全文获取类型
收费全文 | 48347篇 |
免费 | 3232篇 |
国内免费 | 3722篇 |
专业分类
化学 | 25972篇 |
晶体学 | 581篇 |
力学 | 2294篇 |
综合类 | 262篇 |
数学 | 10874篇 |
物理学 | 15318篇 |
出版年
2024年 | 47篇 |
2023年 | 348篇 |
2022年 | 637篇 |
2021年 | 649篇 |
2020年 | 763篇 |
2019年 | 757篇 |
2018年 | 1804篇 |
2017年 | 2071篇 |
2016年 | 1577篇 |
2015年 | 1520篇 |
2014年 | 1641篇 |
2013年 | 2245篇 |
2012年 | 4803篇 |
2011年 | 4139篇 |
2010年 | 3163篇 |
2009年 | 2828篇 |
2008年 | 1997篇 |
2007年 | 1897篇 |
2006年 | 1772篇 |
2005年 | 5413篇 |
2004年 | 4733篇 |
2003年 | 2953篇 |
2002年 | 1151篇 |
2001年 | 870篇 |
2000年 | 587篇 |
1999年 | 607篇 |
1998年 | 426篇 |
1997年 | 325篇 |
1996年 | 323篇 |
1995年 | 264篇 |
1994年 | 262篇 |
1993年 | 208篇 |
1992年 | 328篇 |
1991年 | 294篇 |
1990年 | 260篇 |
1989年 | 205篇 |
1988年 | 188篇 |
1987年 | 120篇 |
1986年 | 105篇 |
1985年 | 94篇 |
1984年 | 67篇 |
1983年 | 59篇 |
1982年 | 39篇 |
1979年 | 39篇 |
1976年 | 86篇 |
1975年 | 40篇 |
1974年 | 45篇 |
1973年 | 54篇 |
1972年 | 40篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
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
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
12.
This study is concerned with a new,explicit approach by means of which forms of the large strain elastic potential for multiaxial rubberlike elasticity may be obtained based on data for a single deformation mode.As a departure from usual studies,here for the first time errors may be estimated and rendered minimal for all possible deformation modes and,furthermore,failure behavior may be incorporated.Numerical examples presented are in accurate agreement with Treloar's well-known data. 相似文献
13.
Yin Pengpeng Liu Chang Wang Ying Guan Lei Chen Xian Xiong Xuejia Jin Hongzhe 《Russian Journal of General Chemistry》2021,91(5):897-903
Russian Journal of General Chemistry - A dinuclear Tb complex, Tb2(H2L)3(phen)2 (1), and two similar N-donor coordination complexes, Fe(phen)3·HL (2), Fe(bipy)3·HL·5H2O (3) (Na2H2L =... 相似文献
14.
15.
We numerically solve the time-dependent Ginzburg–Landau equations for two-gap superconductors using the finite-element technique. The real-time simulation shows that at low magnetic field, the vortices in small-size samples tend to form clusters or other disorder structures. When the sample size is large, stripes appear in the pattern. These results are in good agreement with the previous experimental observations of the intriguing anomalous vortex pattern, providing a reliable theoretical basis for the future applications of multi-gap superconductors. 相似文献
16.
We proposed an electro-optic modulator with two-bus one-ring (TBOR) structure to improve the extinction ratio and reduce insert loss. It has a dual output compared with one-bus one-ring structure. In addition, double-layer graphene makes it possible for the modulation in the visible to mid-infrared wavelength range. It shows that this new electro-optic modulator can present two switching states well with low insertion loss, high absorption and high extinction ratio. At , when the switching states are based on the chemical potential, and , the insertion losses of both output ports are less than 2 dB, the absorption of the output port coupled via a micro-ring reaches 45 dB and the extinction ratio reaches 14 dB. When the refractive index of the dielectric material is 4.2, the applied voltage will be less than 1.2 V, thus can be used in low-voltage CMOS technology. 相似文献
17.
18.
Dr. Feifan Wang Jie Tian Dr. Mengzhu Li Dr. Weizhen Li Dr. Lifang Chen Xiaozhi Liu Dr. Jian Li Aidaer Muhetaer Prof. Dr. Qi Li Prof. Dr. Yuan Wang Prof. Dr. Lin Gu Prof. Dr. Ding Ma Prof. Dr. Dongsheng Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8280-8286
Fully utilizing solar energy for catalysis requires the integration of conversion mechanisms and therefore delicate design of catalyst structures and active species. Herein, a MOF crystal engineering method was developed to controllably synthesize a copper–ceria catalyst with well-dispersed photoactive Cu-[O]-Ce species. Using the preferential oxidation of CO as a model reaction, the catalyst showed remarkably efficient and stable photoactivated catalysis, which found practical application in feed gas treatment for fuel cell gas supply. The coexistence of photochemistry and thermochemistry effects contributes to the high efficiency. Our results demonstrate a catalyst design approach with atomic or molecular precision and a combinatorial photoactivation strategy for solar energy conversion. 相似文献
19.
Jiatian Chen Le Yang Ying Li Qinghua Hou Lanlan Li Peng Jin 《International journal of quantum chemistry》2019,119(16):e25961
Inorganic planar ring-shape molecules with 4n + 2 π electrons are always the focus of experimental synthesis and theoretical research due to their potential aromaticity and stability. In this work, the whole series of five-membered heterocycle monoanions X nY5-n− (X, Y = group 15 elements; n = 1-4) were thoroughly investigated by means of density functional theory calculations. They all have large formation energies and HOMO-LUMO gap energies, suggesting the potential thermodynamic and kinetic stability. Their aromaticities are comparable to that of typical aromatic hydrocarbons. Their thermal stabilities were firmly established by the ab initio molecular dynamics simulations. As most of them are predicted for the first time, their various spectra were simulated for experimental characterization. Furthermore, we demonstrate that these five-membered cyclic anions can be employed as η5-ligand to construct novel all-inorganic metallocenes, which may serve as the building blocks of low-dimensional nanomaterials. 相似文献
20.
非线性光纤方向耦合器孤子动力特性分析 总被引:2,自引:0,他引:2
利用变分方法,导出了双曲正割型光孤子在非线性光纤耦合器中传输时满足的动力学方程组,分析了该方程组的平衡点性态,讨论了光孤子的开关特性.指出参数|β|<2π.是能实现完全的开关操作的必要条件. 相似文献