全文获取类型
收费全文 | 116833篇 |
免费 | 8296篇 |
国内免费 | 12484篇 |
专业分类
化学 | 70737篇 |
晶体学 | 1152篇 |
力学 | 2392篇 |
综合类 | 841篇 |
数学 | 12690篇 |
物理学 | 19170篇 |
无线电 | 30631篇 |
出版年
2024年 | 335篇 |
2023年 | 1416篇 |
2022年 | 2553篇 |
2021年 | 2515篇 |
2020年 | 2927篇 |
2019年 | 2859篇 |
2018年 | 2664篇 |
2017年 | 3816篇 |
2016年 | 3829篇 |
2015年 | 3671篇 |
2014年 | 4643篇 |
2013年 | 7992篇 |
2012年 | 7878篇 |
2011年 | 6965篇 |
2010年 | 5573篇 |
2009年 | 7157篇 |
2008年 | 7502篇 |
2007年 | 8040篇 |
2006年 | 7441篇 |
2005年 | 6336篇 |
2004年 | 5767篇 |
2003年 | 4722篇 |
2002年 | 5672篇 |
2001年 | 3398篇 |
2000年 | 3057篇 |
1999年 | 2788篇 |
1998年 | 2473篇 |
1997年 | 1975篇 |
1996年 | 1687篇 |
1995年 | 1614篇 |
1994年 | 1382篇 |
1993年 | 1119篇 |
1992年 | 1029篇 |
1991年 | 722篇 |
1990年 | 580篇 |
1989年 | 536篇 |
1988年 | 386篇 |
1987年 | 301篇 |
1986年 | 282篇 |
1985年 | 226篇 |
1984年 | 241篇 |
1983年 | 143篇 |
1982年 | 211篇 |
1981年 | 175篇 |
1980年 | 195篇 |
1979年 | 183篇 |
1978年 | 169篇 |
1977年 | 122篇 |
1976年 | 109篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
By the measurements of the solvent and temperature effects of the fluorescence emission spectra and lifetime of N-phenyl phenothiazine (PHZ) and N-(2-pyridine) phenothiazine (PYZ),the existence of strongly twisted intramolecular charge transfer (TICT) state in PYZ emission spectra is proved.The exciplex formed by PHZ, PYZ and dimethyl terephthalate (DMTP) is investigated, and moreover, the transient absorption spectra of positive and negative ions as the results of the dissociation of the exciplex in the polar solvents is observed through the flash photolysis. 相似文献
992.
Journal of Electronic Materials - Low pressure chemical vapor deposition (LPCVD) of tungsten (W) by SiH4 reduction of WF6 on Si(100) surfaces was studied in a single-wafer, cold-wall reactor over a... 相似文献
993.
994.
H. Ebe T. Okamoto H. Nishino T. Saito Y. Nishijima M. Uchikoshi M. Nagashima H. Wada 《Journal of Electronic Materials》1996,25(8):1358-1361
CdTe epilayers were grown directly on (100), (211), and (111) silicon substrates by metalorganic chemical vapor deposition
(MOCVD). The crystallinity and the growth orientation of the CdTe film were dependent on the surface treatment of the Si substrate.
The surface treatment consisted of exposure of the Si surface to diethyltelluride (DETe) at temperatures over 600°C prior
to CdTe growth. Direct growth of CdTe on (100) Si produced polycrystalline films whereas (lll)B single crystals grew when
Si was exposed to DETe prior to CdTe growth. On (211) Si, single crystal films with (133)A orientation was obtained when grown
directly; but produced films with (211)A orientation when the Si surface was exposed to DETe. On the other hand, only (lll)A
CdTe films were possible on (111) Si, both with and without Te source exposure, although twinning was increased after exposure.
The results indicate that the exposure to a Te-source changes the initial growth stage significantly, except for the growth
on (111) Si. We propose a model in which a Te atom replaces a Si atom that is bound to two Si atoms. 相似文献
995.
996.
997.
重金属Pb2+对玉米苗生长的影响 总被引:11,自引:1,他引:10
以水栽培的玉米幼苗为材料,用不同浓度的醋酸铅溶液处理后,分别在第10天、第20天、第30天对玉米苗的根、茎、叶分别进行Pb^2+含量测定。分析结果:Pb^2+在玉米体内的分布表现为根〉叶〉茎;玉米中的叶绿素含量均降低;随着Pb^2+浓度的增大,玉米细胞的膜透性表现根〉叶〉茎依次升高;Pb^2+对玉米的伤害率的大小表现为根〉叶〉茎。该实验为进一步研究农作物对重金属Pb^2+的耐性和重金属Pb^2+在农作物体内的分布提供了可参考的数据。 相似文献
998.
Various phase behavior of blends of poly(vinyl ether)s with homologous acrylic polymers (polymethacrylates or polyacrylates) were examined using differential scanning calorimetry, optical microscopy (OM), and Fourier‐transformed infrared spectroscopy. Effects of varying the pendant groups of either of constituent polymers on the phase behavior of the blends were analyzed. A series of interestingly different phase behavior in the blends has been revealed in that as the pendant group in the acrylic polymer series gets longer, polymethacrylate/poly(vinyl methyl ether) (PVME) blends exhibit immiscibility, upper critical solution temperature (UCST), and miscibility, respectively. This study found that the true phase behavior of poly(propyl methacrylate)/PVME [and poly(isopropyl methacrylate)/PVME)] blend systems, though immiscible at ambient, actually displayed a rare UCST upon heating to higher temperatures. Similarly, as the methyl pendant group in PVE is lengthened to ethyl (i.e., PVME replaced by PVEE), phase behavior of its blends with series of polymethacrylates or polyacrylates changes correspondingly. Analyses and quantitative comparisons on four series of blends of PVE/acrylic polymer were performed to thoroughly understand the effects of pendant groups in either polyethers (PVE's) or acrylic polymers on the phase behavior of the blends of these two constituents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1521–1534, 2007 相似文献
999.
Katsuhiro Inomata Chieko Fukuda Kuniyoshi Hori Hideki Sugimoto Eiji Nakanishi 《Journal of Polymer Science.Polymer Physics》2007,45(2):129-137
The phase behavior and crystallization of graft copolymers consisting of poly(n‐hexyl methacrylate) (PHMA) as an amorphous main chain and poly(ethylene glycol) (PEG) as crystallizable side chains (HMAx with 15 ≤ x ≤ 73, where x represents the weight percentage of PEG) were investigated. Small‐angle X‐ray scattering profiles measured above the melting temperature of PEG suggested that a microdomain structure with segregated PHMA and PEG domains was formed in HMA40 and HMA46. This phase behavior was qualitatively described by a calculated phase diagram based on the mean‐field theory. Because of the segregation of PEG into microdomains, the crystallization temperature of the PEG side chains in HMAx was higher than that in poly(methyl acrylate)‐graft‐poly(ethylene glycol) having a similar value of x, which was considered to be in a disordered state above the melting temperature. In HMAx with x ≤ 40, PEG crystallization was strongly restricted, probably because the PEG microdomains were isolated in the PHMA matrix. As a result, the growth of PEG spherulite was not observed because the PEG crystallization occurred after vitrification of the PHMA segregated domains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 129–137, 2007 相似文献
1000.
Mark E. Greene 《Surface science》2004,559(1):16-28
The ultra-high vacuum scanning tunneling microscope (UHV-STM) was used to investigate the addition of the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical to the Si(1 0 0) surface. Room temperature studies performed on clean Si(1 0 0)-2 × 1 confirm the proposed binding of the unpaired valence electron associated with the singly occupied molecular orbital (SOMO) of the molecule with a Si dangling bond. A strong bias dependence in the topography of isolated molecules was observed in the range of −2.0 to +2.5 V. Semiempirical and density functional calculations of TEMPO bound to a three-dimer silicon cluster model yield occupied state density isosurfaces below the highest occupied (HOMO) and unoccupied state densities isosurfaces above the lowest unoccupied molecular orbital (LUMO) which trend in qualitative agreement with the bias dependent STM topography. Furthermore, the placement of TEMPO molecules on dangling bonds was controlled with atomic precision on the monohydride Si(1 0 0) surface via electron stimulated desorption of H, demonstrating the compatibility of nitroxyl free radical binding chemistries with nanopatterning techniques such as feedback controlled lithography. 相似文献