全文获取类型
收费全文 | 45213篇 |
免费 | 1002篇 |
国内免费 | 1494篇 |
专业分类
化学 | 24497篇 |
晶体学 | 572篇 |
力学 | 1329篇 |
综合类 | 21篇 |
数学 | 5841篇 |
物理学 | 12539篇 |
无线电 | 2910篇 |
出版年
2023年 | 160篇 |
2022年 | 649篇 |
2021年 | 928篇 |
2020年 | 778篇 |
2019年 | 982篇 |
2018年 | 1392篇 |
2017年 | 1492篇 |
2016年 | 2106篇 |
2015年 | 1128篇 |
2014年 | 1848篇 |
2013年 | 3210篇 |
2012年 | 3089篇 |
2011年 | 3242篇 |
2010年 | 2802篇 |
2009年 | 2987篇 |
2008年 | 2940篇 |
2007年 | 2848篇 |
2006年 | 2458篇 |
2005年 | 1942篇 |
2004年 | 1899篇 |
2003年 | 1277篇 |
2002年 | 1181篇 |
2001年 | 760篇 |
2000年 | 1041篇 |
1999年 | 692篇 |
1998年 | 767篇 |
1997年 | 707篇 |
1996年 | 324篇 |
1995年 | 209篇 |
1994年 | 155篇 |
1993年 | 155篇 |
1992年 | 138篇 |
1991年 | 100篇 |
1990年 | 107篇 |
1989年 | 90篇 |
1988年 | 80篇 |
1987年 | 78篇 |
1986年 | 76篇 |
1985年 | 96篇 |
1984年 | 100篇 |
1983年 | 81篇 |
1982年 | 68篇 |
1981年 | 71篇 |
1980年 | 65篇 |
1979年 | 42篇 |
1978年 | 33篇 |
1977年 | 43篇 |
1976年 | 31篇 |
1975年 | 30篇 |
1974年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
811.
G. R. Kosmambetova P. E. Strizhak É. M. Moroz T. E. Konstantinova A. V. Gural’skii V. P. Kol’ko V. I. Gritsenko I. A. Danilenko O. A. Gorban 《Theoretical and Experimental Chemistry》2007,43(2):102-107
The morphological and catalytic properties of samples of nanomeric zirconium dioxide, stabilized with yttrium oxide, manufactured
via the effect of a UHF field during the process of drying precipitated zirconium hydroxide and calcination at temperatures
from 300 to 1000 °C, were studied. It was shown that the highest activity in the oxidation of CO occurred with 40 nm particles
of zirconium dioxide prepared at 1000 °C.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 96–101, March–April, 2007. 相似文献
812.
813.
A. A. Il’ina I. A. Stenina A. G. Veresov A. B. Yaroslavtsev 《Russian Journal of Inorganic Chemistry》2007,52(4):469-474
Potassium magnesium and potassium cobalt molybdates of composition K2M 2 II (MoO4)3 (M = Mg, Co) and the products of their heterovalent doping by scandium(III) and vanadium(V) ions have been studied by impedance spectroscopy, powder X-ray diffraction, and electron microscopy. The compounds have high ion conductivity. Partial heterovalent substitutions of scandium for magnesium or vanadium for molybdenum additionally increases ion conductivity. The high conductivity of potassium magnesium and potassium cobalt molybdates allows us to consider them as promising solid electrolytes with potassium conductivity. 相似文献
814.
This paper describes the optimization of solid-phase microextraction (SPME) conditions for three different fibres (Carboxen-polydimethylsiloxane (CAR-PDMS), divinylbenzene-Carboxen-polydimethylsiloxane (DVB-CAR-PDMS) and polydimethylsiloxane-divinylbenzene (PDMS-DVB)) used to determine trihalomethanes (THMs) in water by headspace solid-phase microextraction and gas chromatography (HS-SPME-GC). The influence of temperature and salting-out effect was examined using a central composite design for each fibre. Extraction time was studied separately at the optimum values found for temperature and sodium chloride concentration (40 degrees C and 0.36g mL-1). The HS-SPME-GC-MS method for each fibre was characterised in terms of linearity, detection (LOD) and quantification (LOQ) limits and repeatability. The fibre PDMS-DVB was selected as it provided a broader linear range, better repeatability and lower detection and quantification limits than the others, particularly CAR-PDMS fibre. The accuracy of the proposed method using the PDMS-DVB fibre was checked by a recovery study in both ultrapure and tap water. A blank analysis study showed the absence of memory effects for this fibre. The reproducibility (expressed as a percentage of relative standard deviation) was 6-11% and the detection limits were between 0.078 and 0.52microgL-1 for bromoform and chloroform, respectively. Finally, the method was applied to determine THM concentration in two drinking water samples. 相似文献
815.
A. N. Krasovskii I. V. Vasil’eva S. V. Myakin N. A. Osmolovskaya S. V. Borisova 《High Energy Chemistry》2011,45(5):390-396
The structure, relaxation, and surface properties of cellulose triacetate (CTA) fibers and films modified by electron-beam
irradiation in the absorbed dose range of D = 0−1000 kGy have been studied. The relation of the glass transition and melting temperatures of the irradiated CTA samples
with the local density and the fractal dimensionality of the macrochain has been revealed. It has been shown that the radiation-chemical
processes associated with the rupture of acetal bonds and the hydrolysis of CTA acetate groups predetermine the change in
the structural and relaxation characteristics of the irradiated samples, as well as a nonmonotonic form of the dependence
of the density and the surface energy of the films upon the absorbed dose near the threshold value of D = 75 kGy. 相似文献
816.
Varela-Álvarez A Sordo JA Piedra E Nebra N Cadierno V Gimeno J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(38):10583-10599
A general mechanism to rationalize Ru(IV) -catalyzed isomerization of the C=C bond in O-allylic substrates is proposed. Calculations supporting the proposed mechanism were performed at the MPWB1K/6-311+G(d,p)+SDD level of theory. All experimental observations in different solvents (water and THF) and under different pH conditions (neutral and basic) can be interpreted in terms of the new mechanism. Theoretical analysis of the transformation from precatalyst to catalyst led to structural identification of the active species in different media. The experimentally observed induction period is related to the magnitudes of the energy barriers computed for that process. The theoretical energy profile for the catalytic cycle requires application of relatively high temperatures, as is experimentally observed. Participation of a water molecule in the reaction coordinate is mechanistically essential when the reaction is carried out in aqueous medium. The new mechanistic proposal helped to develop a new experimental procedure for isomerization of allyl ethers to 1-propenyl ethers under neutral aqueous conditions. This process is an unique example of efficient and selective catalytic isomerization of allyl ethers in aqueous medium. 相似文献
817.
I. A. Khotina A. I. Kovalev N. S. Kushakova M. A. Babushkina Yu. V. Vasil’ev A. S. Peregudov 《Russian Chemical Bulletin》2013,62(10):2234-2244
A series of model cyclotrimers was studied by NMR spectroscopy using 2D COSY, HSQC, and HMBC correlations to establish the structures of branched oligophenylenes, whose branching center is the 1,3,5-triphenyl-substituted benzene ring. 相似文献
818.
L. G. Voskressensky T. N. Borisova T. A. Vorob’eva A. I. Chernyshev A. V. Varlamov 《Russian Chemical Bulletin》2005,54(11):2594-2601
Reactions of substituted tetrahydropyrrolo[3,2-c]pyridines with dimethyl acetylenedicarboxylate in protic and aprotic solvents were studied. A novel single-step method for
the synthesis of pyrrolo[2,3-d]azocine derivatives was developed.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2513–2519, November, 2005. 相似文献
819.
The mass spectra of the dissociative electron-impact ionization products of telomers formed upon the radiation-chemical telomerization
of tetrafluoroethylene in acetone were measured over the range of m/z from 1 to 204. The most intense bands at m/z = 43, 51, and 57 were attributed to the CH3CO+, CF2H+ and CH3COCH2+ cations—the main dissociation products of the H(C2F4)
n
CH2COCH3 telomers. The telomer composition was consistent with a radical telomerization mechanism, in which chain growth and chain
transfer are due to the formation of the CH3COCH2· radical. Based on published data supplemented with quantum-chemical calculations, the enthalpies of formation of the radicals
R(CF2)
n
(n = 2–8; R = H, CH3, CH3CO, and CH3COCH2) were tabulated. The formation of telomers with the same terminal groups is consistent with thermodynamic data and a polymerization
mechanism in which the chain growth reaction is diffusion-limited and the chain transfer reaction is activated hydrogen-atom
transfer. 相似文献
820.
A. P. Voznyakovskii B. M. Ginzburg D. Rashidov D. G. Tochil’nikov Sh. Tuichiev 《Polymer Science Series A》2010,52(10):1044-1050
The effect of modifying additives based on detonation nanodiamonds on the tribological characteristics of polyurethane rubber
is studied. Introduction of modifying additives based on detonation nanodiamonds (0.5 wt %) leads to a marked improvement
in the antifriction and wear-resistance characteristics under conditions of boundary sliding friction for steel and for lubrication
with water. The attained tribological characteristics (total energy loss for friction, weight loss of polymer during tribological
contact, maximum admissible working pressure) are well (∼300%) above the corresponding characteristics of foreign analogs.
Changes in the tribological characteristics of the formed nanocomposite material are observed, but the elastic and strength
characteristics remain unchanged. 相似文献