全文获取类型
收费全文 | 7170篇 |
免费 | 1350篇 |
国内免费 | 722篇 |
专业分类
化学 | 5157篇 |
晶体学 | 43篇 |
力学 | 434篇 |
综合类 | 49篇 |
数学 | 930篇 |
物理学 | 2629篇 |
出版年
2024年 | 19篇 |
2023年 | 152篇 |
2022年 | 180篇 |
2021年 | 280篇 |
2020年 | 374篇 |
2019年 | 273篇 |
2018年 | 242篇 |
2017年 | 224篇 |
2016年 | 341篇 |
2015年 | 365篇 |
2014年 | 391篇 |
2013年 | 496篇 |
2012年 | 651篇 |
2011年 | 715篇 |
2010年 | 459篇 |
2009年 | 414篇 |
2008年 | 458篇 |
2007年 | 427篇 |
2006年 | 408篇 |
2005年 | 292篇 |
2004年 | 256篇 |
2003年 | 163篇 |
2002年 | 190篇 |
2001年 | 120篇 |
2000年 | 135篇 |
1999年 | 149篇 |
1998年 | 127篇 |
1997年 | 142篇 |
1996年 | 129篇 |
1995年 | 116篇 |
1994年 | 101篇 |
1993年 | 100篇 |
1992年 | 70篇 |
1991年 | 59篇 |
1990年 | 58篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 31篇 |
1986年 | 11篇 |
1985年 | 27篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1959年 | 1篇 |
1916年 | 1篇 |
排序方式: 共有9242条查询结果,搜索用时 15 毫秒
911.
The variety of known very stable PF(3) metal derivatives analogous to metal carbonyls suggests the synthesis of SF(3) metal derivatives analogous to metal nitrosyls. However, the only known SF(3) metal complex is the structurally uncharacterized (Et(3)P)(2)Ir(CO)(Cl)(F)(SF(3)) synthesized by Cockman, Ebsworth, and Holloway in 1987 and suggested by electron counting to have a one-electron donor SF(3) group rather than a three-electron donor SF(3) group. In this connection, the possibility of synthesizing SF(3) metal derivatives analogous to metal nitrosyls has been investigated using density functional theory. The [M]SF(3) derivatives with [M] = V(CO)(5), Mn(CO)(4), Co(CO)(3), Ir(CO)(3), (C(5)H(5))Cr(CO)(2), (C(5)H(5))Fe(CO), and (C(5)H(5))Ni analogous to known metal nitrosyl derivatives are all predicted to be thermodynamically disfavored with respect to the corresponding [M](SF(2))(F) derivatives by energies ranging from 19.5 kcal/mol for Mn(SF(3))(CO)(4) to 5.4 kcal/mol for Co(SF(3))(CO)(3). By contrast, the isoelectronic [M]PF(3) derivatives with [M] = Cr(CO)(5), Fe(CO)(4), Ni(CO)(3), (C(5)H(5))Mn(CO)(2), (C(5)H(5))Co(CO), and (C(5)H(5))Cu are all very strongly thermodynamically favored with respect to the corresponding [M](PF(2))(F) derivatives by energies ranging from 64.3 kcal/mol for Cr(PF(3))(CO)(5) to 31.6 kcal/mol for (C(5)H(5))Co(PF(3))(CO). The known six-coordinate (Et(3)P)(2)Ir(CO)(Cl)(F)(SF(3)) is also predicted to be stable relative to the seven-coordinate (Et(3)P)(2)Ir(CO)(Cl)(F)(2)(SF(2)). Most of the metal SF(3) complexes found in this work are singlet structures containing three-electron donor SF(3) ligands with tetrahedral sulfur coordination. However, two examples of triplet spin state metal SF(3) complexes, namely, the lowest energy (C(5)H(5))Fe(SF(3))(CO) structure and a higher energy Co(SF(3))(CO)(3) structure, are found containing one-electron donor SF(3) ligands with pseudo square pyramidal sulfur coordination with a stereochemically active lone electron pair. 相似文献
912.
We describe a hierarchy of approximations (MP2[x]) that allow one to estimate second-order M?ller-Plesset (MP2) energies in a large basis set from small-basis calculations. The most cost-effective approximation, MP2[K], is significantly cheaper than full MP2 but numerical tests on small atoms and molecules indicate that it is nonetheless accurate. We conclude that MP2[K] is an attractive level of theory for large systems. 相似文献
913.
The kinetics of one-step solid-state reaction of Li(4)Ti(5)O(12)/C in a dynamic nitrogen atmosphere was first studied by means of thermogravimetric-differential thermal analysis technique at five different heating rates. According to the double equal-double steps method, the Li(4)Ti(5)O(12)/C solid-state reaction mechanism could be properly described as the Jander equation, which was a three-dimensional diffusion with spherical symmetry, and the reaction mechanism functions were listed as follows: f(α) = (3)/(2)(1 - α)(2/3)[1 - (1 - α)(1/3)](-1), G(α) = [1 - (1 - α)(1/3)](2). In FWO method, average activation energy, frequency factor, and reaction order were 284.40 kJ mol(-1), 2.51 × 10(18) min(-1), and 1.01, respectively. However, the corresponding values in FRL method were 271.70 kJ mol(-1), 1.00 × 10(17) min(-1), and 0.96, respectively. Moreover, the values of enthalpy of activation, Gibbs free energy of activation, and entropy of activation at the peak temperature were 272.06 kJ mol(-1), 240.16 kJ mol(-1), and 44.24 J mol(-1) K(-1), respectively. 相似文献
914.
Hu B Meng M Fossey JS Mo W Hu X Deng WP 《Chemical communications (Cambridge, England)》2011,47(38):10632-10634
Planar chiral nucleophilic catalyst Fc-PIP was employed in the kinetic resolution of bulky (hetero)arylalkyl carbinols delivering unreacted alcohols with extremely high enantiomeric excess (>99.0% ees) in ideal conversions ranging from 50.4-56.7%. 相似文献
915.
Chen J Li C Eda G Zhang Y Lei W Chhowalla M Milne WI Deng WQ 《Chemical communications (Cambridge, England)》2011,47(21):6084-6086
We demonstrate a novel architecture of solar cell by incorporating graphene thin film in a quantum dot sensitized solar cell. Quantum dot sensitized nanorods with a graphene layer exhibited a 54.7% improvement comparing a quantum dot sensitized ZnO nanorods without graphene layer. A fill factor as high as ~62% was also obtained. 相似文献
916.
Deng S Sriwichai S Taranekar P Krueger G Mays JW Advincula RC 《Chemical communications (Cambridge, England)》2011,47(31):8805-8807
A series of thiophene dendrons and dendrimers with peripheral functional groups were designed and synthesized. Two methodologies using thiophene dendrons and dendrons as synthetic building blocks, namely, (1) periphery functionalization; (2) a combination of focal and periphery functionalization have been demonstrated. 相似文献
917.
Liu J Yang K Deng Q Li Q Zhang L Liang Z Zhang Y 《Chemical communications (Cambridge, England)》2011,47(13):3969-3971
A new approach, combining metal-coordination with molecular imprinting technology, was developed to prepare protein-affinity materials, which showed higher specific recognition ability towards the target protein than those prepared using either metal-coordination or molecular imprinting technology. 相似文献
918.
Ren J Shen S Pang Z Lu X Deng C Jiang X 《Chemical communications (Cambridge, England)》2011,47(42):11692-11694
Superparamagnetic Fe(3)O(4) nanoparticles with positive surface ξ-potential were synthesized via a solvothermal route. After Fe(3)O(4) was mixed with HAuCl(4) and NaBH(4), the reduced Au nanoparticles could be directly adsorbed onto the surface of Fe(3)O(4) nanoparticles. The as-synthesized nanocomposites were successfully applied to photothermal destruction of cancer cells. 相似文献
919.
Deng Y Zhang Q Tang S Zhang L Deng S Shi Z Chen G 《Chemical communications (Cambridge, England)》2011,47(24):6828-6830
ZnFe(2)O(4)/C hollow spheres have been synthesized via a facile solvothermal route using low cost raw materials. The resulting composite showed a very high specific capacity of 841 mAh g(-1) after 30 cycles and good rate capability. 相似文献
920.
Significant reduction of harmful compounds in tobacco smoke by the use of titanate nanosheets and nanotubes 总被引:2,自引:0,他引:2
Deng Q Huang C Xie W Zhang J Zhao Y Hong Z Pang A Wei M 《Chemical communications (Cambridge, England)》2011,47(21):6153-6155
Titanate nanosheets and nanotubes have first been introduced into cigarette filter, a great range of harmful compounds including tar, nicotine, ammonia, hydrogen cyanide, selected carbonyls and phenolic compounds can be reduced efficiently. 相似文献