全文获取类型
收费全文 | 2597篇 |
免费 | 33篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 26篇 |
综合类 | 5篇 |
化学工业 | 164篇 |
金属工艺 | 41篇 |
机械仪表 | 40篇 |
建筑科学 | 66篇 |
矿业工程 | 21篇 |
能源动力 | 22篇 |
轻工业 | 124篇 |
水利工程 | 7篇 |
石油天然气 | 6篇 |
无线电 | 120篇 |
一般工业技术 | 210篇 |
冶金工业 | 1642篇 |
原子能技术 | 10篇 |
自动化技术 | 128篇 |
出版年
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 18篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 22篇 |
2015年 | 13篇 |
2014年 | 31篇 |
2013年 | 67篇 |
2012年 | 28篇 |
2011年 | 48篇 |
2010年 | 35篇 |
2009年 | 47篇 |
2008年 | 50篇 |
2007年 | 46篇 |
2006年 | 38篇 |
2005年 | 35篇 |
2004年 | 34篇 |
2003年 | 34篇 |
2002年 | 21篇 |
2001年 | 25篇 |
2000年 | 27篇 |
1999年 | 68篇 |
1998年 | 472篇 |
1997年 | 282篇 |
1996年 | 192篇 |
1995年 | 84篇 |
1994年 | 98篇 |
1993年 | 112篇 |
1992年 | 30篇 |
1991年 | 47篇 |
1990年 | 34篇 |
1989年 | 50篇 |
1988年 | 46篇 |
1987年 | 37篇 |
1986年 | 38篇 |
1985年 | 34篇 |
1984年 | 9篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1980年 | 22篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 52篇 |
1976年 | 81篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有2632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.
3.
This article introduces a special section on the use of taxometrics to examine the categorical versus the dimensional structure of various forms of psychopathology. Paving the way into the special section, this introduction briefly describes 3 taxometric methods--mean above minus below a sliding cut (MAMBAC), maximum covariation (MAXCOV), and maximum eigenvalue (MAXEIG)--and discusses possible threats to statistical conclusion validity that often emerge when such techniques are applied in psychopathology research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
4.
5.
C Diamond ML Huang DH Kedes C Speck GW Rankin D Ganem RW Coombs TM Rose JN Krieger L Corey 《Canadian Metallurgical Quarterly》1997,176(3):775-777
The prevalence of human herpesvirus 8 (HHV-8)/Kaposi's sarcoma (KS)-associated herpesvirus was investigated in the semen of 99 human immunodeficiency virus (HIV)-infected men (median CD4 cell count, 357/mm3) by use of a polymerase chain reaction (PCR) assay capable of detecting <10 copies of HHV-8 DNA. Of the subjects, 95 (96%) self-identified as men who have sex with men (MSM), and 3 had a history of clinical KS. Seminal cell specimens were negative for HHV-8 in 98 subjects. None of the 26 without KS (27.1% of 96 tested) who were seropositive for HHV-8 by IFA for latency-associated nuclear antigens had HHV-8 detected in their semen. The only subject with any evidence for seminal HHV-8 DNA was seropositive for HHV-8 and had active KS. HHV-8 was detected in 10 (10.4%) of 96 peripheral blood mononuclear cell specimens. The prevalence of HHV-8 DNA by PCR in semen of HIV-infected MSM without KS is low. 相似文献
6.
JM Rumsey BC Donohue DR Brady K Nace JN Giedd P Andreason 《Canadian Metallurgical Quarterly》1997,54(12):1481-1489
The influence of ionic strength and composition on the binding and inhibition of human leukocyte elastase by glycosaminoglycans with variable degree and position of sulfation was investigated. The kinetic mechanism of inhibition had a hyperbolic, mixed-type character with a competitive component that was promoted by low ionic strength, reduced by phosphate ions, and which also depended on the substrate and glycosaminoglycan structure. Enzyme binding was a cooperative phenomenon that varied with ionic strength and composition. The inhibition patterns correlated with the cationic character of elastase and with the distribution of arginines on its molecular surface, most notably with residues located in the vicinity of the substrate binding region. The order of affinity for elastase binding was chondroitin 4-sulfate < chondroitin 6-sulfate < dermatan sulfate, iduronate-containing derivatives being superior with respect to the glucuronate-containing counterparts. Additional sulfation at both the 4- and 6- positions or at the N- and 4-positions of the N-acetylgalactosamine moiety decidedly improved the inhibitory efficiency. The results highlight a fundamental physiological role of enzyme-glycosaminoglycan interactions. In the azurophil granule of the human polymorphonuclear neutrophil, elastase and other enzymes are bound to a matrix of chondroitin 4-sulfate because this is the only glycosaminoglycan that simultaneously offers good binding for enzyme compartmentalization together with prompt release from the bound state at the onset of phagocytosis. 相似文献
7.
J Brake TJ Walsh CE Benton JN Petitte R Meijerhof G Pe?alva 《Canadian Metallurgical Quarterly》1997,76(1):144-151
The relative importance of fat and lean tissue mass in determining bone mineral mass among postmenopausal women was examined in this 1-year longitudinal study. Fifty postmenopausal Caucasian women entered the study; 45 of them completed a 1-year follow-up. Dual-energy X-ray absorptiometry was employed for measuring total and regional bone mineral density (BMD) and bone mineral content (BMC), fat tissue mass (FTM), lean tissue mass (LTM), and body weight. Results from linear regression analysis using the cross-sectional data (n = 50) of the study indicated that LTM explained a larger percentage of variation in bone mineral mass than did FTM. FTM and LTM were found to be moderately correlated (r = 0.55); when FTM was entered in the same predicting regression models, LTM was a significant predictor (p < 0.05) of the total and regional BMC, but not BMD. The percent FTM (and inversely %LTM) was correlated with BMD and BMC, but significant correlation was primarily found only for total body BMD (or BMC). Weight was the best predictor of total body BMD and BMC. Longitudinally (n = 45), annual changes in both FTM and weight were significantly associated with annual changes in regional BMD after adjustment for initial bone mineral values (p < 0.05). We conclude that bone mineral mass is more closely related to LTM than to FTM, while annual changes in regional BMD are more closely correlated with changes in FTM in healthy postmenopausal women. Meanwhile, increased body weight is significantly associated with increased bone mineral mass. 相似文献
8.
9.
10.
Widely tunable bottom-emitting vertical-cavity SOAs 总被引:1,自引:0,他引:1
Cole G.D. Bjorlin E.S. Wang C.S. MacDonald N.C. Bowers J.E. 《Photonics Technology Letters, IEEE》2005,17(12):2526-2528
We present bottom-emitting tunable vertical-cavity semiconductor optical amplifiers (VCSOAs) with an effective wavelength tuning range of >20 nm. These devices utilize a high reflectivity micromechanically tunable Bragg mirror as the back reflector. Compared with our first generation tunable VCSOAs, the bottom-emitting devices exhibit a two-fold increase in the effective tuning range as well as a five-fold reduction in the required tuning voltage. 相似文献