全文获取类型
收费全文 | 26357篇 |
免费 | 608篇 |
国内免费 | 158篇 |
专业分类
化学 | 17703篇 |
晶体学 | 219篇 |
力学 | 664篇 |
综合类 | 1篇 |
数学 | 4453篇 |
物理学 | 4083篇 |
出版年
2021年 | 178篇 |
2020年 | 218篇 |
2019年 | 290篇 |
2018年 | 234篇 |
2017年 | 210篇 |
2016年 | 445篇 |
2015年 | 355篇 |
2014年 | 463篇 |
2013年 | 1333篇 |
2012年 | 1205篇 |
2011年 | 1521篇 |
2010年 | 787篇 |
2009年 | 630篇 |
2008年 | 1385篇 |
2007年 | 1431篇 |
2006年 | 1418篇 |
2005年 | 1426篇 |
2004年 | 1251篇 |
2003年 | 1045篇 |
2002年 | 1025篇 |
2001年 | 377篇 |
2000年 | 306篇 |
1999年 | 251篇 |
1998年 | 300篇 |
1997年 | 320篇 |
1996年 | 400篇 |
1995年 | 300篇 |
1994年 | 286篇 |
1993年 | 290篇 |
1992年 | 279篇 |
1991年 | 246篇 |
1990年 | 228篇 |
1989年 | 245篇 |
1988年 | 269篇 |
1987年 | 255篇 |
1986年 | 248篇 |
1985年 | 386篇 |
1984年 | 437篇 |
1983年 | 324篇 |
1982年 | 429篇 |
1981年 | 404篇 |
1980年 | 344篇 |
1979年 | 332篇 |
1978年 | 348篇 |
1977年 | 331篇 |
1976年 | 276篇 |
1975年 | 271篇 |
1974年 | 263篇 |
1973年 | 240篇 |
1972年 | 144篇 |
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
401.
Fackler JP 《Inorganic chemistry》2002,41(26):6959-6972
Inorganic chemistry became a passion for me as a graduate student in the 1950s. It was exciting to be part of the renaissance of the discipline, and I am pleased to have contributed to its strength. Physical concepts applied to the understanding of the properties of transition metal compounds guided our work initially. In the 1970s, probably as a direct result of the world abandoning the gold standard, the chemistry of gold was awakened after a long sleep. Much of the chemistry covered in this review of our work relates to novel compounds of gold and the properties they display which have been uncovered during the last 25 years of the 20th century. Stable metal-metal bonded Au(II) and organometallic Au(III) compounds, bi- and trimetallic oxidative addition, phosphorescent species with microsecond lifetimes, gold chains resulting from aurophilic bonding stronger than H-bonding, and recently, gold binding to organic pi acids have intrigued my group and other gold chemists during this period. 相似文献
402.
The effect of ultrasonic irradiation (45KHz at 25°C) on the solvolysis of -butyl chloride in aqueous ethanol, -propanol and -butanol is (1) to increase the rate constants in the more alcoholic media and (2) to reduce the m values of these reactions. 相似文献
403.
Electron micrographs of parallel arrays of negatively stained ramie cellulose protofibrils were analyzed using the two-dimensional digital autocorrelation function (ACF). The method is based upon the statistical analysis of images in real space. The ACF shows strong parallel streaks of high correlation, and the lateral distance between adjacent streaks allows the mean interfibrillar distance to be estimated as 3.7 nm. The intensity profile along the streaks shows a weak modulation with peaks occurring at integral multiples of 3 or 6 nm. These results provide direct evidence that there is a regular axial texture in the protofibrils, and corroborate the conclusions previously drawn from optical diffraction analysis. Using the difference vectors found in the ACF it has been possible to reduce the picture noise level by linear integration, thereby obtaining an enhanced image. A preliminary result obtained in this way suggests that the projected protofibril morphology associated with the observed axial periodicity is a ribbon-like zigzag structure. Possible applications of the method for future work are discussed. 相似文献
404.
Robin L. Garrell John C. Smyth Frank R. Fronczek Richard D. Gandour 《Journal of inclusion phenomena and macrocyclic chemistry》1988,6(1):73-78
Single crystal X-ray analysis of the 2:1 acetonitrile complex of 18-crown-6 is reported. Crystals of the complex are monoclinic,P21/n, witha=9.123(3),b=8.524(3),c=13.676(4) Å, =104.68(3)°, andD
c
=1.118 g cm–3 forZ=2. The complex lies on a center of symmetry, with the crown in theD
3d conformation. Methyl groups of the acetonitrile molecules have weak interactions with the crown oxygen atoms, and are tilted 31.7° from the host's threefold axis. Methyl hydrogen atoms are rotationally disordered about the acetonitrile axis.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82057 (12 pages). 相似文献
405.
The synthesis and characterisation of five newβ-aminodiketones is reported: (a) 3,3,5,8,10,10-hexamethyl-5,8-diazadodecane-2,11-dione; (b) 3,3,11,11-tetramethyl-5,8-diazatridecane-2,12-dione;
(c) 3,3,12,12-tetramethyl-5,10-diazatetradecane-2,13-dione; (d) 3,3,10,10-tetramethyl-5,8-diphenyl-5,8-diazadodecane-2,11,dione
and (e) 6,7-benzo-3,3,10,10-tetramethyl-5,8-diazadodecane-2,11-dione. These compounds are discussed as potential precursors
in the synthesis of tetra-aza macrocyclic complexes. 相似文献
406.
Bacillus thuringiensis and recombinant Escherichia coli proteinaceous protoxins were subject to proteolysis and analyzed by capillary electrokinetic chromatography. Three resulting toxins (65 kDa) were baseline-resolved within 22 min using a 10 mM borate, pH 11 separation buffer consisting of 25 mM sodium dodecyl sulfate (SDS) and 30 mM phytic acid. The toxins displayed differential interactions with the SDS and phytic acid phases to effect their separation. The ion-pairing interaction between the analyte and phytic acid was also useful in preventing adsorption to the capillary walls and thus enhanced separation resolution and efficiency. The use of electrokinetic chromatography allows achievement of the separation in a significantly shorter time than conventional high-performance liquid chromatography (HPLC) using a diethylaminoethyl (DEAE) weak-anion exchanger. 相似文献
407.
The title compounds were synthesised and characterised as part of a study into new aromatic amines for charge transporting materials. Compounds 12-16, 20-24 and 27-34 are alkene linked triarylamines, compounds 35-36 are hydrazone derivatives and compounds 38-41 are pyrrole substituted triarylamines. Each compound was characterised by cyclic voltammetry. 相似文献
408.
Bedford RB Bruce DW Frost RM Goodby JW Hird M 《Chemical communications (Cambridge, England)》2004,(24):2822-2823
Iron(III) salen and related complexes are active catalysts for the coupling, under mild and simple reaction conditions, of aryl Grignard reagents with primary and secondary alkyl halide substrates bearing beta-hydrogens. 相似文献
409.
The study presented here describes an innovative approach for the detection of surface-confined proteins using chiral second harmonic generation (C-SHG). A unique optical geometry has been employed which allows for the separation of the chiral and achiral nonlinear response. By utilizing this optical arrangement, the detection of chirality originating from melittin adsorbed to a planar supported lipid bilayer has been performed for the first time by C-SHG. Melittin binding to the membrane was monitored as a function of bulk concentration through detection of the C-SHG signal. Analysis of the C-SHG adsorption isotherms reveals Frumkin adsorption behavior with a positive interaction energy. The binding constant (Ka) obtained was determined to be (8.3 +/- 1.0) x 105 M-1. The results of these studies have far-reaching implication in the use of C-SHG for the label-free detection of protein association to surfaces and in the analysis of protein interfacial phenomena. 相似文献
410.
Several related methods for the preparation of differentially substituted 2-thiofurans are described. The general procedure involves the formation of a thionium ion from a gamma-dithianyl substituted carbonyl compound followed by cyclization of this reactive intermediate onto the tethered carbonyl group. Two methods for thionium ion generation were explored. One of these involved an acid-catalyzed reaction of beta-ketenedithioacetals, prepared from the condensation of 2,2-bis(methylsulfanyl)acetaldehyde with a variety of ketones. Cyclization followed by loss of methane thiol gave 2-thiofurans 17, 18 and 23, 24 in 70-90% yield. Attempts to prepare 5-heteroatom substituted 2-thiofurans from the corresponding beta-ketenedithioacetal amides or esters were unsuccessful, leading to 1,2-thio rearranged products. A more successful route involved the reaction of beta-acetoxy-gamma-thianyl carbonyl compounds with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF). Treatment of the dithiane with this reagent resulted in the smooth generation of a thionium ion. Cyclization followed by loss of acetic acid afforded thiofurans 17, 18, 23, 47-49, 51, and 61-64 in 40-100% yield. The N-butenyl substituted thioamido furan furnished a rearranged hexahydropyrroloquinolin-2-one in high yield when heated at 110 degrees C. 相似文献