全文获取类型
收费全文 | 15073篇 |
免费 | 213篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 188篇 |
综合类 | 3篇 |
化学工业 | 2003篇 |
金属工艺 | 361篇 |
机械仪表 | 338篇 |
建筑科学 | 512篇 |
矿业工程 | 60篇 |
能源动力 | 306篇 |
轻工业 | 1218篇 |
水利工程 | 89篇 |
石油天然气 | 118篇 |
无线电 | 1509篇 |
一般工业技术 | 2335篇 |
冶金工业 | 4713篇 |
原子能技术 | 159篇 |
自动化技术 | 1397篇 |
出版年
2021年 | 103篇 |
2019年 | 102篇 |
2018年 | 135篇 |
2017年 | 102篇 |
2016年 | 94篇 |
2015年 | 107篇 |
2014年 | 224篇 |
2013年 | 569篇 |
2012年 | 304篇 |
2011年 | 406篇 |
2010年 | 333篇 |
2009年 | 336篇 |
2008年 | 451篇 |
2007年 | 440篇 |
2006年 | 432篇 |
2005年 | 385篇 |
2004年 | 323篇 |
2003年 | 361篇 |
2002年 | 309篇 |
2001年 | 321篇 |
2000年 | 314篇 |
1999年 | 383篇 |
1998年 | 1319篇 |
1997年 | 835篇 |
1996年 | 600篇 |
1995年 | 422篇 |
1994年 | 376篇 |
1993年 | 394篇 |
1992年 | 274篇 |
1991年 | 240篇 |
1990年 | 256篇 |
1989年 | 213篇 |
1988年 | 218篇 |
1987年 | 203篇 |
1986年 | 194篇 |
1985年 | 249篇 |
1984年 | 208篇 |
1983年 | 205篇 |
1982年 | 200篇 |
1981年 | 177篇 |
1980年 | 191篇 |
1979年 | 128篇 |
1978年 | 134篇 |
1977年 | 235篇 |
1976年 | 316篇 |
1975年 | 135篇 |
1974年 | 125篇 |
1973年 | 107篇 |
1972年 | 78篇 |
1970年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Chase J. Smith Christopher R. Weinberger Gregory B. Thompson 《Journal of the European Ceramic Society》2018,38(15):4850-4866
The phase stability and microstructural formations for a series of hot isostatically pressed (HIP) NbCx compositions was investigated. Based on the composition, single-phase B1 (Fmm) NbC or (P1m) β?Nb2C equiaxed grains were observed as well as β-Nb2C lath precipitation within NbC. Particular discussion is given to the complexities of X-ray and electron diffraction for proper identification for the various poly-types of Nb2C that have been computationally predicted. The phase transformation pathways for these microstructures was revealed by a NbC-Nb diffusion couple from the HIP powders. The migration of vacancies towards the NbC side resulted in a refinement of the NbC grains whereas carbon’s migration into the Nb formed an uniform and distinct reaction front with a mixture of β-Nb2C and Nb grains. This latter microstructure suggests carbon’s reaction through the matrix grain is as significant in the conversion process as is the precipitation of β-Nb2C at the grain boundaries. 相似文献
992.
A Defined and Flexible Pocket Explains Aryl Substrate Promiscuity of the Cahuitamycin Starter Unit–Activating Enzyme CahJ 下载免费PDF全文
Dr. Ashootosh Tripathi Dr. Sung Ryeol Park Dr. Andrew P. Sikkema Dr. Hyo Je Cho Dr. Jianfeng Wu Brian Lee Dr. Chuanwu Xi Prof. Janet L. Smith Prof. David H. Sherman 《Chembiochem : a European journal of chemical biology》2018,19(15):1595-1600
Cahuitamycins are biofilm inhibitors assembled by a convergent nonribosomal peptide synthetase pathway. Previous genetic analysis indicated that a discrete enzyme, CahJ, serves as a gatekeeper for cahuitamycin structural diversification. Here, the CahJ protein was probed structurally and functionally to guide the formation of new analogues by mutasynthetic studies. This analysis enabled the in vivo production of a new cahuitamycin congener through targeted precursor incorporation. 相似文献
993.
A process has been developed for the synthesis of a new photochromic alkylene sulfide derivative. The process involves the synthesis of an alkylene sulfide with terminal free amino groups and a novel unsymmetrical photochromic diarylperfluorocyclopentene containing an aldehyde group, which coupled together to produce the corresponding Schiff base. The structures of the products were confirmed by a range of spectroscopic techniques. 相似文献
994.
995.
A.L. Smith M. Rutten L. Herrmann E. Epifano R.J.M. Konings E. Colineau J.-C. Griveau C. Guéneau N. Dupin 《Journal of the European Ceramic Society》2021,41(6):3664-3686
Thermodynamic measurements on BaMoO4, BaMoO3 and BaMo3O10 are reported, that served as input for the development of a thermodynamic model of the Ba-Mo-O system using the CALPHAD methodology. The valence states of molybdenum in BaMoO4 and BaMoO3 were confirmed to be VI and IV, respectively, from X-ray Absorption Near Edge Structure Spectroscopy measurements at the Mo K-edge. The heat capacity at low temperatures of these compounds was obtained from thermal-relaxation calorimetry. Phase equilibrium data in the BaMoO4-MoO3 section were also measured, and the transition enthalpy associated with the peritectic decomposition of BaMo3O10 was determined using Differential Scanning Calorimetry. The developed thermodynamic model used the compound energy formalism for intermediate compounds, and an ionic two-sublattice model for the liquid phase. The optimized Gibbs energies were assessed with respect to the known thermodynamic and phase equilibrium data. A good agreement is generally obtained, but a number of ill-defined data were also identified. 相似文献
996.
Diana R. Melis Chiao-Yu Hsiao Dr. Jill M. Combrinck Prof. Lubbe Wiesner Prof. Gregory S. Smith 《Chembiochem : a European journal of chemical biology》2021,22(9):1568-1572
A fluorescent analogue of a previously synthesised N,N-chelated IrIII complex was prepared by coordination of the organic ligand to an extrinsic bis(2-phenylpyridine)iridium(III) fluorophore. This cyclometallated IrIII complex in itself displays good, micromolar activity against the chloroquine-sensitive NF54 strain of Plasmodium falciparum. Live-cell confocal microscopy found negligible localisation of the fluorescent complex within the digestive vacuole of the parasite. This eliminated the haem detoxification pathway as a potential mechanism of action. Similarly, no localisation of the complex within the parasitic nucleus was found, thus suggesting that this complex probably does not interfere with the DNA replication process. A substantial saturation of fluorescence from the complex was found near phospholipid structures such as the plasma and nuclear membranes but not in neutral lipid bodies. This indicates that an association with these membranes, or organelles such as the endoplasmic reticulum or branched mitochondrion, could be essential to the efficacies of these types of antimalarial compounds. 相似文献
997.
Dr. Chungsik Kim Mintesinot Kassu Dr. Kenneth P. Smith Prof. James E. Kirby Prof. Roman Manetsch 《ChemMedChem》2021,16(18):2775-2780
Pyrazole-thiazole core-containing compound KP-40 and 20 novel derivatives were designed and synthesized through traditional SAR analysis. These molecules displayed adjunctive activity with meropenem against Gram-negative bacteria evidenced by a range of fractional inhibitory concentration (FIC=0.5–0.25) and minimum adjunctive concentration (MAC=128–32 μM) values. Of this series of molecules, four compounds displayed notable adjunctive potential, with FIC and MAC values of 0.25 and 32 μM, respectively. Moreover, the solubility of these compounds was improved to an acceptable range. Further analysis using our “in house” permeation and efflux multi parameter optimization (PEMPO) algorithm revealed key physicochemical properties that may be critical for the development of active Gram-negative antibacterials. Taking PEMPO scores into consideration prior to executing synthesis of analogs may be a simple, yet rapid and effective strategy that can be used in conjunction with traditional SAR approaches to aid in the design of potent Gram-negative antibacterials. 相似文献
998.
H.H. Janzen K.A. Beauchemin Y. Bruinsma C.A. Campbell R.L. Desjardins B.H. Ellert E.G. Smith 《Nutrient Cycling in Agroecosystems》2003,67(1):85-102
Agroecosystems rely on inputs of nitrogen (N) to sustain productivity. But added N can leak into adjacent environments, affecting the health of other ecosystems and their inhabitants. Worries about global warming have cast further attention on the N cycle in farmlands because farms are a main source of N2O, and because carbon sequestration, proposed to help reduce CO2 loads, requires a build-up of N. Our objective was to estimate, as an illustrative example, the net N balance of Canadian agroecosystems in 1996 and then infer some hypotheses about the routes of N loss, their magnitude, and ways of reducing them. We defined agroecosystems as all agricultural lands in Canada including soil to 1 m depth and all biota, except humans. Only net flows of N across those boundaries were counted in our balance – all others represent internal cycling. Based on our estimates, about 2.35 Tg N entered Canadian agroecosystems from biological fixation, fertilizers, and atmospheric deposition (excluding re-deposited NH3). In the same year, about 1.03 Tg N were exported in crop products and 0.19 Tg were exported in animals and animal products. Consequently, N inputs exceed exports in products by about 1.13 Tg, a surplus that is either accumulating in agroecosystems or lost to the environment. Because potential soil organic matter gains can account for only a small part of the surplus N, most is probably lost to air or groundwater. Our finding, that N losses amount to almost half of N added, concurs with field experiments that show crop recovery of added N in a given year is often not more than 60%. Better management may reduce the fraction lost somewhat but, because N in ecosystems eventually cycles back to N2, substantive gains in efficiency may not come easily. As well as trying to reduce losses, research might also focus on steering losses directly to N2, away from more harmful intermediates. If some of the `missing N' can be assimilated into organic matter, agricultural soils in Canada may need little added N to achieve C sequestration targets. 相似文献
999.
We present analytical solutions to the steady state nucleation-condensation-coagulation equation of aerosols in the atmosphere. These solutions are appropriate under different limits but more general than previously derived analytical solutions. For example, we provide an analytic solution to the coagulation limit plus a condensation correction. Our solutions are then compared with numerical results. We show that the solutions can be used to estimate the sensitivity of the cloud condensation nuclei number density to the nucleation rate of small condensation nuclei and to changes in the formation rate of sulfuric acid.
© 2016 American Association for Aerosol Research 相似文献
1000.
Tae Hui Kang Brett G. Compton William T. Heller Shuo Qian Gregory S. Smith Volker S. Urban Chad E. Duty Changwoo Do 《Polymer Engineering and Science》2019,59(Z2):E65-E70
Carbon fiber (CF)‐embedded acrylonitrile butadiene styrene polymer composites printed on the large‐scale printer at Oak Ridge National Laboratory were investigated by small‐angle neutron scattering to correlate the microstructure of the composites with their mechanical strength. The microstructure of the polymer domains and the alignment of CF were characterized across the interfaces between layers of the hot‐melt extruded material and were compared with CF‐free ABS. The small‐angle neutron scattering data show that the CF‐containing material displays strong anisotropic scatterings suggesting molecular alignment along the printing direction that is not present in the CF‐free ABS. Scattering data analysis across the interfacial layer revealed enhanced molecular alignment along the printing direction near the boundaries and inhomogeneous size distribution of polymer domains upon the addition of CF. We attribute the compromised strength across interfacial layers from CF‐containing material to this inhomogeneous size distribution which prevents effective lateral interaction between layers. POLYM. ENG. SCI., 59:E65–E70, 2019. © 2018 Society of Plastics Engineers 相似文献