全文获取类型
收费全文 | 4474篇 |
免费 | 151篇 |
国内免费 | 28篇 |
专业分类
化学 | 2917篇 |
晶体学 | 15篇 |
力学 | 214篇 |
数学 | 776篇 |
物理学 | 731篇 |
出版年
2023年 | 20篇 |
2022年 | 31篇 |
2021年 | 65篇 |
2020年 | 61篇 |
2019年 | 71篇 |
2018年 | 56篇 |
2017年 | 59篇 |
2016年 | 128篇 |
2015年 | 116篇 |
2014年 | 146篇 |
2013年 | 255篇 |
2012年 | 325篇 |
2011年 | 388篇 |
2010年 | 202篇 |
2009年 | 211篇 |
2008年 | 271篇 |
2007年 | 280篇 |
2006年 | 297篇 |
2005年 | 284篇 |
2004年 | 224篇 |
2003年 | 219篇 |
2002年 | 197篇 |
2001年 | 51篇 |
2000年 | 52篇 |
1999年 | 36篇 |
1998年 | 40篇 |
1997年 | 53篇 |
1996年 | 48篇 |
1995年 | 41篇 |
1994年 | 51篇 |
1993年 | 32篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 9篇 |
排序方式: 共有4653条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
15.
Gas‐phase conformations of capistruin – comparison of lasso,branched‐cyclic and linear topologies 下载免费PDF全文
16.
Dr. Miguel Cortijo Dr. Ángela Valentín-Pérez Dr. Andrei Rogalev Dr. Fabrice Wilhelm Dr. Philippe Sainctavit Dr. Patrick Rosa Dr. Elizabeth A. Hillard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(59):13363-13366
An original method for determining the handedness of individual non-centrosymmetric crystals in a mixture using a tightly-focused, circularly polarized X-ray beam is presented. The X-ray natural circular dichroism (XNCD) spectra recorded at the metal K-edge on selected crystals of [Δ-M(en)3](NO3)2 and [Λ-M(en)3](NO3)2 (M=CoII, NiII) show extrema at the metal pre-edge (7712 eV for Co, 8335 eV for Ni). A mapping of a collection of some 220 crystals was performed at the respective energies by using left and right circular polarizations. The difference in absorption for the two polarizations, being either negative or positive, directly yielded the handedness of the crystal volume probed by the beam. By using this technique, it was found that the addition of l -ascorbic acid during the synthesis of [Co(en)3](NO3)2 resulted in an enantiomeric enrichment of the Λ-isomer of 67±13 %, whereas the Ni analogue was similarly, but conversely, enriched in the Δ-isomer (65±22 %). 相似文献
17.
Wenbin Guo Dr. Nathalie Daro Dr. Sébastien Pillet Dr. Mathieu Marchivie Dr. El-Eulmi Bendeif Dr. Elodie Tailleur Dr. Kittipong Chainok Dominique Denux Dr. Guillaume Chastanet Prof. Philippe Guionneau 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(57):12927-12930
The current craze for research around the spin crossover phenomenon can be justified to some extent by the mechanical properties due to the decrease of volume associated with the transition of the metal ion from the HS state to the LS state. As demonstrated here, the molecular complex [Fe(PM-pBrA)2(NCS)2] exhibits, on the contrary, an increase of the unit-cell volume from HS to LS. This counter-intuitive and unprecedented behavior that concerns both the thermal and the photoexcited spin conversions is revealed by a combination of single-crystal and powder X-ray diffraction complemented by magnetic measurements. Interestingly, this abnormal volume change appears concomitant with the wide rotation of a phenyl ring which induces a drastic modification, though reversible, of the structural packing within the crystal. In addition, the light-induced HS state obtained through the Light-Induced Excited Spin-State Trapping shows a remarkably high relaxation temperature, namely T(LIESST), of 109 K, one of the highest so far reported. The above set of quite unusual characteristics opens up new fields of possibilities within the development of spin crossover materials. 相似文献
18.
Dr. Antoine Nitelet Dr. Damien Thevenet Dr. Bruno Schiavi Dr. Christophe Hardouin Dr. Jean Fournier Dr. Rodolphe Tamion Prof. Dr. Xavier Pannecoucke Prof. Dr. Philippe Jubault Prof. Dr. Thomas Poisson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3262-3266
The copper-photocatalyzed borylation of aryl, heteroaryl, vinyl and alkyl halides (I and Br) was reported. The reaction proceeded using a new heteroleptic Cu complex under irradiation with blue LEDs, giving the corresponding boronic-acid esters in good to excellent yields. The reaction was extended to continuous-flow conditions to allow an easy scale-up. The mechanism of the reaction was studied and a mechanism based on a reductive quenching (CuI/CuI*/Cu0) was suggested. 相似文献
19.
Farah Naz Bibimaryam Mousavi Zhixiong Luo Christia Jabbour Philippe M. Heynderickx Somboon Chaemchuen Francis Verpoort 《应用有机金属化学》2019,33(5)
A series of spray dried zeolitic imidazolate frameworks (ZIFs = ZIF‐8, ZIF‐67, and Zn/Co‐ZIF) are used as a catalyst for the bulk ring‐opening polymerization of δ‐valerolactone without any co‐catalyst to generate polyvalerolactone. Interestingly, using the same catalyst under the same reaction conditions could manipulate the structure of the product polymer, and thus its physical properties. Thus, using a dried substrate leads to the formation of the cyclic polymer while a linear polymer was formed on using the commercially available substrate. An activated monomer mechanism has been suggested where the propagating zinc alkoxide undergoes an intramolecular transesterification to release cyclic or linear polyvalerolactone. The ROP of δ‐VL without drying shows that the polymeric zwitterions have little tendency to cyclize in the presence of moisture. At 140 °C, ZIF‐8 shows a superior catalytic activity resulting in the production of cyclic polyvalerolactone having a high molecular weight as compared to ZIF‐67 or Zn/Co‐ZIF due to the presence of highly active sites. The catalyst could be recycled and reused without any significant loss of catalytic activity. 相似文献
20.
Queueing Systems - In this paper, a stochastic model of a call center with a two-level architecture is analyzed. A first-level pool of operators answers calls, identifies, and handles non-urgent... 相似文献