全文获取类型
收费全文 | 5559篇 |
免费 | 93篇 |
国内免费 | 111篇 |
专业分类
化学 | 3135篇 |
晶体学 | 125篇 |
力学 | 203篇 |
综合类 | 35篇 |
数学 | 1198篇 |
物理学 | 1067篇 |
出版年
2023年 | 21篇 |
2022年 | 63篇 |
2021年 | 115篇 |
2020年 | 98篇 |
2019年 | 112篇 |
2018年 | 125篇 |
2017年 | 117篇 |
2016年 | 127篇 |
2015年 | 90篇 |
2014年 | 96篇 |
2013年 | 182篇 |
2012年 | 86篇 |
2011年 | 84篇 |
2010年 | 86篇 |
2009年 | 128篇 |
2008年 | 130篇 |
2007年 | 139篇 |
2006年 | 112篇 |
2005年 | 256篇 |
2004年 | 472篇 |
2003年 | 372篇 |
2002年 | 322篇 |
2001年 | 257篇 |
2000年 | 205篇 |
1999年 | 155篇 |
1998年 | 121篇 |
1997年 | 121篇 |
1996年 | 177篇 |
1995年 | 142篇 |
1994年 | 188篇 |
1993年 | 134篇 |
1992年 | 126篇 |
1991年 | 67篇 |
1990年 | 59篇 |
1989年 | 57篇 |
1988年 | 49篇 |
1987年 | 69篇 |
1986年 | 49篇 |
1985年 | 39篇 |
1984年 | 41篇 |
1982年 | 39篇 |
1981年 | 37篇 |
1980年 | 43篇 |
1979年 | 58篇 |
1978年 | 48篇 |
1977年 | 50篇 |
1976年 | 37篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 17篇 |
排序方式: 共有5763条查询结果,搜索用时 171 毫秒
111.
František Kopecký Božena Kopecká Pavol Kaclík 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):215-217
The solubility of nimodipine was measured in aqueous solutions of the following cyclodextrins: content/h214053r4t534605/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-cyclodextrin (content/h214053r4t534605/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-CD), hydroxypropyl-content/h214053r4t534605/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-CD (HP-content/h214053r4t534605/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-CD), content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin (content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD), random substituted methyl-content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD (M-content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD), three hydroxypropyl-content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CDs (HP-content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD) with mutually different average degree of substitution, and hydroxypropyl-content/h214053r4t534605/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-cyclodextrin (HP-content/h214053r4t534605/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-CD). From the determined linear solubility diagrams the values of the binding constant K11 of the inclusion complexes of nimodipine with the respective CDs were evaluated. The content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CDs efficiently solubilized sparingly soluble nimodipine, the highest value of K11 was found for M-content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD (1680 M-1), followed by content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD (550 M-1) and HP-content/h214053r4t534605/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CDs, where the higher degree of substitution lowered K11. Only slight solubilization of nimodipine was observed in the solutions of the content/h214053r4t534605/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-CDs and HP-content/h214053r4t534605/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-CD. 相似文献
112.
Yu. M. Evtushenko B. E. Zaitsev V. M. Ivanov K. M. Gitis 《Chemistry of Heterocyclic Compounds》2000,36(9):1054-1057
The reaction of maleic anhydride with 2-methylimidazole in acetonitrile and DMF is accompanied by the appearance of strong absorption bands in the visible part of the spectrum due to the formation of molecular complexes. In acetonitrile the reaction proceeds by two routes via the formation of an amide and the molecular complex. Phthalic anhydride reacts with 2-methylimidazole to give amide but not to form molecular complexes. 相似文献
113.
A new representative of hetarylketene aminals, ethyl 3,3-diamino-2-(2-p-tolylpyrimidin-4-yl)acrylate, was synthesized by the reaction ofp-toluamidine with the condensation product of dimethylformamide dimethyl acetal and the difluoroboron chelate of acetyl(ethoxycarbonyl)ketene (N-benzoyl)aminal. This synthesis is an example of pyrimidine ring assembly using the methodology based on transformations of chelate complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1638–1640, September, 1994.This research was partially supported by the International Science Foundation (Grant No. M5QOOO). 相似文献
114.
115.
The adsorption of ovalbumin, content/vg346089n13m2880/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-globulin, and lysozyme on uniform spherical hematite and chromium hydroxide particles in aqueous media has been studied as a function of the pH at a constant ionic strength. The uptake of ovalbumin and content/vg346089n13m2880/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-globulin was greatest at their isoelectric points and differed little at 10–2 and 10–3 mol dm–3 NaNO3. The adsorption of lysozyme was strongly influenced by the ionic strength.The deposition of ovalbumin on hematite in the presence of Mg (NO3)2 was significantly greater than that with NaNO3 under otherwise comparable conditions. Dialysis experiments with ovalbumin against magnesium nitrate solutions showed Mg2+ to be specifically bound to the protein.The shapes of isotherms indicated monolayer coverage for ovalbumin and multilayer coating for lysozyme for both adsorbents. The shapes of isotherms of content/vg346089n13m2880/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-globulin on hematite point to a rearrangement of the protein on the particle surface, while a monolayer was found on chromium hydroxide particles.Supported by the NSF Grant CHE-9108420Part of a Ph.D. thesis 相似文献
116.
Z. A. Starikova A. I. Yanovsky Yu. T. Struchkov S. V. Zubkov I. I. Seifullina 《Russian Chemical Bulletin》1996,45(9):2157-2162
The crystal structure of the product of the condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni2+ ion template, K[Ni(C15H10N5O4)] · DMF, has been studied. It was established that a planar Ni complex, consisting of isolated [NiL]– anions and solvated [K+ · DMF] cations, is formed. The negative charge of the anion is localized mainly on the O atoms of the nitro group. The nitroguanidine fragment of the ligand occurs in the tautomeric form, which was not reported previously.Deceased in 1995Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2273–2277, September, 1996. 相似文献
117.
An accurate primary Fourier transform infrared (FTIR) method for the determination of moisture in mineral and ester based lubricants has been developed based on the extraction of moisture into dry acetonitrile. FTIR evaluation of acetonitrile extracts from new and used lubricants as well as common lubricant additives and contaminants which might co-extract indicated that phenolic constituents interfered significantly with moisture measurements. By measuring moisture at 3676 cm−1 on the shoulder of the asymmetric OH stretching band, spectral interferences from extracted phenolic constituents were minimized. The spectra of calibration standards (0-2100 ppm), prepared by gravimetric addition of water to dry acetonitrile, were recorded in a 1000-μm CaF2 transmission flow cell and produced linear standard curves having an S.D. of ∼±20 ppm. Lubricant sample preparation involved the vigorous shaking (20 min) of a 1:1.5 (w/v) mixture of lubricant and dry acetonitrile, centrifugation to separate the phases, acquisition of the FTIR spectrum of the upper acetonitrile layer, and subtraction of the spectrum of the dry acetonitrile used for extraction. A Continuous Oil Analyzer and Treatment (COAT®) FTIR system was programmed to allow the automated analysis of acetonitrile extracts, and the methodology was validated by analyzing 58 new and used oils, independently analyzed by the Karl Fischer (KF) method. Linear regression of FTIR versus KF results for these oils produced a linear plot with a between-method S.D. of ±80 ppm. As implemented on the COAT® system, this FTIR method is capable of analyzing 72 acetonitrile extracts/h and provides a high-speed alternative to the KF titrimetric procedures for the determination of water in lubricants. 相似文献
118.
Junko Kuwahara Hideo Akisada Tamaki Kato Norikazu Nishino 《Colloid and polymer science》2005,283(7):747-752
A series of peptides containing various hydrophobic amino acids [methionine (Met), leucine (Leu), norleucine (Nle), phenylalanine (Phe), 2-aminooctanoic acid (Aoc), and 2-aminodecanoic acid (Ade)] were synthesized and their conformations were studied using circular dichroism (CD) spectroscopy in different solvents such as water, methanol, and aqueous solution of ammonium tetradecanesulfonate. Peptides containing hydrophobic amino acids with linear side chains formed content/rktjqutxh31x0n8e/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-sheets in water and methanol. Electrostatic interaction between the charged side chain (lysine) and a micelle consisting of an anionic surfactant, ammonium tetradecanesulfonate, is necessary for the formation of content/rktjqutxh31x0n8e/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-helices in micellar environments. The conformational transition from content/rktjqutxh31x0n8e/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-helix to content/rktjqutxh31x0n8e/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-sheet structure required moderate hydrophobicity and linear side chains. This conformational transition depended on the surfactant concentration. 相似文献
119.
Aránzazu Espina Enrique Jaimez Sergei A. Khainakov Camino Trobajo José R. García Julio Rodríguez 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(4):333-352
The intercalation of some amines (aniline, benzylamine, cyclohexylamine,piperidine, pyridine, pyrazine and piperazine) into content/p0743q6176344180/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-titaniumphosphate, Ti(HPO4)2×H2O,has been investigated by the batch method and/or by exposing the host to thevapour of the amines. The changes in the interlayer distance of the solidduring the intercalation process was followed by X-ray powder diffraction.The new intercalates were characterised by chemical and thermal analysis.Materials with a monolaminar and/or bilaminar arrangement of amine moleculesin the phosphate interlayer region are obtained depending on the nature ofthe amine. Due to steric hindrance, saturated phases are not obtained forall amines studied. The thermal decomposition of the intercalates (nitrogenatmosphere), takes place in three stages: dehydration, removal of amines andcondensation of the hydrogenphosphate to pyrophosphate groups. 相似文献
120.
Zur Synthese von fungizid wirksamen Isocamphanderivaten: Synthesen in der Isocamphanreihe, 34. Mitt.
Gerhard Buchbauer Helmut Spreitzer Margarete Kneidinger 《Monatshefte für Chemie / Chemical Monthly》1990,121(6-7):549-554
Summary Some esters of isocamphenilanic acid (4) have been prepared and tested for their fungicidal and insecticidal activity. Esters of various acids with isocamphanyl ethylalcohol (5) have also been synthesized and included in the fungicidal/acaricidal/insecticidal screening programme. All esters bear a geminal dimethyl group at C-3 of the bicyclus which is important because of its shielding effect. 相似文献