全文获取类型
收费全文 | 120444篇 |
免费 | 2281篇 |
国内免费 | 468篇 |
专业分类
电工技术 | 1125篇 |
综合类 | 2346篇 |
化学工业 | 18671篇 |
金属工艺 | 5454篇 |
机械仪表 | 3760篇 |
建筑科学 | 4246篇 |
矿业工程 | 673篇 |
能源动力 | 2180篇 |
轻工业 | 6596篇 |
水利工程 | 1709篇 |
石油天然气 | 465篇 |
武器工业 | 6篇 |
无线电 | 11692篇 |
一般工业技术 | 22534篇 |
冶金工业 | 9574篇 |
原子能技术 | 545篇 |
自动化技术 | 31617篇 |
出版年
2023年 | 221篇 |
2022年 | 452篇 |
2021年 | 719篇 |
2020年 | 492篇 |
2019年 | 653篇 |
2018年 | 15054篇 |
2017年 | 13908篇 |
2016年 | 10667篇 |
2015年 | 1390篇 |
2014年 | 1310篇 |
2013年 | 2689篇 |
2012年 | 4861篇 |
2011年 | 11414篇 |
2010年 | 9839篇 |
2009年 | 7091篇 |
2008年 | 8558篇 |
2007年 | 9462篇 |
2006年 | 1781篇 |
2005年 | 2689篇 |
2004年 | 2331篇 |
2003年 | 2319篇 |
2002年 | 1624篇 |
2001年 | 823篇 |
2000年 | 762篇 |
1999年 | 682篇 |
1998年 | 686篇 |
1997年 | 647篇 |
1996年 | 623篇 |
1995年 | 613篇 |
1994年 | 571篇 |
1993年 | 543篇 |
1992年 | 524篇 |
1991年 | 324篇 |
1990年 | 435篇 |
1989年 | 409篇 |
1988年 | 351篇 |
1987年 | 367篇 |
1986年 | 324篇 |
1985年 | 435篇 |
1984年 | 447篇 |
1983年 | 336篇 |
1982年 | 315篇 |
1981年 | 295篇 |
1980年 | 286篇 |
1979年 | 280篇 |
1978年 | 264篇 |
1977年 | 236篇 |
1976年 | 224篇 |
1975年 | 209篇 |
1974年 | 192篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
This paper introduces the segmented bidirectional single-loop (SBSL) flow topology for carrier-based material handling systems. This configuration is based on a single-loop flow-path structure that is divided into non-overlapping segments, each containing a single carrier operating in a bidirectional mode. The design procedure comprises a 0 - 1 mixed-integer formulation to determine the single-loop including the pickup and delivery station location. The second stage is a segmentation procedure to determine the non-overlapping segments in the loop. Finally the performance of the SBSL is evaluated by means of simulation. 相似文献
83.
David Lloyd Suzie Morrell Helle N. Carlsen Hans Degn Phillip E. James Christopher C. Rowlands 《Yeast (Chichester, England)》1993,9(8):825-833
Saccharomyces cerevisiae HSc was grown with ethanol at concentrations up to 10% (v/v). The immediate effects of additions of externally added ethanol on CO2 production and O2 consumption of washed organisms were studied by stopped-flow membrane inlet quadrupole mass spectrometry. Fermentative activities of organisms grown with ethanol (0–5% v/v) showed similar sensitivities to inhibition by ethanol, whereas those grown with 10% (v/v) ethanol had become protected and were markedly less sensitive. The fluidity of subcellular membrane fractions was measured by determination of the temperature dependence of the rotational order parameter of the spin label 5-doxyl stearic acid (free radical) by electron spin resonance. Mitochondria prepared from yeasts grown with 0, 7 and 9% (v/v) ethanol showed similar overall fluidity, although differences in temperature-dependent behaviour indicate altered lipid composition or lateral phase separations. On the other hand the microsomal fraction from organisms grown with 9% ethanol showed a remarkable increase in fluidity. These data suggest that the protective effects of growth with ethanol near the limit of tolerance on fermentative activities may arise from altered plasma membrane fluidity properties. 相似文献
84.
85.
86.
Chih-Chun Hsieh Tao-Chih Chang Dong-Yih Lin Ming-Che Chen Weite Wu 《Metals and Materials International》2007,13(5):411-416
The purpose of this study is to investigate the precipitation characteristics of σ phase in the fusion zone of stainless steel
welds at various welding passes during a tungsten are welding (GTAW) process. The morphology, quantity, and chemical composition
of the δ-ferrite and σ phase were analyzed using optical microscopy (OM), a ferritscope (FS), a X-ray diffractometer (XRD),
scanning electron microscopy (SEM), an electron probe micro-analyzer (EPMA), and a wavelength dispersive spectrometer (WDS),
respectively. Massive δ-ferrite was observed in the fusion zone of the first pass welds during welding of dissimilar stainless
steels. The σ phase precipitated at the inner δ-ferrite particles and decreased δ-ferrite content during the third pass welding.
The σ and δ phases can be stabilized by Si element, which promoted the phase transformation of σ→ϱ+λ2 in the fusion zone of the third pass welds. It was found that the σ phase was a Fe−Cr−Si intermetallic compound found in
the fusion zone of the third pass welds during multi-pass welding. 相似文献
87.
Six measures of divergent thinking were administered to 825 men ranging in age from 17 to 101 over the period from 1959 to 1972; repeat administrations were given to a subset of 278 men after a 6-year interval. Cross-sectional analyses showed curvilinear trends, with an increase in scores for men under 40 and a decline thereafter. Repeated measures analyses on subjects initially aged 33 to 74 generally replicated this finding, whereas cross-sequential analyses suggested a decline for all cohorts tested at a later time. Additional analyses suggested that not all of the decline could be attributed to reduced speed of response production. These longitudinal findings confirm earlier cross-sectional reports of decline in divergent thinking abilities with age. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
89.
Whether tolerance develops to the "anorexia" induced by haloperidol (HAL) was determined. Rats were given HAL (2.5 or 5 mg/kg) either before or after access to milk for 53 days. Controls were given injections of saline. On Day 54, when all groups received pretest injections of the drug, only rats previously given posttest injections of HAL were tolerant. The absence of tolerance in rats previously given pretest injections suggests that tolerance is suppressed when rats are given access to food in the drugged state. It is concluded that tolerance develops to HAL as a result of pharmacological exposure but is suppressed by the "anhedonic" effect of the drug. The relevance of these findings to the role of reinforcement in behavioral tolerance is briefly discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
90.