全文获取类型
收费全文 | 4983篇 |
免费 | 131篇 |
国内免费 | 29篇 |
专业分类
化学 | 3141篇 |
晶体学 | 32篇 |
力学 | 156篇 |
综合类 | 1篇 |
数学 | 635篇 |
物理学 | 1178篇 |
出版年
2021年 | 45篇 |
2020年 | 61篇 |
2019年 | 54篇 |
2018年 | 40篇 |
2017年 | 45篇 |
2016年 | 74篇 |
2015年 | 82篇 |
2014年 | 71篇 |
2013年 | 196篇 |
2012年 | 204篇 |
2011年 | 237篇 |
2010年 | 118篇 |
2009年 | 114篇 |
2008年 | 214篇 |
2007年 | 250篇 |
2006年 | 250篇 |
2005年 | 217篇 |
2004年 | 209篇 |
2003年 | 183篇 |
2002年 | 163篇 |
2001年 | 129篇 |
2000年 | 111篇 |
1999年 | 76篇 |
1998年 | 54篇 |
1997年 | 56篇 |
1996年 | 70篇 |
1995年 | 91篇 |
1994年 | 80篇 |
1993年 | 73篇 |
1992年 | 78篇 |
1991年 | 57篇 |
1990年 | 61篇 |
1989年 | 70篇 |
1988年 | 68篇 |
1987年 | 53篇 |
1986年 | 48篇 |
1985年 | 73篇 |
1984年 | 64篇 |
1983年 | 61篇 |
1982年 | 90篇 |
1981年 | 58篇 |
1980年 | 68篇 |
1979年 | 51篇 |
1978年 | 64篇 |
1977年 | 51篇 |
1976年 | 61篇 |
1975年 | 75篇 |
1974年 | 46篇 |
1973年 | 55篇 |
1972年 | 39篇 |
排序方式: 共有5143条查询结果,搜索用时 15 毫秒
991.
Coskun A Banaszak M Astumian RD Stoddart JF Grzybowski BA 《Chemical Society reviews》2012,41(1):19-30
The development and fabrication of mechanical devices powered by artificial molecular machines is one of the contemporary goals of nanoscience. Before this goal can be realized, however, we must learn how to control the coupling/uncoupling to the environment of individual switchable molecules, and also how to integrate these bistable molecules into organized, hierarchical assemblies that can perform significant work on their immediate environment at nano-, micro- and macroscopic levels. In this tutorial review, we seek to draw an all-important distinction between artificial molecular switches which are now ten a penny-or a dime a dozen-in the chemical literature and artificial molecular machines which are few and far between despite the ubiquitous presence of their naturally occurring counterparts in living systems. At the single molecule level, a prevailing perspective as to how machine-like characteristics may be achieved focuses on harnessing, rather than competing with, the ineluctable effects of thermal noise. At the macroscopic level, one of the major challenges inherent to the construction of machine-like assemblies lies in our ability to control the spatial ordering of switchable molecules-e.g., into linear chains and then into muscle-like bundles-and to influence the cross-talk between their switching kinetics. In this regard, situations where all the bistable molecules switch synchronously appear desirable for maximizing mechanical power generated. On the other hand, when the bistable molecules switch "out of phase," the assemblies could develop intricate spatial or spatiotemporal patterns. Assembling and controlling synergistically artificial molecular machines housed in highly interactive and robust architectural domains heralds a game-changer for chemical synthesis and a defining moment for nanofabrication. 相似文献
992.
993.
We show how to bridge the divide between atomic systems and electronic devices by engineering a coupling between the motion of a single ion and the quantized electric field of a resonant circuit. Our method can be used to couple the internal state of an ion to the quantized circuit with the same speed as the internal-state coupling between two ions. All the well-known quantum information protocols linking ion internal and motional states can be converted to protocols between circuit photons and ion internal states. Our results enable quantum interfaces between solid state qubits, atomic qubits, and light, and lay the groundwork for a direct quantum connection between electrical and atomic metrology standards. 相似文献
994.
Choi SK Coldea R Kolmogorov AN Lancaster T Mazin II Blundell SJ Radaelli PG Singh Y Gegenwart P Choi KR Cheong SW Baker PJ Stock C Taylor J 《Physical review letters》2012,108(12):127204
We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model on the honeycomb lattice. We observe spin-wave excitations below 5 meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zigzag magnetic order. The onset of long-range magnetic order below T(N)=15.3 K is confirmed via the observation of oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we propose a revised crystal structure model with significant departures from the ideal 90° Ir-O-Ir bonds required for dominant Kitaev exchange. 相似文献
995.
Experimental demonstration of terahertz metamaterial absorbers with a broad and flat high absorption band 总被引:2,自引:0,他引:2
We present the design, numerical simulations and experimental measurements of terahertz metamaterial absorbers with a broad and flat absorption top over a wide incidence angle range for either transverse electric or transverse magnetic polarization depending on the incident direction. The metamaterial absorber unit cell consists of two sets of structures resonating at different but close frequencies. The overall absorption spectrum is the superposition of individual components and becomes flat at the top over a significant bandwidth. The experimental results are in excellent agreement with numerical simulations. 相似文献
996.
在激光惯性约束核聚变(ICF)精确打靶中,对激光束变换、整形和控制要求苛刻,通过数字在线操控技术能够在线实现激光系统的自动校准,而频率变换是数字在线操控技术中的关键一环。在不进行逼近迭代计算的情况下,基于可逆的傅里叶变换和龙格-库塔算法,对神光II终端靶场系统中负单轴晶体KDP的"I+II"类频率变换的逆问题进行了探讨和相应的算法研究,并给出了对应的模拟计算结果。最后,与神光装置运行的实验数据进行比对,验证了频率变换逆问题算法的正确性和稳定性。 相似文献
997.
Taylor WS Matthews CC Hicks AJ Fancher KG Chen LC 《The journal of physical chemistry. A》2012,116(3):943-951
Reactions of Au(+)((1)S) and Au(+)((3)D) with CH(3)F and CH(3)Cl have been carried out in a drift cell in He at a pressure of 3.5 Torr at both room temperature and reduced temperatures in order to explore the influence of the electronic state of the metal on reaction outcomes. State-specific product channels and overall two-body rate constants were identified using electronic state chromatography. These results indicate that Au(+)((1)S) reacts to yield an association product in addition to AuCH(2)(+) in parallel steps with both neutrals. Product distributions for association vs HX elimination were determined to be 79% association/21% HX elimination for X = F and 50% association/50% HX elimination when X = Cl. Reaction of Au(+)((3)D) with CH(3)F also results in HF elimination, which in this case is thought to produce (3)AuCH(2)(+). With CH(3)Cl, Au(+)((3)D) reacts to form AuCH(3)(+) and CH(3)Cl(+) in parallel steps. An additional product channel initiated by Au(+)((3)D) is also observed with both methyl halides, which yields CH(2)X(+) as a higher-order product. Kinetic measurements indicate that the reaction efficiency for both Au(+) states is significantly greater with CH(3)Cl than with CH(3)F. The observed two-body rate constant for depletion of Au(+)((1)S) by CH(3)F represents less than 5% of the limiting rate constant predicted by the average dipole orientation model (ADO) at room temperature and 226 K, whereas CH(3)Cl reacts with Au(+)((1)S) at the ADO limit at both room temperature and 218 K. Rate constants for depletion of Au(+)((3)D) by CH(3)F and CH(3)Cl were measured at 226 and 218 K respectively, and indicate that Au(+)((3)D) is consumed at approximately 2% of the ADO limit by CH(3)F and 69% of the ADO limit by CH(3)Cl. Product formation and overall efficiency for all four reactions are consistent with previous experimental results and available theoretical models. 相似文献
998.
Hanisch M Mačković M Taccardi N Spiecker E Klupp Taylor RN 《Chemical communications (Cambridge, England)》2012,48(36):4287-4289
Here we report that silver nanoparticle necklaces can be readily formed by treatment of colloidal silica with ammoniacal silver complex solution followed by washing, deposition and ageing. We investigate the morphology of the produced materials and elucidate the key variables that influence this promising new approach to one-dimensional nanostructuring. 相似文献
999.
AK Peacock SI Cauët A Taylor P Murray SR Williams JV Weaver DJ Adams MJ Rosseinsky 《Chemical communications (Cambridge, England)》2012,48(75):9373-9375
Poly[2-(methacryloyloxy)ethylphosphorylcholine]-coated SPIONs were prepared through ATRP and amidation coupling reactions. The coated SPIONs exhibited high stability and re-dispersability in phosphate buffered saline and uptake in a stem cell line, with high T(2) relaxivity. 相似文献
1000.
RE Fairbairn R McLellan RD McIntosh SM Taylor EK Brechin SJ Dalgarno 《Chemical communications (Cambridge, England)》2012,48(68):8493-8495
Rare-earth octahedra have been previously synthesised using p-tert-butylcalix[4]arene as a cluster support. Introduction of a heteroatom bridge in the calixarene framework, with concomitant alteration to the nature of the metal binding pocket, influences lanthanide composition in the cluster. 相似文献