全文获取类型
收费全文 | 488篇 |
免费 | 7篇 |
国内免费 | 11篇 |
专业分类
化学 | 329篇 |
晶体学 | 1篇 |
力学 | 32篇 |
综合类 | 13篇 |
数学 | 43篇 |
物理学 | 88篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 19篇 |
2020年 | 16篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 9篇 |
2016年 | 18篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 41篇 |
2012年 | 38篇 |
2011年 | 33篇 |
2010年 | 22篇 |
2009年 | 19篇 |
2008年 | 23篇 |
2007年 | 33篇 |
2006年 | 20篇 |
2005年 | 21篇 |
2004年 | 6篇 |
2003年 | 18篇 |
2002年 | 28篇 |
2001年 | 6篇 |
2000年 | 1篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有506条查询结果,搜索用时 296 毫秒
461.
Anjan Biswas Anwar Ja'afar Muhammad Jawad Wayne N. Manrakhan Amarendra K. Sarma Kaisar R. Khan 《Optics & Laser Technology》2012,44(7):2265-2269
The Schrödinger–Hirota equation governs the propagation of optical solitons in a dispersive optical fiber. In this paper, this equation will be solved by the ansatz method for bright and dark 1-soliton solution. The power law nonlinearity will be assumed. By using the tanh method, some additional solutions will be derived. Finally, the numerical simulations will be given. 相似文献
462.
Gaber O. Moustafa Ahmed Shalaby Ahmed M. Naglah Marwa M. Mounier Heba El-Sayed Manal M. Anwar Eman S. Nossier 《Molecules (Basel, Switzerland)》2021,26(15)
Glycyrrhetinic acid (GA) is one of many interesting pentacyclic triterpenoids showing significant anticancer activity by triggering apoptosis in tumor cell lines. This study deals with the design and synthesis of new glycyrrhetinic acid (GA)–amino acid peptides and peptide ester derivatives. The structures of the new derivatives were established through various spectral and microanalytical data. The novel compounds were screened for their in vitro cytotoxic activity. The evaluation results showed that the new peptides produced promising cytotoxic activity against the human breast MCF-7 cancer cell line while comparing to doxorubicin. On the other hand, only compounds 3, 5, and 7 produced potent activity against human colon HCT-116 cancer cell line. The human liver cancer (HepG-2) cell line represented a higher sensitivity to peptide 7 (IC50; 3.30 μg/mL), while it appeared insensitive to the rest of the tested peptides. Furthermore, compounds 1, 3, and 5 exhibited a promising safety profile against human normal skin fibroblasts cell line BJ-1. In order to investigate the mode of action, compound 5 was selected as a representative example to study its in vitro effect against the apoptotic parameters and Bax/BCL-2/p53/caspase-7/caspase-3/tubulin, and DNA fragmentation to investigate beta (TUBb). Additionally, all the new analogues were subjected to antimicrobial assay against a panel of Gram-positive and Gram-negative bacteria and the yeast candida Albicans. All the tested GA analogues 1–8 exhibited more antibacterial effect against Micrococcus Luteus than gentamicin, but they exhibited moderate antimicrobial activity against the tested bacterial and yeast strains. Molecular docking studies were also simulated for compound 5 to give better rationalization and put insight to the features of its structure. 相似文献
463.
In this paper, we present a theoretical calculation of a highly nonlinear germanium (Ge) doped photonic crystal fiber with all-normal group velocity dispersion to design a supercontinuum (SC) light source at 1.55 μm. By doping 3% higher refractive index Ge inside the host silica, the nonlinear coefficient is increased to a value as large as 60.5 W?1 km?1 at 1.55 μm. A 10 dB bandwidth of a 120 nm SC spectrum for a 2.5 ps input optical pulse and a 10 dB bandwidth of a 190 nm SC spectrum for a 1.0 ps input optical pulse have been found using the same fiber length of 200m and input optical power of 18 W. The coherent lengths of the generated SC light sources are found to be 8.8 μm for a 2.5 ps input optical pulse and 5.6 μm for a 1.0 ps input optical pulse. Therefore, the highest longitudinal resolution at 1.55 μm is found to be about 4.0 μm for biological tissues. 相似文献
464.
This paper describes the simulation of a simple technique of superresolution based on holographic imaging in spectral domain. The input beam assembly containing 25 optical fibers with different orientations and positions is placed to illuminate the object in the 4f optical system. The position and orientation of each fiber is calculated with respect to the central fiber in the array. The positions and orientations of the fibers are related to the shift of object spectrum at aperture plane. During the imaging process each fiber is operated once in the whole procedure to illuminate the input object transparency which gives shift to the object spectrum in the spectral domain. This shift of the spectrum is equal to the integral multiple of the pass band aperture width. During the operation of single fiber (ON-state) all other fibers are in OFF-state at that time. The hologram recorded by each fiber at the CCD plane is stored in computer memory. At the end of illumination process total 25 holograms are recorded by the whole fiber array and by applying some post processing and specific algorithm single super resolved image is obtained. The superresolved image is five times better than the band-limited image. The work is demonstrated using computer simulation only. 相似文献
465.
Anwar Hossain Talukder 《Annals of the Institute of Statistical Mathematics》1968,20(1):441-455
The theory on regression estimate based on one auxiliary variable has been extended to that for more than one auxiliary variable. It has been found that the multivariate regression estimate (MRE) is not unbiased in general. The form of the approximate standard error of MRE is the same as that of simple regression estimate based on one auxiliary variable with the exception that the multiple correlation coefficient replaces the total correlation coefficient in the expression. It has also been found that the precision of MRE is non-decreasing, rather usually increasing as the number of auxiliary variables correlated with the dependent variable increases, assuming sample size to be large compared to the number of auxiliary variables. 相似文献
466.
S. S. Tahir Rauf Naseem Anwar ul Haq Khalid Saeed 《Accreditation and quality assurance》2005,10(7):362-368
This inter-laboratory comparison study was arranged for 28 laboratories from different public and private sector organizations
in Pakistan having wastewater testing capabilities aimed at improving the quality and comparability of test results. This
national inter-laboratory study was started in December 2003 and completed in July 2004. Laboratories were invited to analyze
the wastewater collected from printed circuit board (PCB) industry for lead and copper contamination. The samples fulfill
the criteria for homogeneity and stability as done by the reference laboratory. The results obtained from participating laboratories
were analyzed in terms of Hampel Test for outliers, while the performance evaluation of the participating laboratories was
done on the basis of Z-score. An assigned value derived from the participant's results was compared with a reference value provided by a reference
laboratory. Overall >50% of the participating laboratories have shown good performance in this PT-program 相似文献
467.
John RP Sreekanth A Prathapachandra Kurup MR Usman A Ibrahim AR Fun HK 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(6):1349-1358
The spectral studies and structure of a ternary complex of copper(II) with 2-hydroxyacetophenone 3-hexamethyliminylthiosemicarbazonate (L(2-)) and 1,10-phenanthroline (phen) are reported. The thiosemicarbazone binds to the metal as a dianionic ONS-donor (L(2-)) ligand, and forms a complex of the stoichiometry [CuLphen]. The copper(II) complex was characterized by IR and UV/Vis spectroscopies, as well as by solid state room-temperature magnetic susceptibility. Spin Hamiltonian and bonding parameters of the compound are calculated from the EPR spectra. Computer simulation of EPR spectrum in DMF at 77 K aided the calculation of magnetic and bonding parameters of the compound. The structure of the compound is solved by single crystal X-ray diffraction. The geometry around copper is distorted square pyramidal. 相似文献
468.
Zhang Ze Liu Qing-Liang Yang Jia-Xiang Wu Jie-Ying Tian Yu-Peng Jin Bao-kang Fun Hoong-Kun Chantrapromma Suchada Usman Anwar 《Transition Metal Chemistry》2003,28(8):930-934
The title complex [Mn2(phen)4(FCA)2](ClO4)2·H2O (1) (FCA = dianion of 3-ferrocenyl-2-crotonic acid, phen = 1,10-phenanthroline) has been prepared, and its structure determined by single crystal X-ray diffraction analysis. The structure consists of a dinuclear cation [Mn2(phen)4(FCA)2]2+, non-coordinated perchlorate anions and a water molecule. The two MnII ions are separated by 4.374 Å in the cation and are dicarboxylate-bridged by carboxylate ligands containing ferrocenyl units. Each FCA is bound to two MnII ions through carboxylate oxygens with the syn–anti bridging mode. The MnII ion is coordinated in an octahedral N4O2 geometry by two chelate phen ligands and two -carboxylate oxygen atoms. Electrochemical properties of (1) are discussed. 相似文献
469.
Syed Raza Shah Zarbad Shah Najeeb Ullah Javid Hussain Rashid Al-Harrasi Ajmal Khan Jeremy M. Rawson Ahmed Al-Harrasi Muhammad U. Anwar 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(3):294-303
Reactions of 1,10‐phenanthroline (phen) and 2‐(3,4‐dichlorophenyl)acetic acid (dcaH) with Mn(CO3) (M = LiI, NaI and MgII; n = 1 and 2) in MeOH yield the mononuclear lithium complex aqua[2‐(3,4‐dichlorophenyl)acetato‐κO](1,10‐phenanthroline‐κ2N,N′)lithium(I), [Li(C8H5Cl2O2)(C12H8N2)(H2O)] or [Li(dca)(phen)(H2O)] ( 1 ), the dinuclear sodium complex di‐μ‐aqua‐bis{[2‐(3,4‐dichlorophenyl)acetato‐κO](1,10‐phenanthroline‐κ2N,N′)sodium(I)}, [Na2(C8H5Cl2O2)2(C12H8N2)2(H2O)2] or [Na2(dca)2(phen)2(H2O)2] ( 2 ), and the one‐dimensional chain magnesium complex catena‐poly[[[diaqua(1,10‐phenanthroline‐κ2N,N′)magnesium]‐μ‐2‐(3,4‐dichlorophenyl)acetato‐κ2O:O′] 2‐(3,4‐dichlorophenyl)acetate monohydrate], {[Mg(C8H5Cl2O2)(C12H8N2)(H2O)2](C8H5Cl2O2)·H2O}n or {[Mg(dca)(phen)(H2O)2](dca)·H2O}n ( 3 ). In these complexes, phen binds via an N,N′‐chelate pocket, while the deprotonated dca? ligands coordinate either in a monodentate (in 1 and 2 ) or bidentate (in 3 ) fashion. The remaining coordination sites around the metal ions are occupied by water molecules in all three complexes. Complex 1 crystallizes in the triclinic space group P with one molecule in the asymmetric unit. The Li+ ion adopts a four‐coordinated distorted seesaw geometry comprising an [N2O2] donor set. Complex 2 crystallizes in the triclinic space group P with half a molecule in the asymmetric unit, in which the Na+ ion adopts a five‐coordinated distorted spherical square‐pyramidal geometry, with an [N2O3] donor set. Complex 3 crystallizes in the orthorhombic space group P212121, with one Mg2+ ion, one phen ligand, two dca? ligands and three water molecules in the asymmetric unit. Both dcaH ligands are deprotonated, however, one dca? anion is not coordinated, whereas the second dca? anion coordinates in a bidentate fashion bridging two Mg2+ ions, resulting in a one‐dimensional chain structure for 3 . The Mg2+ ion adopts a distorted octahedral geometry, with an [N2O4] donor set. Complexes 1 – 3 were evaluated against urease and α‐glucosidase enzymes for their inhibition potential and were found to be inactive. 相似文献
470.
Blazina D Duckett SB Halstead TK Kozak CM Taylor RJ Anwar MS Jones JA Carteret HA 《Magnetic resonance in chemistry : MRC》2005,43(3):200-208
We describe a number of studies used to establish that parahydrogen can be used to prepare a two-spin system in a pure state, which is suitable for implementing NMR quantum computation. States are generated by pulsed and continuous-wave (CW) UV laser initiation of a chemical reaction between Ru(CO)(3)(L(2)) [where L(2) = dppe = 1,2-bis(diphenylphosphino)ethane or L(2) = dpae = 1,2-bis(diphenylarsino)ethane] with pure parahydrogen (generated at 18 K). This process forms Ru(CO)(2)(dppe)(H)(2) and Ru(CO)(2)(dpae)(H)(2) on a sub-microsecond time-scale. With the pulsed laser, the spin state of the hydride nuclei in Ru(CO)(2)(dppe)(H)(2) has a purity of 89.8 +/- 2.6% (from 12 measurements). To achieve comparable results by cooling would require a temperature of 6.6 mK, which is unmanageable in the liquid state, or an impractical magnetic field of 0.44 MT at room temperature. In the case of CW initiation, reduced state purities are observed due to natural signal relaxation even when a spin-lock is used to prevent dephasing. When Ru(CO)(3)(dpae) and pulsed laser excitation are utilized, the corresponding dihydride product spin state purity was determined as 106 +/- 4% of the theoretical maximum. In other words, the state prepared using Ru(CO)(3)(dpae) as the precursor is indistinguishable from a pure state. 相似文献