全文获取类型
收费全文 | 8881篇 |
免费 | 1385篇 |
国内免费 | 827篇 |
专业分类
化学 | 5089篇 |
晶体学 | 84篇 |
力学 | 328篇 |
综合类 | 84篇 |
数学 | 528篇 |
物理学 | 1936篇 |
无线电 | 3044篇 |
出版年
2024年 | 55篇 |
2023年 | 207篇 |
2022年 | 315篇 |
2021年 | 359篇 |
2020年 | 379篇 |
2019年 | 376篇 |
2018年 | 307篇 |
2017年 | 333篇 |
2016年 | 427篇 |
2015年 | 495篇 |
2014年 | 559篇 |
2013年 | 650篇 |
2012年 | 717篇 |
2011年 | 688篇 |
2010年 | 555篇 |
2009年 | 564篇 |
2008年 | 576篇 |
2007年 | 509篇 |
2006年 | 470篇 |
2005年 | 409篇 |
2004年 | 286篇 |
2003年 | 281篇 |
2002年 | 251篇 |
2001年 | 188篇 |
2000年 | 170篇 |
1999年 | 139篇 |
1998年 | 93篇 |
1997年 | 89篇 |
1996年 | 94篇 |
1995年 | 74篇 |
1994年 | 69篇 |
1993年 | 49篇 |
1992年 | 52篇 |
1991年 | 47篇 |
1990年 | 43篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1974年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Bivas Mondal Rakesh Maiti Xing Yang Jun Xu Weiyi Tian Jia-Lei Yan Xiangyang Li Yonggui Robin Chi 《Chemical science》2021,12(25):8778
4,5-Dihydropyridazinones bearing an aryl substituent at the C6-position are important motifs in drug molecules. Herein, we developed an efficient protocol to access aryl-dihydropyridazinone molecules via carbene-catalyzed asymmetric annulation between dinucleophilic arylidene hydrazones and bromoenals. Key steps in this reaction include polarity-inversion of aryl aldehyde-derived hydrazones followed by chemo-selective reaction with enal-derived α,β-unsaturated acyl azolium intermediates. The aryl-dihydropyridazinone products accessed by our protocol can be readily transformed into drugs and bioactive molecules.Polarity inversion of arylidene hydrazones to react with bromoenals via carbene organic catalysis is disclosed. The reaction enantioselectively affords 6-aryl-4,5-dihydropyridazinones and related drugs with proven commercial applications. 相似文献
72.
二水草酸锌脱水的热分解动力学研究 总被引:10,自引:0,他引:10
提出一种多升温速率-等温法确定机理函数g(α)的新方法;并用迭代的等转化率法求出较为可靠的活化能Ea;在Ea和g(α)的基础上计算出指前因子A.用该法对二水草酸锌(ZnC2O4•2H2O)脱水反应的热分解动力学三因子进行了求算,得出Ea为87.22 kJ•mol-1, A为4.2120×108~7.2328×108 s-1;以及随机成核和随后生长型机理函数Am(Avrami-Erofeer),其积分形式g(α)=[-ln(1-α)] 1/m和微分形式f(α)=m(1-α)•[-ln(1-α)](1-1/m),调节因子m=1.85~2.00. 相似文献
73.
74.
Y Masuo H Wang D Pélaprat Z Q Chi W Rostène 《Chemical & pharmaceutical bulletin》1992,40(9):2520-2524
We have recently demonstrated that [3H]ohmefentanyl, a non-peptidergic opioid ligand which was suggested to cross the blood brain barrier in contrast to other peptidergic opioid ligands, bound not only to mu opioid receptor sites but also to sigma sites. In order to examine whether [3H]ohmefentanyl can be used as a marker for mu sites, we investigated the effects of brain lesions on [3H]ohmefentanyl binding site densities, as compared with [3H][D-Ala2, MePhe4, Gly-ol5]enkephalin ([3H]DAGO), a selective mu ligand. These binding site densities were measured by quantitative autoradiography in the rat striatum and substantia nigra, two brain structures known to contain a high density of mu receptors, following lesions of the nigro-striatal dopaminergic pathway and striatal intrinsic neurons. Following unilateral nigral lesion with 6-hydroxydopamine, [3H]ohmefentanyl binding site densities were decreased in the patches (-35%) and matrix (-20%) of the ipsilateral striatum and in the lesioned substantia nigra pars compacta (-49%). Unilateral striatal lesion with quinolinic acid induced 72%, 61% and 50% decreases in [3H]ohmefentanyl binding in the patches and matrix of the lesioned striatum and in the ipsilateral substantia nigra pars reticulata, respectively. Similar results were obtained in the binding of [3H]DAGO. Indeed, a significant linear correlation was observed between [3H]ohmefentanyl and [3H]DAGO binding site densities. Therefore, mu opioid receptors may be mainly located on intrinsic neurons in the striatum, dopaminergic cell bodies in the substantia nigra pars compacta and nerve terminals of striatal efferents in the substantia nigra pars reticulata.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
75.
SHI Wei-Feng JIANG Nan WANG Jian-Bo 《有机化学》2003,23(Z1):17-17
In the process of preparing α-diazo carbonyl compound 2 by imidation of 1, we unexpectedly observed a direct conversion of the hydroxyl group into trichloroacetylamino group. In this presentation, we report this unprecedented reaction, as well as the Rh2(OAc)4-catalyzed reaction of the resulting β-(trichloroacetyl)amino β-diazo carbonylcompounds 3. [ 1] 相似文献
76.
民参军是军民融合的重要组成内容,政府支持对于民参军的顺利进行发挥着关键作用。本文通过建立军民融合背景下的地方政府支持与民企参军行为的演化博弈模型,考察了参与者的决策演化过程,分析了参与者的进化稳定策略及影响因素。研究表明,增加地方政府对民企的资金奖励、加大民企参军税收优惠、民企资金收益率的提升,以及积极参军成本的降低,会使民企策略选择向积极参军方向演化,但却使地方政府行为向弱力度支持策略演化;而提升中央政府对地方政府的资金补助,降低地方政府支持民企积极参军的服务成本,不仅促使民企选择积极参军策略,还能促使地方政府选择强力度支持策略。最后,对模型结果进行算例分析,验证了结论的合理性。研究结果可以为当前民参军实践提供一定的理论指导。 相似文献
77.
78.
With the expansion of smart grid and Internet of things (IoT) technology, edge computing has a wide variety of applications in these domains. The criteria for real-time monitoring and accuracy are particularly high in the field of online real-time monitoring of electricity lines. Based on edge technology, high-quality real-time monitoring can be performed for transmission lines using image processing techniques. Therefore, we propose an image denoising method, which can learn clean images using a stream-based generative model. The stream model uses a two-stage approach in the network to handle the different training periods of denoising separately. Experimental results show that the proposed method has good denoising performance. 相似文献
79.
80.
Zihao Zhang Zirong He Nan Wang Fengmei Wang Chongyu Du Jiafeng Ruan Qin Li Dalin Sun Fang Fang Fei Wang 《Advanced functional materials》2023,33(27):2214648
Rechargeable aqueous zinc batteries are promising energy storage devices because of their low cost, high safety, and high energy density. However, their performance is plagued by the unsatisfied cyclability due to the dendrite growth and hydrogen evolution reaction (HER) at the Zn anode. Herein, it is demonstrated that the concentrated hybrid aqueous/non-aqueous ZnCl2 electrolytes constitute a peculiar chemical environment for not only the Zn-ions but also water molecules. The high concentration of chloride ions substitutes the H2O molecular in the solvation structure of Zn2+, while the acetonitrile further interacts with H2O to decrease its activity. The hybrid electrolytes both inhibit the dendrite formation and HER, enabling an ultrahigh average Coulombic efficiency of 99.9% in the Zn||Cu half-cell and a highly reversible Zn plating/stripping with a low overpotential of 21 mV. Using this hybrid electrolyte, the Zn||polytriphenylamine (PTPAn) full cell deliveres a high discharge capacity of 110 mAh g−1, a high power density of 9200 W kg−1 at 100 °C and maintains 85% of the capacity for over 6000 cycles at 10 °C. This study provides a deep understanding between the solvation structure and columbic efficiency of Zn anode, thus inspiring the development for stable Zn batteries. 相似文献