首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   26185篇
  免费   4421篇
  国内免费   3348篇
化学   19142篇
晶体学   320篇
力学   1531篇
综合类   240篇
数学   3104篇
物理学   9617篇
  2024年   30篇
  2023年   475篇
  2022年   586篇
  2021年   780篇
  2020年   980篇
  2019年   1053篇
  2018年   850篇
  2017年   835篇
  2016年   1126篇
  2015年   1163篇
  2014年   1527篇
  2013年   2023篇
  2012年   2406篇
  2011年   2690篇
  2010年   1853篇
  2009年   1856篇
  2008年   1960篇
  2007年   1792篇
  2006年   1549篇
  2005年   1254篇
  2004年   1000篇
  2003年   776篇
  2002年   757篇
  2001年   639篇
  2000年   587篇
  1999年   473篇
  1998年   385篇
  1997年   326篇
  1996年   365篇
  1995年   307篇
  1994年   256篇
  1993年   215篇
  1992年   193篇
  1991年   167篇
  1990年   138篇
  1989年   130篇
  1988年   76篇
  1987年   59篇
  1986年   63篇
  1985年   48篇
  1984年   39篇
  1983年   30篇
  1982年   20篇
  1981年   17篇
  1980年   9篇
  1979年   15篇
  1977年   7篇
  1976年   9篇
  1975年   7篇
  1957年   7篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
1.
2.
Liang  Guiming  Huang  Yunbao  Li  Haiyan  Lin  Jingliang 《Nonlinear dynamics》2021,105(4):3393-3407
Nonlinear Dynamics - The modal truncation is usually used in the dynamic response analysis of flexible multibody systems, in which, appropriate selection of modal shapes is very critical to achieve...  相似文献   
3.
Zheng  Xinyan  Hu  Po  Yao  Ruxian  cheng  Jinhe  Chang  Yiheng  Wu  Haitao  Mei  Hongying  Sun  Shuxiang  Chen  Qingtai  liu  Fang  Chen  Shujing  Wen  Hua 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(5):2217-2226
Journal of Radioanalytical and Nuclear Chemistry - Enhancement of U(VI) biomineralization by Saccharomyces cerevisiae through addition of inorganic phosphorus was studied in this work. The addition...  相似文献   
4.
5.
Hou  Gaoyuan  Zhao  Sishun  Peng  Liyuan  Fang  Zhiqiang  Isogai  Akira 《Cellulose (London, England)》2022,29(13):7365-7376
Cellulose - A bleached softwood kraft pulp was phosphorylated with (NH4)2HPO4 and urea at 150 ℃ for 0‒40 min, and the structures and properties of the resulting...  相似文献   
6.
Given a graph sequence denote by T3(Gn) the number of monochromatic triangles in a uniformly random coloring of the vertices of Gn with colors. In this paper we prove a central limit theorem (CLT) for T3(Gn) with explicit error rates, using a quantitative version of the martingale CLT. We then relate this error term to the well-known fourth-moment phenomenon, which, interestingly, holds only when the number of colors satisfies . We also show that the convergence of the fourth moment is necessary to obtain a Gaussian limit for any , which, together with the above result, implies that the fourth-moment condition characterizes the limiting normal distribution of T3(Gn), whenever . Finally, to illustrate the promise of our approach, we include an alternative proof of the CLT for the number of monochromatic edges, which provides quantitative rates for the results obtained in [7].  相似文献   
7.
Acridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the “living”/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain-end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst.  相似文献   
8.
Surface plasmon can trigger or accelerate many photochemical reactions, especially useful in energy and environmental industries. Recently, molecular adsorption has proven effective in modulating plasmon-mediated photochemistry, however the realized chemical reactions are limited and the underlying mechanism is still unclear. Herein, by using in situ dark-field optical microscopy, the plasmon-mediated oxidative etching of silver nanoparticles (Ag NPs), a typical hot-hole-driven reaction, is monitored continuously and quantitatively. The presence of thiol or thiophenol molecules is found essential in the silver oxidation. In addition, the rate of silver oxidation is modulated by the choice of different thiol or thiophenol molecules. Compared with the molecules having electron donating groups, the ones having electron accepting groups accelerate the silver oxidation dramatically. The thiol/thiophenol modulation is attributed to the modulation of the charge separation between the Ag NPs and the adsorbed thiol or thiophenol molecules. This work demonstrates the great potential of molecular adsorption in modulating the plasmon-mediated photochemistry, which will pave a new way for developing highly efficient plasmonic photocatalysts.  相似文献   
9.
Zhang  Zhen  Gao  Zhi-Tong  Fang  Bo  Zhang  Ye-Wei 《Nonlinear dynamics》2022,109(3):1259-1275
Nonlinear Dynamics - As a simplified model of structures of many kinds, the Euler Bernoulli beam has proved useful for studying vibration suppression. In order to meet engineering design...  相似文献   
10.
Four photo-catalysts of the general formula [Ir(CO6/ppy)2(L)]Cl where CO6=coumarin 6 ( Ir1 – Ir3 ), ppy=2-phenylpyridine ( Ir4 ), L=4′-(3,5-di-tert-butylphenyl)-2,2′ : 6′,2′′-terpyridine ( Ir1 ), 4′-(3,5-bis(trifluoromethyl)phenyl)-2,2′ : 6′,2′′-terpyridine ( Ir2 and Ir4 ), and 4-([2,2′ : 6′,2′′-terpyridin]-4′-yl)-N,N-dimethylaniline ( Ir3 ) were synthesized and characterized. These photostable photo-catalysts ( Ir1 – Ir3 ) showed strong visible light absorption between 400–550 nm. Upon light irradiation (465 and 525 nm), Ir1 – Ir3 generated singlet oxygen and induced rapidly photo-catalytic oxidation of cellular coenzymes NAD(P)H. Ir1 – Ir3 showed time-dependent cellular uptake with excellent intracellular retention efficiency. Upon green light irradiation (525 nm), Ir2 provided a much higher photo-index (PI=793) than the clinically used photosensitizer, 5-aminolevulinicacid (5-ALA, PI>30) against HeLa cancer cells. The observed necro-apoptotic anticancer activity of Ir2 was due to the Ir2 triggered photo-induced intracellular redox imbalance (by NAD(P)H oxidation and ROS generation) and change in the mitochondrial membrane potential. Remarkably, Ir2 showed in vivo photo-induced catalytic anticancer activity in mouse models.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号