全文获取类型
收费全文 | 548篇 |
免费 | 6篇 |
国内免费 | 71篇 |
专业分类
化学 | 340篇 |
晶体学 | 2篇 |
力学 | 3篇 |
综合类 | 1篇 |
数学 | 24篇 |
物理学 | 255篇 |
出版年
2024年 | 3篇 |
2023年 | 33篇 |
2022年 | 9篇 |
2021年 | 3篇 |
2020年 | 11篇 |
2019年 | 11篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 71篇 |
2012年 | 50篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 19篇 |
2008年 | 38篇 |
2007年 | 72篇 |
2006年 | 21篇 |
2005年 | 25篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 33篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有625条查询结果,搜索用时 31 毫秒
101.
Anna G. Scott Diogo Alves Galico Isabel Bogacz Paul H. Oyala Junko Yano Elizaveta A. Suturina Muralee Murugesu Theodor Agapie 《Angewandte Chemie (International ed. in English)》2023,62(49):e202313880
Atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp*4W4Fe13S12 , displaying a Fe13 core with M−M bonds that has precedent only in main group and late metal chemistry. M13 clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp*4W4Fe13S12 displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements. 相似文献
102.
We previously reported that a deletion mutant (P478) with a residue Arg deleted at the C terminus of d-hydantoinase (P479) from Pseudomonas putida YZ-26 was dissociated into the monomer from its dimeric state. Based on the above result, a series of mutants of the enzyme
with the C-terminal residues either deleted or substituted were prepared. The size-exclusion chromatography and bioactivity
assay show that a C-terminal-substituted enzyme (R479D) and several truncated mutants (P478, P477, P476, and P475) are dissociated
into the monomeric state as well, but their activities are largely retained. In contrast, two other mutants (R474 and R479A)
are expressed in the form of random aggregates without any activity. Our experiments demonstrate that only the last four amino
acids (-PVQR) at the C terminus of the enzyme can be deleted without seriously affecting its activity, although the enzyme
is dissociated from a dimer into a monomer. These mutants also reveal some unique properties such as the enzymatic activity
in vivo or in vitro, the effect of divalent metal ions, and the thermostability etc. in comparison to wild-type enzyme (P479).
In addition, the three-dimensional structural modeling shows that the intact structure of the enzyme is essential, and the
flexibility of the non-conservative region at the C terminus of the enzyme is quite limited. 相似文献
103.
María E. Ramos Pablo R. Bonelli Ana L. Cukierman 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,324(1-3):86-92
Five different cellulose-based fabrics were used to prepare activated carbon cloths (ACCs) by phosphoric acid activation at pre-established experimental conditions, in an attempt to explore the effect of the precursor's nature on properties of the resulting ACCs. Characterization by elemental analysis, nitrogen (77 K) adsorption, and scanning electron microscopy was carried out. Electrical properties of the developed ACCs were investigated to examine the possibility of regenerating the ACCs by direct electrical heating. Thermal behavior of the raw precursor and of one of the acid-treated fabrics was also studied by thermogravimetric analysis and noticeable differences due to the precursors’ characteristics and acid impregnation were detected, respectively. The ACCs derived from a denim precursor showed BET surface area (784 m2 g−1) and total pore volume (0.40 cm3 g−1) lower than those obtained from the four other precursors (1058–1183 m2 g−1, 0.55–0.67 cm3 g−1), whereas carbon content and yield for the former were higher. Morphology and physical appearance of the ACCs were dependent on the raw fabric employed, with most of the samples presenting well-preserved fibres integrity. Besides, the denim-derived ACCs also showed the lowest electrical resistivity (8.10−3 Ωm). It was properly correlated with the elemental carbon content and total pore volume of the developed ACCs. 相似文献
104.
呼和满都拉 《原子与分子物理学报》2016,33(6)
本文采用密度泛函理论中的M05方法对比研究了一类双席夫碱及其衍生物与金属Co、Ni和Cu配位后配合物的结构,非线性光学性质以及激发态性质. 结果表明,Co配合物的三重态,Ni配合物的二重态以及Cu配合物的单重态为最佳稳定结构. 通过最佳稳定结构计算得到的配合物非线性光学性质表明,三种金属配合物中Cu配合物表现出较高的一阶和二阶超极化率. 通过对其激发态性质分析表明在配体苯环上引入甲氧基使电子跃迁种类减少,导致超极化率下降,非线性光学性质减弱. 相似文献
105.
采用共沉淀法合成了掺杂 L a、 Gd、 Y的 Tb-邻氨基苯甲酸配合物 ,研究其荧光性能 ,结果显示 ,掺杂L a、Gd、Y后 ,对 Tb配合物的发光有增敏作用 ,讨论了不同的掺杂离子 (L a、Gd、Y)及掺杂量对其荧光性能的影响。发现 ,当掺杂离子取代大部分 Tb3+时 ,其发光增强仍十分显著。 相似文献
106.
I. Shim K.A. Gingerich 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(2):163-172
The low-lying electronic states of the molecule FeC have been investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) and multi reference configuration interaction (MRCI) calculations. The
relativistic corrections for the one-electron Darwin contact term and the relativistic mass-velocity correction have been
determined in perturbation calculations. The electronic structure of the FeC molecule is interpreted as antiferromagnetic
couplings of the localized angular momenta of the ions and resulting in a triple bond in the valence bond sense. The electronic ground state is confirmed as being . The spectroscopic constants for the ground state and eleven excited states have been derived from the results of the MRCI
calculations. The spectroscopic constants for the ground state have been determined as and ,and for the low-lying state as and . The values for the ground state agree well with the available experimental data. The FeC molecule is polar with charge transfer
from Fe to C. The dipole moment has been determined as in the ground state and as 1.51 D in the state. From the results of the MRCI calculations the dissociation energy, , is determined as 2.79 eV, and D0 as 2.74 eV.
Received: 2 October 1998 / Received in final form: 30 March 1999 相似文献
107.
Gunther Mair Hans Georg von Schnering Michael Wrle Reinhard Nesper 《无机化学与普通化学杂志》1999,625(7):1207-1211
Li2B6 is formed from the elements as transparent red microcrystalline compound (Li : B = 1 : 3; Mo crucible in closed Nb ampoule; 1723 K; 4 h). Single crystals are grown from a lithium silicide melt with large Li excess at 1923 K. Li2B6 is a semiconductor with electron as well as Li+ ionic conductivity which dominates above 600 K. Microcrystalline samples react with H2O liberating gases and forming a brownish amorphous product, but larger crystals are not very sensitive. – Li2B6 crystallizes tetragonally in a new tP16 structure type which is a variant of the CaB6 structure (a = 5.975 Å, c = 4.189 Å; Z = 2; space group P4/mbm). The [B62–] net of the polymeric octahedro-anion is slightly distorted to give space for the insertion of a (32434) net of the Li+ cations in the cavities (d(B–B)endo = 1.766 Å; d(B–B)exo = 1.720 Å; d(Li–B) = 2.363 Å; d(Li–Li) = 3.094 Å). The incomplete occupancy of the Li position (80%) and the electron density at a further position (20%) indicate the mobility of the Li+ cations. 相似文献
108.
在还原气氛中合成了CaO-B2O3-SiO2:Eu^2+玻璃体系,研究了该玻璃体系中Eu^2+的激发光谱和发射光谱,并归属了其相应的跃迁发射。研究了掺杂Eu^2+浓度对其发光强度的影响,结果表明,Eu^2+掺杂量在0.20%时发光强度达到最大值,在该玻璃体系中没有观察到浓度猝灭现象。研究了合成条件与Eu离子在玻璃中发光性质的关系,说明还原能力H2〉CO〉空气,空气几乎不具备还原能力。研究了玻璃中Eu^2+的电子自旋共振谱(ESR)性质,证实了玻璃体系中Eu^2+的存在,得到了玻璃体系中Eu^2+的能级图。 相似文献
109.
双邻位甲基取代的聚芳醚酮合成与表征 总被引:3,自引:0,他引:3
两种单体 2 ,2′ ,6 ,6′ 四甲基 4 ,4′ 二苯氧基二苯酮 (o M2 DPOBP)和 2 ,2′ ,6 ,6′ 四甲基 4 ,4′ 二苯氧基三苯二酮 (o M2 DPOTPDK) ,分别与对苯二甲酰氯 (TPC)和间苯二甲酰氯 (IPC)低温亲电溶液缩聚 ,合成了 4种含双邻位甲基侧基聚醚酮醚酮酮 (DM PEKEKK和DM PEKEKMK)及含双邻位甲基侧基聚醚酮酮醚酮酮 (DM PEKKEKK和DM PEKKEKMK)聚合物 .用FT IR、1 H NMR、DSC、TGA、WAXD等方法对聚合物进行了表征 ,研究了聚合物的溶解性能 .结果表明 ,该 4种聚合物具有较高的玻璃化转变温度 ,良好的热稳定性和优良的溶解性能 . 相似文献
110.
纳米SiO2改性超高分子量聚乙烯纤维的制备及其结构性能研究 总被引:3,自引:0,他引:3
采用萃取阶段加入纳米粒子的方式,制得纳米SiO2改性的超高分子量聚乙烯(UHMWPE)纤维.借助于扫描电镜、声速法、WAXD、DSC、TMA和强力测试等手段,研究了纳米SiO2对UHMWPE纤维结构和性能的影响.结果表明,纳米SiO2粒子在UHMWPE纤维中可达到均匀分散,分散尺寸约为50~100nm;改性后纤维取向度、结晶度基本不变,纤维横向晶粒尺寸大大降低,纤维力学强度稍有增加,力学模量大大增加(由1359.2cNdtex增加到1505.9cNdtex),同时,纤维热性能和热力学性能也得到大大改善. 相似文献