全文获取类型
收费全文 | 1206篇 |
免费 | 44篇 |
国内免费 | 6篇 |
专业分类
化学 | 1027篇 |
晶体学 | 11篇 |
力学 | 19篇 |
数学 | 49篇 |
物理学 | 150篇 |
出版年
2023年 | 3篇 |
2021年 | 15篇 |
2020年 | 21篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 24篇 |
2013年 | 44篇 |
2012年 | 67篇 |
2011年 | 83篇 |
2010年 | 38篇 |
2009年 | 48篇 |
2008年 | 65篇 |
2007年 | 64篇 |
2006年 | 69篇 |
2005年 | 80篇 |
2004年 | 64篇 |
2003年 | 61篇 |
2002年 | 57篇 |
2001年 | 25篇 |
2000年 | 33篇 |
1999年 | 17篇 |
1998年 | 20篇 |
1997年 | 20篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 9篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 27篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 6篇 |
排序方式: 共有1256条查询结果,搜索用时 15 毫秒
11.
Poly(N-isopropylacrylamide) (PNIPAM) has a low critical solution temperature (LCST) at 32°C in water and the hydrophilicity changes through the LCST. The microspheres whose surface was composed of PNIPAM exhibited phase transition behavior around 32°C. Therefore, the interactions between PNIPAM micropheres and granulocytes depended on the temperature. That is, the oxygen consumption and active oxygen production by cells in contact with PNIPAM-containing microspheres and adhesion of the microspheres to the cell surface were more enhanced above the LCST of PNIPAM than below it, whereas no significant temperature dependence of cell–microspheres interaction was observed in nonthermosensitive microsphere systems. It was suggested that the function of cells could be controlled with temperature using the temperature-sensitive microspheres. 相似文献
12.
Bromomagnesium ureide-carbon dioxide adducts, models of the carboxylated biotin complex, undergo caboxylation of a variety of carbonyl compounds in good yield. 相似文献
13.
Chisuzu Tokoh Keiji Takabe Minoru Fujita Hiroshi Saiki 《Cellulose (London, England)》1998,5(4):249-261
Acetobacter xylinum was cultured in Hestrin-Schramm medium (control medium) and Hestrin-Schramm medium containing acetyl glucomannan (mannan medium). Loose bundles of the cellulose microfibrils are formed in the mannan medium in contrast to the normal ribbons being produced in the control medium. Rapid-freeze and substitution method followed by metal-shadowing revealed the droplet-like structures around the microfibril synthesized in the mannan medium. The cellulose synthesized in the mannan medium was stained heavily by the periodic acid-thiocarbohydrazide-silver proteinate (PATAg) method, while the cellulose synthesized in the control medium was not stained. X-ray diffractometry and FT-IR spectroscopy indicated that the addition of mannan induced a change in the crystal structure from the algal-bacterial type to the cotton-ramie type. Thus the presence of acetyl glucomannan in the medium prevents the assembly of cellulose microfibrils and changes the crystal structure of cellulose. 相似文献
14.
A simple relationship is derived which expresses the change in oscillation frequency of a quartz crystal in contact with a fluid in terms of material parameters of the fluid and the quartz. The relationship is Δf = ?f0(ηL?L/πμQ?Q), where f0 is the oscillation frequency of the free (dry) crystal, ηL and ?L are the absolute viscosity and density of the liquid, respectively, and μQ and ?Q are the elastic modulus and density of the quartz. This relation is obtained from a simple physical model which couples the shear wave in the quartz to a damped shear wave in the fluid. Quantitative comparisons with two test cases, aqueous solutions of glucose and ethanol at various concentrations, demonstrate the accuracy of this model. 相似文献
15.
Oguchi T Tozuka Y Hanawa T Mizutani M Sasaki N Limmatvapirat S Yamamoto K 《Chemical & pharmaceutical bulletin》2002,50(7):887-891
The solid-state complexation between cholic acid (CA) and either methyl p-hydroxybenzoate (MPB) or ibuprofen (IBP) was investigated. Powder X-ray diffractometry, IR spectroscopy and thermal analysis suggested the complex formation between CA and MPB as well as between CA and IBP by co-grinding method. The stoichiometry of CA-MPB was 1 : 1 while that of CA-IBP was 2 : 1, reflecting the effect of guest size on complex formation. The guest compounds were assumed to be included in the channel of complexes formed by hydrogen bonds among CA molecules. 相似文献
16.
Thermolysis of 2,5-diphenyl-1,4-dithiin-1-oxide afforded 2-formyl-2,4-diphenyl-1,3-dithiole, which was obtained also in photolysis along with another rearranged product, 2-benzoyl-4-phenyl-1,3-dithiole. 相似文献
17.
A microanalytical method for the determination of traces of natural brassinosteroids as their dansylaminophenylboronates by liquid chromatography with fluorimetric detection is described. The boronates are easily prepared by the reaction of brassinosteroids with dansylaminophenylboronic acid (DABA), which was newly synthesized as a precolumn fluorogenic reagent for brassinosteroids. The potential of the method is demonstrated by the separation of a standard brassinosteroid mixture and the analysis of a biologically active fraction sample obtained from an extract of Zea mays L. pollen. The detection limit of the DABA derivative was found to be 25 pg for brassinolide, which is superior to that of the phenanthreneboronate derivative. 相似文献
18.
Kajihara M Sugie T Sano A Fujioka K Urabe Y Tanihara M Imanishi Y 《Chemical & pharmaceutical bulletin》2003,51(1):11-14
Silicone has been utilized as a carrier material for sustained release system of lipophilic drugs. Extensive studies revealed that drug release rate is influenced by factors such as physicochemical properties of the drug and additives.(1-5)) When a lipophilic drug is highly potent at low concentrations, the drug release rate should be strictly controlled so as to avoid side effects. In this study, using vitamin D(3) (VD(3)) as an example of such drugs, we investigated novel method to suppress initial burst and to modify drug release rate from silicone matrix. As a result, it was found that (a). addition of human serum albumin (HSA) suppressed initial burst and enhanced release rate in the later stage, resulting constant release of VD(3), (b). covering a matrix formulation with a membrane of low diffusivity (core-rod formulation) suppressed initial burst and released drug in a constant rate, and (3) using materials for which the drug has high affinity as dissolution solvent (reservoir formulation), the drug release rate was reduced. 相似文献
19.
The pressure effect on the decay rate of chemically induced dynamic electron spin polarization (CIDEP) was investigated on several free-radical intermediates in photolysis, and the spin-lattice relaxation times for these radicals were estimated from the decay rates of CIDEP signals at various pressures. The spin-lattice relaxation rates were retarded by increasing external pressure. From the pressure dependence of the spin-lattice relaxation rates the activation volume was estimated. The activation volumes of these radicals divide into two groups; ≈30 cm3 mol−1 for negative ions and ≈10 cm3 mol−1 for neutral radicals. 相似文献
20.
Chisuzu Tokoh Keiji Takabe Junji Sugiyama Minoru Fujita 《Cellulose (London, England)》2002,9(3-4):351-360
Acetobacter
xylinum was cultured in Schramm–Hestrin medium containing pectin (pectin medium), xylan (xylan medium), or glucomannan (mannan medium). X-ray diffractometry revealed that xylan and glucomannan affected the size of the cellulose crystals and their d-spacing values. Solid-state cross polarization magic angle spinning carbon-13 nuclear magnetic resonance spectroscopy indicated that the ratio of cellulose I was reduced by the addition of polysaccharides. These effects were more remarkable on the cellulose in the mannan medium than that in the xylan medium, and were scarcely observed in the pectin medium. Electron diffraction analysis revealed that these effects on hemicelluloses along cellulose microfibrils are continuous in the mannan medium and discontinuous in the xylan medium. These findings suggest that the uronic acid in the polysaccharides prevents interactions with cellulose leading to alterations of the structure of the cellulose crystal. 相似文献