全文获取类型
收费全文 | 41006篇 |
免费 | 6381篇 |
国内免费 | 5788篇 |
专业分类
化学 | 30304篇 |
晶体学 | 536篇 |
力学 | 2430篇 |
综合类 | 509篇 |
数学 | 4504篇 |
物理学 | 14892篇 |
出版年
2024年 | 72篇 |
2023年 | 594篇 |
2022年 | 1046篇 |
2021年 | 1286篇 |
2020年 | 1435篇 |
2019年 | 1428篇 |
2018年 | 1214篇 |
2017年 | 1116篇 |
2016年 | 1806篇 |
2015年 | 1895篇 |
2014年 | 2235篇 |
2013年 | 3002篇 |
2012年 | 3484篇 |
2011年 | 3748篇 |
2010年 | 2614篇 |
2009年 | 2527篇 |
2008年 | 2867篇 |
2007年 | 2563篇 |
2006年 | 2440篇 |
2005年 | 2043篇 |
2004年 | 1843篇 |
2003年 | 1502篇 |
2002年 | 1602篇 |
2001年 | 1310篇 |
2000年 | 1105篇 |
1999年 | 907篇 |
1998年 | 673篇 |
1997年 | 639篇 |
1996年 | 574篇 |
1995年 | 543篇 |
1994年 | 489篇 |
1993年 | 417篇 |
1992年 | 416篇 |
1991年 | 322篇 |
1990年 | 287篇 |
1989年 | 239篇 |
1988年 | 144篇 |
1987年 | 136篇 |
1986年 | 121篇 |
1985年 | 119篇 |
1984年 | 70篇 |
1983年 | 62篇 |
1982年 | 50篇 |
1981年 | 39篇 |
1980年 | 25篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
12.
13.
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes 下载免费PDF全文
Prof. Biao Wu Dr. Shaoguang Li Prof. Yibo Lei Prof. Huaiming Hu Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Jennifer S. Mathieson Dr. De‐Liang Long Prof. Leroy Cronin Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2588-2593
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes. 相似文献
14.
Sulfur hexafluoride (SF6) is considered as a potent greenhouse gas, whose effective degradation is challenging. Here we report a computational study on the nucleophilic activation of sulfur hexafluoride by N-heterocyclic carbenes and N-heterocyclic olefins. The result shows that the activation of SF6 is both thermodynamically and kinetically favorable at mild condition using NHOs with fluoro-substituted azolium and sulfur pentafluoride anion being formed. The Gibbs free energy barrier during the activation of SF6 has a linear relationship with the energy of HOMO of substrates, which could be a guideline for applying those compounds that feature higher energy in HOMO to activate SF6 in high efficiency. 相似文献
15.
S. Q. Hou W. Wang Z. Y. Wang Z. W. Hu K. Liu 《Journal of Applied Mechanics and Technical Physics》2018,59(1):153-162
In order to investigate the characteristics of force chains in a granular flow system, a parallel plate shear cell is constructed to simulate the shear movement of an infinite parallel plate and observe variations in relevant parameters. The shear dilatancy process is divided into three stages, namely, plastic strain, macroscopic failure, and granular recombination. The stickslip phenomenon is highly connected with the evolution of force chains during the shear dilatancy process. The load–distribution rate curves and patterns of the force chains are utilized to describe the load-carrying behaviors and morphologic changes of force chains separately. Force chains, namely, “diagonal gridding,” “tadpole-shaped,” and “pinnate” are defined according to the form of the force chains in the corresponding three stages. 相似文献
16.
17.
以1,4-二溴-2,5-二甲基苯和4-吡啶硼酸为原料,经两步合成了一种新颖的含吡啶基团的二羧酸配体。通过核磁共振氢谱及傅里叶变换红外光谱对配体结构进行表征,通过热重分析对配体的热稳定性进行了测试;通过溶剂热法对配体的单晶进行培养,并考察反应温度、时间、pH和溶剂等条件对单晶培养的影响。结果表明:在反应温度为80 ℃,反应时间为12 h、溶剂为蒸馏水、溶液pH=5的条件下可获得高质量单晶。该配体为单斜晶系,属于C2/c空间群,结构中含有4个氧原子和2个氮原子,可为金属离子的配位提供足够的位点,有望应用于配合物的设计或催化、吸附和医药载体等行业。 相似文献
18.
Jia Tian-Cong Guo Jin-Tao Wang Zhen Zhu Xiao-Shan Zhang Qian-Xin Chen Ping Yao Kun Lv Wen-Ying Liu Guo-Guang 《Journal of Radioanalytical and Nuclear Chemistry》2019,321(3):823-829
Journal of Radioanalytical and Nuclear Chemistry - In the present work the final products of coumarin radiation chemical transformation are investigated by chromatography. During radiolysis of... 相似文献
19.
20.