全文获取类型
收费全文 | 218篇 |
免费 | 15篇 |
国内免费 | 38篇 |
专业分类
化学 | 156篇 |
力学 | 9篇 |
数学 | 32篇 |
物理学 | 74篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 13篇 |
2013年 | 12篇 |
2012年 | 24篇 |
2011年 | 28篇 |
2010年 | 19篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 18篇 |
2006年 | 13篇 |
2005年 | 4篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有271条查询结果,搜索用时 15 毫秒
31.
Qin W Zhang Y Liu W Tan M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(13):3085-3092
Two open-chain carboxylate crown ether ligands and their terbium(III) and europium(III) complexes were synthesized and characterized. The terbium and europium ions were found to coordinate to the carboxylate oxygens. The fluorescence properties of europium complexes in the solid state and terbium complexes in the solid state and in the organic solvent were studied in detail, respectively. Under the excitation of ultraviolet light, strong green fluorescence of solid terbium complexes and red fluorescence of solid europium complexes were observed. These observations show that the two ligands favor energy transfer to the emitting energy level of Tb(3+). Some factors that influencing the fluorescent intensity were also discussed. 相似文献
32.
In this paper, a novel adaptive fractional-order feedback controller is first developed by extending an adaptive integer-order feedback controller. Then a simple but practical method to synchronize almost all familiar fractional-order chaotic systems has been put forward. Through rigorous theoretical proof by means of the Lyapunov stability theorem and Barbalat lemma, sufficient conditions are derived to guarantee chaos synchronization. A wide range of fractional-order chaotic systems, including the commensurate system and incommensurate case, autonomous system, and nonautonomous case, is just the novelty of this technique. The feasibility and validity of presented scheme have been illustrated by numerical simulations of the fractional-order Chen system, fractional-order hyperchaotic Lü system, and fractional-order Duffing system. 相似文献
33.
The first-passage problem is an important issue in the theory of dynamical systems; it determines whether the system is safe and reliable or destroyed. Therefore, taking a suitable force to control first-passage failure is very significant for such systems. In this paper, we study the reliability of a stochastically complex dynamical system by using the stochastic averaging method. The reliability results show that the reliability function is monotonically decreasing with respect to time, and that the reliability of the system is relatively worse, with external and parametric white-noise excitations. A bang–bang feedback control is used to improve the reliability for the original system. Numerical results display that even a small control force can greatly enhance the reliability of the original system. 相似文献
34.
In this paper, both theoretical investigation and experimental verification of microwave photonic filter based on a fiber-Bragg-grating (FBG) delay line and a broadband light source have been carried out, in which the effects of spectrum and dispersion characteristics of the FBGs on the frequency response of the microwave photonic filter have been taken into consideration. Theoretical and experimental results agree well, and both results show that FBG's characteristics affect not only the free spectrum range (FSR) of microwave photonic filter's response, but also results in the frequency dependent power degrading. 相似文献
35.
J Jiang W Liu J Cheng L Yang H Jiang D Bai W Liu 《Chemical communications (Cambridge, England)》2012,48(67):8371-8373
A highly sensitive and selective fluorescent probe for inorganic and organic mercury species displays colorimetric and ratiometric response in a buffer solution via mercury promoted cleavage reaction. The probe is demonstrated to detect CH(3)HgCl in living cells. 相似文献
36.
Chemical Constituents from the Flowers of Carthamus tinctorius L. and Their Lung Protective Activity
Yanling Liu Mengna Wang Yangang Cao Mengnan Zeng Qinqin Zhang Yingjie Ren Xu Chen Chen He Xiling Fan Xiaoke Zheng Weisheng Feng 《Molecules (Basel, Switzerland)》2022,27(11)
A new flavonoid, saffloflavanside (1), a new sesquiterpene, safflomegastigside (2), and a new amide, saffloamide (3), together with twenty-two known compounds (4–25), were isolated from the flowers of Carthamus tinctorius L. Their structures were determined based on interpretation of their spectroscopic data and comparison with those reported in the literature. The protective effects against lipopolysaccharide (LPS)-stimulated damage on human normal lung epithelial (BEAS-2B) cells of the compounds were evaluated using MTT assay and cellular immunofluorescence assay. The results showed that compounds 2–3, 8–11, and 15–19 exhibited protective effects against LPS-induced damage to BEAS-2B cells. Moreover, compounds 2–3, 8–11, and 15–19 can significantly downregulate the level of nuclear translocation of NF-κB p-p65. In summary, this study revealed chemical constituents with lung protective activity from C. tinctorius, which may be developed as a drug for the treatment of lung injury. 相似文献
37.
38.
设计激光投影机光学系统需要从如何减小光学系统的体积和提高激光光源的光效两个方面考虑。研究了激光显示照明系统中的复眼透镜,并对设计的复眼小透镜矩形单元进行了优化,发现在复眼透镜整体尺寸和单颗复眼小透镜焦距一定的情况下,整个复眼透镜上的阵列越多,即复眼透镜上蜂窝的数量越多,其匀光效果就越好,且此时投影机系统的体积也较小。为了提高激光光源的光效,设计中对复眼透镜在不同数值孔径照明光束下的匀光效果进行了讨论。并对优化设计后的复眼透镜进行40 000条光线追迹,实验显示其光线透过率可以达到92.5%,且几乎无杂散光。 相似文献
39.
Weisheng Hu Yaohui Jin Chun Jiang YUE Wang Xiaodong WANG Chunlei ZHANG Yang Lu Buwei Xu Peigang Hu Qingji Zeng 《光学学报》2003,23(Z1)
We build an automatically switched optical network (ASON) testbed with four optical cross-connect nodes. Many fundamental ASON features are demonstrated, which is implemented by control protocols based on generalized multi-protocol label switching (GMPLS) framework. 相似文献
40.
本文研究了聚砜酰胺超滤膜制备的工艺条件和膜分离性能之间的关系。求得膜的分离性能随预压时间、蒸发时间、沉淀浴温度和溶剂种类而变化的规律。 相似文献