全文获取类型
收费全文 | 2966篇 |
免费 | 119篇 |
专业分类
化学 | 1574篇 |
晶体学 | 15篇 |
力学 | 56篇 |
数学 | 391篇 |
物理学 | 1049篇 |
出版年
2021年 | 33篇 |
2020年 | 33篇 |
2019年 | 32篇 |
2016年 | 112篇 |
2015年 | 115篇 |
2014年 | 150篇 |
2013年 | 287篇 |
2012年 | 104篇 |
2011年 | 80篇 |
2010年 | 84篇 |
2009年 | 62篇 |
2008年 | 63篇 |
2007年 | 40篇 |
2006年 | 86篇 |
2005年 | 28篇 |
2004年 | 31篇 |
2003年 | 33篇 |
2002年 | 48篇 |
2001年 | 36篇 |
2000年 | 59篇 |
1999年 | 37篇 |
1998年 | 43篇 |
1997年 | 38篇 |
1996年 | 39篇 |
1995年 | 43篇 |
1994年 | 37篇 |
1993年 | 39篇 |
1992年 | 31篇 |
1991年 | 34篇 |
1990年 | 35篇 |
1989年 | 27篇 |
1988年 | 50篇 |
1987年 | 39篇 |
1986年 | 35篇 |
1985年 | 56篇 |
1984年 | 54篇 |
1983年 | 37篇 |
1982年 | 32篇 |
1981年 | 32篇 |
1980年 | 41篇 |
1979年 | 40篇 |
1978年 | 39篇 |
1977年 | 49篇 |
1976年 | 48篇 |
1975年 | 42篇 |
1974年 | 56篇 |
1973年 | 37篇 |
1972年 | 29篇 |
1969年 | 28篇 |
1962年 | 27篇 |
排序方式: 共有3085条查询结果,搜索用时 281 毫秒
111.
A procedure is described for the determination of the total concentration of organophosphorus pesticides in aqueous solution based on conversion of the compounds to orthophosphoric acid by oxygen-flask combustion and spectrophotometric determination as phosphomolybdenum blue. The procedure is particularly sensitive when preceded by efficient and selective accumulation of pesticides. The adsorption of malathion, parathion and phosalone on Amberlite XAD-4 resin from 1 l of 7–36 μM water solutions, followed by combustion of 500 μl of eluate yields of orthophosphoric acid with 90–105% recoveries. The detection limit is ca. 150 ng ml?1 pesticide in an aqueous sample. Inorganic phosphates and most of some commonly present non-pesticide phosphorus compounds are eliminated from the water sample during the adsorption step. In combination with a test for monitoring traces of cholinesterase inhibitors in surface waters, the determination of the total amount of organophosphorus pesticides as a cumulative parameter offers reliable information on the pollution level of the water environment. Application of such a combined procedure to a pond water from an apple orchard showed good correlation between phosphrus content and the cholinesterase inhibition. 相似文献
112.
Daniela Walterová Zdeně;K Stránský Vladimír Preininger Prof. Dr. Vilím Šimánek 《Electrophoresis》1985,6(3):128-132
The isotachophoretic behavior of quaternary benzo/c/phenanthridine, protoberberine and aporphine alkaloids in different electrolyte systems is described. The concentration of the leading ion and the pH value of the leading electrolyte affect the relative effective mobilities of the alkaloids. The system of pH 4.7, containing the leading ion K+ (0.005 M) counter ion acetate, and the terminating ion β-alanine (0.02 M), has been selected for the quantitative determination of the studied alkaloids in model mixtures and plant extracts. 相似文献
113.
J. Krištiak O. Šauša P. Bandžuch J. Bartoš 《Journal of Radioanalytical and Nuclear Chemistry》1996,210(2):563-570
The temperature dependence of positron annihilation characteristics,
3 andI
3, has been studied on sample of poly(butadiene), poly(isobutylene) and poly(chloroprene). The temperature range was between 15 and 470 K. The rate of expansion of holes or free-volume in all samples was deduced belowT
g as well aboveT
g as appr. 3·10–3 K–1 and 2·10–2 K–1, respectively. These values are very close to the rate of the mean squared displacement of scatterer<r
2>observed in neutron scattering experiments. A possibility to use an inverse value of free-volume,V
f
–1
for study of viscoelastic state of polymers is demonstrated. 相似文献
114.
Z. Šimša V. Roskovec F. Zounová P. Novotný W. Keilig 《Czechoslovak Journal of Physics》1977,27(1):88-98
An extended version of the noncollinear spin model bySawatzky et al. is developed to derive a dependence of the differential high field susceptibility on the degree of inversion of the ferrite MnFe2O4. Using the available data on the main molecular field coefficients it is shown that the present model imposes restrictions on values of. Determination of from the measurements of the field dependence of the saturated moments at low temperatures on samples with varying degrees of inversion reveals good quantitative agreement with the present model. 相似文献
115.
D. Šokčević Z. Lenac R. Brako M. Šunjić 《Zeitschrift für Physik B Condensed Matter》1977,28(4):273-281
We develop a theory of low energy electron loss spectroscopy of vibrational modes of molecules adsorbed on metal surfaces. Differential and total cross sections are calculated in the Distorted Wave Born Approximation, assuming i) strong elastic scattering on the metal surface, ii) direct electron-molecule interaction via the electric dipole field associated with the molecular vibration. The angular distributions are calculated and discussed for molecules adsorbed at various distances above the metal surface and for several electron energies and impact angles. The influence of electronic screening of dipolar oscillations is discussed and the consequences of the classical induced image dipoles are explored. It is shown that the metal surface selection rule known in IR spectroscopy is only approximately valid in electron scattering. Finally, we give numerical estimates of the inelastic scattering cross sections for the stretching vibrations of CO molecule adsorbed on transition metal surfaces, in reasonable agreement with experiments. 相似文献
116.
Nataša Bukovec Peter Bukovec Jože Šiftar 《Monatshefte für Chemie / Chemical Monthly》1980,111(4):957-961
Compounds of the type CsLn(SO4)2, (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were prepared at 300°C. IR spectra were recorded in the range 4,000-250cm–1 and tentatively assigned. The number of observed bands exceeds the predicted number by site symmetry selection rules. Streching bands show bathochromic shifts whereas the deformations exibit hypsochromic shifts on going to heavier lanthanides. At the same time there is an increased splitting of these bands in the same direction. All these facts indicate an increased coupling in the layer structure which is in accordance with the lanthanide contraction.
N. Bukovec, P. Bukovec undJ. iftar, Vest. Slov. Kem. Drus.26, 103 (1979). 相似文献
117.
Maria Zaharescu Maria Crisan I. MuŠeviČ 《Journal of Sol-Gel Science and Technology》1998,13(1-3):769-773
Atomic Force Microscopy (AFM) was used to study the influence of thermal treatments on the structural and textural properties of the sol-gel TiO2 films obtained from Ti(OC3H7i)4. X-ray diffraction (XRD), ellipsometric and porosity measurements have also been made.The TiO2 sol-gel films were homogeneous, transparent and amorphous. Heat treatments in the 400–600°C range indicate that the films have a strong tendency to crystallization. The high initial homogeneity of the TiO2 films was preserved during the crystallization process. AFM shows that the thermally treated films exhibit uniform, monodispersed crystals. 相似文献
118.
J. Planinić Z. Faj B. Šuveljak V. Radolić J. Vaupotič I. Kobal 《Journal of Radioanalytical and Nuclear Chemistry》1996,210(1):227-231
The radon concentration in the air and water of the Bizovac spa was measured by the Radhome silicon detector and the average values were obtained as 70 Bq/m3 in the indoor pool, 40 Bq/m3 in the hotel room, 135 Bq/m3 in the closed therapeutic bathroom, but the geothermal water had a Rn concentration of 25.3 kBq/m3 and the potable one 2.7 kBq/m3. The Rn transfer factor (f) from water to air in the indoor pool and therapeutic bathroom was 10 and 40 times higher than for normal dwellings (f
n=10–4), respectively. The effective equivalent dose of inhaled radon for permanent personnel under the worst conditions in the spa was 5.4 mSv/y, but visitors spending two weeks in the spa could receive the dose of 77 Sv. 相似文献
119.
F. Šeršeň G. Čík L. Szabo L. Dlháň 《Journal of Radioanalytical and Nuclear Chemistry》1996,212(1):1-9
The magnetic properties of poly(3-dodecyl-thiophene) (PDDT) irradiated by -beams have been studied by measuring the magnetic susceptibility and EPR spectra. The irradiated PDDT is characterized, similarly as the non-irradiated one, by an antiferromagnetic course of magnetic susceptibility with a Néel temperature of 237 K. It is suggested that the antiferromagnetic properties of PDDT are caused by transformation of polarons to bipolarons, which takes place at lower temperatures. 相似文献
120.
The
aim of our research was to prepare yellow pigments based on structure of pseudobrookite
Fe2TiO5. Part of Fe was substituted
with Li and Ti from Fe2TiO5
to Li0.05Fe0.07Ti2.44O5.
Synthesis and pigmentary-application properties in the Li2O–Fe2O3–TiO2 system were studied for 800 and 900°C using classical ceramic
method of preparation. The main attention was aimed to usage of four different
sources of titanium compounds as raw materials. We studied the influence of
different sources of titanium compounds on the structural and the colour properties
of the prepared pigments. The thermal analysis was used for characterization
of titanium compounds and determination of their thermal stability. 相似文献