全文获取类型
收费全文 | 26779篇 |
免费 | 3019篇 |
国内免费 | 1763篇 |
专业分类
化学 | 19146篇 |
晶体学 | 230篇 |
力学 | 161篇 |
综合类 | 47篇 |
数学 | 76篇 |
物理学 | 11901篇 |
出版年
2024年 | 33篇 |
2023年 | 186篇 |
2022年 | 570篇 |
2021年 | 722篇 |
2020年 | 864篇 |
2019年 | 834篇 |
2018年 | 711篇 |
2017年 | 801篇 |
2016年 | 1285篇 |
2015年 | 1262篇 |
2014年 | 1274篇 |
2013年 | 2301篇 |
2012年 | 1616篇 |
2011年 | 1773篇 |
2010年 | 1475篇 |
2009年 | 1881篇 |
2008年 | 1766篇 |
2007年 | 1870篇 |
2006年 | 1722篇 |
2005年 | 1365篇 |
2004年 | 1170篇 |
2003年 | 1001篇 |
2002年 | 781篇 |
2001年 | 629篇 |
2000年 | 555篇 |
1999年 | 518篇 |
1998年 | 423篇 |
1997年 | 388篇 |
1996年 | 313篇 |
1995年 | 270篇 |
1994年 | 201篇 |
1993年 | 181篇 |
1992年 | 151篇 |
1991年 | 114篇 |
1990年 | 70篇 |
1989年 | 63篇 |
1988年 | 112篇 |
1987年 | 50篇 |
1986年 | 30篇 |
1985年 | 32篇 |
1984年 | 36篇 |
1983年 | 8篇 |
1982年 | 27篇 |
1981年 | 28篇 |
1980年 | 27篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1976年 | 10篇 |
1973年 | 11篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
901.
The high-resolution 1H and 13C NMR spectra of 1-vinylimidazole complexes with iron group metals were recorded. The contact coupling in these systems was
established in the 1H and 13C NMR spectra. The applicability of the NMR spectra transformed by long-range hyperfine coupling for elucidating the molecular
structure of the ligand was shown.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1430–1433, June, 2005. 相似文献
902.
A.?R.?MustafinaEmail author L.?S.?Kuznetsova A.?S.?Michailov V.?E.?Kataev A.?I.?Konovalov W.?D.?Habicher 《Journal of solution chemistry》2004,33(10):1257-1276
The complexation of a macrocycle containing thiopyrimidine and uracil moieties (M) with amino acids and some dicarboxylic acids was studied by pH-metric, UV-VIS, 1H NMR spectroscopy methods in chloroform, methanol, aqueous 1,4-dioxane, and biphasic water–chloroform media. The complexation of M with acids is too weak to solubilize them from the solid state into chloroform solutions containing M. The 1H NMR spectra and pH-metric data of aqueous 1,4-dioxane (80 vol.%) reveal the pH-dependent 1:1 binding between M and the acids studied. The protonation of M is not a prerequisite for binding of fumaric, succinic, o-phtalic acids and the series of amino acids, whereas binding of maleic acid requires the protonation of both thiopyrimidine moieties of M. Therefore,M·(H+)2 exhibits strong selectivity towards maleic acid in aqueous 1,4-dioxane and in biphasic water–chloroform media. 相似文献
903.
ESR spectra of binuclear copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones (H4L) [Cu2L·2Py], in which the coordination polyhedra are linked by the polymethylene chain with different lengths (from one to five units), were studied. The spectra of the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids exhibit weak exchange interactions between the paramagnetic sites. These interactions induce seven HFS lines from two equivalent copper nuclei with the constant 40·10–4 cm–1 in the ESR spectra of liquid solutions. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of the complex based on heptadioic acyldihydrazone contains the signal of four HFS lines with the constant 72·10–4 cm–1, which is common for the copper(ii) monomeric compounds. 相似文献
904.
We studied the interactions of nylon‐6 with water by following the Fourier transform infrared spectra of a hydrated thin film during dehydration. Very small changes in the spectra caused by the interactions were clearly revealed by the application of spectral subtraction. The water was found to interact with amide groups to form hydrogen bonds with non‐hydrogen‐bonded or free C?O and NH groups in the amorphous portion in the first hydration sphere. This was deduced from an analysis of minus and plus peaks appearing around the absorptions of the NH stretching, amide I band, and amide II bands in the difference spectra between the spectra during dehydration and the one at the most dehydration. The interactions of the amide groups with water were significantly stronger than the hydrogen bond between CO and NH in the crystalline portion, according to the magnitude of the frequency shift of relevant bands. Water, as the interacting counterpart, showed a distorted OH stretching absorption with two close peaks at about 3450 cm?1. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1722–1729, 2003 相似文献
905.
906.
M. Inguscio S. Marchetti A. Moretti F. Strumia 《International Journal of Infrared and Millimeter Waves》1982,3(1):97-116
The optoacoustic spectrum of CH3Br around 10 m band lines of a tunable cw waveguide CO2 laser is investigated. Several new infrared absorptions are observed and most of the correspond ing molecular transitions are assigned. Far infra red laser action is reported by pumping with the same CO2 laser: pump offsets are given using the Transferred Lambs dip (TLD) technique. A new FIR laser emission is obtained and assigned. An optoacoustic Laser Stark spectroscopy technique is used to investigate off resonance infrared tran sitions. 相似文献
907.
L. H. Johnston S. R. Raju G. R. Sudhakaran R. M. Lees 《International Journal of Infrared and Millimeter Waves》1982,3(4):517-527
Laser-Stark spectra have been observed for methyl alcohol using the 311 m line of the HCN laser. Partial assignments are presented for the three most distinctive structures in the spectra. The low field structure is clearly associated with a member of the J=2019qRa-type multiplet, and is tentatively identified as the k=13 A vt=0 transition. The other two structures originate from the 9382 E vt=0 transition, and from a member of the k= 65 A vt=1 Q branch, tentatively assigned as the J=32 member. 相似文献
908.
F. Meyer J. Dupré C. Meyer C. Lambeau M. De Vleeschouwer J. -G. Lahaye A. Fayt 《International Journal of Infrared and Millimeter Waves》1982,3(1):83-95
The 5 band of methylacetylene has been studied simultaneously by means of CO2 Laser Stark spectroscopy and high resolution infrared absorption spectroscopy (0.012 cm–1). The primary aim of this work was to assign all the Stark coïncidences. Effective vibration-rotation parameters and the dipole moment of the v5=1 state have been determined. 相似文献
909.
《Arabian Journal of Chemistry》2020,13(1):1198-1228
Vanadate and vanadium compounds exist in many environmental, biological and clinical matrices, and despite the need only limited progress has been made on the analysis of vanadium compounds. The vanadium coordination chemistry of different oxidation states is known, and the result of the characterization and speciation analysis depends on the subsequent chemistry and the methods of analysis. Many studies have used a range of methods for the characterization and determination of metal ions in a variety of materials. One successful technique is high performance liquid chromatography (HPLC) that has been used mainly for measuring total vanadium level and metal speciation. Some cases have been reported where complexes of different oxidation states of vanadium have been separated by HPLC. Specifically reversed phase (RP) HPLC has frequently been used for the measurement of vanadium. Other HPLC methods such as normal phase, anion-exchange, cation-exchange, size exclusion and other RP-HPLC modes such as, ion-pair and micellar have been used to separate selected vanadium compounds. We will present a review that summarizes and critically analyzes the reported methods for analysis of vanadium salts and vanadium compounds in different sample matrices. We will compare various HPLC methods and modes including sample preparation, chelating reagents, mobile phase and detection methods. The comparison will allow us to identify the best analytical HPLC method and mode for measuring vanadium levels and what information such methods provide with regard to speciation and quantitation of the vanadium compounds. 相似文献
910.