全文获取类型
收费全文 | 169319篇 |
免费 | 37678篇 |
国内免费 | 31098篇 |
专业分类
化学 | 76949篇 |
晶体学 | 1450篇 |
力学 | 7440篇 |
综合类 | 386篇 |
数学 | 14750篇 |
物理学 | 64837篇 |
综合类 | 72283篇 |
出版年
2024年 | 798篇 |
2023年 | 1801篇 |
2022年 | 2529篇 |
2021年 | 2826篇 |
2020年 | 3573篇 |
2019年 | 6480篇 |
2018年 | 6336篇 |
2017年 | 7184篇 |
2016年 | 8057篇 |
2015年 | 8288篇 |
2014年 | 8874篇 |
2013年 | 10692篇 |
2012年 | 11051篇 |
2011年 | 12648篇 |
2010年 | 15063篇 |
2009年 | 14699篇 |
2008年 | 8353篇 |
2007年 | 7775篇 |
2006年 | 6621篇 |
2005年 | 6561篇 |
2004年 | 7288篇 |
2003年 | 5964篇 |
2002年 | 5655篇 |
2001年 | 5330篇 |
2000年 | 4096篇 |
1999年 | 4570篇 |
1998年 | 3893篇 |
1997年 | 3668篇 |
1996年 | 3830篇 |
1995年 | 4066篇 |
1994年 | 4081篇 |
1993年 | 4067篇 |
1992年 | 3545篇 |
1991年 | 3236篇 |
1990年 | 2673篇 |
1989年 | 2648篇 |
1988年 | 2619篇 |
1987年 | 1630篇 |
1986年 | 1597篇 |
1985年 | 1182篇 |
1984年 | 1157篇 |
1982年 | 997篇 |
1981年 | 817篇 |
1980年 | 848篇 |
1979年 | 603篇 |
1978年 | 595篇 |
1977年 | 688篇 |
1976年 | 1098篇 |
1973年 | 506篇 |
1972年 | 562篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Ingrid Lukkari Jaromir Ruzicka Gary D. Christian 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):813-818
Summary Automated methods for the determination of ammonium and ammonia are reviewed, and techniques based on gas diffusion using a semi-permeable membrane were selected for the determination of both total ammonium-nitrogen and free ammonia in fermentation samples. A simple and robust instrument based on sequential injection analysis (SIA) consisting of a piston pump and two selector valves was used. Two different methods of ammonia detection, the Berthelot method and detection using pH-indicators, have been evaluated and compared. The indicator method showed higher reproducibility and the range of determination could easily be adjusted to match the concentrations of the samples. The range of determination could be adjusted from 0.05 mmol/l to 350 mmol/l, depending on choice of acceptor solution. This method has been evaluated with fermentation medium samples and tested on-line in a yeast fermentation process.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
73.
To incorporate an acceptor type polythiophene segment onto a supramolecular block copolymer for potential light harvesting applications, effective synthetic routes for the end‐functionalized and acceptor‐substituted polythiophenes are critical. The Ullmann coupling reaction can be utilized to obtain electron‐deficient polythiophenes and to attach terminal thiophene units that carry functional groups. In this article, the reactions involving a 2,5‐dibromothiophene monomer containing an electron‐withdrawing fluorinated ester and 5‐bromo‐2‐thiophenecarboxaldehyde (the end‐capper) were studied in detail. It was found that the Ullmann coupling reaction of the dibromide is very fast (completed in a few minutes) and the terminal bromine group does not survive long under the reaction condition. These findings lead to the development of an effective procedure for aldehyde end‐capping of electron‐deficient polythiophenes. Polymers with molecular weights around 4000 Da are routinely obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 41–47, 2007 相似文献
74.
75.
The Mathematical Intelligencer encourages comments about the material in this issue. Letters to the editor should be sent
to either of the editors-in-chief, Chandler Davis or Marjorie Senechal. 相似文献
76.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献
77.
78.
79.
Tensile impact experiments of EC8.0−24×7 glass fiber bundles at different low temperaturesT(14°C, −40°C and −10°C) and strain rates ɛ were carried out, and complete stress-strain curves were obtained. Within the range
of the experiment temperatures and strain rates, it is found that the initial modulusE, the ultimate strength σmax and the unstable strain ɛ
b
of the glass fiber bundles all increase with ɛ at an identicalT. At an identical ɛ, with the decrease ofT, E and σmax increase; but ɛ
b
increases when 10°C>T>−40°C and decreases when −40°C>T>−100°C. The strain-rate- and temperature-dependent bimodal Weibull statistical constitutive theory was adopted for the statistical
analysis of the experimental results, and the Weibull parameters of single fiber were obtained. The results show that the
bimodal Weibull distribution function is suitable to represent the strength distribution of the glass fiber at low temperature
and different strain rates. The differences in the mechanical properties between EC8.0−24×7 and EC5.5−12 ×14 glass fiber bundles
were also discussed.
Project supported by the National Natural Science Foundation of China (No. 19772058). 相似文献
80.
孙智宏 《淮阴师范学院学报(自然科学版)》2002,1(1):13-15
设{Bn}为Bernoulli数,m、n为自然数,本文证明了同余式(2-22n)B2n≡1-4n ∑mk=1(2n)/(2k)24kB2k (mod 24m 3)与(3-32n)B2n≡2-6n 2∑mk=1(2n)/(2k)32kB2k (mod 32m 1).取m=1,2,得到[5]中宣布的(2-22n)B2n(mod 27)与(3-32n)B2n(mod 35)的简单同余式. 相似文献