全文获取类型
收费全文 | 4056篇 |
免费 | 189篇 |
国内免费 | 588篇 |
专业分类
化学 | 4121篇 |
晶体学 | 105篇 |
力学 | 24篇 |
综合类 | 11篇 |
数学 | 2篇 |
物理学 | 570篇 |
出版年
2024年 | 11篇 |
2023年 | 81篇 |
2022年 | 63篇 |
2021年 | 65篇 |
2020年 | 91篇 |
2019年 | 130篇 |
2018年 | 74篇 |
2017年 | 143篇 |
2016年 | 120篇 |
2015年 | 148篇 |
2014年 | 161篇 |
2013年 | 269篇 |
2012年 | 399篇 |
2011年 | 229篇 |
2010年 | 193篇 |
2009年 | 211篇 |
2008年 | 256篇 |
2007年 | 268篇 |
2006年 | 229篇 |
2005年 | 219篇 |
2004年 | 219篇 |
2003年 | 155篇 |
2002年 | 146篇 |
2001年 | 123篇 |
2000年 | 119篇 |
1999年 | 119篇 |
1998年 | 87篇 |
1997年 | 63篇 |
1996年 | 55篇 |
1995年 | 63篇 |
1994年 | 59篇 |
1993年 | 36篇 |
1992年 | 35篇 |
1991年 | 52篇 |
1990年 | 35篇 |
1989年 | 30篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有4833条查询结果,搜索用时 15 毫秒
991.
研究了咪唑桥联异三核配合物[(NH_3)_5CoImCu(dien)ImCo(NH_3)_5](ClO_4)_6·4H_2O与同构配合物[(NH_3)_5CoImZn(dien)ImCo(NH_3)_5]·4H_2O混合单晶在低温(100 K)下的ESR。应用适于求非同轴g张量和A张量的最小二乘法拟合技术,解出标题配合物的g张量和A张量主值分别为:g_1=2.246,g_2=2.093,g_3=2.048,A_1=1.63×10~(-2)cm~(-1),A_2=0.38×10~(-2)cm~(-1),A_3=0.17×10~(-2)cm~(-1)及g_1=2.245,g_2=2.090,g_3=2.051,A_1=1.64×10~(-2)cm~(-1),A_2=0.37×10~(-2)cm~(-1),A_3=0.17×10~(-2)cm~(-1)。配合物Cu~(2+)的4s、3d轨道上的电子自旋密度分别为0.018和0.557。Cu~(2+)与配体间的键有较强的共价性。 相似文献
992.
本文合成了两个新型Co(Ⅱ)配合物,[LCo(μ-C2O4)CoL]·(ClO4)2·2CH3CN (1)和[CoL(SCN)]·ClO4 (2),其中,L即三(3,5-二甲基吡唑甲基)胺。在配合物1中,Co与来自三脚架配体的4个氮和草酸根桥联配体的2个氧原子配位,处于扭曲八面体配位环境。由草酸根桥联两套LCo,构成了一个双核结构。在单核配合物2中,Co(Ⅱ)处于三角双锥配位构型,SCN-通过N配位与中心离子Co(Ⅱ)键联。在同一晶胞中有两个构型略微不同的分子,两个分子之间通过SCN的S原子有弱相互作用。对化合物1和2在溶液中的光谱性质做了进一步的研究和讨论。 相似文献
993.
Tamas Bartik Berit Bartik Ipin Guo Brian E. Hanson 《Journal of organometallic chemistry》1994,480(1-2):15-21
The electron donating water soluble phosphines, P{(CH2)nC6H4-p-SO3Na}3,n = 1, 2, 3 and 6, react rapidly with Co2(CO)8 under two phase reaction conditions to yield the disproportionation products, [Co(CO)3(P{(CH2)nC6H4-p-SO3Na3}2] [Co(CO)4]. Selective precipitation yields the formally zwitterionic complex anions as the sodium salt, [Co(CO)3(P{(CH2)nC6H4-p-SO3} 3)2]5−. The anions can be used as precursors to water soluble cobalt hydroformylation catalysts under two phase and supported aqueous phase conditions. The tendency to form alcohol products is low with these complexes. The behavior of the catalysts is consistent with an active species that remains water soluble during the reaction and is not leached into the nonaqueous phase. 相似文献
994.
Cellulose acetate fibers with supported highly dispersed aluminum phosphate were prepared by reacting aluminum-containing cellulose acetate (Al2O3=3.5 wt.%; 1.1 mmol g−1 aluminum atom per gram of the material) with phosphoric acid. Solid-state NMR spectra (CPMAS 31P NMR) data indicated that HPO42− is the species present on the fiber surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.50 mmol g−1. The ion exchange capacities for Li+, Na+ and K+ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g−1): Li+=0.03, Na+=0.44 and K+=0.50. The H+/Li+ exchange corresponds to the model of the ideal ion exchange with a small value of the corresponding equilibrium constant K=1.1×10−2. Due to the strong cooperative effect, the H+/Na+ and H+/K+ ion exchange is non-ideal. These ion exchange equilibria were treated with the use of models of fixed bi- or tridentate centers, which consider the surface of the sorbent as an assemblage of polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants were discussed by taking into consideration the sequence of the ionic hydration radii for Li+, Na+ and K+. The matrix affinity order for the ions decreases as the hydration radii of the cations increase, i.e. Li+>Na+>K+. The high values of the separation factors SNa+/Li+ and SK+/Li+ (up to several hundred) provide quantitative separation of Na+ and K+ from Li+ from a mixture containing these three ions. 相似文献
995.
磷酸脲可作为反刍动物饲料添加剂和青贮饲料保藏剂,高浓度NP复合肥、聚磷酸和净化湿法磷酸的中间体,以及阻燃剂、清洗剂等。国外众多研究者对磷酸脲结构、性能和应用进行了广泛的研究。但对磷酸脲离解反应的热力学研究甚少,尚未见详尽报道。本文就磷酸脲 相似文献
996.
Synthesis and Structure of an Ammonium Diamidodioxophosphate(V), NH4PO2(NH2)2 The ammonolysis of P3N5 under ammonothermal conditions (T = 400°C, p(NH3) = 6 kbar, 14 d in autoclaves) in the presence of small definite amounts of water leads to the formation of NH4PO2(NH2)2. The structure was solved by single crystal X-ray methods. NH4PO2(NH2)2: P21/c (Nr. 14), a = 6.886(1) Å, b = 8.366(2) Å, c = 9.151(2) Å, β = 111.78(3)°, Z = 4, R1/wR2 = 0.026/0.072, Z(F > 2σ(F)) = 1183, N(variables) = 87. In NH4PO2(NH2)2 the anions [PO2(NH2)2]? are linked to chains by N? H …? N and N? H …? O bridge bonds. The ammonium ions are located between these chains and are donors for N? H …? O bridge bonds which connect the chains three-dimensionally. 相似文献
997.
Madleine Al-Hamra 《Tetrahedron letters》2005,46(34):5711-5714
The synthesis of second and third generation dendrimers based on poly-(l-lysine) with a pentaamine cobalt(III) metal complex at the core is described. The synthesis and purification of these dendrimers were facilitated by using the metal complex as the C-terminal protecting group. 相似文献
998.
R. Rozik R. Oriňàková K. Markušová L. Trnková 《Journal of Solid State Electrochemistry》2006,10(7):423-429
This paper describes a process of electrolytic deposition of nickel–cobalt (Ni–Co) binary alloy on Fe powder. Electrochemical behavior of this binary alloy was studied by cyclic voltammetry with a paraffin impregnated graphite electrode as a working electrode. Deposition of individual metals (Ni, Co), as well as the simultaneous nickel–cobalt co-deposition, was performed in aqueous solutions (Watts-type electrolyte) both with and without Fe powder. Special attention was paid to the influence of suspension density on the electrode process. This density affects on the quality of iron powder electroplating. Preferential deposition of the less noble metal (Co) leading to its higher content in the deposit was observed in contrast to the more noble one (Ni) in spite of higher content of Ni in the plating solution. This anomalous phenomenon–known already for other metals (Zn, Cd, Sn)–has been confirmed and investigated for iron-group metals (Fe, Co, Ni) in this work. Electrolytic deposition of Ni–Co binary alloys, including anomalous behavior is a complicated process. Understanding the anomalous behavior would lead to better control of the deposition process and to explanation of the mechanism of Ni–Co co-deposition. 相似文献
999.
1000.
Cyanide Bridged Trinuclear Complexes with Central M(Cyclam) Units Reactions between metal cyclam complexes M(Cyclam)Xn and organometallic cyanides LnM′‐CN yielded trinuclear complexes LnM′‐CN‐M(Cyclam)‐NC‐M′Ln with M = Mn, Fe, Co, Ni and M′ = Cr, Fe, Ru. They were probed with structural, spectroscopic and electrochemical methods for electronic interactions between the involved metal centers. 相似文献