全文获取类型
收费全文 | 2483篇 |
免费 | 169篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 31篇 |
综合类 | 1篇 |
化学工业 | 795篇 |
金属工艺 | 38篇 |
机械仪表 | 42篇 |
建筑科学 | 87篇 |
矿业工程 | 5篇 |
能源动力 | 83篇 |
轻工业 | 542篇 |
水利工程 | 11篇 |
石油天然气 | 8篇 |
无线电 | 108篇 |
一般工业技术 | 330篇 |
冶金工业 | 299篇 |
原子能技术 | 7篇 |
自动化技术 | 273篇 |
出版年
2024年 | 4篇 |
2023年 | 27篇 |
2022年 | 105篇 |
2021年 | 121篇 |
2020年 | 76篇 |
2019年 | 77篇 |
2018年 | 90篇 |
2017年 | 92篇 |
2016年 | 85篇 |
2015年 | 99篇 |
2014年 | 94篇 |
2013年 | 156篇 |
2012年 | 147篇 |
2011年 | 184篇 |
2010年 | 133篇 |
2009年 | 128篇 |
2008年 | 123篇 |
2007年 | 99篇 |
2006年 | 88篇 |
2005年 | 50篇 |
2004年 | 58篇 |
2003年 | 53篇 |
2002年 | 53篇 |
2001年 | 51篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 109篇 |
1997年 | 68篇 |
1996年 | 48篇 |
1995年 | 35篇 |
1994年 | 27篇 |
1993年 | 27篇 |
1992年 | 3篇 |
1991年 | 13篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 10篇 |
1975年 | 3篇 |
排序方式: 共有2660条查询结果,搜索用时 0 毫秒
991.
Adriana Miller Agnieszka Matera-Witkiewicz Aleksandra Mikoajczyk Joanna Wty Dean Wilcox Danuta Witkowska Magdalena Rowiska-yrek 《International journal of molecular sciences》2021,22(13)
The antimicrobial activity of surfactant-associated anionic peptides (SAAPs), which are isolated from the ovine pulmonary surfactant and are selective against the ovine pathogen Mannheimia haemolytica, is strongly enhanced in the presence of Zn(II) ions. Both calorimetry and ITC measurements show that the unique Asp-only peptide SAAP3 (DDDDDDD) and its analogs SAAP2 (GDDDDDD) and SAAP6 (GADDDDD) have a similar micromolar affinity for Zn(II), which binds to the N-terminal amine and Asp carboxylates in a net entropically-driven process. All three peptides also bind Cu(II) with a net entropically-driven process but with higher affinity than they bind Zn(II) and coordination that involves the N-terminal amine and deprotonated amides as the pH increases. The parent SAAP3 binds Cu(II) with the highest affinity; however, as shown with potentiometry and absorption, CD and EPR spectroscopy, Asp residues in the first and/or second positions distinguish Cu(II) binding to SAAP3 and SAAP2 from their binding to SAAP6, decreasing the Cu(II) Lewis acidity and suppressing its square planar amide coordination by two pH units. We also show that these metal ions do not stabilize a membrane disrupting ability nor do they induce the antimicrobial activity of these peptides against a panel of human pathogens. 相似文献
992.
993.
994.
Preparation of Composite Electrospun Membranes Containing Strontium‐Substituted Bioactive Glasses for Bone Tissue Regeneration 下载免费PDF全文
Martin E. Santocildes‐Romero Rebecca L. Goodchild Paul V. Hatton Aileen Crawford Ian M. Reaney Cheryl A. Miller 《大分子材料与工程》2016,301(8):972-981
Barrier membranes used for the treatment of bone tissue defects caused by periodontitis lack the ability to promote new bone tissue regeneration. However, the addition of an osteogenic component to membranes may enhance their regenerative potential. Here the manufacturing of composite membranes made of poly(caprolactone) and strontium‐substituted bioactive glass is described using the solution‐electrospinning technique, with particles located both inside and on the surface of the fibers. All membranes are characterized using scanning electron microscopy and energy dispersive X‐ray spectroscopy, and glass dissolution from within the fibers is investigated in water. In vitro material cytotoxicity is determined using a rat osteosarcoma cell line. Electrospun fibers exhibit porous surfaces and regions of increased diameter where the particles are accumulated. The glass dissolves after immersion in water, releasing dissolution products that are associated with increased pH. Further evidence suggests accelerated polymer degradation due to interactions between both components, which may provide the additional benefit of reducing the pH changes associated with glass dissolution. All compositions are biocompatible in vitro, with the exception of membranes with >50 μg of glass on their surface. In conclusion, these membranes show great potential for bone healing applications, including guided bone regeneration and scaffolds for musculoskeletal tissue engineering.
995.
Synthesis and in vivo Evaluation of Fluorine‐18 and Iodine‐123 Pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine Derivatives as PET and SPECT Radiotracers for Mapping A2A Receptors 下载免费PDF全文
Dr. Christine Vala Dr. Thomas J. Morley Dr. Xuechun Zhang Dr. Caroline Papin Dr. Adriana Alexandre S. Tavares Dr. H. Sharon Lee Dr. Cristian Constantinescu Dr. Olivier Barret Dr. Vincent M. Carroll Dr. Ronald M. Baldwin Dr. Gilles D. Tamagnan Dr. David Alagille 《ChemMedChem》2016,11(17):1936-1943
Imaging agents that target adenosine type 2A (A2A) receptors play an important role in evaluating new pharmaceuticals targeting these receptors, such as those currently being developed for the treatment of movement disorders like Parkinson′s disease. They are also useful for monitoring progression and treatment efficacy by providing a noninvasive tool to map changes in A2A receptor density and function in neurodegenerative diseases. We previously described the successful evaluation of two A2A‐specific radiotracers in both nonhuman primates and in subsequent human clinical trials: [123I]MNI‐420 and [18F]MNI‐444. Herein we describe the development of both of these radiotracers by selection from a series of A2A ligands, based on the pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine core of preladenant. Each of this series of 16 ligands was found to bind to recombinant human A2A receptor in the low nanomolar range, and of these 16, six were radiolabeled with either fluorine‐18 or iodine‐123 and evaluated in nonhuman primates. These initial in vivo results resulted in the identification of 7‐(2‐(4‐(4‐(2‐[18F]fluoroethoxy)phenyl)piperazin‐1‐yl)ethyl)‐2‐(furan‐2‐yl)‐7H‐pyrazolo[4,3‐e][1,2,4]triazolo[1,5‐c]pyrimidin‐5‐amine ([18F]MNI‐444) and 7‐(2‐(4‐(2‐fluoro‐4‐[123I]iodophenyl)piperazin‐1‐yl)ethyl)‐2‐(furan‐2‐yl)‐7H‐imidazo[1,2‐c]pyrazolo[4,3‐e]pyrimidin‐5‐amine ([123I]MNI‐420) as PET and SPECT radiopharmaceuticals for mapping A2A receptors in brain. 相似文献
996.
Raquel Casasola Juan M. Pérez Maximina Romero 《Journal of the American Ceramic Society》2016,99(2):484-491
A study on the devitrification of fluorophyllosilicate glass precursors is presented. The research has been focused on the early stages of the crystallization process and shows the variation in the crystallization mechanism with increasing the fluorine content. The devitrification process has been studied by means of differential scanning calorimetry (DSC) and field‐emission scanning electron microscopy (FESEM). These complementary techniques established that both surface (heterogeneous nucleation) and volume (internal homogeneous nucleation) mechanisms are present in the crystallization process of fluorophlogopite‐based glasses, the latter being predominant. By increasing the percentage of fluorine in the parent glass, a variation in the location of the first crystals developed from the internal volume of the glass toward the external surface was observed. Such an alteration in the crystallization mechanism was also checked by examining the microstructure of crystallized samples prepared under short‐time treatments. 相似文献
997.
Hoffmeister CR Durli TL Schaffazick SR Raffin RP Bender EA Beck RC Pohlmann AR Guterres SS 《Nanoscale research letters》2012,7(1):251
The aim of the present study was to develop a transdermal system for controlled delivery of melatonin combining three strategies: nanoencapsulation of melatonin, drying of melatonin-loaded nanocapsules, and incorporation of nanocapsules in a hydrophilic gel. Nanocapsules were prepared by interfacial deposition of the polymer and were spray-dried using water-soluble excipients. In vitro drug release profiles were evaluated by the dialysis bag method, and skin permeation studies were carried out using Franz cells with porcine skin as the membrane. The use of 10% (w/v) water-soluble excipients (lactose or maltodextrin) as spray-drying adjuvants furnished redispersible powders (redispersibility index approximately 1.0) suitable for incorporation into hydrogels. All formulations showed a better controlled in vitro release of melatonin compared with the melatonin solution. The best controlled release results were achieved with hydrogels prepared with dried nanocapsules (hydrogels > redispersed dried nanocapsules > nanocapsule suspension > melatonin solution). The skin permeation studies demonstrated a significant modulation of the transdermal melatonin permeation for hydrogels prepared with redispersible nanocapsules. In this way, the additive effect of the different approaches used in this study (nanoencapsulation, spray-drying, and preparation of semisolid dosage forms) allows not only the control of melatonin release, but also transdermal permeation. 相似文献
998.
A novel α-l-rhamnosidase with potential applications in citrus juice industry and in winemaking 总被引:1,自引:0,他引:1
Adriana E. Alvarenga Cintia M. Romero Guillermo R. Castro 《European Food Research and Technology》2013,237(6):977-985
The production of monoglycosylated flavonoids by α-l-rhamnosidases (EC 3.2.1.40) is an interesting development in biocatalysis. Applications of rhamnosidases in industry include removal of bitterness caused by naringin from citrus juices. In the present work, a psychrotolerant bacterial strain with α-l-rhamnosidase activity was isolated. The α-l-rhamnosidase was found to be able to degrade naringin and was purified and characterized. The α-l-rhamnosidase from Brevundimonas sp. Ci19 was able to release both rhamnose and prunin from naringin. The enzyme was partially purified with a performance of 2.7-fold purification. The α-l-rhamnosidase showed an optimum pH between 6.00 and 7.00 with substantial residual activity at pH 5.00 (85.3 %). The optimum temperature was between 20 and 37 °C. The enzyme showed activation in the presence of Ca2+ and Cd2+ ions and at a high ethanol concentration level (10 % v/v). Activity was found for β-d-glucosidase (EC 3.2.1.21) in the partially purified extract, but it was inactive in the acid pH region. This result indicates the potential for inactivation of β-d-glucosidase along with the high level of α-l-rhamnosidase activity necessary for the production of flavonoid glycosides. The α-l-rhamnosidase from Brevundimonas sp. Ci19 showed interesting properties for potential use not only in the citrus juice industry but also in winemaking. 相似文献
999.
Luminita-Ioana Buruiana Ecaterina Avram Adriana Popa Valentina Elena Musteata Silvia Ioan 《Polymer Bulletin》2012,68(6):1641-1661
Quaternized polysulfone with triphenylphosphonium pendant groups was investigated, as to its optical and electronic properties.
Optical properties were analyzed by refractivity and transmission spectra. To obtain the optical parameters, the approach
proposed by Tauc for amorphous semiconductors has been used, because of the similarity of the absorption edges. Values of
pseudogap energy and Urbach energy of 3.89 eV and 168 meV, respectively, were obtained. The dielectric properties and AC-conductivity
were also studied as a function of temperature and frequency. Decrease in the dielectric constant was observed with the increase
in frequency and decrease in temperature. Also, quaternized polysulfone films were characterized by two relaxation processes,
γ and β relaxation, which appear at different temperatures, depending on the pendant group. The frequency–temperature-dependent
conductivity showed that conductivity increases with frequency and also that the quaternized polysulfones possess typical
semiconducting properties. All parameters have been found as slightly influenced by the polymer chain structure. 相似文献
1000.
de Souza Pinto R Castilho G Paim BA Machado-Lima A Inada NM Nakandakare ER Vercesi AE Passarelli M 《Lipids》2012,47(5):443-450
We investigated the role of aminoguanidine and benfotiamine on the inhibition of reactive oxygen species (ROS) generation
in macrophages induced by advanced glycated albumin (AGE-albumin) and its relationship with cell cholesterol homeostasis,
emphasizing the expression of the ATP binding cassette transporter A-1 (ABCA-1). AGE-albumin was made by incubating fatty
acid-free albumin with 10 mM glycolaldehyde. ROS production and ABCA-1 protein level were determined by flow cytometry in
J774 macrophages treated along time with control (C) or AGE-albumin alone or in the presence of aminoguanidine or benfotiamine.
Mitochondrial function was evaluated by oxygraphy. Compared to C-albumin, AGE-albumin increased ROS production in macrophages,
which was ascribed to the activities of NADPH oxidase and of the mitochondrial system. Mitochondrial respiratory chain activity
was reduced in cells incubated with AGE-albumin. ROS generation along time was associated with the reduction in macrophage
ABCA-1 protein level. Aminoguanidine prevented ROS elevation and restored the ABCA-1 content in macrophages; on the other
hand, benfotiamine that promoted a lesser reduction in ROS generation was not able to restore ABCA-1 levels. Inhibition of
oxidative stress induced by AGE-albumin prevents disturbances in reverse cholesterol transport by curbing the reduction of
ABCA-1 elicited by advanced glycation in macrophages and therefore may contribute to the prevention of atherosclerosis in
diabetes mellitus. 相似文献