全文获取类型
收费全文 | 346篇 |
免费 | 14篇 |
国内免费 | 10篇 |
专业分类
化学 | 233篇 |
晶体学 | 10篇 |
力学 | 2篇 |
数学 | 75篇 |
物理学 | 50篇 |
出版年
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 13篇 |
2014年 | 10篇 |
2013年 | 28篇 |
2012年 | 8篇 |
2011年 | 19篇 |
2010年 | 8篇 |
2009年 | 18篇 |
2008年 | 13篇 |
2007年 | 21篇 |
2006年 | 19篇 |
2005年 | 14篇 |
2004年 | 14篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1960年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有370条查询结果,搜索用时 15 毫秒
1.
2.
Adam S. Paziak Lech Celewicz Krzysztof Ciszewski Krzysztof Golankiewicz 《Journal of mass spectrometry : JMS》1993,28(5):643-646
The electron impact mass spectra of 6-methyltetrazolo[1,5-c]pyrimidin-5(6H)-one, its 7- and 8-methyl derivatives, three 8-halo derivatives and two related nucleosides are reported. On the basis of the high-resolution data and detected metastable ions, the fragmentation routes of their molecular ions are proposed. Coexistence of the tautomeric forms of the title compounds of cyclic (tetrazole) or linear (azide) structure can be suggested owing to the fragmentation pathways identified for the bases. Decomposition of the related nucleosides lies in the breaking of nucleoside bonds to produce the appropriate base and sugar fragments. 相似文献
3.
Azaindolizines, which contain all possible combinations of nitrogen atoms within the five-membered ring moiety, are used as models for the investigation of a relationship between electron charge distribution and 13C shifts. A linear correlation is observed between the shifts and total rather than π-charge densities as calculated by the INDO-MO method. The average excitation energy (AEE) approximation in the theory of nuclear screening is shown to hold separately for the CH moieties and the carbon atoms at the ring junction in indolizines. An empirical correlation with charge densities is obtained from the AEE method, as a result of the compensation of effects within the local paramagnetic term and the prevailing contribution to the latter of the effective nuclear charge.13C shifts afford a reasonable measure of the total net charges at the carbon atoms of indolizines. The INDO calculations indicate that the π-charges follow the pattern suggested by simple resonance structures but the overall charge density depends heavily on σ-core polarization effects. 相似文献
4.
Zbigniew Kisiel Lech Pszczó?kowski Steven B. Charnley 《Journal of Molecular Spectroscopy》2007,241(2):220-229
The rotational spectrum of pyruvic acid has been investigated for the first time in the millimeter-wave region, at 160-314 GHz, and also in supersonic expansion, at 10-17.4 GHz. The analysis of the broadband spectra recorded in this work was carried out with the newly developed AABS software package for Assignment and Analysis of Broadband Spectra, and precise spectroscopic constants are reported for the ground state, the first excited state of the low-frequency skeletal torsional mode ν24, and the first excited state of the methyl torsional mode ν23. Limited results have also been obtained for several higher excited states. The dataset for the ground state currently exceeds 1500 lines and for both the A and E internal rotor sublevels spans the complete range of values of Ka at the mid values of J for the measured transitions. The results were analysed with three freely available computer programs employing different strategies for dealing with internal rotation and a comparative discussion of their merits is made. 相似文献
5.
6.
7.
McAllister LA Turner KL Brand S Stefaniak M Procter DJ 《The Journal of organic chemistry》2006,71(17):6497-6507
A sulfur HASC (alpha-hetero-atom substituted carbonyl) linker has been utilized in solid-phase approaches to oxindoles and tetrahydroquinolones. The route to oxindoles employs the first Pummerer cyclizations on solid phase, whereas the route to tetrahydroquinolones involves a microwave-assisted Heck reaction followed by a Michael cyclization. In both cases, the linker is cleaved in a traceless fashion by electron transfer from samarium(II) iodide. The routes illustrate the compatibility of the linker system with a number of reaction types and its utility for library synthesis. 相似文献
8.
Iwona Łakomska Anna Kaźnica Romana Joachimiak Andrzej Marszałek Jerzy Sitkowski Lech Kozerski Tomasz Drewa 《Chemical Papers》2011,65(3):308-314
A novel platinum(IV) coordination compound with 6-mercaptopurine (6-Hmp) has been synthesised and characterised by IR and
NMR spectroscopy. Spectroscopic parameters indicate the presence of two chelate (S-6, N-7) monodeprotonated ligands and two
chloride ions in the coordination sphere of [PtCl2(6-mp)2] · H2O (I). Two Pt(IV) coordination compounds, [PtCl2(6-mp)2] · H2O (I) and [PtCl4(dbtp)2] (II), were used in the in vivo test against B16 mouse melanoma tumours. Cytotoxic activity of compound II against the tumour cells was found to be high (LC10 = 2.6 μM, LC50 = 17.0 μM, LC90 = 58.0 μM) compared to that of cisplatin. 相似文献
9.
Mateusz Kuczyski Mateusz uba Tomasz Mikoajczyk Bogusaw Pieroyski Agnieszka Jasiecka-Mikoajczyk Lech Smoczyski Piotr Soowiej Pawe Wojtacha 《Molecules (Basel, Switzerland)》2021,26(15)
Traditional wastewater purification processes are based on a combination of physical, chemical, and biological methods; however, typical electrochemical techniques for removing pollutants require large amounts of electrical energy. In this study, we report on a process of wastewater purification, through continuous anodic dissolution of iron anode for aerated Cu/Fe galvanic cell in synthetic Na2SO4 wastewater solution. Electrochemical experiments were conducted by means of a laboratory size electrolyzer, where electrocoagulation along with electrooxidation phenomena were examined for wastewater containing Acid Mixture dye. The above was visualized through the employment of electrochemical (cyclic voltammetry and ac impedance spectroscopy techniques) along with instrumental spectroscopy analyses. 相似文献
10.
Wojciech Bocian Jarosław Jaźwínski Lech Stefaniak Graham A. Webb 《Chemistry of Heterocyclic Compounds》1995,31(9):1103-1107
1H,13C,14N and15N NMR measurements are reported for four mesoionic 1-oxa-2, 3, 4-triazoles containing exocyclic nitrogenous groups. The NMR signal assignments are discussed and compared with those previously published for some corresponding oxatriazoles. The results obtained support the proposed cyclic mesoionic structures for the compounds studied. The questions of possible charge delocalization and valence tautomerism are addressed. Compound with N– H as a exocyclic group (Fig. 1) is found to be relatively unstable, this is attributed to proton migration in the corresponding non-cyclic form of this molecule.Published in Khimiya Geterotsikiicheskikh Soedinenii, No. 9, pp. 1260–1263, September, 1995. 相似文献