全文获取类型
收费全文 | 45228篇 |
免费 | 7472篇 |
国内免费 | 6164篇 |
专业分类
化学 | 33927篇 |
晶体学 | 659篇 |
力学 | 2449篇 |
综合类 | 480篇 |
数学 | 4967篇 |
物理学 | 16382篇 |
出版年
2024年 | 103篇 |
2023年 | 869篇 |
2022年 | 1512篇 |
2021年 | 1570篇 |
2020年 | 1770篇 |
2019年 | 1795篇 |
2018年 | 1498篇 |
2017年 | 1522篇 |
2016年 | 2108篇 |
2015年 | 2110篇 |
2014年 | 2575篇 |
2013年 | 3305篇 |
2012年 | 4118篇 |
2011年 | 4310篇 |
2010年 | 3107篇 |
2009年 | 2866篇 |
2008年 | 3174篇 |
2007年 | 3012篇 |
2006年 | 2738篇 |
2005年 | 2293篇 |
2004年 | 1658篇 |
2003年 | 1362篇 |
2002年 | 1277篇 |
2001年 | 1053篇 |
2000年 | 955篇 |
1999年 | 934篇 |
1998年 | 692篇 |
1997年 | 657篇 |
1996年 | 563篇 |
1995年 | 536篇 |
1994年 | 521篇 |
1993年 | 409篇 |
1992年 | 336篇 |
1991年 | 329篇 |
1990年 | 293篇 |
1989年 | 197篇 |
1988年 | 157篇 |
1987年 | 140篇 |
1986年 | 118篇 |
1985年 | 93篇 |
1984年 | 61篇 |
1983年 | 42篇 |
1982年 | 43篇 |
1981年 | 24篇 |
1980年 | 19篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1971年 | 4篇 |
1957年 | 8篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Yi Jiang Chuan-Lei Jia Xue-Lin Wang Ke-Ming Wang Hong-Ji Ma 《Applied Surface Science》2006,253(5):2674-2677
A planar optical waveguide has been formed in a LiB3O5 crystal using 6.0 MeV Cu+-ions with a dose of 1 × 1015 ions/cm2 at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE0 and TM0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change. 相似文献
122.
Imaging mass spectrometry requires the acquisition and interpretation of hundreds to thousands of individual spectra in order to map the mineral phases within heterogeneous geomatrices. A fuzzy logic inference engine (FLIE) was developed to automate data interpretation. To evaluate the strengths and limitations of FLIE, the chemical images obtained using FLIE were compared with those developed using two chemometric methods: principle component analysis (PCA) and cluster analysis (K-Means). Two heterogeneous geomatrices, a low-grade chalcopyrite ore and basalt, were imaged using a laser-desorption Fourier transform mass spectrometer. Similar mineral distribution patterns in the chalcopyrite ore sample were obtained by the three data analysis methods with most of the differences occurring at the interfaces between mineral phases. PCA missed one minor mineral phase in the chalcopyrite ore sample and did not clearly differentiate among the mineral classes of the basalt. K-Means cluster analysis differentiated among the various mineral phases in both samples, but improperly grouped some spectra in the chalcopyrite sample that only contained unanticipated high mass peaks. Unlike the chemometric methods, FLIE was able to classify spectra as unknowns for those spectra that fell below the confidence level threshold. A nearest neighbor approach, included in FLIE, was used to classify the unknowns to form a visually complete image; however, the unknowns identified by FLIE can be informative because they highlight potential problems or overlooked results. In conclusion, this study validated the fuzzy logic-based approach used in our laboratory and reveald some limitations in the three techniques that were evaluated. 相似文献
123.
采用固相反应合成了四羟基苯基卟啉与与Fe^2+,Co^2+金属离子的配合物,在室温下,将其与分子O2作用,提纯后得到两种固态氧合配合物.通过元素分析、红外光谱(IR)、核磁共振氢谱(^1HNMR)、电导、热分析(TG/DTA)、紫外光谱(UV)等测试手段确定了氧合配合物的组成为[Co·THPP·O2](NO3)2·2H2O、[Fe·THPP·O2]Cl2·2H2O],可知1mol配合物吸收了1molO2,采用失重法测定了氧合配合物中的配位氧,确定1mol金属配合物吸收1molO2形成超氧配合物. 相似文献
124.
Jiang Tongsong Liu Yonghui Wei Musheng 《高校应用数学学报(英文版)》2006,21(1):113-118
This paper derives a theorem of generalized singular value decomposition of quaternion matrices (QGSVD),studies the solution of general quaternion matrix equation AXB -CYD= E,and obtains quaternionic Roth's theorem. This paper also suggests sufficient and necessary conditions for the existence and uniqueness of solutions and explicit forms of the solutions of the equation. 相似文献
125.
Tao Jin Feng-Xian Jiang Xiao-Li Li Fang Wang Xiao-Hua Shen Rui-Qiang Zhang Hai-Shun Wu 《Applied Surface Science》2006,253(5):2708-2712
CoPt/Ag and [C/CoPt]n/Ag thin films have been prepared onto the glass substrates by magnetron sputtering. We investigated the evolution of texture and magnetic properties of CoPt/Ag and [C/CoPt]n/Ag films. The results show that C-doping plays an important role in improving (0 0 1) texture, improving the order parameter S, reducing the intergrain interactions, and making the magnetization reversal mechanism more close to Stoner-Wolfarth rotational mechanism. The growth mechanism of (0 0 1) texture also seems to be related strongly to the films thickness. Our results show that the highly (0 0 1)-oriented films with ordered fct phase have a significant potential for the perpendicular media of extremely high-density recording. 相似文献
126.
127.
128.
基于一个描述夸克胶子火柱演化的相对论流体力学模型,研究了夸克相、强子相互作用以及非热过程(DrellYan对、粲强子衰变)的中等质量双轻子的产生.发现由于相边对夸克胶子物质演化的影响和RHIC能量核碰撞产生的夸克胶子物质具有高的初始温度,夸克相对双轻子的贡献显著增强,比那些来自强子相互作用的贡献重要,甚至能与来自非热的贡献比较.表明中等质量双轻子的增强是一个在核碰撞中产生了夸克胶子物质的可能信号.
关键词:
夸克-胶子物质
双轻子增强
相对论流体力学模型 相似文献
129.
130.
Jie Xue Liang Chen Li Zhou Zhifeng Jia Yanping Wang Xinyuan Zhu Deyue Yan 《Journal of Polymer Science.Polymer Physics》2006,44(15):2050-2057
α‐Cyclodextrin (α‐CD) has been complexed with various poly(ethylene glycol) (PEG) derivatives in aqueous solution. It has been found that the end groups of PEG derivatives affect the complexation kinetics greatly, but have only a little influence on the thermodynamic behavior. By increasing the hydrophobicity of end groups, the complexation speeds up rapidly. On the other hand, the bulky end groups slow down the threading of polymeric guests into the cavity of CD. By changing the hydrophobicity and the size of end groups, the complexation rate can be adjusted in the range of several orders of magnitudes, which should be quite useful in the design of new supramolecular systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2050–2057, 2006 相似文献