全文获取类型
收费全文 | 5076篇 |
免费 | 58篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 23篇 |
综合类 | 2篇 |
化学工业 | 294篇 |
金属工艺 | 39篇 |
机械仪表 | 34篇 |
建筑科学 | 77篇 |
矿业工程 | 6篇 |
能源动力 | 61篇 |
轻工业 | 267篇 |
水利工程 | 21篇 |
石油天然气 | 2篇 |
无线电 | 233篇 |
一般工业技术 | 277篇 |
冶金工业 | 3573篇 |
原子能技术 | 23篇 |
自动化技术 | 205篇 |
出版年
2023年 | 12篇 |
2022年 | 16篇 |
2021年 | 22篇 |
2020年 | 10篇 |
2019年 | 18篇 |
2018年 | 25篇 |
2017年 | 25篇 |
2016年 | 37篇 |
2015年 | 30篇 |
2014年 | 23篇 |
2013年 | 80篇 |
2012年 | 51篇 |
2011年 | 100篇 |
2010年 | 63篇 |
2009年 | 68篇 |
2008年 | 91篇 |
2007年 | 93篇 |
2006年 | 98篇 |
2005年 | 76篇 |
2004年 | 56篇 |
2003年 | 57篇 |
2002年 | 68篇 |
2001年 | 60篇 |
2000年 | 35篇 |
1999年 | 139篇 |
1998年 | 1126篇 |
1997年 | 672篇 |
1996年 | 365篇 |
1995年 | 238篇 |
1994年 | 215篇 |
1993年 | 230篇 |
1992年 | 48篇 |
1991年 | 52篇 |
1990年 | 51篇 |
1989年 | 70篇 |
1988年 | 54篇 |
1987年 | 49篇 |
1986年 | 41篇 |
1985年 | 46篇 |
1984年 | 26篇 |
1983年 | 25篇 |
1982年 | 35篇 |
1981年 | 26篇 |
1980年 | 42篇 |
1979年 | 12篇 |
1978年 | 15篇 |
1977年 | 84篇 |
1976年 | 183篇 |
1975年 | 13篇 |
1973年 | 10篇 |
排序方式: 共有5137条查询结果,搜索用时 31 毫秒
61.
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
62.
63.
64.
65.
66.
67.
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
68.
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
69.
70.
RA Reinhardt MP Masada GK Johnson LM DuBois GJ Seymour AC Allison 《Canadian Metallurgical Quarterly》1993,20(7):514-519
Interleukin (IL)-1 alpha and beta are cytokines which can mediate inflammatory, bone resorbing, and reparative effects in the periodontium, but few longitudinal data exist exploring their role following periodontal therapy. This study examined gingival crevicular fluid (GCF) concentrations of IL-1 alpha and IL-1 beta at sites with shallow sulci (SS) or inflamed moderate/advanced pockets (M/AP) before and 6 months after treatment with closed scaling/root planing (SC/RP) or papillary flap debridement (PFD), all in the same subject (n = 14 patients). No significant differences were noted in IL-1 alpha or beta concentrations (determined with two-site enzyme-linked immunosorbent assays) between SS and M/AP sites at baseline. While both therapies improved clinical parameters of periodontal disease, IL-1 alpha concentration increased significantly (p < 0.05) in M/AP-PFD sites 6 months after treatment, but were unchanged in other groups. IL-1 beta concentrations were numerically lower after therapy, except for a significant increase (p < 0.05) in M/AP-PFD sites. These data suggest that surgical wound healing in an inflamed, plaque-infected site (M/AP-PFD) results in prolonged production of IL-1, which may be a reflection of the extent of tissue trauma and delayed wound healing. In spite of increased IL-1 levels, these sites demonstrated significant short-term improvement in clinical attachment level (+ 1.8 mm, p < or = 0.001) postoperatively. 相似文献