全文获取类型
收费全文 | 6665篇 |
免费 | 103篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 262篇 |
综合类 | 7篇 |
化学工业 | 984篇 |
金属工艺 | 154篇 |
机械仪表 | 99篇 |
建筑科学 | 72篇 |
矿业工程 | 2篇 |
能源动力 | 107篇 |
轻工业 | 288篇 |
水利工程 | 8篇 |
石油天然气 | 17篇 |
无线电 | 551篇 |
一般工业技术 | 1014篇 |
冶金工业 | 2762篇 |
原子能技术 | 160篇 |
自动化技术 | 300篇 |
出版年
2023年 | 14篇 |
2022年 | 50篇 |
2021年 | 97篇 |
2020年 | 37篇 |
2019年 | 56篇 |
2018年 | 59篇 |
2017年 | 59篇 |
2016年 | 75篇 |
2015年 | 56篇 |
2014年 | 83篇 |
2013年 | 182篇 |
2012年 | 168篇 |
2011年 | 233篇 |
2010年 | 158篇 |
2009年 | 160篇 |
2008年 | 171篇 |
2007年 | 183篇 |
2006年 | 154篇 |
2005年 | 156篇 |
2004年 | 139篇 |
2003年 | 141篇 |
2002年 | 105篇 |
2001年 | 105篇 |
2000年 | 105篇 |
1999年 | 169篇 |
1998年 | 1003篇 |
1997年 | 564篇 |
1996年 | 395篇 |
1995年 | 255篇 |
1994年 | 202篇 |
1993年 | 201篇 |
1992年 | 85篇 |
1991年 | 103篇 |
1990年 | 80篇 |
1989年 | 85篇 |
1988年 | 65篇 |
1987年 | 81篇 |
1986年 | 76篇 |
1985年 | 72篇 |
1984年 | 54篇 |
1983年 | 37篇 |
1982年 | 49篇 |
1981年 | 60篇 |
1980年 | 54篇 |
1979年 | 33篇 |
1978年 | 32篇 |
1977年 | 52篇 |
1976年 | 148篇 |
1975年 | 18篇 |
1974年 | 14篇 |
排序方式: 共有6787条查询结果,搜索用时 15 毫秒
81.
SB Guze 《Canadian Metallurgical Quarterly》1993,181(10):593-594
82.
83.
Cell recognition, signal induction, and symmetrical gene activation at the dorsal-ventral boundary of the developing Drosophila wing 总被引:2,自引:0,他引:2
Appendage formation in insects and vertebrates depends upon signals from both the anterior-posterior and dorsal-ventral (DV) axes. In Drosophila, wing formation is organized symmetrically around the DV boundary of the growing wing imaginal disc and requires interactions between dorsal and ventral cells. Compartmentalization of the wing disc, dorsal cell behavior, and the expression of two dorsally expressed putative signaling molecules, fringe (fng) and Serrate (Ser), are regulated by the apterous selector gene. Here, we demonstrate that fng and Ser have distinct roles in a novel cell recognition and signal induction process. fng serves as a boundary-determining molecule such that Ser is induced wherever cells expressing fng and cells not expressing fng are juxtaposed. Ser in turn triggers the expression of genes involved in wing growth and patterning on both sides of the DV boundary. 相似文献
84.
JG Jefferys RM Empson MA Whittington SB Prusiner 《Canadian Metallurgical Quarterly》1994,1(1-2):25-30
The human prion encephalopathy Creutzfeldt-Jakob disease often is manifest as rapidly progressing dementia with myoclonus and synchronous, periodic discharges. To investigate the electrophysiology of prion disease we used intra- and extra-cellular recordings from brain slices from Tg(SHaPrP+/+) 81 mice, which express Syrian hamster prion protein and which are susceptible to hamster-passaged scrapie isolates. Forty days after intracerebral inoculation with scrapie isolate Sc237, we recorded prolonged, epileptiform discharges in cortex and hippocampus. Neurological signs were subtle and histopathology was minimal. Central nervous system (CNS) dysfunction progressed; by 57 days the mice were ataxic, had spongiform histopathology and they died in <63 days. During the terminal phase, intrinsic neuronal properties changed dramatically and action potentials broadened from <4 to 20-100 ms in 30% of cortical cells. We conclude that brain dysfunction in experimental scrapie precedes clinical signs and spongiform histopathology, and is preserved in slices maintained in vitro, making it accessible to electrophysiological analysis. 相似文献
85.
86.
PURPOSE: Previous research has demonstrated that testosterone therapy causes a profound suppression of autoimmune disease in lacrimal glands of female mouse models of Sj?gren's syndrome. The aim of the present study was to determine whether other anabolic androgens, nonandrogenic steroids, or immunosuppressive agents might duplicate this hormonal effect. For comparative purposes, we also evaluated the influence of these various pharmacologic compounds on the tear volume, the magnitude of lymphocyte infiltration in the submandibular gland, and the extent of mucosal and peripheral lymphadenopathy. METHODS: Female MRL/MpJ-lpr/lpr mice were administered vehicle, steroids, or immunosuppressive compounds for 21 days after the onset of disease. Lacrimal glands and tears, as well as submandibular glands, spleens, and superior cervical and mesenteric lymph nodes were collected immediately before or after treatment and then processed for analysis. RESULTS: Our results showed that: (1) the immunosuppressive impact of testosterone on lymphocyte infiltration in lacrimal tissue was reproduced by the administration of 19-nortestosterone or cyclophosphamide, but not by therapy with 17 beta-estradiol, danazol, the experimental steroid Org 4094, cyclosporine A or dexamethasone; (2) treatment with testosterone, 19-nortestosterone, cyclophosphamide, or dexamethasone significantly reduced the extent of inflammation in salivary glands; (3) exposure to cyclophosphamide markedly diminished the size of lymphatic and splenic tissues, whereas glucocorticoid treatment only decreased the weight of superior cervical lymph nodes; and (4) administration of 17 beta-estradiol, Org 4094, or dexamethasone led to a significant decrease in tear volume. CONCLUSIONS: Overall, these results demonstrate that androgen or cyclophosphamide therapy may successfully ameliorate autoimmune expression in lacrimal and salivary glands of a female mouse model of Sj?gren's syndrome. 相似文献
87.
88.
89.
Y Tanaka N Enomoto S Kojima L Tang M Goto F Marumo C Sato 《Canadian Metallurgical Quarterly》1993,13(4):203-208
To examine HCV infection histologically, we attempted non-radioactive in situ hybridization of HCV-RNA in the liver. We amplified cDNA probe (360 base pairs) by PCR using the primers deduced from the core region of the HCV genome. The probe was labelled with digoxigenin by PCR and used for in situ hybridization on paraformaldehyde-fixed frozen liver sections. The hybrids were visualized immunohistochemically with alkaline-phosphatase-conjugated anti-digoxigenin and alkaline-phosphatase substrates. HCV-RNA-cDNA hybrids were detected in 21 of 24 patients with positive serum HCV markers, whereas there were no positive signals in the liver of 12 cases without HCV infection. The signal intensity of HCV-RNA-cDNA hybrids was abolished after RNase treatment. Various other specificity experiments also verified specific hybridization of HCV-RNA-cDNA. HCV-RNA was visualized in liver cells and most of them were regarded as hepatocytes from their characteristic features. The infected hepatocytes were frequently associated with mononuclear cell infiltration. Hepatocytes positive for HCV-RNA were sometimes binuclear and distributed in various patterns among cases tested. The present in situ hybridization of HCV RNA is highly sensitive and specific and the results suggest the host immune response to HCV-infected cells. 相似文献
90.