全文获取类型
收费全文 | 14180篇 |
免费 | 1668篇 |
国内免费 | 2656篇 |
专业分类
化学 | 9097篇 |
晶体学 | 135篇 |
力学 | 1414篇 |
综合类 | 77篇 |
数学 | 3376篇 |
物理学 | 4405篇 |
出版年
2024年 | 38篇 |
2023年 | 618篇 |
2022年 | 637篇 |
2021年 | 798篇 |
2020年 | 951篇 |
2019年 | 682篇 |
2018年 | 684篇 |
2017年 | 816篇 |
2016年 | 900篇 |
2015年 | 919篇 |
2014年 | 1214篇 |
2013年 | 1511篇 |
2012年 | 1384篇 |
2011年 | 1220篇 |
2010年 | 999篇 |
2009年 | 1019篇 |
2008年 | 672篇 |
2007年 | 642篇 |
2006年 | 672篇 |
2005年 | 368篇 |
2004年 | 229篇 |
2003年 | 217篇 |
2002年 | 195篇 |
2001年 | 261篇 |
2000年 | 154篇 |
1999年 | 239篇 |
1998年 | 138篇 |
1997年 | 110篇 |
1996年 | 82篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 9篇 |
1992年 | 19篇 |
1991年 | 5篇 |
1990年 | 19篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1959年 | 1篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
991.
A group G is said to satisfy the maximal permutizer condition if the permutizer of any maximal subgroup M of G in G, PG(M), is G. In this paper, we characterize the supersolubility of finite groups by using the maximal permutizer condition. We also get some results for when both G/N and N are supersoluble, which implies that G is supersoluble. Our results unify or generalize some known results. 相似文献
992.
Used digital speckle correlation method (DSCM) to realize orientation function of optical mouse is researched. The experiment is designed to obtain the dynamic speckle patterns which are shot by CCD, then the DSCM is used to process the sequential images and also the experiment is simulated. The experimental results show the DSCM can confirm orientation function of the optical mouse, and have a good agreement with the simulation results, and the resolution we obtained is higher than the resolution of mouse on the market. 相似文献
993.
《Nonlinear Analysis: Real World Applications》2008,9(2):651-662
With China's entry into the WTO, this article sets up a dynamic model describing a situation in which both foreign enterprises and Chinese financial institutions are investing in Chinese state-owned enterprises while the state-owned assets withdraw gradually. This model may contribute to the control of the chaotic phenomenon. We can apply the straight-line stabilization method to chaos control successfully through controlling parameter perturbation. 相似文献
994.
YueFeng Tang Jun Qi ZhengBin Gu ZhiPeng Huang AiDong Li YanFeng Chen 《Applied Surface Science》2008,254(8):2229-2232
Fabrication of porous materials with uniform pore size distribution remains a challenge. In this paper, a kind of uniform porous alumina material was fabricated on a template of polystyrene microspheres by radio frequency (RF) magnetron sputtering. Surface of samples was observed by scanning electron microscopy (SEM), and the phase of porous materials was confirmed by X-ray diffraction (XRD). The pore size distribution of samples was tested by mercury intrusion method. 相似文献
995.
Homodesmotic reactions were designed for the computation of strain energies (SE) for four nitro-substituted 1,3,5,7-tetraazacubane
derivatives. Total energies of the optimized geometric structures at the DFT-B3LYP/6-31G* and DFT-B3LYP/6-311G** levels were
used to derive the SE. The variation of SE with respect to the number of substituents is similar with both basis sets. The
SE value is 237.32 kcal/mol at the B3LYP/6-311G** level for 2,4,6,8-tetranitro-1,3,5,7-tetraazacubane, which is unexpectedly
much larger than that of its cubane analogue. The SE increases remarkably with more nitro groups being attached to the cage
skeleton of tetraazacubane. The ‘bending’ of the bonds within the cubic skeleton attributes to the increase of strains as
the attached number of nitro groups increases. 相似文献
996.
非线性伪抛物方程由于其来源于一些重要的物理过程而成为研究热点.对于一类三阶非线性伪抛物方程的初边值问题,给出了Hilbert空间中相应的强制不等式,利用同胚理论及推广的反函数定理,得到了非线性方程初边值问题解的大范围存在定理.对于相应的半线性方程给出了初边值问题解的大范围存在性、唯一性定理. 相似文献
997.
Prof. Bao Li Junrui Wang Guangliang Tu Guodong Ju Kehan Zhou Prof. Yingsheng Zhao 《European journal of organic chemistry》2023,26(12):e202201458
Diaryl sulfides are a class of important synthetic chemical units. Herein, we report a new method for direct preparation of diphenyl sulfides using P-toluenesulfonyl chloride as an effective thiophenyl radical precursor with assistance from Hemin. Various substituted anisoles and benzenesulfonyl chlorides are well tolerated, resulting in moderate to good yields of diaryl sulfides. The potential of the proposed method is validated by good yields obtained in gram scale reactions. 相似文献
998.
Ling‐Hai Xie Xian‐Yu Deng Lin Chen Shu‐Fen Chen Ran‐Ran Liu Xiao‐Ya Hou King‐Young Wong Qi‐Dan Ling Wei Huang 《Journal of polymer science. Part A, Polymer chemistry》2009,47(20):5221-5229
The combination of π‐stacked with π‐conjugated building blocks offers an essential strategy to construct multifunctional organic semiconductors (MOSs) with the unique optoelectrical properties. Covalent hybrids can efficiently avoid the intrinsic phase‐separation defects in corresponding blend system. In this contribution, poly(vinylcarbazole) tethered with terfluorene, PVK‐TF, as a double‐channeled π‐stacked and π‐conjugated hybrid (SCH), has been constructed via Friedal‐Crafts click postmodification (FCCP). The chemical structure and optoelectrical property were determined by GPC, UV–vis, PL, TGA, DSC, and CV. Its PL spectra in the annealing thin film at N2 atmosphere without low‐energy emission bands centered at the 530 nm indicates that no π‐stacks between carbazole and TF or among TFs dominate the whole condensed phase, which is in agreement with the intrachain T‐shaped π‐pitched motifs in molecular modeling simulation due to steric hindrance effect in complicated diarylfluorenes (CDAFs). A supporting prototype stable deep‐blue PLED was successfully obtained with an Internationale de l'Eclairage (CIE) coordinates of (0.20, 0.10) and a width at half maximum (FWHM) of about 60 nm at high current density of 100 mA/cm2 (35 V). Deep‐blue PVK‐TF is a promising MOS for hole‐transporting and host materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5221–5229, 2009 相似文献
999.
In this work the changes in thermal degradation characteristics of polyamide 6 (PA6) in the presence of melamine (Me) or melamine cyanurate (MC) were investigated systematically via direct pyrolysis mass spectrometry. Though thermal stability of PA6 was not affected by the presence of flame retardants, the changes in the products and in their distributions were detected. The reaction of carbonyl groups of PA6 with amine groups of melamine was the main cause for the changes in the product distribution. In the presence of melamine cyanurate, new products due to the reaction of cyanic acid generated by the decomposition of cyanurate, with the amine groups of PA6 were detected. Significant increases in the evolution temperatures of melamine and melamine cyanurate in the presence of PA6 were attributed to intermolecular interactions, most probably by H-bonding, with PA6. 相似文献
1000.
Xiao‐Hui Dai Chang‐Ming Dong 《Journal of polymer science. Part A, Polymer chemistry》2008,46(3):817-829
Biomimetic star‐shaped poly(ε‐caprolactone)‐b‐poly(gluconamidoethyl methacrylate) block copolymers (SPCL‐PGAMA) were synthesized from the atom transfer radical polymerization (ATRP) of unprotected GAMA glycomonomer using a tetra(2‐bromo‐2‐methylpropionyl)‐terminated star‐shaped poly(ε‐caprolactone) (SPCL‐Br) as a macroinitiator in NMP solution at room temperature. The block length of PGAMA glycopolymer within as‐synthesized SPCL‐PGAMA copolymers could be adjusted linearly by controlling the molar ratio of GAMA glycomonomer to SPCL‐Br macroinitiator, and the molecular weight distribution was reasonably narrow. The degree of crystallization of PCL block within copolymers decreased with the increasing block length ratio of outer PGAMA to inner PCL. Moreover, the self‐assembly properties of the SPCL‐PGAMA copolymers were investigated by NMR, UV‐vis, DLS, and TEM, respectively. The self‐assembled glucose‐installed aggregates changed from spherical micelles to worm‐like aggregates, then to vesicles with the decreasing weight fraction of hydrophilic PGAMA block. Furthermore, the biomolecular binding of SPCL‐PGAMA with Concanavalin A (Con A) was studied by means of UV‐vis, fluorescence spectroscopy, and DLS, which demonstrated that these SPCL‐PGAMA copolymers had specific recognition with Con A. Consequently, this will not only provide biomimetic star‐shaped SPCL‐PGAMA block copolymers for targeted drug delivery, but also improve the compatibility and drug release properties of PCL‐based biomaterials for hydrophilic peptide drugs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 817–829, 2008 相似文献