全文获取类型
收费全文 | 3985篇 |
免费 | 815篇 |
国内免费 | 336篇 |
专业分类
化学 | 2557篇 |
晶体学 | 144篇 |
力学 | 416篇 |
综合类 | 66篇 |
数学 | 469篇 |
物理学 | 1484篇 |
出版年
2024年 | 14篇 |
2023年 | 70篇 |
2022年 | 200篇 |
2021年 | 206篇 |
2020年 | 259篇 |
2019年 | 200篇 |
2018年 | 175篇 |
2017年 | 176篇 |
2016年 | 250篇 |
2015年 | 208篇 |
2014年 | 238篇 |
2013年 | 408篇 |
2012年 | 226篇 |
2011年 | 244篇 |
2010年 | 193篇 |
2009年 | 219篇 |
2008年 | 227篇 |
2007年 | 231篇 |
2006年 | 209篇 |
2005年 | 190篇 |
2004年 | 178篇 |
2003年 | 126篇 |
2002年 | 87篇 |
2001年 | 70篇 |
2000年 | 70篇 |
1999年 | 65篇 |
1998年 | 72篇 |
1997年 | 46篇 |
1996年 | 51篇 |
1995年 | 34篇 |
1994年 | 20篇 |
1993年 | 16篇 |
1992年 | 18篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 20篇 |
1987年 | 10篇 |
1986年 | 28篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1971年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有5136条查询结果,搜索用时 46 毫秒
991.
Ying Xuan Huiying Quan Prof. Zhurui Shen Chenxi Zhang Xiyuan Yang Prof. Lan-Lan Lou Prof. Shuangxi Liu Prof. Kai Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(10):2285-2292
It is known that the low lifetime of photogenerated carriers is the main drawback of elemental photocatalysts. Therefore, a facile and versatile one-step strategy to simultaneously achieve the oxygen covalent functionalization of amorphous red phosphorus (RP) and in situ modification of CdCO3 is reported. This strategy endows RP with enhanced charge carrier separation ability and photocatalytic activity by coupling band-gap engineering and heterojunction construction. The as-prepared nCdCO3/SO-RP (n=0.1, 0.25, 0.5, 1.0) composites exhibited excellent photocatalytic H2 evolution activity (up to 516.3 μmol g−1 h) from visible-light-driven water splitting (λ>400 nm), which is about 17.6 times higher than that of pristine RP. By experimental and theoretical investigations, the roles of surface oxygen covalent functionalization, that is, prolonging the lifetime of photogenerated carriers and inducing the negative shift of the conduction band potential, were studied in detail. Moreover, the charge transfer mechanism of these composites has also been proposed. In addition, these composites are stable and can be reused at least for three times without significant activity loss. This work may provide a good example of how to promote the activity of elemental photocatalysts by decorating their atomic structure. 相似文献
992.
A new flexible hydrogen-bonded supramolecular host based on two deoxypyridinoline-bioinspired 6-hexanoic acid-substituted 3-hydroxypyridinium cations that adopt the twist and planar conformations and construct the orthogonal single helical scaffold and sheet structures with the triangular NO3− and spherical Br− guest anions, respectively. The results demonstrated not only the importance of rotational flexibility, anion shapes, and robust C—H⋯O hydrogen bonding, but also the good antibacterial activity with the potential antibacterial application. 相似文献
993.
Haiyang Cui Dr. Hao Cao Dr. Haiying Cai Prof. Dr. Karl-Erich Jaeger Dr. Mehdi D. Davari Prof. Dr. Ulrich Schwaneberg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(3):643-649
A main remaining challenge in protein engineering is how to recombine beneficial substitutions. Systematic recombination studies show that poorly performing variants are usually obtained after recombination of 3 to 4 beneficial substitutions. This limits researchers in exploiting nature's potential in generating better enzymes. The Computer-assisted Recombination (CompassR) strategy provides a selection guide for beneficial substitutions that can be recombined to gradually improve enzyme performance by analysis of the relative free energy of folding (ΔΔGfold). The performance of CompassR was evaluated by analysis of 84 recombinants located on 13 positions of Bacillus subtilis lipase A. The finally obtained variant F17S/V54K/D64N/D91E had a 2.7-fold improved specific activity in 18.3 % (v/v) 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). In essence, the deducted CompassR rule allows recombination of beneficial substitutions in an iterative manner and empowers researchers to generate better enzymes in a time-efficient manner. 相似文献
994.
995.
Liszt Y. C. Madruga Rosangela C. Balaban Ketul C. Popat Matt J. Kipper 《Macromolecular bioscience》2021,21(1)
This study presents a new type of biocompatible nanofiber based on poly(vinyl alcohol) (PVA) and carboxymethyl‐kappa‐carrageenan (CMKC) blends, produced with no generation of hazardous waste. The nanofibers are produced by electrospinning using PVA:CMKC blends with ratios of 1:0, 1:0.25, 1:0.4, 1:0.5, and 1:0.75 (w/w PVA:CMKC) in aqueous solution, followed by thermal crosslinking. The diameter of the fibers is in the nanometer scale and below 300 nm. Fourier transform infrared spectroscopy shows the presence of the carboxyl and sulfate groups in all the fibers with CMKC. The nanofibers from water‐soluble polymers are stabilized by thermal crosslinking. The incorporation of CMKC improves cytocompatibility, biodegradability, cell growth, and cell adhesion, compared to PVA nanofibers. Furthermore, the incorporation of CMKC modulates phenotype of human adipose‐derived stem cells (ADSCs). PVA/CMKC nanofibers enhance ADSC response to osteogenic differentiation signals and are therefore good candidates for application in tissue engineering to support stem cells. 相似文献
996.
XianTong Yan YuanKai Jin XueMei Chen Chao Zhang ChongLei Hao ZuanKai Wang 《中国科学:物理学 力学 天文学(英文版)》2020,(2):32-46
Learning from nature has traditionally and continuously provided important insights to drive a paradigm shift in technology.In particular,recent studies show that many biological organisms exhibit spectacular surface topography such as shape,size,spatial organization,periodicity,interconnectivity,and hierarchy to endow them with the capability to adapt dynamically and responsively to a wide range of environments.More excitingly,in a broader perspective,these normally neglected topological features have the potential to fundamentally change the way of how engineering surface works,such as how fluid flows,how heat is transported,and how energy is generated,saved,and converted,to name a few.Thus,the design of nature-inspired surface topography for unique functions will spur new thinking and provide paradigm shift in the development of the new engineering surfaces.In this review,we first present a brief introduction to some insights extracted from nature.Then,we highlight recent progress in designing new surface topographies and demonstrate their applications in emerging areas including thermal-fluid transport,anti-icing,water harvesting,power generation,adhesive control,and soft robotics.Finally,we offer our perspectives on this emerging field,with the aim to stimulate new thinking on the development of next-generation of new materials and devices,and dramatically extend the boundaries of traditional engineering. 相似文献
997.
998.
Dr. Aipeng Li Ting Wang Qing Tian Dr. Xiaohong Yang Dongming Yin Prof. Yong Qin Prof. Lianbing Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(20):6283-6294
Enzyme stereoselectivity control is still a major challenge. To gain insight into the molecular basis of enzyme stereo-recognition and expand the source of antiPrelog carbonyl reductase toward β-ketoesters, rational enzyme design aiming at stereoselectivity inversion was performed. The designed variant Q139G switched the enzyme stereoselectivity toward β-ketoesters from Prelog to antiPrelog, providing corresponding alcohols in high enantiomeric purity (89.1–99.1 % ee). More importantly, the well-known trade-off between stereoselectivity and activity was not found. Q139G exhibited higher catalytic activity than the wildtype enzyme, the enhancement of the catalytic efficiency (kcat/Km) varied from 1.1- to 27.1-fold. Interestingly, the mutant Q139G did not lead to reversed stereoselectivity toward aromatic ketones. Analysis of enzyme–substrate complexes showed that the structural flexibility of β-ketoesters and a newly formed cave together facilitated the formation of the antiPrelog-preferred conformation. In contrast, the relatively large and rigid structure of the aromatic ketones prevents them from forming the antiPrelog-preferred conformation. 相似文献
999.
Tinasadat Khadivjam Huy Che-Quang Dr. Thierry Maris Zvart Ajoyan Prof. Ashlee J. Howarth Prof. James D. Wuest 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(31):7026-7040
Ordered materials with predictable structures and properties can be made by a modular approach, using molecules designed to interact with neighbors and hold them in predetermined positions. Incorporating 4,6-diamino-1,3,5-triazin-2-yl (DAT) groups in modules is an effective way to direct assembly because each DAT group can form multiple N−H⋅⋅⋅N hydrogen bonds according to established patterns. We have found that modules with high densities of N(DAT)2 groups can be made by base-induced double triazinylations of readily available amines. The resulting modules can form structures held together by remarkably large numbers of hydrogen bonds per molecule. Even simple modules with only 1–3 N(DAT)2 groups and fewer than 70 non-hydrogen atoms can crystallize to form highly open networks in which each molecule engages in over 20 N−H⋅⋅⋅N hydrogen bonds, and more than 70 % of the volume is available for accommodating guests. In favorable cases, guests can be removed to create rigorously porous crystalline solids analogous to zeolites and metal–organic frameworks. 相似文献
1000.