全文获取类型
收费全文 | 4757篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 33篇 |
化学工业 | 88篇 |
金属工艺 | 8篇 |
机械仪表 | 13篇 |
建筑科学 | 21篇 |
能源动力 | 18篇 |
轻工业 | 22篇 |
水利工程 | 10篇 |
石油天然气 | 2篇 |
无线电 | 46篇 |
一般工业技术 | 94篇 |
冶金工业 | 4308篇 |
原子能技术 | 16篇 |
自动化技术 | 90篇 |
出版年
2021年 | 8篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 9篇 |
2013年 | 47篇 |
2012年 | 16篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 17篇 |
2008年 | 17篇 |
2007年 | 21篇 |
2006年 | 30篇 |
2005年 | 23篇 |
2004年 | 23篇 |
2003年 | 24篇 |
2002年 | 22篇 |
2001年 | 17篇 |
2000年 | 18篇 |
1999年 | 138篇 |
1998年 | 1328篇 |
1997年 | 741篇 |
1996年 | 485篇 |
1995年 | 279篇 |
1994年 | 202篇 |
1993年 | 268篇 |
1992年 | 54篇 |
1991年 | 53篇 |
1990年 | 52篇 |
1989年 | 76篇 |
1988年 | 66篇 |
1987年 | 70篇 |
1986年 | 48篇 |
1985年 | 53篇 |
1984年 | 6篇 |
1983年 | 12篇 |
1982年 | 25篇 |
1981年 | 33篇 |
1980年 | 35篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 113篇 |
1976年 | 221篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1972年 | 3篇 |
1923年 | 3篇 |
1922年 | 3篇 |
1921年 | 3篇 |
排序方式: 共有4769条查询结果,搜索用时 31 毫秒
1.
Jennie O'Loughlin Silvia Napolitano Fahad Alkhathami Cillian O'Beirne Daniel Marhöfer Megan O'Shaughnessy Prof. Orla Howe Prof. Matthias Tacke Dr. Marina Rubini 《Chembiochem : a European journal of chemical biology》2021,22(6):1093-1098
Antibiotic resistance is a growing problem for public health and associated with increasing economic costs and mortality rates. Silver and silver-related compounds have been used for centuries due to their antimicrobial properties. In this work, we show that 1,3-dibenzyl-4,5-diphenyl-imidazol-2-ylidene silver(I) acetate/NHC*-Ag-OAc (SBC3) is a reversible, high affinity inhibitor of E. coli thioredoxin reductase (TrxR; Ki=10.8±1.2 nM). Minimal inhibition concentration (MIC) tests with different E. coli and P. aeruginosa strains demonstrated that SBC3 can efficiently inhibit bacterial cell growth, especially in combination with established antibiotics like gentamicin. Our results show that SBC3 is a promising antibiotic drug candidate targeting bacterial TrxR. 相似文献
2.
Lake Sammamish has shown a decrease in its mean annual concentration of phosphorus following diversion of about one third of the external loading in 1968. During 1971–1975 the P concentration averaged 27 μg l−1, in contrast to the prediversion (1964–1966) concentration of 33 μg l−1, and may be equilibrating near the predicted steady state concentration of 22 μg l−1. Neither phytoplankton biomass or Secchi visibility has changed following diversion, however the blue green component of the phytoplankton decreased by nearly 50%. The failure of biomass and visibility to improve is probably a result of similar pre- and postdiversion winter spring epilimnetic P concentrations. The marked reduction in P since diversion occurred during and prior to fall overturn and may have represented a supply of P for later summer early fall blue green algal populations that declined after diversion.Runoff from a rapidly developing westside portion (18%) of the watershed is contributing substantially to P loading of the lake. Development to a density of about ten dwellings ha−1 has increased loading possibly on the order of 14%. Future development of the eastside portion (26% of watershed) may increase loading by 20% and be equivalent to nearly one half of the P previously diverted in 1968. 相似文献
3.
This paper provides a spatial vector autoregressive (SpVAR) analysis of growth spillovers for the Spanish regions over the period 1965–2003. First, a spatial Granger causality analysis is performed that indicates the relevant impact of spatial spillover effects across regions in Spain. Second, the empirical research offers a contribution in the context of the SpVAR modelling estimating the push‐in (from the neighbours to the region) and push‐out (from the region to its neighbours) effects of growth spillovers within a regional economic system. Finally, the proposed methodology reveals empirical evidence about both the short‐run and long‐term regional growth adjustment processes in space and time. The results for the Spanish regional panel data suggest the existence of strong spatiotemporal regional spillovers of growth output. This has important implications for the choice of regional policy goals and regional policy instruments. 相似文献
4.
5.
Arrays of precisely positioned single crystal silicon nanopillars, nanoneedles, and nanoblades with minimum feature sizes as small as 30 nm are fabricated using entirely scalable top-down fabrication techniques. Using the same scalable technologies, devices consisting of electrically connected silicon nanopillars with multiple addressable electrodes for each nanostructure are realized. The arrays of nanopillars, nanoneedles, and nanoblades are shown to exhibit Raman signal enhancement on 1,2-benzenedithiol monolayers, opening a path to nanodevices that manipulate, position, detect and analyze molecules. 相似文献
6.
7.
Zun Chen Scott Speakman Jane Howe Hsin Wang Wally Porter Rodney Trice 《Journal of the European Ceramic Society》2009,29(8):1403-1411
The phase evolution occurring during the reaction between corrosive V2O5 (Tm = 690 °C) and a plasma-sprayed 7 wt.% Y2O3–ZrO2 (YSZ) coating from 700 to 900 °C has been investigated in situ by X-ray diffraction. The temperature and time of interaction between the V2O5 and YSZ coating determines the phases observed. Between 700 and 750 °C, reaction products of ZrV2O7 and YVO4 were observed within minutes of reaching the test temperature. m-ZrO2 was observed after 220 and 60 min at 700 and 750 °C, respectively. The simultaneous formation of both ZrV2O7 and YVO4 at the beginning of the reaction along with the delay of the m-ZrO2 formation suggests similar reactivity between both Zr and Y with V2O5. The weight percent of the ZrV2O7 phase began to diminish after 150 and 60 min at 700 and 750 °C, respectively. For reaction temperatures of 800 and 900 °C, there is a rapid decrease in the amount of t′-ZrO2 and a rapid increase in the amount of m-ZrO2 with reaction time. YVO4 was also observed at these reaction temperatures. SEM and TEM microstructural observations confirmed the phases detected from the in situ XRD experiments. Reactions between YSZ and V2O5 suggest that the formation of a liquid phase due to the high solubility of both zirconia and yttria in vanadia is the dominate mechanism that damages the coating. The thermal conductivity of a plasma-sprayed YSZ coating reacted with up to 1 wt.% V2O5 did not significantly change due to the small volume affected. 相似文献
8.
9.
JD Ribaya-Mercado M Mazariegos G Tang ME Romero-Abal I Mena NW Solomons RM Russell 《Canadian Metallurgical Quarterly》1999,69(2):278-284
BACKGROUND: Deuterated retinol dilution (DRD) gives quantitative estimates of total body stores of vitamin A. OBJECTIVES: In elderly people, we studied 1) the time when an oral dose of deuterated vitamin A equilibrates with body stores, 2) whether serum ratios of deuterated to nondeuterated retinol (D:H) at 3 or 6 d postdosing predicted body stores, and 3) the ability of DRD to detect changes in the size of the body vitamin A pool. DESIGN: A 10-mg oral dose of [2H4]retinyl acetate was administered to 60-81-y-old Guatemalans (n = 47); percentage enrichment of serum retinol with deuterated retinol was determined at 1-3 time points per subject at 3, 6, 7, 14, 20, 21, and 54 d. In subjects from whom blood was obtained at 3 and 21 d (n = 15) and at 6 and 20 d (n = 9), total body stores were calculated by using the formula of Furr et al (Am J Clin Nutr 1989;49:713-6) with 21- or 20-d data and correlated with serum D:H at 3 or 6 d postdosing. Nine subjects received diets containing 982+/-20 microg RE (x+/-SEM) plus 800 microg RE as retinyl acetate supplements for 32 d. DRD, serum retinol, and relative dose response were used to assess vitamin A status before and after the intervention. RESULTS: Deuterated retinol equilibrated with the body pool by 20 d postdosing. Vitamin A supplementation for 32 d increased body stores, although unexplained exaggerated increases were seen in some subjects. An inverse linear relation was found between estimates of body stores and serum D:H at 3 d postdosing (r = -0.75, P = 0.002); at 6 d postdosing, the correlation was weaker. CONCLUSIONS: DRD can detect changes in total body stores of vitamin A, although factors affecting serum D:H need to be elucidated. Serum D:H 3 d postdosing might be used as an early indicator of total body stores of vitamin A, although a predictive equation will need to be developed. 相似文献
10.
JD Amsterdam F Garcia-Espana J Fawcett FM Quitkin FW Reimherr JF Rosenbaum C Beasley 《Canadian Metallurgical Quarterly》1999,19(1):9-14
PURPOSE: To evaluate the potential diagnostic role of mediastinal sonography in patients with cystic fibrosis (CF), we screened the mediastinum of adult CF patients with and without signs of infection and healthy controls. METHODS: Fifty-four consecutive adult patients with CF and 53 healthy volunteers underwent high-resolution mediastinal sonography. The paratracheal region and aorticopulmonary window of each subject were examined for lymph nodes. Each patient was screened for clinical signs of infection. RESULTS: Lymph nodes were detectable in the mediastinum of 39 of 50 CF patients (78%); the mean total lymph node volume was 1.5 +/- 1.7 cm3. Lymph nodes were detectable in the mediastinum of 31 of 50 controls (62%); the mean total lymph node volume in this group was 0.3 +/- 0.3 cm3 (p < 0.001). In the 30 CF patients with signs of infection, the mean total lymph node volume was larger (2.0 +/- 1.8 cm3) than in the 20 CF patients without signs of infection (0.7 +/- 0.9 cm3; p = 0.002). CONCLUSIONS: These results indicate that lymph node volume determination by high-resolution mediastinal sonography may help assess inflammatory activity in patients with CF. 相似文献