全文获取类型
收费全文 | 1741篇 |
免费 | 343篇 |
国内免费 | 255篇 |
专业分类
化学 | 1226篇 |
晶体学 | 45篇 |
力学 | 121篇 |
综合类 | 24篇 |
数学 | 212篇 |
物理学 | 711篇 |
出版年
2024年 | 3篇 |
2023年 | 39篇 |
2022年 | 69篇 |
2021年 | 74篇 |
2020年 | 85篇 |
2019年 | 72篇 |
2018年 | 66篇 |
2017年 | 77篇 |
2016年 | 85篇 |
2015年 | 86篇 |
2014年 | 116篇 |
2013年 | 112篇 |
2012年 | 160篇 |
2011年 | 171篇 |
2010年 | 122篇 |
2009年 | 124篇 |
2008年 | 128篇 |
2007年 | 82篇 |
2006年 | 98篇 |
2005年 | 76篇 |
2004年 | 51篇 |
2003年 | 52篇 |
2002年 | 54篇 |
2001年 | 36篇 |
2000年 | 21篇 |
1999年 | 30篇 |
1998年 | 30篇 |
1997年 | 31篇 |
1996年 | 30篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 19篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 17篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有2339条查询结果,搜索用时 31 毫秒
991.
Nanocrystalline europium-doped tine oxide (SnO2:Eu) were synthesized by a polyacrylamide gel method. The effects of heat treatment on structure, grain size and luminescence properties of SnO2:Eu were studied with X-ray powder diffraction, transmission electron microscopy and photoluminescence measurements. The results indicate that high heat treatments can enhance greatly luminescence intensity of the samples. Furthermore, the presence of carbon network/cages in the polyacrylamide gel can effectively prevent particles agglomeration, so even when sintered at higher temperatures (1000 °C), the grain size is still below 20 nm. 相似文献
992.
分别以10-十一碳烯酸和丙炔醇为起始原料,通过炔化物路线(第1个中间体是10-十一碳炔醇-1(5),第2个中间体是10-十六碳炔醇-1(8))分别立体选择性合成了桃柱螟性信息素成分(E)-10-十六碳烯醛(1)和(Z)-10-十六碳烯醛(2)。 相似文献
993.
994.
995.
Equilibrium geometries and relative stabilities of 24 possible isomers for C78O4 based on C78 (C2v) were studied by intermediate neglect of differential overlap (INDO) calculations. It was indicated that the most stable geometry is 28,29,30,31,52,53,73,78‐C78O4, where three oxygen atoms are added to the same hexagon, through which the longest axis of C78 (C2v) goes, and the forth oxygen atom is added to the C(73)? C(78) bond intersected by the shortest axis of C78 (C2v), and epoxide structures are formed. Electronic spectra of C78O4 isomers were investigated based on the optimized geometries. The blue shift of the first absorption for 28,29,30,31,52,53,73,78‐C78O4 compared with that of C78 (C2v) was rationalized and nature of transition for the peaks discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
996.
Photosensitizing agents are essential for precise and efficient photodynamic therapy (PDT). However, most of the conventional photosensitizers still suffer from limitations such as aggregation-caused quenching (ACQ) in physiological environments and toxic side-effects on normal tissues during treatment, leading to reduced therapeutic efficacy. Thus, integrating excellent photophysical properties and accurate carcinoma selectivity in a photosensitizer system remains highly desired. Herein, a “dual lock-and-key” supramolecular photosensitizer BIBCl–PAE NPs for specific and enhanced cancer therapy is reported. BIBCl–PAE NPs are constructed by encapsulating a rationally designed glutathione (GSH)-activatable photosensitizer BIBCl in a pH-responsive diblock copolymer. In normal tissues, BIBCl is “locked” in the hydrophobic core of the polymeric micelles due to ACQ. Under the “dual key” activation of low pH and high levels of GSH in a tumor microenvironment, the disassembly of micelles facilitates the reaction of BIBCl with GSH to release water-soluble BIBSG with ideal biocompatibility, enabling the highly efficient PDT. Moreover, benefiting from the Förster resonance energy transfer effect of BIBSG, improved light harvesting ability and 1O2 production are achieved. In vitro and vivo experiments have demonstrated that BIBCl–PAE NPs are effective in targeting and inhibiting carcinoma. BIBCl–PAE NPs show superior anticancer efficiency relative to non-activatable controls.The “dual lock-and-key” supramolecular photosensitizers enable specific and enhanced photodynamic therapy (PDT). 相似文献
997.
Hong-xiang Teng Wen-hong Tang Yi Shi Xi-gao Jin State Key Laboratory of Polymer Physics Chemistry Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing China Department of Chemistry Jilin University Changchun China 《高分子科学》2002,(4):339-345
Based on thermal analysis, the isothermal and nonisothemal crystallization kinetics of Ziegler-Natta catalyzedlinear low density polyethylene (Z-N LLDPE) and metallocene catalyzed LLDPE (m-LLDPE) were studied. Treating theresults with the Avrami equation and the Ozawa equation, the crystallization constant lgk and the Avrami exponent n wereobtained. Some other crystallization parameters were also discussed. According to the different characteristics of the chainstructures of Z-N LLDPE and metallocene LLDPE, their crystallizaton behaviors were analyzed. It is indicated that thehomogeneity and heterogeneity of the two polymers act in different way during the crystallization process of polymers,including the nucleation and the growth of crystals under various conditions. 相似文献
998.
In the present paper, N,N'-dinaphthyl-N,N'-diphenyl-3,6-dioxaoctanediamide acts as a specific reagent for enhancing the fluorescence intensity of Eu(III) complex with thenoyl trifluoroacetone (TTA), the spectrofluorimetric determination of trace amounts of Eu(III) based on the above system was carried out and its luminescence mechanism was studied. The excitation and emission wavelengths are 343.6 and 613.3 nm, respectively. The fluorescence intensities vary linearly with the concentration of europium(III) in the range 3.647x10(-3)-3.039 mug ml(-1) for the original fluorescence with a detection limit down to 2.279x10(-4) mug ml(-1) and the standard deviation is 0.063 mug ml(-1) for 10 times measurements, and in the range 7.598x10(-4)-0.0243 mug ml(-1) (SD=0.035 for 15 times measurements), 0.06078-0.6100 mug ml(-1) (SD=0.52 for 10 times measurements) for the first derivative fluorescence signal with a detection limit down to 8.566x10(-5) mug ml(-1). The interferences of other rare earths and some of inorganic ions are described. This method is a direct, rapid, selective and sensitive analytical method for the determination of trivalent europium in rare earth ore samples and high purity of rare earth oxides. 相似文献
999.
Eu3+在碱土金属卤磷酸盐中的格位对称性及电荷迁移态 总被引:2,自引:0,他引:2
在254nm紫外光激发下研究了Eu~(3+)在Sr_3Ca_2(PO_4)_3Cl基质中的发光光谱.以Eu~(3+)为结构探针测定了Eu~(3+)所处晶格的点对称性.研究了M_5(PO_4)_3X(M=Ca,Sr,Ba;X=F,Cl,Br)基质组成改变对Eu~(3+)电荷迁移态的影响,以及温度对Ca_5(PO_4)_3Cl:Eu~(3+)发光强度的影响. 相似文献
1000.
Chuan-Pin Lee Yi-Lin Jan Pei-Lun Lan Yuan-Yaw Wei Shi-Ping Teng Chun-Nan Hsu 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(1):145-151
This study is focused on sorption and determination of distribution ratios (R
d) of cesium and selenium on mudrock, which is the potential host rock for waste disposal in Taiwan. Batch tests including
sorption kinetic and isotherms tests have been performed in synthetic groundwater at aerobic and anaerobic conditions which
might be found in the deep geologic environment. It is found that R
d for sorption of cesium did not have an obvious difference in both conditions with various contact time. However, R
d in anaerobic condition for sorption of selenium was greater than that in aerobic condition. Selenium is a redox sensitive
element and its solubility in reducing conditions is controlled by the formation of metallic or precipitable selenium. It
demonstrated variation of R
d with time in both conditions for Se sorption kinetic experiments was equal (10 ml/g) and indicated a part formation (10%)
of precipitable selenium (Se0, FeSe or FeSe2) in the solution. Moreover, it was not enough to form precipitable selenium completely in reducing condition as to insufficient
experimental period (2 weeks) and in the presence of Fe2+. The Freundlich and Langmuir isotherm for the concentration ranges (i.e., 10−3–10−7M) conducted in both conditions seem to be adequate to quantitatively describe the sorption of cesium and selenium, respectively. 相似文献