全文获取类型
收费全文 | 2646篇 |
免费 | 89篇 |
国内免费 | 17篇 |
专业分类
化学 | 1734篇 |
晶体学 | 9篇 |
力学 | 52篇 |
数学 | 485篇 |
物理学 | 472篇 |
出版年
2023年 | 22篇 |
2022年 | 60篇 |
2021年 | 74篇 |
2020年 | 73篇 |
2019年 | 59篇 |
2018年 | 54篇 |
2017年 | 55篇 |
2016年 | 102篇 |
2015年 | 82篇 |
2014年 | 86篇 |
2013年 | 218篇 |
2012年 | 213篇 |
2011年 | 217篇 |
2010年 | 126篇 |
2009年 | 108篇 |
2008年 | 159篇 |
2007年 | 169篇 |
2006年 | 148篇 |
2005年 | 108篇 |
2004年 | 100篇 |
2003年 | 81篇 |
2002年 | 83篇 |
2001年 | 27篇 |
2000年 | 26篇 |
1999年 | 32篇 |
1998年 | 20篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 20篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 3篇 |
排序方式: 共有2752条查询结果,搜索用时 15 毫秒
61.
The hydrothermal reaction of Ln(2)O(3) (Ln = Dy and Ho), Cu(OAc)(2).2H(2)O, and oxydiacetic acid in the approximate mole ratio of 1:3:8 resulted in the formation of two new members of the isostructural series of polymers formulated as [(Cu(3)Ln(2)(oda)(6)(H(2)O)(6)).12H(2)O](n), crystallizing in the hexagonal crystal system, space group P6/mcc (No. 192). Temperature-dependent magnetic susceptibilities and EPR spectra are reported for the heterometallic compounds Cu-Dy 1, Cu-Ho 2, Cu-Er 3, and Cu-Y 4. The results are discussed in terms of the structure of the compounds, the electronic properties of the lanthanide ions, and the exchange interactions between the magnetic ions. 相似文献
62.
Eleonora Freire Sergio Baggio Juan Carlos Muoz Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):m455-m458
The structure of bis(1,10‐phenanthroline‐κ2N,N′)(thiosulfato‐κ2O:S)manganese(II) methanol solvate, [Mn(S2O3)(C12H8N2)2]·CH3OH, is made up of Mn2+ centers coordinated to two bidentate phenanthroline (phen) groups and an S,O‐chelating thiosulfate anion, forming monomeric entities. The structure of catena‐poly[[diaqua(2,9‐dimethyl‐1,10‐phenanthroline‐κ2N,N′)manganese(II)]‐μ‐thiosulfato‐κ2O:S], [Mn(S2O3)(C14H12N2)(H2O)2]n, is polymeric, consisting of Mn(dmph)(H2O)2 units (dmph is 2,9‐dimethyl‐1,10‐phenanthroline) linked by thiosulfate anions acting in an S,O‐chelating manner. 相似文献
63.
Eleonora Freire Sergio Baggio Juan Carlos Muoz Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(4):m221-m224
Two new nickel nitrates, diaquabis(3,4,7,8‐tetramethyl‐1,10‐phenanthroline‐κ2N,N′)nickel(II) dinitrate methanol solvate, [Ni(C16H16N2)2(H2O)2](NO3)2·CH4O, (I), and triaqua[2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine‐κ3N1,N2,N6]nickel(II) dinitrate trihydrate, [Ni(C18H12N6)(H2O)3](NO3)2·3H2O, (II), are reported. In both structures, the cation is octahedrally coordinated, to two bidentate 3,4,7,8‐tetramethyl‐1,10‐phenanthroline (tmp) and two water molecules in (I), and to one tridentate 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine (tpt) and three water molecules in (II). Both structures are stabilized by extensive hydrogen‐bonding interactions. 相似文献
64.
Schäfer T Di Paolo RE Franco R Crespo JG 《Chemical communications (Cambridge, England)》2005,(20):2594-2596
We report on the molecular interactions between room-temperature ionic liquids (RTILs) and Nafion and PDMS membranes, proving that in contact with these polymers RTILs behave like electrolytes rather than solvents. 相似文献
65.
Marcos Mandaji Tiago Buckup Rafael Rech Ricardo Rego Bordalo Correia Tarso Ledur Kist 《Talanta》2007,71(5):1998-2002
The performance of fluorescence detectors in capillary electrophoresis is maximized when the excitation light intensity is modulated in time with optimal frequencies. This is especially true when photomultiplier tubes are used to detect the fluorescent light. The photomultiplier tube amplified raw output signal can in principle be captured directly by a personal computer sound card (PCSC) and processed by a lock-in emulated by software. This possibility is demonstrated in the present work and the performance of this new setup is compared with a traditional data acquisition system. The results obtained with this “PCSC and lock-in emulated by software” were of the same quality or even better compared to that obtained by conventional time integrators (Boxcars) and data acquisition boards. With PCSC the limits of detection (LOD) found for both naphthalene-2,3-dicarboxaldehyde-derivatized tyrosine and alanine were 3.3 and 3.5 fmol (injection of 5 nL of samples at 0.66 and 0.70 μmol/L), respectively. This is at least three times better compared to conventional systems when light emitting diodes (LEDs) are used as the excitation source in fluorescence detectors. The PCSC linear response range was also larger compared to conventional data acquisition boards. This scheme showed to be a practical and convenient alternative of data acquisition and signal processing for detection systems used in capillary electrophoresis. 相似文献
66.
Chromatographic evaluations of a C18 dimethylurea phase in 150 mm x 3.9 mm HPLC columns were performed using the Tanaka and Engelhardt test mixtures. The applicability of the new C18 dimethylurea phase was also evaluated with a mixture of some herbicides and their metabolites. An artificial aging procedure was also performed by passing a potassium phosphate mobile phase buffered at pH 7.0 through C18 50 mm x 3.9 mm dimethylurea columns. The column stability was evaluated by means of the chromatographic parameters obtained for the separation of some compounds from the Neue test mixture, using apolar, polar and highly basic analytes. 相似文献
67.
Diego R. Pérez Susana H. Tarulli Oscar V. Quinzani Dr. Jorge Dristas Ricardo Faccio Leopoldo Suescun Alvaro W. Mombrú 《无机化学与普通化学杂志》2007,633(7):1066-1073
Four new lead(II) thiosaccharinate complexes: [Pb(tsac)2H2O] (1) (tsac: thiosaccharinate anion), [Pb2(tsac)4(py)4] (2) (py: pyridine), [Pb(tsac)(o‐phen)2](tsac)·CH3CN (3) (o‐phen: 1,10‐phenantroline), and [Pb(tsac)2(bipy)] (4) (bipy: 2,2′‐bipyridine) were prepared. The infrared and electronic spectra as well as the thermal analysis of all the compounds were recorded and discussed. The thiosaccharinate anion acts in three different coordination forms, one of then reported for the first time. The crystal structures of complexes 2 and 3 have been determined by single crystal X‐ray diffractometry. In complex 2 , two monomeric moieties are joined together forming a symmetric bis‐μ‐sulphur bridged dimer by interaction of two lead(II) atoms through the exocyclic sulphur atoms of two thiosaccharinate ligands. The seven‐fold coordination sphere of each lead atom is completed by two pyridine nitrogen atoms and by another sulfur and two nitrogen atoms of the thiosaccharinate anions. In complex 3 , the lead(II) atom is coordinated by four nitrogen atoms of two 1,10‐phenantroline molecules and by the sulfur and nitrogen atoms of one thiosaccharinate ion. The second anion has an electrostatic interaction with the nucleus. 相似文献
68.
Development of a bionematicide with Paecilomyces lilacinus to control Meloidogyne incognita 总被引:1,自引:0,他引:1
Brand D Roussos S Pandey A Zilioli PC Pohl J Soccol CR 《Applied biochemistry and biotechnology》2004,118(1-3):81-88
Root-knot disease caused by Meloidogyne incognita is a matter of grave concern because it affects several economically important crop plants. The use of solid-state fermentation
(SSF) may help to elaborate efficient formulations with fungi to be employed in the biologic control of nematodes. Attempts
were made to select low-cost substrates for spore production of a strain of Paecilomyces lilacinus with known nematicide capacity. Coffee husks, cassava bagasse, and defatted soybean cake were utilized as substrates, and
sugarcane bagasse was used as support. Fermentations were carried out in flasks covered with filter paper at 28°C for 10 d.
The products obtained by SSF were evaluated for their nematicide activity in pot experiments containing one seedling of the
plant Coleus inoculated with the nematode M. incognita. The plants were evaluated 2 mo after inoculation. Fermented products showed a reduction in the number of nematodes. The
best results were obtained with defatted soybean cake, which showed almost 100% reduction in the number of nematodes; the
reduction with coffee husk was 80% and with cassava bagasse was about 60%. 相似文献
69.
A method for the analytical determination of sotolon [4,5-dimethyl-3-hydroxy-2(5H)-furanone], maltol [3-hydroxy-2-methyl-4H-pyran-4-one] and free furaneol [2,5-dimethyl-4-hydroxy-3(2H)-furanone] in wine has been developed. The analytes are extracted from 50 ml of wine in a solid-phase extraction cartridge filled with 800 mg of LiChrolut EN resins. Interferences are removed with 15 ml of a pentane-dichloromethane (20:1) solution, and analytes are recovered with 6 ml of dichloromethane. The extract is concentrated up to 0.1 ml and analyzed by GC-ion trap MS. Maltol and sotolon were determined by selected ion storage of ions in the m/z ranges 120-153 and 79-95, using the ions m/z 126 and 83 for quantitation, respectively. Furaneol was determined by non-resonant fragmentation of the m/z 128 mother ion and subsequent analysis of the m/z 81 ion. The detection limits of the method are in all cases between 0.5 and 1 microg l(-1), well below the olfactory thresholds of the compounds. The precision of the method is in the 4-5% range for levels in wine around 20 microg l(-1). Linearity holds at least up to 400 microg l(-1), and is satisfactory in all cases. The recoveries of maltol and sotolon are constant (70 and 64%, respectively) and do not depend on the type of wine. On the contrary, in the case of furaneol, red wines show constant and high recoveries (97%), while the recoveries on white wines range between 30 and 80%. Different experiments showed that this behavior is probably due to the existence of complexes formed between furaneol and sulphur dioxide or catechols. Sensory experiments confirmed that the complexed forms found in white wines are not perceived by orthonasal olfaction, and that the furaneol determined by the method can be considered as the free and odor-active fraction. 相似文献
70.
H. Oliveira E. A. N. Fernandes E. S. B. Ferraz 《Journal of Radioanalytical and Nuclear Chemistry》1997,217(1):125-129
The elemental composition of pine trees as a function of age was achieved by the tree-ring method. By using instrumental neutron activation analysis, trace elements were determined in individual rings ofPinus elliottii var.elliottii of 32, 14 and 9 years, from an implanted forest ofPinus sp., Buri, São Paulo, far away from industrial pollution. Different components of the system such as needles, pith, bark, soil and litter were also analyzed for 18 elements (As, Br, Ce, Co, Cs, Eu, Fe, Hf, K, La, Mn, Na, Rb, Sc, Sm, Yb, Zn, and Zr). Al, B, Ba, Ca, Fe, K, Mg, and P concentrations were determined by atomic absorption and/or emission spectrometry (AAS; ICP-AES). Some elements have showed similar radial distribution of the concentration for the three ages. Abrupt concentration changes in the pith and ring-bark boundary corresponding to the first and last growth rings were observed. 相似文献