全文获取类型
收费全文 | 686篇 |
免费 | 75篇 |
国内免费 | 59篇 |
专业分类
化学 | 479篇 |
晶体学 | 14篇 |
力学 | 39篇 |
综合类 | 6篇 |
数学 | 102篇 |
物理学 | 180篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 12篇 |
2021年 | 23篇 |
2020年 | 19篇 |
2019年 | 19篇 |
2018年 | 8篇 |
2017年 | 18篇 |
2016年 | 21篇 |
2015年 | 39篇 |
2014年 | 33篇 |
2013年 | 46篇 |
2012年 | 50篇 |
2011年 | 62篇 |
2010年 | 41篇 |
2009年 | 39篇 |
2008年 | 39篇 |
2007年 | 34篇 |
2006年 | 27篇 |
2005年 | 38篇 |
2004年 | 31篇 |
2003年 | 27篇 |
2002年 | 14篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 20篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1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820条查询结果,搜索用时 15 毫秒
81.
本文利用EXAFS(Extended X-ray Absorption Fine Structure)对铑基担载液相催化剂(Supported Liquid Phase Catalyst SLPC)进行了结构表征。采用球面波理论对SLPC的EXAFS结果进行了多参数拟合。结果表明,在新鲜催化剂上,铑络合物以二聚物形式存在,推测其结构为(PPh_3)_2(CO)Rh-Rah(CO)(PPh_3)_2,Rh-C-O偏离共线分布。在经过羰化反应活化的活性SLPC上,铑络合物为单核的HRh(CO)_2(PPh_3)或Rh(CO)_2(PPh_32)_3。文中还讨论了SLPC的XRD谱。 相似文献
82.
83.
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
84.
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
85.
86.
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
87.
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
88.
建立了用液相色谱-串联质谱检测血清中15种甾体激素的方法。在血清样品中加入含内标的乙腈沉淀蛋白质后,用100 mmol/L盐酸羟胺衍生,经Agilent-C18柱(50 mm×3.0 mm,2.7μm)分离,内标法定量。质谱分析采用电喷雾电离(ESI)正离子扫描,多反应监测(MRM)模式检测。数据显示,13种激素在0.05~20 ng/mL范围内线性关系良好(相关系数(R2)不小于0.995 6),检出限不大于1 ng/mL;皮质醇及脱氢表雄酮硫酸酯在50~2 000ng/mL范围内线性关系良好(R2不小于0.997 9),检出限不大于0.5 ng/mL。将该方法应用于女性月经周期激素变化规律的研究,结果表明,15种甾体激素在一个完整的月经周期内有不同特征的动态变化,其中雄激素在滤泡期的后期达到最高值,孕(雌)激素在黄体期达到最高值,而皮质激素则波动不明显。该方法灵敏度高、重复性好,为临床诊疗提供了参考。 相似文献
89.
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
90.
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