全文获取类型
收费全文 | 6554篇 |
免费 | 1080篇 |
国内免费 | 745篇 |
专业分类
化学 | 4612篇 |
晶体学 | 72篇 |
力学 | 382篇 |
综合类 | 39篇 |
数学 | 788篇 |
物理学 | 2486篇 |
出版年
2024年 | 15篇 |
2023年 | 129篇 |
2022年 | 176篇 |
2021年 | 214篇 |
2020年 | 237篇 |
2019年 | 264篇 |
2018年 | 208篇 |
2017年 | 201篇 |
2016年 | 297篇 |
2015年 | 315篇 |
2014年 | 351篇 |
2013年 | 425篇 |
2012年 | 567篇 |
2011年 | 629篇 |
2010年 | 392篇 |
2009年 | 339篇 |
2008年 | 400篇 |
2007年 | 372篇 |
2006年 | 375篇 |
2005年 | 294篇 |
2004年 | 228篇 |
2003年 | 209篇 |
2002年 | 154篇 |
2001年 | 153篇 |
2000年 | 158篇 |
1999年 | 180篇 |
1998年 | 145篇 |
1997年 | 132篇 |
1996年 | 123篇 |
1995年 | 118篇 |
1994年 | 111篇 |
1993年 | 74篇 |
1992年 | 78篇 |
1991年 | 86篇 |
1990年 | 53篇 |
1989年 | 34篇 |
1988年 | 33篇 |
1987年 | 32篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 9篇 |
1983年 | 19篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有8379条查询结果,搜索用时 31 毫秒
961.
962.
We have performed an unbiased search for the global minimum geometries of small-to-medium sized germanium clusters Gen(12< or =n< or =18) as well as a biased search (using seeding method) for Gen(17< or =n< or =20). We employed the basin-hopping algorithm coupled with the plane-wave pseudopotential density functional calculations. For each size, we started the unbiased search with using several structurally very different initial clusters, or we started the biased search with three different seeds. Irrespective of the initial structures of clusters we found that the obtained lowest-energy clusters of the size n=12-16 and 18 are the same. Among them, the predicted global minima of Gen(12< or =n< or =16) are identical to those reported previously [Shvartsburg et al., Phys. Rev. Lett. 83, 167 (1999)]. For n=17-20, we have identified two or three nearly isoenergetic low-lying isomers (for each size) that compete for the global minimum. Nearly all the low-lying clusters in the size range of 12< or =n< or =20 contain the tri-caped trigonal prism motif and are all prolate in geometry, in agreement with the experiment. 相似文献
963.
Yuan L Sanford AR Feng W Zhang A Zhu J Zeng H Yamato K Li M Ferguson JS Gong B 《The Journal of organic chemistry》2005,70(26):10660-10669
[structures: see text] This article describes the synthetic procedures for the preparation of crescent (and helical) aromatic oligoamides developed in recent years in our laboratory. The large-scale preparation of a variety of monomers derived from various tetrasubstituted benzenes is presented. Three different strategies for constructing various oligomers consisting of meta- and meta/para-linked benzene residues are discussed. Factors affecting coupling efficiency and yields are analyzed. The developed synthetic methods have provided the basis for the preparation of longer oligomers and for the development of solid-phase synthesis. 相似文献
964.
An ionic liquid piezoelectric gas sensor was demonstrated for detection of polar and nonpolar organic vapors at high temperature with fast linear and reversible response. 相似文献
965.
Uniform estimate for maximum of randomly weighted sums with applications to insurance risk theory 总被引:1,自引:0,他引:1
WANG Dingcheng~ SU Chun~ & ZENG Yong~ . School of Management School of Applied Mathematics University of Electronic Science Technology of China Chengdu China . Department of Statistics Finance University of Science Technology of China Hefei China 《中国科学A辑(英文版)》2005,48(10):1379-1394
This paper obtains the uniform estimate for maximum of sums of independent and heavy-tailed random variables with nonnegative random weights,which can be arbi- trarily dependent of each other.Then the applications to ruin probabilities in a discrete time risk model with dependent stochastic returns are considered. 相似文献
966.
将1,4-二(萘[2,1-d]并(口恶)唑-2’)苯(BNOB)包埋在增塑的聚氯乙烯膜中,基于甲硝唑对BNOB的可逆猝灭,研制了一种甲硝唑荧光光纤传感器,传感器可逆性好,响应时间小于40s,响应线性范围为8.0×1O~(-6)~1.0×10~(-(?))mol·L~(-1),检出限为4.O×10~(-6)mol·L~(-1),常见的无机离子、药物不干扰甲硝唑的测定,传感器用于药品制剂中甲硝唑的测定,结果与药典法一致. 相似文献
967.
Shiyong Liu Xiangbo Zeng Wenbo Peng Haibo Xiao Wenjie Yao Xiaobing Xie Chao Wang Zhanguo Wang 《Journal of Non》2011,357(1):121-125
We develop a double-layer p-type hydrogenated nanocrystalline silicon (p-nc-Si:H) structure consisting of a low hydrogen diluted i/p buffer layer and a high hydrogen diluted p-layer to improve the hydrogenated amorphous silicon (a-Si:H) n-i-p solar cells. The electrical, optical and structural properties of p-nc-Si:H films with different hydrogen dilution ratio (RH) are investigated. High conductivity, low activation energy and wide band gap are achieved for the thin films. Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) analyses indicate that the thin films contain nanocrystallites with grain size around 3-5 nm embedded in the amorphous silicon matrix. By inserting a p-nc-Si:H buffer layer at the i/p interface, the overall performance of the solar cell is improved significantly compared to the bufferless cell. The improvement is correlated with the reduction of the density of defect states at the i/p interface. 相似文献
968.
采用Crosslight APSYS这一行业专业软件对p-GaN,InGaN/InGaN多量子阱,n-GaN和蓝宝石的芯片结构研究了不同电极形状与器件的光电性能之间的关系.优化设计了普通指形电极、对称型指形电极、h形指形电极、旋转形电极、中心环绕形电极、树形电极等6种电极结构.通过电极优化设计,电流分布更加均匀,减小了电流的聚集效应.优化后的电极结构结果表明:芯片的电特性得到了提高,芯片的光特性得到了明显改善,芯片的出光效率大幅度提高,芯片的转化效率得到了提升. 相似文献
969.
基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,对闪锌矿结构(ZB)和岩盐结构(RS)的ZnSe在0—20GPa高压下的几何结构、态密度、能带结构进行了计算研究,分析了闪锌矿结构ZnSe和岩盐结构ZnSe的几何结构.在此基础上,研究了ZnSe的结构相变、弹性常数、成键情况以及相变压强下电子结构的变化机理.结果发现:通过焓相等原理得到的ZB相到RS相的相变压强为15.3GPa,而由弹性常数判据得到的相变压强为11.52GPa,但在9.5GPa左右并没有发现简单立方相的出现;在结构相变过程中,sp3轨道杂化现象并未消除,Zn原子的4s电子在RS相ZnSe的导电性中起主要贡献. 相似文献
970.