全文获取类型
收费全文 | 48504篇 |
免费 | 7745篇 |
国内免费 | 5267篇 |
专业分类
化学 | 34239篇 |
晶体学 | 488篇 |
力学 | 2926篇 |
综合类 | 370篇 |
数学 | 6023篇 |
物理学 | 17470篇 |
出版年
2024年 | 42篇 |
2023年 | 1004篇 |
2022年 | 981篇 |
2021年 | 1504篇 |
2020年 | 1945篇 |
2019年 | 1793篇 |
2018年 | 1521篇 |
2017年 | 1350篇 |
2016年 | 2154篇 |
2015年 | 2124篇 |
2014年 | 2656篇 |
2013年 | 3459篇 |
2012年 | 4349篇 |
2011年 | 4363篇 |
2010年 | 3038篇 |
2009年 | 2774篇 |
2008年 | 3051篇 |
2007年 | 2779篇 |
2006年 | 2561篇 |
2005年 | 2216篇 |
2004年 | 1792篇 |
2003年 | 1429篇 |
2002年 | 1309篇 |
2001年 | 1106篇 |
2000年 | 923篇 |
1999年 | 1034篇 |
1998年 | 910篇 |
1997年 | 819篇 |
1996年 | 908篇 |
1995年 | 789篇 |
1994年 | 730篇 |
1993年 | 623篇 |
1992年 | 572篇 |
1991年 | 480篇 |
1990年 | 407篇 |
1989年 | 323篇 |
1988年 | 279篇 |
1987年 | 239篇 |
1986年 | 169篇 |
1985年 | 198篇 |
1984年 | 173篇 |
1983年 | 137篇 |
1982年 | 99篇 |
1981年 | 71篇 |
1980年 | 59篇 |
1979年 | 34篇 |
1978年 | 29篇 |
1976年 | 29篇 |
1975年 | 31篇 |
1974年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Ligand-promoted copper-catalyzed cascade reactions have become a robust tool for the synthesis of cyclic compounds. Although numerous ligands have been developed, this review focuses on the introduction of commercially available 1,10-phenanthroline-promoted copper-catalyzed cascade reactions in recent years. Moreover, based on original articles, this review highlights product yields in the presence and absence of the ligand, and the possible mechanistic role of the ‘copper/1,10-phenanthroline’ catalytic system. 相似文献
92.
A novel metal-doped metal–organic framework (MOF) was developed by incorporating salen–Mg into NH2–MIL-101(Cr) structure under ambient conditions. The Schiff base complex was successfully prepared by condensing salicylaldehyde with a free amino group and then coordinating metal ions. Such a structure can endow the sample with higher CO2 adsorption performance. At 0°C and 1 bar, the salen–Mg-modified sample achieves the maximum adsorption capacity of 2.18 mmol g−1 for CO2, which was 5.8% higher than the pristine salen–MOF under the same conditions. Notably, the Freundlich model indicates that the CO2 adsorption process of all samples conforms to reversible adsorption. However, the correlation coefficients (R2) of the Mg-doped sample are lower than that of the pristine sample. Besides, the CO2/N2 adsorption selectivity and isosteric heat also show a similar trend. These results indicate that the salen–Mg can enhance the interaction between the material and CO2 molecules. 相似文献
93.
In a dissipative system with cubic–quintic nonlinearity, the curious evolution of optical vortex beams characterized by different topological charges (TCs) is simulated numerically and presented their evolution profiles. We find that new vortices will be induced during propagation, and the behavior of vortices, as affected by the TC and the number of beads of the incident beam, as well as its size, is also discussed. Common rules associated with the initial conditions coming from various incident beams are developed to determine the number of induced vortices and the corresponding rotation direction. Attributed to the nonlinearity, during propagation we see the beams slowly expand to induce new vortices, which commonly appear in oppositely charged pairs, while the net topological charge of the vortex is conserved. Our results not only deepen the understanding of optical vortices, but also widen their potential applications. 相似文献
94.
95.
96.
In quantum mechanics, the expectation value of an operator can be measured by using the projective measurement, ifthe coupling between the measured system and pointer is strong enough. However in the weak coupling regime, the pointercan not show all the eigenvalue of the physical quantity directly due to the overlapping among the pointer states, whichmakes the measurement of the expectation value difficult. In this paper, we propose an expectation value measurementmethod in the weak coupling regime inspired by the weak measurement scheme. Compared to the projective measurement,our scheme has two obvious advantages. Experimentally we use the internal state and motional state of a single trapped40Ca+ to establish the measurement scheme and realize the proof of principle demonstration of the scheme. 相似文献
97.
Acoustical Physics - In order to suppress the vibration and noise in the middle and low frequency band of the wheel-driven bus, this paper explores the application of the locally resonant phononic... 相似文献
98.
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
99.
Hong Song Ya Li Qi-Jun Yao Liang Jin Lei Liu Yan-Hua Liu Prof. Dr. Bing-Feng Shi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(16):6638-6642
The atroposelective synthesis of axially chiral styrenes remains a formidable challenge due to their relatively lower rotational barriers compared to the biaryl atropoisomers. Herein, we describe the construction of axially chiral styrenes through PdII-catalyzed atroposelective C−H olefination, using a bulky amino amide as a transient chiral auxiliary. Various axially chiral styrenes were produced with good yields and high enantioselectivity (up to 95 % yield and 99 % ee). Carboxylic acid derivatives of the resulting axially chiral styrenes showed superior enantiocontrol over the biaryl counterparts in CoIII-catalyzed enantioselective C(sp3)−H amidation of thioamide. Mechanistic studies suggest that C−H cleavage is the enantioselectivity-determining step. 相似文献
100.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers. 相似文献