全文获取类型
收费全文 | 1316376篇 |
免费 | 29596篇 |
国内免费 | 7728篇 |
专业分类
化学 | 654868篇 |
晶体学 | 20314篇 |
力学 | 74221篇 |
综合类 | 103篇 |
数学 | 239757篇 |
物理学 | 364437篇 |
出版年
2021年 | 13438篇 |
2020年 | 15873篇 |
2019年 | 16009篇 |
2018年 | 12687篇 |
2016年 | 27659篇 |
2015年 | 20693篇 |
2014年 | 30271篇 |
2013年 | 74064篇 |
2012年 | 36639篇 |
2011年 | 32878篇 |
2010年 | 36628篇 |
2009年 | 39123篇 |
2008年 | 32751篇 |
2007年 | 28278篇 |
2006年 | 34497篇 |
2005年 | 27226篇 |
2004年 | 28455篇 |
2003年 | 27120篇 |
2002年 | 28298篇 |
2001年 | 26575篇 |
2000年 | 23784篇 |
1999年 | 22028篇 |
1998年 | 20781篇 |
1997年 | 20797篇 |
1996年 | 20995篇 |
1995年 | 19078篇 |
1994年 | 18504篇 |
1993年 | 18064篇 |
1992年 | 17817篇 |
1991年 | 18150篇 |
1990年 | 17383篇 |
1989年 | 17420篇 |
1988年 | 17008篇 |
1987年 | 17029篇 |
1986年 | 15925篇 |
1985年 | 22368篇 |
1984年 | 23668篇 |
1983年 | 19875篇 |
1982年 | 21575篇 |
1981年 | 20821篇 |
1980年 | 20171篇 |
1979年 | 20286篇 |
1978年 | 21615篇 |
1977年 | 21204篇 |
1976年 | 20898篇 |
1975年 | 19635篇 |
1974年 | 19237篇 |
1973年 | 19765篇 |
1972年 | 14257篇 |
1967年 | 12488篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
Profiling engineered data with robust mining methods continues attracting attention in knowledge engineering systems. The purpose of this article is to propose a simple technique that deals with non-linear multi-factorial multi-characteristic screening suitable for knowledge discovery studies. The method is designed to proactively seek and quantify significant information content in engineered mini-datasets. This is achieved by deploying replicated fractional-factorial sampling schemes. Compiled multi-response data are converted to a single master-response effectuated by a series of distribution-free transformations and multi-compressed data fusions. The resulting amalgamated master response is deciphered by non-linear multi-factorial stealth stochastics intended for saturated schemes. The stealth properties of our method target processing datasets which might be overwhelmed by a lack of knowledge about the nature of reference distributions at play. Stealth features are triggered to overcome restrictions regarding the data normality conformance, the effect sparsity assumption and the inherent collapse of the ‘unexplainable error’ connotation in saturated arrays. The technique is showcased by profiling four ordinary controlling factors that influence webpage content performance by collecting data from a commercial browser monitoring service on a large scale web host. The examined effects are: (1) the number of Cascading Style Sheets files, (2) the number of JavaScript files, (3) the number of Image files, and (4) the Domain Name System Aliasing. The webpage performance level was screened against three popular characteristics: (1) the time to first visual, (2) the total loading time, and (3) the customer satisfaction. Our robust multi-response data mining technique is elucidated for a ten-replicate run study dictated by an L9(34) orthogonal array scheme where any uncontrolled noise embedded contribution has not been necessarily excluded. 相似文献
242.
Dr. Qing Xu Dr. Shanshan Tao Dr. Qiuhong Jiang Prof. Donglin Jiang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(11):4587-4593
A strategy based on covalent organic frameworks for ultrafast ion transport involves designing an ionic interface to mediate ion motion. Electrolyte chains were integrated onto the walls of one-dimensional channels to construct ionic frameworks via pore surface engineering, so that the ionic interface can be systematically tuned at the desired composition and density. This strategy enables a quantitative correlation between interface and ion transport and unveils a full picture of managing ionic interface to achieve high-rate ion transport. Moreover, the effect of interfaces was scaled on ion transport; ion mobility is increased in an exponential mode with the ionic interface. This strategy not only sets a benchmark system but also offers a general guidance for designing ionic interface that is key to systems for energy conversion and storage. 相似文献
243.
Richiro Ushimaru Zhang Chen Houyuan Zhao Po-hsun Fan Prof. Dr. Hung-wen Liu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3586-3590
Albomycin δ2 is a sulfur-containing sideromycin natural product that shows potent antibacterial activity against clinically important pathogens. The l -serine-thioheptose dipeptide partial structure, known as SB-217452, has been found to be the active seryl-tRNA synthetase inhibitor component of albomycin δ2. Herein, it is demonstrated that AbmF catalyzes condensation between the 6′-amino-4′-thionucleoside with the d -ribo configuration and seryl-adenylate supplied by the serine adenylation activity of AbmK. Formation of the dipeptide is followed by C3′-epimerization to produce SB-217452 with the d -xylo configuration, which is catalyzed by the radical S-adenosyl-l -methionine enzyme AbmJ. Gene deletion suggests that AbmC is involved in peptide assembly linking SB-217452 with the siderophore moiety. This study establishes how the albomycin biosynthetic machinery generates its antimicrobial component SB-217452. 相似文献
244.
245.
Yi Han Zibo Xue Dr. Guangwu Li Dr. Yanwei Gu Dr. Yong Ni Dr. Shaoqiang Dong Prof. Chunyan Chi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9111-9116
Incorporation of a non-hexagonal ring into a nanographene framework can lead to new electronic properties. During the attempted synthesis of naphthalene-bridged double [6]helicene and heptagon-containing nanographene by the Scholl reaction, an unexpected azulene-embedded nanographene and its triflyloxylated product were obtained, as confirmed by X-ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring-fused substructure containing two formal azulene units is formed, but only one of them shows an azulene-like electronic structure. The formation of this unique structure is explained by arenium ion mediated 1,2-phenyl migration and a naphthalene to azulene rearrangement reaction according to an in-silico study. This report represents the first experimental example of the thermodynamically unfavorable naphthalene to azulene rearrangement and may lead to new azulene-based molecular materials. 相似文献
246.
Jie Lu Ju-Kang Wu Yao Jiang Dr. Peng Tan Lin Zhang Yu Lei Prof. Xiao-Qin Liu Prof. Lin-Bing Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(16):6490-6496
Hierarchically porous metal–organic frameworks (HP-MOFs) are promising in various applications. Most reported HP-MOFs are prepared based on the generation of mesopores in microporous frameworks, and the formed mesopores are connected by microporous channels, limiting the accessibility of mesopores for bulky molecules. A hierarchical structure is formed by constructing microporous MOFs in uninterrupted mesoporous tunnels. Using the confined space in as-prepared mesoporous silica, highly dispersed metal precursors for MOFs are coated on the internal surface of mesoporous tunnels. Ligand vapor-induced crystallization is employed to enable quantitative formation of MOFs in situ, in which sublimated ligands diffuse into mesoporous tunnels and react with metal precursors. The obtained hierarchically porous composites exhibit record-high adsorption capacity for the bulky molecule trypsin. The thermal and storage stability of trypsin is improved upon immobilization on the composites. 相似文献
247.
Su X. F. Zhang Y. L. Maximov A. L. Zhang K. Xin Q. Feng C. Q. Bai X. F. Wu W. 《Russian Journal of Applied Chemistry》2020,93(1):127-136
Russian Journal of Applied Chemistry - Nanoscale ZSM-5 (AlZ5-D) and Ga-substituted ZSM-5 zeolites ((Al,Ga)Z5-D and GaZ5-D) were synthesized by a green dry-gel conversion strategy. For comparison,... 相似文献
248.
Gurenkova Yu. S. Kornyakov I. V. Ostrovsky V. A. Skrylnikova M. A. Khramchikhin A. V. 《Russian Journal of General Chemistry》2020,90(7):1202-1206
Russian Journal of General Chemistry - 8-Phenyltetrazolo[5,1-b][1,3,4]thiadiazepine was obtained as a result of intermolecular cyclization of 1-amino-1H-tetrazole-5-thiol and 3-phenyl-2-propynal.... 相似文献
249.
250.