全文获取类型
收费全文 | 17136篇 |
免费 | 538篇 |
国内免费 | 111篇 |
专业分类
化学 | 10823篇 |
晶体学 | 82篇 |
力学 | 393篇 |
综合类 | 2篇 |
数学 | 3605篇 |
物理学 | 2880篇 |
出版年
2023年 | 99篇 |
2022年 | 202篇 |
2021年 | 371篇 |
2020年 | 324篇 |
2019年 | 296篇 |
2018年 | 665篇 |
2017年 | 464篇 |
2016年 | 523篇 |
2015年 | 411篇 |
2014年 | 463篇 |
2013年 | 930篇 |
2012年 | 955篇 |
2011年 | 1594篇 |
2010年 | 687篇 |
2009年 | 665篇 |
2008年 | 941篇 |
2007年 | 942篇 |
2006年 | 850篇 |
2005年 | 796篇 |
2004年 | 613篇 |
2003年 | 568篇 |
2002年 | 479篇 |
2001年 | 285篇 |
2000年 | 328篇 |
1999年 | 216篇 |
1998年 | 167篇 |
1997年 | 167篇 |
1996年 | 189篇 |
1995年 | 135篇 |
1994年 | 139篇 |
1993年 | 134篇 |
1992年 | 122篇 |
1991年 | 108篇 |
1990年 | 117篇 |
1989年 | 100篇 |
1988年 | 83篇 |
1987年 | 81篇 |
1986年 | 82篇 |
1985年 | 100篇 |
1984年 | 123篇 |
1983年 | 88篇 |
1982年 | 100篇 |
1981年 | 94篇 |
1980年 | 73篇 |
1979年 | 56篇 |
1978年 | 76篇 |
1977年 | 62篇 |
1976年 | 64篇 |
1975年 | 54篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
21.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents. 相似文献
22.
We characterise the abelianisation of a group that has a presentation for which the set of relations is invariant under the full symmetric group acting on the set of generators. This improves a result of Emerson.
23.
It is a well-known feature of odd space-time dimensions d that there exist two inequivalent fundamental representations A and B of the Dirac gamma matrices. Moreover, the parity transformation swaps the fermion fields living in A and B. As a consequence, a parity-invariant Lagrangian can only be constructed by incorporating both the representations. Based upon these ideas and contrary to long-held belief, we show that in addition to a discrete exchange symmetry for the massless case, we can also define chiral symmetry provided the Lagrangian contains fields corresponding to both the inequivalent representations. We also study the transformation properties of the corresponding chiral currents under parity and charge-conjugation operations. We work explicitly in 2 + 1 dimensions and later show how some of these ideas generalize to an arbitrary number of odd dimensions. 相似文献
24.
The function lattice, or generalized Boolean algebra, is the set of ℓ-tuples with the ith coordinate an integer between 0 and a bound ni. Two ℓ-tuples t-intersect if they have at least t common nonzero coordinates. We prove a Hilton–Milner type theorem for systems of t-intersecting ℓ-tuples.Received September 29, 2004 相似文献
25.
26.
27.
Rodrigo París José Luis de la Fuente 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3538-3549
Different diblock copolymers constituted by one segment of a monomer supporting a reactive functional group, like allyl methacrylate (AMA), were synthesized by atom transfer radical polymerization (ATRP). Bromo‐terminated polymers, like polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(butyl acrylate) (PBA) were employed as macroinitiators to form the other blocks. Copolymerizations were carried out using copper chloride with N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as the catalyst system in benzonitrile solution at 70 °C. At the early stage, the ATRP copolymerizations yielded well‐defined linear block copolymers. However, with the polymerization progress a change in the macromolecular architecture takes place due to the secondary reactions caused by the allylic groups, passing to a branched and/or star‐shaped structure until finally yielding gel at monomer conversion around 40% or higher. The block copolymers were characterized by means of size exclusion chromatography (SEC), 1H NMR spectroscopy, and differential scanning calorimetry (DSC). In addition, one of these copolymers, specifically P(BA‐b‐AMA), was satisfactorily modified through osmylation reaction to obtain the subsequent amphiphilic diblock copolymer of P(BA‐b‐DHPMA), where DHPMA is 2,3‐dihydroxypropyl methacrylate; demonstrating the feasibility of side‐chain modification of the functional obtained copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3538–3549, 2007 相似文献
28.
We present a new verified optimization method to find regions for Hénon systems where the conditions of chaotic behaviour
hold. The present paper provides a methodology to verify chaos for certain mappings and regions. We discuss first how to check
the set theoretical conditions of a respective theorem in a reliable way by computer programs. Then we introduce optimization
problems that provide a model to locate chaotic regions. We prove the correctness of the underlying checking algorithms and
the optimization model. We have verified an earlier published chaotic region, and we also give new chaotic places located
by the new technique. 相似文献
29.
Electronic properties of model quantum-dot structures in zero and finite magnetic fields 总被引:1,自引:0,他引:1
H. Saarikoski E. Räsänen S. Siljamäki A. Harju M.J. Puska R.M. Nieminen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):241-252
We have computed electronic structures and total energies of circularly confined two-dimensional quantum dots and their lateral
dimers in zero and finite uniform external magnetic fields using different theoretical schemes: the spin-density-functional
theory (SDFT), the current-and-spin-density-functional theory (CSDFT), and the variational quantum Monte Carlo (VMC) method.
The SDFT and CSDFT calculations employ a recently-developed, symmetry-unrestricted real-space algorithm allowing solutions
which break the spin symmetry. Results obtained for a six-electron dot in the weak confinement limit and in zero magnetic
field as well as in a moderate confinement and in finite magnetic fields enable us to draw conclusions about the reliability
of the more approximative SDFT and CSDFT schemes in comparison with the VMC method. The same is true for results obtained
for the two-electron quantum dot dimer as a function of inter-dot distance. The structure and role of the symmetry-breaking
solutions appearing in the SDFT and CSDFT calculations for the above systems are discussed.
Received 16 October 2001 and Received in final form 17 January 2002 相似文献
30.
Csilla Bujtás 《Discrete Applied Mathematics》2007,155(11):1395-1407
For a mixed hypergraph H=(X,C,D), where C and D are set systems over the vertex set X, a coloring is a partition of X into ‘color classes’ such that every C∈C meets some class in more than one vertex, and every D∈D has a nonempty intersection with at least two classes. A vertex-orderx1,x2,…,xn on X (n=|X|) is uniquely colorable if the subhypergraph induced by {xj:1?j?i} has precisely one coloring, for each i (1?i?n). We prove that it is NP-complete to decide whether a mixed hypergraph admits a uniquely colorable vertex-order, even if the input is restricted to have just one coloring. On the other hand, via a characterization theorem it can be decided in linear time whether a given color-sequence belongs to a mixed hypergraph in which the uniquely colorable vertex-order is unique. 相似文献