全文获取类型
收费全文 | 71807篇 |
免费 | 9905篇 |
国内免费 | 6652篇 |
专业分类
化学 | 47913篇 |
晶体学 | 699篇 |
力学 | 4701篇 |
综合类 | 515篇 |
数学 | 8639篇 |
物理学 | 25897篇 |
出版年
2024年 | 228篇 |
2023年 | 1410篇 |
2022年 | 2310篇 |
2021年 | 2503篇 |
2020年 | 2563篇 |
2019年 | 2449篇 |
2018年 | 2218篇 |
2017年 | 1975篇 |
2016年 | 3016篇 |
2015年 | 3109篇 |
2014年 | 3700篇 |
2013年 | 4946篇 |
2012年 | 5971篇 |
2011年 | 6111篇 |
2010年 | 4129篇 |
2009年 | 4062篇 |
2008年 | 4239篇 |
2007年 | 3855篇 |
2006年 | 3632篇 |
2005年 | 3146篇 |
2004年 | 2525篇 |
2003年 | 1938篇 |
2002年 | 1713篇 |
2001年 | 1534篇 |
2000年 | 1433篇 |
1999年 | 1580篇 |
1998年 | 1338篇 |
1997年 | 1179篇 |
1996年 | 1240篇 |
1995年 | 1080篇 |
1994年 | 1021篇 |
1993年 | 877篇 |
1992年 | 780篇 |
1991年 | 674篇 |
1990年 | 566篇 |
1989年 | 495篇 |
1988年 | 375篇 |
1987年 | 362篇 |
1986年 | 306篇 |
1985年 | 313篇 |
1984年 | 218篇 |
1983年 | 186篇 |
1982年 | 153篇 |
1981年 | 126篇 |
1980年 | 109篇 |
1979年 | 67篇 |
1978年 | 72篇 |
1977年 | 68篇 |
1976年 | 67篇 |
1975年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
1 引言
小波分析是结合泛函分析、应用数学、逼近论、调和分析、广义函数论等数学知识的结晶,具有深刻的理论意义和广泛的应用范围,被称为”数学显微镜”.基于其多分辨分析的特点以及在时、频两域都具有表征信号局部特征的功能,应用它可以解决许多Fourier变换不能解决的难题,为工程应用提供了一种新的、更有效的分析工具[1],由... 相似文献
993.
Addition of C60 moiety, a powerful electron acceptor to poly(N-vinylcarbazole) (PVK) by chemical reaction modifies considerably the physical and chemical properties of PVK. The characterization techniques employed are UV-visible, IR, DSC, TGA, ESR, 13C-NMR spectroscopy, scanning electron microscopy, XRD, and cyclic voltammetry. The fullerenated PVK, which has a visibly earthy yellow cast when compared with the unreacted polymer, has a new structure in the UV-vis absorption spectrum with the active range extending from about 280 to 870 nm, its apparent temperature sensitivity is intriguing, and an unusual temperature dependence for the ESR spectrum is observed. Considerable difference of electronic structure between pure PVK and C60-PVK copolymer is indicated. The thermal stability and oxidation-reduction activation of pure PVK are enhanced by C60-chemical modification. © 1996 John Wiley & Sons, Inc. 相似文献
994.
Multiwavelength light attenuation measurements have been acquired as part of thermal/optical carbon analysis in the U.S.Chemical Speciation Network(CSN)and the ... 相似文献
995.
This work reported the discovery of N-triflimide (NTf)-based zwitter-ionic liquids (ZILs) that exhibit UCST-type phase transitions in water, and their further structural optimization in fine-tuning polarity to ultimately afford newfangled thermosensitive materials carrying attractive and biocompatible Tc values that clearly demonstrated the true value of the tunability of ZIL structure. This research established that with non-aromatic, acyclic ZILs as small-molecule thermoresponsive materials, their mixing and de-mixing with water triggered by temperatures are entirely reversible. 相似文献
996.
997.
Zengqing Sun Qingyu Tang Xiaohui Fan Min Gan Xuling Chen Zhiyun Ji Xiaoxian Huang 《Molecules (Basel, Switzerland)》2022,27(1)
Alkali-activated materials (AAMs) are considered to be alternative cementitious materials for civil infrastructures. Nowadays, efforts have been made in developing AAMs with self-compacting ability. The obtained self-compacting AAMs (SCAAMs) accomplish superior passing and filling properties as well as excellent mechanical and environmental advantages. This work critically revisits recent progresses in SCAAMs including mixture proportions, fresh properties, mechanical strength, microstructure, acid and sulfate resistance, high temperature behaviors, impact resistance and interface shear strength. To facilitate direct comparison and interpretation of data from different publications, mixture proportions were normalized in terms of the content of key reactive components from precursors and activators, and correlation with mechanical behaviors was made. Moreover, special attention was paid to current research challenges and perspectives to promote further investigation and field application of SCAAMs as advanced construction material. 相似文献
998.
Tehrim Motiwala Blessing Oluebube Akumadu Sbahle Zuma Mbalenhle Sizamile Mfeka Wanping Chen Ikechukwu Achilonu Khajamohiddin Syed Thandeka Khoza 《Molecules (Basel, Switzerland)》2022,27(1)
Caseinolytic proteins (Clp), which are present in both prokaryotes and eukaryotes, play a major role in cell protein quality control and survival of bacteria in harsh environmental conditions. Recently, a member of this protein family, ClpK was identified in a pathogenic strain of Klebsiella pneumoniae which was responsible for nosocomial infections. ClpK is linked to the thermal stress survival of this pathogen. The genome wide analysis of Clp proteins in Klebsiella spp. indicates that ClpK is present in only 34% of the investigated strains. This suggests that the uptake of the clpk gene is selective and may only be taken up by a pathogen that needs to survive harsh environmental conditions. In silico analyses and molecular dynamic simulations show that ClpK is mainly α-helical and is highly dynamic. ClpK was successfully expressed and purified to homogeneity using affinity and anion exchange chromatography. Biophysical characterization of ClpK showed that it is predominantly alpha-helical, and this is in agreement with in silico analysis of the protein structure. Furthermore, the purified protein is biologically active and hydrolyses ATP in a concentration- dependent manner. 相似文献
999.
假设C是有限域Fq上的[n,k]线性码,如果码字的每个坐标是其它至多r个坐标的函数,称C是(n,k,r)线性码,这里r是较小的数.本文在代数函数域上构造出了局部恢复码,它的码长不受字符集大小的限制,实际上,它的码长可以远远大于字符集的大小;并将此方法应用于广义Hermite函数域,得到了一类广义Hermite函数域上的... 相似文献
1000.
Well-aligned open-ended multi-walled carbon nanotube (MWCNT) arrays were prepared via chemical vapor deposition (CVD) method in porous anodic aluminum oxide (AAO) templates without depositing any transition metals as catalyst. Effects of the CVD temperature and heat treatment were studied in detail.Well-aligned open-ended MWCNT arrays were obtained at the CVD temperature above 600 ℃; when CVD temperature is reduced to around 550 ℃, CNTs, CNFs and other structures existed at the same time; no CNTs or carbon nanofibres (CNFs) could be found as the CVD temperature is below 500 ℃, and only amorphous carbon in the porous AAO template was found. Experimental results showed that the AAO template is catalytic during the CVD process, and it has the following two effects: to catalyze thermal decomposition of acetylene and to catalyze conversion of carbon decomposed from acetylene into CNTs or CNFs. Heat treatment could improve the graphitization degree, but it might also introduce new defects. 相似文献