全文获取类型
收费全文 | 13540篇 |
免费 | 581篇 |
国内免费 | 130篇 |
专业分类
化学 | 9743篇 |
晶体学 | 126篇 |
力学 | 580篇 |
综合类 | 3篇 |
数学 | 1644篇 |
物理学 | 2155篇 |
出版年
2023年 | 106篇 |
2022年 | 725篇 |
2021年 | 654篇 |
2020年 | 518篇 |
2019年 | 523篇 |
2018年 | 505篇 |
2017年 | 395篇 |
2016年 | 676篇 |
2015年 | 434篇 |
2014年 | 533篇 |
2013年 | 1240篇 |
2012年 | 840篇 |
2011年 | 894篇 |
2010年 | 586篇 |
2009年 | 497篇 |
2008年 | 613篇 |
2007年 | 579篇 |
2006年 | 479篇 |
2005年 | 368篇 |
2004年 | 368篇 |
2003年 | 315篇 |
2002年 | 319篇 |
2001年 | 141篇 |
2000年 | 137篇 |
1999年 | 106篇 |
1998年 | 81篇 |
1997年 | 80篇 |
1996年 | 96篇 |
1995年 | 78篇 |
1994年 | 88篇 |
1993年 | 75篇 |
1992年 | 82篇 |
1991年 | 76篇 |
1990年 | 80篇 |
1989年 | 84篇 |
1988年 | 79篇 |
1987年 | 61篇 |
1986年 | 63篇 |
1985年 | 80篇 |
1984年 | 65篇 |
1983年 | 49篇 |
1982年 | 58篇 |
1981年 | 56篇 |
1980年 | 50篇 |
1979年 | 43篇 |
1978年 | 44篇 |
1977年 | 33篇 |
1976年 | 31篇 |
1975年 | 25篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
K. Adu-Wusu N. M. Hassan C. A. Nash J. C. Marra 《Journal of Radioanalytical and Nuclear Chemistry》2006,267(2):381-388
Summary The removal of cesium from aqueous waste solution was investigated in a column setup using a relatively coarse SuperLigò644 resin. The bed volume (BV=140) at the onset of breakthrough surpassed the design requirement of 100 BV at 50% breakthrough,
and also corresponds to 99.96% cesium removal. Cesium elution with 0.5M HNO3was satisfactory with a peak BV of 2.5. The elution BV for C/C0=0.01 was 10, which is less than the target of 15 BV. The percent of sorbed cesium eluted was 99.88%. Further, the BV of the
various solutions used for the supporting process steps was sufficient. 相似文献
62.
Abnormal cilia were demonstrated in the lining epithelial cells of three cases of intraspinal endodermal (bronchogenic) cyst. The changes comprised a wide spectrum of ultrastructural abnormalities, including (a). cilia with abnormal axonemal microtubules, (b). swollen cilia, (c). compound cilia with or without excessive ciliary matrix, (d). naked cilia without limiting membrane, and (e). intracytoplasmic cilia and aggregates of microtubules. Of these, compound cilia and swollen cilia were most common. Cilia with dynein arm deficiency were not observed. Ciliary abnormalities found in the present study were very similar to those described in the bronchial epithelium of various diseases. The present findings suggest that the lining epithelium of intraspinal endodermal cyst shares similar ciliogenesis and susceptibility to abnormal ciliary formation as that of the bronchial epithelium. 相似文献
63.
64.
Mohamed JazouliDominique Guianvarc'h Mohamed SoufiaouiPierre Vierling Rachid Benhida 《Tetrahedron letters》2003,44(31):5807-5810
A short route to a series of 2′-deoxy-C-nucleosides featuring substituted nucleobases has been developed. The key step is the formation of the cyclized products following Mukaiyama's type amide coupling and a simple dehydration, starting from readily accessible synthons. The epimerization of the C1′-stereogenic center was avoided under mild and controlled conditions. 相似文献
65.
66.
67.
Mohamed Haouas Amine Harrane Mohamed Belbachir Francis Taulelle 《Journal of Polymer Science.Polymer Physics》2007,45(22):3060-3068
Results of multinuclear MAS NMR spectroscopy are reported for poly (ε‐caprolactone)/maghnite nanocomposite formation, with ε‐caprolactone in situ polymerized in the presence of maghnite, a proton exchanged montmorillonite clay. Exfoliated and intercalated materials with different maghnite loading in the range 3–15 wt % were investigated. 1H NMR evidences Brønsted acid hydroxyl groups in the silicate layers and shows that their broad signal at 7.6 ppm present in the parent clay disappears in the nanocomposite material. 27Al MAS NMR results show that beside the hexacoordinated aluminum signal, two additional peaks corresponding to two different tetrahedral Al sites are present in the clay framework. The NMR signal intensity of only one of them was found to be affected in the nanocomposites compared with the parent maghnite, suggesting that these specific aluminum sites are the reactive ones at the initial stages of the polymerization. However almost no changes occurred in the 29Si NMR spectra, confirming that the polymer grafting, as indicated earlier by atomic force microscopy, took place on the aluminum tetracoordinated sites rather than on the silicon sites. A mechanism of maghnite surface catalyzed polymerization of ε‐caprolactone was proposed, involving Brønsted and Lewis acid sites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3060–3068, 2007 相似文献
68.
An efficient one-step method for the synthesis of fully substituted thiophenes, from thiomorpholides and α-halo ketones, was developed. A mechanism has also been proposed for the course of reaction. 相似文献
69.
Ahmed Jalal Uddin Yutaka Ohkoshi Yasuo Gotoh Masanobu Nagura Tetsuya Hara 《Journal of Polymer Science.Polymer Physics》2003,41(22):2878-2891
The effect of moisture on the mechanical relaxation processes of semiaromatic semicrystalline polyamides synthesized by a long‐chain aliphatic diamine and terephthalic acid was investigated by dynamic viscoelastic analysis (DVA) and differential scanning calorimetry (DSC). Moreover, the implication of moisture with the amorphous and crystalline domains was also examined by temperature‐dependent wide‐angle X‐ray diffraction and Fourier transform infrared spectra. The characteristics of the relaxations such as α, β, γ, and the pronounced peak shoulder appeared at 25–100 °C in DVA tan δ curves were found to be strongly susceptible to the presence of moisture. With moisture evaporation, the peak shoulder of 25–100 °C and the β‐relaxation disappeared. The former is anticipated to originate from to the side group motion of hydrogen‐bonded water, whereas the later one is from the motions of the amide–water complex units. With the disappearance of the β‐relaxation, the γ‐relaxation appeared simultaneously in much lower temperatures and ultimately coupled with the δ‐relaxation. The γ‐relaxation is attributed to be associated with the molecular motion of the amide group and δ‐relaxation with for the motion of the methylene units. The existence of two types of water was identified in the polymer, namely, tightly bound and loosely bound. The tightly bound water is believed to be directly connected by hydrogen bonding with the strong polar groups and the loosely bound water weakly links with those connected water making hydrogen bridges. The moisture acts as a plasticizer in the polymer matrix, which causes quite a large depression in its glass transition temperature (Tg). WAXD and FTIR studies corroborated the existence of water solely in amorphous regions, i.e., no rapport of water with the crystalline parts. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2878–2891, 2003 相似文献
70.
We investigate some relations concerning the first and the second Beltrami operators corresponding to the fundamental forms I, II, III of a surface in the Euclidean space E3 and we study surfaces which are of finite type in the sense of B.-Y. Chen with respect to the fundamental forms II and III. 相似文献