全文获取类型
收费全文 | 4459篇 |
免费 | 172篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 51篇 |
综合类 | 3篇 |
化学工业 | 837篇 |
金属工艺 | 87篇 |
机械仪表 | 72篇 |
建筑科学 | 142篇 |
矿业工程 | 8篇 |
能源动力 | 104篇 |
轻工业 | 455篇 |
水利工程 | 24篇 |
石油天然气 | 20篇 |
无线电 | 368篇 |
一般工业技术 | 664篇 |
冶金工业 | 1217篇 |
原子能技术 | 40篇 |
自动化技术 | 543篇 |
出版年
2023年 | 29篇 |
2022年 | 76篇 |
2021年 | 97篇 |
2020年 | 44篇 |
2019年 | 53篇 |
2018年 | 92篇 |
2017年 | 83篇 |
2016年 | 119篇 |
2015年 | 79篇 |
2014年 | 97篇 |
2013年 | 223篇 |
2012年 | 178篇 |
2011年 | 254篇 |
2010年 | 146篇 |
2009年 | 186篇 |
2008年 | 199篇 |
2007年 | 194篇 |
2006年 | 178篇 |
2005年 | 127篇 |
2004年 | 111篇 |
2003年 | 106篇 |
2002年 | 109篇 |
2001年 | 89篇 |
2000年 | 65篇 |
1999年 | 87篇 |
1998年 | 300篇 |
1997年 | 201篇 |
1996年 | 147篇 |
1995年 | 97篇 |
1994年 | 89篇 |
1993年 | 77篇 |
1992年 | 53篇 |
1991年 | 42篇 |
1990年 | 46篇 |
1989年 | 49篇 |
1988年 | 33篇 |
1987年 | 42篇 |
1986年 | 28篇 |
1985年 | 40篇 |
1984年 | 35篇 |
1983年 | 37篇 |
1982年 | 31篇 |
1981年 | 18篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 16篇 |
1977年 | 39篇 |
1976年 | 57篇 |
1975年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有4635条查询结果,搜索用时 15 毫秒
31.
Denis Rodrigue 《加拿大化工杂志》2002,80(2):289-292
Recently, the author (Rodrigue, 2001 a, b) proposed a generalized correlation for the steady rise of gas bubbles in uncontaminated viscous Newtonian fluids of infinite extent. It is the purpose of this note to show that this model can be modified for inelastic non‐Newtonian power‐law fluids. Using data taken from six different studies, it is shown that the modified model can predict quite nicely the bubble velocity for these non‐Newtonian inelastic fluids. 相似文献
32.
MM Simon P Pavlik A Hartig M Binder H Ruis WJ Cook CL Denis B Schanz 《Canadian Metallurgical Quarterly》1995,249(3):289-296
We examined the hypoxic tolerance phenomenon in vitro. Brief exposure to hypoxia induced the production of basic fibroblast growth factor (bFGF) mRNA and protein in rat cortical neurons and protected them from hypoxic injury. Cortical neurons were cultured from 18th-day rat embryos in a serum-free medium and subjected to brief (4 h) and/or prolonged (24 h) hypoxia. Neuronal damage was assessed by quantifying lactate dehydrogenase (LDH) activity in the medium. After brief hypoxia, LDH release was identical to that of the controls, whereas prolonged hypoxia caused a significant increase in LDH release, indicating neuronal death. However, if brief hypoxia was applied 2 days prior to the prolonged hypoxia, no increase in LDH release was observed. The bFGF mRNA expression was assessed with Northern blot and protein immunoreactivity with Western blot analysis. The brief period of hypoxia caused a 2.5-fold increase in bFGF mRNA and considerable bFGF protein expression 1 day later, but prolonged hypoxia caused increase in the expression of bFGF mRNA at 2 days and no protein expression until 3 days after the start of the hypoxia. When cells were subjected to prolonged hypoxia 2 days after brief hypoxia, however, no increase in bFGF mRNA was observed, while bFGF protein was expressed continuously. We also observed that exogenously applied bFGF reduced neuronal injury produced by prolonged hypoxia. The results obtained with this model suggest that brief hypoxia induces bFGF protein and thus tolerance to subsequent lethal hypoxia. Basic FGF might play a role as a tolerance-associated factor in this process. Thus, an in vitro model is useful for assessing the response of cortical neurons to hypoxic stress and for researching new factors related to ischemic tolerance. 相似文献
33.
This paper presents a dynamic integration algorithm to triangulate a surface from multiple range views. This integration technique is based on the reparameterization of the canonic subsets of the Venn diagram of the set of range views. We compute a model based onN views from a model based onN–1 views by processing only the surface segments visible in theN
th view. An experimental result shows that the proposed integration algorithm can process complex multipart objects containing holes. 相似文献
34.
The effect of fibre orientation on the dry sliding wear of continuous B(SiC) fibre reinforced aluminium alloy composites was investigated using a pin-on-disc wear testing machine. The metal-matrix composites (MMC) samples were tested in the normal (N), parallel (P) and antiparallel (AP) orientations sliding against a steel counter disc at a fixed speed of 1 m s–1 under loads of from 12 to 60 N.The results showed that for the matrix alloy and MMCs, the average wear increased linearly with load. Wear of the MMCs was insensitive to fibre content but for composites with fibre contents at or above the minimum of 16 vol% used for this work, the wear rate was about 18% of that of the unreinforced matrix. Fibre orientation had a minor effect on wear rate; the N orientation gave the lowest wear rate with the AP orientation slightly higher and the P orientation significantly higher.The average coefficients of friction of the MMCs in N and AP orientations decreased linearly with increased wear rate and non-linearly with increased load, but the P orientation was insensitive to either variable.It was concluded from these results and a metallographic examination that the mechanism of wear of MMCs was essentially oxidative wear of the matrix. The hard fibres modified this to slightly different degrees depending on their orientation relative to the wear surface and sliding direction. 相似文献
35.
Seven hundred three members of the Society for Industrial and Organizational Psychology indicated agreement or disagreement with 49 propositions regarding cognitive ability tests in organizations. There was consensus that cognitive ability tests are valid and fair, that they provide good but incomplete measures, that different abilities are necessary for different jobs, and that diversity is valuable. Items dealing with the unique status of cognitive ability were most likely to generate polarized opinions. A 2-factor model, classifying items as those reflecting societal concerns over the consequences of ability testing and those reflecting an emphasis on the unique status of "g," fit the data well, and these factors proved especially important for predicting responses to the more controversial items. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
36.
37.
38.
39.
Fast atom bombardment ionization with tandem mass spectrometry of both positive and negative ions is a useful technique for the identification of intact glycerophosphoethanolamine (GPE) phospholipids, providing information as to polar head group and fatty acyl substituents. In the identification of GPE molecular species, positive ion neutral loss scanning for 141 units was attempted to confirm the presence of the phosphoethanolamine polar head group. This scan was found to discriminate against the abundant subclass of phospholipids having an 1-O-alk-1'-enyl linkage, termed plasmalogens, as well as 1-O-alkyl ether species. The neutral loss process is suggested to involve attack of a carbonyl oxygen from either sn-1 or sn-2 on the sn-3 methylene carbon with loss of neutral phosphoethanolamine. Using FAB/MS/MS alone, it is not possible to differentiate between plasmalogens and other 1-O-alkyl ether molecular species having the same molecular weight. The combination of mild acid hydrolysis, which selectively hydrolyzes the labile 1-O-alk-1'-enyl bond, with subsequent FAB/MS/MS distinguished species of these distinct subclasses. Using these techniques and precursor ion scans for the arachidonoyl carboxylate anion, m/z 303, the arachidonic acid containing glycerophosphoethanolamine molecular species were identified and the relative abundance of arachidonoyl plasmalogen, alkylacyl, and 1,2-diacyl GPE molecular species in the human polymorphonuclear leukocyte (neutrophil) was determined to be 75.4%, 12.1%, and 12.5%, respectively. These values were not significantly different from that reported in the literature using conventional methodology. 相似文献
40.
Mary J. Garson Mary P. Zimmermann Christopher N. Battershill Janet L. Holden Peter T. Murphy 《Lipids》1994,29(7):509-516
The tropical marine spongeAmphimedon terpenensis (family Niphatidae, order Haplosclerida) has previously been shown to possess unusual lipids, including unusual fatty acids.
The biosynthetic origin of these fatty acids is of interest as the sponge supports a significant population of eubacterial
and cyanobacterial symbionts. The total fatty acid composition of the sponge was analyzed by gas chromatography/mass spectrometry
of the methyl esters. Among the most abundant of the fatty acids in intact tissue were 16∶0, 18∶0 and 3,7,11,15-tetramethylhexadecanoic
(phytanic) acid. In addition, three brominated fatty acids, (5E,9Z)-6-bromo-5,9-tetracosadienoic acid (24∶2Br), (5E,9Z)-6-bromo-5,9-pentacosadienoic acid (25∶2Br) and (5E,9Z)-6-bromo-5,9-hexacosadienoic acid (26∶2Br) were also present. The three brominated fatty acids, together with phytanic acid,
were isolated from both ectosomoal (superficial) and choanosomal (internal) regions of the sponge. Analysis of extracts prepared
from sponge/symbiont cells, partitioned by density gradient centrifugation on Ficoll, indicated that phytanic acid and the
three brominated fatty acids were associated with sponge cells only. Further, a fatty acid methyl ester sample from intact
tissue ofA. terpenensis was partitioned according to phospholipid class, and the brominated fatty acids were shown to be associated with the phosphatidylserine
and phosphatidylethanolamine fractions that are commonly present in marine sponge lipids. The phosphatidylcholine and phosphatidylglycerol
fractions were rich in the relatively shorter chain fatty acids (16∶0 and 18∶0). The association of brominated long-chain
fatty acids (LCFA) with sponge cells has been confirmed. The findings allow comment on the use of fatty acid profiles in chemotaxonomy
and permit further interpretation of LCFA biosynthetic pathways in sponges. The assignment of the sponge studied, which is
currently placed asA. terpenensis, is being supported to some extent, but the species is unusual in having C25 fatty acids as the major constituent in this group. Other factors, such as season or microenvironmental conditions, may influence
observed fatty acid composition which tends to reduce the usefulness of fatty acid profiles as markers in sponge chemotaxonomy. 相似文献