全文获取类型
收费全文 | 2390篇 |
免费 | 50篇 |
国内免费 | 23篇 |
专业分类
化学 | 1436篇 |
晶体学 | 29篇 |
力学 | 26篇 |
数学 | 328篇 |
物理学 | 644篇 |
出版年
2023年 | 11篇 |
2022年 | 16篇 |
2021年 | 35篇 |
2020年 | 20篇 |
2019年 | 33篇 |
2018年 | 66篇 |
2017年 | 48篇 |
2016年 | 102篇 |
2015年 | 75篇 |
2014年 | 95篇 |
2013年 | 208篇 |
2012年 | 122篇 |
2011年 | 160篇 |
2010年 | 100篇 |
2009年 | 99篇 |
2008年 | 119篇 |
2007年 | 107篇 |
2006年 | 116篇 |
2005年 | 88篇 |
2004年 | 87篇 |
2003年 | 74篇 |
2002年 | 55篇 |
2001年 | 48篇 |
2000年 | 34篇 |
1999年 | 29篇 |
1998年 | 33篇 |
1997年 | 32篇 |
1996年 | 20篇 |
1995年 | 27篇 |
1994年 | 11篇 |
1993年 | 18篇 |
1992年 | 20篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 24篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1975年 | 12篇 |
1973年 | 8篇 |
1972年 | 8篇 |
排序方式: 共有2463条查询结果,搜索用时 15 毫秒
41.
A sensitive flotation—spectrophotometric method, based on the ion associate formed by the anionic thiocyanate complex of osmium with the basic dye methylene blue (MB) is described. The ion associate precipitates when the aqueous solution is shaken with toluene, and the separated and washed compound is dissolved in acetone. The molar absorptivity is 2.2 × 105 l mol-1 cm-1 at 655 nm. Beer's law is obeyed. The molar ratio of Os:SCN:MB in the separated and washed ion associate is 1:6:3. Ruthenium reacts similarly. The method is applied to the determination of traces of osmium in crucible platinum after separation of osmium by distillation as tetroxide. 相似文献
42.
The extraction of Am, Eu, Ce(III), Zr(IV), and Sr from aqueous nitric acid— nitrate media by dibutyl N,N-diethylcarbamylphosphonate
and dibutyl N,N-diethylcar-bamylmethylenephosphonate dissolved in carbon tetrachloride was studied. The trivalent actinide
and lanthanide elements may be separated in certain aqueous phase acidity regions from Fe(III), Zr(IV), and Sr, whereas the
separation of actinide elements from the lanthanide elements is poor. The extractant to metal ratio in the extracted complexes
of Am, Eu, and Ce(III) is 3. The interferences in the extraction due to acidic impurities in the extracting agent are discussed. 相似文献
43.
Krystyna Cieśla H. Rahier Grażyna Zakrzewska-Trznadel 《Journal of Thermal Analysis and Calorimetry》2004,77(1):279-293
One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated
cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment
and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation
processes. A large amount of non-freezable strongly bounded water was also detected.
Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction
occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module
at 90°C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected
during the first, the second and the third heating.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
44.
Kubíček Vladimír Kučová Daria Císarř Prřemysl Burešová Vlasta 《Mikrochimica acta》2003,142(4):273-276
An ion-pair extraction spectrophotometry method was developed for the determination of fenpiverine bromide in tablets. To determine this substance it was necessary to find experimental conditions that would allow eliminating the influence of other components of the tablets. Attention was paid to the fact that a suitable pH of water phase was necessary to achieve high selectivity.Received December 11, 2002; accepted April 24, 2003
Published online July 28, 2003 相似文献
45.
Chai OH Lee HK Lee YC Lee MS Han EH Kim HT Song CH 《Experimental & molecular medicine》2005,37(5):408-417
Trimellitic anhydride (TMA) is widely used industrially to make epoxy and alkyd resins, plasticizers and surfactants. The purpose of this study was to investigate whether contact hypersensitivity (CHS) is induced by repeated TMA challenge and the role of TNF-alpha and IgE in the TMA-induced CHS. The repetition of the challenge enlarged the extent of an early and a late phase of CHS in TNF-alpha+/+ (B6129SF2/J) and Balb/c mice. In the late phase of TMA-induced CHS, the peak of ear swelling responses by single challenge showed at 24 h after challenge, but the peak was observed at 8 h after repeated challenge. In the TNF-alpha knockout TNF-alpha-/- (B6;129S-Tnftm1Gk1) mice, the repetition of the TMA challenges enlarged the extent of the late phase of CHS, but less than those in TNF-alpha+/+ mice. Injection of anti-TNF-alpha antibody into the peritoneal cavity of Balb/c mice significantly decreased the extent of the late phase of CHS. Subcutaneous injection of anti-IgE antibody into Balb/c mice also decreased the extent of the late phase of CHS in dose-dependent manner. Histologically, infiltration of polymorphonuclear leukocytes and eosinophils was more pronounced in repeatedly TMA-challenged TNF-alpha+/+ and Balb/c mice than in the TNF-alpha-/- mice and anti-TNF-alpha or anti-IgE antibodies treated Balb/c mice. These results indicate that mice sensitized by TMA could possibly offer a useful model to study the mechanism of CHS, and TNF-alpha and IgE may act as potential modulators in the late phase of TMA-induced CHS. Neutralization of TNF-alpha and IgE by anti-TNF-alpha or anti-IgE antibodies may provide therapeutic tools for the treatment of TMA-induced CHS. 相似文献
46.
[structure: see text] We have synthesized novel fluorophores by using Sonogashira reactions of 1,4-bis(dibromovinyl)benzene and 2,5-bis(dibromovinyl)thiophene with various aromatic bromides. The emission maxima of these fluorophores vary from the indigo blue to the reddish-orange region, depending on the structures of aromatic nuclei and peripheral moieties. 相似文献
47.
J. Maślińska-Solich 《European Polymer Journal》1975,11(1):43-46
The copolymerization of 2-furyl-5,5-dimethyl-1,3-dioxane with maleic anhydride in the presence of a radical catalyst yields equimolar, alternating copolymers in which the furyl units have 2,5-linkage. It has been shown that 2-furyl-5,5-dimethyl-1,3-dioxane forms a charge transfer complex with maleic anhydride. The equilibrium constant for the complex was determined by NMR spectroscopy. 相似文献
48.
[reaction: see text] The phosphoramidite 11 was prepared in three steps from methyl 2-mercaptoacetate and demonstrated efficiency in the synthesis of conventional 5'-/3'-phosphate/thiophosphate monoester derivatives of 2'-deoxyribonucleosides and DNA oligonucleotides. Moreover, the use of 11 has enabled the preparation of the dinucleoside phosphorothioate analogue 26 in high yields (>95%) with minimal cleavage (<2%) of the thermolytic thiophosphate protecting group. 相似文献
49.
Summary A new method of collection of representative air samples for the determination of TC and TOC from volatile air pollutants has been developed. The organic substances undergo combustion and only the carbon dioxide produced is concentrated on molecular sieve 5 A at ambient temperature. The CO2 is subsequently liberated by thermal desorption at ca. 380°C in a stream of purified gas. Atmospheric CO2 must be removed first and this can be done (at the sample flow rate of 700 ml/min) by a layer of Ascarite heated at 90° C. Organic compounds passing through the layer are then combusted by a dynamic method utilizing Körbl catalyst and the CO2 formed is concentrated on a molecular sieve 5 A, followed by thermal desorption and final determination. Organic acids are also retained by the first CO2 absorber. A diffusion cell for preparation of the mixtures of purified air with vapours of organic compounds is described.
Zusammenfassung Eine neue Anreicherungsmethode zur Gewinnung representativer Luftproben zur Bestimmung des Gesamtkohlenstoffgehaltes und des Gehaltes an organischem Kohlenstoff (TOC) aus flüchtigen Luftverunreinigungen wurde entwickelt. Während der Probenahme werden die flüchtigen Verunreinigungen verbrannt und nur das entstandene Kohlendioxid bei Zimmertemperatur am Molekularsieb 5A angereichert. Anschließend wird CO2 bei ca. 380° C im gereinigten Gasstrom thermisch desorbiert. Bei der TOC-Bestimmung muß atmosphärisches CO2 vorangehend aus dem Luftstrom entfernt werden und wird an einer auf 90° C erwärmten Ascariteschicht gebunden. Die durchfließenden organischen Verbindungen werden dann im dynamischen System am Körblkatalysator oxydiert, das entstandene CO2 am Molekularsieb 5A angereichert, thermisch desorbiert und einer Endbestimmung zugeführt. Organische Säuren werden gleichfalls durch den ersten CO2-Absorber gebunden. Eine Diffusionszelle zur Herstellung von Gemischen gereinigter Luft mit Dämpfen organischer Verbindungen wurde beschrieben.相似文献
50.
Adsorptive stripping voltammetric (AdSV) methods are presented for the determination of titanium and iron in quartz and silica glass samples obtained after pressure decomposition. Mandelic acid and catechol were used as complexing agents for titanium and iron, respectively. The method for titanium determination is based on the catalytic effect of chlorate ions. An insoluble residue remaining after decomposition of quartz and silica glass samples in HF+H2SO4 mixture was checked by energy-dispersive X-ray analyses. ET-AAS was applied as a reference method to AdSV measurements. 相似文献