全文获取类型
收费全文 | 2839篇 |
免费 | 621篇 |
国内免费 | 978篇 |
专业分类
化学 | 2029篇 |
晶体学 | 116篇 |
力学 | 252篇 |
综合类 | 90篇 |
数学 | 485篇 |
物理学 | 1466篇 |
出版年
2024年 | 1篇 |
2023年 | 23篇 |
2022年 | 95篇 |
2021年 | 104篇 |
2020年 | 102篇 |
2019年 | 99篇 |
2018年 | 87篇 |
2017年 | 184篇 |
2016年 | 76篇 |
2015年 | 146篇 |
2014年 | 174篇 |
2013年 | 250篇 |
2012年 | 275篇 |
2011年 | 249篇 |
2010年 | 287篇 |
2009年 | 269篇 |
2008年 | 308篇 |
2007年 | 238篇 |
2006年 | 223篇 |
2005年 | 180篇 |
2004年 | 163篇 |
2003年 | 99篇 |
2002年 | 117篇 |
2001年 | 118篇 |
2000年 | 124篇 |
1999年 | 69篇 |
1998年 | 44篇 |
1997年 | 36篇 |
1996年 | 24篇 |
1995年 | 38篇 |
1994年 | 30篇 |
1993年 | 34篇 |
1992年 | 28篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有4438条查询结果,搜索用时 46 毫秒
101.
应用原子吸收光谱法测定了内蒙古地产的笃斯茎、叶中的Cu,Fe,Zn,Mn,Ca,Mg等六种人体必需微量元素及宏量元素的含量。从而为评价笃斯的品质及其药理、药效提供了具有一定价值的数据。 相似文献
102.
Novel macrocyclic monooxa-diselkylene-1,ω-dioxy substituted calix[4]arene derivatives 1a-5a were synthesized by the reaction of calix[4]arene dibromides 1-5 with the disodium salt of bis(2-selenylethyl)ether in the yields between 28% and 64%. Their structures were characterized by proton and carbon NMR spectra. X-Ray structure analysis of la further confirmed the cone conformation of compounds 1a-5a. An interesting host-guest complex of la with dichloromethane via CH/π and C1/π interactions was elucidated. Extraction experiments showed that these novel monooxa-diselkylene-1,ω-dioxy substituted calix[4]arene derivatives 1a-5a had strong extraction ability towards mercury ion. The interaction of Hg^2+with the calix ligand has also been investigated by 1^H NMR titration. 相似文献
103.
Study of the rare and forbidden decays of η/η offers a sensitive probe to test fundamental symmetries of quantum chromodynamics and search for new physics beyond the Standard Model. To study the rare decays of η/η to π + π - e + e - , π + π - μ + μ - and e + e - μ + μ - at the BES detector, we developed several event generators based on the vector meson dominant model with finite-width corrections and the pseudoscalar mesons mixing theory. The various distributions from event generators are in good agreement with the theoretical predictions, which indicates that the event generators work very well after implemention in the BES Monte Carlo simulation package. In the BES physics analysis, the performance of the event generators will be improved in accordance with the distributions of different variables of η/η from data and the improvement on the theoretical calculations. 相似文献
104.
The research on aggregation-induced emission (AIE) has drawn increasing interests in the past decade. With the efforts scientists paid, a variety of AIE systems have been developed, among which the tetraphenylethelene and silole derivatives are the most studied. Development of new AIE systems could further enrich the AIE molecules and promote the development of AIE area. In this communication, we prepared a new AIE system based on 1,2,4,6-tetraphenylpyridinium ions according to the restriction of intramolecular rotation mechanism. These molecules could be facilely synthesized via one-step and one-pot reaction. The ionic AIE-active molecules could find wide application in sensing and optoelectronic areas. 相似文献
105.
106.
107.
A Simple Interconnection Layer for Tandem Organic Solar Cells with Improved Efficiency and Fill Factor 下载免费PDF全文
We demonstrate a simple interconnection layer (ICL) that can be employed in tandem organic solar cells. An ICL with an optimized structure of Ca/Au/MoO3 is used between two sub cells composed of identical regioregularpoly(3-hexylthiophen) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM) photoactive layers. Power conversion efficiency (PCE) of 3.24% and fill factor (FF) of 68.0% are achieved with such an ICL under simulated sunlight (1 O0 m W. cm- 2 ). Compared with the best values of devices with ICLs of Ca/Al/MoOa, PCE is improved by 68.9% and FF is improved by 15.5%. The improved performances are attributed to the optical and electrical balances in both sub cells. The presented ICL extracts free charges efficiently from both sub cells thereby suppressing the exaction recombination in each sub cell. 相似文献
108.
在试验设计中,一阶回归模型通常被作为合格拟合模型用来从众多因子中筛选出效应显著的特殊因子,而Q和Q_B准则能够比较简单地从大量的合格拟合模型中找出具有最优性质的设计.主要探讨了当拟合模型为一阶回归模型时,二水平的初始设计d与其Double设计(d d d -d)在Q和Q_B准则下的最优关系.给出了初始设计d的Q和Q_B值与其Double设计的Q和Q_B值之间的解析关系,从而得到在Q或Q_B准则下如果初始设计d是最优的,那么其Double设计也是最优的.此外,也分别给出了初始设计d及其Double设计的Q值和Q_B值的一个下界. 相似文献
109.
为满足便携式投影仪的市场需求,设计了一种基于LED微型阵列的投影系统。该系统由显示单元和投影物镜构成。采用尺寸为12 mm×9 mm的自发光LED微型阵列作为系统的显示单元,利用光学设计软件设计了投影物镜。投影物镜采用反远距光学结构,全视场角为80°,焦距为8 mm,属于强光、广角镜头。在空间频率20 lp/mm处,该物镜的调制传递函数大于0. 85,畸变小于2%,符合投影系统的设计要求。该投影系统具有体积小,结构简单,投影效果好,易加工等诸多优势,可为第三代投影技术的发展提供参考。 相似文献
110.