全文获取类型
收费全文 | 1918篇 |
免费 | 66篇 |
国内免费 | 12篇 |
专业分类
化学 | 1551篇 |
晶体学 | 14篇 |
力学 | 9篇 |
数学 | 93篇 |
物理学 | 329篇 |
出版年
2023年 | 13篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 28篇 |
2019年 | 33篇 |
2018年 | 16篇 |
2017年 | 23篇 |
2016年 | 39篇 |
2015年 | 39篇 |
2014年 | 53篇 |
2013年 | 127篇 |
2012年 | 96篇 |
2011年 | 137篇 |
2010年 | 65篇 |
2009年 | 58篇 |
2008年 | 120篇 |
2007年 | 107篇 |
2006年 | 120篇 |
2005年 | 102篇 |
2004年 | 111篇 |
2003年 | 89篇 |
2002年 | 94篇 |
2001年 | 37篇 |
2000年 | 42篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 20篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 25篇 |
1984年 | 24篇 |
1983年 | 8篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1974年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有1996条查询结果,搜索用时 0 毫秒
41.
A wide range of o-alkynylanilines undergo a copper-catalyzed direct C-H/N-H coupling with azoles followed by benzannulation to form the corresponding N-azolylindoles in good yields. The domino reaction proceeds effectively with molecular oxygen as the sole oxidant and provides a new dehydrogenative access to the titled compounds of interest in pharmaceutical and material sciences. 相似文献
42.
Kiyoshi Koyama Masato Nishimura 《Journal of polymer science. Part A, Polymer chemistry》1972,10(9):2601-2608
The polymerization of vinyl monomers initiated by binary initiator systems composed of a copper–amine complex type resin and organic halides has been studied. These binary systems initiated the polymerization of various vinyl monomers. A kinetic study of the polymerization of methyl methacrylate initiated by the copper–amine complex resin–CCl4 system was carried out, and it was found that the polymerization proceeds by way of a radical mechanism. This fact was also supported by the copolymerization of methyl methacrylate with styrene. The overall activation energy of the polymerization of methyl methacrylate was estimated as 8.4 kcal/mole. The activity of the initiator systems was greatly dependent upon the dissociation energy of carbon–halogen bonds in the organic halides. A possible initiation mechanism with the binary systems is proposed and discussed. 相似文献
43.
Conformational and Intermolecular Interaction Dynamics of Photolyase/Cryptochrome Proteins Monitored by the Time‐Resolved Diffusion Technique 下载免费PDF全文
Cryptochrome (CRY), a blue light sensor protein, possesses a similar domain structure to photolyase (PHR) that, upon absorption of light, repairs DNA damage. In this review, we compare the reaction dynamics of these systems by monitoring the reaction kinetics of conformational change and intermolecular interaction change based on time‐dependent diffusion coefficient measurements obtained by using the pulsed laser‐induced transient grating technique. Using this method, time‐dependent biomolecular interactions, such as transient dissociation reactions in solution, have been successfully detected in real time. Conformational change in (6‐4) PHR has not been detected after the photoexcitation by monitoring the diffusion coefficient. However, the repaired DNA dissociates from PHR with a time constant of 50 μs, which must relate to a minor conformational change. However, CRY exhibits a considerable diffusion change with a time constant of 400 ms, which indicates that the protein–solvent interaction is changed by the conformational change. The C‐terminal domain of CRY is shown to be responsible for this change. 相似文献
44.
45.
Tanaka T Murakami K Kanda A Patra D Yamamoto S Satoh N Kim SW Rahman SM Ohno H Iwata C 《The Journal of organic chemistry》2001,66(21):7107-7112
A total synthesis of (+/-)-stemodinone, a tetracyclic stemodane diterpene, from the known tricyclic methyl olefin 11 is described. The key steps involve an efficient ring-exchange reaction and palladium(0)-catalyzed lactone migration. The ring-exchange strategy for controlling the stereochemistry was based on an initial Diels-Alder reaction to form a new ring followed by cleavage of the original ring. Cleavage of the original ring of the Diels-Alder adduct 9 was achieved by an initial regio- and chemoselective Baeyer-Villiger oxidation followed by the Pd(0)-catalyzed lactone-migration reaction reported by us. 相似文献
46.
47.
Vitamin E glycosides were synthesized and enzymatic hydrolysis was examined for use as potential pro-drugs, however, the glycoside bond was found to be stable. On the other hand, among the glycosides synthesized, dl-alpha-tocopherylglucoside (6b) and dl-alpha-tocopherylmannoside (6c) showed strong inhibitory action on histamine release from mast cells. In addition, 6c also showed a suppressive action on IgE antibody formation. Thus, tocopheryl glycoside showed new properties compared to tocopherol (vitamin E). In particular, 6c was shown to be a novel lead compound with excellent manifold anti-allergic activity and anti-inflammatory activity. 相似文献
48.
Ikuo Ashikawa Mariko Kito Kimiyuki Satoh Hiroyuki Koike Yorinao Inoue Kayoko Saiki Kiyoshi Tsukida Yasushi Koyama 《Photochemistry and photobiology》1987,46(2):269-275
All- trans β-carotene-5,6-epoxide has been found in the thylakoid membranes of spinach and of the cyanobacterium Synechococcus vulcanus Copeland. The epoxide was extracted from the thylakoid membranes with acetone, and was isolated by high-performance liquid chromatography (HPLC). The structure of the epoxide was identified by means of mass, Raman, and electronic absorption spectroscopy. Changes in the amount of the epoxide, as a result of epoxidation and (apparent) de-epoxidation reactions in the membranes, were traced by analysis of extracts on HPLC. In isolated thylakoid membranes, only the epoxidation reaction took place. The reaction was caused by irradiation or by the addition of ferricyanide, suggesting that electron transport reactions in the membranes are involved in the epoxidation. In intact spinach leaves, however, both epoxidation and de-epoxidation took place; the extent of epoxidation correlated with the intensity of light incident on the leaves. The epoxidation and de-epoxidation of all- trans β-carotene are contrasted with those of xanthophylls (in the violaxanthin cycle). 相似文献
49.
Seiji Miyano Osamu Yamashita Kunihiro Sumoto Keiyu Shima Mariko Hayashimatsu Fumio Satoh 《Journal of heterocyclic chemistry》1987,24(1):271-274
The method for preparing 7a-substituted hexahydro-1H-pyrrolizines 2 from 1,2,3,5,6,7-hexahydropyrrol-izinium Perchlorate (3) was investigated, by which introduction of a wide variety of functionalities on C(7a) could be achieved easily. 相似文献
50.
Tadashi Miyasaka Hiromichi Tanaka Kazue Satoh Mie Imahashi Kentaro Yamaguchi Yoichi Iitaka 《Journal of heterocyclic chemistry》1987,24(3):873-875
A highly efficient intramolecular nitrene insertion was observed upon irradiation of 6-azidouridine derivatives. The N6,2′-cyclo structure of the product was determined unequivocally by X-ray crystallography. 相似文献