全文获取类型
收费全文 | 90816篇 |
免费 | 16368篇 |
国内免费 | 9217篇 |
专业分类
化学 | 61751篇 |
晶体学 | 916篇 |
力学 | 5771篇 |
综合类 | 513篇 |
数学 | 10135篇 |
物理学 | 37315篇 |
出版年
2024年 | 347篇 |
2023年 | 2048篇 |
2022年 | 3309篇 |
2021年 | 3575篇 |
2020年 | 3935篇 |
2019年 | 3513篇 |
2018年 | 3219篇 |
2017年 | 2874篇 |
2016年 | 4591篇 |
2015年 | 4365篇 |
2014年 | 5325篇 |
2013年 | 6774篇 |
2012年 | 8231篇 |
2011年 | 8415篇 |
2010年 | 5559篇 |
2009年 | 5391篇 |
2008年 | 5793篇 |
2007年 | 5069篇 |
2006年 | 4774篇 |
2005年 | 3841篇 |
2004年 | 2947篇 |
2003年 | 2302篇 |
2002年 | 2115篇 |
2001年 | 1822篇 |
2000年 | 1609篇 |
1999年 | 1847篇 |
1998年 | 1596篇 |
1997年 | 1583篇 |
1996年 | 1565篇 |
1995年 | 1329篇 |
1994年 | 1154篇 |
1993年 | 998篇 |
1992年 | 860篇 |
1991年 | 787篇 |
1990年 | 651篇 |
1989年 | 503篇 |
1988年 | 370篇 |
1987年 | 308篇 |
1986年 | 324篇 |
1985年 | 265篇 |
1984年 | 151篇 |
1983年 | 118篇 |
1982年 | 100篇 |
1981年 | 57篇 |
1980年 | 42篇 |
1979年 | 15篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
We provide evidence for a finite-temperature ferromagnetic transition in two dimensions as H -->0 in thin films of 3He on graphite, a model system for the study of two-dimensional magnetism. We perform pulsed and cw NMR experiments at fields of 0.03-0.48 mT on 3He at areal densities of 20.5-24.2 atoms/nm(2). At these densities, the second layer of 3He has a strongly ferromagnetic tendency. With decreasing temperature, we find a rapid onset of magnetization that becomes independent of the applied field at temperatures in the vicinity of 1 mK. Both the dipolar field and the NMR linewidth grow rapidly as well, which is consistent with a large (order unity) polarization of the 3He spins. 相似文献
822.
Chuncheng Hao Zuolin Cui Yansheng Yin Zhikun Zhang 《Journal of nanoparticle research》2002,4(1-2):107-110
Nanostructured Fe3Al intermetallic compounds were produced by using hydrogen arc plasma method. The transmission electron microscopy experiments showed that the average particle size of the as-synthesized was about 40-nm. The change in hardness of Fe3Al nanostructured intermetallic compounds with annealing temperatures was observed and evaluated. 相似文献
823.
After having introduced by ion implantation 57Fe to a local concentration of 7 at% into Co6Ag94, we observed it by conversion electron Mössbauer spectroscopy in the as-prepared state and after isochronal annealing. A superferromagnetic state is inferred, which is correlated with the ordering of the magnetic moments on the Fe clusters through chain-like or dendritic Co/Fe linear structures. The magnetic moment disordering temperature lies above 473 K. 相似文献
824.
A modified derivative sign binary method is proposed to extract fringe skeletons from interferometric fringe patterns. A fringe direction map ranging from 0° to 360° is obtained with an unambiguous relationship between the grayscale and fringe tangent direction. Using this approach, the derivative sign binary map is detected without a fringe direction jump. The dark (light) fringe intensity minimum (maximum) can be extracted automatically to define fringe skeletons. In addition, two different anisotropic one-dimensional filters are described that can be used for further improving the fringe quality. Examples are provided for a holographic interferogram and a Moiré fringe pattern to illustrate applications and benefits of the approach. 相似文献
825.
Considering the complexity of common phased array, and relatively slow mechanical scanning of the single transducer, a new-style transducer that has a changeable focus and a simple control system is needed. The sector phased array transducer, which has many advantages including easy fabrication, movable focus, and a simple control system, can reach the desired requirements. This paper has demonstrated its feasibility by the computation of acoustic field in (y, z) plane. The 24-element phased array, of which the length of the focal region is about 10 mm, and the maximum lateral diameter is about 1.5 mm, can accomplish the adjustment of the focus position. The maximum lateral displacement is 1.5 mm, and the treatment area is about 9 multiples of the single transducer, and only six power amplifiers are needed. 相似文献
826.
827.
On the differentiability of depth distribution function of deposited energy, momentum and ion range 下载免费PDF全文
Based on the translational invariance of a medium,a new theorem has been proposed and proved rigorously:the depth distributions of the deposited energy,momentum and ion range must be infinitely differentiable functions in amorphous or polycrystalline infinite targets by ion bombardment,if these functions exist.The origin of the “discontinuity”,derived by Dr Glazov in 1995 in J.Phys.:Condens.Matter 7 6365,has been analysed in detail.For the power cross section,neglecting electronic stopping,the linear transport equations determining the depth distribution functions of the deposited energy and monentum (by taking the threshold enerkgy into account )have been solved asymptotically.An important formula derived by Dr Glazov has been confirmed and generalized.The results agree with the new theorem. 相似文献
828.
Field-ion microscopy(FIM),a tool for surface analysis with atomic resolution,has been employed to observe the end structure of single-walled carbon nanotubes(SWCNTs).FIM images revealed the existence of open SWCNT ends,Amorphous carbon atoms were also observed to occur around SWCNTs and traditional field evaporation failed to remove them.Heat treatment was found to be efficacious in altering the end structures of SWCNT bundles.Carbon and oxygen atoms released from heated tungsten filament are believed to be responsible for the decoration imposed on the SWCNT ends. 相似文献
829.
A scanning superconducting quantum interference device microscope for room temperature samples 下载免费PDF全文
We have constructed a scanning low-Tc superconducting quantum interference device (SQUID) microscope, in which the SQUID is mounted on the lower end of a copper rod and cooled to liquid helium temperature. There is a 65μm thick sapphire window under the SQUID. The sample at room temperature underneath the window can be scanned to produce magnetic images. The microscope has a spatial resolution of 100-150μm and a magnetic field sensitivity of 3-60pT/$\sqrt{Hz}$ in a magnetically unshielded environment. We have used this scanning SQUID microscope to measure various room temperature samples. 相似文献
830.
Koga T Seo YS Zhang Y Shin K Kusano K Nishikawa K Rafailovich MH Sokolov JC Chu B Peiffer D Occhiogrosso R Satija SK 《Physical review letters》2002,89(12):125506
We report an anomalous swelling of polymer thin films in carbon dioxide (CO(2)) which is associated (in both locus and form) with the density fluctuation ridge that forms along the extension of the coexistence curve of gas and liquid in the P-T phase diagram. Neutron reflectivity results showed that CO(2) could be sorbed to a large extent ( approximately 60%) in thin polymer films even when the bulk miscibility of the polymer with CO(2) is very poor. The anomalous swelling is found to scale with the polymer radius of gyration (R(g)) and extends to a distance approximately 10 R(g). 相似文献