全文获取类型
收费全文 | 6155篇 |
免费 | 525篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 63篇 |
综合类 | 3篇 |
化学工业 | 1750篇 |
金属工艺 | 163篇 |
机械仪表 | 212篇 |
建筑科学 | 144篇 |
矿业工程 | 13篇 |
能源动力 | 206篇 |
轻工业 | 1421篇 |
水利工程 | 89篇 |
石油天然气 | 41篇 |
无线电 | 296篇 |
一般工业技术 | 1022篇 |
冶金工业 | 513篇 |
原子能技术 | 69篇 |
自动化技术 | 691篇 |
出版年
2024年 | 27篇 |
2023年 | 78篇 |
2022年 | 211篇 |
2021年 | 387篇 |
2020年 | 239篇 |
2019年 | 314篇 |
2018年 | 323篇 |
2017年 | 315篇 |
2016年 | 286篇 |
2015年 | 217篇 |
2014年 | 306篇 |
2013年 | 417篇 |
2012年 | 422篇 |
2011年 | 443篇 |
2010年 | 337篇 |
2009年 | 335篇 |
2008年 | 277篇 |
2007年 | 246篇 |
2006年 | 179篇 |
2005年 | 136篇 |
2004年 | 106篇 |
2003年 | 103篇 |
2002年 | 89篇 |
2001年 | 74篇 |
2000年 | 67篇 |
1999年 | 70篇 |
1998年 | 168篇 |
1997年 | 103篇 |
1996年 | 85篇 |
1995年 | 62篇 |
1994年 | 54篇 |
1993年 | 34篇 |
1992年 | 25篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 26篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 16篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 12篇 |
1974年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有6696条查询结果,搜索用时 15 毫秒
31.
AR Santos JC Nery NC Duppre ME Gallo JT Filho PN Suffys WM Degrave 《Canadian Metallurgical Quarterly》1997,46(2):170-172
A case is described in which a pericardial branch of a nongrafted left internal mammary artery communicated directly with the distal left anterior descending artery, following saphenous vein bypass grafting. This type of collateralization following coronary artery bypass surgery seems to be very rare, and perhaps could protect the myocardium from severe ischemia. 相似文献
32.
By Cooperative Editing we mean the coordinated manipulation of information by a group of authors. During the editing process the (co-)authors need to communicate their ideas, drafts and constraints (remotely or face-to-face) until a final version of the information is achieved. For the different phases of this process - discussion of ideas, editing, cross-checking - different media or media integration are adequate. Furthermore, analysing the transition from individual work to group work, within different human activities, two pitfalls are often detected if computer support is considered: a) technological communication difficulties, especially if the group is remotely located on heterogeneous hardware, associated with a fall in productivity and frequent social inadequacies of the group's computer support; b) the lack of integrated media processing tools available for group editing. In order to solve these problems, we suggest that Multimedia can be applied in two ways: to effectively support the necessary group communication links; and to enhance the expressiveness of the information edited. To test this statement we have been conceptualising and implementing a prototype system. Most of the techniques involved can be used in other tools that need multimedia capabilities or that support other specific types of group activities. The innovative aspects of the work are the use of multimedia techniques to support demanding applications, possibly on cross-platforms, and the integration of several concepts to support cooperation. 相似文献
33.
Adelino Santos 《计算机科学技术学报》1993,8(3):67-79
CoMEdiA is a groupware tool which enables co-authors to cooperatively produce hypermedia documents.CoMEdiA allows co-authors to communicate their ideas,drafts,guidelines,constraints and annotations to other co-authors.In uses a mix of communication patterns,media and document organization to enable co-authors to keep on exchanging information(remotely or face-to-face),improving passages and modifying notes until a final document is achieved.We did not concentrate on th depth but on the breath of the features.Our efforts were on integrating and corrdinating concepts from collaboration,multimedia and hyper organization rather than on making a specialized system in any of them.We began with the text medium and are now including bitmaps and raster images.Later sound and video will also be integrated.In this paper we describe and sustain the available capacites. 相似文献
34.
35.
Highly transparent and conducting fluorine (F) doped cadmium oxide (CdO) thin films were deposited on glass slides by the sol-gel method. The films were doped by the addition of ammonium fluoride to the precursor solution whose optimum concentration was determined. The films were fired in an open atmosphere at 350 °C and after that, exposed to annealing treatments in different atmospheres (N2, N2/H2 mixture and Ar) at the same temperature. The films were characterized by ultraviolet-visible spectroscopy, X‐ray diffraction and scanning electron microscopy. The resistivity was determined by the four probes method and current-voltage measurements in accordance with the standard Van der Pauw configuration. The CdO:F thin films obtained, showed high polycrystalline quality and high transmission in the visible region (≥ 90%), shifting towards the blue region of the absorption edge as the fluorine concentration in the precursor solution was increased from 0 to 30 at.%. The lowest resistivity values were reached for the samples with F content higher or equal to 5% and annealed in either N2 or a 96/4 N2/H2 gas mixture. Our resistivity value reached in the CdO:F layers was 4.5 × 10− 4 Ω cm (20 Ω/square). 相似文献
36.
K M Cooper L Ribeiro P Alves V Vozikis S Tsitsamis G Alfredsson T L?vgren M Tuomola H Takalo A Iitia S S Sterk M Blokland D G Kennedy 《Food Additives & Contaminants》2003,20(9):804-812
Many zeranol immunoassay test kits cross-react with toxins formed by naturally occurring Fusarium spp. fungi, leading to false-positive screening results. This paper describes the evaluation and application of recently published, dry reagent time-resolved fluoroimmunoassays (TR-FIA) for zeranol and the toxin alpha-zearalenol. A ring test of bovine urine fortified with zeranol and/or alpha-zearalenol in four European Union National Reference Laboratories demonstrated that the TR-FIA tests were accurate and robust. The alpha-zearalenol TR-FIA satisfactorily quantified alpha-zearalenol in urine fortified at 10-30 ng ml(-1). The specificity-enhanced zeranol TR-FIA accurately quantified zeranol in the range 2-5 ng ml(-1) and gave no false-positive results in blank urine, even in the presence of 30 ng ml(-1) alpha-zearalenol. Zeranol TR-FIA specificity was demonstrated further by analysing incurred zeranol-free urine samples containing natural Fusarium spp. toxins. The TR-FIA yielded no false-positive results in the presence of up to 22 ng ml(-1) toxins. The performance of four commercially available zeranol immunoassay test kits was more variable. Three kits produced many false-positive results. One kit produced only one potential false-positive using a protocol that was longer than that of the TR-FIA. These TR-FIAs will be valuable tools to develop inspection criteria to distinguish illegal zeranol abuse from contamination arising from in vivo metabolism of Fusarium spp. toxins. 相似文献
37.
38.
Glutathione content and glutathione-dependent enzymes were measured in the liver of two fish species, gudgeon (Gobio gobio) and roach (Rutilus arcasii), from the river Bernesga (Spain) caught downstream and upstream of the waste site of several chemical industries. Animals from contaminated sites display a reduced glutathione concentration and a tendency to the decrease of glutathione S-transferase activity. Glutathione peroxidase activity was significantly elevated only in the liver of Gobio gobio and glutathione reductase activity in that of Rutilus arcasii. Our data indicate that the glutathione system constitutes a sensitive biochemical indicator of chemical pollution. Relative changes of glutathione and glutathione-dependent enzymes in both fish species suggest a different susceptibility to toxins. 相似文献
39.
BM Sandmaier R Storb KL Bennett FR Appelbaum EB Santos 《Canadian Metallurgical Quarterly》1998,91(9):3494-3502
Primary graft rejection after marrow transplantation occurs more frequently in patients receiving HLA-haploidentical compared with HLA-identical sibling transplants. Both human and experimental animal data suggest that the cells responsible for this phenomenon are either host natural killer (NK) cells, T cells, or both. To investigate the mechanisms of graft rejection, we have developed a canine model of marrow transplantation, which uses DLA-nonidentical unrelated donors in the absence of postgrafting immunosuppression. In this model most animals rejected their marrow grafts after a preparative regimen of 9.2 Gy total body irradiation (TBI). However, engraftment of DLA-nonidentical marrow can be facilitated when the recipients are pretreated with monoclonal antibody (MoAb) S5, which recognizes CD44. In this report, we extended these observations by first cloning the canine CD44 and, next, mapping the epitope recognized by S5, which was located in a region conserved among human and canine CD44 and was distinct from the hyaluronan binding domain. However, in vitro binding of S5 caused a conformational change in CD44, which allowed increased hyaluronan binding. Then, we reexamined the in vivo model of marrow transplantation and compared results with MoAb S5 to those with two other anti-CD44 MoAbs, IM7 and S3. Only MoAb S5 significantly increased the engraftment rate of DLA-nonidentical unrelated marrow, whereas the two other anti-CD44 MoAbs were ineffective. The enhanced in vivo effect was not related to differences in the MoAbs' avidities, since both S5 and IM7 had equivalent binding to CD44, but most likely related to the specific epitope that S5 recognizes. Thus, this study shows that the effect of the anti-CD44 MoAb S5 in facilitating engraftment is epitope specific and if one is to use an anti-CD44 to facilitate engraftment of marrow in humans, one cannot assume that any anti-CD44 would work. 相似文献
40.