全文获取类型
收费全文 | 77355篇 |
免费 | 11883篇 |
国内免费 | 8571篇 |
专业分类
化学 | 40763篇 |
晶体学 | 756篇 |
力学 | 3362篇 |
综合类 | 414篇 |
数学 | 6491篇 |
物理学 | 21726篇 |
无线电 | 24297篇 |
出版年
2024年 | 327篇 |
2023年 | 1921篇 |
2022年 | 2625篇 |
2021年 | 3285篇 |
2020年 | 3185篇 |
2019年 | 2912篇 |
2018年 | 2474篇 |
2017年 | 2566篇 |
2016年 | 3410篇 |
2015年 | 3774篇 |
2014年 | 4494篇 |
2013年 | 5574篇 |
2012年 | 6570篇 |
2011年 | 6496篇 |
2010年 | 4854篇 |
2009年 | 4799篇 |
2008年 | 5057篇 |
2007年 | 4495篇 |
2006年 | 4134篇 |
2005年 | 3617篇 |
2004年 | 2708篇 |
2003年 | 2154篇 |
2002年 | 2037篇 |
2001年 | 1686篇 |
2000年 | 1478篇 |
1999年 | 1693篇 |
1998年 | 1329篇 |
1997年 | 1212篇 |
1996年 | 1165篇 |
1995年 | 1007篇 |
1994年 | 864篇 |
1993年 | 738篇 |
1992年 | 612篇 |
1991年 | 520篇 |
1990年 | 413篇 |
1989年 | 301篇 |
1988年 | 222篇 |
1987年 | 188篇 |
1986年 | 184篇 |
1985年 | 157篇 |
1984年 | 107篇 |
1983年 | 103篇 |
1982年 | 63篇 |
1981年 | 47篇 |
1980年 | 32篇 |
1979年 | 20篇 |
1977年 | 21篇 |
1976年 | 21篇 |
1975年 | 24篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
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
12.
13.
We investigate terahertz radiation(T-rays) from a pentacene organic diode at room temperature. The quantum chemistry calculation for frequency-related Huang–Rhys factor of pentacene is also carried out. The results demonstrate that the T-rays can come from a bending vibration of pentacene skeleton after the energy of pentacene exciton transferring to the vibrational excited state via electron–phonon coupling. Frequency and natural bond orbital analytics of pentacene and its derivatives are performed in order to explain the result and develop new materials to get higher emission. This work provides a new way to produce T-rays with a simple device at room temperature. 相似文献
14.
A nanomaterials-based novel molecular beacon has attracted growing attentions in fluorescent assays as many nanomaterials possess excellent quenching efficiency. In this work, a gold-based nanobeacon probe was established to detect organophosphorus pesticides for the first time. The constructed gold-based nanobeacon acted as a signal indicator and could display the decreasing of the intensity in the presence of targets, which competitively bound to single strand DNA. To achieve a high sensitive probe, some parameters including solution pH, temperature and reaction time were investigated and optimized. The gold-based nanobeacon probe assay was proved to be rapid and sensitive to achieve a detection limit of 0.035 μM for isocarbophos, 0.134 μM for profenofos, 0.384 μM for phorate and 2.35 μM for omethoate, respectively. The prepared nanobeacon effectively reduced the background and improved the detection sensitivity and selectivity. The probe is stable, easy to operate and does not need sophisticated instruments. These features makes the probe feasible for screening trace organophosphorus pesticides in real samples. 相似文献
15.
Identification of metabolites of rupestonic acid in rat urine by liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry 下载免费PDF全文
Dongyu Gu Yi Yang Qibin Chen Madina Habasi Jiangyu Zhao Haji Akber Aisa 《Biomedical chromatography : BMC》2015,29(4):595-603
Rupestonic acid, a potential anti‐influenza agent, is an important and characteristic compound in Artemisia rupestris L., a well‐known traditional Uighur medicine for the treatment of colds. In the present study, high‐performance liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry was used to detect and identify the metabolites in rat urine after oral administration of rupestonic acid. A total of 10 metabolites were identified or partially characterized. The structure elucidations of the metabolites were performed by comparing the changes in accurate molecular masses and fragment ions with those of the parent compound. The results showed that the main metabolites of rupestonic acid in rat urine were formed by oxidation, hydrogenation and glucuronidation. A metabolism pathway was proposed for the first time based on the characterized structures. This metabolism study can provide essential information for drug discovery, design and clinical application of rupestonic acid. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
16.
17.
18.
19.
20.