全文获取类型
收费全文 | 35490篇 |
免费 | 5552篇 |
国内免费 | 4811篇 |
专业分类
化学 | 25749篇 |
晶体学 | 569篇 |
力学 | 2167篇 |
综合类 | 402篇 |
数学 | 3943篇 |
物理学 | 13023篇 |
出版年
2024年 | 57篇 |
2023年 | 564篇 |
2022年 | 819篇 |
2021年 | 1103篇 |
2020年 | 1257篇 |
2019年 | 1318篇 |
2018年 | 1123篇 |
2017年 | 1189篇 |
2016年 | 1614篇 |
2015年 | 1663篇 |
2014年 | 1892篇 |
2013年 | 2578篇 |
2012年 | 3022篇 |
2011年 | 3193篇 |
2010年 | 2203篇 |
2009年 | 2217篇 |
2008年 | 2485篇 |
2007年 | 2297篇 |
2006年 | 2143篇 |
2005年 | 1698篇 |
2004年 | 1442篇 |
2003年 | 1213篇 |
2002年 | 1311篇 |
2001年 | 1041篇 |
2000年 | 850篇 |
1999年 | 793篇 |
1998年 | 625篇 |
1997年 | 550篇 |
1996年 | 580篇 |
1995年 | 467篇 |
1994年 | 464篇 |
1993年 | 355篇 |
1992年 | 298篇 |
1991年 | 276篇 |
1990年 | 205篇 |
1989年 | 166篇 |
1988年 | 141篇 |
1987年 | 116篇 |
1986年 | 114篇 |
1985年 | 102篇 |
1984年 | 64篇 |
1983年 | 53篇 |
1982年 | 40篇 |
1981年 | 31篇 |
1980年 | 33篇 |
1979年 | 20篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 8篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
In order to improve the signal-to-noise ratio and mitigate the damage of noise to the communication quality,an effective interference suppression algorithm,which is based on the improved density-based spatial clustering of applications with noise algorithms,is proposed for visible light communication systems using the complementary metal–oxide–semiconductor image sensor as the receiver.Experimental results show that the algorithm can learn the region where the payload data is located,filter out the noise data,and greatly decrease the interference.The effect of the algorithm is also studied through bit error ratio performance. 相似文献
32.
Dr. Feifan Wang Jie Tian Dr. Mengzhu Li Dr. Weizhen Li Dr. Lifang Chen Xiaozhi Liu Dr. Jian Li Aidaer Muhetaer Prof. Dr. Qi Li Prof. Dr. Yuan Wang Prof. Dr. Lin Gu Prof. Dr. Ding Ma Prof. Dr. Dongsheng Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8280-8286
Fully utilizing solar energy for catalysis requires the integration of conversion mechanisms and therefore delicate design of catalyst structures and active species. Herein, a MOF crystal engineering method was developed to controllably synthesize a copper–ceria catalyst with well-dispersed photoactive Cu-[O]-Ce species. Using the preferential oxidation of CO as a model reaction, the catalyst showed remarkably efficient and stable photoactivated catalysis, which found practical application in feed gas treatment for fuel cell gas supply. The coexistence of photochemistry and thermochemistry effects contributes to the high efficiency. Our results demonstrate a catalyst design approach with atomic or molecular precision and a combinatorial photoactivation strategy for solar energy conversion. 相似文献
33.
34.
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
35.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
36.
37.
A rapid method had been used for comparative study on Artemisia halodendron Turcz. and its two related plants by gas phase-mass spectrometry (GC-MS). The comparison of the volatile oils obtained in three plants by GC-MS were similar in 20 compositions. However, n-Hexadecanoic acid (10.40%), Biphenyl (7.867%) and 9,12-Octadecadienoic acid (7.25%) were the predominant in the volatile oils of A. halodendron Turcz., whereas these constituents did not exist in the other two plants. And the study investigated the effect of three plants against CCl4-induced hepatotoxicity in mice. 70% ethanol extracts of A. halodendron Turcz. showed weaker protective effect than the other two plants. It suggested that they provide a basis for the identification of the A. halodendron Turcz. from the other two plants and the ethanol extract from three plants exerted a protecting effect against hepatotoxicity. 相似文献
38.
39.
We investigate the statistics of polymer capture by a nanopore using Brownian dynamics simulations. It is found that when the velocity flux is greater than a critical velocity flux, the capture picture is a random selection process, otherwise it tends to a statistical process governed by energetic considerations. In addition, the chain ends capture probability decreases as the chain length increases and satisfies a power-law scaling of P0(N)~N-0.8. 相似文献
40.