全文获取类型
收费全文 | 9190篇 |
免费 | 451篇 |
国内免费 | 393篇 |
专业分类
化学 | 4767篇 |
晶体学 | 129篇 |
力学 | 315篇 |
综合类 | 42篇 |
数学 | 2888篇 |
物理学 | 1893篇 |
出版年
2023年 | 32篇 |
2022年 | 75篇 |
2021年 | 74篇 |
2020年 | 136篇 |
2019年 | 317篇 |
2018年 | 181篇 |
2017年 | 205篇 |
2016年 | 177篇 |
2015年 | 155篇 |
2014年 | 212篇 |
2013年 | 314篇 |
2012年 | 217篇 |
2011年 | 424篇 |
2010年 | 322篇 |
2009年 | 549篇 |
2008年 | 432篇 |
2007年 | 486篇 |
2006年 | 424篇 |
2005年 | 445篇 |
2004年 | 565篇 |
2003年 | 503篇 |
2002年 | 479篇 |
2001年 | 335篇 |
2000年 | 294篇 |
1999年 | 227篇 |
1998年 | 187篇 |
1997年 | 198篇 |
1996年 | 216篇 |
1995年 | 179篇 |
1994年 | 217篇 |
1993年 | 169篇 |
1992年 | 142篇 |
1991年 | 85篇 |
1990年 | 72篇 |
1989年 | 76篇 |
1988年 | 60篇 |
1987年 | 77篇 |
1986年 | 61篇 |
1985年 | 64篇 |
1984年 | 63篇 |
1982年 | 58篇 |
1981年 | 60篇 |
1980年 | 60篇 |
1979年 | 99篇 |
1978年 | 66篇 |
1977年 | 74篇 |
1976年 | 50篇 |
1975年 | 26篇 |
1974年 | 29篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
151.
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
152.
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
153.
一步室温固相化学反应合成纳米氨基酸杂多电荷转移配合物(HPhe)3PMo12O40·2H2O 总被引:3,自引:0,他引:3
以Keggin结构的钼磷酸(H3PMo12O40·13H2O)与苯丙氨酸(Phe)为原料,利用一步固相化学反应于室温合成了纳米氨基酸杂多电荷转移配合物(HPhe)3PMo12O40·2H2O,采用元素分析,IR,XRD,TEM,UV和循环伏安法等手段对其进行了结构表征及性质研究.结果表明,标题化合物纳米粒子为均匀的球状,粒径约为30~40nm.该化合物中杂多阴离子部分仍保持Keggin结构,但在钼磷酸与苯丙氨酸之间发生了显著的电荷转移. 相似文献
154.
The adsorption of ovalbumin, -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 -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 -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
155.
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
156.
Several aspects of past and current studies in the area of iminium salt photochemistry are discussed. Investigations of olefin-iminium salt photoaddition and photocyclization reactions are reviewed and conclusions about electron-transfer pathways for fluorescence quenching and reaction are discussed. The results of recent studies of alcohol and ether photoaddition to 2-phenyl-1-pyrrolinium salts are presented. These C-C bond forming processes occur in moderate yields to produce β-amino alcohol or ether products. In addition, alcohols and ethers serve as efficient quenchers of pyrrolinium salt fluorescence. Rate constants for quenching appear to be dependent upon both the oxidation potential of the alcohols and ethers and the availability of C-H bond α to oxygen. This data along with deuterium isotope effects on quenching combine to suggest a common mechanism for both fluorescence quenching and photoaddition. The nature of this mechanism is tested using the comparative quenching effeciencies of the tertiary alcohols t-butyl alcohol and 1,2,2-trimethyl-1-cyclopropanol. The latter alcohol having a weak C-C bond adjacent to the hydroxyl function quenches the fluorescence of 2-phenyl-1-pyrrolium salts at a rate two orders of magnitude greater than for t-butyl alcohol. The observations made are interpreted in terms of a sequential electron-proton transfer mechanism for quenching and photoaddition. Lastly, the relationship of iminium salt photochemical studies to other investigations of electron-transfer photochemistry is discussed. 相似文献
157.
Bhattacharya S Schiavone M Nayak A Bhattacharya SK 《Applied biochemistry and biotechnology》2005,120(3):159-167
Our laboratory has recently developed a device employing immobilized F0F1 adenosine triphosphatase (ATPase) that allows synthesis of adenosine triphosphate (ATP) from adenosine 5′-diphosphate and
inorganic phosphate using solar energy. We present estimates of total solar energy received by Earth’s land area and demonstrate
that its efficient capture may allow conversion of solar energy and storage into bonds of biochemicals using devices harboring
either immobilized ATPase or NADH dehydrogenase. Capture and storage of solar energy into biochemicals may also enable fixation
of CO2 emanating from polluting units. The cofactors ATP and NADH synthesized using solar energy could be used for regeneration
of acceptor d-ribulose-1,5-bisphosphate from 3-phosphoglycerate formed during CO2 fixation. 相似文献
158.
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 -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 -helices in micellar environments. The conformational transition from -helix to -sheet structure required moderate hydrophobicity and linear side chains. This conformational transition depended on the surfactant concentration. 相似文献
159.
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 -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
160.
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