全文获取类型
收费全文 | 3533篇 |
免费 | 95篇 |
国内免费 | 20篇 |
专业分类
化学 | 2516篇 |
晶体学 | 30篇 |
力学 | 94篇 |
数学 | 488篇 |
物理学 | 520篇 |
出版年
2021年 | 19篇 |
2020年 | 33篇 |
2019年 | 39篇 |
2018年 | 28篇 |
2017年 | 30篇 |
2016年 | 60篇 |
2015年 | 57篇 |
2014年 | 61篇 |
2013年 | 185篇 |
2012年 | 173篇 |
2011年 | 222篇 |
2010年 | 103篇 |
2009年 | 84篇 |
2008年 | 210篇 |
2007年 | 215篇 |
2006年 | 192篇 |
2005年 | 179篇 |
2004年 | 184篇 |
2003年 | 142篇 |
2002年 | 122篇 |
2001年 | 35篇 |
2000年 | 30篇 |
1999年 | 29篇 |
1998年 | 30篇 |
1997年 | 39篇 |
1996年 | 49篇 |
1995年 | 48篇 |
1994年 | 53篇 |
1993年 | 43篇 |
1992年 | 33篇 |
1991年 | 34篇 |
1990年 | 42篇 |
1989年 | 34篇 |
1988年 | 44篇 |
1987年 | 44篇 |
1986年 | 40篇 |
1985年 | 77篇 |
1984年 | 54篇 |
1983年 | 54篇 |
1982年 | 66篇 |
1981年 | 56篇 |
1980年 | 61篇 |
1979年 | 42篇 |
1978年 | 36篇 |
1977年 | 40篇 |
1976年 | 25篇 |
1975年 | 27篇 |
1974年 | 35篇 |
1973年 | 32篇 |
1972年 | 12篇 |
排序方式: 共有3648条查询结果,搜索用时 15 毫秒
1.
Gary W. Breton Lauren A. Hahn Kenneth L. Martin 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(9):1208-1212
Tetrahydrotetrazoles are five‐membered‐ring heterocycles containing four contiguous saturated nitrogen atoms. Very few examples of such compounds have been reported in the literature. Our previous attempt at the synthesis of a member of this class of compound suggested that the N—N bonds may be more labile than expected. This finding raised the question as to whether the structures of any of the previously reported tetrahydrotetrazoles had been properly assigned. We have reproduced the synthesis of a reported tetrahydrotetrazole, namely 1,2‐di‐tert‐butyl 3‐phenyl‐1H,2H,3H,10bH‐[1,2,3,4]tetrazolo[5,1‐a]isoquinoline‐1,2‐dicarboxylate, C25H30N4O4, and have now confidently confirmed its structure via X‐ray crystallography. However, while sufficiently stable in the crystal phase, we discovered that it remains very labile in solution (having a half‐life of only 15 min at 20 °C in CDCl3). A tentative reaction pathway for its dissociation based on 1H NMR spectral evidence is provided. 相似文献
2.
Kamila B. Muchowska Dominic J. Pascoe Stefan Borsley Ivan V. Smolyar Ioulia K. Mati Catherine Adam Gary S. Nichol Kenneth B. Ling Scott L. Cockroft 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(34):14710-14716
Interactions between carbonyl groups are prevalent in protein structures. Earlier investigations identified dominant electrostatic dipolar interactions, while others implicated lone pair n→π* orbital delocalisation. Here these observations are reconciled. A combined experimental and computational approach confirmed the dominance of electrostatic interactions in a new series of synthetic molecular balances, while also highlighting the distance-dependent observation of inductive polarisation manifested by n→π* orbital delocalisation. Computational fiSAPT energy decomposition and natural bonding orbital analyses correlated with experimental data to reveal the contexts in which short-range inductive polarisation augment electrostatic dipolar interactions. Thus, we provide a framework for reconciling the context dependency of the dominance of electrostatic interactions and the occurrence of n→π* orbital delocalisation in C=O⋅⋅⋅C=O interactions. 相似文献
3.
4.
Durgesh V. Wagle Steven P. Kelley Gary A. Baker Kanishka Sikligar Jerry L. Atwood 《Angewandte Chemie (International ed. in English)》2020,59(21):8062-8065
A hexameric metal–organic nanocapsule is assembled from pyrogallol[4]arene units, which are stitched together with indium ions. This indium‐seamed capsule is the first instance of a M24L6 type hexameric coordination cage held together exclusively by trivalent metal ions. Explicitly, unlike previously reported pyrogallol[4]arene‐based metal‐seamed capsules, the current In3+ seamed capsule is entirely supported by O→In coordinate bonds. This work demonstrates the important proof of concept of the ability of pyrogallol[4]arene to react with metals in higher oxidation states to assemble into atomically‐precise hexameric coordination cages. As such, these results open up exciting avenues toward the assembly of previously unanticipated metal–organic capsules, for example offering inspiration for tackling metals exhibiting high valence states such as in the lanthanide and actinide series. 相似文献
5.
6.
Chris Lorenc Josep Saurí Arvin Moser Alexei V Buevich Antony J Williams R Thomas Williamson Gary E Martin Mark W Peczuh 《ChemistryOpen》2015,4(5):541-580
Invited for this month''s cover picture is the group of Professor Mark Peczuh at the University of Connecticut. The cover picture compares the rearrangement of a small molecule to the process of turning a stuffed animal inside out. The recycled, inside-out stuffed animals are both artistic and philosophically provocative. They capture the essence of the rearrangement reaction because the compounds themselves turn inside out over the course of the reaction, extending the diversity of products that can arise from simple starting materials. Small molecules often have functional groups with latent reactivity; under the appropriate conditions, those groups can react with other compounds (e.g., reagents) and also with other groups in the same molecule in an intramolecular reaction. The research team found that the epoxidation of some highly functionalized spiroketal compounds promoted rearrangements of their structures that turned them inside out. Some of the features of the products led them to use X-ray crystallography or a combination of computer-assisted structure elucidation, computation, and a new version of the 1,1-ADEQUATE NMR experiment to determine their structures. For more details, see the Communication on p. 577 ff. 相似文献
7.
8.
9.
10.
Impaction of spray droplets on leaves: influence of formulation and leaf character on shatter,bounce and adhesion 总被引:5,自引:0,他引:5
Gary J. Dorr Shuangshuang Wang Lisa C. Mayo Scott W. McCue W. Alison Forster Jim Hanan Xiongkui He 《Experiments in fluids》2015,56(7):143
This paper combines experimental data with simple mathematical models to investigate the influence of spray formulation type and leaf character (wettability) on shatter, bounce and adhesion of droplets impacting with cotton, rice and wheat leaves. Impaction criteria that allow for different angles of the leaf surface and the droplet impact trajectory are presented; their predictions are based on whether combinations of droplet size and velocity lie above or below bounce and shatter boundaries. In the experimental component, real leaves are used, with all their inherent natural variability. Further, commercial agricultural spray nozzles are employed, resulting in a range of droplet characteristics. Given this natural variability, there is broad agreement between the data and predictions. As predicted, the shatter of droplets was found to increase as droplet size and velocity increased, and the surface became harder to wet. Bouncing of droplets occurred most frequently on hard-to-wet surfaces with high-surface-tension mixtures. On the other hand, a number of small droplets with low impact velocity were observed to bounce when predicted to lie well within the adhering regime. We believe this discrepancy between the predictions and experimental data could be due to air layer effects that were not taken into account in the current bounce equations. Other discrepancies between experiment and theory are thought to be due to the current assumption of a dry impact surface, whereas, in practice, the leaf surfaces became increasingly covered with fluid throughout the spray test runs. 相似文献