全文获取类型
收费全文 | 5887篇 |
免费 | 897篇 |
国内免费 | 1323篇 |
专业分类
化学 | 5038篇 |
晶体学 | 99篇 |
力学 | 335篇 |
综合类 | 133篇 |
数学 | 709篇 |
物理学 | 1793篇 |
出版年
2024年 | 21篇 |
2023年 | 137篇 |
2022年 | 204篇 |
2021年 | 227篇 |
2020年 | 285篇 |
2019年 | 285篇 |
2018年 | 209篇 |
2017年 | 261篇 |
2016年 | 324篇 |
2015年 | 320篇 |
2014年 | 380篇 |
2013年 | 476篇 |
2012年 | 522篇 |
2011年 | 563篇 |
2010年 | 366篇 |
2009年 | 399篇 |
2008年 | 408篇 |
2007年 | 342篇 |
2006年 | 315篇 |
2005年 | 296篇 |
2004年 | 222篇 |
2003年 | 239篇 |
2002年 | 277篇 |
2001年 | 232篇 |
2000年 | 164篇 |
1999年 | 139篇 |
1998年 | 66篇 |
1997年 | 40篇 |
1996年 | 55篇 |
1995年 | 60篇 |
1994年 | 57篇 |
1993年 | 44篇 |
1992年 | 25篇 |
1991年 | 19篇 |
1990年 | 26篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1959年 | 4篇 |
1957年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有8107条查询结果,搜索用时 15 毫秒
101.
Zhao‐Hui Yan Zhu‐Zhen Han Xian‐Qing Hu Qing‐Xin Liu Wei‐Dong Zhang Run‐Hui Liu Hui‐Liang Li 《Helvetica chimica acta》2013,96(1):85-92
Two new sesquiterpenes, 1 and 2 , as well as the five known compounds 3 – 7 , were isolated from the stems of Euonymus alatus. Compounds 2 – 7 have a β‐dihydroagarofuran skeleton. The structures of these compounds were elucidated mainly by spectroscopic methods (1D‐, 2D‐NMR, ESI‐MS, and HR‐ESI‐MS). We also report the X‐ray crystal structure of evonine ( 3 ) for the first time. 相似文献
102.
The BiCl3‐catalyzed reaction of pyrroles with electron‐deficient olefins generated the corresponding Michael adducts in high yields. 相似文献
103.
The Knoevenagel condensation of Meldrum's acid with aromatic aldehydes proceeded efficiently in a reusable ionic liquid, ethylammonium nitrate, at room temperature in the absence of any catalyst with high yields. 相似文献
104.
The reaction of diaryliodonium salts with β-substituted-α,β-enones in the presence of a palladium catalyst affords Hβ-substituted products with excellent yields. 相似文献
105.
A facile one‐pot synthesis of 2,5‐disubstituted oxazoles was developed via cyclization of aldoximes and phenylacetylene then dehydrogenation oxidation. 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone was studied for the selective oxidation of oxazolines using Cu2+/Li+ as catalyst and O2 as indirect oxidant. The reaction results showed that this catalyst system can effectively catalyze the oxidation of oxazolines to the corresponding oxazoles. Thus, a variety of polysubstituted oxazoles was easily synthesized in high yields by catalytic oxidation of 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone/CuCl2/LiCl/O2. 相似文献
106.
Li Zhang Sheng-mei Yuan Li-ming Yang Zhen Fang Guang-chao Zhao 《Mikrochimica acta》2013,180(7-8):627-633
A glassy carbon electrode was modified with β-manganese dioxide (β-MnO2), and glucose oxidase (GOx) was immobilized on its surface. The β-MnO2 nanowires were prepared by a hydrothermal method and characterized by scanning electron microscopy and powder X-ray diffraction. They were then dispersed in Nafion solution and cast on the glassy carbon electrode (GCE) to form an electrode modified with β-MnO2 nanowires that exhibits improved sensitivity toward hydrogen peroxide. If GOx is immobilized in the surface, the β-MnO2 acts as a mediator, and Nafion as a polymer backbone. The fabrication process was characterized by electrochemical impedance spectroscopy, and the sensor and its materials were characterized by cyclic voltammetry and amperometry. The biosensor enables amperometric detection of glucose with a sensitivity of 38.2 μA?·?mM?1?·?cm?2, and a response time of?<?5 s. This study also demonstrates the feasibility of realizing inexpensive, reliable, and high-performance biosensors using MnO2 nanowires. Figure
The sensitive determination of glucose was realized at a β-MnO2 NWs modified glassy carbon electrode by amperometry. The relatively fast, reproducible and low-cost manufacturing procedure suggests that it can offer an excellent platform for glucose oxidase-biosensing applications. 相似文献
107.
108.
Dong‐Jun Yu Jun Hu Yan Huang Hong‐Bin Shen Yong Qi Zhen‐Min Tang Jing‐Yu Yang 《Journal of computational chemistry》2013,34(11):974-985
Understanding the interactions between proteins and ligands is critical for protein function annotations and drug discovery. We report a new sequence‐based template‐free predictor (TargetATPsite) to identify the Adenosine‐5′‐triphosphate (ATP) binding sites with machine‐learning approaches. Two steps are implemented in TargetATPsite: binding residues and pockets predictions, respectively. To predict the binding residues, a novel image sparse representation technique is proposed to encode residue evolution information treated as the input features. An ensemble classifier constructed based on support vector machines (SVM) from multiple random under‐samplings is used as the prediction model, which is effective for dealing with imbalance phenomenon between the positive and negative training samples. Compared with the existing ATP‐specific sequence‐based predictors, TargetATPsite is featured by the second step of possessing the capability of further identifying the binding pockets from the predicted binding residues through a spatial clustering algorithm. Experimental results on three benchmark datasets demonstrate the efficacy of TargetATPsite. © 2013 Wiley Periodicals, Inc. 相似文献
109.
Fei Geng Ting Lu Zhen Li Liqiang Zheng Ganzuo Li 《Journal of Dispersion Science and Technology》2013,34(9):1209-1213
The effects of Tris-HCl buffer solution on the cmc of cetyltrimethylammonium bromide (CTAB) were studied by surface tension measurement. The result shows that the effect of the buffer solution depends on the interaction between CTAB and NaCl and the structure accelerants of water, Tris. A series of parameters, including the critical micelle concentration (cmc), the surface tension at cmc (γcmc), the adsorption efficiency (pC20), and the effectiveness of surface tension reduction (∏cmc) were obtained from the surface tension measurements in the presence of glycine with different concentration in the Tris-HCl buffer solution at 27°C. In addition, maximum surface excess concentration (Γ max) and minimum surface area per molecule (Amin) at the air-water interface were estimated according to the Gibbs adsorption isotherm. The thermodynamic parameters (Δ C p,m , Δ H m,tr , Δ C p,m,tr ) of micellization for CTAB in the absence and presence of glycine at different temperature were also been obtained. 相似文献
110.
在线质谱仪检测植物排放的挥发性有机物 总被引:2,自引:0,他引:2
利用在线检测质谱仪(SPIMS-1000)分别对高温烘烤、长时间密封保存、机械损伤等处理过的松科松属马尾松(Pinus Massoniana L.)样品排放的挥发性有机物(VOCs)与新鲜样品进行对比检测。SPIMS-1000在线检测质谱仪能够检测出植物排放的异戊二烯(m/z 68)和单萜(m/z 136),及其它一些特异性组分,如(Z)-3-己烯醛(m/z 98)等。利用在线检测质谱仪实现敞开环境中原位植物排放气体的检测。实验表明,在线检测质谱仪被广泛应用于环境中VOCs的实时、在线、定性快速检测。 相似文献