全文获取类型
收费全文 | 7501篇 |
免费 | 1375篇 |
国内免费 | 1175篇 |
专业分类
化学 | 5622篇 |
晶体学 | 112篇 |
力学 | 405篇 |
综合类 | 98篇 |
数学 | 920篇 |
物理学 | 2894篇 |
出版年
2024年 | 29篇 |
2023年 | 157篇 |
2022年 | 286篇 |
2021年 | 317篇 |
2020年 | 332篇 |
2019年 | 330篇 |
2018年 | 306篇 |
2017年 | 285篇 |
2016年 | 364篇 |
2015年 | 444篇 |
2014年 | 478篇 |
2013年 | 521篇 |
2012年 | 686篇 |
2011年 | 743篇 |
2010年 | 537篇 |
2009年 | 433篇 |
2008年 | 534篇 |
2007年 | 468篇 |
2006年 | 398篇 |
2005年 | 347篇 |
2004年 | 288篇 |
2003年 | 281篇 |
2002年 | 346篇 |
2001年 | 251篇 |
2000年 | 144篇 |
1999年 | 141篇 |
1998年 | 91篇 |
1997年 | 69篇 |
1996年 | 79篇 |
1995年 | 78篇 |
1994年 | 55篇 |
1993年 | 37篇 |
1992年 | 38篇 |
1991年 | 35篇 |
1990年 | 39篇 |
1989年 | 22篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Hai‐Yang Liu Hong‐Ping He Suo Gao Chang‐Xiang Chen Yue‐Mao Shen Xiao‐Jiang Hao 《Helvetica chimica acta》2006,89(5):1017-1022
Two new diterpenoids, pedunculatic acid A (= (4R,5α,7α)‐7‐ethoxy‐9β,13β‐dioxyabiet‐8(14)‐en‐18‐oic acid; 1 ) and pedunculatic acid B (= (4S,5α,12β)‐8β,14β‐epoxy‐12‐hydroxy‐11‐oxototaran‐19‐oic acid; 2 ), together with three known sesquiterpenoids, were isolated from the Chinese medicinal herb Callicarpa pedunculata R. Brown . Their structures were elucidated by spectroscopic analyses, including 1D‐ and 2D‐NMR, and by high‐resolution mass spectrometry. 相似文献
912.
Ming‐Zhong Wang Yan‐Yan Zhang Shun‐Lin Li Xiang‐Hai Cai Xiao‐Dong Luo 《Helvetica chimica acta》2006,89(12):3104-3108
A new norsesquiterpene named eupatorone (= (4S,4aR,6R)‐1‐acetyl‐6‐(acetyloxy)‐4,4a,5,6‐tetrahydro‐4,7‐dimethylnaphthalen‐2(3H)‐one; 1 ) and a new sesquiterpene derivative named 2‐deoxo‐2‐(acetyloxy)‐9‐oxoageraphorone (= (1R,4S,4aR,6R,8aS)‐6‐(acetyloxy)‐3,4,4a,5,6,8a‐hexahydro‐4,7‐dimethyl‐1‐(1‐methylethyl)naphthalen‐2(1H)‐one; 2 ), together with the five known cadinene derivatives 3 – 7 were isolated from the flower of Eupatorium adenophorum (Spreng. ). Their structures were established by extensive NMR experiments, including 1D and 2D NMR. 相似文献
913.
Yan Tang Hui‐Ran Yang Hui‐Bin Sun Prof. Shu‐Juan Liu Jing‐Xia Wang Prof. Qiang Zhao Dr. Xiang‐Mei Liu Dr. Wen‐Juan Xu Prof. Sheng‐Biao Li Prof. Wei Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1311-1319
Biothiols, such as cysteine (Cys) and homocysteine (Hcy), play very crucial roles in biological systems. Abnormal levels of these biothiols are often associated with many types of diseases. Therefore, the detection of Cys (or Hcy) is of great importance. In this work, we have synthesized an excellent “OFF‐ON” phosphorescent chemodosimeter 1 for sensing Cys and Hcy with high selectivity and naked‐eye detection based on an IrIII complex containing a 2,4‐dinitrobenzenesulfonyl (DNBS) group within its ligand. The “OFF‐ON” phosphorescent response can be assigned to the electron‐transfer process from IrIII center and C^N ligands to the DNBS group as the strong electron‐acceptor, which can quench the phosphorescence of probe 1 completely. The DNBS group can be cleaved by thiols of Cys or Hcy, and both the 3M LCT and 3LC states are responsible for the excited‐state properties of the reaction product of probe 1 and Cys (or Hcy). Thus, the phosphorescence is switched on. Based on these results, a general principle for designing “OFF‐ON” phosphorescent chemodosimeters based on heavy‐metal complexes has been provided. Importantly, utilizing the long emission‐lifetime of phosphorescence signal, the time‐resolved luminescent assay of 1 in sensing Cys was realized successfully, which can eliminate the interference from the short‐lived background fluorescence and improve the signal‐to‐noise ratio. As far as we know, this is the first report about the time‐resolved luminescent detection of biothiols. Finally, probe 1 has been used successfully for bioimaging the changes of Cys/Hcy concentration in living cells. 相似文献
914.
采用三维全息原子场作用矢量(3D-HoVAIF)对20个TIBO类衍生物抗艾滋病药物进行定量构效关系(QSAR)研究。运用偏最小二乘回归(Partial Least Square Regression,PLS)建模,同时采用内部及外部双重验证的办法对所得模型稳定性能进行深入分析和检验。PLS建模的复相关系数(Rcum)、留一法(Leave-one-out,LOO)交互校验(Cross-validation,CV)复相关系数(QCV)和外部样本校验复相关系数(Qext)分别为0.837、0.804、0.812。结果表明,3D-HoVAIF能较好表征TIBO类衍生物抗艾滋病药物分子结构信息, 相似文献
915.
基于第一性原理模拟, 我们构建了一种具有石墨烯电极的纳米间隙生物分子传感器件的理论模型. 研究发现,当碱基分子胞嘧啶、甲基化胞嘧啶和羟甲基化胞嘧啶分别通过器件时, 器件横向电流的大小差异约有1个数量级, 器件对此类分子具有一定的分辨能力. 分子之间的区分度大小受单链脱氧核糖核酸(DNA)中相邻碱基分子间的相互作用及碱基分子构型的影响. 研究工作表明, 此类石墨烯基分子传感器可准确高效地区分具有不同结构的碱基分子, 为准确定位DNA链中的变异碱基分子提出了一种新的思路. 相似文献
916.
半夹芯16e化合物CpCoS2C2B10H10(Cp:cyclopentadienyl)(1)与2-呋喃炔酮在物质的量比为1:1.5时反应分离得到1个顺磁性化合物CpCoS2C2B10H9(C12H10O2)(2)。在化合物2的合成过程中,一分子1中的Cp环与另一分子1中的B(3)/B(6)位连接;同时,该Cp环与1个2-呋喃炔酮分子发生Diels-Alder反应,生成1个双环[2.2.1]-2-庚烯基结构单元。此外,呋喃炔酮分子中的末端炔基碳原子与原料1中的1个硫原子相连,从而使得产物2中的钴中心离子是个17e中心。化合物2用红外、核磁、元素分析,质谱和单晶X-射线衍射分析等方法进行了表征。晶体属三斜晶系,空间群P1,晶胞参数:a=0.96657(11)nm,b=1.54423(15)nm,c=1.75650(18)nm,α=114.0800(10)°,β=105.433(2)°,γ=98.6390(10)°。 相似文献
917.
Two types of β‐enaminoketone derivatives of 3‐(2‐oxo‐2‐arylethylidene)‐3,4‐dihydro‐1H‐quinoxalin‐2‐ones and 3‐(2‐oxo‐2‐arylethylidene)‐3,4‐dihydro‐benzo[1,4]oxazin‐2‐ ones were effectively and conveniently prepared in good to excellent yields under solvent‐free conditions via the catalysis of sulfamic acid in the corresponding condensations of o‐phenylenediamine and o‐aminophenol with ethyl 2,4‐dioxo‐4‐arylbutyrate respectively. The compounds were confirmed by IR, 1H NMR, and 13C NMR, and a representative was further determined by X‐ray crystallography. 相似文献
918.
采用基于密度泛函理论的第一性原理计算方法, 研究了扶手椅型二硫化钼纳米带的几何构型与电子结构, 发现其稳定性与电子性质敏感地依赖于边缘修饰. 随着边缘修饰的H原子数增加, 纳米带变得更加稳定, 并在间接带隙半导体、半金属和直接带隙半导体之间转变. 纳米带的能带结构和电子态密度显示, 其费米能级附近的能带主要由边缘态贡献. 当二硫化钼纳米带两边用不同数目的H原子修饰时, 纳米带同时具有由这两种修饰引起的边缘态并且两种边缘态的相互影响很小. 研究了三类纳米带带隙与宽度的关系, 对于每个原胞修饰0个或8个H原子的纳米带, 带隙随宽度以3为周期振荡变化; 而对于每个原胞修饰4个H原子的纳米带, 带隙振荡不再具有周期并且振荡幅度变小. 相似文献
919.
Ying Chen Ping Xiang Gang Li Hui-Lan Chen Kandasamy Chinnakali Hoong-Kun Fun 《Supramolecular chemistry》2013,25(4):339-346
The crystal and molecular structures of alkylcobaloxime/ g -cyclodextrin ( g -CD) inclusion complexes: butyl(aqua)cobaloxime/ g -CD ( 1 ). hexyl(aqua)cobaloxime/ g -CD ( 2 ) and cyclohexyl(aqua)cobaloxime/ g -CD ( 3 ) were determined by X-ray diffraction analyses. Crystal data for 1 14H 2 O: P 2 1 2 1 2 1 , a =15.1335(3), b =18.9630(2), c =28.1545(5) Å, Z =4; 2 12H 2 O: P 2 1 2 1 2 1 , a =15.1135(4), b =19.1477(5), c =28.2715(7) Å, Z =4; 3 10H 2 O: P 2 1 2 1 2 1 , a =15.6898(2), b =16.9094(2), c =28.9762(2) Å, Z =4. The structural and conformational comparisons for the three g -CD inclusion complexes with their guest molecules as well as other CD inclusion analogs are discussed. 相似文献
920.
Lu Xiang Yunlong Zhu Shuai Gu Dongyang Chen Xian Fu Yindong Zhang Guipeng Yu Chunyue Pan Yuehua Hu 《Macromolecular rapid communications》2015,36(17):1566-1571
A hypercrosslinked conjugated microporous polymer (HCMP‐1) with a robustly efficient absorption and highly specific sensitivity to mercury ions (Hg2+) is synthesized in a one‐step Friedel–Crafts alkylation of cost‐effective 2,4,6‐trichloro‐1,3,5‐triazine and dibenzofuran in 1,2‐dichloroethane. HCMP‐1 has a moderate Brunauer–Emmett–Teller specific surface (432 m2 g−1), but it displays a high adsorption affinity (604 mg g−1) and excellent trace efficiency for Hg2+. The π–π* electronic transition among the aromatic heterocyclic rings endows HCMP‐1 a strong fluorescent property and the fluorescence is obviously weakened after Hg2+ uptake, which makes the hypercrosslinked conjugated microporous polymer a promising fluorescent probe for Hg2+ detection, owning a super‐high sensitivity (detection limit 5 × 10−8 mol L−1).