全文获取类型
收费全文 | 3509篇 |
免费 | 219篇 |
国内免费 | 359篇 |
专业分类
化学 | 1362篇 |
晶体学 | 51篇 |
力学 | 27篇 |
综合类 | 6篇 |
数学 | 2077篇 |
物理学 | 564篇 |
出版年
2024年 | 4篇 |
2023年 | 17篇 |
2022年 | 22篇 |
2021年 | 42篇 |
2020年 | 53篇 |
2019年 | 76篇 |
2018年 | 76篇 |
2017年 | 70篇 |
2016年 | 60篇 |
2015年 | 63篇 |
2014年 | 91篇 |
2013年 | 255篇 |
2012年 | 163篇 |
2011年 | 263篇 |
2010年 | 236篇 |
2009年 | 254篇 |
2008年 | 289篇 |
2007年 | 322篇 |
2006年 | 255篇 |
2005年 | 172篇 |
2004年 | 154篇 |
2003年 | 145篇 |
2002年 | 96篇 |
2001年 | 102篇 |
2000年 | 86篇 |
1999年 | 71篇 |
1998年 | 68篇 |
1997年 | 67篇 |
1996年 | 55篇 |
1995年 | 79篇 |
1994年 | 65篇 |
1993年 | 50篇 |
1992年 | 40篇 |
1991年 | 30篇 |
1990年 | 29篇 |
1989年 | 25篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1974年 | 3篇 |
排序方式: 共有4087条查询结果,搜索用时 46 毫秒
1.
Peng-Yan Gui Xiao-Hui Yan Wen-Juan Yuan Yuan-Liang Ma Xiao Ding Shuai Liu 《Natural product research》2019,33(19):2830-2836
A new A, D-seco limonoid, named 12-acetyloxyperforatin (1), along with three known ones, were isolated from the leaves of Harrisonia perforata. Their structures were elucidated on the basis of spectroscopic analysis, including extensive NMR techniques and computational modelling. These compounds showed no inhibitory activity against the 11β-HSD1 enzyme. 相似文献
2.
Dr. Rong-Lin Zhong Dr. Feng-Wei Gao Dr. Hong-Liang Xu Prof. Zhong-Min Su 《Chemphyschem》2019,20(14):1879-1884
The nature of the 2e/12c bond and its conversion to a carbon-carbon single bond in phenalenyl dimers have prompted a great deal of interests recently. In this work, we theoretically investigated a series of π-stacking phenalenyl derivatives with 2e/12c bonding character by density functional theory (DFT) calculations to elucidate origin of this unusual bond conversion. Results show that bond-conversion of the phenalenyl dimer easily occurs at room-temperature both dynamically and thermodynamically. However, bond-conversion of hetero π-stacking adducts, in which the two center carbon atoms were substituted by boron and nitrogen atoms, respectively, is much more difficult, because the 2e/12c bond is stabilized by its charge transfer character. Consequently, the bond-conversion is an endothermic process, albeit with a low conversion barrier. Interestingly, Lewis acid-base interactions would be induced by substitution of the center nitrogen atom to phosphorus atom. The 2e/12c bond is further stabilized by 5.9 kcal mol−1 and its conversion is also thermodynamically unfavorable. 相似文献
3.
4.
We introduce a new notion for the deformation of Gabor systems. Such deformations are in general nonlinear and, in particular, include the standard jitter error and linear deformations of phase space. With this new notion we prove a strong deformation result for Gabor frames and Gabor Riesz sequences that covers the known perturbation and deformation results. Our proof of the deformation theorem requires a new characterization of Gabor frames and Gabor Riesz sequences. It is in the style of Beurling's characterization of sets of sampling for bandlimited functions and extends significantly the known characterization of Gabor frames “without inequalities” from lattices to non-uniform sets. 相似文献
5.
通过对角化364×364完全能量矩阵的理论方法,对掺杂在Bi4Ge3O12晶体中的Er3+的Stark能级和EPR参数进行了研究,同时,定量分析了高阶晶体场混合效应和J-J混合效应对EPR g因子的影响。研究结果表明:对Er3+来说,最主要的J-J混合效应来源于多重态谱项2K15/2,其对EPR g因子的贡献约占2.5%,而最主要的高阶晶体场混合效应来源于第一激发多重态4I13/2和基态多重态4I15/2之间的晶体场混合,其对各向异性g因子中g⊥的贡献大致是g//的两倍(即g⊥约占 0.21%,g//约占0.092%),其他更高阶的晶体场混合和J-J混合效应可以忽略不计。因此,对于Er3+掺杂的络合物系统来说,只考虑基态多重态4I15/2对EPR g因子的贡献应该是一个很好的近似。 相似文献
6.
Yuyan Shi Xiaoyi Fu Prof. Yao Yin Fangqi Peng Xia Yin Prof. Guoliang Ke Prof. Xiaobing Zhang 《化学:亚洲杂志》2021,16(8):857-867
Clustered regularly interspaced short palindromic repeats (CRISPR) is a promising technology in the biological world. As one of the CRISPR-associated (Cas) proteins, Cas12a is an RNA-guided nuclease in the type V CRISPR-Cas system, which has been a robust tool for gene editing. In addition, due to the discovery of target-binding-induced indiscriminate single-stranded DNase activity of Cas12a, CRISPR-Cas12a also exhibits great promise in biosensing. This minireview not only gives a brief introduction to the mechanism of CRISPR-Cas12a but also highlights the recent developments and applications in biosensing and gene regulation. Finally, future prospects of the CRISPR-Cas12a system are also discussed. We expect this minireview will inspire innovative work on the CRISPR-Cas12a system by making full use of its features and advantages. 相似文献
7.
Polyamide 12 (PA12) is used in a variety of applications when low moisture absorption, good dimensional stability, and toughness are required. Polyamide 12 is one of the polymers most frequently employed to fabricate angioplasty balloon catheters; however, its high hydrophobicity and chemical inertness require the application of coatings to make its surface more hydrophilic and biocompatible. In this work, an alternative method, based on the photochemical reaction of PA12 with a hydrophilic aromatic azide, was developed. Static and dynamic contact angle measurements evidenced that the surface modification process was able to improve PA12 wettability and that the effects were retained even after 12 months from surface treatment. Polyamide 12 modification resulted in an increase of its surface free energy, as evaluated by the van Oss, Good, and Chaudhury method. X‐ray photoelectron spectroscopy confirmed the presence of the aromatic azide on PA12 surface. Finally, compliance tests showed that the modification process did not reduce the mechanical performance of balloons. 相似文献
8.
Chelsea C. Buck Patrick B. Dennis Maneesh K. Gupta Marcus T. Grant Marquise G. Crosby Joseph M. Slocik Peter A. Mirau Kellie A. Becknell Kristen K. Comfort Rajesh R. Naik 《Macromolecular bioscience》2019,19(3)
The suckerin family of proteins, identified from the squid sucker ring teeth assembly, offers unique mechanical properties and potential advantages over other natural biomaterials. In this study, a small suckerin isoform, suckerin‐12, is used to create enzymatically crosslinked, macro‐scale hydrogels. Upon exposure to specific salt conditions, suckerin‐12 hydrogels contracted into a condensed state where mechanical properties are found to be modulated by the salt anion present. The rate of contraction is found to correlate well with the kosmotropic arm of the Hofmeister anion series. However, the observed changes in hydrogel mechanical properties are better explained by the ability of the salt to neutralize charges in suckerin‐12 by deprotonization or charge screening. Thus, by altering the anions in the condensing salt solution, it is possible to tune the mechanical properties of suckerin‐12 hydrogels. The potential for suckerins to add new properties to materials based on naturally‐derived proteins is highlighted. 相似文献
9.
Ciprian A. Tudor Nakahiro Yoshida 《Stochastic Processes and their Applications》2019,129(9):3499-3526
We develop the asymptotic expansion theory for vector-valued sequences of random variables in terms of the convergence of the Stein–Malliavin matrix associated with the sequence . Our approach combines the classical Fourier approach and the recent Stein–Malliavin theory. We find the second order term of the asymptotic expansion of the density of and we illustrate our results by several examples. 相似文献
10.