全文获取类型
收费全文 | 1535篇 |
免费 | 152篇 |
国内免费 | 102篇 |
专业分类
电工技术 | 18篇 |
综合类 | 88篇 |
化学工业 | 764篇 |
金属工艺 | 50篇 |
机械仪表 | 15篇 |
建筑科学 | 9篇 |
矿业工程 | 12篇 |
能源动力 | 28篇 |
轻工业 | 116篇 |
石油天然气 | 52篇 |
武器工业 | 9篇 |
无线电 | 70篇 |
一般工业技术 | 512篇 |
冶金工业 | 17篇 |
原子能技术 | 19篇 |
自动化技术 | 10篇 |
出版年
2024年 | 9篇 |
2023年 | 46篇 |
2022年 | 45篇 |
2021年 | 53篇 |
2020年 | 65篇 |
2019年 | 70篇 |
2018年 | 75篇 |
2017年 | 67篇 |
2016年 | 91篇 |
2015年 | 96篇 |
2014年 | 117篇 |
2013年 | 133篇 |
2012年 | 151篇 |
2011年 | 142篇 |
2010年 | 99篇 |
2009年 | 102篇 |
2008年 | 80篇 |
2007年 | 93篇 |
2006年 | 61篇 |
2005年 | 42篇 |
2004年 | 38篇 |
2003年 | 19篇 |
2002年 | 21篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 14篇 |
1996年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有1789条查询结果,搜索用时 15 毫秒
91.
92.
聚乳酸微球制备工艺的研究 总被引:1,自引:0,他引:1
采用O/W乳化-溶剂挥发法,选择聚氧乙烯山梨醇酐单硬脂酸酯(Tween60)为乳化剂,天然高分子明胶作为共表面活性剂,制备出了形态较好的聚乳酸微球,而且在可确定因素固定下来后,在保证成球质量的基础上,可以分别通过调节Tween60和明胶的用量在一定范围内来控制微球的平均粒径。 相似文献
93.
The morphology and textural characteristics of silica products formed via the hydrolysis and condensation of tetraethyl orthosilicate in increasing diluted dodecylamine solutions have been investigated. The results show that the pH values of the synthesis media increase with the initial additions of water. The formation of silica speeds up as the solution is diluted. As a result, microporous silica microspheres with increasing surface areas, pore volumes, pore and particle sizes are formed by a monomer addition mechanism. Further increases in the amount of water result in the decrease of the concentrations of OH?. Consequently, the formed silica seeds become less active and the diffusion of silica species is accelerated. The monomer addition process thus becomes difficult. The self-nucleation of silica species leads to the formation of large quantities of primary silica nano particles. In order to minimise the internal energy of the reaction system, the nanoparticles aggregate to form micrometre-sized silica microspheres with a relatively loose structure. The synthesised microspheres can be used in the removal of organic pollutants in water. It is shown that the nanoporous silica microspheres formed by the aggregation mechanism have a faster dye adsorption rate and a higher adsorption capacity than those formed by the monomer addition mechanism. 相似文献
94.
Synthesis and in vitro bioactivity of novel mesoporous hollow bioactive glass microspheres 总被引:1,自引:0,他引:1
The remarkable tissue-repairing bioactivity and biocompatibility of bioactive glass make it suitable for a wide range of applications. Here, novel mesoporous hollow bioactive glass microspheres (MHBGMs) with a uniform diameter range of 2-5 µm were prepared by a sol-gel method. Structural characterization indicated that the shell of hollow sphere had a mesopore size range between 2 and 10 nm and a thickness about 500 nm. The in vitro bioactivity test indicated that the novel structure exhibited high in vitro bioactivity. The uniform microspherical morphology and mesoporous hollow structure of MHBGMs, together with their high bioactivity, turn them into a good candidate as an injectable and drug-loading biomaterial for in vivo tissue regeneration and drug control release. 相似文献
95.
96.
In this paper, we fabricated hierarchical self-assembled hollow rose-like flower microspheres (HRFM) and hollow burr-like flower microspheres (HBFM) hydroxyapatite (HAP) using dehydroabietyl phosphate tri-ester (DDPT) as an organic phosphorus source, a regulating agent, and a soft template simultaneously via a one-step solvothermal method. The HBFM and HRFM have been explored for their application in drug delivery, using doxorubicin (DOX) as a drug model. The formation mechanisms of HRFM and HBFM were proposed on the basis of the electrostatic potential diagrams and self-assembled behavior of DDPT organic molecule. After the rosin-based terpene functional groups were incorporated, both HRFM and HBFM exhibited low cytotoxicity against Hela cell, pH-dependent sustained drug release properties, and high drug loading capacity. The drug-loading capacities of HBFM and HRFM were 116.6?mg?g?1 and 148.3?mg?g?1, respectively. Thus, the as-prepared HRFM and HBFM are promising for the applications in drug delivery. 相似文献
97.
《Ceramics International》2022,48(8):10472-10479
Porous mullite ceramics are widely used in heat insulation owing to their high temperature and corrosion resistant properties. Reducing the thermal conductivity by increasing porosity, while ensuring a high compressive strength, is vital for the synthesis of high-strength and lightweight porous mullite ceramics. In this study, ceramic microspheres are initially prepared from pre-treated high-alumina fly ash by spray drying, and then used to successfully prepare porous mullite ceramics with enhanced compressive strength via a simple direct stacking and sintering approach. The influence of sintering temperature and time on the microstructure and properties of porous mullite ceramics was evaluated, and the corresponding formation mechanism was elucidated. Results show that the porous mullite ceramics, calcined at 1550 °C for 3 h, possess a porosity of 47%, compressive strength of 31.4 MPa, and thermal conductivity of 0.775 W/(m?K) (at 25 °C), similar to mullite ceramics prepared from pure raw materials. The uniform pore size distribution and sintered neck between the microspheres contribute to the high compressive strength of mullite ceramics, while maintaining high porosity. 相似文献
98.
A nonspecific chitosan hydrolytic enzyme, cellulase, was immobilized onto magnetic chitosan microspheres, which was prepared in a well spherical shape by the suspension crosslinking technique. The morphology characterization of the microspheres was carried out with scanning electron microscope and the homogeneity of the magnetic materials (Fe3O4) in the microspheres was determined from optical micrograph. Factors affecting the immobilization, and the properties and stabilities of the immobilized enzyme were studied. The optimum concentration of the crosslinker and cellulase solution for the immobilization was 4% (v/v) and 6 mg/mL, respectively. The immobilized enzyme had a broader pH range of high activity and the loss of the activity of immobilized cellulase was lower than that of the free cellulase at high temperatures. This immobilized cellulase has higher apparent Michaelis–Menten constant Km (1.28 mg/mL) than that of free cellulase (0.78 mg/mL), and the maximum apparent initial catalytic rate Vmax of immobilized cellulase (0.39 mg mL?1 h?1) was lower than free enzyme (0.48 mg mL?1 h?1). Storage stability was enhanced after immobilization. The residual activity of the immobilized enzyme was 78% of original after 10 batch hydrolytic cycles, and the morphology of carrier was not changed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1334–1339, 2006 相似文献
99.
In arterioles of the lung the intravascular blood pressures are lower than in comparable vessels in the systemic circulation and the arteriole walls are thinner. Therefore, it is very difficult to distinguish between arterioles and venules of the same size using scanning electron microscopy. This study describes a novel application of latex microsphere perfusion and scanning electron microscopy which distinguishes between pulmonary arterioles and venules on the basis of endothelial cell morphology. Microspheres, 90 and 45 μm in diameter, were perfused into the arterial side of the pulmonary circulation of guinea-pig and rabbit lungs. Scanning electron microscopy of the arterioles on both sides of the lodged microspheres indicated that the endothelial cells are spindle shaped. In contrast, the endothelial cells of equal diameter venules are polygonal. Furthermore, the nuclei of the arteriolar endothelial cells were significantly (P = 0·019) narrower than those of endothelial cells in venules of equal diameter. Finally, it was observed that the differences between arteriole and venule endothelial cells persisted distally to the capillaries. 相似文献
100.
Aqueous preparation and evaluation of albumin-chitosan microspheres containing indomethacin 总被引:3,自引:0,他引:3
Bayomi MA 《Drug development and industrial pharmacy》2004,30(4):329-339
Controlled-release egg albumin-chitosan microspheres containing indomethacin as a model drug were successfully prepared by coacervation method. The proposed method can offer a simple method for microsphere preparation in an aqueous system with the elimination of the use of organic solvents that are usually needed in conventional techniques of microencapsulation. The interaction between negatively charged egg albumin molecules in phosphate buffer, pH 7.2, or sodium hydroxide solution and positively charged chitosan molecules dissolved in diluted acetic acid to form an insoluble precipitate was the principle for the formation of the microspheres. The effects of many process variables, such as amount of formaldehyde as a cross-linking agent, stirring time, final pH of encapsulation medium, initial drug loading, and albumin concentration or albumin-to-chitosan weight ratio, on the properties of the prepared microspheres were investigated. Incorporation efficiencies of the microspheres to the drug were high in most cases and ranged between 63.3 ± 3.6% and 92.39 ± 3.2%, while particle sizes were 435.2 ± 12.6 up to 693.9 ± 34.6 µm for the different tested batches. On the other hand, the values of angles of repose and compressibility indices were in the range of 23.5 ± 0.4 to 32.0 ± 0.7 degrees and 11.1 ± 0.7% to 23.6 ± 0.7% respectively, which indicate overall good free flowing nature of the microspheres of all batches. The maximum required amount of the cross-linking agent was determined to avoid excessive unnecessary chemicals. It was also noticed that excessive time of stirring and excessive initial drug loading are not recommended as it may lead to microspheres of low properties. The pH of the encapsulation media (pH 3.77 up to pH 4.91) significantly affected the properties of the microspheres. As the pH of the encapsulation media was increased, the incorporation efficiency, particle size, and flowability decreased, along with increase of drug release rate, which could be related to incomplete cross linking of the microspheres matrix. It was also observed that high concentration of albumin solution and accordingly the increase of albumin-to-chitosan weight ratio were accompanied with increases in incorporation efficiency and particle size with improved microsphere flowability and slow indomethacin release. Thus, the proposed microspheres showed the ability to control the release of indomethacin, and their properties were highly affected by many process variables that could be controlled to obtain an optimized system. 相似文献