全文获取类型
收费全文 | 1623篇 |
免费 | 49篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 233篇 |
金属工艺 | 19篇 |
机械仪表 | 40篇 |
建筑科学 | 77篇 |
矿业工程 | 3篇 |
能源动力 | 27篇 |
轻工业 | 231篇 |
水利工程 | 11篇 |
无线电 | 80篇 |
一般工业技术 | 222篇 |
冶金工业 | 574篇 |
原子能技术 | 12篇 |
自动化技术 | 135篇 |
出版年
2023年 | 10篇 |
2022年 | 14篇 |
2021年 | 25篇 |
2020年 | 27篇 |
2019年 | 32篇 |
2018年 | 22篇 |
2017年 | 31篇 |
2016年 | 29篇 |
2015年 | 37篇 |
2014年 | 40篇 |
2013年 | 88篇 |
2012年 | 73篇 |
2011年 | 87篇 |
2010年 | 59篇 |
2009年 | 47篇 |
2008年 | 71篇 |
2007年 | 59篇 |
2006年 | 48篇 |
2005年 | 44篇 |
2004年 | 46篇 |
2003年 | 37篇 |
2002年 | 40篇 |
2001年 | 37篇 |
2000年 | 28篇 |
1999年 | 31篇 |
1998年 | 79篇 |
1997年 | 41篇 |
1996年 | 33篇 |
1995年 | 50篇 |
1994年 | 35篇 |
1993年 | 29篇 |
1992年 | 22篇 |
1991年 | 11篇 |
1990年 | 26篇 |
1989年 | 30篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 24篇 |
1985年 | 12篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 7篇 |
1979年 | 18篇 |
1978年 | 8篇 |
1977年 | 14篇 |
1976年 | 19篇 |
1973年 | 6篇 |
1967年 | 5篇 |
排序方式: 共有1674条查询结果,搜索用时 15 毫秒
1.
Kathryn C. Sole John Parker Peter M. Cole Michael B. Mooiman 《Mineral Processing and Extractive Metallurgy Review》2019,40(3):194-206
The price of cobalt has increased by some 450% in the past two years, mainly due to increasing demand for lithium–ion batteries. With an official 2017 production of 64 kt, the Democratic Republic of Congo produces more than half of the world’s cobalt. African Copperbelt operations have traditionally focused on copper production; however, it has now become imperative to also consider cobalt recovery from these ores. A plethora of processing routes is possible. Most hydrometallurgical flowsheets recover cobalt from the raffinate of the low-grade copper solvent-extraction circuit. Downstream purification processes include sequential precipitation with a variety of reagents, solvent extraction, and ion exchange. Product choices include hydroxide, carbonate, sulfate, and metal cathode. This study assesses technical and economic advantages and limitations of various approaches to the hydrometallurgical processing of cobalt in an African context. 相似文献
2.
Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
3.
Dr. Emilianne M. Limbrick Audrey E. Yñigez-Gutierrez Callie C. Dulin Dagmara K. Derewacz Dr. Jeffrey M. Spraggins Dr. Kathryn M. McCulloch Prof. T. M. Iverson Prof. Brian O. Bachmann 《Chembiochem : a European journal of chemical biology》2020,21(23):3349-3358
Everninomicins are orthoester oligosaccharide antibiotics with potent activity against multidrug-resistant bacterial pathogens. Everninomicins act by disrupting ribosomal assembly in a distinct region in comparison to clinically prescribed drugs. We employed microporous intergeneric conjugation with Escherichia coli to manipulate Micromonospora for targeted gene-replacement studies of multiple putative methyltransferases across the octasaccharide scaffold of everninomicin effecting the A1, C, F, and H rings. Analyses of gene-replacement and genetic complementation mutants established the mutability of the everninomicin scaffold through the generation of 12 previously unreported analogues and, together with previous results, permitted assignment of the ten methyltransferases required for everninomicin biosynthesis. The in vitro activity of A1- and H-ring-modifying methyltransferases demonstrated the ability to catalyze late-stage modification of the scaffold on an A1-ring phenol and H-ring C-4’ hydroxy moiety. Together these results establish the potential of the everninomicin scaffold for modification through mutagenesis and in vitro modification of advanced biosynthetic intermediates. 相似文献
4.
5.
6.
Hopkins R. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1994,82(4):554-563
A public process has been in place in the United States for six years to establish an HDTV terrestrial broadcasting standard. The process, having moved through a planning phase, a competition phase, and an examination phase, has now entered a cooperation phase. Remarkable progress has been made-a testament to the process. During 1994 the American digital HDTV terrestrial broadcasting system will be tested, fully documented, and recommended to the FCC for adoption 相似文献
7.
KJ Shon M Grilley R Jacobsen GE Cartier C Hopkins WR Gray M Watkins DR Hillyard J Rivier J Torres D Yoshikami BM Olivera 《Canadian Metallurgical Quarterly》1997,36(31):9581-9587
A paralytic peptide, psi-conotoxin Piiie has been purified and characterized from Conus purpurascens venom. Electrophysiological studies indicate that the peptide inhibits the nicotinic acetylcholine receptor (nAChR). However, the peptide does not block the binding of alpha-bungarotoxin, a competitive nAChR antagonist. Thus, psi-conotoxin Piiie appears to inhibit the receptor at a site other than the acetylcholine-binding site. As ascertained by sequence analysis, mass spectrometry, and chemical synthesis, the peptide has the following covalent structure: HOOCCLYGKCRRYOGCSSASCCQR* (O = 4-trans hydroxyproline; * indicates an amidated C-terminus). The disulfide connectivity of the toxin is unrelated to the alpha- or the alphaA-conotoxins, the Conus peptide families that are competitive inhibitors of the nAChR, but shows homology to the mu-conotoxins (which are Na+ channel blockers). 相似文献
8.
Kathryn Kromroy Kathleen Ward Paul Castillo Jennifer Juzwik 《Landscape and urban planning》2007,80(4):375-385
Urbanization was associated with loss and transformation of the oak forest in the Twin Cities (Minneapolis and St. Paul) metropolitan area (TCMA) over a recent 7-year interval. Between 1991 and 1998, urbanization increased based on several indicators: population density, area of developed land, and area of impervious surface—total impervious area and area within three classes of increasing degree of imperviousness (protected, affected, and degraded). We quantified relationships between changes in urbanization and changes in several parameters describing the oak forest at the scale of ecological subsection. Increased total and affected impervious area were strongly correlated with decreased area of oak forest when changes of the urbanization indicators and oak were expressed as percentages of the subsection area. Relationships were reversed when changes were expressed as percentages of the 1991 values. Increased population density was strongly correlated with increased loss in numbers and increased isolation of oak patches, but weakly correlated with loss of oak forest area. This is the first study to quantify relationships between changes in urbanization and changes in a specific forest cover type. Our results demonstrate complexities of urbanization impacts on a metropolitan forest resource, and highlight the importance of selected variables, spatial and temporal scales, and expressions of change when quantifying these relationships. 相似文献
9.
Diane M. Hopkins Alan D. Jackson Kenneth Oates 《Microscopy research and technique》1991,18(2):176-182
The standardisation of frozen hydrated bulk biological specimens using gelatin standards is described. The relationship between corrected elemental X-ray counts and ionic concentration was found to be linear, and minimum detectable limits for each element are stated. Variations in uncorrected standard curves were found to be due to changes in aluminium coating thickness. There was an inverse relationship between coating thickness and elemental X-ray counts. The factors causing this are discussed. To avoid errors arising from inconsistent aluminium thickness, experimental material should only be compared with standards of similar aluminium net counts. This can be achieved most easily by mounting and analysing specimen and standard together. 相似文献
10.
Replies to comments by J. Read (see record 2007-07130-012), D. Gleaves et al (see record 2007-07130-013), V. Edwards et al (see record 2007-07130-014), M. Black and R. Black (see record 2007-07130-015), and S. Ullman (see record 2007-07130-016), which raised important points about the authors' original article (see record 2006-03947-003). Those comments extend our thinking about how to ask participants about abuse in an ethical way. Together, the comments point to the importance of researchers examining our own reasons for asking--or not asking--about abuse and of paying attention to how we respond when we ask. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献