全文获取类型
收费全文 | 7189篇 |
免费 | 1112篇 |
国内免费 | 801篇 |
专业分类
化学 | 5509篇 |
晶体学 | 117篇 |
力学 | 378篇 |
综合类 | 44篇 |
数学 | 708篇 |
物理学 | 2346篇 |
出版年
2024年 | 19篇 |
2023年 | 137篇 |
2022年 | 217篇 |
2021年 | 246篇 |
2020年 | 341篇 |
2019年 | 304篇 |
2018年 | 276篇 |
2017年 | 289篇 |
2016年 | 360篇 |
2015年 | 393篇 |
2014年 | 368篇 |
2013年 | 557篇 |
2012年 | 601篇 |
2011年 | 602篇 |
2010年 | 445篇 |
2009年 | 403篇 |
2008年 | 449篇 |
2007年 | 393篇 |
2006年 | 397篇 |
2005年 | 360篇 |
2004年 | 292篇 |
2003年 | 225篇 |
2002年 | 226篇 |
2001年 | 123篇 |
2000年 | 126篇 |
1999年 | 117篇 |
1998年 | 51篇 |
1997年 | 64篇 |
1996年 | 64篇 |
1995年 | 42篇 |
1994年 | 25篇 |
1993年 | 37篇 |
1992年 | 37篇 |
1991年 | 23篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 35篇 |
1986年 | 26篇 |
1985年 | 28篇 |
1984年 | 39篇 |
1983年 | 17篇 |
1982年 | 37篇 |
1981年 | 32篇 |
1980年 | 40篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1976年 | 19篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 17篇 |
排序方式: 共有9102条查询结果,搜索用时 78 毫秒
51.
The structure of senecicannabine(), a new mcrocyclic pyrrolizidine alkaloid isolated from , has been established by chemical study and X-ray analysis. 相似文献
52.
硅杂环丁烷在有机硅化学中是一类非常重要的小分子环系化合物。由于硅杂环丁烷和环丁烷的环张力相似,因而显示出较高的反应活性。例如能与某些试剂作用,生成开环产物;在光解或热解条件下,产生具有Si=C结构的高活性中间体,可用以合成多种有机硅化合物。 相似文献
53.
54.
55.
表面包覆改性对纳米CeO2分散性的影响 总被引:1,自引:0,他引:1
了改善纳米CeO2在Zn-Al类共晶合金中的分散性,采用超声液相包覆法对纳米CeO2进行表面活性剂表面包覆改性,并用AES测定了包覆层的厚度,用TEM研究了CeO2的团聚状况,用TGA分析了有机物包覆层的炭化温度范围,最后用FE-SEM观察了CeO2在复合材料中的分散情况。结果表明,包覆在纳米CeO2表面的厚度约为20 nm的表面活性剂层提高了微粒的分散性,而且该包覆层在495℃时已经炭化。热力学计算的结果也表明,炭化层能与氧化膜反应,该反应提高了CeO2与基体间的润湿性,并使其均匀分布在基体合金中。 相似文献
56.
Hideki Nishimori Masahiro Tatsumisago Tsutomu Minami 《Journal of Sol-Gel Science and Technology》1997,9(1):25-31
Monodispersed silica particles up to ca. 1.2 μm in diameter were prepared by hydrolysis of tetraethoxysilane in the presence
of sodium dodecyl sulfate (SDS). The particle size was increased with an increase of SDS added. The geometrical standard deviation
of the particles was decreased with an increase of SDS. In the earlier reaction stage, double spherical particles by the coalescence
of the particles were frequently observed when large amounts of SDS were added. Particle size was gradually increased after
the coalescence occurred and spherical particles were finally obtained. The results of Nielsen’s chronomal analysis suggest
that the polynuclear layer growth took place after the coalescence of the particles in the presence of larger amount of SDS. 相似文献
57.
A series of methacrylamide-based C16 monolithic columns were prepared and characterized to determine how their porous structural properties and chromatographic behavior are affected by the percentages of functional monomer, base monomer, and cross-linker in the polymerization solution. Baseline separation of 6 neutral compounds can be readily obtained in an optimized column. Furthermore, the effects of organic additive in the mobile phase, operating voltages, and temperature on retention behaviors and separation efficiencies were also studied. The separation mechanism is also discussed. High column efficiency and good reproducibility indicate that the monolithic columns hold considerable promise. 相似文献
58.
Huiping Chen Duane R. Bujalski Kai Su 《Journal of the American Society for Mass Spectrometry》2005,16(4):524-534
This paper describes the characterization of low molecular weight components of four materials using electrospray ionization Fourier transform mass spectrometry (ESI-FTMS). The materials in the current study are [(ViMe2SiO1/2)x(PhSiO3/2)y(SiO4/2)z] (MTQ), [(ViMe2SiO1/2)x(SiO4/2)y] (MQ), and [(SiO4/2)x(HO1/2)y(tBuO1/2)z] (Q) silsesquioxanes. Accurate mass measurements coupled with knowledge of resin chemistry afforded siloxane composition determination that was used to propose specific structures for the oligomers. Branched or linear (TnQmMn+2m+2), and monocyclic (TnQmMn+2m) structures are predominant structures for the low molecular weight species in MTQ. For MQ and Q, more condensed structures, such as partially opened cage structures (QmM2m?6 and QmM2m?8), were identified. The differences between MQ, Q, and MTQ are likely attributed to differences in intrinsic structure and reactivity of T and Q building blocks. The structural information obtained for these oligomeric species will ultimately provide a better understanding of new resin materials and their associated physical properties. 相似文献
59.
60.
Atsunori Matsuda Tatsuo Matoda Yoshinori Kotani Toshihiro Kogure Masahiro Tatsumisago Tsutomu Minami 《Journal of Sol-Gel Science and Technology》2003,26(1-3):517-521
Anatase nanocrystals were precipitated mainly at the surface of the silica-titania gel films with hot water treatment, whereas the addition of poly(ethylene glycol) (PEG) in the films led to the dispersion of anatase nanocrystals in the whole of the films after the treatment. Both films with and without PEG showed high photocatalytic activities for acetaldehyde, NO
x
and stearic acid in the gas-solid system, and for methylene blue and potassium iodide in the liquid-solid system. The addition of PEG improved the photocatalytic activities of the resultant films due to the smaller anatase crystallites and the porous film structure. The residual silica under-layer of the superficially anatase-precipitated films is expected to act as a protective one for an organic polymer substrate against the photocatalytic degradation. 相似文献