全文获取类型
收费全文 | 402篇 |
免费 | 33篇 |
国内免费 | 24篇 |
专业分类
化学 | 241篇 |
晶体学 | 1篇 |
力学 | 15篇 |
数学 | 27篇 |
物理学 | 175篇 |
出版年
2022年 | 20篇 |
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 19篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 27篇 |
2015年 | 9篇 |
2014年 | 15篇 |
2013年 | 21篇 |
2012年 | 26篇 |
2011年 | 19篇 |
2010年 | 12篇 |
2009年 | 16篇 |
2008年 | 24篇 |
2007年 | 19篇 |
2006年 | 15篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 15篇 |
2002年 | 17篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有459条查询结果,搜索用时 15 毫秒
421.
The symmetric coupling of mixed finite element and boundaryelement methods is analysed for a model interface problem withthe Laplacian. The coupling involves a further continuous ansatzfunction on the interface to link the discontinuous displacementfield to the necessarily continuous boundary ansatz function.Quasi-optimal a priori error estimates and sharp a posteriorierror estimates are established which justify adaptive mesh-refiningalgorithms. Numerical experiments prove the adaptive couplingas an efficient tool for the numerical treatment of transmissionproblems. 相似文献
422.
423.
The effects of axisymmetric flow of a Powell-Eyring fluid over an impermeable radially stretching surface are presented. Characteristics of the heat transfer process are analyzed with a more realistic condition named the convective boundary condition. Governing equations for the flow problem are derived by the boundary layer approximations. The modeled highly coupled partial differential system is converted into a system of ordinary differential equations with acceptable similarity transformations. The convergent series solutions for the resulting system are constructed and analyzed. Optimal values are obtained and presented in a numerical form using an optimal homotopy analysis method (OHAM). The rheological characteristics of different parameters of the velocity and temperature profiles are presented graphically. Tabular variations of the skin friction coefficient and the Nusselt number are also calculated. It is observed that the temperature distribution shows opposite behavior for Prandtl and Biot numbers. Furthermore, the rate of heating/cooling is higher for both the Prandtl and Biot numbers. 相似文献
424.
Muhammad Saleem Muhammad Rafiq Muhammad Hanif Muhammad Ashraf Shaheen Sung-Yum Seo 《Journal of fluorescence》2018,28(1):97-165
The design and development of the fluorescence reporting molecules for the trace recognition of the metallic ions in the aqueous, mixed organic aqueous media, environmental specimen, living things e.g., body fluids, serum, urine etc is the evergreen research area. Among several methodologies utilized for these purposes, the fluorescent techniques have wonderful impact in the era of metal sensor development due to their acclamatory features of non-invasive detection process and appreciable sensitivity. The utilization of small organic molecules for the sensation of metallic ions through the fluorescent techniques harvested the wonderful results having some interesting features of chromogenic response on metal binding, robustness in the preparation and applicability to establish the metallic accumulation level inside the live cells via bioimaging studies. The detailed knowledge and background about the several reported chemosening strategies have the utmost importance in order to understand or to design the novel molecules for metal sensing purposes. The objective of the presents review was to compile the best ever used copper sensing strategies via fluorescent means in the running decade. We have summarized the values of optical positions of the spectral lines, spectral shifting upon metal binding, binding/association/dissociation constants, chromogenic changes in the reaction mixture, proposed complexation mechanism of the ligand with the copper, ligand sensitivities toward the copper recognition, binding stoichiometries and the detailed bioimaging results where applicable. 相似文献
425.
Aubert B Bona M Boutigny D Karyotakis Y Lees JP Poireau V Prudent X Tisserand V Zghiche A Garra Tico J Grauges E Lopez L Palano A Pappagallo M Eigen G Stugu B Sun L Abrams GS Battaglia M Brown DN Button-Shafer J Cahn RN Groysman Y Jacobsen RG Kadyk JA Kerth LT Kolomensky YG Kukartsev G Lopes Pegna D Lynch G Mir LM Orimoto TJ Osipenkov IL Ronan MT Tackmann K Tanabe T Wenzel WA del Amo Sanchez P Hawkes CM Watson AT Koch H Schroeder T Walker D Asgeirsson DJ Cuhadar-Donszelmann T Fulsom BG Hearty C 《Physical review letters》2008,100(8):081801
We report the observation of the b-->d penguin-dominated decay B;{0}-->K;{*0}K[over ];{*0} with a sample of 383.2+/-4.2 million BB[over ] pairs collected with the BABAR detector at the PEP-II asymmetric-energy e;{+}e;{-} collider at the Stanford Linear Accelerator Center. The measured branching fraction is B(B;{0}-->K;{*0}K[over ];{*0})=[1.28_{-0.30};{+0.35}+/-0.11]x10;{-6} and the fraction of longitudinal polarization is f_{L}(B;{0}-->K;{*0}K[over ];{*0})=0.80_{-0.12};{+0.10}+/-0.06. The first error quoted is statistical and the second systematic. We also obtain an upper limit at the 90% confidence level on the branching fraction for B(B;{0}-->K;{*0}K;{*0})<0.41x10;{-6}. 相似文献
426.
Aubert B Bona M Boutigny D Karyotakis Y Lees JP Poireau V Prudent X Tisserand V Zghiche A Garra Tico J Grauges E Lopez L Palano A Pappagallo M Eigen G Stugu B Sun L Abrams GS Battaglia M Brown DN Button-Shafer J Cahn RN Groysman Y Jacobsen RG Kadyk JA Kerth LT Kolomensky YG Kukartsev G Lopes Pegna D Lynch G Mir LM Orimoto TJ Osipenkov IL Ronan MT Tackmann K Tanabe T Wenzel WA Del Amo Sanchez P Hawkes CM Watson AT Koch H Schroeder T Walker D Asgeirsson DJ Cuhadar-Donszelmann T Fulsom BG Hearty C 《Physical review letters》2008,100(6):061803
We measure time-integrated CP-violating asymmetries of neutral charmed mesons in the modes D0 --> K(-) K(+) and D0 --> pi(-) pi(+) with the highest precision to date by using D0 --> K(-) pi(+) decays to correct detector asymmetries. An analysis of 385.8 fb(-1) of data collected with the BABAR detector yields values of a(CP)(KK)=(0.00+/-0.34(stat)+/-0.13(syst))% and a(CP)(pipi)=(-0.24+/-0.52(stat)+/-0.22(syst))%, which agree with standard model predictions. 相似文献
427.
摘要:用化学酶法合成聚己内酯(PCL)和聚N,N-二甲氨基甲基丙烯酸乙酯(PDMAEMA)双亲嵌段聚合物(PCL-b-PDMAEMA)。通过核磁共振(1H NMR),红外光谱仪(FTIR-IR),凝胶渗透色谱(GPC) 对其结构以及分子量与其分子量分布情况进行了表征。对聚合物的溶液性质进行了研究,结果表明:临界胶束浓度(CMC)嵌段聚合物中疏水链段增多有利于形成胶束,表现为CMC降低,并具有较高的热力学稳定性。PDMAEMA是PH和温度敏感材料,研究发现,在不同的温度和pH值条件下表现不同的聚集状态, 当聚合物的pH值降低时平均流体力学直径增加,温度升高平均流体力学直径降低。 相似文献
428.
Murtaza Saleem Saadat A. Siddiqi Shahid Atiq M. Sabieh Anwar Saira Riaz 《化学物理学报(中文版)》2010,23(4):469-472
Mn doped ZnO nano-crystallites were synthesized by state of the art sol-gel derived auto-combustion technique. As-burnt powder was investigated with different characterization techniques to explore the properties of Mn doped ZnO dilute magnetic semiconductor. X-ray diffraction measurements indicate that Mn doped ZnO retain wurtzite type hexagonal crystal structure like ZnO. Compositional and morphological studies were carried out by energy dispersive X-ray analysis and scanning electron microscopy, respectively. Tempera-ture dependent resistivity of the sample exhibited the semiconducting behavior of the DMS material. Room temperature magnetic properties determined by vibrating sample magne-tometer, revealed the presence of ferromagnetic and diamagnetic contributions in Mn doped ZnO. 相似文献
429.
DFT-based structural optimisations of Fe2NiZ (Z?=?Al, Ga, Si, Ge) Heusler compounds confirm the stability of these alloys in F-43m phase. While defining the electronic structure, onsite Hubbard approximation scheme for exchange correlations predicted better results than the generalised gradient approximation. Calculated band structure and densities of states together with spin magnetic moments designate the half-metallic character of these alloys. Indirect band gaps, 1.2?eV for Fe2NiAl, 0.98?eV for Fe2NiGa, 1.3?eV for Fe2NiSi and 1.1?eV for Fe2NiGe in spin-down states are observed. The ferromagnetic spin moments amount to an integral value of 5μB for (Al, Ga) and 6μB for (Si, Ge) systems with a maximum contribution from transition metal atom (Fe). To forecast the possible turnout of the thermopower, Seebeck coefficients, electrical and thermal conductivities are calculated, which directly hints the thermoelectric response of these materials. This study creates a possibility of these alloys in thermoelectrics and spintronics. 相似文献
430.
A possibility of self‐organization of magnetized four‐component dusty plasmas to double Beltrami (DB) state is explored. It is found that for a specific set of Beltrami parameters, the four‐component dusty plasma self‐organizes to DB state. The DB state characterized by two scale parameters may represent a paramagnetic or diamagnetic field structure. The impact of Beltrami parameters, charge and densities of dust grains on formation of self‐organized structures has also been investigated. This study has potential relevance to the formation of large‐scale structures in astrophysical plasmas. 相似文献