全文获取类型
收费全文 | 28139篇 |
免费 | 4740篇 |
国内免费 | 2848篇 |
专业分类
化学 | 19743篇 |
晶体学 | 287篇 |
力学 | 1667篇 |
综合类 | 131篇 |
数学 | 3280篇 |
物理学 | 10619篇 |
出版年
2024年 | 34篇 |
2023年 | 623篇 |
2022年 | 659篇 |
2021年 | 950篇 |
2020年 | 1120篇 |
2019年 | 1143篇 |
2018年 | 1062篇 |
2017年 | 912篇 |
2016年 | 1439篇 |
2015年 | 1293篇 |
2014年 | 1582篇 |
2013年 | 2126篇 |
2012年 | 2532篇 |
2011年 | 2664篇 |
2010年 | 1782篇 |
2009年 | 1651篇 |
2008年 | 1887篇 |
2007年 | 1623篇 |
2006年 | 1514篇 |
2005年 | 1187篇 |
2004年 | 960篇 |
2003年 | 702篇 |
2002年 | 737篇 |
2001年 | 537篇 |
2000年 | 465篇 |
1999年 | 625篇 |
1998年 | 438篇 |
1997年 | 408篇 |
1996年 | 411篇 |
1995年 | 371篇 |
1994年 | 305篇 |
1993年 | 317篇 |
1992年 | 227篇 |
1991年 | 241篇 |
1990年 | 200篇 |
1989年 | 157篇 |
1988年 | 129篇 |
1987年 | 104篇 |
1986年 | 89篇 |
1985年 | 84篇 |
1984年 | 77篇 |
1983年 | 44篇 |
1982年 | 44篇 |
1981年 | 28篇 |
1980年 | 30篇 |
1978年 | 18篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1973年 | 17篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Hierarchical motion planning at the acceleration level based on task priority matrix for space robot
Nonlinear Dynamics - A capacitive micromachined ultrasonic transducer (CMUT) due to many benefits is being considered as an imaging and therapeutic technology recently. The critical challenge is to... 相似文献
22.
Jia Tian-Cong Guo Jin-Tao Wang Zhen Zhu Xiao-Shan Zhang Qian-Xin Chen Ping Yao Kun Lv Wen-Ying Liu Guo-Guang 《Journal of Radioanalytical and Nuclear Chemistry》2019,321(3):823-829
Journal of Radioanalytical and Nuclear Chemistry - In the present work the final products of coumarin radiation chemical transformation are investigated by chromatography. During radiolysis of... 相似文献
23.
Ding Q. Yao M. Wu Sh. Zeng M. Xue N. Wu D. Xu J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the... 相似文献
24.
Teobald Kupka Małgorzata A. Broda Piotr P. Wieczorek 《Magnetic resonance in chemistry : MRC》2020,58(6):584-593
The biologically active alkaloid muscimol is present in fly agaric mushroom (Amanita muscaria), and its structure and action is related to human neurotransmitter γ-aminobutyric acid (GABA). The current study reports on determination of muscimol form present in water solution using multinuclear 1H and 13C nuclear magnetic resonance (NMR) experiments supported by density functional theory molecular modeling. The structures of three forms of free muscimol molecule both in the gas phase and in the presence of water solvent, modeled by polarized continuous model, and nuclear magnetic isotropic shieldings, the corresponding chemical shifts, and indirect spin–spin coupling constants were calculated. Several J-couplings observed in proton and carbon NMR spectra, not available before, are reported. The obtained experimental spectra, supported by theoretical calculations, favor the zwitterion form of muscimol in water. This structure differs from NH isomer, previously determined in dimethyl sulfoxide (DMSO) solution. In addition, positions of signals C3 and C5 are reversed in both solvents. 相似文献
25.
We propose a system of time-division multiplexing(TDM) and spatial frequency-division multiplexing(SFDM). Extrinsic Fabry–Perot interferometric sensors are applied to detect weak acoustic signals. The broadband source is employed, the light from it is modulated by a pulse signal sequence and is efficiently amplified by semiconductor optical amplifiers. Experimental results show that the equivalent noise pressure spectrum level is-97.2 d B re 1 rad/√Hz below 1250 Hz, and the cross talk between two sensors in one TDM channel is-32.7 d B with a cavity length difference of 60 μm. The number of sensors in this multiplexing system can theoretically reach 160. 相似文献
26.
27.
Zhang Kailun Wu Hongjuan Wang Tian Yao Meng Xie Jixing Jiao Yunhong 《Journal of Thermal Analysis and Calorimetry》2021,145(6):3067-3075
Journal of Thermal Analysis and Calorimetry - A phosphazene-based flame retardant (PBFA) was synthesized by hexachlorocyclotriphosphazene and N-aminoethylpiperazine. To improve the flame retardancy... 相似文献
28.
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
29.
It is known that a distance-regular graph with valency k at least three admits at most two Qpolynomial structures. We show that all distance-regular graphs with diameter four and valency at least three admitting two Q-polynomial structures are either dual bipartite or almost dual bipartite. By the work of Dickie(1995) this implies that any distance-regular graph with diameter d at least four and valency at least three admitting two Q-polynomial structures is, provided it is not a Hadamard graph, either the cube H(d, 2)with d even, the half cube 1/2H(2d + 1, 2), the folded cube?H(2d + 1, 2), or the dual polar graph on [2A2d-1(q)]with q 2 a prime power. 相似文献
30.
基于深度学习的方法,在HL-2A装置上开发出了一套边缘局域模(ELM)实时识别算法。算法使用5200次放电数据(约24.19万数据切片)进行学习,得到一个深度为22层的卷积神经网络。为衡量算法的识别能力,识别了HL-2A装置自2009年实现稳定ELMy H模放电以来所有历史数据(约26000次放电数据),共识别出1665次H模放电,其中误识别35次,误报率为2.10%。在实际的1634次H模放电中,漏识别4次,漏识别率为0.24%。该误报率和漏报率可以满足ELM实时识别的精度要求。识别算法在实时控制环境下,对单个时间点的平均计算时间为0.46ms,可以满足实时控制的计算速度要求。 相似文献