全文获取类型
收费全文 | 132459篇 |
免费 | 22458篇 |
国内免费 | 11502篇 |
专业分类
化学 | 103025篇 |
晶体学 | 1315篇 |
力学 | 7006篇 |
综合类 | 730篇 |
数学 | 13735篇 |
物理学 | 40608篇 |
出版年
2024年 | 359篇 |
2023年 | 2013篇 |
2022年 | 3499篇 |
2021年 | 3847篇 |
2020年 | 4774篇 |
2019年 | 5796篇 |
2018年 | 4182篇 |
2017年 | 3599篇 |
2016年 | 7381篇 |
2015年 | 7597篇 |
2014年 | 8488篇 |
2013年 | 10712篇 |
2012年 | 11244篇 |
2011年 | 10753篇 |
2010年 | 8498篇 |
2009年 | 8235篇 |
2008年 | 8291篇 |
2007年 | 7098篇 |
2006年 | 6490篇 |
2005年 | 5756篇 |
2004年 | 4688篇 |
2003年 | 3871篇 |
2002年 | 4405篇 |
2001年 | 3434篇 |
2000年 | 3098篇 |
1999年 | 2515篇 |
1998年 | 1902篇 |
1997年 | 1694篇 |
1996年 | 1723篇 |
1995年 | 1528篇 |
1994年 | 1377篇 |
1993年 | 1151篇 |
1992年 | 1050篇 |
1991年 | 898篇 |
1990年 | 763篇 |
1989年 | 643篇 |
1988年 | 462篇 |
1987年 | 427篇 |
1986年 | 398篇 |
1985年 | 376篇 |
1984年 | 241篇 |
1983年 | 220篇 |
1982年 | 168篇 |
1981年 | 134篇 |
1980年 | 89篇 |
1979年 | 54篇 |
1978年 | 56篇 |
1977年 | 52篇 |
1975年 | 58篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
12.
Qipeng Guo Fei Chen Ke Wang Ling Chen 《Journal of Polymer Science.Polymer Physics》2006,44(21):3042-3052
An amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) (PEO–PDMS) diblock copolymer was used to template a bisphenol A type epoxy resin (ER); nanostructured thermoset blends of ER and PEO–PDMS were prepared with 4,4′‐methylenedianiline (MDA) as the curing agent. The phase behavior, crystallization, hydrogen‐bonding interactions, and nanoscale structures were investigated with differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, and small‐angle X‐ray scattering. The uncured ER was miscible with the poly(ethylene oxide) block of PEO–PDMS, and the uncured blends were not macroscopically phase‐separated. Macroscopic phase separation took place in the MDA‐cured ER/PEO–PDMS blends containing 60–80 wt % PEO–PDMS diblock copolymer. However, the composition‐dependent nanostructures were formed in the cured blends with 10–50 wt % PEO–PDMS, which did not show macroscopic phase separation. The poly(dimethylsiloxane) microdomains with sizes of 10–20 nm were dispersed in a continuous ER‐rich phase; the average distance between the neighboring microdomains was in the range of 20–50 nm. The miscibility between the cured ER and the poly(ethylene oxide) block of PEO–PDMS was ascribed to the favorable hydrogen‐bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3042–3052, 2006 相似文献
13.
赵志伟 《光谱学与光谱分析》2002,22(6):895-897
在化学发光分析中,常常要用到碱性条件下鲁米诺与过氧化氢的反应系统,通过催化剂辣根过氧化物酶使反应顺利进行。如果再加入适当的增强剂,则灵敏度提高且发光时间延长,可改善测定的重现性。实验证明,对位酚类衍生物,如:对叔丁基苯酚,对甲苯酚的发光增强作用明显,其发光效率可上升几十倍,发光时间也获得有效延长。 相似文献
14.
Chunguang Du Hongyi Chen Shiqun Li 《量子光学学报》2006,12(B08):70-71
Recently, research on left-handed materials (LHMs) has attracted considerable attentions. The LHMs are a kind of metameterial which have negative permittivity and negative permeability, which lead to negative refractive index in a frequency range. The LHMs that have been available so far are in the microwave range and are usually composed of classical particles, such as split-ring resonators. Some quantum phenomena such as spontaneous emission of atoms in the LHMs which are considered to be 'classical background' have also been investigated. Many potential applications of LHMs have been proposed, such as superlenses which, in principle, can achieve arbitrary subwavelength resolution. 相似文献
15.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献
16.
17.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献
18.
A convenient route was developed to synthesize S-oxo-[(methylthio)-methyl]cysteinols on a large scale from cheap l-serine as the starting material. The structures of diastereoisomers were determined by NMR, CD spectra, and X-ray diffraction analysis. All four diastereoisomers were examined for their ability to inhibit certain bacteria from growing. 相似文献
19.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
20.