全文获取类型
收费全文 | 10261篇 |
免费 | 1498篇 |
国内免费 | 1252篇 |
专业分类
化学 | 7933篇 |
晶体学 | 282篇 |
力学 | 262篇 |
综合类 | 95篇 |
数学 | 418篇 |
物理学 | 4021篇 |
出版年
2024年 | 24篇 |
2023年 | 133篇 |
2022年 | 415篇 |
2021年 | 386篇 |
2020年 | 475篇 |
2019年 | 401篇 |
2018年 | 340篇 |
2017年 | 340篇 |
2016年 | 490篇 |
2015年 | 444篇 |
2014年 | 484篇 |
2013年 | 836篇 |
2012年 | 511篇 |
2011年 | 602篇 |
2010年 | 527篇 |
2009年 | 551篇 |
2008年 | 572篇 |
2007年 | 702篇 |
2006年 | 680篇 |
2005年 | 544篇 |
2004年 | 512篇 |
2003年 | 430篇 |
2002年 | 360篇 |
2001年 | 268篇 |
2000年 | 289篇 |
1999年 | 234篇 |
1998年 | 207篇 |
1997年 | 208篇 |
1996年 | 174篇 |
1995年 | 124篇 |
1994年 | 127篇 |
1993年 | 91篇 |
1992年 | 106篇 |
1991年 | 67篇 |
1990年 | 58篇 |
1989年 | 55篇 |
1988年 | 42篇 |
1987年 | 36篇 |
1986年 | 30篇 |
1985年 | 33篇 |
1984年 | 22篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1974年 | 6篇 |
1972年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
E. A. Dikusar N. G. Kozlov V. I. Potkin T. D. Zvereva A. P. Yuvchenko M. P. Bei N. V. Kovganko 《Chemistry of Natural Compounds》2006,42(5):539-542
Previously unreported esters 1b–20b were synthesized from natural terpene alcohols, sterols, plant phenols, and camphar oxime (1a–20a) by reaction with o-carborane-C-carboxylic acid chloride.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 434–436, September–October, 2006. 相似文献
102.
From phasebarograms it is possible to construct phase diagrams. We show on example of the system Bi/Se/O how follow ternary sections from the total pressure measurements in equilibrium and how we can attribute the barogram of the ternary region Bi2Se3/Bi2O2Se/Se to the binary system Bi2Se3/Se. The knowledge of the ternary system Bi/Se/I and its coexistent pressure courses allow to followT-p-x conditions for the chemical transport of phases from this system. 相似文献
103.
GIAO/DFT evaluation of 13C NMR chemical shifts of selected acetals based on DFT optimized geometries
DFT/B3LYP calculations of the ground-state conformation of eight cyclic and acyclic acetals are presented and compared with experimental data. Results of single-point GIAO/DFT calculations at five different levels of theory show that isotropic shieldings need to be empirically scaled to achieve agreement with experimental chemical shifts. Statistical evaluation of data indicates that the most accurate prediction of 13C chemical shifts is achieved at the MPW1PW91/6-311G** level of theory. An empirical equation describing the relationship between delta values and shielding constants is postulated. This equation has been applied to the non-chair ground-state conformation of the six-membered acetonide and to the conformationally flexible benzodioxonine derivative. The agreement observed between the experimental and predicted chemical shifts shows that calculations at the MPW1PW91/6-311G** level of theory are adequate for addressing questions of conformation. 相似文献
104.
报道从中国南海网胰藻Hydroclathrus clathratus中分离得到3个单体化合物,经过MS,IR,1HNMR,13CNMR(DEPT),HMQC和HMBC等波谱技术鉴定为:(6R,7aS)-6-羟基-4,4,7a-三甲基-2,4,5,6,7,7a-六氢苯并呋喃-2-酮(1),1-(2-脱氧-β-D-呋喃核糖)-5-甲基-1,2,3,4-四氢嘧啶-2,4-二酮(2),尿嘧啶(3),并通过X射线单晶衍射实验确定化合物1的立体结构,其中化合物1是首次从自然界中分离得到. 相似文献
105.
106.
ISSIe山和W6flSChllh山子1960年首次用pdCI。和二苯基磷合成出黄色的二聚络合物,后被H。yieY*确认为具有pRZ的桥式结构.此后一系列该类结构的化合物被合成并引起了广泛的兴趣.磷可以和两个甚至多个金属原子络合构成多核金属络合物,在催化反应中有重要应用.磷原子存在多种电子态,其3d空轨道也能参与成键.P乃1的NMR谱是研究含磷化合物立体结构的有力工具.P-31与其它核素之间的耦合常数以及P-31的化学位移对阐明化合物的立体构象以及电子结构具有重要作用.近年来,West饲用计算机神经网络技术预测P-:if的化学位移,但仅… 相似文献
107.
Tingmin Wang Jerald S. Bradshaw Janet C. Curtis Peter Huszthy Reed M. Izatt 《Journal of inclusion phenomena and macrocyclic chemistry》1993,16(2):113-122
Significant - interaction is found in the complexes of (S, S)-dimethylpyridino-18-crown-6 with (R)- and (S)-[-(1-naphthyl)ethyl]ammonium perchlorate. This finding is supported by the1H NOESY NMR spectral technique, greater chemical shift changes of aromatic protons in both host and guest molecules upon complexation, and by molecular mechanics calculations. Because of the flexibility of the ligand, the tripod hydrogen bonding causes13C relaxation times of all periphery carbons to decrease without significant selectivity. Rotational energy barrier calculations of the methyl groups of the complexed ligand also show that the (S, S)-host-(R)-guest is the more stable complex. 相似文献
108.
DFT calculations have been performed to determine the isomer shift for a series of iron(II) clusters with nitrogen-containing ligands which serve as models of coordination units in Fe(II) complexes with 1,2,4-triazoles possessing a 1 A 1 ? 5 T 2 spin transition. Good agreement has been found between the theoretical and experimental values of the isomer shift for both low-and high-spin phases. Our calculations confirmed the hypothesis about relationship between the experimentally observed differences in the isomer shift for the low-spin phases of the complexes and variations of the Fe-N mean bond length. 相似文献
109.
110.