全文获取类型
收费全文 | 1265篇 |
免费 | 30篇 |
国内免费 | 4篇 |
专业分类
化学 | 952篇 |
晶体学 | 11篇 |
力学 | 24篇 |
数学 | 34篇 |
物理学 | 278篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 21篇 |
2021年 | 24篇 |
2020年 | 24篇 |
2019年 | 33篇 |
2018年 | 37篇 |
2017年 | 41篇 |
2016年 | 50篇 |
2015年 | 32篇 |
2014年 | 50篇 |
2013年 | 114篇 |
2012年 | 88篇 |
2011年 | 86篇 |
2010年 | 60篇 |
2009年 | 64篇 |
2008年 | 74篇 |
2007年 | 70篇 |
2006年 | 48篇 |
2005年 | 45篇 |
2004年 | 40篇 |
2003年 | 27篇 |
2002年 | 27篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1974年 | 8篇 |
排序方式: 共有1299条查询结果,搜索用时 15 毫秒
91.
Kalawati Meena Sudesh Kumari Jitender M. Khurana Amita Malik Chetan Sharma Harsh Panwar 《中国化学快报》2017,28(1):136-142
A simple and efficient three component procedure has been developed for the synthesis of highly substituted spiro[indolo-3,10'-indeno[1,2-b]quinolin]-2,4,11'-triones by one pot three component condensation of enaminones, isatin and indane-1,3-dione in ethanol:water (1:1) in presence of ceric ammonium nitrate (CAN) as catalyst. This method provides several advantages such as lesser reaction time, high yield of products and operational simplicity. The antimicrobial activity of some of the compounds has been investigated against six microbial strains, some of the tested compounds showed good antimicrobial activity. 相似文献
92.
Prebiotic Oligosaccharides: Special Focus on Fructooligosaccharides,Its Biosynthesis and Bioactivity
Sudhir P. Singh Jyoti Singh Jadaun Lokesh K. Narnoliya Ashok Pandey 《Applied biochemistry and biotechnology》2017,181(2):613-626
MicroRNAs (miRNAs) are important nonprotein-coding genes involved in almost all biological processes during biotic and abiotic stresses in plants. To investigate the miRNA-mediated plant response to drought stress, two drought-tolerant (C-306 and NI-5439) and two drought-sensitive (HUW-468 and WL-711) wheat genotypes were exposed to 25 % PEG 6000 for 1, 12 and 24 h. Temporal expression patterns of 12 drought-responsive miRNAs and their corresponding nine targets were monitored by quantitative real-time PCR (qRT-PCR). The results showed differential expression of miRNAs and their targets with varying degree of upregulation and downregulation in drought-sensitive genotypes. Likewise, in drought-tolerant wheat genotypes, maximum accumulation of miR393a and miR397a was observed at 1 h of stress. In addition, nearly perfect negative correlation was observed in four miRNA and target pairs (miR164-NAC, miR168a-AGO, miR398-SOD and miR159a-MYB) across all the temporal period studied which could be a major player during drought response in wheat. We, for the first time, validated the presence of miR529a and miR1029 in wheat. These findings gives a clue for temporal and variety-specific differential regulation of miRNAs and their targets in wheat in response to osmotic shock and could help in defining the potential roles of miRNAs in plant adaptation to osmotic stress in future. 相似文献
93.
Ashok Kumar Bharati Prem Lama Joanna Trojan–Piegza Alina Bieńko 《Journal of Coordination Chemistry》2017,70(24):3959-3970
Assembly of orotic acid (H3Or, 1,2,3,6-tetrahydro-2,6-dioxo-4-pyrimidinecarboxylic) and Cd(NO3)·6H2O yielded a coordination polymer, [(Cd(Hor)·2.5H2O)2]n (1), which has been characterized by X-ray single-crystal diffraction, TGA, and ?uorescence spectra. Single-crystal X-ray structural analyses reveal that 1 is a hydrogen-bonded binuclear Cd-orotate coordination polymer in which both Cd2+ ions have different coordination environments with identical distorted octahedral geometry. Crystal data for 1: monoclinic, space group P21/n, a = 7.0209(10) Å, b = 13.974(2) Å, c = 17.541(3) Å, β = 98.842(2)°, V = 1700.5(4) Å, Z = 4, R1 = 0.0269, wR2 = 0.0612, θmax = 25.960. The emission spectrum of the Cd-complex recorded with 265 nm excitation wavelength reveals the complex has strong blue luminescence with the peak maximum 420 nm (2.95 eV) as a result of the n–π* and π–π* transitions on the H3Or ligand. 相似文献
94.
Ashok K. Singh Amar Singh Ranjana Gupta Madhu Saxena Bharat Singh 《Transition Metal Chemistry》1992,17(5):413-416
The kinetics of oxidation of three aldoses (glucose, mannose and galactose) byN-bromoacetamide (NBA) in the presence of an alkaline solution of RuO4 as catalyst and Hg(OAc)2 as co-catalyst and as a scavenger for bromide have been investigated. The main products of the oxidation are the corresponding
aldonic acids. The reaction is zero order with respect to aldose and OH−. First order dependence of the reaction on both NBA and RuO4 at low concentrations shifts to zero order at higher concentrations. Addition of acetamide decreases the reaction rate, while
addition of Hg(OAc)2 has the opposite effect. No significant effect of ionic strength was observed. OBr− is postulated as the reactive oxidising species and a mechanism involving co-catalysis by RuO4 and HgII is proposed.
TMC 2588 相似文献
95.
A note on ratio and product type estimators 总被引:1,自引:0,他引:1
S. K. Ray Ashok Sahai Ajit Sahai 《Annals of the Institute of Statistical Mathematics》1979,31(1):141-144
Summary The use of ratio and product estimators for the mean of a finite population is well known. This paper proposes transformed
estimators obtained through parametric linear combination of the ratio, or product, and the usual unbiased estimator of the
mean for any sample design. To the first degree of approximation, the proposed estimators have smaller mean square error than
that of the ratio, product and the usual unbiased estimator, for suitable choice of the parameter. The superiority of the
proposed estimators over others for small samples has been studied empirically. 相似文献
96.
A facile method for the synthesis of silver-silica(Ag-SiO2) Janus particles with functionalities suitable for textile applications is reported.Silica nanoparticles prepared by the Stober method were functionalized with epoxy,amine,and thiol groups,which were confirmed by Fourier transform infrared analysis.The functionalized silica nanoparticles were used to produce Pickering emulsions,and the exposed surface was used for the attachment of silver nanoparticles(AgNPs) via the low-temperature chemical reduction method.The morphology and structure of the Ag-SiO2 Janus particles were characterized by scanning electron microscopy,scanning transmission electron microscopy,high-resolution transmission electron microscopy,energy-dispersive X-ray analysis,and UV-vis spectroscopy.Because of their specific functionalities,these Ag-SiO2 Janus particles are proposed for applications on textile substrates,as they can overcome several drawbacks of direct application of AgNPs on textiles,such as leaching,agglomeration,and instability during storage. 相似文献
97.
98.
The stability of regioregular poly(3-hexylthiophene 2,5-diyl) (P3HT) thin films sandwiched between indium tin oxide (ITO)
and aluminium (Al) electrodes have been investigated under normal environmental conditions (25°C and RH∼45–50%). Electrical
and optical properties of ITO/P3HT/Al devices have been studied over a period of 30 days. Mobility μ of the order of 10−4 cm2/V-s has been obtained from the V
2 law in the as-deposited P3HT films. Scanning electron microscopy (SEM) investigations show blistering of Al contacts in devices
with a poly(3,4-ethylenedioxythiophene) (PEDOT) interlayer on application of voltage whereas no blistering is seen in devices
without PEDOT. The results have been explained in terms of trap generation and propagation and the moisture-absorbing nature
of PEDOT.
相似文献
99.
Ashok Razdan 《Pramana》2002,58(3):537-544
In this paper we study Bombay stock exchange (BSE) index financial time series for fractal and multifractal behaviour. We
show that BSE index time series is monofractal and can be represented by a fractional Brownian motion. 相似文献
100.
Sensitivity of Bayes decisions for the success probability for samples from a nonbinomial population
Ashok K. Bansal 《Annals of the Institute of Statistical Mathematics》1982,34(1):143-149
Summary A family of generalised negative binomial distributions is employed to investigate inference robustness of the Bayes estimator
of the unknown parameter of the binomial distribution. A zone of sensitivity for the test of significance is constructed to
forewarn the pro-Jeffreys Bayesians against indiscriminate choice of the probability in favour of the null hypothesis. A few
selected tables are presented to illustrate the effect of relaxation of the ‘binomiality’ assumption. 相似文献