全文获取类型
收费全文 | 5898篇 |
免费 | 1168篇 |
国内免费 | 1832篇 |
专业分类
化学 | 4597篇 |
晶体学 | 228篇 |
力学 | 483篇 |
综合类 | 137篇 |
数学 | 872篇 |
物理学 | 2581篇 |
出版年
2024年 | 9篇 |
2023年 | 59篇 |
2022年 | 148篇 |
2021年 | 198篇 |
2020年 | 193篇 |
2019年 | 215篇 |
2018年 | 194篇 |
2017年 | 245篇 |
2016年 | 234篇 |
2015年 | 308篇 |
2014年 | 363篇 |
2013年 | 460篇 |
2012年 | 425篇 |
2011年 | 490篇 |
2010年 | 493篇 |
2009年 | 521篇 |
2008年 | 541篇 |
2007年 | 522篇 |
2006年 | 481篇 |
2005年 | 412篇 |
2004年 | 377篇 |
2003年 | 305篇 |
2002年 | 355篇 |
2001年 | 326篇 |
2000年 | 254篇 |
1999年 | 169篇 |
1998年 | 94篇 |
1997年 | 51篇 |
1996年 | 54篇 |
1995年 | 57篇 |
1994年 | 72篇 |
1993年 | 44篇 |
1992年 | 47篇 |
1991年 | 45篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有8898条查询结果,搜索用时 15 毫秒
51.
Yuanyuan Yu Dr. Guang Li Long Jiang Prof. Dr. Liansuo Zu 《Angewandte Chemie (International ed. in English)》2015,54(43):12627-12631
An indoxyl‐based strategy for the synthesis of indolines and indolenines via unprecedented aza‐pinacol and aza‐semipinacol rearrangements was developed. This method provides direct access to the core structures of several classes of indole alkaloids. The synthetic utility was demonstrated by the divergent synthesis of an array of functionalized polycyclic structures from a common intermediate and the formal total synthesis of the indoline natural product minfiensine. The reversed reactivity of indoxyl as a building block compared to that of indole offers a conceptually distinct disconnection strategy for indoline‐ and indolenine‐containing heterocycles and natural products. 相似文献
52.
53.
54.
Syntheses,Structures, and Magnetic Properties of Two Cobalt(II) Metal‐Organic Frameworks Based on Y‐shaped 3,5,4′‐Azobenzenetricarboxylic Acid and Different N‐donor Ligands 下载免费PDF全文
Yu‐Ting Yang Chang‐Zheng Tu Jiao‐Jiao Miao Jun‐Li Li Guang Chen Hong‐Ju Yin Fei‐Xiang Cheng 《无机化学与普通化学杂志》2015,641(15):2576-2580
Two metal‐organic frameworks, [Co2(ABTC)(bimh)(OH)] · 2H2O ( 1 ) and [Co3(ABTC)2(dimb)4]n ( 2 ) [H3ABTC = 3,4′,5‐azobenzenetricarboxylic acid, bimh = 1,1′‐(1,4‐hexanediy)bis(imidazole), dimb = 1,4‐bis(1H‐imidazol‐1‐yl)benzene], were prepared under solvothermal conditions and structurally characterized. Complex 1 demonstrates a complicated 3D (3,8)‐connected tfz‐d net with (43)2(46.617.85) topology. The framework of 2 can be classified as a rare 3D (3,6,6)‐connected net with the Schäfli symbol of (4.62)2(42.610.83)(44.610.8), and exhibits an intriguing self‐penetrating motif. Meanwhile, the thermal stabilities and magnetic properties for 1 and 2 were also probed. 相似文献
55.
Application of Löwdin's canonical orthogonalization method to the Slater‐type orbital configuration‐interaction basis set 下载免费PDF全文
We apply Löwdin's canonical orthogonalization method to investigate the linearly dependent problem arising from the variational calculation of atomic systems using Slater‐type orbital configuration‐interaction (STO‐CI) basis functions. With a specific arithmetic precision used in numerical computations, the nonorthogonal STO‐CI basis is easily linearly dependent when the number of basis functions is sufficiently large. We show that Löwdin's canonical orthogonalization method can successfully overcome such problem and simultaneously reduce the dimension of basis set. This is illustrated first through an S‐wave model He atom, and then the real two‐electron atoms in both the ground and excited states. In all of these calculations, the variational bound state energies of the two‐electron systems are obtained in reasonably high accuracy using over‐redundant STO‐CI bases, however, without using extended high‐precision technique. © 2015 Wiley Periodicals, Inc. 相似文献
56.
Shao‐Fu Yu Xiao‐Jun Huang Shu‐Na Fu Chun Wu Wen‐Cai Ye Guang‐Xiong Zhou 《Helvetica chimica acta》2015,98(9):1267-1272
One new lactone, cyclopentanepyrone A ( 1 ), and two new monoterpenoids, gardeterpenone A ( 2 ) and jasminoside V ( 3 ), were isolated from the fruits of Gardenia jasminoides var. radicans, along with four known monoterpenoids, 4 – 7 , which were isolated from this plant for the first time. The structures of the isolates were elucidated by extensive spectroscopic studies, including UV, IR, 1D‐ and 2D‐NMR, ESI‐MS, HR‐ESI‐MS, and CD experiments. 相似文献
57.
Wen‐Hao Chen Chang‐Ri Han Yang Hui Da‐Shuai Zhang Xin‐Ming Song Guang‐Ying Chen Xiao‐Ping Song 《Helvetica chimica acta》2015,98(5):724-730
Two new eremophilane‐type sesquiterpenoids, 1α‐hydroxyeremophila‐6,9,11‐trien‐8‐one ( 1 ), 4α‐hydroxyeremophila‐1,9‐diene‐3,8‐dione ( 2 ), and a new friedelane‐type triterpenoid, friedelane‐3α,16β‐diol ( 4 ), along with six known terpenoids, 3 and 5 – 9 , have been isolated from the stems of Drypetes congestiflora. Their structures and relative configurations were elucidated on the basis of detailed spectroscopic analyses and by comparison of their NMR data with those reported in the literature. All of the compounds, 1 – 9 , were isolated for the first time from this species. Compound 3 exhibited moderate cytotoxic activities against the A549 and B16F10 cell lines. 相似文献
58.
Structure and Absolute Configuration of Aspergilumamide A,a Novel Lumazine Peptide from the Mangrove‐Derived Fungus Aspergillus sp. 下载免费PDF全文
Cai‐Juan Zheng Lu‐Yong Wu Xiao‐Bao Li Xin‐Ming Song Zhi‐Gang Niu Xiao‐Ping Song Guang‐Ying Chen Chang‐Yun Wang 《Helvetica chimica acta》2015,98(3):368-373
A novel lumazine peptide, aspergilumamide A ( 1 ), as well as a known analog penilumamide ( 2 ), were isolated from the mycelia of a marine‐derived fungus Aspergillus sp. (33241), obtained from the mangrove Bruguiera sexangula var. rhynchopetala collected from the South China Sea. The structure of 1 was identified by comprehensive spectroscopic analysis, including 1D‐ and 2D‐NMR, ESI‐MS, and MS/MS experiments. The absolute configuration of 1 was determined by Marfey's method. 相似文献
59.
The Convenient Synthesis of 11‐Methyl‐3,8‐disubstituted‐12‐aryl‐3,4,7,8,9,12‐hexahydro‐1H‐chromeno[2,3‐b]quinoline‐1,10(2H)‐dione Derivatives 下载免费PDF全文
Guang‐Fan Han Li‐Jun Zhao Li‐Zhuang Chen Jia‐Wei Du Zhong‐Xia Wang 《Journal of heterocyclic chemistry》2015,52(4):1219-1225
The 2‐arylidene‐3‐oxobutanenitrile derivatives 2 were prepared by the Knoevenagel condensation between aldehydes and 3‐oxobutanenitrile 1 , which was obtained by acid hydrolysis of β‐aminocrotononitrile. 3‐Acetyl‐2‐amino‐4H‐chromen‐5(6H)‐one derivatives 3 were synthesized by reaction of 2‐arylidene‐3‐oxobutanenitrile 2 and 5‐substituted‐1,3‐cyclohexanedione in ethylene glycol. The 11‐methyl‐3,8‐disubstituted‐12‐aryl‐3,4,7,8,9,12‐hexahydro‐1H‐chromeno[2,3‐b]quinoline‐1,10(2H)‐dione derivatives 4 were obtained by Friedländer reaction of compounds 3 with 5‐substituted‐1,3‐cyclohexanedione, using p‐toluenesulfonic acid monohydrate as catalyst. The structures of all novel compounds were characterized by elemental analysis, IR, MS, and 1H NMR spectra. The crystal and molecular structure of compound 4f has been determined by single crystal XRD analysis. 相似文献
60.
基于三氧化钼易升华的特性,建立了一种纯化浓缩钼同位素试剂的新方法.采用天然丰度掺杂样品Synthetic-Mo对纯化过程中的氧化时间、样品加入量及真空蒸发温度等条件进行了优化.用高分辨等离子体质谱分析了样品中杂质的含量,计算得到纯化后95Mo和98Mo浓缩同位素试剂的纯度分别为99.992%和99.990%.通过多接收器等离子体质谱测定纯化前后样品中钼同位素的组成,δX/95Mo(X=92,94,96,97,98,100)值均在仪器测量精度(0.3‰)范围之内,未观察到明显的质量分馏现象.该方法能够满足校正质谱法对浓缩同位素试剂的要求,对建立高准确度的钼同位素丰度比测量方法具有重要意义. 相似文献