全文获取类型
收费全文 | 3534篇 |
免费 | 63篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 24篇 |
化学工业 | 387篇 |
金属工艺 | 63篇 |
机械仪表 | 41篇 |
建筑科学 | 107篇 |
矿业工程 | 35篇 |
能源动力 | 53篇 |
轻工业 | 227篇 |
水利工程 | 22篇 |
石油天然气 | 13篇 |
无线电 | 250篇 |
一般工业技术 | 305篇 |
冶金工业 | 1714篇 |
原子能技术 | 31篇 |
自动化技术 | 329篇 |
出版年
2021年 | 33篇 |
2020年 | 26篇 |
2019年 | 24篇 |
2018年 | 30篇 |
2017年 | 43篇 |
2016年 | 31篇 |
2015年 | 26篇 |
2014年 | 42篇 |
2013年 | 145篇 |
2012年 | 57篇 |
2011年 | 92篇 |
2010年 | 64篇 |
2009年 | 71篇 |
2008年 | 95篇 |
2007年 | 82篇 |
2006年 | 71篇 |
2005年 | 79篇 |
2004年 | 58篇 |
2003年 | 76篇 |
2002年 | 58篇 |
2001年 | 57篇 |
2000年 | 55篇 |
1999年 | 99篇 |
1998年 | 415篇 |
1997年 | 285篇 |
1996年 | 198篇 |
1995年 | 125篇 |
1994年 | 117篇 |
1993年 | 131篇 |
1992年 | 49篇 |
1991年 | 42篇 |
1990年 | 53篇 |
1989年 | 51篇 |
1988年 | 40篇 |
1987年 | 31篇 |
1986年 | 41篇 |
1985年 | 32篇 |
1984年 | 27篇 |
1983年 | 26篇 |
1982年 | 33篇 |
1981年 | 26篇 |
1980年 | 41篇 |
1979年 | 36篇 |
1978年 | 33篇 |
1977年 | 59篇 |
1976年 | 118篇 |
1975年 | 21篇 |
1974年 | 20篇 |
1973年 | 19篇 |
1971年 | 15篇 |
排序方式: 共有3601条查询结果,搜索用时 15 毫秒
21.
Acute and chronic antidepressant drug treatments respectively decrease and increase the aggressive behaviour of resident rats during encounters with unfamiliar conspecifics. We have now examined the effect of the 5-hydroxytryptamine1A receptor antagonist, WAY-100635, on fluoxetine-, paroxetine- or venlafaxine-induced changes in aggression. WAY-100635 (0.1 mg/kg), which did not modify behaviour when given alone, potentiated the venlafaxine (5.54 mg/kg)-induced reduction in aggression after acute treatment and, during chronic treatment, accelerated the fluoxetine (0.34 mg/kg/day)-induced increase in aggression, from day 5 to day 2. A similar change in time course was seen with paroxetine (0.33 mg/kg/day), although the increase in aggression was smaller. Venlafaxine (5.54 mg/kg/day, alone or co-administered with WAY-100635) increased aggression by day 2. During chronic treatment, therefore, venlafaxine, at the dose used, had a more rapid onset of action than either fluoxetine or paroxetine, whereas the fluoxetine- and paroxetine-, but not the venlafaxine-, induced increase in aggression was accelerated by WAY-100635. These studies further support the hypothesis that selective blockade of the 5-hydroxytryptamine1A receptor augments the effects of antidepressant drugs in an animal model predictive of antidepressant activity, presumably by concomitant blockade of the somatodendritic 5-hydroxytryptamine1A autoreceptor-mediated negative feedback system of serotonergic neurones. 相似文献
22.
HJ Voeller M Augustus V Madike GS Bova KC Carter EP Gelmann 《Canadian Metallurgical Quarterly》1997,57(20):4455-4459
Loss of heterozygosity at chromosome 8p21-22 is common in human prostate cancer, suggesting the presence of one or more tumor suppressor genes at this locus. A homeobox gene that is expressed specifically in adult human prostate, NKX3.1, the expression of which is regulated by androgen, maps to chromosome 8p21. Fine structure in situ mapping showed that NKX3.1 is proximal to MSR32 (macrophage scavenger receptor type II) and LPL (human lipoprotein lipase) and very close to NEFL (human neurofilament light chain) on 8p21. Single-strand conformational polymorphism analysis of 48 radical prostatectomy cancer specimens and 3 metastases for the entire coding region of NKX3.1 showed no tumor-specific sequence alterations in 50 specimens and total absence of the gene in 1 specimen known to have a biallelic deletion of 8p21. NKX3.1 was found to have a polymorphism at nucleotide 154 in codon 52 that resulted in a CGC-->TGC sequence change and an Arg-->Cys amino acid alteration (R52C). This polymorphism was present in 20% of DNA samples. If NKX3.1 is a target of the 8p21 LOH, it is not via disruption of the coding region of the gene. 相似文献
23.
The effects of azadirachtin, salannin, nimbin, and 6-desacetylnimbin on ecdysone 20-monooxygenase (E-20-M) activity were examined in three insect species. Homogenates of wandering stage third instar larvae of Drosophila melanogaster, or abdomens from adult female Aedes aegypti, or fat body or midgut from fifth instar larvae of Manduca sexta were incubated with radiolabeled ecdysone and increasing concentrations (from 1 x 10(-8) to 1 x 10(-3) M) of the four compounds isolated from seed kernels of the neem tree, Azadirachta indica. All four neem tree compounds were found to inhibit, in a dose-dependent fashion, the E-20-M activity in three insect species. The concentration of these compounds required to elicit a 50% inhibition of this steroid hydroxylase activity in the three insect species examined ranged from approximately 2 x 10(-5) to 1 x 10(-3). 相似文献
24.
AD Mitchell AE Auletta D Clive PE Kirby MM Moore BC Myhr 《Canadian Metallurgical Quarterly》1997,394(1-3):177-303
The L5178Y/tk+/- (-)3.7.2C mouse lymphoma assay (MLA) which detects mutations affecting the heterozygous thymidine kinase (tk) locus is capable of responding to chemicals acting as clastogens as well as point mutagens. Improvements in the assay to enhance detection of this spectrum of genetic events are summarized, and criteria for evaluating the data are defined. Using these criteria, the Phase III Work Group reviewed and evaluated literature containing MLA results published from 1976 through 1993. The data base included 602 chemicals of which 343 were evaluated as positive, 44 negative, 18 equivocal, 54 apparently inappropriate for evaluation in this test system with the published protocols, and 142 that were inadequately tested, and thus a definitive call could not be made. The overall performance of the assay is summarized by chemical class, and the outcome of testing 260 chemicals in the MLA is compared with Gene-Tox and National Toxicology Program evaluations of rodent carcinogenesis bioassay results for the same chemicals. Based on the Work Group's evaluation of published MLA data for chemicals that were considered adequately tested, it is concluded that for most chemicals the L5178Y/tk+/- mouse lymphoma assay is eminently well suited for genotoxicity testing and for predicting the potential for carcinogenicity. 相似文献
25.
D Barry J Bea D Bernd T DeFauw C Marr T McCormick JK Mitchell M O'Neil M Pittman D Strum 《Canadian Metallurgical Quarterly》1994,68(11):42, 44-46, 48
In cooperation with McManis Associates, Hospitals & Health Networks recently convened a CEO summit on physician/hospital integration activities. In the third report of a three-part series on the summit, leading health care executives discuss investor capital needs, strategic information management needs, and the management competencies required for capitated managed care success. 相似文献
26.
Sucrose synthesis of nanoparticulate alumina 总被引:6,自引:0,他引:6
L. D. Mitchell P. S. Whitfield J. Margeson J. J. Beaudoin 《Journal of Materials Science Letters》2002,21(22):1773-1775
27.
Two polypeptide antigens with molecular sizes of 34,000 daltons (34 kDa) and 38 kDa were separated from heated cells of a human clinical treponeme strain G7201 and Treponema denticola ATCC 35404, respectively. The rabbit polyclonal antisera against these antigens were produced and examined for their immunological reactions with the two heated antigens or intact spirochetal cells. Immunoblot analysis showed that the 34-kDa protein was also detected in T. denticola ATCC 35404 and ATCC 33520, and the 38-kDa protein was detected only in the two ATCC strains. Immunoelectron microscopy using the two rabbit antisera and protein A-gold complexes demonstrated that the 38-kDa protein antigen was present on the axial flagella of two T. denticola strains, and that the 34-kDa protein was located in the axial flagella of the G7201 cell, but neither in axial flagella nor on outer envelopes of the two ATCC strains cells, suggesting that the native 34-kDa axial flagellar protein of the G7201 strain may be different from that of T. denticola in terms of immunological reactivity. 相似文献
28.
29.
EF Bernstein FJ Sullivan JB Mitchell GD Salomon E Glatstein 《Canadian Metallurgical Quarterly》1993,20(3):435-453
Radiation therapy exerts both acute and chronic effects on normal tissue included within treatment fields. The physics of radiation therapy and treatment techniques to minimize deleterious effects of radiation are presented. Management of radiation-damaged skin is discussed. Radiation effect on tissue, wound healing, and tumorigenesis also are reviewed. 相似文献
30.
EL Nazarenko RP Gorshkova VA Zubkov AS Shashkov EP Ivanova IuS Ovodov 《Canadian Metallurgical Quarterly》1993,19(7):733-739
An acidic polysaccharide from Alteromonas sp. 4MC17 is built up of trisaccharide repeating units containing D-glucose, D-mannose and D-galacturonic acid residues. On the basis of methylation studies, 1H and 13C NMR-spectroscopy data, including two-dimensional homonuclear correlation spectroscopy and nuclear Overhauser effects, the following structure was suggested for the polysaccharide repeating unit: -->4)-beta-D-Glcp-(1-->4)-beta-D-GalpA-(1-->4)-beta-D-Manp-( 1-->. 相似文献