全文获取类型
收费全文 | 603篇 |
免费 | 37篇 |
国内免费 | 6篇 |
专业分类
化学 | 456篇 |
晶体学 | 1篇 |
力学 | 13篇 |
数学 | 35篇 |
物理学 | 68篇 |
无线电 | 73篇 |
出版年
2024年 | 4篇 |
2023年 | 3篇 |
2022年 | 21篇 |
2021年 | 35篇 |
2020年 | 29篇 |
2019年 | 31篇 |
2018年 | 16篇 |
2017年 | 14篇 |
2016年 | 28篇 |
2015年 | 11篇 |
2014年 | 35篇 |
2013年 | 58篇 |
2012年 | 48篇 |
2011年 | 34篇 |
2010年 | 31篇 |
2009年 | 32篇 |
2008年 | 25篇 |
2007年 | 35篇 |
2006年 | 17篇 |
2005年 | 20篇 |
2004年 | 28篇 |
2003年 | 24篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有646条查询结果,搜索用时 15 毫秒
31.
V. P. Kiran R. G. Kumar A. K. Singh S. Gurunarayanan 《International Journal of Electronics》2013,100(5):295-302
In the present communication we have presented a detailed theoretical analysis of the performance of the sub-micron device in the presence of the discontinuity at the Si–SiO2 interface. It is assumed that due to interface discontinuity a potential develops at the edges (Source/Drain) in addition to the built-in-potential. This potential, called Edge Potential, measures directly the extent of the interface roughness. The effect of this potential is more critical in the case of short channel device where drain and source are in close proximity. Our analysis shows that the discontinuity is dominant at the edges but not in the channel. Drive current as well as saturation transconductance decreases in the presence of edge potential. These results suggest that the performance of the device degrades due to the interface roughness. Effect of interface roughness near the edges can be reduced at high gate voltage but it will result more interface roughness scattering. 相似文献
32.
The dendrobatid alkaloid (-)-251F was synthesized. The key steps of the synthesis were (1) an asymmetric Diels-Alder reaction to establish four of the necessary stereocenters in the target, (2) a ring-opening/ring-closing metathesis reaction to establish a key [3.3.0] bicyclic intermediate, and (3) an intramolecular Schmidt reaction. 相似文献
33.
Rajneesh Mohan Kiran Singh Shovit Bhattacharya N.K. Gaur S.K. Gupta 《Solid State Communications》2007,141(11):605-609
Both oxygen and calcium play important roles in inducing superconductivity in Y Ba2Cu3Oy (YBCO), which is an antiferromagnetic insulator at low O and Ca content. O induces superconductivity in Ca-free YBCO, while Ca does similarly in oxygen-deficient YBCO. For doping oxygen HgO was used as it decomposes at 476 °C into Hg, which escapes from the matrix leaving the crystal unaltered, and O, which provide a way to dope O in YBCO. Considering these facts, polycrystalline samples of Y 1−xCaxBa2Cu3Oy with x=0, 0.1 and 0.2 with and without HgO addition were prepared through a solid-state reaction method. The samples were sintered at 950 °C in open atmosphere. These synthesized samples were characterized through using the X-ray diffraction technique (XRD) for phase evaluation, scanning electron microscopy (SEM) for grain morphology, energy dispersive X-ray analysis (EDX) for compositional analysis and the four-contact measurement technique for determining the superconducting transition temperature. 相似文献
34.
Tushar K. Chakraborty V. Ramakrishna Reddy S. Uday Kumar S. Kiran Kumar Archna Mathur Neena Gupta 《Tetrahedron》2004,60(38):8329-8339
Conformational analysis of vasoactive intestinal peptide (VIP) receptor binding inhibitor Leu1-Met2-Tyr3-Pro4-Thr5-Tyr6-Leu7-Lys81 by various NMR techniques and constrained molecular dynamics (MD) simulation studies revealed that the molecule had a turn structure involving its Tyr3-Pro4-Thr5-Tyr6 moiety with intramolecular hydrogen bond between Tyr6NH→Tyr3CO. In order to mimic the structure of 1, peptidomimetic analogs 2-4 were synthesized using conformationally constrained scaffolds of 3,4-dideoxy furanoid sugar amino acids (2S,5R)-ddSaa1 5 and its enantiomer (2R,5S)-ddSaa2 6. All these analogs displayed well defined three-dimensional structures akin to that found in 1. Peptides 2 and 3, which differed only in the sugar amino acid stereochemistry, show propensity of structures with identical intramolecular hydrogen bonds between ThrNH→MetCO. A similar structure with a hydrogen bond between TyrNH→MetCO was observed in 4. 相似文献
35.
Kumar MR Prabhakar S Kumar MK Reddy TJ Vairamani M 《Rapid communications in mass spectrometry : RCM》2004,18(10):1109-1115
The negative ion electrospray ionization (ESI) mass spectra of a series of dicarboxylic acids, a pair of isomeric (cis/trans) dicarboxylic acids and two pairs of isomeric (positional) substituted benzoic acids, including a pair of hydroxybenzoic acids, were recorded in the presence of halide ions (F(-), Cl(-), Br(-) and I(-)). The ESI mass spectra contained [M--H](-) and [M+X](-) ions, and formation of these ions is found to be characteristic of both the analyte and the halide ion used. The analytes showed a greater tendency to form adduct ions with Cl(-) under ESI conditions compared with the other halide ions used. The isomeric compounds yielded distinct spectra by which the isomers could be easily distinguished. The collision-induced dissociation mass spectra of [M+X](-) ions reflected the gas-phase basicities of both the halide ion and [M--H](-) ion of the analyte. However, the relative ordering of gas-phase basicities of all analyte [M--H](-) and halide ions could not account for the dominance of chloride ion adducts in ESI mass spectra of the analytes mixed with equimolar quantities of the four halides. 相似文献
36.
Pentacoordinate complex cations of the general formula [(C6F5)2SbL3]3+ stabilized as solid salts in combination with tetraphenylborate (BPh4), tetrafluorobroate (BF4) anions, where L=DMSO, Ph3AsO, PyO, DMF, α-, β- and γ-picoline have been isolated. The newly formed complexes were characterized by elemental analysis, molar conductance measurements, solid-state IR and and NMR. From these results, a five-fold coordination around antimony was required. 相似文献
37.
Bandcrossing in 31 rotational bands of 25 different odd-A nuclei in the rare-earth region has been analysed by using a two-band mixing formalism with a constant band interaction within
the framework of the effective decoupling picture. The interband interaction strengthV between the one-quasiparticle band and the three-quasiparticle band exhibits a variation with the neutron number which is
not different from the oscillatory behaviour observed in even-even nuclei and does not show signs of any appreciable phase
shifting as predicted by theory. However, the overall range of variation ofV is greater than that observed in even-even systems. 相似文献
38.
A Facile Diversity‐Oriented Multicomponent One‐Pot Synthesis of 3‐Amino‐6,7‐dihydrobenzo[c]thiophen‐4(5H)‐one Derivatives from α‐Oxo‐N,S‐ketene Acetal 下载免费PDF全文
Swapnil G. Yerande Sunil D. More Mayur Bhandari Kiran M. Newase Kareem Khoury Kan Wang Alexander Dömling 《Journal of heterocyclic chemistry》2014,51(Z1):E358-E363
A convenient one‐pot multicomponent method for the preparation of 3‐amino‐6,7‐dihydrobenzo[c]thiophen‐4(5H)‐one derivative has been developed. Reaction of 1,3‐cyclohexanedione and phenyl isothiocynate gave α‐oxo‐N,S‐ketene acetal that were reacted in situ with 2‐chloromethylquniazoline‐4‐one derivatives, in the presence of sodium hydride to afford the target compound in reasonable overall yields. 相似文献
39.
K Bhaskaran-Nair J Brabec E Aprà HJ van Dam J Pittner K Kowalski 《The Journal of chemical physics》2012,137(9):094112
In this paper we discuss the performance of the non-iterative state-specific multireference coupled cluster (SS-MRCC) methods accounting for the effect of triply excited cluster amplitudes. The corrections to the Brillouin-Wigner and Mukherjee's MRCC models based on the manifold of singly and doubly excited cluster amplitudes (BW-MRCCSD and Mk-MRCCSD, respectively) are tested and compared with exact full configuration interaction results for small systems (H(2)O, N(2), and Be(3)). For the larger systems (naphthyne isomers) the BW-MRCC and Mk-MRCC methods with iterative singles, doubles, and non-iterative triples (BW-MRCCSD(T) and Mk-MRCCSD(T)) are compared against the results obtained with single reference coupled cluster methods. We also report on the parallel performance of the non-iterative implementations based on the use of processor groups. 相似文献
40.
Kiran R. Chaudhari Abhinesh Kumar Vinoth Kumar Megraj Khandelwal Anil K. Mishra Jukka Monkkonen Rayasa S. Ramachandra Murthy 《Advanced functional materials》2012,22(19):4101-4114
In an attempt to improve tumor localization of docetaxel (DTX)‐loaded nanoparticles (NPs), zoledronic acid (ZOL) is used as a ligand to target bone metastasis. DTX‐loaded ZOL‐conjugated polyethylene glycol (PEG)ylated polybutyl cyanoacrylate (PBCA) NPs are prepared using an anionic polymerization technique. PBCA‐PEG‐ZOL NPs are subjected to cytotoxic assay in both BO2 and MCF‐7 cell lines. Cell cycle arrest and apoptosis induced by the PBCA‐PEG‐ZOL NPs are studied. Quantitative cellular uptake, NP uptake route characterization, confocal microscopy and IPP/ApppI levels are performed. PBCA‐PEG‐ZOL NPs show an enhanced cytotoxic effect in both BO2 as well as MCF‐7 cell lines due to higher uptake following ZOL‐mediated endocytosis. The molecular basis of apoptosis reveals the involvement of a cytoplasmic protein in activating the programmed cell death pathway. Route characterization studies reveal that PBCA‐PEG‐ZOL NPs uptake is not completely blocked even by using both inhibitors (genistein and phenyl arsinoxide) simultaneously, conferring that uptake is not entirely based upon clathrin or caveolae. PBCA‐PEG‐ZOL NPs showed 7 and 5.3 times increase in IPP and ApppI production, in comparison to ZOL treatment, and 138 times higher than the control group in MCF‐7 cell line. In BO2 cell line, after treatment with NPs, IPP was 5.35 times higher than ZOL solution. No ApppI in BO2 cell line after treatment with NPs and ZOL solution was found. NP distribution in tumor infected bone is also significantly high in comparison to the normal bone at any time point. It is concluded that ZOL‐conjugated NPs provide an efficient and targeted delivery of DTX, with synergistic effects. Thus, these NPs present a promising treatment in the near future, by actively targeting metastatic tumor. 相似文献