全文获取类型
收费全文 | 3455篇 |
免费 | 84篇 |
国内免费 | 393篇 |
专业分类
化学 | 3054篇 |
晶体学 | 48篇 |
力学 | 21篇 |
综合类 | 1篇 |
数学 | 6篇 |
物理学 | 802篇 |
出版年
2024年 | 17篇 |
2023年 | 406篇 |
2022年 | 101篇 |
2021年 | 128篇 |
2020年 | 130篇 |
2019年 | 119篇 |
2018年 | 87篇 |
2017年 | 94篇 |
2016年 | 135篇 |
2015年 | 108篇 |
2014年 | 187篇 |
2013年 | 177篇 |
2012年 | 179篇 |
2011年 | 183篇 |
2010年 | 175篇 |
2009年 | 197篇 |
2008年 | 156篇 |
2007年 | 209篇 |
2006年 | 163篇 |
2005年 | 149篇 |
2004年 | 136篇 |
2003年 | 70篇 |
2002年 | 72篇 |
2001年 | 75篇 |
2000年 | 49篇 |
1999年 | 54篇 |
1998年 | 46篇 |
1997年 | 47篇 |
1996年 | 32篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 19篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 13篇 |
1988年 | 31篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 2篇 |
排序方式: 共有3932条查询结果,搜索用时 16 毫秒
961.
962.
本文应用PPP-SCF-MO法研究了吡啶偶氮苯衍生物结构与吸收光谱的关系。本文认为吡啶偶氮苯波长最长的吸收峰为分子內荷移光谱。本文还研究了取代基对吸收光谱的影响,得到了λ_(最大)与“净电荷”Q的线性方程。 相似文献
963.
964.
965.
The analytical performance of Pd, Au, Rh, Ir and their mixtures used as chemical modifiers has been investigated for mercury determination by graphite furnace atomic absorption spectrometry. The aim of this work was to evaluate whether chemical modification assures uniform atomization of analyte independent of its chemical form; mercury was used for this study. The investigations were performed for mercury introduced in the form of inorganic Hg(II) or organic PhHg(I). The best conditions, i.e. maximum pyrolysis temperature (450 °C), lowest temperature for atomization (1100 °C), provided almost the same sensitivity for both forms of mercury when a thermally reduced mixed modifier composed of Pd/Rh was used. The accuracy of the selected conditions was evaluated by a recovery test for various natural waters. 相似文献
966.
The continuing diminishing sources of fresh waters has stimulated the search for unconventional water resources, such as effluents from municipal sewage treatment plants, which can be reused for purposes of irrigation in agriculture, cooling water in industry, groundwater aquifer recharge and in the long term even for drinking water. The main problem of using effluents is the presence of pathogenic bacteria and viruses that can affect human and animal health. Therefore, disinfection has been used for many years to control and reduce waterborne diseases.At the moment, most water treatment plants use sodium hypochlorite as their primary biocide. However, the toxicity of chlorinated organic compounds produced during the treatment has led to increased interest in the use of alternative agents. One possible candidate as viable substitute of free chlorine is chlorine dioxide. Before this disinfectant can be recommended for routine use, it is imperative that its safety be assessed.In this research we have investigated the presence of chlorite and chlorate in sewage disinfected with chlorine dioxide. The effect of initial concentration of biocide and contact time was evaluated using a pilot plant fed with the effluent of a municipal treatment plant. Moreover, the influence of ClO2 generator performance was analyzed and discussed. 相似文献
967.
Y. L. Teng Y. H. Kan Z. M. Su Y. Liao S. Y. Yang R. S. Wang 《Theoretical chemistry accounts》2007,117(1):1-5
The molecular structures of the ground state and the first singlet excited state for diphenylboron analogs of Alq3 [Ph2Bq where q is 8-hydroxyquinoline (QH)] and its three derivatives were optimized with the Density Functional Theory and ab initio “configuration interaction with single excitations” method, respectively. The frontier molecular orbital characteristics of Ph2Bq were analyzed systematically in order to study the electronic transition mechanism. Electronic and spectroscopic properties of complexes have been investigated with Time-Dependent Density Functional Theory, which indicates that the emissions of Ph2Bq and its derivatives originate from the electronic π → π* transitions within the QH ligands. That means that one might tune the emission wavelengths and improve charge transfer properties through the effect of substituent on the 8-hydroxyquinoline ligand. Similar calculations were carried out for isolated QH and its three derivatives for comparison. We found that the highest occupied molecular orbital and the lowest unoccupied molecular orbital of Ph2Bq are similar to those of QH and their spectroscopic properties change similarly when they are substituted by the same group, which suggests that one can search possibility of a red or blue emission from Ph2Bq derivatives by analyzing QH and its derivatives. 相似文献
968.
《Electroanalysis》2004,16(24):2022-2029
Films of electrogenerated polypyrrole and hydrophilic alginate, both functionalized with biotin moieties, were used to allow for the transfer of polyphenol oxidase activity in organic media. Enzyme electrodes, based on multilayered structures, were protected at the molecular level by the affinity binding of alginate as a hydrophilic additive, and were then transferred into chlorobenzene, dichloromethane, chloroform, ethyl acetate or acetonitrile. The biosensor performance for the detection of catechol at ?0.2 V was investigated, highlighting the main influence of the hydrophobicity of the solvent and, to a lesser extent, the dielectric constant. The effect of the substrate hydrophobicity on the biosensor response was examined in chlorobenzene. 相似文献
969.
Summary A capillary electrophoretic method has been developed for the determination of the main product as well as of by-products in technical samples of substituted pyrimidines. Both zone electrophoresis and micellar electrokinetic chromatography have been used for the separation employing electrolytes consisting of borate buffers (pH 9 to 9.4) with or without sodium dodecylsulfate. Optimization of separation selectivity could be achieved by addition of up to 20% 2-propanol or methanol to the carrier electrolyte. Quantification by internal standards resulted in relative standard deviations between 0.2 and 0.8%. By-products could be analyzed down to levels of 0.1% in technical samples.
Analyse von Pyrimidinderivaten mitteles Kapillarelektrophorese
Zusammenfassung Für die Bestimmung von Haupt- und Nebensubstanzen in technischen Proben von substituierten Pyrimidinen wurde ein kapillarelektrophoretisches Analysenverfahren entwickelt. Sowohl Zonenelektrophorese als auch mizellare elektrokinetische Chromatographie mit Trägerelektrolyten bestehend aus Boratpuffern (pH 9 bis 9.4) mit oder ohne Natriumdodecylsulfat wurden für die Trennung eingesetzt. Eine Optimierung der Trennselektivität war durch die Zugabe von bis zu 20% 2-Propanol oder Methanol zum Trägerelektrolyten möglich. Quantifizierung mittels interner Standards ergab relative Standardabweichungen zwischen 0.2 und 0.8%. Nebenprodukte konnten in technischen Proben bis zu Gehalten von 0.1% analysiert werden.相似文献
970.
Colombini MP Carmignani A Modugno F Frezzato F Olchini A Brecoulaki H Vassilopoulou V Karkanas P 《Talanta》2004,63(4):839-848
The materials used in the decoration of three painted astragaloi (knucklebones) from the Koroneia cave (Greece) were investigated by means of sequential application of non-destructive and destructive techniques: optical microscopy, environmental scanning electron microscopy coupled with X-ray microanalysis (ESEM-EDX), Fourier transform infrared spectroscopy (FTIR) with micro-attenuated total reflection (μ-ATR) technique, high performance liquid chromatography (HPLC) coupled with UV-fluorescence and gas chromatography-mass spectrometry (GC-MS) were used.The main results highlighted that the three astragaloi were prepared with a ground of ochre or iron clay and painted with a proteinaceous matter such as binder egg tempera. Both FTIR and GC-MS agree in the detection of lipids that can be related to egg. Organic dyestuffs identified as madder lake and shellfish purple were used together with inorganic pigments. 相似文献