全文获取类型
收费全文 | 5058篇 |
免费 | 137篇 |
国内免费 | 44篇 |
专业分类
化学 | 3696篇 |
晶体学 | 29篇 |
力学 | 113篇 |
数学 | 673篇 |
物理学 | 728篇 |
出版年
2022年 | 23篇 |
2021年 | 48篇 |
2020年 | 54篇 |
2019年 | 68篇 |
2018年 | 47篇 |
2017年 | 39篇 |
2016年 | 106篇 |
2015年 | 76篇 |
2014年 | 91篇 |
2013年 | 214篇 |
2012年 | 268篇 |
2011年 | 344篇 |
2010年 | 144篇 |
2009年 | 154篇 |
2008年 | 259篇 |
2007年 | 311篇 |
2006年 | 302篇 |
2005年 | 321篇 |
2004年 | 281篇 |
2003年 | 240篇 |
2002年 | 224篇 |
2001年 | 101篇 |
2000年 | 71篇 |
1999年 | 44篇 |
1998年 | 52篇 |
1997年 | 48篇 |
1996年 | 77篇 |
1995年 | 46篇 |
1994年 | 55篇 |
1993年 | 67篇 |
1992年 | 48篇 |
1991年 | 50篇 |
1989年 | 40篇 |
1988年 | 44篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 59篇 |
1984年 | 54篇 |
1983年 | 45篇 |
1982年 | 53篇 |
1981年 | 69篇 |
1980年 | 51篇 |
1979年 | 34篇 |
1978年 | 40篇 |
1977年 | 42篇 |
1976年 | 43篇 |
1975年 | 31篇 |
1974年 | 39篇 |
1973年 | 41篇 |
1972年 | 29篇 |
排序方式: 共有5239条查询结果,搜索用时 15 毫秒
991.
Craig P ButtsMikael Jazdzyk Thomas DrewelloSotirios Kotsiris 《Tetrahedron letters》2003,44(17):3565-3567
The 1H NMR spectrum of the piperazine-C60 monoadduct has been assigned for the first time almost 10 years after it was synthesised. The preparation and characterisation of the first (C2-substituted piperazine)-C60 monoadduct are also described, revealing the C2-substituent as occupying an exo position on the addend. 相似文献
992.
Craig R. Guilbault 《Topology》2007,46(2):89-102
A compactum X is an ‘absolute cone’ if, for each of its points x, the space X is homeomorphic to a cone with x corresponding to the cone point. In 1971, J. de Groot conjectured that each n-dimensional absolute cone is an n-cell. In this paper, we give a complete solution to that conjecture. In particular, we show that the conjecture is true for n≤3 and false for n≥5. For n=4, the absolute cone conjecture is true if and only if the 3-dimensional Poincaré Conjecture is true. 相似文献
993.
The purpose of this study was to describe relationships among instructor and student goals, course design, and student strategies for learning physics in a traditional introductory undergraduate physics course for nonmajors. The procedures included 16 hours ofnonparticipant observation, during which detailed field notes and photographs were taken and documents were collected. Audiotaped open-ended interviews were given to instructors and students, and all students participated in a limited survey. The data were analyzed using qualitative methods of the Chicago School. Results indicated that both differing goals of students and instructors and the structure of the course inhibited the understanding of physics and were conducive to students engaging in unexpected behaviors designed to help them successfully pass the course. The consequences of the structure of the course and subsequent student behaviors inhibited their understanding and appreciation of physics and deterred them from enrolling in further science courses. The paper includes implications for teaching introductory college physics. 相似文献
994.
995.
996.
997.
Anzar Khan Michael Malkoch Martha F. Montague Craig J. Hawker 《Journal of polymer science. Part A, Polymer chemistry》2008,46(18):6238-6254
Hyperbranched polymers were prepared from a variety of mono‐ and difunctional monomers and used in the development of novel UV‐imprint lithography (UV‐IL) resists. The unique physical and chemical properties of these hyperbranched materials significantly increase the range of molecular systems that could be imprinted. Traditional challenges, such as the use of monomers that have low boiling points or the use of insoluble/highly crystalline momomers, are overcome by the preparation of hyperbranched polymers that incorporate these repeat units. In addition, the low viscosity of the hyperbranched macromolecules and the large number of reactive chain ends overcome many difficulties that are traditionally associated with the use of polymeric materials as imprint resists. Hyperbranched polymers containing up to 12 mol % pendant vinyl groups, needed for secondary crosslinking during imprinting, were prepared with a wide range of repeat unit structures and successfully imprinted with features from tens of microns to ∼ 100 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6238–6254, 2008 相似文献
998.
Benzo[b]thiophenes substituted at the 3 position with methyl or carboxymethyl and at the 5 position with methyl, methoxy, chloro, bromo and nitro were prepared by cyclization of thiophenyl-acetals and ketones using a suspension of polyphosphoric acid in refluxing chlorobenzene. The overall efficiency of this method is superior to literature procedures because of the lower temperature and the limited amount of PPA used. 相似文献
999.
Lawrence Corwin 《Journal of Functional Analysis》1985,61(3):328-341
Let π be an irreducible representation occurring in 2(Г?N), where N is a nilpotent Lie group and Γ is a discrete, cocompact subgroup. The projection onto the π-equivariant subspace is given by convolution against a distribution Dπ. For certain π, we obtain an estimate on the order of Dπ. The condition on π involves an extension of the “canonical objects” associated to elements of the Kirillov orbit of π; there does not appear to be an example in the literature where it is not satisfied. 相似文献
1000.
We consider general constraints on baryosynthesis in low-energy SU(3) × SU(2) × U(1) theories. We find in general that phenomenologically acceptable models exist, which are unifiable at higher energies-but which all require exotic fermion content. 相似文献