全文获取类型
收费全文 | 348357篇 |
免费 | 3514篇 |
国内免费 | 1193篇 |
专业分类
化学 | 164566篇 |
晶体学 | 4991篇 |
力学 | 17942篇 |
综合类 | 2篇 |
数学 | 64155篇 |
物理学 | 101408篇 |
出版年
2021年 | 2027篇 |
2020年 | 2425篇 |
2019年 | 2667篇 |
2018年 | 13387篇 |
2017年 | 13099篇 |
2016年 | 11149篇 |
2015年 | 4442篇 |
2014年 | 5533篇 |
2013年 | 13168篇 |
2012年 | 13598篇 |
2011年 | 21574篇 |
2010年 | 13569篇 |
2009年 | 13677篇 |
2008年 | 16952篇 |
2007年 | 18806篇 |
2006年 | 10216篇 |
2005年 | 10437篇 |
2004年 | 9811篇 |
2003年 | 9219篇 |
2002年 | 8078篇 |
2001年 | 8099篇 |
2000年 | 6418篇 |
1999年 | 4932篇 |
1998年 | 4197篇 |
1997年 | 3980篇 |
1996年 | 4020篇 |
1995年 | 3524篇 |
1994年 | 3492篇 |
1993年 | 3563篇 |
1992年 | 3638篇 |
1991年 | 3763篇 |
1990年 | 3533篇 |
1989年 | 3395篇 |
1988年 | 3438篇 |
1987年 | 3292篇 |
1986年 | 3148篇 |
1985年 | 4244篇 |
1984年 | 4420篇 |
1983年 | 3547篇 |
1982年 | 3763篇 |
1981年 | 3669篇 |
1980年 | 3528篇 |
1979年 | 3628篇 |
1978年 | 3728篇 |
1977年 | 3638篇 |
1976年 | 3725篇 |
1975年 | 3393篇 |
1974年 | 3396篇 |
1973年 | 3465篇 |
1972年 | 2403篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
S. Aravinda N. Shamala Rituparna S. Roy P Balaram 《Journal of Chemical Sciences》2003,115(5-6):373-400
An overview of the use of non-protein amino acids in the design of conformationally well-defined peptides, based on work from
the author’s laboratory, is discussed. The crystal structures of several designed oligopeptides illustrate the useα-aminoisobutyric acid (Aib) in the construction of helices, D-amino acids in the design of helix termination segments andDPro-Xxx segments for nucleating ofβ-hairpin structures.β- andγ-amino acid residues have been used to expand the range of designed polypeptide structures.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
62.
Bed ich Ko ata V clav Kozmik Ji í Svoboda Vladimí ra Novotn P emysl Van k Milada Glogarov 《Liquid crystals》2003,30(5):603-610
Four series of new [1]benzothieno[3,2- b ][1]benzothiophene derivatives have been synthesized. In the non-chiral series a SmA phase occurs, while the chiral series exhibits a rather wide antiferroelectric SmC * A phase just below the SmA phase. The SmA-SmC * A phase transition has been studied using DSC and dielectric spectroscopy. In the SmC * A phase the spontaneous quantities have been measured. The tilt angle shows a typical temperature dependence and the values of spontaneous polarization are rather moderate. The length of the helical pitch increases on increasing the length of the non-chiral alkyl chain. 相似文献
63.
Received: 14 September 2001 / in final form: 28 April 2002 // Published online: 20 March 2003 相似文献
64.
I. P. Kuranova K. M. Polyakov E. A. Smirnova W. E. Höhne V. S. Lamzin R. Meijer 《Crystallography Reports》2003,48(6):953-958
Crystals of Saccharomyces cerevisiae inorganic pyrophosphatase suitable for X-ray diffraction study were grown by cocrystallization of the enzyme with cobalt chloride and imidodiphosphate. Saccharomyces cerevisiae is a metal-dependent enzyme which catalyzes hydrolysis of inorganic pyrophosphate to orthophosphate. The three-dimensional structure of this enzyme was solved by the molecular-replacement method and refined at 1.8 Å resolution to an R factor of 19.5%. Cobalt and phosphate ions were revealed in the active centers of both identical subunits (A and B) of the pyrophosphatase molecule. In subunit B, a water molecule was found between two cobalt ions. It is believed that this water molecule acts as an attacking nucleophile in the enzymatic cleavage of the pyrophosphate bond. It was demonstrated that cobalt ions and a phosphate group occupy only part of the potential binding sites (two chemically identical and crystallographically independent subunits have different binding sites). The arrangement of ligands and the structure of the nucleophile-binding site are discussed in relation to the mechanism of action of the enzyme and the nature of the metal activator. 相似文献
65.
66.
V. L. Gilyarov A. I. Slutsker V. P. Volodin L. A. Laius 《Physics of the Solid State》1997,39(1):132-135
The dependence of the energy characteristics on an adiabatically slowly increasing external force is determined analytically
for an anharmonic oscillator. The analytical results are confirmed by a numerical calculation. The nature of the force dependences
of the energy characteristics are determined and discussed.
Fiz. Tverd. Tela (St. Petersburg) 39, 153–157 (January 1997) 相似文献
67.
Flowing and static gas-phase samples of HNO3 in O2 and N2 were analyzed by long-path ultraviolet/visible (UV/VIS) spectroscopy to reveal the presence of both NO2 and NO3, the concentrations of which were calculated using differential absorption cross sections. NO2 is produced predominantly by the heterogeneous decomposition of HNO3, whereas NO3 is generated in the gas phase by the thermal decomposition of N2O5, a product of the self-disproportionation of liquid HNO3. © 1993 John Wiley & Sons, Inc. 相似文献
68.
The gauge compensation fields induced by the differential operators of the Stueckelberg-Schrödinger equation are discussed, as well as the relation between these fields and the standard Maxwell fields; An action is constructed and the second quantization of the fields carried out using a constraint procedure. The properties of the second quantized matter fields are discussed. 相似文献
69.
Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate combination of these mechanisms can be used to counteract the usual convective flows (buoyancy- and/or thermocapillary-driven) inherent to crystal growth processes from the liquid phase. While vibrational convection is rather complex due to these identified mechanisms, the new modeling used in the present paper opens up very promising perspectives to efficiently control heat and mass transfer during real industrial applications of crystal growth from the liquid phase. 相似文献
70.