全文获取类型
收费全文 | 20065篇 |
免费 | 3761篇 |
国内免费 | 3253篇 |
专业分类
化学 | 15510篇 |
晶体学 | 319篇 |
力学 | 1119篇 |
综合类 | 250篇 |
数学 | 2347篇 |
物理学 | 7534篇 |
出版年
2024年 | 20篇 |
2023年 | 426篇 |
2022年 | 574篇 |
2021年 | 780篇 |
2020年 | 990篇 |
2019年 | 932篇 |
2018年 | 793篇 |
2017年 | 789篇 |
2016年 | 1037篇 |
2015年 | 1071篇 |
2014年 | 1338篇 |
2013年 | 1649篇 |
2012年 | 1916篇 |
2011年 | 1967篇 |
2010年 | 1462篇 |
2009年 | 1375篇 |
2008年 | 1446篇 |
2007年 | 1288篇 |
2006年 | 1249篇 |
2005年 | 979篇 |
2004年 | 747篇 |
2003年 | 588篇 |
2002年 | 619篇 |
2001年 | 463篇 |
2000年 | 391篇 |
1999年 | 357篇 |
1998年 | 287篇 |
1997年 | 242篇 |
1996年 | 233篇 |
1995年 | 193篇 |
1994年 | 165篇 |
1993年 | 121篇 |
1992年 | 114篇 |
1991年 | 99篇 |
1990年 | 88篇 |
1989年 | 75篇 |
1988年 | 54篇 |
1987年 | 28篇 |
1986年 | 42篇 |
1985年 | 33篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1957年 | 4篇 |
1930年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
目前,针对空间电磁场作用有耗介质层上传输线的电磁耦合,仍缺乏有效的数值分析方法.因此,本文提出一种高效的时域混合算法,很好地解决了有耗介质层上传输线电磁耦合建模难的问题.首先,对经典传输线方程进行改进,推导了适用于有耗介质层上多导体传输线电磁耦合分析的修正传输线方程.然后,结合时域有限差分方法和相应插值技术,求解修正传输线方程,获得多导线及其端接负载上的电压和电流响应,并实现空间电磁场辐射与多导线瞬态响应的同步计算.最后,通过相应计算实例的数值模拟,与CST软件的仿真结果进行对比,验证了时域混合算法的正确性和高效性. 相似文献
52.
Nonlinear Dynamics - This paper extends the RGD model originally proposed by Richard et al. (J Sound Vib 305(3):432–456, 2007, https://doi.org/10.1016/j.jsv.2007.04.015) to investigate... 相似文献
53.
Yolk‐Shell Porous Microspheres of Calcium Phosphate Prepared by Using Calcium L‐Lactate and Adenosine 5′‐Triphosphate Disodium Salt: Application in Protein/Drug Delivery 下载免费PDF全文
Guan‐Jun Ding Prof. Dr. Ying‐Jie Zhu Chao Qi Tuan‐Wei Sun Dr. Jin Wu Dr. Feng Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9868-9876
A facile and environmentally friendly approach has been developed to prepare yolk‐shell porous microspheres of calcium phosphate by using calcium L ‐lactate pentahydrate (CL) as the calcium source and adenosine 5′‐triphosphate disodium salt (ATP) as the phosphate source through the microwave‐assisted hydrothermal method. The effects of the concentration of CL, the microwave hydrothermal temperature, and the time on the morphology and crystal phase of the product are investigated. The possible formation mechanism of yolk‐shell porous microspheres of calcium phosphate is proposed. Hemoglobin from bovine red cells (Hb) and ibuprofen (IBU) are used to explore the application potential of yolk‐shell porous microspheres of calcium phosphate in protein/drug loading and delivery. The experimental results indicate that the as‐prepared yolk‐shell porous microspheres of calcium phosphate have relatively high protein/drug loading capacity, sustained protein/drug release, favorable pH‐responsive release behavior, and a high biocompatibility in the cytotoxicity test. Therefore, the yolk‐shell porous microspheres of calcium phosphate have promising applications in various biomedical fields such as protein/drug delivery. 相似文献
54.
Xi‐Sha Zhang Yun‐Fei Zhang Zhao‐Wei Li Fei‐Xian Luo Zhang‐Jie Shi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(18):5568-5572
A rhodium(III)‐catalyzed cross‐coupling of benzyl thioethers and aryl carboxylic acids through the two directing groups is reported. Useful structures with diverse substituents were efficiently synthesized in one step with the cleavage of four bonds (C H, C S, O H) and the formation of two bonds (C C, C O). The formed structure is the privileged core in natural products and bioactive molecules. This work highlights the power of using two different directing groups to enhance the selectivity of a double C H activation, the first of such examples in cross‐oxidative coupling. 相似文献
55.
Cover Picture: One‐Step Synthesis of Silver Nanoparticle‐Decorated Hydroxyapatite Nanowires for the Construction of Highly Flexible Free‐Standing Paper with High Antibacterial Activity (Chem. Eur. J. 32/2016) 下载免费PDF全文
56.
57.
58.
Kinetic Resolution of Racemic Allylic Alcohols by Catalytic Asymmetric Substitution of the OH Group with Monosubstituted Hydrazines 下载免费PDF全文
Liang Yan Jing‐Kun Xu Chao‐Fan Huang Zeng‐Yang He Ya‐Nan Xu Prof. Dr. Shi‐Kai Tian 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(37):13041-13045
A new strategy has been established for the kinetic resolution of racemic allylic alcohols through a palladium/sulfonyl‐hydrazide‐catalyzed asymmetric OH‐substitution under mild conditions. In the presence of 1 mol % [Pd(allyl)Cl]2, 4 mol % (S)‐SegPhos, and 10 mol % 2,5‐dichlorobenzenesulfonyl hydrazide, a range of racemic allylic alcohols were smoothly resolved with selectivity factors of more than 400 through an asymmetric allylic alkylation of monosubstituted hydrazines under air at room temperature. Importantly, this kinetic resolution process provided various allylic alcohols and allylic hydrazine derivatives with high enantiopurity. 相似文献
59.
60.