全文获取类型
收费全文 | 8952篇 |
免费 | 133篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 118篇 |
综合类 | 3篇 |
化学工业 | 987篇 |
金属工艺 | 97篇 |
机械仪表 | 144篇 |
建筑科学 | 263篇 |
矿业工程 | 16篇 |
能源动力 | 123篇 |
轻工业 | 485篇 |
水利工程 | 56篇 |
石油天然气 | 8篇 |
武器工业 | 1篇 |
无线电 | 694篇 |
一般工业技术 | 945篇 |
冶金工业 | 4413篇 |
原子能技术 | 71篇 |
自动化技术 | 675篇 |
出版年
2022年 | 37篇 |
2021年 | 44篇 |
2019年 | 40篇 |
2018年 | 77篇 |
2017年 | 56篇 |
2016年 | 67篇 |
2015年 | 72篇 |
2014年 | 97篇 |
2013年 | 258篇 |
2012年 | 159篇 |
2011年 | 199篇 |
2010年 | 142篇 |
2009年 | 157篇 |
2008年 | 199篇 |
2007年 | 201篇 |
2006年 | 199篇 |
2005年 | 195篇 |
2004年 | 176篇 |
2003年 | 158篇 |
2002年 | 146篇 |
2001年 | 146篇 |
2000年 | 150篇 |
1999年 | 212篇 |
1998年 | 1235篇 |
1997年 | 693篇 |
1996年 | 516篇 |
1995年 | 309篇 |
1994年 | 313篇 |
1993年 | 293篇 |
1992年 | 145篇 |
1991年 | 137篇 |
1990年 | 128篇 |
1989年 | 126篇 |
1988年 | 134篇 |
1987年 | 131篇 |
1986年 | 129篇 |
1985年 | 142篇 |
1984年 | 105篇 |
1983年 | 84篇 |
1982年 | 97篇 |
1981年 | 93篇 |
1980年 | 86篇 |
1979年 | 71篇 |
1978年 | 74篇 |
1977年 | 130篇 |
1976年 | 237篇 |
1975年 | 45篇 |
1974年 | 42篇 |
1973年 | 51篇 |
1972年 | 43篇 |
排序方式: 共有9099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.
4.
AD Santin PL Hermonat JC Hiserodt J Fruehauf V Schranz D Barclay S Pecorelli GP Parham 《Canadian Metallurgical Quarterly》1997,64(3):477-480
Tumor cells from eight freshly isolated cervical cancers (i.e., four adenocarcinomas and four squamous carcinomas) were analyzed for their production of the immune-inhibitory cytokine transforming growth factor-beta (TGF-beta) in vitro. All fresh adenocarcinomas secreted significant levels of TGF-beta (mean 397, range between 207 and 782 pg/ml/10(5) cells/48 hr). In contrast, no detectable TGF-beta was present in the supernatants from the four fresh squamous carcinoma cultures (P < 0.001). These data suggest that major differences in the secretion of the immunoinhibitory cytokine TGF-beta exist between squamous cell carcinomas and adenocarcinomas of the uterine cervix. Furthermore, these findings suggest that at least some of the differences in the natural biologic behavior, as well as in the response to radiation treatment, between these two histologic types of cervical cancer could be related to differences in secretion of this immune-inhibitory cytokine. 相似文献
5.
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
6.
7.
8.
9.
10.