全文获取类型
收费全文 | 896篇 |
免费 | 49篇 |
国内免费 | 2篇 |
专业分类
化学 | 767篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 78篇 |
物理学 | 90篇 |
出版年
2024年 | 1篇 |
2023年 | 17篇 |
2022年 | 35篇 |
2021年 | 35篇 |
2020年 | 25篇 |
2019年 | 29篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 37篇 |
2015年 | 35篇 |
2014年 | 32篇 |
2013年 | 54篇 |
2012年 | 66篇 |
2011年 | 84篇 |
2010年 | 51篇 |
2009年 | 46篇 |
2008年 | 57篇 |
2007年 | 56篇 |
2006年 | 48篇 |
2005年 | 45篇 |
2004年 | 36篇 |
2003年 | 34篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 12篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有947条查询结果,搜索用时 703 毫秒
11.
The development of a surface plasmon resonance (SPR) affinity biosensor based on DNA hybridisation is described. This biosensor has been applied to genetically modified organisms (GMOs) detection. Single stranded DNA (ssDNA) probes were immobilised on the sensor chip of an SPR device and the hybridisation between the immobilised probe and the complementary sequence (target) was monitored. The probe sequences were internal to the sequence of 35S promoter and NOS terminator which are inserted sequences in the genome of GMO regulating the transgene expression. The system has been optimised using synthetic oligonucleotides, then applied to real samples analysis. Samples, containing the transgenic target sequences, were amplified by polymerase chain reaction (PCR) and then detected with the SPR biosensor. 相似文献
12.
Elisa Brinis Udeschini 《General Relativity and Gravitation》1980,12(6):429-437
In a Riemannian space-time, the difference between the third-order tensor potentialH
of the Riemann tensor (presented in a precedent paper) and the Lanczos generating function of the Weyl tensor is here shown to be characterized by a vectorV
, obtained by contractionH
. The significant role of such a vector, in the context of general relativity, is then discussed. Particular attention is paid to the scalar potential which characterizes the irrotational part ofV
: such a scalar field satisfies a space-time wave equation of the Poisson type. Weak fields are also considered: in the particular case of a static metric, the scalar is found to be proportional to the classic Newtonian potential.This work was done in the sphere of activity of the C.N.R. Groups for mathematical research. 相似文献
13.
Sessler JL Tomat E Mody TD Lynch VM Veauthier JM Mirsaidov U Markert JT 《Inorganic chemistry》2005,44(7):2125-2127
The coordination chemistry of the Schiff base polypyrrolic octaaza macrocycle 1 toward late first-row transition metals was investigated. Binuclear complexes with the divalent cations Ni(II), Cu(II), and Zn(II) and with the monovalent cation Cu(I) were prepared and characterized. Air oxidation of the Cu(I) ions in the latter complex to their divalent oxidation state resulted in a change in the coordination mode relative to the macrocycle. 相似文献
14.
Melissa L. E. Gutarra Elisa D. C. Cavalcanti Leda R. Castilho Denise M. G. Freire Geraldo L. Sant’Anna Jr. 《Applied biochemistry and biotechnology》2005,121(1-3):105-116
The production of lipase by Penicillium simplicissimum in solid-state fermentation was studied using babassu cake as the basal medium. Tray-type and packed-bed bioreactors were employed. In the former, the influence of temperature; content of the medium, and medium supplementation with olive oil, sugarcane molasses, corn steep liquor, and yeast hydrolysate was studied. For all combinations of supplements, a temperature of 30°C, a moisture content of 70%, and a concentration of carbon source of 6.25% (m/m, dry basis) provided optimum conditions for lipase production. When used as single supplements olive oil and molasses also were able to provide high lipase activities (20 U/g). Using packed-bed bioreactors and molasses-supplemented medium, optimum conditions for enzyme production were air superficial velocities above 55 cm/min and temperatures below 28°C. The lower temperature optimum found for these reactors is probably related to radial heat gradient formation inside the packed bed. Maximum lipase activities obtained in these bioreactors (26.4 U/g) were 30% higher than in tray-type reactors. 相似文献
15.
Anise Akhundi Elisa I. García-López Giuseppe Marcì Aziz Habibi-Yangjeh Leonardo Palmisano 《Research on Chemical Intermediates》2017,43(9):5153-5168
Carbon nitride photocatalysts have been prepared by different methodologies, such as chemical ultrasonic irradiation (sonochemical treatment), hydrothermal and ball milling and thermoexfoliation, and have been used for the selective oxidation of 5-hydroxymethyl-2-furaldehyde (HMF) to form 2,5-furandicarboxyaldehyde (FDC) in water suspension both under UV and natural solar irradiation. The physico-chemical features of the photocatalysts have been studied by X-ray diffraction, infrared spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, and specific surface area measurements. The results indicate that exfoliation of carbon nitrides can increase the conversion of HMF and the selectivity to FDC. In particular, samples exfoliated by both thermal and acidic ultrasonic irradiation treatments showed the best photocatalytic performance. 相似文献
16.
17.
Elisa Maria Alessi Gerard GómezJosep J. Masdemont 《Communications in Nonlinear Science & Numerical Simulation》2012,17(2):854-866
We extend the analysis, started in a previous work [1], concerning the formation of lunar impact craters due to low-energy trajectories. First, we adopt the Circular Restricted Three-Body Problem and consider different choices of initial conditions inside the stable invariant manifold associated with the central invariant one in the neighborhood of the L2 equilibrium point in the Earth-Moon system. Then we move to the Bicircular Restricted Four-Body Problem to study the effect of the Sun on the distribution of impacts on the Moon’s surface. 相似文献
18.
Paulo Igor M. Firmino Raquel S. Farias Amanda N. Barros Patrícia G. C. Landim Gervina B. M. Holanda Elisa Rodríguez Alexandre C. Lopes André B. dos Santos 《Applied biochemistry and biotechnology》2018,184(4):1187-1199
As the addition of low concentrations of oxygen can favor the initial degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds, this work verified the applicability of the microaerobic technology to enhance BTEX removal in an anaerobic bioreactor supplemented with high and low co-substrate (ethanol) concentrations. Additionally, structural alterations on the bioreactor microbiota were assessed throughout the experiment. The bioreactor was fed with a synthetic BTEX-contaminated water (~ 3 mg L?1 of each compound) and operated at a hydraulic retention time of 48 h. The addition of low concentrations of oxygen (1.0 mL min?1 of atmospheric air at 27 °C and 1 atm) assured high removal efficiencies (> 80%) for all compounds under microaerobic conditions. In fact, the applicability of this technology showed to be viable to enhance BTEX removal from contaminated waters, especially concerning benzene (with a 30% removal increase), which is a very recalcitrant compound under anaerobic conditions. However, high concentrations of ethanol adversely affected BTEX removal, especially benzene, under anaerobic and microaerobic conditions. Finally, although bacterial community richness decreased at low concentrations of ethanol, in general, the bioreactor microbiota could deal with the different operational conditions and preserved its functionality during the whole experiment. 相似文献
19.
Elisa Musella Dr. Isacco Gualandi Dr. Erika Scavetta Dr. Massimo Gazzano Arianna Rivalta Dr. Elisabetta Venuti Dr. Meganne Christian Dr. Vittorio Morandi Prof. Dr. Domenica Tonelli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(71):16301-16310
Layered double hydroxides (LDHs) have been widely studied for their plethora of fascinating features and applications. The potentiostatic electrodeposition of LDHs has been extensively applied in the literature as a fast and direct method to substitute classical chemical routes. However, the electrochemical approach does not usually allow for a fine control of the MII/MIII ratio in the synthesized material. By employing a recently proposed potentiodynamic method, LDH films of controlled composition are herein prepared with good reproducibility, using different ratios of the trivalent (Fe or Al) to bivalent (Co) cations in the electrolytic solution. All the obtained materials are shown to be effective oxygen evolution reaction (OER) catalysts, and are thoroughly characterized by a multi-technique approach, including FE-SEM, XRD, Raman, AES and a wide range of electrochemical procedures. 相似文献