全文获取类型
收费全文 | 3193篇 |
免费 | 249篇 |
国内免费 | 307篇 |
专业分类
化学 | 403篇 |
晶体学 | 7篇 |
力学 | 371篇 |
综合类 | 75篇 |
数学 | 2410篇 |
物理学 | 483篇 |
出版年
2023年 | 20篇 |
2022年 | 25篇 |
2021年 | 39篇 |
2020年 | 52篇 |
2019年 | 75篇 |
2018年 | 77篇 |
2017年 | 124篇 |
2016年 | 80篇 |
2015年 | 66篇 |
2014年 | 112篇 |
2013年 | 274篇 |
2012年 | 98篇 |
2011年 | 138篇 |
2010年 | 141篇 |
2009年 | 136篇 |
2008年 | 210篇 |
2007年 | 207篇 |
2006年 | 175篇 |
2005年 | 186篇 |
2004年 | 166篇 |
2003年 | 144篇 |
2002年 | 173篇 |
2001年 | 150篇 |
2000年 | 136篇 |
1999年 | 107篇 |
1998年 | 119篇 |
1997年 | 92篇 |
1996年 | 96篇 |
1995年 | 37篇 |
1994年 | 41篇 |
1993年 | 15篇 |
1992年 | 32篇 |
1991年 | 21篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1936年 | 3篇 |
排序方式: 共有3749条查询结果,搜索用时 31 毫秒
101.
The critical group C(G) of a graph G is a refinement of the number of spanning trees of the graph and is closely connected with the Laplacian matrix. Let r(G) be the minimum number of generators (i.e., the rank) of the group C(G) and β(G) be the number of independent cycles of G. In this paper, some forbidden induced subgraphs are given for r(G) = n − 3 and all graphs with r(G) = β(G) = n − 3 are characterized. 相似文献
102.
103.
设G是有限群,Ns(G)表示G的子群共轭类长构成的集合.本文研究Ns(G)中只有两个元素时有限群G的结构,在非幂零情形时给出了G的完全分类,在幂零情形时获得了G的一些性质. 相似文献
104.
构造了一类新的可解群,使得其中的每个成员均不能同构于M-群的正规子群,推广了R.W.van der Waall关于M-群的一个类似结果. 相似文献
105.
In this paper, the structure of the critical group of the graph K
m
× C
n
is determined, where m, n ≥ 3. 相似文献
106.
Paolo Casini 《International Journal of Non》2011,46(1):142-150
The non-linear modal properties of a vibrating 2-DOF system with non-smooth (piecewise linear) characteristics are investigated; this oscillator can suitably model beams with a breathing crack or systems colliding with an elastic obstacle. The system having two discontinuity boundaries is non-linearizable and exhibits the peculiar feature of a number of non-linear normal modes (NNMs) that are greater than the degrees of freedom. Since the non-linearities are concentrated at the origin, its non-linear frequencies are independent of the energy level and uniquely depend on the damage parameter. An analysis of the NNMs has been performed for a wide range of damage parameter by employing numerical procedures and Poincaré maps. The influence of damage on the non-linear frequencies has been investigated and bifurcations characterized by the onset of superabundant modes in internal resonance, with a significantly different shape than that of modes on fundamental branch, have been revealed. 相似文献
107.
108.
Fuxing Pan Lukas Guggolz Florian Weigend Stefanie Dehnen 《Angewandte Chemie (International ed. in English)》2020,59(38):16638-16643
The Zintl anion (Ge2As2)2? represents an isostructural and isoelectronic binary counterpart of yellow arsenic, yet without being studied with the same intensity so far. Upon introducing [(PPh3)AuMe] into the 1,2‐diaminoethane (en) solution of (Ge2As2)2?, the heterometallic cluster anion [Au6(Ge3As)(Ge2As2)3]3? is obtained as its salt [K(crypt‐222)]3[Au6(Ge3As)(Ge2As2)3]?en?2 tol ( 1 ). The anion represents a rare example of a superpolyhedral Zintl cluster, and it comprises the largest number of Au atoms relative to main group (semi)metal atoms in such clusters. The overall supertetrahedral structure is based on a (non‐bonding) octahedron of six Au atoms that is face‐capped by four (GexAs4?x)x? (x=2, 3) units. The Au atoms bind to four main group atoms in a rectangular manner, and this way hold the four units together to form this unprecedented architecture. The presence of one (Ge3As)3? unit besides three (Ge2As2)2? units as a consequence of an exchange reaction in solution was verified by detailed quantum chemical (DFT) calculations, which ruled out all other compositions besides [Au6(Ge3As)(Ge2As2)3]3?. Reactions of the heavier homologues (Tt2Pn2)2? (Tt=Sn, Pb; Pn=Sb, Bi) did not yield clusters corresponding to that in 1 , but dimers of ternary nine‐vertex clusters, {[AuTt5Pn3]2}4? (in 2 – 4 ; Tt/Pn=Sn/Sb, Sn/Bi, Pb/Sb), since the underlying pseudo‐tetrahedral units comprising heavier atoms do not tend to undergo the said exchange reactions as readily as (Ge2As2)2?, according to the DFT calculations. 相似文献
109.
Shao-Dong Li Feng Su Miao-Li Zhu Li-Ping Lu 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(9):863-868
A new coordination polymer (CP), namely, poly[[diaquatris[μ2‐1,4‐bis(1H‐imidazol‐1‐yl)benzene]bis[μ6‐4‐(2,4‐dicarboxylatophenoxy)phthalato]tetracobalt(II)] hexahydrate], {[Co4(C16H6O9)2(C12H10N4)3(H2O)2]·6H2O}n, has been synthesized by solvothermal reaction. The CP was fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single‐crystal X‐ray diffraction. It presents a three‐dimensional (3D) structure based on tetranuclear CoII secondary building units (SBUs) with a tfz‐d net and point symbol (43)2(46·618·84). The 4‐(2,4‐dicarboxyphenoxy)phthalic acid (H4dcppa) ligands are completely deprotonated and link {Co4(COO)4}4? SBUs into two‐dimensional (2D) layers. Furthermore, adjacent layers are connected by 1,4‐bis(1H‐imidazol‐1‐yl)benzene (bib) ligands, giving rise to a 3D supramolecular architecture. Interestingly, there are numerous elliptical cavities in the CP where isolated unique discrete hexameric water clusters have been observed. The results of thermogravimetric and magnetic analyses are described in detail. 相似文献
110.