全文获取类型
收费全文 | 7734篇 |
免费 | 307篇 |
国内免费 | 52篇 |
专业分类
化学 | 5682篇 |
晶体学 | 73篇 |
力学 | 191篇 |
综合类 | 1篇 |
数学 | 945篇 |
物理学 | 1201篇 |
出版年
2023年 | 53篇 |
2022年 | 49篇 |
2021年 | 151篇 |
2020年 | 144篇 |
2019年 | 126篇 |
2018年 | 103篇 |
2017年 | 88篇 |
2016年 | 209篇 |
2015年 | 190篇 |
2014年 | 228篇 |
2013年 | 384篇 |
2012年 | 543篇 |
2011年 | 594篇 |
2010年 | 332篇 |
2009年 | 243篇 |
2008年 | 495篇 |
2007年 | 515篇 |
2006年 | 524篇 |
2005年 | 514篇 |
2004年 | 431篇 |
2003年 | 359篇 |
2002年 | 287篇 |
2001年 | 108篇 |
2000年 | 90篇 |
1999年 | 74篇 |
1998年 | 72篇 |
1997年 | 81篇 |
1996年 | 128篇 |
1995年 | 69篇 |
1994年 | 69篇 |
1993年 | 70篇 |
1992年 | 49篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 28篇 |
1988年 | 42篇 |
1987年 | 29篇 |
1986年 | 34篇 |
1985年 | 70篇 |
1984年 | 47篇 |
1983年 | 27篇 |
1982年 | 54篇 |
1981年 | 29篇 |
1980年 | 23篇 |
1979年 | 27篇 |
1978年 | 34篇 |
1977年 | 29篇 |
1976年 | 25篇 |
1975年 | 21篇 |
1974年 | 24篇 |
排序方式: 共有8093条查询结果,搜索用时 390 毫秒
21.
22.
23.
Casey Chun Zhou Eric J. Stoner Kent D. Stewart L. Steven Hollis Edmund D. Matayoshi Gregory M. Brill 《Tetrahedron》2004,60(47):10611-10618
Oritavancin is a semi-synthetic glycopeptide antibiotic which is structurally related to vancomycin. When oritavancin bisphosphate is dried in vacuo with heat, a new compound forms. This new compound is stable only in the solid state and reverts to oritavancin in solution. Highly enriched samples of this compound were obtained by preparative HPLC and the structure of this compound was elucidated by using one and two-dimensional (1H and 13C) NMR spectroscopy in conjunction with computer-assisted molecular modeling. It has been determined that oritavancin adopts a conformation similar to that of vancomycin in solution, while the new compound is the unnatural R-AB-biaryl atropisomer of oritavancin. This is the first observation and isolation of an AB-biaryl atropisomer in an intact member of the vancomycin family of glycopeptide antibiotics. 相似文献
24.
Surface-wave gas discharges sustained under the conditions of a diffusion controlled regime are studied on the basis of the fluid plasma model. The self-consistent behaviour of the plasma density and of the field intensity along the discharge length is obtained. It is shown that the nonlinearity in the particle balance equation due to stepwise ionisation determines the plasma density in terms of the field intensity and ensures self-consistent behaviour of the wave ? discharge characteristics in a diffusion controlled regime. 相似文献
25.
Multiple-zero multiple-pole optical filter transfer functions may be implemented more efficiently in an integrated optics architecture if higher order N × M optical couplers are utilized. For example, a coherent ring resonator made from two 3×3 couplers offers some advantages over the three mirror Fabry-Perot etalon, which is its analog. To this end we develop the formalism for obtaining the transfer functions and scattering matrices of ring resonators made from two N × M couplers. We then present a methodology for analyzing serial and parallel systems of N × M optical coupler ring resonators. 相似文献
26.
27.
Sridevi Kaiti Eric Fossum 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):2099-2106
A thorough study of the polymerization behavior of 4‐fluoro‐4′‐hydroxytriphenyl‐phosphine oxide, 2 , under nucleophilic aromatic substitution reactions has been carried out. The synthesis of 2 was achieved in excellent yields by the reaction of bis(4‐fluorophenyl)phenylphosphine oxide, 1 , with one equivalent of potassium hydroxide in DMSO/water. The structure and purity of 2 were confirmed via 1H, 13C, and 31P NMR spectroscopy along with elemental analysis. Polymerization reactions of 2 in NMP or DMSO at 180 °C provided the corresponding linear poly(arylene ether phosphine oxide)s, PAEPOs, with number average molecular weights, Mn, ranging from 11,700 to 36,500 Da. All of the polymer samples were completely soluble in chloroform, tetrahydrofuran, DMSO, NMP, and DMAc. The polymerization reactions were accompanied by a competing intramolecular process that resulted in the formation of cyclic oligomeric species that were removed via a final precipitation from methanol. Analysis using 31P NMR spectroscopy and size exclusion chromatography (SEC) confirmed that the majority of the lower molecular weight cyclic species were removed via this process. The polymer samples formed tough films when chloroform solutions were slowly evaporated on a glass slide. The PAEPO samples prepared in this study exhibited excellent thermal stability with Td (5%) values between 503 and 542 in air while the glass transition temperatures ranged from 223 to 237 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2099–2106, 2006 相似文献
28.
29.
30.