全文获取类型
收费全文 | 19202篇 |
免费 | 2815篇 |
国内免费 | 1897篇 |
专业分类
化学 | 10878篇 |
晶体学 | 181篇 |
力学 | 816篇 |
综合类 | 67篇 |
数学 | 1805篇 |
物理学 | 4711篇 |
无线电 | 5456篇 |
出版年
2024年 | 45篇 |
2023年 | 531篇 |
2022年 | 560篇 |
2021年 | 838篇 |
2020年 | 874篇 |
2019年 | 730篇 |
2018年 | 648篇 |
2017年 | 573篇 |
2016年 | 882篇 |
2015年 | 942篇 |
2014年 | 993篇 |
2013年 | 1403篇 |
2012年 | 1557篇 |
2011年 | 1569篇 |
2010年 | 1090篇 |
2009年 | 1140篇 |
2008年 | 1285篇 |
2007年 | 1090篇 |
2006年 | 1048篇 |
2005年 | 958篇 |
2004年 | 666篇 |
2003年 | 572篇 |
2002年 | 552篇 |
2001年 | 427篇 |
2000年 | 377篇 |
1999年 | 392篇 |
1998年 | 278篇 |
1997年 | 221篇 |
1996年 | 256篇 |
1995年 | 209篇 |
1994年 | 176篇 |
1993年 | 147篇 |
1992年 | 131篇 |
1991年 | 113篇 |
1990年 | 116篇 |
1989年 | 85篇 |
1988年 | 72篇 |
1987年 | 53篇 |
1986年 | 47篇 |
1985年 | 52篇 |
1984年 | 42篇 |
1983年 | 23篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1972年 | 7篇 |
1971年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
21.
Dongping Wang Jie Dong Wenjing Fan Prof. Dr. Xiang-Ai Yuan Prof. Dr. Jian Han Prof. Dr. Jin Xie 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(22):8508-8512
An unprecedented Mn(I)-catalyzed selective hydroarylation and hydroalkenylation of unsaturated amides with commercially available organic boronic acids is reported. Alkenyl boronic acids have been successfully employed for the first time in Mn(I)-catalyzed carbon–carbon bond formation. A wide array of β-alkenylated amide products can be obtained in moderate to good yields, which offers practical access to five- and six-membered lactams. This protocol has predictable regio- and chemoselectivity, excellent functional group compatibility and ease of operation in air, representing a significant step-forward towards manganese-catalyzed C−C coupling. 相似文献
22.
Quantitative analysis of polyhexamethylene guanidine (PHMG) oligomers via matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry with an ionic‐liquid matrix
下载免费PDF全文
![点击此处可从《Rapid communications in mass spectrometry : RCM》网站下载免费的PDF全文](/ch/ext_images/free.gif)
23.
24.
Development of an LC‐MS/MS method for determining the pharmacokinetics of clonidine following oral administration of Zhenju antihypertensive compound
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jing Qin Limin Wang Lihong Wu Jun Chen Teng Shen Yongji Li Limei Han Jianxin Wang 《Biomedical chromatography : BMC》2015,29(7):1068-1075
Zhenju antihypertensive compound (ZJAHC) is a combined Chinese–Western medicine formula including clonidine (CLO), hydrochlorothiazide (HCT), rutin, Chrysanthemum indicum extract and pearl powder. Compared with CLO preparations, ZJAHC shows improved activities and decreased adverse effects. It is believed that the side effects of CLO are caused by its high peak plasma concentration. Hence, study of the influence of ZJAHC on the pharmacokinetic behaviors of clonidine seems essential. In present study, the plasma concentrations of CLO were determined with a liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method. The MS/MS transitions monitored for clonidine and internal standard were 230.2 → 213.1 and 152.2 → 110.2, respectively. The analyte was quantified in a single run within 3 min. The pharmacokinetic study showed that the area under the plasma concentration–time curve of CLO in ZJAHC (60 µg/kg CLO) was similar to that of CLO‐HCT‐high (120 µg/kg CLO) but the peak concentration was much lower than that in CLO‐HCT‐high. ZJAHC could enhance the bioavailability without greatly increasing peak concentration of clonidine. This comprehensive effect of enhancing the bioavailability and avoiding the high peak plasma concentration for CLO might mainly result from the co‐contribution of Western medicine and traditional Chinese medicine (TCM), while the effect of TCM was stronger than that of Western medicine. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
25.
Dr. Si-Yong Qin Yan Jiang Dr. Han Sun Han Liu Prof. Ai-Qing Zhang Prof. Xinxiang Lei 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(39):17245-17251
Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self-assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD3OD, [D6]DMSO, and D2O. The preparation of the OPA-based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy. 相似文献
26.
文章针对使用USB存储设备造成的内部泄密问题,提出了一种USB存储设备访问控制方案,该方案对用户的身份认证基于安全强度很高的椭圆曲线数字签名算法,同时使用过滤器驱动程序实现了USB存储设备的读写控制,因而此方案具有较好的安全性、实用性和通用性。 相似文献
27.
A new excimer laser annealing (ELA) process that uses a floating amorphous-Silicon (a-Si) thin film with a multichannel structure is proposed for high-performance poly-Si thin-film transistors (TFTs). The proposed ELA method produces two-dimensional (2-D) grain growth, which can result in a high-quality grain structure. The dual-gate structure was employed to eliminate the grain boundaries perpendicular to the current flow in the channel. A multichannel structure was adapted in order to arrange the grain boundary to be parallel to the current flow. The proposed poly-Si TFT exhibits high-performance electrical characteristics, which are a high mobility of 504 cm/sup 2//Vsec and a low subthreshold slope of 0.337 V/dec. 相似文献
28.
Young-Geun Han Sang Hyuck Kim Sang Bae Lee Un-Chul Paek Youngjoo Chung 《Electronics letters》2003,39(15):1107-1108
A novel fabrication method of the core mode blocker by exposing H/sub 2/-loaded Ge-B codoped fibres to local electric arc discharge for application to the LPFGs-based tunable all-fibre bandpass filter with 6.5 nm bandwidth and 40 nm tuning range is presented. 相似文献
29.
30.
论文提出了一种混沌通信系统的噪音衰减算法,该算法利用混沌同步现象在接收端获得正确的噪音估计值,从而从接收信号中滤除噪音恢复出正确的信号。通过数值仿真试验表明该方法是可行的。 相似文献