全文获取类型
收费全文 | 787篇 |
免费 | 86篇 |
国内免费 | 68篇 |
专业分类
化学 | 557篇 |
晶体学 | 15篇 |
力学 | 40篇 |
综合类 | 6篇 |
数学 | 128篇 |
物理学 | 195篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 14篇 |
2021年 | 24篇 |
2020年 | 28篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 15篇 |
2016年 | 22篇 |
2015年 | 47篇 |
2014年 | 39篇 |
2013年 | 44篇 |
2012年 | 55篇 |
2011年 | 71篇 |
2010年 | 47篇 |
2009年 | 41篇 |
2008年 | 44篇 |
2007年 | 38篇 |
2006年 | 31篇 |
2005年 | 47篇 |
2004年 | 32篇 |
2003年 | 34篇 |
2002年 | 22篇 |
2001年 | 22篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 20篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1957年 | 2篇 |
1945年 | 1篇 |
排序方式: 共有941条查询结果,搜索用时 31 毫秒
101.
随着x的增加,多晶La0.6-xGdxSr1.4MnO4(x=0, 0.1, 0.2, 0.4, 0.6)的零场冷却 曲线从类自旋玻璃型转变成顺磁型,并且每条零场冷却 曲线都有一在20K的拐点。这一行为可以从Gd和Mn各自对材料总磁性的不同贡献来理解。另外,在所有的样品中,从100K到室温,都观察到了热激活导电行为。由于Mn-Mn间强的反铁磁耦和,直到外场达到50 kOe,都没有观察到明显的磁电阻效应。 相似文献
102.
C. S. Kou 《International Journal of Infrared and Millimeter Waves》1997,18(10):1897-1915
The effects of the sever on two-stage gyro-TWT amplifiers were characterized by a self-consistent slow time scale model. Utilization
of a sever was demonstrated to be capable of inducing additional launching losses as well as ballistic bunching effects. In
addition, some electrons could bunch on an electron phase equal to 3π/2 at the beginning of the second stage as a result of a large and sharp change of the wave’s phase if the modulation of the
electron beam in the first stage was strong. Calculated results further indicated that the performance was more sensitive
to the position of sever than the length of the sever. Asymmetric interaction structures with the first stage being shorter
than the second stage demonstrated higher saturated powers and wider bandwidths along with exhibiting more resistance to the
velocity spread of the electron beam. 相似文献
103.
104.
We describe a Rh-catalyzed desymmetrization of all-carbon quaternary centers from α,α-bis(allyl)aldehydes by a cascade featuring isomerization and hydroacylation. This desymmetrization competes with two other novel olefin functionalizations that are triggered by C–H bond activation, including carboacylation and bisacylation. A BIPHEP ligand promotes enantioselective formation of α-vinylcyclopentanones. Mechanistic studies support irreversible and enantioselective olefin-isomerization followed by olefin-hydroacylation. 相似文献
105.
Xu Zhang Lei Zhang Meng‐Jie Wang Kou‐Lin Zhang 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(9):776-782
Two new coordination polymers (CPs) formed from 5‐iodobenzene‐1,3‐dicarboxylic acid (H2iip) in the presence of the flexible 1,4‐bis(1H‐imidazol‐1‐yl)butane (bimb) auxiliary ligand, namely poly[[μ2‐1,4‐bis(1H‐imidazol‐1‐yl)butane‐κ2N3:N3′](μ3‐5‐iodobenzene‐1,3‐dicarboxylato‐κ4O1,O1′:O3:O3′)cobalt(II)], [Co(C8H3IO4)(C10H14N4)]n or [Co(iip)(bimb)]n, (1), and poly[[[μ2‐1,4‐bis(1H‐imidazol‐1‐yl)butane‐κ2N3:N3′](μ2‐5‐iodobenzene‐1,3‐dicarboxylato‐κ2O1:O3)zinc(II)] trihydrate], {[Zn(C8H3IO4)(C10H14N4)]·3H2O}n or {[Zn(iip)(bimb)]·3H2O}n, (2), were synthesized and characterized by FT–IR spectroscopy, thermogravimetric analysis (TGA), solid‐state UV–Vis spectroscopy, single‐crystal X‐ray diffraction analysis and powder X‐ray diffraction analysis (PXRD). The iip2− ligand in (1) adopts the (κ1,κ1‐μ2)(κ1, κ1‐μ1)‐μ3 coordination mode, linking adjacent secondary building units into a ladder‐like chain. These chains are further connected by the flexible bimb ligand in a trans–trans–trans conformation. As a result, a twofold three‐dimensional interpenetrating α‐Po network is formed. Complex (2) exhibits a two‐dimensional (4,4) topological network architecture in which the iip2− ligand shows the (κ1)(κ1)‐μ2 coordination mode. The solid‐state UV–Vis spectra of (1) and (2) were investigated, together with the fluorescence properties of (2) in the solid state. 相似文献
106.
针对物理化学教材中有关光化学初级过程和次级过程、初级过程的量子产率、初级过程的反应速率表示以及是否是零级反应等问题发表了看法。 相似文献
107.
目前光学陀螺的主要工作原理是Sagnac效应, 如何提高Sagnac效应的测量精度是提高陀螺精度的一个重要研究课题. 传统的光学陀螺利用光短波长的特性来提高检测精度. 但考虑到微波的相位(频率)检测精度远高于光波的相位(频率)检测精度, 如果能够利用微波实现Sagnac效应的检测, 就能得到比光学陀螺更高的检测精度, 从而为实现高精度的微波陀螺提供了可能. 利用基于光电振荡器的光载微波结构实现了微波Sagnac效应的检测. 实验结果证明了微波检测Sagnac效应的可行性, 为将来实现高精度的微波谐振陀螺打下基础. 相似文献
108.
Hui-Lu Wu Ke Li Tao Sun Fan Kou Fei Jia Jing-Kun Yuan Bin Liu Bao-Liang Qi 《Transition Metal Chemistry》2011,36(1):21-28
Tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and its two complexes, [Mn(Mentb)(DMF)(H2O)](pic)2
1 and [Zn(Mentb)(pic)](pic) 2 (pic = picrate), have been synthesized and characterized by physico-chemical and spectroscopic methods. Single crystal X-ray
diffraction revealed that the two complexes have different structures. In complex 1, the coordination sphere around Mn(II) is distorted octahedral, whereas in complex 2 the coordination sphere around Zn(II) is distorted trigonal bipyramidal. The DNA-binding properties of the free ligand and
its two complexes have been investigated by electronic absorption, fluorescence, and viscosity measurements. The results suggest
that the ligand and its two complexes bind to DNA via an intercalation binding mode, and their binding affinity for DNA follows
the order 1 > 2 > ligand. 相似文献
109.
Huilu Wu Fei Jia Fan Kou Bin Liu Jingkun Yuan Ying Bai 《Transition Metal Chemistry》2011,36(8):847-853
A new Schiff base ligand N-(2-hydroxylacetophenone)-3-oxapentane-1,5-diamine (HL) and its Ni complex, [Ni2(L)2(NO3)2], have been synthesized and characterized by physicochemical and spectroscopic methods. The X-ray crystal structure of [Ni2(L)2(NO3)2] shows it to be a dinuclear 2:2 complex, in which each Ni(II) atom is in a distorted octahedral geometry. The two Ni(II)
atoms are dibridged by two phenoxo ligands, forming a Ni2O2 parallelogram-type moiety. The interactions between free HL and the complex with calf thymus DNA have been investigated,
and the binding constant and linear Stern–Volmer quenching constant suggest that the two compounds bind to DNA via the intercalation
mode. The binding affinity of the complex was higher than that of HL. Antioxidant assays in vitro showed that the Ni(II) complex
possesses significant antioxidant activity. 相似文献
110.
Total synthesis of the proposed structure 2 for phomopsin B was achieved by using an intramolecular olefin metathesis as a key step. The spectral data, however, did not match with those of the natural product reported. Re-examination of the reported NMR data led to the structural revision of phomopsin B to known dothiorelone A 18. The R configuration of dothiorelone A was determined by total synthesis through a cross-metathesis with a chiral olefin 19. 相似文献