全文获取类型
收费全文 | 1045篇 |
免费 | 185篇 |
国内免费 | 100篇 |
专业分类
化学 | 711篇 |
晶体学 | 5篇 |
力学 | 85篇 |
综合类 | 2篇 |
数学 | 81篇 |
物理学 | 446篇 |
出版年
2024年 | 2篇 |
2023年 | 21篇 |
2022年 | 25篇 |
2021年 | 27篇 |
2020年 | 37篇 |
2019年 | 52篇 |
2018年 | 30篇 |
2017年 | 24篇 |
2016年 | 48篇 |
2015年 | 40篇 |
2014年 | 37篇 |
2013年 | 66篇 |
2012年 | 108篇 |
2011年 | 114篇 |
2010年 | 76篇 |
2009年 | 64篇 |
2008年 | 67篇 |
2007年 | 49篇 |
2006年 | 49篇 |
2005年 | 40篇 |
2004年 | 48篇 |
2003年 | 24篇 |
2002年 | 25篇 |
2001年 | 20篇 |
2000年 | 29篇 |
1999年 | 31篇 |
1998年 | 23篇 |
1997年 | 16篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1330条查询结果,搜索用时 15 毫秒
961.
Hughes H Allix MM Bridges CA Claridge JB Kuang X Niu H Taylor S Song W Rosseinsky MJ 《Journal of the American Chemical Society》2005,127(40):13790-13791
The perovskite Bi2Mn4/3Ni2/3O6 is polar and combines relative permittivity behavior consistent with ferroelectricity with the magnetic response of a concentrated spin-glass. Bi2Mn4/3Ni2/3O6 is accessible by ambient pressure synthesis despite the instability of the end-members BiMnO3 and BiNiO3 under these conditions. 相似文献
962.
Yanping He Yunyan Kuang Fener Chen Suxi Wang Lei Ji Erik De Clercq Jan Balzarini Christophe Pannecouque 《Monatshefte für Chemie / Chemical Monthly》2005,136(7):1233-1245
Summary. A series of 6-naphthylmethyl substituted HEPT analogues bearing a β-carbonyl and a terminal phenyl ring or ester groups on the N-1 side chain of uracil were synthesized, and the in vitro anti-HIV activity was evaluated. Most of these HEPTs were considerably less potent and selective or inactive, only a few compounds showed moderate or high activity against HIV-1. The results demonstrated that the anti-HIV-1 activity of 6-naphthylmethyl substituted HEPT analogues was diminished or eliminated when the β-oxygen of N-1 side chain was replaced by a carbonyl group. 相似文献
963.
钴系非晶合金超细微粒金属微观状态的研究 总被引:3,自引:0,他引:3
过渡金属(Fe、Co、Ni)一类金属(B、P)非品合金超细微粒催化剂金属-类金属的相互作用是影响其催化性能的重要因素.B、P组元的加入能显著地改变过渡金属的催化活性和催化选择性;许多研究者都认为在过渡金属与B、P之间存在化学键合作用且有电子的转移,但对电子转移的方向仍有争议.前文我们报导了CoB非晶态合金超细微粒催化剂的表面性质和催化性能问,以及掺入P后对CoB已非晶态合金超细微粒催化剂性能的影响.本文采用了乙烯加氢反应作为探针,通过测定金属Co和CoB、CoPB非晶态合金超细微粒催化剂的乙烯加氢反应活化能;获得了… 相似文献
964.
Bingyou Yang Qiuhong Wang Yonggang Xia Weisheng Feng Haixue Kuang 《Helvetica chimica acta》2007,90(8):1522-1528
Three new withanolide compounds named baimantuoluoline A ( 1 ), B ( 2 ), and C ( 3 ) and the two known withanolides withafastuosin E ( 4 ) and withametelin C ( 5 ) were isolated from the fraction exhibiting activity for psoriasis in the flower of Datura metel L. The three new structures were determined as (5α,6α,7α,12β,15β,22R)‐6,7‐epoxy‐5,12,15‐trihydroxy‐1‐oxowitha‐2,24‐dienolide ( 1 ), (5α,6β,15β,22R)‐ 5,6,15,21‐tetrahydroxy‐1‐oxowith‐24‐enolide ( 2 ), and (5α,6β,12β,22R)‐5,6,12,21‐tetrahydroxy‐27‐methoxy‐1‐oxowitha‐2,24‐dienolide ( 3 ) on the basis of extensive spectroscopic data (HR‐ESI‐MS, 1H‐ and 13C‐NMR, 1H,1H‐COSY, HSQC, HMBC, and NOESY) (withanolide=22‐hydroxyergostan‐26‐oic acid δ‐lactone). 相似文献
965.
烯丙醇电还原自由基中间产物的ESR研究张敬东,旷亚非,黄树坤,谢乃贤(湖南大学化学化工系,长沙410082)汪风珍,陈德文(中南工业大学测试中心,长沙410083)(中国科学院化学研究所,北京100080)Horanyi[1]、陈剑[2]等人对酸性水... 相似文献
966.
Electrospinning has been used to obtain poly(methyl methacrylate) (PMMA) microfibers and nanofibers and PMMA/vapor grown carbon nanofibers (VGCNFs or CNFs) composite fibers with micrometer and nanometer size diameters. Thermogravimetric analysis (TGA) indicated that addition of CNFs caused a decrease in the thermal stability of the composite fibers. Scanning electron microscopy (SEM) was used to confirm the micro‐ and nano‐ nature of the fibers and transmission electron microscopy (TEM) was utilized to confirm the presence of CNFs embedded within the polymer matrix and along the surface. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
967.
Three new iridoid glycosides, hedycorysides A–C ( 1 – 3 , resp.), were isolated from the whole plant of Hedyotis corymbosa (Linn .) Lam ., along with four known compounds. Their structures were elucidated by extensive 1D‐ and 2D‐NMR analysis, as well as by HR‐ESI‐MS experiments. The three new compounds are the first benzoylated geniposide derivatives from Hedyotis. 相似文献
968.
969.
4-(2-Benzothiazolylazo)pyrocatechol (BTAPC), a new organic reagent, reacts with Fe(II) to form a stable, water-soluble, violet, positively charged, binary complex over a pH range of 6.3 to 6.8. Some water-miscible organic solvents and surfactants have solubilization and sensibilization effects. In 40% acetone-water medium at 25 °C, a (ionic strength) value of 0.1 and a pH value of 6.5, the ratio of Fe(II) to BTAPC in the complex is 1 2 with an apparent stability constant of 1.97 × 109 and two absorption peaks at 535 and 615 nm. If the absorbance is measured at 615 nm, not only the sensitivity is high (615 = 1.10 × 105 1 · mol–1 · cm–1) and the contrast () is large (90 nm), but also the selectivity is fairly good. Beer's law is obeyed for iron along the range of 0 to 16 g per 25 ml. The satisfactory results have been achieved after applying the method to the determination of traces of iron in water. 相似文献
970.
The substitution of the mu-acetato ligands in cis-Re(2)(mu-O(2)CCH(3))(2)Cl(2)(mu-dppm)(2) (1, dppm = Ph(2)PCH(2)PPh(2)) and trans-Re(2)(mu-O(2)CCH(3))(2)Cl(2)(mu-dppE)(2) (2, dppE = Ph(2)PC(=CH(2))PPh(2)) by [4-Ph(2)PC(6)H(4)CO(2)](-) occurs with retention of stereochemistry to give cis-Re(2)(mu-O(2)CC(6)H(4)-4-PPh(2))(2)Cl(2)(mu-dppm)(2) (3) and trans-Re(2)(mu-O(2)CC(6)H(4)-4-PPh(2))(2)Cl(2)(mu-dppE)(2) (6), respectively. The uncoordinated phosphine groups in complexes 3 and 6 have been used to form mixed-metal assemblies with Au(I) and Pd(II), including the Re(2)Pd(2) complex cis-Re(2)(mu-O(2)CC(6)H(4)-4-PPh(2))(2)Cl(2)(mu-dppm)(2)(Pd(2)Cl(4)) (5), in which the planar [(P)ClPd(mu-Cl)(2)PdCl(P)] unit has the unusual cis structure. The crystal structures of 3 and 5 have been determined. 相似文献