全文获取类型
收费全文 | 2497篇 |
免费 | 210篇 |
国内免费 | 112篇 |
专业分类
化学 | 975篇 |
晶体学 | 6篇 |
力学 | 148篇 |
综合类 | 4篇 |
数学 | 83篇 |
物理学 | 1603篇 |
出版年
2024年 | 6篇 |
2023年 | 21篇 |
2022年 | 33篇 |
2021年 | 34篇 |
2020年 | 41篇 |
2019年 | 42篇 |
2018年 | 42篇 |
2017年 | 56篇 |
2016年 | 59篇 |
2015年 | 75篇 |
2014年 | 94篇 |
2013年 | 114篇 |
2012年 | 131篇 |
2011年 | 175篇 |
2010年 | 164篇 |
2009年 | 169篇 |
2008年 | 164篇 |
2007年 | 193篇 |
2006年 | 149篇 |
2005年 | 142篇 |
2004年 | 104篇 |
2003年 | 96篇 |
2002年 | 84篇 |
2001年 | 46篇 |
2000年 | 45篇 |
1999年 | 51篇 |
1998年 | 42篇 |
1997年 | 48篇 |
1996年 | 37篇 |
1995年 | 27篇 |
1994年 | 34篇 |
1993年 | 38篇 |
1992年 | 26篇 |
1991年 | 23篇 |
1990年 | 31篇 |
1989年 | 22篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 28篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1976年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
排序方式: 共有2819条查询结果,搜索用时 15 毫秒
51.
B. Sourd P. André J. Aubreton M.-F. Elchinger 《Plasma Chemistry and Plasma Processing》2007,27(1):35-50
In this paper, calculated values of the viscosity and thermal conductivity of atomic nitrogen, taking into account three species
(the ground and two excited states), are presented. The calculations, which assume that the temperature dependent probability
of occupation of the states is given by the Boltzmann factor, are performed for atmospheric-pressure in the temperature range
from 1,000 to 20,000 K. Six collision integrals are used in calculating the transport coefficients and we have introduced
new averaged collision integrals where the weight associated at each interacting species pair is the probable collision frequency.
The influence of the collision integral values and energy transfer between two different species is studied. These results
are compared which those of published theoretical studies. 相似文献
52.
本文着重综述了烃,含氮、氧的有机化合物,碳氟化合物以及有机硅化合物的等离子体聚合。同时还系统地介绍了等离子体聚合物在制备反渗透膜、分离膜、材料表面的涂层等方面的国内外的最新研究成果。 相似文献
53.
Epoxy resins in the solid state, liquid state and during polymerisation were treated by microwave oxygen plasma and analysed by FTIR spectra. Curing, etching and oxidation kinetics of epoxy resin were observed. In the liquid resin and polymerising mixture the effect of structure modification was observed more intensively than in the case of solid sample due to a mixing process. A modification of bulk layers of liquid epoxy resin was observed under plasma action. The polymerisation reaction of epoxy resin with amine hardening agent can be released in plasma discharge at low pressure. 相似文献
54.
单扫描极谱法测定注射液及血清中维生素K1 总被引:5,自引:0,他引:5
建立了维生素K1的极谱测定方法.在0.05 mol·L-1 NH4Cl-NH3(pH 8.58)缓冲溶液中,维生素K1可产生一极谱还原峰,峰电位Ep为-0.39 V ;其二阶微分峰峰电流ip″与维生素K1的浓度在1.1×10-7 ~2.2×10-5 mol·L-1范围内呈线性关系,相关系数r=0.998 6(n= 9 );方法的检出限为4.0×10-8 mol·L-1.13次平行测定2.2×10-5 mol·L-1维生素K1还原波二阶导数峰峰电流ip″的相对标准偏差(RSD)为1.83%.本法可直接用于注射液及血清中维生素K1含量的测定. 相似文献
55.
Summary A sensitive HPLC method with marbofloxacin (MAR) as internal standard and fluorescence detection is described for the analysis
of ofloxacin (OFL) enantiomers in plasma samples. Plasma samples were prepared by adding phosphate buffer (pH 7.4, 0.1m), then extracted with trichloromethane.S-OFL,R-OFL, and the internal standard were separated on a reversed-phase column with water-methanol, 85.5∶14.5, as mobile phase.
The concentrations ofS-OFL andR-OFL eluting from the column (retention times 7.5 and 8.7 min, respectively) were monitored by fluorescence detection withλ
ex = 331 andλ
em = 488 nm. The detection and quantitation limits were 10 and 20 ng mL−1, respectively, forS-OFL and 11 and 21 ng mL−1 forR-OFL. Response was linearly related to concentration in the range 10 to 2500 ng mL−1. Recovery was close to 93% for both compounds. The method was applied to determination of the enantiomers of OFL in plasma
samples collected during pharmacokinetic studies. 相似文献
56.
Methane, mixed with argon, has been polymerized by means of a hollow-cathode discharge system. Two types of cathodes were studied; one was made of a solid solution of 81% tungsten and 19% platinum, while the other was of pure tungsten. Under identical operating conditions, a higher polymer yield was found in the case of the platinum cathode (90% against 70% for tungsten). The work function of the solid solution was estimated to be 6.3 eV, compared with 4.4 eV for tungsten. In terms of the data available, the thermionic current, which is the main source of energetic electrons, is about one order of magnitude lower for the solid solution cathode when compared with the tungsten cathode thermionic current. However, the polymer yield observed is higher in the former case. The concentration of the CH species in the hollow cathode was found to differ greatly for the cathodes tested and was about 5 times higher in the case of tungsten-platinum cathodes. Since no excited platinum vapor could be detected in the gas phase, the increase in CH concentration was attributed to a catalytic effect of the cathode inside surface. An evaluation of the plasma polymer deposition rate yields 70 nm·s–1 for the platinum-tungsten type hollow cathode and 42 nm·s–1 for the tungsten one. In both cases, the deposition rate is much higher than those obtained from the most widely used methods for plasma polymer deposition (0.10–1.0 nm·s–1) implying methane-argon mixtures, and is comparable to the results obtained with a new type of plasma polymer deposition reactor described in the literature. 相似文献
57.
Girault J. Longueville D. Malgouyat J. M. Istin B. Lecomte G. Fourtillan J. B. 《Chromatographia》1994,39(3-4):228-238
Summary A simple and sensitive assay has been developed for the quantitative measurement of a new platelet activating factor antagonist (BN50730), and its two main metabolites (BN50727 and BN50922), at the picomole level in human plasma and urine. The three compounds of interest and the internal standard (BN50765) were measured by combined LC-negative chemical ionization MS. A simple solid-liquid extraction procedure was used to isolate the parent drug and the two metabolites. The MS was tuned to monitor the intense ionm/z 333 generated in the ion source by a dissociative capture process. The assay was on 1 ml plasma or 0.1 ml urine and the quantitation limit was calculated as 1 ng·ml–1. The very low relative standard deviations and mean percentages of error calculated for within-day or between-day repeatability assays demonstrate the ruggedness of the technique for routine determination in biological fluids. Some preliminary results on the pharmacokinetics of the parent drug and its two main metabolites illustrate the applicability of this method. 相似文献
58.
A membrane having an amine moiety was prepared by plasma-grafting 2-(N,N-dimethyl)aminoethyl methacrylate (DAMA) onto a microporous polyethylene substrate. Permselectivity of the membrane for CO2 over N2 was achieved in both dry and water swollen conditions. When the CO2 partial pressure in the feed gas was 0.047 atm, the selectivity of CO2 over N2 reached 130 for the highly swollen water containing membrane. This value was found to agree with that obtained with a mobile carrier membrane (supported liquid membrane) using DAMA as the carrier. The effects of several experimental conditions such as degree of grafting, feed partial pressure and temperature on the membrane performance were studied. It was suggested that the membrane acted as a fixed carrier membrane for CO2 facilitated transport in under the dry condition and acted as a fixed reaction site membrane in the water swollen condition. The carrier transport mechanism is discussed for dry and aqueous membranes. 相似文献
59.
Aigars Vītiņš Ģirts Vītiņš Jānis Krastiņš Ints Šteins Ilmārs Zālīte Andrejs Lūsis 《Journal of Solid State Electrochemistry》1998,2(5):299-307
Ceramic specimens have been obtained from the powder of ZrO2-7.5 mol% Y2O3 having a specific surface area of 30 m2/g synthesized in air plasma. The novelty of this research lies in the fact that the plasma process makes it possible to prepare
so-called nanopowders with a particle size less than 100 nm, possessing specific physical, chemical and technological properties.
The sintered density of the specimens was 94–96% of the theoretical value, 6.001 g/cm3. The X-ray diffraction pattern of the specimens corresponded to a face-centered cubic lattice. Impedance in the frequency
range of 100 Hz–15 MHz and d.c. polarization curves in a potential range of −10 to 10 mV were measured in the temperature
range 200–850 °C in heating and cooling cycles. The intragrain, the grain boundary and the total bulk conductivities, the
electrode polarization resistance and their activation energies were determined. The thermal stability of the studied system
was proved in three measurement series up to 600–850 °C in heating and cooling cycles. The results obtained have shown that
the conductivity of ZrO2-7.5 mol% Y2O3 ceramics is not solely a function of temperature, but also depends on the previous thermal state of the ceramics.
Received: 16 October 1997 / Accepted: 19 January 1998 相似文献
60.
J. W. Lee S. J. Pearton C. J. Santana E. S. Lambers C. R. Abernathy W. S. Hobson F. Ren 《Plasma Chemistry and Plasma Processing》1996,16(3):365-378
Electron cyclotron resonance (ECR) plasma etching with additional rf-biasing produces etch rates 2,500 A/min for InGaP and AlInP in CH4/H2/Ar. These rates are an order of magnitude or much higher than for reactive ion etching conditions (RIE) carried out in the same reactor. N2 addition to CH4/H2/Ar can enhance the InGaP etch rates at low flow rates, while at higher concentrations it provides an etch-stop reaction. The InGaP and AlInP etched under ECR conditions have somewhat rougher morphologies and different stoichiometries up to 200 Å from the sur face relative to the RIE samples. 相似文献