全文获取类型
收费全文 | 940篇 |
免费 | 12篇 |
国内免费 | 4篇 |
专业分类
化学 | 708篇 |
晶体学 | 26篇 |
力学 | 5篇 |
数学 | 63篇 |
物理学 | 154篇 |
出版年
2023年 | 4篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2016年 | 6篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 29篇 |
2012年 | 28篇 |
2011年 | 40篇 |
2010年 | 19篇 |
2009年 | 20篇 |
2008年 | 45篇 |
2007年 | 62篇 |
2006年 | 57篇 |
2005年 | 42篇 |
2004年 | 48篇 |
2003年 | 39篇 |
2002年 | 38篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 15篇 |
1994年 | 25篇 |
1993年 | 18篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1983年 | 7篇 |
1982年 | 22篇 |
1981年 | 15篇 |
1980年 | 27篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 8篇 |
1971年 | 4篇 |
1970年 | 5篇 |
排序方式: 共有956条查询结果,搜索用时 19 毫秒
71.
Unidirectional crystallization of charged colloidal silica due to the diffusion of a base 总被引:1,自引:0,他引:1
Murai M Yamada H Yamanaka J Onda S Yonese M Ito K Sawada T Uchida F Ohki Y 《Langmuir : the ACS journal of surfaces and colloids》2007,23(14):7510-7517
Dilute aqueous dispersions of charged colloidal silica (particle volume fraction = approximately 0.03-0.04, particle diameter = 110 nm) exhibit unidirectional crystal growth due to the diffusion of a weak base, pyridine (Py). Similar diffusion-crystallization is enabled by a salt of a weak acid and a strong base, sodium hydrogen carbonate (NaHCO3). The resulting crystals consist of columnar (or cubic) crystal grains with a maximum height of a few centimeters and a maximum width of 1 cm. The crystal growth process is attributed to a combination of (i) the diffusion of Py or NaHCO3 accompanied by a charging reaction of the silica particles and (ii) the charge-induced crystallization of the silica colloids. Theoretical growth curves based on the reaction-diffusion model for the case of Py were in good agreement with the observed curves. We also report the immobilization of the resulting large crystals by using a polymer hydrogel matrix. 相似文献
72.
The molecular assembly of thiacalix[6]arene was formed by π-π stacking and π-DMF interactions between thiacalix[6]arene and adjoining thiacalix[6]arene and between thiacalix[6]arene and DMF, respectively. The X-ray crystal analysis also revealed that hydroxyl groups of thiacalix[6]arene adopted novel two sets of hydrogen bond with two DMF and intramolecular hydrogen bond between phenolic units, which cause to make 1,2,3-alternate configuration structure of thiacalix[6]arene. 相似文献
73.
Mibu N Yokomizo K Kashige N Miake F Miyata T Uyeda M Sumoto K 《Chemical & pharmaceutical bulletin》2007,55(1):111-114
N-Monoacyl-2,6-diaminopyridines (2a-c) and N,N'-diacyl-2,6-diaminopyridines (3a-c) were synthesized from 2,6-diaminopyridine by acylation with the corresponding acyl halide or by dehydration with the corresponding carboxylic acid using 1,3-dicyclohexylcarbodiimide (DCC). The antiviral activities of N-monoacyl- and N,N'-diacyl-2,6-diaminopyridines (2a-c and 3a-c) were estimated using plaque reduction assay with HSV-1. All N-monoacyl derivatives (2a-c) showed significant anti-herpes simplex virus (HSV)-1 activity (EC(50) = 15.3-18.5 microg/ml). The CC(50) values of 2a-c measured using Vero cells ranged at 37.5-50.0 microg/ml. These compounds showed no significant antibacterial activities with Escherichia coli or Staphylococcus aureus even at a concentration of 1 mg/ml. The N,N'-diacyl derivatives (3a-c) showed no significant anti-HSV-1 activity. 相似文献
74.
Miyuki Narita Fumio Hamada Mayumi Sato Iwao Suzuki Tetsuo Osa 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(4):421-430
Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modified -cyclodextrins (-1, -2, -3, and -4, respectively) have been synthesized as a sensing molecule for organic guests including terpenoids and bile acids. These host compounds show a pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I0, where I and I0 are fluorescence intensities in the presence and absence of a guest and I is I0- I, was used as a parameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeoxycholic acid, and ursodeoxycholic acid. The behaviors of the appended moieties of these hosts when host–guest complexation occurs are studied by induced circular dichroism (ICD) spectra and fluorescence spectral change on accommodation of a guest. The ICD pattern of these hosts alone or on accommodation of a guest is very similar, indicating that the behavior of the appended moieties are very similar. The guest-induced variations in the fluorescence or ICD intensity suggest that the appended moieties act as a hydrophobic cap that enables the cyclodextrin to form 1 : 1 host–guest complexes. 相似文献
75.
Abstract— The photoreaction cycle of 13- cis -bacteriorhodopsin (13- cis -bR) was investigated by low temperature spectrophotometry using two different preparations; 13- cis -bR constituted from bacterioopsin and 13- cis -retinal, and dark-adapted bacteriorhodopsin (bRD ), which is an equi-molar mixture of 13- cis -bR and trans -bR.
By irradiation with 500 nm light at — 190°C, 13- cis -bR was converted to its batho-product, batho-13- cis -bR (batho-bR13 ), which is different from batho-product from trans -bR, batho-bRt . On warming batho-bR13 to -5°C in the dark, it completely changed to trans -bR. We estimated the composition of 13- cis -bR and trans -bR in the warmed sample spectrophotometrically and then the absorption spectrum of batho-bR13 was calculated. The absorption maximum lies at 608 nm, 1250 cm−1 longer than that of 13- cis -bR; the molar extinction coefficient (ε) is about 74000 M −1 cm−1 , larger than that of 13- cis -bR (52000 M −1 cm−1 ).
On the warming the sample containing batho-bR13 formed by irradiating 13- cis -bR or bRD at — 190°C, we could not detect other intermediates such as the lumi- or meta-intermediates seen in trans-bR system. 相似文献
By irradiation with 500 nm light at — 190°C, 13- cis -bR was converted to its batho-product, batho-13- cis -bR (batho-bR
On the warming the sample containing batho-bR
76.
Masanori Morishita Fumio Kawamura Minoru Kawahara Masashi Yoshimura Yusuke Mori Takatomo Sasaki 《Journal of Crystal Growth》2004,270(3-4):402-408
The dependency of LPE growth rate and dislocation density on supersaturation in the growth of GaN single crystals in the Na flux was investigated. When the growth rate was low during the growth of GaN at a small value of supersaturation, the dislocation density was much lower compared with that of a substrate grown by the Metal Organic Chemical Vapor Deposition method (MOCVD). In contrast, when the growth rate of GaN was high at a large value of supersaturation, the crystal was hopper including a large number of dislocations. The relationship between the growth conditions and the crystal color in GaN single crystals grown in Na flux was also investigated. When at 800 °C the nitrogen concentration in Na–Ga melt was low, the grown crystals were always tinted black. When the nitrogen concentration at 850 °C was high, transparent crystals could be grown. 相似文献
77.
Fumio Hamada G. William Orr Hongming Zhang Jerry L. Atwood 《Journal of chemical crystallography》1993,23(8):681-684
The title compound has been prepared by the addition of bromocalix[4]arene methyl ether to CuCN in N-methylpyrrolidone. The crystals belong to the monoclinic space groupP21/n witha=13.591(3),b=24.778(5),c=11.057(3)Å,=93.58(2)°, andD
c=1.09 g cm–3 forZ=4. Refinement based on 1118 observed reflections led to a finalR value of 0.085. The molecule exhibits the partial cone conformation. 相似文献
78.
We will discuss the Gorenstein property of the singularity which is blown down from the minimal section of a ruled surface in terms of the extension class. In the case that the base field has positive characteristic, we find a new example (3.4) of Gorenstein singularity in connection with Theorem B. 相似文献
79.
Kouji Kuramochi Ryo Takeuchi Masaharu Takemura Kengo Sakaguchi Susumu Kobayashi Fumio Sugawara 《Tetrahedron》2006,62(34):8006-8015
Synthesis of plakevulin A and structure-activity relationships of its related compounds against DNA polymerases is described. We have achieved a total synthesis and revised the structure of plakevulin A. Several analogues including untenone A, manzamenone A, and optically active plakevulin A, were prepared and tested with an enzyme inhibition assay for mammalian DNA polymerases. The effect of the methyl ester moiety, and the substituents at the 1- and 4-positions of plakevulin A on DNA polymerase activities are discussed. 相似文献
80.
Curved Ferroelectric Liquid Crystal Matrix Displays Driven by Field-Sequential-Color and Active-Matrix Techniques 总被引:1,自引:0,他引:1
Hideo Fujikake Hiroto Sato Takeshi Murashige Yoshihide Fujisaki Taiichiro Kurita Tadahiro Furukawa Fumio Sato 《Optical Review》2006,13(1):14-19
This paper describes a curved field-sequential-color matrix display using fast-response ferroelectric liquid crystal. Black
matrix and transparent electrode patterns were formed on a thin plastic substrate by a transfer method from a glass substrate.
While a composite film of liquid crystal and micro-polymers of walls and fibers was formed between the flexible substrates
by printing, laminating and curing processes of a solution of monomers and liquid crystal, the mechanical stability was enhanced
by use of multi-functional monomers to form large display panels. The image pixels of the matrix panel were driven by an active
matrix scheme using an external switch transistor array at a frequency of 180 Hz for intermittent three-primary-color backlight
illumination. The flexible A4-paper-sized color display with 24 × 16 pixels and 60 Hz field frequency was demonstrated by
illuminating it with sequential three-primary-color lights from light-emitting diodes of the backlight. Our display system
is useful in various information displays because of its freedom of setting and location. 相似文献