全文获取类型
收费全文 | 2270篇 |
免费 | 251篇 |
国内免费 | 193篇 |
专业分类
化学 | 1713篇 |
晶体学 | 29篇 |
力学 | 96篇 |
综合类 | 12篇 |
数学 | 219篇 |
物理学 | 645篇 |
出版年
2024年 | 3篇 |
2023年 | 40篇 |
2022年 | 70篇 |
2021年 | 68篇 |
2020年 | 77篇 |
2019年 | 96篇 |
2018年 | 69篇 |
2017年 | 54篇 |
2016年 | 91篇 |
2015年 | 86篇 |
2014年 | 111篇 |
2013年 | 151篇 |
2012年 | 179篇 |
2011年 | 200篇 |
2010年 | 126篇 |
2009年 | 108篇 |
2008年 | 141篇 |
2007年 | 135篇 |
2006年 | 118篇 |
2005年 | 116篇 |
2004年 | 68篇 |
2003年 | 54篇 |
2002年 | 76篇 |
2001年 | 48篇 |
2000年 | 35篇 |
1999年 | 33篇 |
1998年 | 31篇 |
1997年 | 30篇 |
1996年 | 33篇 |
1995年 | 32篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 30篇 |
1991年 | 13篇 |
1990年 | 23篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1961年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2714条查询结果,搜索用时 62 毫秒
991.
利用耦合非线性薛定谔方程(CNLSE)为非线性偏振旋转(NPE)锁模自相似光纤激光器建立了一种新的数值模型.模型中,用CNLSE描述脉冲在单模光纤中的传播,在增益光纤中同时考虑了增益带宽和增益饱和作用,用传输矩阵描述构成NPE锁模的光学元件.优化了腔内净色散和光纤长度等参数,模拟了脉冲在激光腔内的演化特性,得到了典型的自相似脉冲运行区域及特点.在最佳自相似脉冲运行区域内,得到了能量约为7 nJ、脉宽约11 ps、线性啁啾的抛物脉冲.比较了不同腔内净色散条件下输出脉冲的特点,给出了三阶色散对输出脉冲的影响.
关键词:
自相似脉冲
非线性偏振旋转锁模
耦合非线性薛定谔方程
数值模拟 相似文献
992.
Zhi‐Min Jin Hai Feng Bing Tu Mei‐Chao Li Mao‐Lin Hu 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(10):o593-o595
The title complex, C8H6O4·2C6H7N, consists of two crystallographically independent 1:2 clusters of benzene‐1,3‐dicarboxylic acid and 4‐methylpyridine. Each cluster, the components of which are linked by O—H⋯N hydrogen bonds, is almost planar by alignment of C—H⋯O hydrogen bonds. Herring‐bone ribbons of clusters are formed by other C—H⋯O hydrogen bonds, and these ribbons are further packed to form a laminar structure by π–π interactions. 相似文献
993.
利用原子的塞曼光谱对半导体激光器进行稳频 总被引:4,自引:1,他引:3
中性原子的超精细能级在磁场中产生塞曼分裂 ,另外 ,左旋和右旋圆偏振光激发下原子的跃迁选择定则不同 ,因此 ,原子在超精细塞曼能级间的吸收谱峰相对无磁场条件下的吸收谱峰有一定的移动。利用这一点 ,验证了一种简单、灵活的方法对半导体激光器进行稳频 ,使激光器的线宽稳到小于 1MHz。通过对实验结果的分析 ,发现由左旋和右旋圆偏振光激发引起的原子吸收谱峰移动之和与饱和吸收峰半高宽相等时 ,稳频效果最好 相似文献
994.
995.
996.
The trend of miniaturization in bioanalytical chemistry is shifting from technical development to practical application. In matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), progress in miniaturizing sample spots has been driven by the needs to increase sensitivity and speed, to interface with other analytical microtechnologies, and to develop miniaturized instrumentation.We review recent developments in miniaturizing sample spots for MALDI-MS. We cover both target modification and microdispensing technologies, and we emphasize the benefits with respect to sensitivity, throughput and automation.We hope that this review will encourage further method development and application of miniaturized sample spots for MALDI-MS, so as to expand applications in analytical chemistry, protein science and molecular biology. 相似文献
997.
An expeditious and high-yield formal synthesis of hirsutene has been achieved. This synthesis features Rh(I)-catalyzed [(5+2)+1] cycloaddition to construct a bicyclic cyclooctenone, which can be efficiently transformed to bicyclic diketone, an advanced intermediate for racemic and asymmetric syntheses of hirsutene. 相似文献
998.
Xiao-Yan Gao Yong Jiang Jian-qiu Lu Peng-Fei Tu 《Journal of chromatography. A》2009,1216(11):2118-2123
Due to the complexity of the chemical constitution of traditional Chinese medicines (TCMs), now there is a trend to establish methods, using multi-components analysis, for the effective quality control of TCMs. However, the limited availability of multiple reference substances hinders the wide popularization for routine quality control of TCMs. Using an easily available single component contained in the analyte as an internal standard to determine multiple analogues should be a practical option. In this study, we selected rhubarb rhizome as an example, and used emodin, the easily available active component, as the external standard to determine directly the content of emodin in rhubarb, and the same component as the internal standard to simultaneously determine the other six anthraquinones in rhubarb. Compared with the results obtained using the external standard method, this alternative method was found to have no statistically significant differences in our laboratory as verified by the F-test (p = 95%, n = 6). However, due to weak robustness caused by the fluctuation of relative response factors in different laboratories, such a method can only serve as a practical measure to solve the lack of so many chemical standard substances when relative response factors have been determined. This alternative method can then be used without reference substances. Once the corresponding chemical standards are available and are acceptable as well as cost-effective, then the external standard method for the simultaneous determination of multiple components (SDMC) in TCMs will prevail. 相似文献
999.
1000.