全文获取类型
收费全文 | 73992篇 |
免费 | 23319篇 |
国内免费 | 17390篇 |
专业分类
化学 | 46200篇 |
晶体学 | 1006篇 |
力学 | 5046篇 |
综合类 | 85篇 |
数学 | 9681篇 |
物理学 | 52683篇 |
出版年
2024年 | 456篇 |
2023年 | 675篇 |
2022年 | 698篇 |
2021年 | 592篇 |
2020年 | 835篇 |
2019年 | 1390篇 |
2018年 | 1338篇 |
2017年 | 2014篇 |
2016年 | 2076篇 |
2015年 | 2330篇 |
2014年 | 2161篇 |
2013年 | 3907篇 |
2012年 | 4174篇 |
2011年 | 5737篇 |
2010年 | 9192篇 |
2009年 | 9449篇 |
2008年 | 3283篇 |
2007年 | 2779篇 |
2006年 | 2476篇 |
2005年 | 2865篇 |
2004年 | 3738篇 |
2003年 | 2990篇 |
2002年 | 2809篇 |
2001年 | 3099篇 |
2000年 | 2308篇 |
1999年 | 2514篇 |
1998年 | 2132篇 |
1997年 | 1925篇 |
1996年 | 2254篇 |
1995年 | 2711篇 |
1994年 | 2778篇 |
1993年 | 2852篇 |
1992年 | 2430篇 |
1991年 | 2090篇 |
1990年 | 1742篇 |
1989年 | 1850篇 |
1988年 | 1837篇 |
1987年 | 1126篇 |
1986年 | 1181篇 |
1985年 | 844篇 |
1984年 | 968篇 |
1982年 | 888篇 |
1981年 | 732篇 |
1980年 | 769篇 |
1979年 | 526篇 |
1978年 | 530篇 |
1977年 | 633篇 |
1976年 | 1042篇 |
1973年 | 437篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
961.
The liquid-phase C-alkylation of hidroquinone with isobutene catalyzed by heteropoly acids H3PW12O40, H6P2W18O62 and H6P2W21O71 (HPA) under phase-transfer conditions in a two-phase system, including toluene (upper phase) and HPA dioxane etherate, HPA·xC4H8O12·yH2O, (lower phase) has been studied. 相似文献
962.
Y. E. Kutsovsky A. G. Mariasov Y. I. Aristov V. N. Parmon 《Reaction Kinetics and Catalysis Letters》1990,42(1):19-24
The ESE method was successfully used for investigating the texture of the adsorbents and catalysts. Equations were obtained for the kinetics of ESE signal decay due to dipole-dipole interaction between motionless paramagnetic centers distributed uniformly on the fractal surface of solid.
, . , , .相似文献
963.
964.
R. G?tz P. Enge P. Friesel K. Roch B. Schilling B. Hartmann H. Wunsch 《Fresenius' Journal of Analytical Chemistry》1994,348(10):694-695
Sampling and determination of dissolved and particlebound PCBs and HCB in the river Elbe are described. A new filtration/adsorption unit for sampling of dissolved lipophilic contaminants was developed. The detection limit for dissolved PCBs and HCB was 5 pg/l. The data show that more than 98% of the PCBs and of HCB in the water of the river Elbe are particle-bound. 相似文献
965.
Study on the oligomerization of cyclopentadiene and dicyclopentadiene to tricyclopentadiene through diels-alder reaction 总被引:3,自引:0,他引:3
Zhongqiang Xiong Zhentao Mi Xiangwen Zhang 《Reaction Kinetics and Catalysis Letters》2005,85(1):89-97
Summary The oligomerization of cyclopentadiene (CPD) and its dimer, dicyclopentadiene (DCPD), to tricyclopentadiene (TCPD) through Diels-Alder reaction at temperatures between 120 and 150°C was investigated. The results show that reaction temperature, pressure and solvent influence the product yield; at 150°C up to 50% yield of TCPD was obtained in the absence of solvents. The ratios of isomers A to B in the product can be adjusted by using different solvents. The kinetics indicate that the rate is more sensitive to the concentration of CPD than to that of DCPD. 相似文献
966.
GuoXiangCHENG GuangLingPEI LingGangZENG LiYongZHANG ChaoLIU 《中国化学快报》2004,15(2):242-245
In this paper, the surface imprinted cross-linked polystyrene beads were prepared via suspension polymerization with styrene (St), divinylbezene (DVB), polyvinyl alcohol (PVA1788),the mixture of Span 85 and xylene or the mixture of Span 85 and paraffin as monomer,cross-linking agent, dispersion stabilizer and templates, respectively. The results indicate that there are dense cavities on the surface of beads, and the diameter and density of cavity are related with the composition and amount of emulsion template. The forming mechanism of cavity from thermodynamics and dynamics was proposed. 相似文献
967.
968.
Amr Nour Al-Deen Douglas J. Cecchini Roger W. Giese 《Journal of chromatography. A》1992,600(2):229-233
A method has been developed in which the DNA of leukocytes (as the buffy coat from blood) is isolated in the form of its constituent deoxynucleotides. The steps in this method are as follows: (1) lyse the leukocytes with sodium dodecyl sulfate (SDS) and enzymatically digest the proteins and RNA, (2) remove the SDS on a non-polar adsorbent (Bio-Beads SM-4) and then trap the DNA on a quaternary amine silica cartridge, (3) wash the column with 1 M NaCl-buffer, (4) digest the DNA on the column with staphylococcal nuclease and (5) elute the digested DNA with 0.5 M NaCl-buffer and digest it further with bovine spleen phosphodiesterase II to deoxynucleotide-3′-monophosphates. From a 40-μl sample of butty coat was obtained 126 ± 14 μg (two experiments, eight sample total) of deoxynucleotides. Reversed-phase high-performance liquid chromatography, which removed the added enzymes, showed only peaks for deoxynucleotides. For comparison, the amount of deoxynucleotides obtained from the leukocytes by an automated phenol extraction procedure was 101 ± 5.4 μg (one experiment in triplicate). 相似文献
969.
Kinetics of the bis(2,2,6,2-terpyridine) iron(II)-cobalt(III) electron transfer reaction in sulfuric acid medium has been studied using stopped-flow spectrophotometry. The reaction is first order both in substrate and oxidant. Hydrogen ions accelerate the reaction, whereas bisulfate ions retard. A suitable mechanism is proposed considering Co3+, CoSO
4
+
and Co(SO4)
2
–
as the reactive oxidizing species.
(2,2,6,2-)(II)(III) . , , . , -. , Co3+, CoSO4 + Co(SO4)2 – .相似文献
970.
The possibility has been shown of using IR spectroscopy in the investigation of the changes in the polysaccharide component of wood in the process of acid hydrolysis. The method of determining the relative optical density (ROD) was used for the quantitative evaluation of the changes in the functional groups of the lignocellulose.Deceased.Siberian Scientific Research Institute of Cellulose and Board, Bratsk. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 683–687, September–October, 1990. 相似文献