全文获取类型
收费全文 | 1277篇 |
免费 | 120篇 |
国内免费 | 90篇 |
专业分类
化学 | 995篇 |
晶体学 | 13篇 |
力学 | 36篇 |
综合类 | 3篇 |
数学 | 165篇 |
物理学 | 275篇 |
出版年
2024年 | 5篇 |
2023年 | 22篇 |
2022年 | 28篇 |
2021年 | 34篇 |
2020年 | 36篇 |
2019年 | 50篇 |
2018年 | 38篇 |
2017年 | 31篇 |
2016年 | 49篇 |
2015年 | 52篇 |
2014年 | 48篇 |
2013年 | 67篇 |
2012年 | 102篇 |
2011年 | 85篇 |
2010年 | 69篇 |
2009年 | 53篇 |
2008年 | 72篇 |
2007年 | 61篇 |
2006年 | 65篇 |
2005年 | 66篇 |
2004年 | 52篇 |
2003年 | 39篇 |
2002年 | 61篇 |
2001年 | 59篇 |
2000年 | 39篇 |
1999年 | 33篇 |
1998年 | 14篇 |
1997年 | 20篇 |
1996年 | 26篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1487条查询结果,搜索用时 15 毫秒
241.
The mechanical behavior of graphene nanoribbons (GNRs) was investigated by molecular dynamics (MD) simulations. The simulation results showed that GNRs behave nonlinear elastically under tensile loads. When the strain exceeds 18%, the stress stiffening causes an increase in the Young's modulus. The width of a GNR has slight effects on the Young modulus and fracture strength. The maximum strain at which fracture occurs can reach 30.26% with an intrinsic strength of about 0.175 TPa. The excellent flexibility is attributed to the elongation of the CC bonds and the variations of the bond angles. 相似文献
242.
采用聚硅氮烷前驱体在高温常压下热裂解的方法制备了3C-SiC纳米棒,在室温下观察到来自纳米棒的378 nm(33?eV) 强紫外发射. 利用扫描电子显微镜、透射电子显微镜、高分辨透射电子显微镜和X射线衍射对样品的形貌和结构进行表征,观察到在该结构中存在类似6H-SiC结构的三层堆垛层错. 利用室温荧光光谱和室温荧光衰减曲线研究了强紫外发射的产生机理,紫外发射来源于3C-SiC纳米棒中的三层堆垛层错的发光.
关键词:
碳化硅
纳米棒
光致发光 相似文献
243.
Xiangfu Wang Siguo Xiao Yanyan Bu Xiaoliang Yang J.W. Ding 《Journal of luminescence》2009,129(3):325-353
A luminescent material β-Na(Y1.5Na0.5)F6 doped with Tm3+ was synthesized by a solid-state reaction method for a steady phosphor of blue upconversion. Under the 671 nm laser excitation, the green emission band of 511 nm due to the 1D2→3H5 transition is obtained for the first time, while the ultraviolet emission band is also observed at 368 nm, associated with the 1D2→3H6 transition. Especially, a wide band of blue emissions is obtained at the wavelength region of 440-490 nm, originated mainly from the 1D2→3F4 (450 nm) and 1G4→3H6 (471-487 nm) transitions, which have potential application in tunable solid-state blue laser of Tm3+. The upconversion mechanism is explored in terms of the energy-level structures of Tm3+ ion and the power dependence of upconverted emission intensity, which is believed to be performed by excited-state absorption. 相似文献
244.
Vilas B. Phapale Manuel Guisán‐Ceinos Elena Buñuel Prof. Dr. Diego J. Cárdenas Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(46):12681-12688
Optimal conditions for a general Ni‐catalysed Negishi cross‐coupling of alkyl zinc halides with aryl, heteroaryl and alkenyl halides have been determined. These conditions allow the reaction to take place smoothly, with low catalyst loading, and in the presence of a wide variety of functional groups to afford products in good yields at room temperature. DFT studies on the mechanism support the occurrence of a catalytic cycle involving transmetalation of the alkyl zinc halide to NiI followed by oxidative addition of the haloarene and C? C reductive elimination. 相似文献
245.
Ying Peng Huo Xu Qiu Wei Yan Shao Lin Kun An Xian Zhang Bu Lian Quan Gu 《中国化学快报》2009,20(11):1291-1295
Series of new 2-aryl-6-styryl-2,3-dihydropyridin-4(1H)-one derivatives were synthesized in acceptable to good yields by treatment of the curcuminoids with aqueous ammonia,the mechanism was proposed.By modification of the primary products,total 13 new compounds were obtained.The structures of all products were elucidated by spectroscopy analysis including HR-MS,~1H NMR and ~(13)C NMR. 相似文献
246.
This paper reports two new coordination polymers formed by carboxylate-substituted benzoimidazole and formate ligands: [Mn(L)·(HCO2)]n (1) and [Co(L)·(HCO2)]n (2) (L = benzoimidazol-1-yl-acetate). Com-plexes 1 and 2 are isomorphous and adopt a new 3,6-connected three-nodal topology showing inter-esting magnetic properties: spin canted antiferromagnetism for MnⅡ complex 1, but simple antiferro-magnetic coupling for CoⅡ complex 2. 相似文献
247.
Feng Chen Dr. Wenbo Bu Prof. Yu Chen Dr. Yuchi Fan Dr. Qianjun He Dr. Min Zhu Dr. Xiaohang Liu Dr. Liangping Zhou Prof. Shengjian Zhang Dr. Weijun Peng Prof. Jianlin Shi Prof. 《化学:亚洲杂志》2009,4(12):1809-1816
Oleic acid stabilized superparamagnetic iron oxide nanoparticles (SPION) were selected as the cores for fabrication of sub‐50‐nm monodisperse single‐loaded SPION@SiO2 core–shell nanostructures. Parameters that influence the formation of SPION@SiO2 in the water‐in‐oil reverse microemulsion system have been systematically investigated. The sufficiently high concentration of well‐dispersed SPION, together with an appropriately low injection rate of tetraethoxysilane, were found to be the keys to efficiently prevent the homogeneous nucleation of silica and obtain a high‐quality single‐loaded core–shell nanocomposite. A more detailed mechanism for incorporating oleic acid capped inorganic functional nanoparticles into silica is proposed on the basis of previous reports and our new experimental results. Finally, the as‐synthesized SPION@SiO2 nanospheres are exploited as an MRI‐enhanced contrast agent, and their contrast effect in solution is tested by using a clinical MRI instrument. 相似文献
248.
A graph G is equitably k-choosable if for any k-uniform list assignment L, there exists an L-colorable of G such that each color appears on at most vertices. Kostochka, Pelsmajer and West introduced this notion and conjectured that G is equitably k-choosable for k>Δ(G). We prove this for planar graphs with Δ(G)≥6 and no 4- or 6-cycles. 相似文献
249.
Towards auction algorithms for large dense assignment problems 总被引:1,自引:0,他引:1
In this paper, we focus on the problem of solving large-scale instances of the linear sum assignment problem by auction algorithms.
We introduce a modified auction algorithm, called look-back auction algorithm, which extends the forward auction algorithm
by the ability of reusing information from previous bids. We show that it is able to reuse information from the previous bids
with high efficiency for all tested types of input instances. We discuss then the design and implementation of a suite of
sequential and distributed memory auction algorithms on a Linux cluster with the evaluation on several types of input instances
of the linear sum assignment problem. Our results show that the look-back auction algorithm solves sequentially nearly all
types of dense instances faster than other evaluated algorithms and it is more stable than the forward-reverse auction algorithm
for sparse instances. Our distributed memory auction algorithms are fully memory scalable.
This research has been supported by IGA CTU under grant CTU0308013 and under research program MSMT 6840770014. 相似文献
250.
基于图G的Mycielski图M(G),研究xb(G,TG)与xb(M(G),T’)之间的关系以及xb(G,TG)与xb(M(G),T")之间的关系,其中Tc为G的生成树,T’,T"分别为M(G)的两类特殊生成树.并给出当G为二部图,完全图以及Halin图时,Xb(M(G),T")的值. 相似文献