条查询结果,搜索用时 31 毫秒
911.
John D. Buynak M.Narayana Rao Ramalakshmi Yegna Chandrasekaran Elizabeth Haley Patrice de Meester Shirley C. Chu 《Tetrahedron letters》1985,26(41):5001-5004
Synthetically valuable α-alkylidene-β-lactams are produced from the addition of chlorosulfonyl isocyanate to allenyl sulfides. 相似文献
912.
Titanium oxide on silica-alumina support is found to be effective for oligomerisation of phenyl acetylene. Cyclic trimerisation of the acetylene leading to trisubstituted benzene was also found to occur during the oligomerisation, in addition to the formation of small quantities of a ketone by the reaction of phenyl acetylene with moisture over the catalyst surface. 相似文献
913.
914.
915.
From a careful examination of the diurnal variation of cosmic ray intensity at high energies and the interplanetary field
characteristics, the average characteristics of diurnal variation were recently explained by us in terms of a balance between
outward convection and field aligned diffusion, the latter arising out of a positive radial density gradient. In this paper,
we extend this new concept to explain the large variability observed in the diurnal variation on a day-to-day basis and further
demonstrate that the measurement of diurnal anisotropy characteristic of cosmic ray particles on a day-to-day basis can be
used directly to infer the nature and scale sizes of interplanetary field parameters. Comparing with the magnetic field vector,
we show that this simple concept holds good on more than 80% of days. On the rest 20% of days which have a predominant morning
maxima, the diurnal anisotropy characteristics seem to indicate the presence of a significant component of transverse diffusion
current in addition to the normal convection and diffusion flow. Such days are found to be present in the form of trains of
consecutive days and are found to be associated with abrupt changes in the interplanetary field direction having scale sizes
>4 hr. The value ofK
⊥/K
‖ which is normally about ⩽0.05 is found to be ≈1.0 on non-field aligned days. 相似文献
916.
S. S. Rao R. Chandrasekaran K. P. K. Nair 《Journal of Optimization Theory and Applications》1973,11(6):627-637
In this paper, a two-person zero-sum discounted stochastic game with a finite state space is considered. The movement of the game from state to state is jointly controlled by the two players with a finite number of alternatives available to each player in each of the states. We present two convergent algorithms for arriving at minimax strategies for the players and the value of the game. The two algorithms are compared with respect to computational efficiency. Finally, a possible extension to nonzero sum stochastic game is suggested.This research was supported in part by funds allocated to the Department of Operations Research, School of Management, Case Western Reserve University under Contract No. DAHC 19-68-C-0007 (Project Themis) with the U.S. Army Research Office, Durham, North Carolina. The authors thank the referees for their valuable suggestions. 相似文献
917.
918.
The g-factors of the 10? isomeric states in 202Bi and 204Bi have been measured by the method of in-beam TDPAD. The experimental values confirm the previously suggested shell-model configuration. 相似文献
919.
B. S. Maruthiprasad M. N. Sastri S. Rajagopal K. Seshan K. R. Krishnamurthy T. S. R. Prasada Rao 《Journal of Chemical Sciences》1988,100(6):459-462
The preparation of a novel nickel trihydroxy isocyanate, along with its distinguishing physicochemical characteristics has
been reported for the first time. 相似文献
920.
Hypoiodite oxidises sulphides much more rapidly than does iodate under comparable experimental conditions. A procedure is reported for the determination of soluble and insoluble sulphides by oxidation to sulphate with hypoiodite. This is an improvement over Bethge's iodate method. 相似文献