全文获取类型
收费全文 | 380篇 |
免费 | 7篇 |
国内免费 | 35篇 |
专业分类
化学 | 194篇 |
晶体学 | 1篇 |
力学 | 67篇 |
数学 | 17篇 |
物理学 | 143篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 18篇 |
2013年 | 49篇 |
2012年 | 13篇 |
2011年 | 26篇 |
2010年 | 15篇 |
2009年 | 20篇 |
2008年 | 16篇 |
2007年 | 22篇 |
2006年 | 19篇 |
2005年 | 13篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 13篇 |
1998年 | 3篇 |
1997年 | 13篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有422条查询结果,搜索用时 9 毫秒
111.
原子力显微镜 ( AFM)自 1 986年发明以来得到了广泛的应用和发展 [1,2 ] ,成为众多研究领域中的强有力工具 ,并为其它的研究技术提供了良好的互补手段 .DNA是 AFM首次研究的生物样品之一 ,它使人类首次观察到 DNA分子的原始形貌 ,并实现了接近生理条件下的操作 ,使得随时监测生物大分子的生化反应过程成为现实 [3,4 ] .在 DNA的 AFM研究中 ,样品的制备是其关键 .以阳离子 (如 Mg2 + ,Ba2 + ,Mn2 +和 Ca2 +等 [5] )固定法较为常见 ,其操作简单 ,固定效果好 ,基底效应小 ,但也有一定的局限性 ,如存在限制性内切酶时 ,这些简单离子会… 相似文献
112.
Mehmet Somer 《无机化学与普通化学杂志》2000,626(12):2478-2480
The vibrational spectra of the cluster anions [E4]4– (E = Si, Ge) in the metallic compounds Ba2E4 and Na4E4 have been measured and assigned based on the Td symmetry of the discrete tetrahedranide anion. Due to the lower site‐symmetries in the respective crystals all degenerate modes are split, but to different extends. The characteristic breathing frequency ν(E–E) of the [E4]4– cluster appears exclusively in the Raman spectrum and is almost unaffected by the nature of counterions: ν(E–E) = 486 cm–1 (E = Si) and 276 and 278 (Ge), respectively. The calculated valence force constants fd (Si–Si) = 1.17 Ncm–1 ( Na ); 1.15 Ncm–1 ( Ba ) and fd (Ge–Ge) = 0.98 Ncm–1 ( Na ); 0.94 Ncm–1 ( Ba ) are in good agreement with those previously reported. 相似文献
113.
B. Mahltig J.-F. Gohy R. Jérôme C. Bellmann M. Stamm 《Colloid and polymer science》2000,278(6):502-508
The adsorption of the diblock polyampholyte poly (methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate) from aqueous solution on silicon substrates was investigated as a function of polymer
concentration and pH. Dynamic light scattering and electrokinetic measurements were used to characterize the polyampholyte
in solution. The amount of polymer adsorbed was determined by ellipsometry and lateral structures of the polymer layer were
investigated by scanning force microscopy. The amount of polymer adsorbed was found to be strongly influenced by the pH of
the polymer solution, while the size of the polyampholyte micelles adsorbed on the surface was hardly affected by pH during
adsorption. From investigations by scanning force microscopy well-seperated micelles were seen in the dried monolayers adsorbed
directly from solution. The structures at the surface are correlated to structures in solution, and the adsorbed amount depends
on the relative charge of the micelles and the surface.
Received: 13 September 1999 Accepted in revised form: 8 December 1999 相似文献
114.
Hans Peter Lüthi 《Theoretical chemistry accounts》1997,97(1-4):211-226
Distributed computation over local and wide-area networks is gaining importance and may soon become the primary means in
high performance computing. The development in all areas of scientific computing is closely coupled with the development of
efficient application software that fully utilizes the power of the modern computer resources. In numerical quantum chemistry,
the adaptation of method and program development to parallel and distributed-parallel computing has shown remarkable results.
The contributions of Jan Alml?f in this area of research are briefly reviewed in this paper. The integral-direct Hartree-Fock
calculation (zeroth, first and second derivatives) will be used as a model to investigate network-computing techniques and
paradigms.
Received: 2 February 1997 / Accepted: 24 March 1997 相似文献
115.
V.K Rastogi C.B Arora S.K Singhal D.N Singh R.A Yadav 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2505-2510
Raman spectrum of 2,6-difluorobenzonitrile in the powder form has been recorded in the region 50–4000 cm−1 on a Jasco K-500 spectrophotometer using the 488.0 nm radiation from an argon laser. IR spectra in the region 200–4000 cm−1 have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer and in liquid and vapour phases on a Jasco FTIR/7000 spectrometer. Using these observed frequencies force field calculations for the planar and non-planar modes have been carried out assuming a general valence force field. 相似文献
116.
Sergey M. Shevchenko George W. Bailey Leonid G. Akim 《Journal of Molecular Structure》1999,460(1-3):179-190
Molecular mechanics calculations and simulated annealing were applied to model humic polyanions originating from lignin. The dynamic behavior of such oxidized lignins in model soil organic complexes, such as an oxidized lignin-carbohydrate complex (LCC) and humic (oxidized LCC)-clay aggregates, was analyzed. Neither ionization nor hydrogen bonding bring significant changes in the conformational properties of oxidized lignin and LCC. Oxidized lignin and LCC oligomers (humic substances in soil) bind to the mineral surfaces, a process that was exemplified in computational experiments on complexes with muscovite. Upon ionization, a lignin-derived oligomer develops strong attractive organo-mineral interactions through cation bridges. Without metal cations, electrostatic repulsion between negatively charged anions and the oxygen-mineral surface prevails, and the two parts of the organo-mineral complex drift apart. This tendency is typical of an oxidized lignin oligomer but not of a topological oxidized LCC. 相似文献
117.
N. Yasuda M. Yamamoto K. Amemiya H. Takahashi A. Kyan K. Ogura 《Radiation measurements》1999,31(1-6):203-208
Atomic Force Microscope (AFM) has been applied to evaluate the surface roughness and the track sensitivity of CR-39 track detector. We experimentally confirmed the inverse correlation between the track sensitivity and the roughness of the detector surface after etching. The surface of CR-39 (CR-39 doped with antioxidant (HARZLAS (TD-1)) and copolymer of CR-39/NIPAAm (TNF-1)) with high sensitivity becomes rough by the etching, while the pure CR-39 (BARYOTRAK) with low sensitivity keeps its original surface clarity even for the long etching. 相似文献
118.
Phase dynamics of effective drag and lift components in vortex-induced vibration at low mass–damping
In this work, we investigate the dynamics of vortex-induced vibration of an elastically mounted cylinder with very low values of mass and damping. We use two methods to investigate this canonical problem: first we calculate the instantaneous phase between the cylinder motion and the fluid forcing; second we decompose the total hydrodynamic force into drag and lift components that act along and normal to, respectively, the instantaneous effective angle of attack. We focus on the phase dynamics in the large-amplitude–response range, consisting of the initial, upper and lower “branches” of response. The instantaneous phase between the transverse force and displacement shows repeated phase slips separating periods of constant, or continuous-drifting, phase in the second half of the upper branch. The phase between the lift component and displacement shows strong phase locking throughout the large-amplitude range – the average phase varies linearly with the primary frequency – however the modulation of this phase is largest in the second half of the upper branch. These observations suggest that the large-amplitude–response dynamics is driven by two distinct limit cycles – one that is stable over a very small range of reduced velocity at the beginning of the upper branch, and another that consists of the lower branch. The chaotic oscillation between them – the majority of the upper branch – occurs when neither limit cycle is stable. The transition between the upper and lower branches is marked by intermittent switching with epochs of time where different states exist at a constant reduced velocity. These different states are clearly apparent in the phase between the lift and displacement, illustrating the utility of the force decomposition employed. The decomposed force measurements also show that the drag component acts as a damping factor whereas the lift component provides the necessary fluid excitation for free vibration to be sustained. 相似文献
119.
This paper discusses two concepts of “moment” (infinitesimal) used successively by Newton in his calculus and relates these two concepts to the two concepts of force that Newton presented in Law II and Def. VIII of the Principia, to which the approximations to the action of a centripetal force known as the polygonal and parabolic models are considered to be related. It is shown that in the context of the application of the calculus to mechanics, the transition in the use of these concepts of “moment” took place in 1684, between the writing of De Motu and its first revision. 相似文献
120.
Mechanical, thermal and optical properties of modified cyclo-olefin copolymers COC were studied by molecular dynamics simulations and ab initio calculations. The COC chains were modified by substituting the norbornane rings with methyl groups and replacing ethane units with propane. A modified Dreiding 2.21 force field was developed for the molecular dynamics simulations. The bulk and Young’s moduli increased when the norbornane rings of COC were substituted with methyl groups and when the ethane units were replaced with propane. The highest glass transition temperature was obtained when the norbornane rings were substituted with methyl groups. Ab initio calculations of isotropic polarizability and refractive index were sensitive to the applied basis set and level of theory. Good agreement with available experimental data was obtained with the B3LYP/6-311G** method. Replacement of ethane units with propane lowered the refractive index significantly, whereas other structural modifications had practically no effect. 相似文献