全文获取类型
收费全文 | 3987篇 |
免费 | 147篇 |
国内免费 | 58篇 |
专业分类
化学 | 2482篇 |
晶体学 | 15篇 |
力学 | 133篇 |
数学 | 790篇 |
物理学 | 772篇 |
出版年
2024年 | 4篇 |
2023年 | 28篇 |
2022年 | 105篇 |
2021年 | 115篇 |
2020年 | 102篇 |
2019年 | 118篇 |
2018年 | 115篇 |
2017年 | 98篇 |
2016年 | 162篇 |
2015年 | 125篇 |
2014年 | 146篇 |
2013年 | 268篇 |
2012年 | 294篇 |
2011年 | 296篇 |
2010年 | 196篇 |
2009年 | 165篇 |
2008年 | 262篇 |
2007年 | 219篇 |
2006年 | 260篇 |
2005年 | 235篇 |
2004年 | 184篇 |
2003年 | 137篇 |
2002年 | 124篇 |
2001年 | 60篇 |
2000年 | 43篇 |
1999年 | 47篇 |
1998年 | 29篇 |
1997年 | 24篇 |
1996年 | 25篇 |
1995年 | 22篇 |
1994年 | 27篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 17篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 6篇 |
1973年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有4192条查询结果,搜索用时 15 毫秒
101.
102.
Paulo Igor M. Firmino Raquel S. Farias Amanda N. Barros Patrícia G. C. Landim Gervina B. M. Holanda Elisa Rodríguez Alexandre C. Lopes André B. dos Santos 《Applied biochemistry and biotechnology》2018,184(4):1187-1199
As the addition of low concentrations of oxygen can favor the initial degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds, this work verified the applicability of the microaerobic technology to enhance BTEX removal in an anaerobic bioreactor supplemented with high and low co-substrate (ethanol) concentrations. Additionally, structural alterations on the bioreactor microbiota were assessed throughout the experiment. The bioreactor was fed with a synthetic BTEX-contaminated water (~ 3 mg L?1 of each compound) and operated at a hydraulic retention time of 48 h. The addition of low concentrations of oxygen (1.0 mL min?1 of atmospheric air at 27 °C and 1 atm) assured high removal efficiencies (> 80%) for all compounds under microaerobic conditions. In fact, the applicability of this technology showed to be viable to enhance BTEX removal from contaminated waters, especially concerning benzene (with a 30% removal increase), which is a very recalcitrant compound under anaerobic conditions. However, high concentrations of ethanol adversely affected BTEX removal, especially benzene, under anaerobic and microaerobic conditions. Finally, although bacterial community richness decreased at low concentrations of ethanol, in general, the bioreactor microbiota could deal with the different operational conditions and preserved its functionality during the whole experiment. 相似文献
103.
Two-degree-of-freedom Hamiltonian systems with an elliptic equilibrium at the origin are characterised by the frequencies of the linearisation. Considering the frequencies as parameters, the system undergoes a bifurcation when the frequencies pass through a resonance. These bifurcations are well understood for most resonances , but not the semisimple cases and . A two-degree-of-freedom Hamiltonian system can be approximated to any order by an integrable normal form. The reason is that the normal form of a Hamiltonian system has an additional integral due to the normal form symmetry. The latter is intimately related to the ratio of the frequencies. For a rational frequency ratio this leads to -symmetric systems. The question we wish to address is about the co-dimension of such a system in resonance with respect to left-right-equivalence, where the right action is -equivariant. The result is a co-dimension five unfolding of the central singularity. Two of the unfolding parameters are moduli and the remaining non-modal parameters are the ones found in the linear unfolding of this system. 相似文献
104.
105.
Jorge Ferreira Raquel Zilz Igor S. Boeira Sabrina M. da Silva Adriana C.A. Casagrande Osvaldo L. Casagrande 《应用有机金属化学》2019,33(3)
A new set of Cr(III) complexes, {L}CrCl3(THF), based on thiophene–imine ( 2a , L = PhOC6H4(N═CH)‐2‐SC4H3; 2b , L = PhOC2H4(N═CH)‐2‐SC4H3; 2c , L = Ph(NH)C2H4(N═CH)‐2‐SC4H3; 2d , L = PhOC6H4(N═CH)‐2‐SC4H2‐5‐Ph; 2e , L = Ph(NH)C2H4(N═CH)‐2‐SC4H2‐5‐Ph) have been prepared and characterized using elemental analysis and infrared spectroscopy. Upon activation with methylaluminoxane, all the chromium complexes generated active systems affording a nonselective distribution of α‐olefins with turnover frequencies in the range 9500–93 500 (mol ethylene) (mol Cr)?1 h?1, and producing mostly oligomers (95.0–99.3 wt% of total products). Small amounts of polymer were produced in these oligomerization reactions (0.8–8.2 wt%). The catalytic activities were quite sensitive to the ligand environment. Moreover, the effects of oligomerization parameters (temperature, [Al]/[Cr] molar ratio, time) on the activity and on the product distribution were examined. 相似文献
106.
We present a study of resonant optical properties of gold‐protected silver nanoisland films. Silver nanoislands were grown on a glass substrate using out‐diffusion technique, the growth was followed by the deposition of nanometer‐thick gold coatings. Scanning electron microscopy and optical spectroscopy were used to characterize morphology and extinction spectra of the grown combined silver–gold nanostructures. Micro Raman spectroscopy of the combined nanoislands has demonstrated their signal enhancement factor exceeding that one of the initial silver nanoislands. 相似文献
107.
108.
109.
110.