全文获取类型
收费全文 | 9968篇 |
免费 | 1711篇 |
国内免费 | 1999篇 |
专业分类
化学 | 7729篇 |
晶体学 | 120篇 |
力学 | 604篇 |
综合类 | 149篇 |
数学 | 1316篇 |
物理学 | 3760篇 |
出版年
2024年 | 6篇 |
2023年 | 231篇 |
2022年 | 300篇 |
2021年 | 363篇 |
2020年 | 483篇 |
2019年 | 468篇 |
2018年 | 366篇 |
2017年 | 402篇 |
2016年 | 554篇 |
2015年 | 556篇 |
2014年 | 597篇 |
2013年 | 831篇 |
2012年 | 772篇 |
2011年 | 874篇 |
2010年 | 657篇 |
2009年 | 618篇 |
2008年 | 706篇 |
2007年 | 583篇 |
2006年 | 548篇 |
2005年 | 507篇 |
2004年 | 416篇 |
2003年 | 349篇 |
2002年 | 384篇 |
2001年 | 310篇 |
2000年 | 271篇 |
1999年 | 229篇 |
1998年 | 178篇 |
1997年 | 128篇 |
1996年 | 149篇 |
1995年 | 112篇 |
1994年 | 132篇 |
1993年 | 99篇 |
1992年 | 73篇 |
1991年 | 94篇 |
1990年 | 89篇 |
1989年 | 42篇 |
1988年 | 39篇 |
1987年 | 29篇 |
1986年 | 34篇 |
1985年 | 37篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1971年 | 1篇 |
1957年 | 3篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
71.
Ganoderma mushrooms are widely used as effective medicines for treating and preventing chronic diseases. In this study, five new meroterpenoids, dayaolingzhiols A (1) and B (2) featuring a 6/6/6 ring system, dayaolingzhiols C?E (3–5) harboring a γ-lactone motif, along with eight known ones (6–13), were purified from G. lucidum. To clarify their chemical structures, spectroscopic and ECD and OR computational methods were used. In addition, the inhibition of all the new meroterpenoids against AChE was evaluated, disclosing that (+)-4 and (±)-5 possess potent AChE inhibitory activities with respective IC50 values of 8.52?±?1.90?μM and 7.37?±?0.52?μM. 相似文献
72.
Xinming Zhang Tianzhan Zhang Shuanli Guo Yang Zhang Rongtian Sheng Ruimeng Sun Lixia Chen Ruijuan Lv Yanfei Qi 《Molecules (Basel, Switzerland)》2020,25(24)
Fungal infections pose a serious threat to human health. Polyoxometalates (POMs) are metal–oxygen clusters with potential application in the control of microbial infections. Herein, the Ag3PW12O40 composites have been synthesized and verified by Fourier transform infrared (FT-IR) spectrum, transmission electron microscopy (TEM), scanning electron microscope (SEM), elemental analysis, and X-ray diffraction (XRD). The antifungal activities of Ag3PW12O40 were screened in 19 Candida species strains through the determination of minimum inhibitory concentration (MIC) by the microdilution checkerboard technique. The minimum inhibitory concentration (MIC50) values of Ag3PW12O40 are 2~32 μg/mL to the Candida species. The MIC80 value of Ag3PW12O40 to resistant clinical isolates C. albicans HL963 is 8 μg/mL, which is lower than the positive control, fluconazole (FLC). The mechanism against C. albicans HL963 results show that Ag3PW12O40 can decrease the ergosterol content. The expressions of ERG1, ERG7, and ERG11, which impact on the synthesis of ergosterol, are all prominently upregulated by Ag3PW12O40. It indicates that Ag3PW12O40 is a candidate in the development of new antifungal agents. 相似文献
73.
空间填充设计在计算机试验中应用十分广泛,当拟合回归模型时,正交的空间填充设计保证了因子效应估计的独立性.基于广义正交设计,文章给出了构造二阶正交拉丁超立方体设计和列正交设计的方法,新构造的设计不仅满足任意两列之间相互正交,还能保证每一列与任一列元素平方组成的列以及任两列元素相乘组成的列都正交.当某些正交的空间填充设计不存在时,具有较小相关系数的近似正交设计可作为替代设计使用.设计构造的灵活性为计算机试验在实践中的广泛应用提供了必要的支持. 相似文献
74.
75.
Xiao Jun-An Cheng Xiu-Liang Peng Hai Li Jin-Lian Xie Zhen-Zhen Chen Wen-Qiang Liu Zhi-Ping Xiao Qi Su Wei Yang Hua 《中国科学:化学(英文版)》2020,63(6):785-791
A diastereoselectivity-controllable formal [3+2]-cycloaddition of arylvinyl oxirane 2,2-diesters with cyclic N-sulfonyl imines is developed, affording the corresponding tricyclic oxazolidine derivatives in moderate to excellent yields with excellent diastereoselectivities in the presence of palladium(0) or scandium(III) triflate. This protocol allows selective synthesis of diastereomers of tricyclic oxazolidine derivatives under switchable and mild conditions. Further transformations of the obtained products were conducted by removing ester groups and arylvinyl moieties. 相似文献
76.
77.
78.
Prof. Dr. Wenze Li Ke Qi Xingyu Lu Yujie Qi Jialong Zhang Bingsen Zhang Prof. Dr. Wei Qi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(38):e202200622
A novel electrochemically assisted cycloaddition process is proposed, in which highly efficient coupling of CO2 with styrene oxide (SO) can be achieved to form styrene carbonate (SC) as a high-value-added product. A series of Cu catalysts with different morphologies and chemical states were fabricated on carbon paper (CP) by using in-situ electrodeposition, and the sample with nano-dendrimer structure was found to exhibit a relatively high activity of 74.8 % SC yield with 92.7 % SO conversion under gentle reaction conditions, thus showing its potential for practical applications. The relatively high electrochemically active surface area and charge transfer ability of dendrimer-like Cu benefited the electrochemical reaction. In particular, the Cu2+ species that were formed in situ during the reaction played a vital role in enhancing the activity and selectivity of the proposed Cu/CP hybrid catalyst. Cu2+ atoms served as active sites that can not only electrochemically activate CO2 but also facilitate the ring opening of SO. Mechanistic analysis suggested that the reaction followed electrochemical and liquid-phase heterogeneous paths, which provide a new green and sustainable route for efficient utilization of CO2 resources for fine chemical electrosynthesis. 相似文献
79.
Designs, Codes and Cryptography - The Learning-With-Errors (LWE) problem (and its variants including Ring-LWE and Module-LWE), whose security are based on hard ideal lattice problems, has proven to... 相似文献
80.
Ping Lv Xin Shen Zhiliyu Cui Bo Li Qiangqiang Xu Zhuo Yu Weijie Lu Haonan Shao Yan Ge Zhenhui Qi 《Journal of polymer science. Part A, Polymer chemistry》2021,59(23):3001-3008
Fiber-reinforced-concrete (FRC) mechanism refers short discrete fibers that are uniformly distributed and randomly oriented, which offers an effective way to improve the mechanical performance of concrete. In the design of supramolecular polymers, an analogous concept of FRC appears to have been considered very rarely-although fibrous structure has been frequently observed/generated during the supramolecular polymerization. In this work, we apply the alkane thermosets, octadecane (C18H38) and tetracosane (C24H50), taking the role of “concrete”, and the low-molecular-weight monomer with long alkyl chains as the essential “fiber” component, to fabricate the “fiber reinforced supramolecular polymer”. Very much like FRC mechanism in material science, the resulting fiber reinforced supramolecular polymer thus exhibit unusually high mechanical strength and stiffness, which is unprecedented in the conventional supramolecular strategy. 相似文献