全文获取类型
收费全文 | 3669篇 |
免费 | 105篇 |
国内免费 | 26篇 |
专业分类
化学 | 2150篇 |
晶体学 | 40篇 |
力学 | 75篇 |
数学 | 595篇 |
物理学 | 940篇 |
出版年
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 52篇 |
2019年 | 35篇 |
2018年 | 40篇 |
2017年 | 44篇 |
2016年 | 78篇 |
2015年 | 73篇 |
2014年 | 83篇 |
2013年 | 214篇 |
2012年 | 244篇 |
2011年 | 232篇 |
2010年 | 151篇 |
2009年 | 126篇 |
2008年 | 219篇 |
2007年 | 214篇 |
2006年 | 234篇 |
2005年 | 263篇 |
2004年 | 194篇 |
2003年 | 154篇 |
2002年 | 154篇 |
2001年 | 51篇 |
2000年 | 46篇 |
1999年 | 37篇 |
1998年 | 27篇 |
1997年 | 29篇 |
1996年 | 55篇 |
1995年 | 42篇 |
1994年 | 38篇 |
1993年 | 47篇 |
1992年 | 32篇 |
1991年 | 22篇 |
1990年 | 25篇 |
1989年 | 34篇 |
1988年 | 17篇 |
1987年 | 24篇 |
1986年 | 36篇 |
1985年 | 38篇 |
1984年 | 20篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 17篇 |
1977年 | 28篇 |
1976年 | 27篇 |
1975年 | 24篇 |
1973年 | 12篇 |
1970年 | 13篇 |
排序方式: 共有3800条查询结果,搜索用时 46 毫秒
41.
Jacques Kagan Chris P. Kolyvas Jeffery A. Jaworski Edgard D. Kagan Isabelle A. Kagan Li-Hsin Zang 《Photochemistry and photobiology》1984,40(4):479-483
Abstract 2,5-Diphenyloxazole (POP) is widely used for the determination of radioactivity by scintillation counting. It has been found to be phototoxic to the yeasts Saccharomyces cerevisiae and Candida utilis , to the first instar larvae of the mosquito Aedes aegypti , to the crustaceans Daphnia magna and Artemia salida , as well as to the eggs of Drosophila melanogaster . The related molecule 1,4-bis(5-phenyloxazol-2-yl)benzene (POPOP) is also phototoxic, but to a lesser degree. Both POP and POPOP can sensitize the formation of singlet oxygen. 相似文献
42.
Rogelio P. Frutos Isabelle Gallou Diana Reeves Yibo Xu Dhileepkumar Krishnamurthy Chris H. Senanayake 《Tetrahedron letters》2005,46(48):8369-8372
Expedient and practical new methodology for the synthesis of substituted imidazoles was developed to provide a rapid access to a variety of 2-substituted, 1,2-disubstituted and 1,2,4-trisubstituted imidazoles by the direct CuCl-mediated reaction of nitriles with α-amino acetals in an intermolecular as well as intramolecular fashion. 相似文献
43.
44.
The synthesis and transition temperatures of some trans-4-alkylcyclohexylethyl-substituted 2,3-difluorobiphenyls 总被引:1,自引:0,他引:1
Terphenyls with two lateral ortho-fluoro-substituents have proved to be excellent host materials for ferroelectric (SC*) mixtures. The compounds reported here are biphenyls with the same arrangement of lateral substituents but with a trans-4-alkylcyclohexylethyl moiety as one of the terminal substituents. Such three ring systems retain the ability to generate the SC mesophase and have low melting points. Low temperature lithiation procedures were used to prepare phenylboronic acids, which were then used in palladium catalysed cross-coupling procedures to prepare the desired compounds. The effect of molecular structure on the mesophase types and thermal stabilities is discussed and comparisons are made with analogous terphenyls and biphenyls with open chain terminal substituents. 相似文献
45.
46.
An azacrown system has been developed for selective membrane binding of phosphatidylinositol-4,5-bis(phosphate) recognition. Neutral and cationic forms of the metacyclophane macrocycles have been synthesized by divergent routes in acceptable yields. Such diversity will be useful in identifying anion receptors that operate best at membrane interfaces. 相似文献
47.
Plumb RS Stumpf CL Gorenstein MV Castro-Perez JM Dear GJ Anthony M Sweatman BC Connor SC Haselden JN 《Rapid communications in mass spectrometry : RCM》2002,16(20):1991-1996
The application of liquid chromatography/mass spectrometry (LC/MS) followed by principal components analysis (PCA) has been successfully applied to the screening of rat urine following the administration of three candidate pharmaceuticals. With this methodology it was possible to differentiate the control samples from the dosed samples and to identify the components of the mass spectrum responsible for the separation. These data clearly show that LC/MS is a viable alternative, or complementary, technique to proton NMR for metabonomics applications in drug discovery and development. 相似文献
48.
Kate J. Graham Chris P. Schaller Brian J. Johnson John B. Klassen 《The Chemical Educator》2002,7(6):376-378
The incorporation of research projects into undergraduate chemistry courses provides a perspective that is fundamentally unavailable in most laboratory experiences. While independent, multistep synthesis projects in organic chemistry have been reported previously, most efforts have been directed at relatively restricted, closely guided research plans with modest student participation in the experimental design. We have implemented a more open-ended synthesis project, limited principally by cost, safety and availability of materials. In the second semester of the sophomore organic sequence, students develop multiple drafts of a plan for a three-to-four-step synthesis. Subsequently, students obtain their own literature protocols for the individual steps. The synthesis is performed over three four-hour laboratory periods. The students conclude this project with a poster presentation of the results at the end of the semester. Evaluation of the students work focuses not only on the successful synthesis of the target but also on planning, troubleshooting, purification, and spectral analysis. 相似文献
49.
Axel Ingendoh Jan Becher Helen Clausen Helle Chris Nielsen 《Tetrahedron letters》1985,26(9):1249-1252
The high reactivity of the -1-acyloxy-1,3-pentadiene-5-ols as dienes in intramolecular Diels-Alder reactions with maleic anhydride and fumaric acid ethylester monochloride is discussed. 相似文献
50.
Miller CR Vogel R Surawski PP Jack KS Corrie SR Trau M 《Langmuir : the ACS journal of surfaces and colloids》2005,21(21):9733-9740
Thiol-functionalized organosilica microspheres were synthesized via a two-step process: (1) acid-catalyzed hydrolysis and condensation of 3-mercaptopropyltrimethoxysilane (MPTMS), followed by (2) base-catalyzed condensation, which led to the rapid formation of emulsion droplets with a narrow size distribution. These droplets continued to condense to form solid microspheres. Solution (29)Si NMR and optical microscopy were applied to study the mechanism of this novel synthetic route. Solid-state (29)Si NMR, SEM, zeta potential titration, and Coulter counter measurements were used to study the bulk and surface properties and to determine the particle size distributions of the final microspheres. Compared to conventional St?ber silica particles, these microspheres were shown to have a lower degree of cross-linking (average degree of condensation, r = 1.25), a larger average size (up to 6 microm), and a higher isoelectric point (pH = 4.4). Confocal microscopy of dye-labeled microspheres showed an even distribution of dye molecules throughout the interior, characteristic of a readily accessible and permeable organosilica network. These findings have implications for the production of functionalized solid supports for use in catalysis and biological applications, such as optically encoded carriers for combinatorial synthesis. 相似文献