全文获取类型
收费全文 | 591171篇 |
免费 | 7969篇 |
国内免费 | 2161篇 |
专业分类
电工技术 | 11280篇 |
综合类 | 578篇 |
化学工业 | 87824篇 |
金属工艺 | 22073篇 |
机械仪表 | 16766篇 |
建筑科学 | 16349篇 |
矿业工程 | 1247篇 |
能源动力 | 15756篇 |
轻工业 | 60058篇 |
水利工程 | 4516篇 |
石油天然气 | 2896篇 |
武器工业 | 16篇 |
无线电 | 76742篇 |
一般工业技术 | 107755篇 |
冶金工业 | 115922篇 |
原子能技术 | 8236篇 |
自动化技术 | 53287篇 |
出版年
2021年 | 3890篇 |
2019年 | 3530篇 |
2018年 | 5566篇 |
2017年 | 5524篇 |
2016年 | 5936篇 |
2015年 | 4843篇 |
2014年 | 7952篇 |
2013年 | 27386篇 |
2012年 | 13985篇 |
2011年 | 20092篇 |
2010年 | 15747篇 |
2009年 | 17835篇 |
2008年 | 19197篇 |
2007年 | 19547篇 |
2006年 | 17638篇 |
2005年 | 16377篇 |
2004年 | 15792篇 |
2003年 | 15533篇 |
2002年 | 15211篇 |
2001年 | 15479篇 |
2000年 | 14213篇 |
1999年 | 15316篇 |
1998年 | 37019篇 |
1997年 | 26568篇 |
1996年 | 20806篇 |
1995年 | 15941篇 |
1994年 | 14210篇 |
1993年 | 13699篇 |
1992年 | 9981篇 |
1991年 | 9659篇 |
1990年 | 8937篇 |
1989年 | 8663篇 |
1988年 | 8380篇 |
1987年 | 7055篇 |
1986年 | 6965篇 |
1985年 | 8517篇 |
1984年 | 7815篇 |
1983年 | 6903篇 |
1982年 | 6444篇 |
1981年 | 6413篇 |
1980年 | 6025篇 |
1979年 | 5790篇 |
1978年 | 5443篇 |
1977年 | 6782篇 |
1976年 | 9501篇 |
1975年 | 4530篇 |
1974年 | 4373篇 |
1973年 | 4224篇 |
1972年 | 3435篇 |
1971年 | 3014篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Hebb J.P. Jensen K.F. Thomas J. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(4):607-614
The radiative properties of patterned silicon wafers have a major impact on the two critical issues in rapid thermal processing (RTP), namely wafer temperature uniformity and wafer temperature measurement. The surface topography variation of the die area caused by patterning and the roughness of the wafer backside can have a significant effect on the radiative properties, but these effects are not well characterized. We report measurements of room temperature reflectance of a memory die, logic die, and various multilayered wafer backsides. The surface roughness of the die areas and wafer backsides is characterized using atomic force microscopy (AFM). These data are subsequently used to assess the effectiveness of thin film optics in providing approximations for the radiative properties of patterned wafers for RTP applications 相似文献
982.
In this paper, we study the minimum cross-entropy optimization problem subject to a general class of convex constraints. Using a simple geometric inequality and the conjugate inequality we demonstrate how to directly construct a "partial" geometric dual program which allows us to apply the dual perturbation method to derive the strong duality theorem and a dual-to-primal conversion formula. This approach generalizes the previous results of linearly, quadratically, and entropically constrained cross-entropy optimization problems and provides a platform for using general purpose optimizers to generate ε-optimal solution pair to the problem. 相似文献
983.
984.
Attempts have been made to extend SQL to work with multimedia databases. We are reserved on the representation ability of extended SQL to cope with the richness in content of multimedia data. In this paper we present an example of a multimedia database system, Computer Aided Facial Image Inference and Retrieval system (CAFIIR). The system stores and manages facial images and criminal records, providing necessary functions for crime identification. We would like to demonstrate some core techniques for multimedia database with CAFIIR system. Firstly, CAFIIR is a integrated system. Besides database management, there are image analysis, image composition, image aging, and report generation subsystems, providing means for problem solving. Secondly, the richness of multimedia data urges feature-based database for their management. CAFIIR is feature-based. A indexing mechanism,iconic index, has been proposed for indexing facial images using hierarchical self-organization neural network. The indexing method operates on complex feature measures and provides means for visual navigation. Thirdly, special retrieval methods for facial images have been developed, including visual browsing, similarity retrieval, free text retrieval and fuzzy retrieval. 相似文献
985.
The purpose and scope of the human genome project are discussed. Basic biological concepts underlying the project are reviewed. The two processes-logic and experimentation-used to understand DNA sequences are compared, and the process of obtaining the sequence is described. Two problem areas in this collaboration between biologists and computer scientists are examined. They arise from differences in training that can make communication difficult, and nomenclature problems 相似文献
986.
Two glial cell types surround olfactory axons and glomeruli in the olfactory bulb (OB) and may influence synapse development and regeneration. OB astrocytes resemble type-1 astrocytes, and OB ensheathing cells resemble non-myelinating Schwann cells. We have produced clonal OB astrocyte and ensheathing cell lines from rat neonatal and adult OB cultures by SV40 large T antigen transduction. These cell lines have been characterized by morphology, growth characteristics, immunophenotype, and ability to promote neurite outgrowth in vitro. Neonatal and adult ensheathing cell lines were found to support higher neurite outgrowth than OB astrocyte lines. Neonatal OB astrocyte lines were of two types, high and low outgrowth support. The low support astrocyte lines express J1 and a chondroitin sulfate-containing proteoglycan as do astrocytes encircling the neonatal glomeruli in vivo. The adult OB astrocyte cell lines supported lower levels of outgrowth than adult ensheathing cell lines. These results are consistent with a positive role for ensheathing cells in OB synapse regeneration, in vivo. Further, based on our results, we hypothesize that ensheathing cells and high-outgrowth astrocytes facilitate axon growth in vivo, while low outgrowth astrocytes inhibit axon growth and may facilitate glomerulus formation. 相似文献
987.
J Wight 《Canadian Metallurgical Quarterly》1993,27(2):175-176
A conference on 'Rationing of health care in medicine' was organised by the Royal College of Physicians and the Institute of Health Services Management on 11 November 1992. In his opening remarks the President, Professor Leslie Turnberg, declared it an opportune time to be hosting a conference on such a topical subject. Rationing of health services exists; the challenge is to find how to do it rationally. 相似文献
988.
It was found, that To?pa Peat Preparation (TPP) administered to healthy volunteers in doses of 100-300 mg/day during 14 days evoked the stimulation of the phagocytic and bactericidal activity of the granulocytes. The dose of 600 mg/day causes only a transient and insignificant increase of phagocytic and bactericidal properties of the granulocytes. 相似文献
989.
We have measured cardiovascular changes associated with insufflation of carbon dioxide and the reverse Trendelenburg position during laparoscopic cholecystectomy, using transoesophageal echocardiography in 13 healthy patients. End-tidal carbon dioxide values increased after insufflation of carbon dioxide, with values significantly (P < 0.05) increased after lateral tilt positioning. Creation of a pneumoperitoneum was associated with increases (P < 0.05) in left ventricular end-systolic wall stress, concomitant with increases (P < 0.01) in peak airway pressure and systemic arterial pressure. In addition, left ventricular end-diastolic area decreased (P < 0.05) after reverse Trendelenburg positioning. Left ventricular ejection fraction was maintained throughout the study. 相似文献
990.
JM Rolland O Bical A Laradi J Robinault R Benzidia A Vanetti G Herreman 《Canadian Metallurgical Quarterly》1993,86(9):1383-1385
A false left ventricular aneurysm and coronary artery aneurysm were discovered in a 29 year old patient with Beh?et's syndrome. The operation under cardiopulmonary bypass consisted of closing the neck of the false aneurysm by an endo-aneurysmal approach with a Gore-Tex patch. The coronary artery aneurysms were respected. There were no postoperative complications. Cardiac involvement is rare in Beh?et's syndrome (6%). The originality of this case is the association of two aneurysmal pathologies: the coronary and ventricular aneurysms due to the angiitis and the myocardial fragility induced by ischaemia. 相似文献