全文获取类型
收费全文 | 770篇 |
免费 | 26篇 |
国内免费 | 2篇 |
专业分类
化学 | 442篇 |
晶体学 | 10篇 |
力学 | 8篇 |
数学 | 77篇 |
物理学 | 111篇 |
无线电 | 150篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 22篇 |
2021年 | 25篇 |
2020年 | 24篇 |
2019年 | 14篇 |
2018年 | 26篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 92篇 |
2012年 | 49篇 |
2011年 | 50篇 |
2010年 | 40篇 |
2009年 | 50篇 |
2008年 | 50篇 |
2007年 | 39篇 |
2006年 | 42篇 |
2005年 | 27篇 |
2004年 | 16篇 |
2003年 | 31篇 |
2002年 | 25篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有798条查询结果,搜索用时 15 毫秒
51.
G-quadruplexes (G4) are the most actively studied non-canonical secondary structures formed by contiguous repeats of guanines in DNA or RNA strands. Small molecule mediated targeting of G-quadruplexes has emerged as an attractive tool for visualization and stabilization of these structures inside the cell. Limited number of DNA and RNA G4-selective assays have been reported for primary ligand screening. A combination of fluorescence spectroscopy, AFM, CD, PAGE, and confocal microscopy have been used to assess a dimeric carbocyanine dye B6,5 for screening G4-binding ligands in vitro and in cellulo. The dye B6,5 interacts with physiologically relevant DNA and RNA G4 structures, resulting in fluorescence enhancement of the molecule as an in vitro readout for G4 selectivity. Interaction of the dye with G4 is accompanied by quadruplex stabilization that extends its use in primary screening of G4 specific ligands. The molecule is cell permeable and enables visualization of quadruplex dominated cellular regions of nucleoli using confocal microscopy. The dye is displaced by quarfloxin in live cells. The dye B6,5 shows remarkable duplex to quadruplex selectivity in vitro along with ligand-like stabilization of DNA G4 structures. Cell permeability and response to RNA G4 structures project the dye with interesting theranostic potential. Our results validate that B6,5 can serve the dual purpose of visualization of DNA and RNA G4 structures and screening of G4 specific ligands, and adds to the limited number of probes with such potential. 相似文献
52.
Sulyaeva V. S. Gatapova E. Ya. Kozhevnikov A. K. Rogilo D. I. Saraev A. A. Yushina I. V. Khomyakov M. N. Shapovalova A. A. Shayapov V. R. Bhaskar N. Tu R. Kosinova M. L. 《Journal of Structural Chemistry》2021,62(8):1309-1324
Journal of Structural Chemistry - We report a comprehensive study of the effect of the chemical structure of boron carbonitride films on the variability of their functional characteristics. The... 相似文献
53.
The requirement of getting continuous electricity at low cost is essential but challenging. Especially in the undeveloped countries there is no sufficient electricity for the people to do their daily regular works. In order to overcome this problem different renewable energy sources are sought and being explored. One of the approaches is to have a cooking system that is energized from the solar power, not directly using a solar cooker but by storing the energy in the form of heat that can be utilized as per requirement. This paper reports the design and fabrication of an alternative system to generate heat using solar radiation. This chulha is helpful in effective heating with the help of solar radiations at lower costs. A cooking technology is presented consisting of a solar panel directly connected to an electric heater inside of a well-insulated chamber. An insulated container with fixed amount of oil is heated up. The heat is found to be retained in the chamber even after sun set which is sufficient for heating water for making tea. The possible causes of temperature drop and possible remedy has been pointed out and discussed in this paper. 相似文献
54.
Dinesh Prasad D. R. Bhaskar A. K. Singh 《Analog Integrated Circuits and Signal Processing》2009,61(3):309-313
An universal multi input single output type multifunction biquad is proposed. The proposed configuration employs only one
current differencing transconductance amplifier as the active element, two capacitors and three resistors. The circuit realizes
all five filter functions (i.e. Low Pass, High Pass, Band Pass, Notch and All Pass) without changing the circuit topology.
The natural frequency ω0 is independently and electronically tunable. The workability of the proposed multifunction biquad has been verified using
SPICE simulation. 相似文献
55.
Soft-Decision Decoding of Punctured Convolutional Codes in Asynchronous-CDMA Communications Under Perfect Phase-Tracking Conditions 总被引:1,自引:0,他引:1
Vidhyacharan Bhaskar 《International Journal of Wireless Information Networks》2006,13(3):229-237
In this paper, the performance of punctured convolutional codes of short constraint lengths is discussed. The punctured codes are used to provide error protection to a particular user in an asynchronous CDMA system. A perfect phase reference is assumed to be available throughout this paper. A slow fading Rician channel is assumed. Maximum likelihood decoding through a Viterbi algorithm is used to decode the information symbols. Soft-decision decoding of punctured convolutional codes is considered in this paper. The upper bounds with Viterbi decoding are derived and plotted for the various punctured codes considered. The simulated results are found to agree very well with their upper and lower bounds. 相似文献
56.
Experimental work on post-breakdown bulk oscillations in n-type gold-doped phosphorus-compensated p+?i?n+ double-injection diodes is presented. An empirical relationship for the frequency of oscillation in this region is derived for the first time and discussed. 相似文献
57.
Graham LA Fout AR Kuehne KR White JL Mookherji B Marks FM Yap GP Zakharov LN Rheingold AL Rabinovich D 《Dalton transactions (Cambridge, England : 2003)》2005,(1):171-180
The manganese(I) tricarbonyl complexes (Bm(R))Mn(CO)3(R = Me, Bz, But, p-Tol) and (PhBmMe)Mn(CO)3, the first bis(mercaptoimidazolyl)borate derivatives for this metal, have been readily prepared and fully characterized. In particular, the presence of three-center-two-electron Mn...H-B interactions in these species, both in solution and in the solid state, has been investigated using a combination of IR and NMR spectroscopies and, in the case of the methyl-, tert-butyl- and para-tolyl-substituted derivatives, by X-ray crystallography. To complement these synthetic and structural studies, the tris(mercaptoimidazolyl)borate complexes (TmMe)Mn(CO)3(R = Me, Bz, But, p-Tol) and (PhTm(Me))Mn(CO)3, as well as the related pyrazolylbis(mercaptoimidazolyl)borate (pzBmMe)Mn(CO)3, have also been synthesized and characterized by a combination of analytical and spectroscopic techniques. 相似文献
58.
Adams J Adler C Aggarwal MM Ahammed Z Amonett J Anderson BD Anderson M Arkhipkin D Averichev GS Badyal SK Balewski J Barannikova O Barnby LS Baudot J Bekele S Belaga VV Bellwied R Berger J Bezverkhny BI Bhardwaj S Bhaskar P Bhati AK Bichsel H Billmeier A Bland LC Blyth CO Bonner BE Botje M Boucham A Brandin A Bravar A Cadman RV Cai XZ Caines H Calderón de la Barca Sánchez M Carroll J Castillo J Castro M Cebra D Chaloupka P Chattopadhyay S Chen HF Chen Y Chernenko SP Cherney M Chikanian A Choi B 《Physical review letters》2004,92(17):171801
Measurements of the production of forward high-energy pi(0) mesons from transversely polarized proton collisions at sqrt[s]=200 GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at x(F) below about 0.3, and becomes positive and large at higher x(F), similar to the trend in data at sqrt[s]< or =20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with p(T)>1 GeV/c at a polarized proton collider. 相似文献
59.
Spectral Efficiency Evaluation for MRC Diversity Schemes Over Generalized Rician Fading Channels 总被引:1,自引:0,他引:1
Vidhyacharan Bhaskar 《International Journal of Wireless Information Networks》2007,14(3):209-223
In this paper, closed-form expressions for the capacities per unit bandwidth for generalized Rician fading channels are derived
for power and rate adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion
adaptation policies. The closed-form solutions are derived for the single antenna reception (without diversity combining)
and maximal-ratio combining (MRC) diversity cases. Truncated channel inversion adaptation policy is the best policy for the
single antenna reception case, while the channel inversion with fixed rate policy is the best policy for the MRC diversity
case. Constant transmit power policy provides the lowest spectral efficiency as compared to the other policies with and without
diversity. 相似文献
60.
We investigated the molecular binding of n-alkanes on Pd(111) and PdO(101) using conventional density functional theory (DFT) and the dispersion-corrected DFT-D3 method. In agreement with experimental findings, DFT-D3 predicts that the n-alkane desorption energies scale linearly with the molecule chain length on both surfaces, and that n-alkanes bind more strongly on PdO(101) than on Pd(111). The desorption energies computed using DFT-D3 are slightly higher than the measured values for n-alkanes on Pd(111), though the agreement between computation and experiment is a significant improvement over conventional DFT. The measured desorption energies of n-alkanes on PdO(101) and the energies computed using DFT-D3 agree to within better than 2.5 kJ/mol (< 5%) for chain lengths up to n-butane. The DFT-D3 calculations predict that the molecule-surface dispersion energy for a given n-alkane is similar in magnitude on Pd(111) and PdO(101), and that dative bonding between the alkanes and coordinatively unsaturated Pd atoms is primarily responsible for the enhanced binding of n-alkanes on PdO(101). From analysis of the DFT-D3 results, we estimate that the strength of an alkane η(2)(H, H) interaction on PdO(101) is ~16 kJ/mol, while a single η(1) H-Pd dative bond is worth about 10 kJ/mol. 相似文献