全文获取类型
收费全文 | 7242篇 |
免费 | 308篇 |
国内免费 | 82篇 |
专业分类
化学 | 4288篇 |
晶体学 | 221篇 |
力学 | 194篇 |
综合类 | 4篇 |
数学 | 1072篇 |
物理学 | 1853篇 |
出版年
2022年 | 83篇 |
2021年 | 78篇 |
2020年 | 96篇 |
2019年 | 147篇 |
2018年 | 103篇 |
2017年 | 99篇 |
2016年 | 145篇 |
2015年 | 123篇 |
2014年 | 190篇 |
2013年 | 563篇 |
2012年 | 315篇 |
2011年 | 354篇 |
2010年 | 239篇 |
2009年 | 211篇 |
2008年 | 247篇 |
2007年 | 254篇 |
2006年 | 221篇 |
2005年 | 176篇 |
2004年 | 175篇 |
2003年 | 201篇 |
2002年 | 172篇 |
2001年 | 101篇 |
2000年 | 95篇 |
1999年 | 67篇 |
1997年 | 70篇 |
1996年 | 79篇 |
1995年 | 85篇 |
1994年 | 83篇 |
1993年 | 87篇 |
1992年 | 100篇 |
1991年 | 89篇 |
1990年 | 76篇 |
1989年 | 111篇 |
1988年 | 76篇 |
1987年 | 70篇 |
1986年 | 81篇 |
1985年 | 126篇 |
1984年 | 119篇 |
1983年 | 93篇 |
1982年 | 98篇 |
1981年 | 101篇 |
1980年 | 85篇 |
1979年 | 98篇 |
1978年 | 74篇 |
1977年 | 101篇 |
1976年 | 79篇 |
1975年 | 87篇 |
1974年 | 92篇 |
1973年 | 101篇 |
1972年 | 57篇 |
排序方式: 共有7632条查询结果,搜索用时 15 毫秒
991.
992.
Nuclear magnetic double resonance experiments were performed on the strongly coupled two-proton system (AB) in 2-chloroacrylontirile to study the spin relaxation processes. The single resonance parameters of the AB spectrum are (operating frequency 100 MHz): |vA - vB|=9.85±0.1 Hz and J AB=2.8±0.1 Hz. Frequency-sweep double resonance spectra were obtained by irradiating each of the four transitions at different strengths of irradiation in the range 0.015 Hz to 2.35 Hz. These spectra were analysed by using the ‘Bloch approximation’ in the rotating frame for the ‘high’ irradiation strengths and the ‘simple line’ approximation for the ‘low’ irradiation strengths. The analysis showed that the proton relaxation in this molecule can be described by interaction with isotropic random fields of nearly equal strengths at the two nuclei with no appreciable correlation between them. Internal dipole-dipole interaction is not a significant mechanism (at room temperature). It is shown that for analysing ‘low’ irradiation spectra the choice of certain functions of intensity changes would lead to a marked distinction between the different relaxation mechanisms. 相似文献
993.
Previous 19F N.M.R. studies of liquid BF3 have been extended by obtaining the 11B spectrum of BF3 and the 19F spectrum of 10BF3 at various temperatures. Values for the B-F coupling constant and the boron relaxation times have been obtained by computer matching and visual matching of observed and calculated spectra. Relaxation times have the Arrhenius temperature dependence found previously. The temperature dependence of the B-F coupling constant is discussed. Some of the possible advantages of ‘high spin spectra’ are discussed. 相似文献
994.
Huma Rao Saeed Ahmad Asadullah Madni Iqra Rao Mohammed Ghazwani Umme Hani Muhammad Umair Imtiaz Ahmad Nadia Rai Maqsood Ahmed Kashif ur Rehman Khan 《Molecules (Basel, Switzerland)》2022,27(24)
The current study was designed to investigate the feasibility of incorporating the water-insoluble lipophilic drug Alprazolam (Alp) into solid lipid nanoparticles (SLNs) to offer the combined benefits of the quick onset of action along with the sustained release of the drug. Therefore, compritol-based alprazolam-loaded SLNs (Alp-SLNs) would provide early relief from anxiety and sleep disturbances and long-lasting control of symptoms in patients with depression, thereby enhancing patient compliance. The optimized Alp-SLNs analyzed by DLS and SEM showed consistent particle size of 92.9 nm with PI values and standard deviation of the measurements calculated at <0.3 and negative surface charge. These characteristic values demonstrate the desired level of homogeneity and good physical stability of Alp-SLNs. The SLNs had a good entrapment efficiency (89.4%) and high drug-loading capacity (77.9%). SEM analysis revealed the smooth spherical morphology of the SLNs. The physical condition of alprazolam and absence of interaction among formulation components in Alp-SLNs was confirmed by FTIR and DSC analyses. XRD analysis demonstrated the molecular dispersion of crystalline alprazolam in Alp-SLNs. The in vitro release study implied that the release of Alp from the optimized Alp-SLN formulation was sustained as compared to the Alp drug solution because Alp-SLNs exhibited sustained release of alprazolam over 24 h. Alp-SLNs are a promising candidate to achieve sustained release of the short-acting drug Alp, thereby reducing its dosing frequency and enhancing patient compliance. 相似文献
995.
996.
Proceedings - Mathematical Sciences - Populnin is a monoglucoside of populnetin which is shown to be identical with kæmpferol. By the methylation and the subsequent hydrolysis of the glucoside... 相似文献
997.
998.
999.
1000.