全文获取类型
收费全文 | 203969篇 |
免费 | 2434篇 |
国内免费 | 504篇 |
专业分类
化学 | 112337篇 |
晶体学 | 3662篇 |
力学 | 8029篇 |
综合类 | 11篇 |
数学 | 19317篇 |
物理学 | 63551篇 |
出版年
2020年 | 1765篇 |
2019年 | 1973篇 |
2018年 | 2269篇 |
2017年 | 2383篇 |
2016年 | 3603篇 |
2015年 | 2284篇 |
2014年 | 3645篇 |
2013年 | 9247篇 |
2012年 | 6640篇 |
2011年 | 8168篇 |
2010年 | 5826篇 |
2009年 | 5754篇 |
2008年 | 7276篇 |
2007年 | 7179篇 |
2006年 | 6788篇 |
2005年 | 6129篇 |
2004年 | 5586篇 |
2003年 | 5177篇 |
2002年 | 4935篇 |
2001年 | 6186篇 |
2000年 | 4662篇 |
1999年 | 3528篇 |
1998年 | 2756篇 |
1997年 | 2708篇 |
1996年 | 2608篇 |
1995年 | 2452篇 |
1994年 | 2341篇 |
1993年 | 2174篇 |
1992年 | 2833篇 |
1991年 | 2734篇 |
1990年 | 2679篇 |
1989年 | 2696篇 |
1988年 | 2719篇 |
1987年 | 2728篇 |
1986年 | 2594篇 |
1985年 | 3310篇 |
1984年 | 3323篇 |
1983年 | 2605篇 |
1982年 | 2721篇 |
1981年 | 2774篇 |
1980年 | 2540篇 |
1979年 | 2880篇 |
1978年 | 2873篇 |
1977年 | 2988篇 |
1976年 | 2827篇 |
1975年 | 2563篇 |
1974年 | 2516篇 |
1973年 | 2467篇 |
1972年 | 1704篇 |
1968年 | 1705篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
T. N. Sokolova V. R. Kartashov I. V. Timofeev Yu. K. Grishin N. S. Zefirov 《Russian Chemical Bulletin》1994,43(3):461-465
The dependence of the regiochemistry of the mercuration of bornylene on the nature of the mercurating reagent and on the solvent has been found. The structures of the intermediate and transition state in these reactions have been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 501–505, March, 1994. 相似文献
992.
V. E. Kirichenko E. P. Promyshlennikova K. I. Pashkevich 《Russian Chemical Bulletin》1994,43(5):812-815
The dependence of the variations in the differential molar free energy of sorption of polyfluorocarboxamides RFC(O)NR2 (RF = CF3(CF2)
i
,i=0 to 5, R=H or Me) on capillary columns on the molecular structure of the amides, the temperature of analysis, and the nature of the stationary phases (OV-101, XE-60, and PEG-40M) were investigated by GLC. The peculiarities of the variation of the sorption characteristics of amides in XE-60 and PEG-40M polar phases, which cause the inversion of the order of retention of the members of pseudohomologous series, were found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 868–871, May, 1994.We are grateful to R. V. Golovnya and D. N. Grigor'eva (Institute of Food Substances of the RAS, Moscow) for their participation in the discussion of the results obtained. 相似文献
993.
Sokolova T. N. Grishin Yu. K. Timofeev I. V. Kartashov V. R. 《Russian Chemical Bulletin》1994,43(6):1044-1047
Regiochemistry and stereochemistry of the addition of mercury salts to benzobarrelene and tetrafluorobenzobarrelene have been studied in acetic acid and methanol. The effect of the substrate structure on the regiochemistry of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1105–1108, June, 1994. 相似文献
994.
Electrolysis of dimethyl malonate or methyl cyanoacetate in methanol in the presence of LiCl in an undivided cell leads to formation of 1,1,2,2-cyclopropanetetracarboxylic derivatives.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1835–1836, October, 1994.This work was supported by the International Science Foundation (Grant No MHY 000). 相似文献
995.
E. K. Merabet H. K. Yuen W. A. Grote K. L. Deppermann 《Journal of Thermal Analysis and Calorimetry》1994,42(5):895-906
A new sensitive isothermal titration microcalorimeter using polyvinylidene difluoride (PVDF) as detector has been developed. Heat pulses of less than 0.4 μJ can be detected and the baseline noise level (p-p) is 40 nW. The calorimeter is constructed with one reaction cell (0.7 ml) insulated by several radiation shields inside a vacuum chamber. The performance of the instrument was examined by measuring the heat of protonation of Tris with HCl. The enthalpy of reaction was found to be ?49±1 kJ·mol?1, in good agreement with the reported value of ?47.5 kJ·mol?1. 相似文献
996.
997.
998.
Since the early demonstrations of our concept of pulsed microwave catalysis in chemistry, we have witnessed the coming of age of the technique as an enabling technology in the industrial world, despite the inadequate understanding of the basic mechanisms of how microwaves interact with metallic surface sites and the subsequent energy transfer. We shall present here some very recent developments of the microwave-induced acoustic technique and its applications to a better understanding of the basic surface heating and energy transfer phenomena in pulsed microwave catalytic systems. 相似文献
999.
H.-J. Kluge B. A. Bushaw G. Passler K. Wendt N. Trautmann 《Fresenius' Journal of Analytical Chemistry》1994,350(4-5):323-329
Resonance ionization spectroscopy (RIS) and its combination with mass spectrometry (RIMS) have grown to become powerful techniques, which offer high sensitivity as well as elemental and isotopic selectivity. The principles of RIS and RIMS are introduced; they primarily concern the analysis of the optical spectra for the choice of efficient excitation schemes and the suitable design of the experimental apparatus. Recent applications span from studies of short-lived isotopes at on-line mass separators to a wide variety of trace analysis applications for radioactive isotopes, which can range from measurements of solar neutrino flux to environmental assessment.On leave from Pacific Northwest Laboratory, Richland, USA 相似文献
1000.
Marie Vahter 《应用有机金属化学》1994,8(3):175-182
Humans are exposed via air, water and food to a number of different arsenic compounds, the physical, chemical, and toxicological properties of which may vary considerably. In people eating much fish and shellfish the intake of organic arsenic compounds, mainly arsenobetaine, may exceed 1000 μg As per day, while the average daily intake of inorganic arsenic is in the order of 10–20 μg in most countries. Arsenobetaine, and most other arsenic compounds in food of marine origin, e.g. arsenocholine, trimethylarsine oxide and methylarsenic acids, are rapidly excreted in the urine and there seem to be only minor differences in metabolism between animal species. Trivalent inorganic arsenic (AsIII) is the main form of arsenic interacting with tissue constituents, due to its strong affinity for sulfhydryl groups. However, a substantial part of the absorbed AsIII is methylated in the body to less reactive metabolities, methylarsonic acid (MMA) and dimethylarsinic acid (DMA), which are rapidly excreted in the urine. All the different steps in the arsenic biotransformation in mammals have not yet been elucidated, but it seems likely that the methylation takes place mainly in the liver by transfer of methyl groups from S-adenosylmethionine to arsenic in its trivalent oxidation state. A substantial part of absorbed arsenate (AsV) is reduced to AsIII before being methylated in the liver. There are marked species differences in the methylation of inorganic arsenic. In most animal species DMA is the main metabolite. Compared with human subjects, very little MMA is produced. The marmoset monkey is the only species which has been shown unable to methylate inorganic arsenic. In contrast to other species, the rat shows a marked binding of DMA to the hemoglobin, which results in a low rate of urinary excretion of arsenic. 相似文献