全文获取类型
收费全文 | 17120篇 |
免费 | 3261篇 |
国内免费 | 4099篇 |
专业分类
化学 | 13047篇 |
晶体学 | 459篇 |
力学 | 1041篇 |
综合类 | 349篇 |
数学 | 2193篇 |
物理学 | 7391篇 |
出版年
2024年 | 64篇 |
2023年 | 294篇 |
2022年 | 665篇 |
2021年 | 763篇 |
2020年 | 752篇 |
2019年 | 776篇 |
2018年 | 683篇 |
2017年 | 777篇 |
2016年 | 836篇 |
2015年 | 944篇 |
2014年 | 1172篇 |
2013年 | 1485篇 |
2012年 | 1551篇 |
2011年 | 1590篇 |
2010年 | 1334篇 |
2009年 | 1312篇 |
2008年 | 1435篇 |
2007年 | 1287篇 |
2006年 | 1158篇 |
2005年 | 1042篇 |
2004年 | 763篇 |
2003年 | 543篇 |
2002年 | 550篇 |
2001年 | 543篇 |
2000年 | 429篇 |
1999年 | 299篇 |
1998年 | 232篇 |
1997年 | 175篇 |
1996年 | 151篇 |
1995年 | 129篇 |
1994年 | 108篇 |
1993年 | 103篇 |
1992年 | 84篇 |
1991年 | 78篇 |
1990年 | 62篇 |
1989年 | 71篇 |
1988年 | 45篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 28篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 19篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1965年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Polyvinyl alcohol (PVA)-capped CdSe nanoparticles were successfully prepared by a one-step solution growth technique at room temperature and ambient pressure. X-ray diffraction, transmission electron microscopy, infrared spectra, and X-ray photoelectron spectra were used to characterize the final product. The as-prepared CdSe nanocrystals were well dispersed and uniform in shape and the diameter of the particles was confined within 8 nm. Ultraviolet-visible absorption spectra were used to study the confined growth process of PVA-capped CdSe nanoparticles. Photoluminescence measurement showed the near band-edge luminescence of the final product. 相似文献
103.
IntroductionMethaneandcarbondioxidearetWomaincompositionsforthegreenhouseeffectandtheworldglobewanningll].ItisbeneficialtoourlivingenviroIUnenttocontrolthereleaseofthesetwogases.Theconversionofmethanetothecommonfeedstocksynthesisgas(carbonmonoxideandhydro… 相似文献
104.
Mu Jie YANG Kuan LIU 《中国化学快报》2006,17(10):1381-1384
Since the early works of A. J. Heeger, A G. MacDiarmid and Hideki Shirakawa on semiconducting polymers, π-conjugated oligomers and polymers have been actively investigated for a variety of optoelectronic applications, such as field effect transitors (FET… 相似文献
105.
The intermolecular potential function of Smith–Thakkar type for C60 has been proposed, and its expression is as followsThe unit of u(r) is J/mol, r is the distance between two C60 molecules center and the unit is nm. Some properties of C60 in the gas and crystal have been studied using the interaction potential of Smith–Thakkar type, such as stability of C60 crystals, virial coefficient and lattice dynamics. 相似文献
106.
Paul N Nashine VC Hoops G Zhang P Zhou J Bergstrom DE Davisson VJ 《Chemistry & biology》2003,10(9):815-825
The development of novel artificial nucleobases and detailed X-ray crystal structures for primer/template/DNA polymerase complexes provide opportunities to assess DNA-protein interactions that dictate specificity. Recent results have shown that base pair shape recognition in the context of DNA polymerase must be considered a significant component. The isosteric azole carboxamide nucleobases (compounds 1-5; ) differ only in the number and placement of nitrogen atoms within a common shape and therefore present unique electronic distributions that are shown to dictate the selectivity of template-directed nucleotide incorporation by DNA polymerases. The results demonstrate how nucleoside triphosphate substrate selection by DNA polymerase is a complex phenomenon involving electrostatic interactions in addition to hydrogen bonding and shape recognition. These azole nucleobase analogs offer unique molecular tools for probing nonbonded interactions dictating substrate selection and fidelity of DNA polymerases. 相似文献
107.
108.
The enzymatic nitration of phenol and m-cresol catalyzed by horseradish peroxidase was studied in the presence of H2O2 and NaNO2. The results showed that the nitration products of phenol were 2-nitro and 4-nitrophenols. There was also a small amount of by-products of hydroquinone and catechol. The influences of various reaction parameters, including pH, organic solvent type, and concentrations of NaNO2 and H2O2, on the nitration products were investigated. The yields of 4-nitrophenol and 2-nitrophenol were 14% and 12%, respectively. The nitration products of m-cresol were 4-nitro-m-cresol and 6-nitro-m-cresol, and the yields of 4-nitro-m-cresol and 6-nitro-m-cresol were 19% and 30%, respectively. 相似文献
109.
采用两种分子场分析方法即比较分子场分析法(CoMFA)和比较分子相似因子分析法(CoMSIA)进行了37个褪黑激素受体拮抗剂的构效关系研究.计算结果表明,两种方法得到的构效关系模型都具有较好的预测能力.在计算中,还考察了不同格点距离和电荷计算方法对构效关系模型的影响.通过分析分子场等值面图在空间的分布,可以观察到叠合分子周围分子场特征对化合物活性的影响,为设计新的褪黑激素拮抗剂提供了一些理论依据. 相似文献
110.
Reactions in the CsCl? TiCl3? Ti system afford CsTiCl3 (CsNiCl3 type, a = 7.3086(7) Å, c = 6.0670(8) Å) and the new phase CsTi2Cl7, the structure of which was determined by single crystal X-ray diffraction means (P2/c, Z = 2, a = 7.0076(4) Å, b = 6.2256(4) Å, c = 12.000(2) Å, β = 92.175(6)°, R/Rw = 0.026/0.035 for 1403 reflections, 2Θ ≤ 60°, MoKα). The structure can be generated by condensation of TiCl6 groups first through cis edges to form TiCl2Cl4/2 ribbons and then by interconnection of these with one chlorine per titanium to give layers, viz., [Ti(Cl)Cl4/2Cl1/2]?. The remaining, singly bonded chlorine projects into the interlayer region and has a Ti? Cl distance 0.208 Å less than the average for the five, 2.466 Å, reflecting significant pi bonding of the chlorine to titanium. Possible interaction of the d orbitals on adjacent titanium(III) atoms is also considered. 相似文献