全文获取类型
收费全文 | 10922篇 |
免费 | 1378篇 |
国内免费 | 795篇 |
专业分类
化学 | 4333篇 |
晶体学 | 17篇 |
力学 | 273篇 |
综合类 | 65篇 |
数学 | 1789篇 |
物理学 | 1847篇 |
综合类 | 4771篇 |
出版年
2024年 | 43篇 |
2023年 | 123篇 |
2022年 | 278篇 |
2021年 | 335篇 |
2020年 | 376篇 |
2019年 | 287篇 |
2018年 | 329篇 |
2017年 | 325篇 |
2016年 | 425篇 |
2015年 | 437篇 |
2014年 | 623篇 |
2013年 | 881篇 |
2012年 | 733篇 |
2011年 | 743篇 |
2010年 | 661篇 |
2009年 | 677篇 |
2008年 | 709篇 |
2007年 | 765篇 |
2006年 | 600篇 |
2005年 | 514篇 |
2004年 | 444篇 |
2003年 | 420篇 |
2002年 | 295篇 |
2001年 | 267篇 |
2000年 | 239篇 |
1999年 | 207篇 |
1998年 | 211篇 |
1997年 | 224篇 |
1996年 | 209篇 |
1995年 | 156篇 |
1994年 | 114篇 |
1993年 | 102篇 |
1992年 | 75篇 |
1991年 | 46篇 |
1990年 | 50篇 |
1989年 | 39篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 23篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Nano palladium supported on high‐surface‐area metal–organic framework MIL‐101: an efficient catalyst for Sonogashira coupling of aryl and heteroaryl bromides with alkynes
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Manne Annapurna T. Parsharamulu P. Vishnuvardhan Reddy M. Suresh Pravin R. Likhar Mannepalli Lakshmi Kantam 《应用有机金属化学》2015,29(4):234-239
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
4.
Single Crystal to Single Crystal (SC‐to‐SC) Transformation from a Nonporous to Porous Metal–Organic Framework and Its Application Potential in Gas Adsorption and Suzuki Coupling Reaction through Postmodification
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Rupam Sen Debraj Saha Dr. Subratanath Koner Dr. Paula Brandão Dr. Zhi Lin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5962-5971
A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH2 groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m2 g?1. The material also possesses good CO2 (8 wt %) and H2 (1.87 wt %) adsorption capabilities. 相似文献
5.
6.
为了减少能量空洞和延长网络生命周期,在无线传感网中采用移动 Sink 的方式收集节点采集的数据是解决能
量效率问题的有效措施.采集路径的规划问题类似于旅行商问题,无法得到多项式时间的解.提出了将人工免疫算法和粒子群算法相结合,针对移动 sink 数据收集的路径规划问题寻求近似最优解,仿真结果表明: 与其他算法进行性能比较,所提出的优化算法能够有效减少能耗和缩短遍历路径. 相似文献
7.
Mariusz Marć Marek Tobiszewski Bożena Zabiegała Miguel de la Guardia Jacek Namieśnik 《Analytica chimica acta》2015
This review summarizes the different tools and concepts that are commonly applied in air quality monitoring. The monitoring of atmosphere is extremely important as the air quality is an important problem for large communities. Main requirements for analytical devices used for monitoring include a long period of autonomic operation and portability. These instruments, however, are often characterized by poor analytical performance. Monitoring networks are the most common tools used for monitoring, so large-scale monitoring programmes are summarized here. Biomonitoring, as a cheap and convenient alternative to traditional sample collection, is becoming more and more popular, although its main drawback is the lack of standard procedures. Telemonitoring is another approach to air monitoring, which offers some interesting opportunities, such as ease of coverage of large or remote areas, constituting a complementary approach to traditional strategies; however, it requires huge costs. 相似文献
8.
Dr. Man-Bo Li Daniels Posevins Dr. Karl P. J. Gustafson Dr. Cheuk-Wai Tai Dr. Andrey Shchukarev Dr. Youai Qiu Dr. Jan-E. Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(1):210-215
A highly selective and efficient oxidative carbocyclization/borylation of enallenols catalyzed by palladium immobilized on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was developed for diastereoselective cyclobutenol synthesis. The heterogeneous palladium catalyst can be recovered and recycled without any observed loss of activity or selectivity. The high diastereoselectivity of the reaction is proposed to originate from a directing effect of the enallenol hydroxyl group. Optically pure cyclobutenol synthesis was achieved by the heterogeneous strategy by using chiral enallenol obtained from kinetic resolution. 相似文献
9.
梯度网络平稳点集合的Hopfield稳定性与吸引域 总被引:1,自引:1,他引:0
给出梯度神经网络模型的电路实现 ,证明了网络平稳点集合的全局 Hopfield稳定性。对各个平稳点吸引域的几何估计得到了相关结果 ,这为网络初始输入的数量与方向判定提供了基本的量度参数准则。 相似文献
10.
基于神经网络智能天线的一种波达方向估计方法 总被引:1,自引:0,他引:1
该文提出利用径向基函数神经网络来估计无线通信中智能天线的信号到达方向.为了减少输入,利用信号相关阵的对称性质,仅考虑相关阵中的上三角或下三角的部分元素作为网络的输入量,计算量较小.计算机模拟结果表明,该方案是有效的. 相似文献