全文获取类型
收费全文 | 6404篇 |
免费 | 202篇 |
国内免费 | 168篇 |
专业分类
化学 | 3295篇 |
晶体学 | 125篇 |
力学 | 210篇 |
综合类 | 48篇 |
数学 | 1199篇 |
物理学 | 1124篇 |
无线电 | 773篇 |
出版年
2023年 | 34篇 |
2022年 | 139篇 |
2021年 | 152篇 |
2020年 | 132篇 |
2019年 | 136篇 |
2018年 | 141篇 |
2017年 | 150篇 |
2016年 | 162篇 |
2015年 | 137篇 |
2014年 | 154篇 |
2013年 | 239篇 |
2012年 | 146篇 |
2011年 | 150篇 |
2010年 | 134篇 |
2009年 | 176篇 |
2008年 | 170篇 |
2007年 | 181篇 |
2006年 | 150篇 |
2005年 | 292篇 |
2004年 | 503篇 |
2003年 | 395篇 |
2002年 | 353篇 |
2001年 | 279篇 |
2000年 | 230篇 |
1999年 | 163篇 |
1998年 | 133篇 |
1997年 | 127篇 |
1996年 | 182篇 |
1995年 | 154篇 |
1994年 | 194篇 |
1993年 | 139篇 |
1992年 | 129篇 |
1991年 | 71篇 |
1990年 | 60篇 |
1989年 | 57篇 |
1988年 | 49篇 |
1987年 | 70篇 |
1986年 | 50篇 |
1985年 | 40篇 |
1984年 | 41篇 |
1982年 | 39篇 |
1981年 | 38篇 |
1980年 | 44篇 |
1979年 | 58篇 |
1978年 | 48篇 |
1977年 | 50篇 |
1976年 | 37篇 |
1975年 | 11篇 |
1974年 | 14篇 |
1973年 | 17篇 |
排序方式: 共有6774条查询结果,搜索用时 31 毫秒
121.
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
122.
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
123.
R. M. Zolotar' A. I. Bykhovets S. K. Ananich N. V. Kovganko 《Chemistry of Natural Compounds》2002,38(2):164-166
The toxicity of steroid benzoates 4-10 for Colorado beetle (Leptinotarsa decemlineata Say.) larvae was studied by a contact-intestinal method. The most active growth and development regulator for this insect is 3-benzoyloxy-5-hydroxy-7-6-ketosteroid 9a. 相似文献
124.
Heinz Falk Gabriele Streßler Norbert Müller 《Monatshefte für Chemie / Chemical Monthly》1988,119(4):505-508
Using a specific force field model, relative stabilities of 2,2-bipyrrole and 2,2-furylpyrrole conformers as well as of prodigiosene tautomers, configurations, and conformations, are studied. 2,2-Bipyrrole adopts anantiperiplanar conformation in accord with other theoretical calculations and experimental findings. Its rotational barrier calculated by this method compares favourably to the one derived by other means. For the parent prodigiosene the (Z)sp,sp arrangement is found to be the most stable one. The two possible tautomers within its dipyrrin fragment do not show a significant energy difference. 相似文献
125.
作者调查了珠海市568名0~6岁健康儿童的发锌含量,结果表明,集体儿童的低锌发生率为59.1%,门诊儿童为72.04%,在珠海市儿童中低锌有较高的发生率。 相似文献
126.
Pentacoordinate complex cations of the general formula [(C6F5)2SbL3]3+ stabilized as solid salts in combination with tetraphenylborate (BPh4), tetrafluorobroate (BF4) anions, where L=DMSO, Ph3AsO, PyO, DMF, α-, β- and γ-picoline have been isolated. The newly formed complexes were characterized by elemental analysis, molar conductance measurements, solid-state IR and and NMR. From these results, a five-fold coordination around antimony was required. 相似文献
127.
A novel series of the formula NdSrNi1−xCuxO4−δ were synthesized for various values of x ranging from 0 to 1 in 1 atm of O2 gas flow using conventional solid-state methods and were characterized by powder X-ray diffraction and electrical resistivity measurements. The compounds have been shown to adopt the K2NiF4-type structure. The oxygen stoichiometry of the compounds was determined from thermo-gravimetric analysis (TGA). An analysis of the micro-structure of the neodymium strontium nickel copper oxide is described. All the samples were semi-conducting from room temperature down to 77 K. The effect of Cu2+ incorporation on the structural and electrical properties of NdSrNi1−xCuxO4−δ, 0?x?1, are discussed in terms of Jahn-Teller distortion of the (Ni/Cu)O6 octahedra and mixed valence character of copper. 相似文献
128.
Jiandong Zheng Xiaoguang Ren Yongji Song Guoliang Shen 《Reaction Kinetics and Catalysis Letters》2007,92(1):11-17
Manganese-substituted lanthanum hexaaluminates were prepared by the sol-gel method. The effect of water content on the catalyst
preparation was examined. Large water content caused a rapid decrease in the surface area. When the R (R is the mole ratio
of H2O/ Al(OC3H7)3) is equal to 1.5, the catalyst retains a specific surface area of 13.5 m2 g−1 and shows higher activity in CH4 combustion. 相似文献
129.
A cumulative selection procedure for choosing configuration functions for inclusion in CI calculations is described. The objective of the method is to obtain equal energy loss, relative to unselected calculations, for different states and different regions of the potential surface. Results obtained from calculations on the BH molecule indicate an overall advantage in comparison to the threshold selection procedure, particularly with regard to molecular geometry changes. 相似文献
130.
Langlet J. Claverie P. Pullman B. Piazzola D. Daudey J. P. 《Theoretical chemistry accounts》1977,46(2):105-116
The effect of water on the conformational preferences of acetylcholine has been studied within the discrete, the continuum and the combined discrete-continuum models described in parts I and II of this series. All the models lead to the conclusion that the trans-gauche form which is, following refined quantum-mechanical computations, the intrinsically preferred one and the one observed in the crystal of acetylcholine and of a number of analogues should remain also the preferred conformation in water. This result agrees with NMR studies. The results of the empirical discrete model used here compare favorably to those obtained by an ab initio super-molecule treatment. The continuum model utilized here represents a net improvement above such models utilized in other works. 相似文献