全文获取类型
收费全文 | 4475篇 |
免费 | 495篇 |
国内免费 | 482篇 |
专业分类
化学 | 3133篇 |
晶体学 | 85篇 |
力学 | 170篇 |
综合类 | 49篇 |
数学 | 590篇 |
物理学 | 1425篇 |
出版年
2023年 | 77篇 |
2022年 | 118篇 |
2021年 | 108篇 |
2020年 | 131篇 |
2019年 | 134篇 |
2018年 | 138篇 |
2017年 | 129篇 |
2016年 | 165篇 |
2015年 | 171篇 |
2014年 | 198篇 |
2013年 | 270篇 |
2012年 | 345篇 |
2011年 | 329篇 |
2010年 | 239篇 |
2009年 | 244篇 |
2008年 | 267篇 |
2007年 | 239篇 |
2006年 | 207篇 |
2005年 | 197篇 |
2004年 | 165篇 |
2003年 | 147篇 |
2002年 | 164篇 |
2001年 | 113篇 |
2000年 | 79篇 |
1999年 | 85篇 |
1998年 | 62篇 |
1997年 | 44篇 |
1996年 | 58篇 |
1995年 | 52篇 |
1994年 | 47篇 |
1993年 | 53篇 |
1992年 | 53篇 |
1991年 | 38篇 |
1990年 | 40篇 |
1989年 | 38篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 38篇 |
1984年 | 35篇 |
1983年 | 28篇 |
1982年 | 20篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 21篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1974年 | 17篇 |
1973年 | 25篇 |
1972年 | 14篇 |
排序方式: 共有5452条查询结果,搜索用时 15 毫秒
51.
Fe-Co-Ni合金纳米线有序阵列的模板合成与磁性 总被引:10,自引:0,他引:10
以二次阳极氧化的氧化铝膜为模板,用电化学沉积的方法成功地合成了Fe-Co-Ni三组份有序纳米线阵列.扫描电子显微镜(SEM)和透射电子显微镜(TEM)观察表明纳米线表面光滑、有序、高长径比;磁性测量表明,其矫顽力较同组份的膜材料有较大的提高.将样品在惰性气体氛围中不同温度下退火,随着退火温度增加,其纵向矫顽力有一个极值,而对应的横向矫顽力没有类似的变化,关于这一现象的机理,本文进行了初步的讨论. 图5参15 相似文献
52.
53.
固相微萃取参数选择及其对有机锡分析的影响 总被引:1,自引:0,他引:1
固相微萃取是一种新型的、不断发展和完善的样品前处理方法,它与其它技术联用可对多种样品基体中挥发、半挥发性有机化合物进行测定。目前,该技术在毒性金属有机化合物中的应用很少。本文分析参数选择对固相微萃取的影响的同时,还对其在有机锡化合物分析中的应用作了综述。 相似文献
54.
Sajal Sen Mark W. Perrin Adam C. Sedgwick Vincent M. Lynch Jonathan L. Sessler Jonathan F. Arambula 《Chemical science》2021,12(21):7547
Recent decades have witnessed the emergence of Au(i) bis-N-heterocyclic carbenes (NHCs) as potential anticancer agents. However, these systems exhibit little interaction with serum proteins (e.g., human serum albumin), which presumably impacts their pharmacokinetic profile and tumor exposure. Anticancer drugs bound to human serum albumin (HSA) often benefit from significant advantages, including longer circulatory half-lives, tumor targeted delivery, and easier administration relative to the drug alone. In this work, we present Au(i) bis-NHCs complexes, 7 and 9, capable of binding to HSA. Complex 7 contains a reactive maleimide moiety for covalent protein conjugation, whereas its congener 9 contains a naphthalimide fluorophore for non-covalent binding. A similar drug motif was used in both cases. Complexes 7 and 9 were prepared from a carboxylic acid functionalized Au(i) bis-NHC (complex 2) using a newly developed post-synthetic amide functionalization protocol that allows coupling to both aliphatic and aromatic amines. Analytical, and in vitro techniques were used to confirm protein binding, as well as cellular uptake and antiproliferative activity in A549 human lung cancer cells. The present findings highlight a hitherto unexplored approach to modifying Au(i) bis-NHC drug candidates for protein ligation and serve to showcase the relative benefits of covalent and non-covalent HSA binding.Au(i) bis-N-heterocyclic carbenes (NHCs) functionalized using an amide linker were found to bind to human serum albumin (HSA) in covalent and non-covalent fashion. The solubility and in vitro anti-cancer activity of these new conjugates were studied. 相似文献
55.
Sen Gupta JG 《Talanta》1985,32(1):1-6
An improved graphite furnace atomic-absorption method has been developed for the determination of Sc, Y and the rare-earth elements in silicate rocks and related materials. The method, which involves the separation of the lanthanides by ion-exchange followed by their determination by electrothermal atomization, with use of an automatic sampling device, is more rapid than a previous method based on separation by co-precipitation with calcium oxalate and hydrous ferric oxide followed by normal injection of the solution into the furnace. Greater sensitivity (~ 10-40-fold) for La, Ce, Pr, Gd, Tb and Lu is also achieved by using a tantalum foil-lined graphite furnace instead of a pyrolytically-coated furnace. Results obtained for five international reference rock samples, NIM-G, SCo-1, MAG-1, SDC-1 and BHVO-1, are compared with those obtained previously by the oxalate-hydrous oxide co-precipitation method and with other published values. Results are given for four new Canadian iron-formation reference materials, FeR-1 to FeR-4. 相似文献
56.
The distribution of a solute in a gas-liquid Chromatographic column has been discussed from the probability view point and its analogy to the Bernoulli trial system has been shown. It has been shown that the reproduction of column behavior is possible by reproducing the probability. The criterion for the optimum column temperature has also been discussed. Recommendations have been made for determining the optimum column conditions and its reproduction. 相似文献
57.
Y. Lian H. Gao S. X. Dou H. Wang P. Ye Q. Guan J. Wang 《Applied physics. B, Lasers and optics》1994,59(6):655-658
Mechanism transitions of Self-Pumped Phase Conjugation (SPPC) with wavelength and doping concentration are observed in KTN:Fe (KTa1 –x
Nb
x
O3:Fe with
x
= 0.48) crystals. The SPPC mechanism in KTN: Fe (0.4 wt. %) crystal transforms from Stimulated Photorefractive Backscattering and Four-Wave Mixing (SPB-FWM) to cat (or total internal reflection) as the wavelength increases from 514.5 nm to 620 nm. SPPC at 514.5 nm is formed with the cat mechanism in a 0.2 wt. % doped KTN:Fe crystal, while with the SPB-FWM mechanism in a 0.4 wt. % doped one. These mechanism transitions are discussed with respect to the dependence of the backscattering gain coefficient of the crystals on wavelength and doping concentration. 相似文献
58.
Chaotic dynamics of charged particles in the field of two monochromatic waves in a magnetized plasma
We study the dynamics of charged particles in the presence of two electrostatic waves propagating obliquely to an ambient magnetic field. The presence of a second wave makes the problem a two-dimensional and time-dependent one with a complicated phase space behavior. We derive a set of difference equations (maps) for the nonrelativistic particle motion limit and numerically study them to elucidate the various aspects of the phase space dynamics. For the general case of oblique propagation, we observe synergistic effects leading to the lowering of the stochasticity threshold and the concomitant reduction in electric field amplitudes for particle heating applications. These results can be understood in terms of the resonance structures associated with the two waves and we obtain approximate analytic expressions for the thresholds. For the degenerate case of omega(1)=nOmega,omega(2)=mOmega (where omega(1),omega(2) are the frequencies of the two waves, Omega is the cyclotron frequency and n,m are integers) and strictly perpendicular propagation, the problem simplifies to a one-and-one-half-dimensional one. We observe the presence of stochastic webs in this situation. (c) 1996 American Institute of Physics. 相似文献
59.
60.