全文获取类型
收费全文 | 24644篇 |
免费 | 4060篇 |
国内免费 | 3966篇 |
专业分类
化学 | 18313篇 |
晶体学 | 508篇 |
力学 | 1455篇 |
综合类 | 384篇 |
数学 | 2969篇 |
物理学 | 9041篇 |
出版年
2024年 | 38篇 |
2023年 | 365篇 |
2022年 | 663篇 |
2021年 | 780篇 |
2020年 | 904篇 |
2019年 | 871篇 |
2018年 | 714篇 |
2017年 | 820篇 |
2016年 | 1062篇 |
2015年 | 1112篇 |
2014年 | 1315篇 |
2013年 | 1807篇 |
2012年 | 2130篇 |
2011年 | 2239篇 |
2010年 | 1707篇 |
2009年 | 1612篇 |
2008年 | 1815篇 |
2007年 | 1582篇 |
2006年 | 1568篇 |
2005年 | 1392篇 |
2004年 | 1041篇 |
2003年 | 887篇 |
2002年 | 998篇 |
2001年 | 759篇 |
2000年 | 662篇 |
1999年 | 558篇 |
1998年 | 401篇 |
1997年 | 353篇 |
1996年 | 363篇 |
1995年 | 319篇 |
1994年 | 275篇 |
1993年 | 248篇 |
1992年 | 226篇 |
1991年 | 190篇 |
1990年 | 181篇 |
1989年 | 137篇 |
1988年 | 120篇 |
1987年 | 82篇 |
1986年 | 77篇 |
1985年 | 83篇 |
1984年 | 41篇 |
1983年 | 41篇 |
1982年 | 31篇 |
1981年 | 31篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1973年 | 3篇 |
1971年 | 4篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
961.
Hui Li Zejun Jiang Xiaolin Cao Hang Su Hua Shao Fen Jin Lufei Zheng A. M. Abd El-Aty Jing Wang 《Chromatographia》2018,81(2):359-364
962.
Spectrum reservation strategy is an effective technology for conserving communication resources in Cognitive Radio Networks. In order to better adapt to changes of the system load, we present an adaptive control approach to determine the reservation ratio of the licensed spectrum for secondary users and propose a novel adaptive spectrum reservation strategy. We then establish a three-dimensional discrete time Markov Chain model to capture the stochastic behavior of users. By using a method similar to that of the matrix geometric solution, we obtain the steady-state probability distribution for the system model, and derive the formulas for some required performance measures of two types of users. Numerical experiments and simulation experiments indicate that the system performance is sensitive to system parameters like the adaptive control factor and the admission threshold. Finally, we construct a system cost function to balance different performance measures, and present an intelligent searching algorithm to optimize the system parameters with the global minimum system cost. 相似文献
963.
正Living cells are open systems that exist far away from a state of thermodynamical equilibrium.They utilize the high-grade chemical energy provided by food to produce ATP and release ADP and Pi together with heat dissipation.Living cells exist in a non-equilibrium steady state(NESS),they replicate themselves and respond to various environmental changes via 相似文献
964.
965.
966.
967.
Shixiong Chen Xiaotian Zhao Ming Jin Wanqiu Huang Guodong Ye Haiyan Pan Decheng Wan 《Journal of polymer science. Part A, Polymer chemistry》2021,59(17):1899-1911
Four 1,5-diphenyl-3-aromatic heterocyclyl-2-pyrazoline-based sulfonium salt photoacid generators (PAGs) with different aromatic heterocycles substituted on C3 atom and dimethyl sulfonium group on C5 atom were synthesized. These PAGs were highly photosensitive in the 365–425 nm light-emitting diode region, and the intramolecular charge transfer from the pyrazoline ring to sulfonium salts induced efficient photolysis and high ΦH+. The heterocycles as well as their substituted positions significantly influenced the energy of the S2 orbital, which was determined by the electrochemical and absorption properties of the PAGs. The raising of the S2 orbital energy enlarged the energy gap of S0–S2 and S1–S2, resulting in blue shift of the absorption spectra and increase in the quantum yield of photoacid generation (ΦH+), respectively. When the energy of excited electrons was higher than that of the S2 orbital, the transition from S0 to S2 (π–π*) occurred before the C-S cleavage on S1 and the PAGs showed high ΦH+ values (0.52–0.72). The transition from S0 to S1 (π–σ*) occurred when the energy of electrons is lower than that of the S2 orbital, and the PAGs showed low ΦH+ value. The photopolymerization kinetics demonstrated that these PAGs were highly efficient cationic photoinitiators. 相似文献
968.
Ping Lv Xin Shen Zhiliyu Cui Bo Li Qiangqiang Xu Zhuo Yu Weijie Lu Haonan Shao Yan Ge Zhenhui Qi 《Journal of polymer science. Part A, Polymer chemistry》2021,59(23):3001-3008
Fiber-reinforced-concrete (FRC) mechanism refers short discrete fibers that are uniformly distributed and randomly oriented, which offers an effective way to improve the mechanical performance of concrete. In the design of supramolecular polymers, an analogous concept of FRC appears to have been considered very rarely-although fibrous structure has been frequently observed/generated during the supramolecular polymerization. In this work, we apply the alkane thermosets, octadecane (C18H38) and tetracosane (C24H50), taking the role of “concrete”, and the low-molecular-weight monomer with long alkyl chains as the essential “fiber” component, to fabricate the “fiber reinforced supramolecular polymer”. Very much like FRC mechanism in material science, the resulting fiber reinforced supramolecular polymer thus exhibit unusually high mechanical strength and stiffness, which is unprecedented in the conventional supramolecular strategy. 相似文献
969.
970.
Chang Su Jin‐Song Gong Jin‐Peng Ye Ji‐Meng He Rui‐Yi Li Min Jiang Yan Geng Yan Zhang Jing‐Hua Chen Zheng‐Hong Xu Jin‐Song Shi 《Macromolecular bioscience》2020,20(9)
Keratin is widely recognized as a high‐quality renewable protein resource for biomedical applications. Despite their extensive existence, keratin resources such as feathers, wool, and hair exhibit high stability and mechanical properties because of their high disulfide bond content. Consequently, keratin extraction is challenging and its application is greatly hindered. In this work, a biological extraction strategy is proposed for the preparation of bioactive keratin and the fabrication of self‐assembled keratin hydrogels (KHs). Based on moderate and controlled hydrolysis by keratinase, keratin with a high molecular weight of approximately 45 and 28 kDa that retain its intrinsic bioactivities is obtained. The keratin products show excellent ability to promote cell growth and migration and are conferred with significant antioxidant ability because of their intrinsically high cysteine content. In addition, without the presence of any cross‐linking agent, the extracted keratin can self‐assemble into injectable hydrogels. The KHs exhibit a porous network structure and 3D culture ability, showing potential in promoting wound healing. This enzyme‐driven keratin extraction strategy opens up a new approach for the preparation of keratin that can self‐assemble into injectable hydrogels for biomedical engineering. 相似文献