全文获取类型
收费全文 | 153912篇 |
免费 | 12218篇 |
国内免费 | 9324篇 |
专业分类
化学 | 77796篇 |
晶体学 | 1698篇 |
力学 | 11422篇 |
综合类 | 737篇 |
数学 | 40832篇 |
物理学 | 42969篇 |
出版年
2024年 | 169篇 |
2023年 | 1510篇 |
2022年 | 2258篇 |
2021年 | 2609篇 |
2020年 | 2912篇 |
2019年 | 2829篇 |
2018年 | 12330篇 |
2017年 | 12011篇 |
2016年 | 9089篇 |
2015年 | 4332篇 |
2014年 | 4471篇 |
2013年 | 5915篇 |
2012年 | 10350篇 |
2011年 | 17099篇 |
2010年 | 10341篇 |
2009年 | 10573篇 |
2008年 | 11406篇 |
2007年 | 13083篇 |
2006年 | 4485篇 |
2005年 | 4956篇 |
2004年 | 4415篇 |
2003年 | 4208篇 |
2002年 | 3120篇 |
2001年 | 2170篇 |
2000年 | 2010篇 |
1999年 | 1913篇 |
1998年 | 1665篇 |
1997年 | 1404篇 |
1996年 | 1515篇 |
1995年 | 1260篇 |
1994年 | 1154篇 |
1993年 | 1001篇 |
1992年 | 861篇 |
1991年 | 767篇 |
1990年 | 630篇 |
1989年 | 557篇 |
1988年 | 438篇 |
1987年 | 427篇 |
1986年 | 363篇 |
1985年 | 361篇 |
1984年 | 252篇 |
1983年 | 221篇 |
1982年 | 196篇 |
1981年 | 153篇 |
1980年 | 131篇 |
1979年 | 98篇 |
1978年 | 95篇 |
1977年 | 72篇 |
1975年 | 76篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
高能重带电粒子能直接穿透靶原子核外电子层,与原子核发生直接碰撞,发生散裂反应,产生一系列具有放射性的剩余产物核.重带电粒子诱发靶材放射性剩余核与辐射防护和人员安全有着密切联系,当前,大部分剩余核产额主要依靠蒙特卡罗粒子输运程序进行模拟计算,其准确程度亟需通过实验测量进行准确评估.本文利用能量为80.5 MeV/u的(12)^C6+粒子对薄铜靶开展了辐照实验与伽玛射线测量,结合伽玛谱学分析方法,得出了辐照产生的18种放射性剩余产物的初始活度和产生截面值,并与PHITS模拟结果进行对比.结果表明,PHITS模拟程序对放射性剩余核种类的估计具有较高可靠性,在其绝对产额方面,与实验测量仍具有较大偏差. 相似文献
92.
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
93.
94.
95.
96.
Zenon Moszner 《Aequationes Mathematicae》2018,92(4):617-625
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form. 相似文献
97.
98.
Jiatian Chen Le Yang Ying Li Qinghua Hou Lanlan Li Peng Jin 《International journal of quantum chemistry》2019,119(16):e25961
Inorganic planar ring-shape molecules with 4n + 2 π electrons are always the focus of experimental synthesis and theoretical research due to their potential aromaticity and stability. In this work, the whole series of five-membered heterocycle monoanions X nY5-n− (X, Y = group 15 elements; n = 1-4) were thoroughly investigated by means of density functional theory calculations. They all have large formation energies and HOMO-LUMO gap energies, suggesting the potential thermodynamic and kinetic stability. Their aromaticities are comparable to that of typical aromatic hydrocarbons. Their thermal stabilities were firmly established by the ab initio molecular dynamics simulations. As most of them are predicted for the first time, their various spectra were simulated for experimental characterization. Furthermore, we demonstrate that these five-membered cyclic anions can be employed as η5-ligand to construct novel all-inorganic metallocenes, which may serve as the building blocks of low-dimensional nanomaterials. 相似文献
99.
Dr. Zhoulong Fan Katherine L. Bay Dr. Xiangyang Chen Zhe Zhuang Han Seul Park Dr. Kap-Sun Yeung Prof. Dr. K. N. Houk Prof. Dr. Jin-Quan Yu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4800-4807
A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process. 相似文献
100.