全文获取类型
收费全文 | 18524篇 |
免费 | 3295篇 |
国内免费 | 1699篇 |
专业分类
化学 | 12959篇 |
晶体学 | 176篇 |
力学 | 1036篇 |
综合类 | 70篇 |
数学 | 2037篇 |
物理学 | 7240篇 |
出版年
2024年 | 39篇 |
2023年 | 403篇 |
2022年 | 426篇 |
2021年 | 667篇 |
2020年 | 745篇 |
2019年 | 747篇 |
2018年 | 720篇 |
2017年 | 575篇 |
2016年 | 959篇 |
2015年 | 821篇 |
2014年 | 1050篇 |
2013年 | 1386篇 |
2012年 | 1720篇 |
2011年 | 1773篇 |
2010年 | 1167篇 |
2009年 | 1088篇 |
2008年 | 1202篇 |
2007年 | 1042篇 |
2006年 | 995篇 |
2005年 | 795篇 |
2004年 | 605篇 |
2003年 | 431篇 |
2002年 | 437篇 |
2001年 | 334篇 |
2000年 | 279篇 |
1999年 | 392篇 |
1998年 | 285篇 |
1997年 | 295篇 |
1996年 | 285篇 |
1995年 | 242篇 |
1994年 | 209篇 |
1993年 | 214篇 |
1992年 | 144篇 |
1991年 | 160篇 |
1990年 | 131篇 |
1989年 | 104篇 |
1988年 | 89篇 |
1987年 | 71篇 |
1986年 | 73篇 |
1985年 | 56篇 |
1984年 | 59篇 |
1983年 | 30篇 |
1982年 | 32篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1978年 | 13篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 15篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 77 毫秒
961.
Peng Liu Hui Ruan Tiantian Li Jiaqi Chen Fuqiu Ma Duoqiang Pan Wangsuo Wu 《Molecules (Basel, Switzerland)》2021,26(4)
The low cost β-zeolite and ethylenediamine modified β-zeolite (EDA@β-zeolite) were prepared by self-assembly method and used for Cu(II) removal from contaminated aqueous solution. Removal ability of β-zeolite toward Cu(II) was greatly improved after ethylenediamine (EDA) modification, the removal performance was greatly affected by environmental conditions. XPS results illustrated that the amide group played important role in the removal process by forming complexes with Cu(II). The EDA@β-zeolite showed desirable recycling ability. The finding herein suggested that the proposed composite is a promising and suitable candidate for the removal of Cu(II) from contaminated natural wastewater and aquifer. 相似文献
962.
Ping Yu Qian Li Yanmei Feng Sinan Ma Yuying Chen Guichen Li 《Molecules (Basel, Switzerland)》2021,26(5)
Deep eutectic solvents (DESs) are green organic solvents that have broad prospects in the extraction of effective components of traditional Chinese medicine. This work employed the quantitative analysis of multi-components by a single marker (QAMS) method to quantitatively determine the six effective components of glycyrrhizic acid, liquiritin, isoliquiritin apioside, liquiritigenin, isoliquiritin, and glycyrrhetinic acid in Glycyrrhiza uralensis, which was used for comprehensive evaluation of the optimal extraction process by DESs. First, Choline Chloride: Lactic Acid (ChCl-LA, molar ratio 1:1) was selected as the most suitable DES by comparing the extraction yields of different DESs. Second, the extraction protocol was investigated by extraction time, extraction temperature, liquid-to-material ratio, molar ratio, and ultrasonic power. The Box–Behnken design (BBD) combined with response surface methodology (RSM) was used to investigate the optimal DES conditions. The result showed that the best DES system was 1.3-butanediol/choline chloride (ChCl) with the molar ratio of 4:1. The optimal extraction process of licorice was 20 mL/g, the water content was 30%, and the extraction time was 41 min. The comprehensive impact factor (z) was 0.92. At the same time, it was found that the microstructure of the residue extracted by the eutectic solvent was more severely damaged than the residue after the traditional solvent extraction through observation under an electron microscope. The DES has the characteristics of high efficiency and rapidity as an extraction solution. 相似文献
963.
Xifeng Hou Yanhui Zheng Xiaolong Ma Yuheng Liu Zichuan Ma 《Molecules (Basel, Switzerland)》2021,26(4)
To expand the applications of graphene-based materials to biogas purification, a series of reduced graphene oxide aerogels (rGOAs) were prepared from industrial grade graphene oxide using a simple hydrothermal method. The influences of the hydrothermal preparation temperature on the textural properties, hydrophobicity and physisorption behavior of the rGOAs were investigated using a range of physical and spectroscopic techniques. The results showed that the rGOAs had a macro-porous three-dimensional network structure. Raising the hydrothermal treatment temperature reduced the number of oxygen-containing groups, whereas the specific surface area (SBET), micropore volume (Vmicro) and water contact angle values of the rGOAs all increased. The dynamic adsorption properties of the rGOAs towards hexamethyldisiloxane (L2) increased with increasing hydrothermal treatment temperature and the breakthrough adsorption capacity showed a significant linear association with SBET, Vmicro and contact angle. There was a significant negative association between the breakthrough time and inlet concentration of L2, and the relationship could be reliably predicted with a simple empirical formula. L2 adsorption also increased with decreasing bed temperature. Saturated rGOAs were readily regenerated by a brief heat-treatment at 100 °C. This study has demonstrated the potential of novel rGOA for applications using adsorbents to remove siloxanes from biogas. 相似文献
964.
Microwave (MW) heating was proven to efficiently solid-synthesize calcium carbide at 1750 °C, which was about 400 °C lower than electric heating. This study focused on the investigation of the diffusion behaviors of graphite and calcium oxide during the solid-state synthesis of calcium carbide by microwave heating and compared them with these heated by the conventional method. The phase compositions and morphologies of CaO and C pellets before and after heating were carefully characterized by inductively coupled plasma spectrograph (ICP), thermo gravimetric (TG) analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that in both thermal fields, Ca and C inter-diffused at a lower temperature, but at a higher temperature, the formed calcium carbide crystals would have a negative effect on Ca diffusion to carbon. The significant enhancement of MW heating on carbon diffusion, thus on the more efficient synthesis of calcium carbide, manifested that MW heating would be a promising way for calcium carbide production, and that a sufficient enough carbon material, instead of CaO, was beneficial for calcium carbide formation in MW reactors. 相似文献
965.
Xiao-Qian Xu Dr. Li-Hui Cao Yan Yang Xiang-Tian Bai Fang Zhao Dr. Zhen-Hong He Dr. Zheng Yin Prof. Dr. Yang-Min Ma 《化学:亚洲杂志》2021,16(2):142-146
Over the past two decades, progress in chemistry has generated various types of porous materials for removing iodine (129I or 131I) that can be formed during nuclear energy generation or nuclear waste storage. However, most studies for iodine capture are based on the weak host-guest interactions of the porous materials. Here, we present two cationic nonporous macrocyclic organic compounds, namely, MOC-1 and MOC-2 , in which 6I- and 8I− were as counter anions, for highly efficient iodine capture. MOC-1 and MOC-2 were formed by reacting 1,1′-diamino-4,4′-bipyridylium di-iodide with 1,2-diformylbenzene or 1,3-diformylbenzene, respectively. The presence of a large number of I− anions results in high I2 affinity with uptake capacities up to 2.15 g ⋅ g−1 for MOC-1 and 2.25 g ⋅ g−1 for MOC-2 . 相似文献
966.
Can Ren Shuyu Xiao Junzi Li Prof. Lin Ma Prof. Rui Chen Dr. Chuanxiang Ye Prof. Yang Gao Prof. Chenliang Su Prof. Tingchao He 《化学:亚洲杂志》2021,16(4):309-314
Although the production of near-infrared (NIR)-absorbing organic polymers with an excellent nonlinear optical (NLO) response is vital for various optoelectronic devices and photodynamic therapy, the molecular design and relevant photophysical investigation still remain challenging. In this work, large NLO activity is observed for an NIR-absorbing bithiophene-based polymer with a unique head-to-head linkage in the NIR region. The saturable absorption coefficient and modulation depth of the polymer are determined as ∼−3.5×105 cm GW−1 and ∼32.43%, respectively. Notably, the polymer exhibits an intrinsic nonlinear refraction index up to ∼−9.36 cm2 GW−1, which is six orders of magnitude larger than that of CS2. The maximum molar-mass normalized two-photon absorption cross-section (σ2/M) of this polymer can be up to ∼14 GM at 1200 nm. Femtosecond transient absorption measurements reveal significant spectral overlap between the 2PA and excited state absorption in the 1000–1400 nm wavelength range and an efficient triplet quantum yield of ∼36.7%. The results of this study imply that this NIR-absorbing polymer is promising for relevant applications. 相似文献
967.
Hu Pan Renpeng Yan Xudong Li Xin Fa Yufei Ma Rongwei Fan Xin Yu Deying Chen 《Journal of Russian Laser Research》2016,37(3):259-264
We present a compact high-peak-power, high-repetition-rate burst-mode laser from a master-oscillator power amplifier (MOPA) at 1064 nm for laser-based measurement applications. The oscillator is an 808 nm pulsed laser diode side-pumped acousto-optical (A-O) Q-switched Nd:YAG laser at repetition rates ranging from 10–100 kHz, producing a pulse train with a pulse number of 2–25. The maximum output energy of the oscillator is 15.6 mJ at 10 kHz, whereas it is 1.7 mJ at 100 kHz. After twostage amplifiers, a single-pulse energy of 85.2 mJ with a pulse-width of 14.5 ns is achieved at 10 kHz, which produces a peak power of 6.1 MW. At 100 kHz, the total burst energy reaches 220 mJ with a single-pulse energy of 8.8 mJ in the pulse burst laser system. 相似文献
968.
采用密度泛函理论(DFT)中的杂化密度泛函(B3LYP)方法, 在6-31 G基组水平上对C20四聚体进行了几何参数全优化, 得到了基态构型, 并对其稳定性、电子结构、极化率和芳香性进行了计算研究. 结果表明: C20碳笼以[2+2]加成方式结合形成C20四聚体, 具有良好的热力学稳定性; C原子内部以sp2的方式杂化, C原子之间有少量电荷转移; C20 四聚体的IR和Raman光谱都有较多的振动峰; 随碳笼数的增加, C20聚合物中原子间的成键相互作用随之增强; C20四聚体具有芳香性. 相似文献
969.
970.
采用密度泛函理论和非平衡格林函数相结合的方法研究了S原子作为单、双端基的(CH3)2-OPE (齐聚苯乙炔)和(NH2)2-OPE分子在金电极间的电子输运性质. 通过第一性原理优化计算获得分子部分稳定结构, 再置于Au电极之间构成两极系统, 然后再优化整个两极系统获得稳定结构. 另外, 通过非平衡格林函数方法计算了两极系统的电子输运性质. 计算结果表明, 不同的修饰基团和桥接方式可以导致两极系统的开关效应、负微分电阻行为和整流行为等不同的电子输运性质. 通过计算不同偏压下的分子体系投影轨道电子分布、透射谱、态密度, 对这些新异的电输运性质出现的机理进行了解释. 相似文献