全文获取类型
收费全文 | 1675篇 |
免费 | 37篇 |
国内免费 | 5篇 |
专业分类
化学 | 1092篇 |
晶体学 | 19篇 |
力学 | 35篇 |
数学 | 93篇 |
物理学 | 478篇 |
出版年
2024年 | 18篇 |
2023年 | 17篇 |
2022年 | 41篇 |
2021年 | 36篇 |
2020年 | 35篇 |
2019年 | 35篇 |
2018年 | 38篇 |
2017年 | 41篇 |
2016年 | 52篇 |
2015年 | 33篇 |
2014年 | 50篇 |
2013年 | 157篇 |
2012年 | 113篇 |
2011年 | 113篇 |
2010年 | 72篇 |
2009年 | 79篇 |
2008年 | 92篇 |
2007年 | 64篇 |
2006年 | 50篇 |
2005年 | 56篇 |
2004年 | 41篇 |
2003年 | 31篇 |
2002年 | 39篇 |
2001年 | 25篇 |
2000年 | 23篇 |
1999年 | 18篇 |
1998年 | 9篇 |
1997年 | 16篇 |
1996年 | 17篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 21篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1974年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有1717条查询结果,搜索用时 262 毫秒
91.
Several examples of 1′,8′-disubstituted a,c-biladiene salt cyclizations, using copper(II) or iodine/bromine in hot o-dichlorobenzene, to give meso-substituted porphyrins are described. 相似文献
92.
A probable biogenetic type synthesis of coumestans by coupling in-situ generated o-quinones by mushroom tyrosinase oxidation of catechol and 4-hydroxy coumarins is reported. 相似文献
93.
The present paper describes the modification and solar hydrogen production studies employing a new semiconductor-septum (SC-SEP) photoelectrode ns-TiO2/In2O3 based photoelectrochemical solar cell. The current-voltage characteristics of the above SC-SEP cell revealed that an enhancement in short-circuit current (ISC) up to three times (5 ~ 14.6 mA cm?2). The optimum hydrogen production rate was found to be 11.8 lh?1 m?2 for 5M H2SO4 and with a further increase in H2SO4 concentration, the hydrogen production rate was found to be invariant. In yet another part of our study instead of using new SC-SEP solar cell design, we used another new oxide material form such as ns-TiO2/WO3. The ns-TiO2/WO3 exhibited a high photocurrent and photo-voltage of 15.6 mA cm?2, 960 mV, respectively. The ns-TiO2/WO3 electrode exhibited a higher hydrogen gas evolution rate of 13.8 lh?1 m?2. Evidences and arguments are put forward to show that, whereas for the bare ns-TiO2 electrode, the improvement in the performance of this photo-electrode compared with its original form was due to the higher quantum yield. In the case of ns-TiO2/In2O3 and ns-TiO2/WO3 photo-electrodes, the improvement is due to the improved spectral response resulting from decrease of energy band gap. 相似文献
94.
A novel azophenol-quinazoline dyad 1 has been designed, synthesized and demonstrated as an efficient reversible multichannel pH indicator through distinct signalling in aqueous media. Owing to the competence between highly fluorescent quinazoline moiety and a well known fluorescence quencher diazo group, dyad 1 is moderately fluorescent in nature. Under acidic conditions 1 displays diverse fluorogenic changes (blue emission at pH 4.25; green at pH 1.80) while under basic condition (pH 11.80) chromogenic changes were observed. 相似文献
95.
S. Ganesh P. Velavendan N. K. Pandey U. Kamachi Mudali R. Natarajan 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(3):2091-2094
A fiber optic aided spectrophotometric technique has been developed for determination of ruthenium in nitric acid medium. The developed method is simple, accurate and applicable to aqueous streams of nuclear reprocessing. The system obeys Lambert–Beer’s law at 468 nm in the concentration range of 30–360 μg/mL of ruthenium. The molar absorption coefficient, detection limit and Sandell’s sensitivity are 68.477 L Mol?1 cm?1, 31 μg/mL and 0.0124 μg/cm2 respectively. Relative standard deviation was less than 2 % and correlation coefficient was 0.9998. The results obtained by the developed procedure are in good agreement with those obtained by the standard ICP-OES method. Fission products like zirconium and strontium are not interfering. Uranium is interfering and needs prior separation by solvent extraction method. The developed method is adaptable for remote operation and on-line monitoring. 相似文献
96.
Shaila Lalkuwar Bajoria Virendra Kisan Rathod N. K. Pandey U. Kamachi Mudali R. Natarajan 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(1):271-276
Extraction power of solvent depends upon the physical properties of the system. Tri-n-butyl phosphate (TBP) in dodecane is a versatile solvent used in the nuclear fuel reprocessing like PUREX process. The study of physical properties like density, viscosity, interfacial tension and solubility for TBP–nitric acid–dodecane system will be helpful in carrying out different extraction studies during PUREX process. Thus, physical properties like density, viscosity, interfacial tension and solubility have been measured for TBP–nitric acid–dodecane system using pycnometer, viscometer, pendant drop method and high performance liquid chromatography respectively. It has been observed that density and viscosity increases but interfacial tension and solubility decreases with the concentration of TBP in dodecane–nitric acid system. Physical properties of 30 % TBP–nitric acid–dodecane system have also been studied in detail. All these studies will also be useful in stripping out dissolved TBP from the nuclear waste. 相似文献
97.
98.
Nguyen Huy Thuan Ramesh Prasad Pandey Ta Thi Thu Thuy Je Won Park Jae Kyung Sohng 《Applied biochemistry and biotechnology》2013,171(8):1956-1967
Myricetin is an important flavonol whose medically important properties include activities as an antioxidant, anticarcinogen, and antimutagen. The solubility, stability, and other biological properties of the compounds can be enhanced by conjugating aglycon with sugar moieties. The type of sugar moiety also plays a significant role in the biological and physical properties of the natural product glycosides. Reconstructed Escherichia coli containing thymidine diphosphate-α-l-rhamnose sugar gene cassette and Arabidopsis-derived glycosyltransferase were used for rhamnosylation of myricetin. Myricetin (100 μM) was exogenously supplemented to induced cultures of engineered E. coli. The formation of target product—myricetin-3-O-α-l-rhamnoside—was confirmed by chromatographic and NMR analyses. The yield of product was improved by using various mutants and methylated cyclodextrin as a molecular carrier for myricetin in combination with E. coli M3G3. The maximal yield of product is 55.6 μM (3.31-fold higher than the control E. coli MG3) and shows 55.6 % bioconversion of substrate under optimized conditions. 相似文献
99.
Sonika Pandey Avinash Mishra Manish Kumar Patel Bhavanath Jha 《Applied biochemistry and biotechnology》2013,171(1):1-9
Cumin is an annual herbaceous medicinally important plant having diverse applications. An efficient and reproducible method of Agrobacterium-mediated genetic transformation was herein established for the first time. A direct regeneration method without callus induction was optimised using embryos as explant material in Gamborg’s B5 medium supplemented with 0.5-μM 6-benzyladenine and 2.0-μM α-naphthalene acetic acid. About 1,020 embryos (a mean of 255 embryos per batch) were used for the optimisation of transformation conditions. These conditions were an Agrobacterium cell suspension of 0.6 OD600, a co-cultivation time of 72 h, 300-μM acetosyringone and wounding of explants using a razor blade. Pre-cultured elongated embryos were treated using optimised conditions. About 720 embryos (a mean of 180 embryos per batch) were used for transformation and 95 % embryos showed transient β-glucuronidase expression after co-cultivation. Putative transformed embryos were cultured on B5 medium for shoot proliferation and 21 regenerated plants were obtained after selection and allowed to root. T0 plantlets showed β-glucuronidase expression and gene integration was confirmed via PCR amplification of 0.96 and 1.28 kb fragments of the hygromycin-phosphotransferase II and β-glucuronidase genes, respectively. In this study, a transformation efficiency of 1.5 % was demonstrated and a total of 11 transgenic plants were obtained at the hardening stage, however, only four plants acclimatised during hardening. Gene copy number was analysed by Southern blot analysis of hardened plants and single-copy gene integration was observed. This is the first successful attempt of Agrobacterium-mediated genetic transformation of cumin. 相似文献
100.
Theodoros Aggelopoulos Argyro Bekatorou Ashok Pandey Maria Kanellaki Athanasios A. Koutinas 《Applied biochemistry and biotechnology》2013,170(8):1885-1895
The exploitation of various agro-industrial wastes for microbial cell mass production of Kluyveromyces marxianus, kefir, and Saccharomyces cerevisiae is reported in the present investigation. Specifically, the promotional effect of whole orange pulp on cell growth in mixtures consisting of cheese whey, molasses, and potato pulp in submerged fermentation processes was examined. A 2- to 3-fold increase of cell mass was observed in the presence of orange pulp. Likewise, the promotional effect of brewer’s spent grains on cell growth in solid state fermentation of mixtures of whey, molasses, potato pulp, malt spent rootlets, and orange pulp was examined. The cell mass was increased by 3-fold for K. marxianus and 2-fold for S. cerevisiae in the presence of these substrates, proving their suitability for single-cell protein production without the need for extra nutrients. Cell growth kinetics were also studied by measurements of cell counts at various time intervals at different concentrations of added orange pulp. The protein content of the fermented substrates was increased substantially, indicating potential use of mixed agro-industrial wastes of negligible cost, as protein-enriched livestock feed, achieving at the same time creation of added value and waste minimization. 相似文献