全文获取类型
收费全文 | 227129篇 |
免费 | 4746篇 |
国内免费 | 1835篇 |
专业分类
电工技术 | 5691篇 |
综合类 | 2417篇 |
化学工业 | 31879篇 |
金属工艺 | 8903篇 |
机械仪表 | 7168篇 |
建筑科学 | 6097篇 |
矿业工程 | 1471篇 |
能源动力 | 5405篇 |
轻工业 | 17076篇 |
水利工程 | 2330篇 |
石油天然气 | 4624篇 |
武器工业 | 220篇 |
无线电 | 30546篇 |
一般工业技术 | 40730篇 |
冶金工业 | 46596篇 |
原子能技术 | 3900篇 |
自动化技术 | 18657篇 |
出版年
2022年 | 1479篇 |
2021年 | 2343篇 |
2020年 | 1790篇 |
2019年 | 1994篇 |
2018年 | 2899篇 |
2017年 | 3037篇 |
2016年 | 2984篇 |
2015年 | 2645篇 |
2014年 | 4098篇 |
2013年 | 9779篇 |
2012年 | 6506篇 |
2011年 | 8333篇 |
2010年 | 6979篇 |
2009年 | 7717篇 |
2008年 | 8075篇 |
2007年 | 8020篇 |
2006年 | 7413篇 |
2005年 | 6826篇 |
2004年 | 6324篇 |
2003年 | 5900篇 |
2002年 | 5639篇 |
2001年 | 5893篇 |
2000年 | 5516篇 |
1999年 | 6020篇 |
1998年 | 16076篇 |
1997年 | 10708篇 |
1996年 | 8308篇 |
1995年 | 6085篇 |
1994年 | 5247篇 |
1993年 | 5206篇 |
1992年 | 3532篇 |
1991年 | 3374篇 |
1990年 | 3276篇 |
1989年 | 3105篇 |
1988年 | 2848篇 |
1987年 | 2260篇 |
1986年 | 2326篇 |
1985年 | 2624篇 |
1984年 | 2323篇 |
1983年 | 2071篇 |
1982年 | 1910篇 |
1981年 | 2045篇 |
1980年 | 1795篇 |
1979年 | 1661篇 |
1978年 | 1656篇 |
1977年 | 2021篇 |
1976年 | 2702篇 |
1975年 | 1422篇 |
1974年 | 1369篇 |
1973年 | 1316篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Can Ercan S. Esra Safran Artuğ Türkmenoğlu Uğur Karabakal 《Journal of surfactants and detergents》2021,24(1):139-147
Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated. 相似文献
2.
F.T. Munna Vidhya Selvanathan K. Sobayel Ghulam Muhammad Nilofar Asim Nowshad Amin Kamaruzzaman Sopian Md. Akhtaruzzaman 《Ceramics International》2021,47(8):11003-11009
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell. 相似文献
3.
Chenchen Zhou Jia Man Haibo Yu He Xia Luming Man Bin Qi Jianfeng Li 《Ceramics International》2021,47(8):10866-10872
Ceramic microparticles have great potentials in various fields such as materials engineering, biotechnology, microelectromechanical systems, etc. Morphology of the microparticle performs an important role on their application. To date, it remains difficult to find an effective and controllable way for fabricating nonspherical ceramic microparticles with 3D features. This work demonstrates a method that combines UV light lithography and single emulsion opaque-droplet-templated microfluidic molding to prepare the crescent-shaped ceramic microparticles. By tailoring the intensity of UV light and flow rate of fluid, the shapes of microparticles are accordingly tuned. Therefore, varieties of crescent-shaped microparticles and their variations have been fabricated. After sintering, the crescent-shaped alumina ceramic microparticles were obtained. Benefitting from the light absorption and scattering behavior of most ceramic nanoparticles, this system can serve as a general platform to produce crescent-shaped microparticles made from different materials, and hold great potentials for applications in microrobotics, structural materials in MEMS, and biotechnology. 相似文献
4.
Kathleen T. Lauser Amy L. Rueter Michelle A. Calabrese 《American Institute of Chemical Engineers》2022,68(12):e17850
While protein medications are promising for treatment of cancer and autoimmune diseases, challenges persist in terms of development and injection stability of high-concentration formulations. Here, the extensional flow properties of protein-excipient solutions are examined via dripping-onto-substrate extensional rheology, using a model ovalbumin (OVA) protein and biocompatible excipients polysorbate 20 (PS20) and 80 (PS80). Despite similar PS structures, differences in extensional flow are observed based on PS identity in two regimes: at moderate total concentrations where surface tension differences drive changes in extensional flow behavior, and at small PS:OVA ratios, which impact the onset of weakly elastic flow behavior. Undesirable elasticity is observed in ultra-concentrated formulations, independent of PS identity; higher PS contents are required to observe these effects than in analogous polymeric excipient solutions. These studies reveal novel extensional flow behaviors in protein-excipient solutions, and provide a straightforward methodology for assessing the extensional flow stability of new protein-excipient formulations. 相似文献
5.
Prof. Andrea Baier Dr. Anne Kokel Dr. William Horton Ewa Gizińska Dr. Garima Pandey Prof. Ryszard Szyszka Prof. Béla Török Prof. Marianna Török 《ChemMedChem》2021,16(12):1927-1932
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays. 相似文献
6.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration. 相似文献
7.
A. Nakano T. Shimazaki M. Sekiya H. Shiozawa K. Ohtsuka A. Aoyagi T. Iwakiri Z. Mikami M. Sato Y. Sugino K. Kinoshita T. Matsuoka T. Imamura Y. Takayama K. Yamamoto 《International Journal of Hydrogen Energy》2021,46(29):15649-15659
Monitoring the temperature in liquid hydrogen (LH2) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa. 相似文献
8.
Dong Liu Xia Ke Zhong-Ce Hu Yu-Guo Zheng 《Journal of Bioscience and Bioengineering》2021,131(5):518-524
9.
Tongling Xia Yue Qi Xilei Dai Jinyu Liu Can Xiao Ruoyu You Dayi Lai Junjie Liu Chun Chen 《Indoor air》2021,31(6):2020-2032
To evaluate the separate impacts on human health and establish effective control strategies, it is crucial to estimate the contribution of outdoor infiltration and indoor emission to indoor PM2.5 in buildings. This study used an algorithm to automatically estimate the long-term time-resolved indoor PM2.5 of outdoor and indoor origin in real apartments with natural ventilation. The inputs for the algorithm were only the time-resolved indoor/outdoor PM2.5 concentrations and occupants’ window actions, which were easily obtained from the low-cost sensors. This study first applied the algorithm in an apartment in Tianjin, China. The indoor/outdoor contribution to the gross indoor exposure and time-resolved infiltration factor were automatically estimated using the algorithm. The influence of outdoor PM2.5 data source and algorithm parameters on the estimated results was analyzed. The algorithm was then applied in four other apartments located in Chongqing, Shenyang, Xi'an, and Urumqi to further demonstrate its feasibility. The results provided indirect evidence, such as the plausible explanations for seasonal and spatial variation, to partially support the success of the algorithm used in real apartments. Through the analysis, this study also identified several further development directions to facilitate the practical applications of the algorithm, such as robust long-term outdoor PM2.5 monitoring using low-cost light-scattering sensors. 相似文献
10.
Dr. Yibin Zhang Dr. Shuai Xia Shulin Wan Tessa E. Steenwinkel Tara Vohs Prof. Rudy L. Luck Prof. Thomas Werner Prof. Haiying Liu 《Chembiochem : a European journal of chemical biology》2021,22(13):2282-2291
Abnormal levels of glutathione, a cellular antioxidant, can lead to a variety of diseases. We have constructed a near-infrared ratiometric fluorescent probe to detect glutathione concentrations in biological samples. The probe consists of a coumarin donor, which is connected through a disulfide-tethered linker to a rhodamine acceptor. Under the excitation of the coumarin donor at 405 nm, the probe shows weak visible fluorescence of the coumarin donor at 470 nm and strong near-infrared fluorescence of the rhodamine acceptor at 652 nm due to efficient Forster resonance energy transfer (FRET) from the donor to the acceptor. Glutathione breaks the disulfide bond through reduction, which results in a dramatic increase in coumarin fluorescence and a corresponding decrease in rhodamine fluorescence. The probe possesses excellent cell permeability, biocompatibility, and good ratiometric fluorescence responses to glutathione and cysteine with a self-calibration capability. The probe was utilized to ratiometrically visualize glutathione concentration alterations in HeLa cells and Drosophila melanogaster larvae. 相似文献