全文获取类型
收费全文 | 13931篇 |
免费 | 396篇 |
国内免费 | 83篇 |
专业分类
化学 | 10137篇 |
晶体学 | 140篇 |
力学 | 277篇 |
数学 | 1620篇 |
物理学 | 2236篇 |
出版年
2023年 | 68篇 |
2022年 | 93篇 |
2021年 | 134篇 |
2020年 | 188篇 |
2019年 | 180篇 |
2018年 | 149篇 |
2017年 | 123篇 |
2016年 | 267篇 |
2015年 | 265篇 |
2014年 | 327篇 |
2013年 | 594篇 |
2012年 | 769篇 |
2011年 | 966篇 |
2010年 | 490篇 |
2009年 | 438篇 |
2008年 | 905篇 |
2007年 | 871篇 |
2006年 | 946篇 |
2005年 | 960篇 |
2004年 | 828篇 |
2003年 | 682篇 |
2002年 | 630篇 |
2001年 | 202篇 |
2000年 | 197篇 |
1999年 | 165篇 |
1998年 | 174篇 |
1997年 | 203篇 |
1996年 | 216篇 |
1995年 | 128篇 |
1994年 | 155篇 |
1993年 | 139篇 |
1992年 | 130篇 |
1991年 | 102篇 |
1990年 | 84篇 |
1989年 | 86篇 |
1988年 | 87篇 |
1987年 | 104篇 |
1986年 | 77篇 |
1985年 | 128篇 |
1984年 | 124篇 |
1983年 | 89篇 |
1982年 | 106篇 |
1981年 | 120篇 |
1980年 | 119篇 |
1979年 | 96篇 |
1978年 | 72篇 |
1977年 | 76篇 |
1976年 | 58篇 |
1975年 | 57篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Kazuhiko Matsumoto Tetsuya Tsuda Toshiyuki Nohira Rika Hagiwara Yasuhiko Ito Osamu Tamada 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m186-m187
In the title complex, (C6H11N2)3[LaCl6], centrosymmetric octahedral hexachlorolanthanate anions are located at the corners and face‐centers of the monoclinic unit cell. The ring H atoms of the cations interact with the Cl atoms of the anions via hydrogen bonding, and bifurcation of the hydrogen bonding is observed. Cation–cation interactions via hydrogen bonding between the ring H atoms and π‐electrons of aromatic rings are also observed as in other imidazolium salts. 相似文献
92.
M. Jonathan Fray Paul Allen Paul R. Bradley Clare E. Challenger Michael Closier Tim J. Evans Mark L. Lewis John P. Mathias Carly L. Nichols Yvonne M. Po-Ba Hayley Snow Mark H. Stefaniak Hannah V. Vuong 《Tetrahedron》2006,62(29):6869-6875
The synthesis of ten substituted aminomethylene tetrahydro-isoquinolines is described, proceeding in eight steps from 5-hydroxyisoquinoline via reductive amination of N-Boc tetrahydro-isoquinoline 5-carboxaldehyde. Likewise, reductive amination was used to prepare four substituted dihydro-isoindoles from the corresponding aldehyde. The dihydro-isoindole ring system was conveniently accessed via a 2+2+2 cycloaddition reaction. 相似文献
93.
alpha-Tocopherol (alpha-Toc) was solubilized in aqueous solutions using 13 solubilizing agents and the products of oxidation by oxygen in the presence and the absence of Cu(II) were analyzed by HPLC. In the presence of Cu(II), the oxidation was accelerated and 5-formyl-7,8-dimethyltocol and alpha-tocoquinone were the major oxidation products. Their yields greatly increased in the presence of Cu(II). The yields and the rates of formation of the products were dependent on the properties of solubilizing agents and other conditions as well as the presence of Cu(II) or other metal ions. It is suggested that slight changes in the structure of the solubilizing agents affect the course of the reaction. 相似文献
94.
Malkinson JP Anim MK Zloh M Searcey M Hampshire AJ Fox KR 《The Journal of organic chemistry》2005,70(19):7654-7661
[reaction: see text] In this article, the first solid-phase-based total synthesis of TANDEM, a synthetic analogue of triostin A, is described. In initial studies, the synthesis incorporated depsipeptide formation, introduction of chromophores, and disulfide bond formation on the solid phase, prior to a final solution-phase macrolactamization, to give the target molecule. Although pure TANDEM was obtained in an overall yield comparable to those for all syntheses to date, the yield of the final cyclization was low (11%). A more efficient approach involved removal from the solid phase prior to disulfide bond formation. The resulting linear peptide underwent macrolactamization under mild conditions and high dilution. Final disulfide bond formation was essentially quantitative and gave the target molecule, TANDEM, in an overall yield of 18%. The final compound was assessed for its ability to bind to 5'-TpA sequences on DNA by DNase I footprinting. This efficient synthesis sets the stage for a study of the structure-activity relationship of TANDEM and the natural product triostin A, with analogues containing "point mutations" at every site within the cyclic compounds. 相似文献
95.
96.
Masafumi Unno Hiroyuki Murakami Satoshi Kagawa Hideyuki Matsumoto 《Silicon Chemistry》2007,3(3-4):195-198
Two new silanols bearing very bulky silyl groups, (i-Pr3
Si)3SiOH and (t − BuMe2Si)3SiOH were prepared by peracidoxidation of their respective silanes. The X − ray crystallographic analysis revealed that (t − BuMe2Si)3 SiOH forms a dimeric structure with hydrogen bonding, while (i − Pr3 Si)3 SiOH exists as a monomer in the crystal. The effects of the size of the substituents as well as the reactivity of these silanols
are discussed. 相似文献
97.
Applied Biochemistry and Biotechnology - 相似文献
98.
Applied Biochemistry and Biotechnology - 相似文献
99.
100.
Yan B Collins N Wheatley J Irving M Leopold K Chan C Shornikov A Fang L Lee A Stock M Zhao J 《Journal of combinatorial chemistry》2004,6(2):255-261
We have developed a high-throughput purification system to purify combinatorial libraries at a 50-100-mg scale with a throughput of 250 samples/instrument/day. We applied an accelerated retention window method to shorten the purification time and targeted one fraction per injection to simplify data tracking, lower QC workload, and simplify the postpurification processing. First, we determined the accurate retention time and peak height for all compounds using an eight-channel parallel LC/UV/MS system, and calculated the specific preparative HPLC conditions for individual compounds. The preparative HPLC conditions include the compound-specific gradient segment for individual compounds with a fixed gradient slope and the compound-specific UV or ELSD threshold for triggering a fraction collection device. A unique solvent composition or solvent strength was programmed for each compound in the preparative HPLC in order to elute all compounds at the same target time. Considering the possible deviation of the predicted retention time, a 1-min window around the target time was set to collect peaks above a threshold based on UV or ELSD detection. Dual column preparative instruments were used to maximize throughput. We have purified more than 500 000 druglike compounds using this system in the past 3 years. We report various components of this high-throughput purification system and some of our purification results. 相似文献