全文获取类型
收费全文 | 135797篇 |
免费 | 1875篇 |
国内免费 | 537篇 |
专业分类
化学 | 60335篇 |
晶体学 | 1126篇 |
力学 | 7609篇 |
综合类 | 5篇 |
数学 | 41825篇 |
物理学 | 27309篇 |
出版年
2023年 | 394篇 |
2022年 | 604篇 |
2021年 | 829篇 |
2020年 | 886篇 |
2019年 | 917篇 |
2018年 | 11128篇 |
2017年 | 10904篇 |
2016年 | 7848篇 |
2015年 | 2476篇 |
2014年 | 2015篇 |
2013年 | 4057篇 |
2012年 | 7222篇 |
2011年 | 13665篇 |
2010年 | 7803篇 |
2009年 | 7915篇 |
2008年 | 9517篇 |
2007年 | 11410篇 |
2006年 | 2938篇 |
2005年 | 3877篇 |
2004年 | 3705篇 |
2003年 | 3812篇 |
2002年 | 2627篇 |
2001年 | 1522篇 |
2000年 | 1504篇 |
1999年 | 1039篇 |
1998年 | 883篇 |
1997年 | 784篇 |
1996年 | 999篇 |
1995年 | 693篇 |
1994年 | 733篇 |
1993年 | 703篇 |
1992年 | 671篇 |
1991年 | 586篇 |
1990年 | 614篇 |
1989年 | 523篇 |
1988年 | 512篇 |
1987年 | 495篇 |
1986年 | 470篇 |
1985年 | 594篇 |
1984年 | 567篇 |
1983年 | 441篇 |
1982年 | 448篇 |
1981年 | 452篇 |
1980年 | 410篇 |
1979年 | 379篇 |
1978年 | 348篇 |
1977年 | 332篇 |
1976年 | 340篇 |
1974年 | 296篇 |
1973年 | 329篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
P. Selucký N. V. Sistková J. Rais 《Journal of Radioanalytical and Nuclear Chemistry》1997,224(1-2):89-94
A new reagent for the highly selective extraction of cesium (e-1,7–2,2)4,8–8,4-(bis--o-phenylene)bisdicarbollidocobalt(1–)ate, [(C2B9H9)2(C6H4)2Co]–, abbreviated as BISPHECOSAN is described in this paper. The choice of organic solvent and solubilizer, dependence of distribution ratio of Cs+ on acidity and other parameters are studied. The extraction mechanism based on selective binding of Cs+ cation between two phenylene rings is presented and factors influencing the chemical stability of the reagent are determined. 相似文献
92.
J. Mikuski J. Moravec E. Ochab V. Šára 《Journal of Radioanalytical and Nuclear Chemistry》1981,62(1-2):83-90
The structure of the complex Ag·TBDTPP (tetrabutyl S-dithiopyrophosphate) formed in HNO3 medium was studied by IR and NMR methods. The complex is involved in the isomerization of TBDTPP in the presence of Ag+ and NO
3
−
ions. In the IR spectra, we observe the disappearance of P−O−P band and the occurrence of new absorption bands associated
with P−S−P and P=O bonds. The silver ion is coordinated to the thiophosphoryl group of the isomer molecule. The influence
of HNO3 concentration on complex formation is discussed. 相似文献
93.
Principles of two computer programs useful for the evaluation of heterogeneous kinetics are described.The first program ALANTA allows to obtain the non-isothermal kinetic curve from the shape of general DTA peak using the DTA-equation derived elsewhere1.The second program SQUEST determines the kinetic mechanism which is the most appropriate to a given non-isothermal kinetic curve and evaluates the corresponding kinetic parameters. The program decides between 19 kinetic models and uses both integral and differential methods of evaluation. 相似文献
94.
Zinc phosphites ZnPHO3·2.5 H2O, Zn2H2P3H3O9·H2O, Zn3H4P5H5O15·1.5 H2O, ZnH2H2P2H2O6 have been studied at higher temperatures and by X-rays and molecular spectroscopy. Hydrates ZnPHO3·2.5 H2O and Zn2H2P3H3O9·H2O, when heated, yield an anhydrous salt. Thermal decomposition of dihydrogen triorthophosphite and tetrahydrogen pentaorthophosphite leads, before oxidation of the anion, to a mixture of zinc phosphite ZnPHO3 and dihydrogen diorthophosphite ZnH2P2H2O6 and then after loss of water of constitution dihydrogen diorthophosphite converts to zinc diphosphite ZnP2H2O5. The results of the thermal decomposition study were confirmed by X-ray investigation. Anhydrous zinc dihydrogen triorthophosphite Zn2H2P3H3O9 and zinc diphosphite ZnP2H2O5 were hitherto unknown. Infrared spectra confirmed the existence of hydrogen bonding in all the phosphites studied and in the case of zinc phosphite ZnPHO3·2.5 H2O exhibited a symmetry decrease of the anion PHO3
2– from the point group C3v to Cs. In the crystal lattice of ZnPHO3·2.5 H2O hydrogen bonding by water molecules participates, with polyorthophosphites hydrogen bonding shares in the production of anions and in the case of their hydrates there is in addition hydrogen bonding by water molecules.
Mit 3 Abbildungen 相似文献
Mit 3 Abbildungen 相似文献
95.
The rapid gas chromatographic detection and determination of ethylene glycol in biological fluids is described. Phenylboronic acid in acetone was used for the esterification of glycol. The phenylboronates of ethylene glycol and 1,2-propylene glycol are not separated on a packed column of medium polarity (OV-17), but they can be separated on a non-polar column (OV-101). In both instances, 1,3-propylene glycol can be used as an internal standard. The method requires only 100 microliters of serum or urine and is suitable for trace analysis in an emergency toxicological laboratory. The utility of the method is demonstrated on two cases of human intoxication with ethylene glycol. 相似文献
96.
Oleg V. Mikhailov Marina A. Kazymova Tatyana A. Shumilova Galina A. Chmutova Svetlana E. Solovieva 《Transition Metal Chemistry》2005,30(3):299-304
The complexing process proceeding in the NiII–thiocarbohydrazide (H2N–H–NC(=S)–NH–NH2)–propanone triple system in EtOH solution and nickel(II)hexacyanoferrate(II) gelatin-immobilized matrix has been studied. It has been found that in the first case, template synthesis leading, as a minimum, to formation of three coordination compounds of NiII with (N,N,S,S)-donor tetradentate ligands having NiL1, NiL2 and NiL3compositions where L1 is 4,6,6-trimethyl-2,3,7,8-tetraazanonen-3-di(thiohydrazide)-1,9, L2 is 4,6,6,12-tetrametyl-1,9-dithio-2,3,7,8,10,11-hexaazatridekadien-3,11-hydrazide-1 and L3 is 2,8,10,10,16-pentamethyl-5,13-dithio-3,4,6,7,11,12,14,15-octaazaheptadekatrien-2,7,15 is observed, whereas in the gelatin-immobilized matrix, a complexing process in the system considered does not occur. 相似文献
97.
The influence of the buffering medium on the reaction of Hg(II) with Xylenol Orange has been studied. Amine-type compounds are complexed by Hg(II)/Xylenol Orange with a sharp hyperchromic effect on the reagent itself, at 590 nm, but complex formation of Hg(II)/Xylenol Orange in non-amine-type buffer, such as citric acid-phosphate, gives a hypochromic effect on Xylenol Orange at 580 nm. Hg(II) is determined at pH 7.5 in two ranges of concentration, 2-9 ppm in citrate buffer, measured at 580 nm ( = 2.50 x 10(4)), and 6-11 ppm in hexamine buffer, at 590 nm ( = 4.18 x 10(4)). 相似文献
98.
Bengt Wessln Anders Wirsn 《Journal of polymer science. Part A, Polymer chemistry》1975,13(11):2571-2580
Anionic polymerization of vinyl chloride has been studied. Of the organometallic compounds tested as initiators, only butyllithium was found to initiate polymerization. Polymerization in bulk at 0°C and with tert-butyllithium as initiator gave poly(vinyl chloride) in a yield of 38% with M n = 55,000. Tacticity of the anionic PVC was similar to that of conventional PVC prepared at similar temperatures. Anionic PVC was found to be less branched and more heat-stable than the conventional polymer. 相似文献
99.
Zusammenfassung Es wurden eine Reihe von Substitutionsreaktionen mit entwässertem K3[Cr(NCS)6] und aromatischen Aminen, ohne Verwendung von Lösungsmitteln, durchgeführt. Es wurde beobachtet, da die sehr schwachen Basen mit pK-Werten 14–16, wie die isomeren Mono- und Dinitro-aniline, die Anthranil- und Sulfanilsäuren, für diese Substitutionsreaktionen ungeeignet sind. Die Alkyl-anilinderivate, wie daso-, m- undp-Toluidin (pK=10–11) bilden dagegen leicht reineckesalzähnliche Verbindungen: Amin· H[Cr(Toluidin)2(NCS)4]. Die Zusammensetzung der neuen Komplexanionen wurde bei einer Reihe von doppelten Umsetzungsreaktionen mit den Chlorhydraten einiger heterocyclischen Aminen festgestellt.Für die Klärung einiger Strukturfragen wurden spektrophotometrische Untersuchungen im UV und IR durchgeführt und die thermische Stabilität bzw. der Mechanismus des Pyrolysenvorganges auf thermogravimetrischem Wege verfolgt.
Mit 8 Abbildungen 相似文献
Substitution reactions of anhydrous K3[Cr(NCS)6] with aromatic amines without applying of solvents were studied.It was observed, that the very weak bases (pK-values 14–16, e.g. isomeric mono- and dinitro-anilines, the anthranilic and sulfanilic acids) are unsuitable for substitution reactions. The alkylaniline derivates e.g.o-, m- andp-toluidine (pK=10–11) form easily reineckesalt analogous compounds: Amin· ·H[Cr(toluidine)2(NCS)4]·The formula of the 3 new complex anions: [Cr(toluidine)2 (NCS)4]- was established by preparative methods, with a series of double decomposition reactions, using chlorohydrates of some heterocyclic amines for this purpose. From spectroscopical investigations (UV and IR) some structural problems are resolved and discussed.The thermal stability and the mechanism of pyrolysis of these salts was studied by thermogravimetric analysis.
Mit 8 Abbildungen 相似文献
100.
Retention of strontium and promethium on hydroxides (hydrated oxides) and phosphates of iron and chromium prepared by the sol-gel method was studied. The sorption was determined under static conditions depending on the pH of the solution. The sorption isotherms and retention were investigated under dynamic conditions. 相似文献