全文获取类型
收费全文 | 8061篇 |
免费 | 155篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 131篇 |
综合类 | 4篇 |
化学工业 | 1159篇 |
金属工艺 | 125篇 |
机械仪表 | 173篇 |
建筑科学 | 298篇 |
矿业工程 | 28篇 |
能源动力 | 141篇 |
轻工业 | 544篇 |
水利工程 | 62篇 |
石油天然气 | 8篇 |
武器工业 | 1篇 |
无线电 | 742篇 |
一般工业技术 | 1049篇 |
冶金工业 | 2911篇 |
原子能技术 | 72篇 |
自动化技术 | 782篇 |
出版年
2022年 | 69篇 |
2021年 | 71篇 |
2020年 | 45篇 |
2019年 | 57篇 |
2018年 | 90篇 |
2017年 | 66篇 |
2016年 | 85篇 |
2015年 | 90篇 |
2014年 | 131篇 |
2013年 | 312篇 |
2012年 | 194篇 |
2011年 | 243篇 |
2010年 | 186篇 |
2009年 | 183篇 |
2008年 | 227篇 |
2007年 | 233篇 |
2006年 | 231篇 |
2005年 | 206篇 |
2004年 | 195篇 |
2003年 | 168篇 |
2002年 | 164篇 |
2001年 | 162篇 |
2000年 | 162篇 |
1999年 | 182篇 |
1998年 | 763篇 |
1997年 | 428篇 |
1996年 | 332篇 |
1995年 | 216篇 |
1994年 | 216篇 |
1993年 | 204篇 |
1992年 | 140篇 |
1991年 | 117篇 |
1990年 | 112篇 |
1989年 | 110篇 |
1988年 | 113篇 |
1987年 | 112篇 |
1986年 | 118篇 |
1985年 | 129篇 |
1984年 | 110篇 |
1983年 | 84篇 |
1982年 | 95篇 |
1981年 | 95篇 |
1980年 | 76篇 |
1979年 | 76篇 |
1978年 | 75篇 |
1977年 | 104篇 |
1976年 | 156篇 |
1974年 | 45篇 |
1973年 | 53篇 |
1972年 | 44篇 |
排序方式: 共有8230条查询结果,搜索用时 15 毫秒
1.
Wyatt L. Brown Douglas A. Day Harald Stark Demetrios Pagonis Jordan E. Krechmer Xiaoxi Liu Derek J. Price Erin F. Katz Peter F. DeCarlo Catherine G. Masoud Dongyu S. Wang Lea Hildebrandt Ruiz Caleb Arata David M. Lunderberg Allen H. Goldstein Delphine K. Farmer Marina E. Vance Jose L. Jimenez 《Indoor air》2021,31(1):141-155
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations. 相似文献
2.
Hook T.B. Brown J. Cottrell P. Adler E. Hoyniak D. Johnson J. Mann R. 《Electron Devices, IEEE Transactions on》2003,50(9):1946-1951
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon. 相似文献
3.
Antibiotic treatment options for Burkholderia cepacia infection are limited because of high intrinsic resistance. The problem is complicated by development of cross-resistance between antibiotics of different classes. We isolated antibiotic-resistant mutants by stepwise exposure to chloramphenicol (Chlor) and to trimethoprim/sulphamethoxazole (T/S) for four B. cepacia strains: ATCC13945, Per (clinical isolate), Cas and D4 (environmental isolates). Chlor(r) mutants did not produce chloramphenicol acetyl-transferase. Cross-resistance, defined as greater than four-fold increase in MIC by microtitre dilution method, was consistently seen in both types of mutants. For chloramphenicol-resistant (Chlor[r]) and trimethoprim/sulphamethoxazole-resistant (Tr/Sr) mutants of B. cepacia ATCC13945 and Cas, no MIC change was seen for piperacillin, ceftazidime, rifampicin, gentamicin, tobramycin, polymyxin B or azithromycin. B. cepacia-Per and -D4 mutants showed cross-resistance to ceftazidime and to piperacillin. Comparison of outer membrane protein (OMP) profiles of B. cepacia and their mutants by SDS-PAGE revealed Tr/Sr) mutants to be deficient in a major OMP (molecular weight 39-47 kDa). Tr/Sr mutants also expressed additional OMPs not found in wild type strains at 75-77 kDa for B. cepacia-ATCC13945 and -Cas, and 20-21 kDa in B. cepacia-D4 and -Per. No OMP changes occurred in Chlor(r) mutants. Lipopolysaccharide (LPS) profiles of each type of mutant showed new high and low molecular weight LPS bands. Cross-resistance seems to be mediated by alterations in porin and LPS for Tr/Sr mutants, but only by LPS in Chlor(r) mutants. 相似文献
4.
5.
It is essential in the simulation of power electronics applications to model magnetic components accurately. In addition to modeling the nonlinear hysteresis behavior, eddy currents and winding losses must be included to provide a realistic model. In practice the losses in magnetic components give rise to significant temperature increases which can lead to major changes in the component behavior. In this paper a model of magnetic components is presented which integrates a nonlinear model of hysteresis, electro-magnetic windings and thermal behavior in a single model for use in circuit simulation of power electronics systems. Measurements and simulations are presented which demonstrate the accuracy of the approach for the electrical, magnetic and thermal domains across a variety of operating conditions, including static thermal conditions and dynamic self heating 相似文献
6.
7.
Networks are one of the most significant developments in computing and a hallmark of modern society. However, along with increasing efficiency and productivity, both at home and in the workplace, networks have costs. One cost is the additional energy that electronic devices consume when attached to networks. Power management, a standard feature of modern PCs, was primarily developed to increase battery lifetime in laptop PCs, which historically were not network-connected when using battery power. Today, however, many laptops are connected to a network - typically a Wi-Fi network - as are the majority of desktop computers. Three key drivers of energy use are induced consumption by devices prevented by network connections from entering low-power states, increasing link data rates that inherently consume more energy for the network interfaces, and proliferation of network-connected displays that actively update and display data when no one is present. 相似文献
8.
Studies of elemental distributions within discrete coal macerals: Use of secondary ion mass spectrometry and X-ray photoelectron spectroscopy 总被引:3,自引:0,他引:3
N.Stewart Mclntyre Ronald R. Martin William J. Chauvin C.Gordon Winder James R. Brown J.Anthony MacPhee 《Fuel》1985,64(12):1705-1712
Secondary ion mass spectrometry has been used to measure qualitatively the distributions of many trace and minor elements within some well-characterized coal macerals: vitrinite, fusinite and exinite. Complementary information was obtained by using X-ray photoelectron spectroscopy. Within the vitrinite specimens studied, a widely-dispersed largely inorganic aluminosilicate phase was identified, which contained a number of other trace elements. By contrast, within the organic-rich phase of this macerai, titanium was detected in a very even distribution; this suggests that some titanium may be bonded in an organic complex. The fusinite was shown to contain elevated concentrations of calcium, magnesium and fluorine, dispersed over a large portion of the maceral. The high fluorine content could be identified as an organo-fluoro compound using XPS. Exinite was found to contain lower concentrations of most elements, compared to other macerals. The organic composition of this maceral was significantly different from that of surrounding macerals; this could be seen from the enhanced emission of the C2H2-secondary ion and images of this ion thus clearly outlined the position of such macerals. 相似文献
9.
Brown Michael T.; White Michael J.; Gerstein Lawrence H. 《Canadian Metallurgical Quarterly》1989,36(2):183
Examined the association between self-monitoring and occupational preferences. 237 undergraduates completed Snyder and Gangestad's (1986) revised self-monitoring scale and Holland's (1977) Vocational Preference Inventory (VPI). Regression analyses showed that men who valued congruence between their beliefs and behavior (i.e., low self-monitors) preferred social occupations. Men who were inclined to modify their behavior to fit social situations (i.e., high self-monitors) preferred enterprising occupations. In contrast, high self-monitoring women preferred artistic occupations. It is argued that these gender-neutral occupations permit high self-monitoring women to use their social skills but without the constraints found in male dominated enterprising occupations. Results support the assumption that people prefer occupations compatible with their social skills. Implications for career counseling and further research are noted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
Brown Charlotte; Abe-Kim Jennifer S.; Barrio Concepcion 《Canadian Metallurgical Quarterly》2003,34(1):10
What do health care practitioners need to know about providing adequate care for depressed minority women? This article examined the prevalence of depressive symptoms and clinical depression in ethnic minorities, the extent to which current health service utilization is congruent with needs, and the effectiveness of treatments provided to ethnic minorities in the primary care setting. The impact of ethnic minority women's sociocultural context on symptom expression and help-seeking behavior is also discussed. Finally, the clinical implications for accurate assessment and treatment of ethnic minority women by both medical and mental health practitioners working in the primary care sector are addressed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献