全文获取类型
收费全文 | 281397篇 |
免费 | 4544篇 |
国内免费 | 1933篇 |
专业分类
电工技术 | 5780篇 |
技术理论 | 5篇 |
综合类 | 1220篇 |
化学工业 | 44896篇 |
金属工艺 | 11870篇 |
机械仪表 | 8307篇 |
建筑科学 | 7086篇 |
矿业工程 | 1712篇 |
能源动力 | 6129篇 |
轻工业 | 27393篇 |
水利工程 | 3086篇 |
石油天然气 | 6158篇 |
武器工业 | 244篇 |
无线电 | 29986篇 |
一般工业技术 | 52791篇 |
冶金工业 | 52803篇 |
原子能技术 | 5979篇 |
自动化技术 | 22429篇 |
出版年
2021年 | 2612篇 |
2019年 | 2265篇 |
2018年 | 3603篇 |
2017年 | 3570篇 |
2016年 | 3909篇 |
2015年 | 2962篇 |
2014年 | 4819篇 |
2013年 | 12088篇 |
2012年 | 8126篇 |
2011年 | 10886篇 |
2010年 | 8615篇 |
2009年 | 9217篇 |
2008年 | 10073篇 |
2007年 | 10217篇 |
2006年 | 8980篇 |
2005年 | 8015篇 |
2004年 | 7165篇 |
2003年 | 6774篇 |
2002年 | 6749篇 |
2001年 | 6882篇 |
2000年 | 6426篇 |
1999年 | 6405篇 |
1998年 | 14770篇 |
1997年 | 10788篇 |
1996年 | 8222篇 |
1995年 | 6182篇 |
1994年 | 5632篇 |
1993年 | 5521篇 |
1992年 | 4274篇 |
1991年 | 4067篇 |
1990年 | 4136篇 |
1989年 | 4078篇 |
1988年 | 3793篇 |
1987年 | 3264篇 |
1986年 | 3281篇 |
1985年 | 3664篇 |
1984年 | 3515篇 |
1983年 | 3252篇 |
1982年 | 2863篇 |
1981年 | 3091篇 |
1980年 | 2830篇 |
1979年 | 2994篇 |
1978年 | 2878篇 |
1977年 | 3092篇 |
1976年 | 4056篇 |
1975年 | 2577篇 |
1974年 | 2393篇 |
1973年 | 2429篇 |
1972年 | 2065篇 |
1971年 | 1852篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
51.
L Guarente 《Canadian Metallurgical Quarterly》1997,11(19):2449-2455
52.
53.
54.
55.
ME Sutherlin I Nishimori T Caffrey EP Bennett H Hassan U Mandel D Mack T Iwamura H Clausen MA Hollingsworth 《Canadian Metallurgical Quarterly》1997,57(21):4744-4748
The levels of mRNA expression of three UDP-N-acetyl-alpha-D-galactosamine:polypeptide GalNAc N-acetylgalactosaminyltransferases (GalNAc-transferases) were quantified for human adenocarcinoma cell lines from pancreas, colon, stomach, and breast. Two of the GalNAc-transferases, GalNAc-T1 and GalNAc-T2, were expressed constitutively and at low levels in most or all cell lines examined. A third GalNAc-transferase, GalNAc-T3, was differentially expressed. Well-differentiated adenocarcinoma cell lines expressed high levels and moderately differentiated cell lines expressed lower levels of GalNAc-T3. Cell lines classified as poorly differentiated failed to express GalNAc-T3 mRNA at levels that could be detected by Northern blot analysis. Differential expression of the GalNAc-T3 protein was confirmed in these cell lines by Western blotting. We propose that glycosylation in tumor cell lines may be regulated in part by differential expression of GalNAc-transferases, and we suggest that GalNAc-T3 gene expression may be a molecular indicator of differentiated adenocarcinoma. 相似文献
56.
Cresswell M.W. Allen R.A. Guthrie W.F. Sniegowski J.J. Ghoshtagore R.N. Linholm L.W. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(2):182-193
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features 相似文献
57.
P Virsik-Peuckert M Rave-Fr?nk U Langebrake H Schmidberger 《Canadian Metallurgical Quarterly》1997,148(3):209-215
The modulatory role of locally produced cyclooxygenase products and endothelium-derived nitric oxide in controlling vascular tone was investigated in bovine intra-mammary artery. Vascular reactivity initiated by vasoactive compounds, endothelin-1 (ET-1), bradykinin (BK), and substance P (SP) was measured isometrically in an isolated tissue bath. The effects of a cyclooxygenase inhibitor, indomethacin (10(-5) M) and an inhibitor of nitric oxide production, N omega-Nitro L-Arginine (L-NNA: 3 x 10(-4) M) were determined during agonist-mediated responses. Indomethacin alone markedly enhanced vascular contraction produced by ET-1, while L-NNA did not. Inhibition of endothelium-derived nitric oxide synthesis by L-NNA, however, significantly attenuated BK- and SP-induced vascular relaxations, whereas indomethacin had slight influence. The potentiation between indomethacin and L-NNA in regulating vasomotor tone was not observed in this vascular bed. Thus, it appeared that both the cyclooxygenase and endothelium-derived nitric oxide pathways participated in modifying vascular reactivity. Domination of one pathway over the other depended upon the agonist used to stimulate vascular tissue. 相似文献
58.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications 相似文献
59.
A preliminary report presenting the results of fibular strut grafting in the severely resorbed mandibular and maxillary region is presented. Thirteen patients were treated due to severe resorption of alveolar and basilar bone of 49 segments of the mandible and the maxilla. Two patients additionally had pathological fractures of the mandible. In 10 cases the strut graft was harvested by means of a new minimally invasive technique. After modelling the fibular bone it was fixed to the recipient site by miniscrews or implants. After a mean follow-up period of 20 months (max. 31, min. 11 months) a retrospective analysis of clinical and radiological findings was carried out. It showed that a mean augmentation of 16 mm was achieved. Compared to other studies the fibular strut graft was resorbed less, and due to the primary stability it could be used for the treatment of fractures of the mandible. No more than natural resorption was observed when the patients received their prostheses fixed to dental implants. 相似文献
60.
Uses a Markov process to model a real-time expert system architecture characterized by message passing and event-driven scheduling. The model is applied to the performance evaluation of rule grouping for real-time expert systems running on this architecture. An optimizing algorithm based on Kernighan-Lin heuristic graph partitioning for the real-time architecture is developed and a demonstration system based on the model and algorithm has been developed and tested on a portion of the advanced GPS receiver (AGR) and manned manoeuvring unit (MMU) knowledge bases 相似文献