全文获取类型
收费全文 | 193220篇 |
免费 | 9056篇 |
国内免费 | 4579篇 |
专业分类
电工技术 | 6656篇 |
技术理论 | 11篇 |
综合类 | 8718篇 |
化学工业 | 29997篇 |
金属工艺 | 10454篇 |
机械仪表 | 9629篇 |
建筑科学 | 10747篇 |
矿业工程 | 3642篇 |
能源动力 | 4163篇 |
轻工业 | 10123篇 |
水利工程 | 2982篇 |
石油天然气 | 6560篇 |
武器工业 | 695篇 |
无线电 | 22888篇 |
一般工业技术 | 30070篇 |
冶金工业 | 8482篇 |
原子能技术 | 1487篇 |
自动化技术 | 39551篇 |
出版年
2024年 | 434篇 |
2023年 | 1765篇 |
2022年 | 2903篇 |
2021年 | 4028篇 |
2020年 | 3070篇 |
2019年 | 2602篇 |
2018年 | 16913篇 |
2017年 | 16315篇 |
2016年 | 12568篇 |
2015年 | 4466篇 |
2014年 | 5134篇 |
2013年 | 6464篇 |
2012年 | 9606篇 |
2011年 | 16384篇 |
2010年 | 14307篇 |
2009年 | 11533篇 |
2008年 | 12716篇 |
2007年 | 13341篇 |
2006年 | 6160篇 |
2005年 | 6598篇 |
2004年 | 4784篇 |
2003年 | 4345篇 |
2002年 | 3372篇 |
2001年 | 2849篇 |
2000年 | 3050篇 |
1999年 | 3441篇 |
1998年 | 2970篇 |
1997年 | 2576篇 |
1996年 | 2333篇 |
1995年 | 1934篇 |
1994年 | 1571篇 |
1993年 | 1232篇 |
1992年 | 975篇 |
1991年 | 760篇 |
1990年 | 601篇 |
1989年 | 500篇 |
1988年 | 400篇 |
1987年 | 295篇 |
1986年 | 206篇 |
1985年 | 176篇 |
1984年 | 108篇 |
1983年 | 81篇 |
1982年 | 87篇 |
1981年 | 57篇 |
1980年 | 47篇 |
1968年 | 49篇 |
1966年 | 48篇 |
1965年 | 50篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
This paper reports the findings of a detailed study of Web-based systems design (WBSD) practices in Ireland based on data
collected over a 3-year period (2002–2005), the objectives of which were to (1) contribute towards a richer understanding
of the current “real-world” context of WBSD by characterising the profile of a typical project (team size, timeframe, nature
of requirements, etc.) and identifying the key challenges, constraints, and imperatives (i.e. “mediating factors”) faced by
Web-based system designers, and (2) understand how those contextual parameters and mediating factors influence the activity
of WBSD as regards the selection and enactment of whatever design practices are therefore engaged (i.e. the use of methods,
procedures, etc.). Data was gathered through a survey which yielded 165 usable responses, and later through a series of semi-structured
qualitative interviews. Using grounded theory, an explanatory conceptual framework is derived, based on an extension of the
“method-in-action” model, the application of which to WBSD has not been previously investigated in depth. It is proposed that
this framework of WBSD issues is valuable in a number of ways to educators, researchers, practitioners, and method engineers. 相似文献
143.
144.
We present some sufficient and necessary conditions for convergent splitting of a non-Hermitian indefinite matrix. Some sufficient
conditions to determinate a matrix with a (strongly) dominant symmetric part for a class of boundary value problem are also
obtained. These results are applicable to identify the convergence of iterative methods for solving large sparse systems of
linear equations. 相似文献
145.
From the rhizomes of Polygonatum alte-lobatum, two new homologous series of 1,4-benzoquinones, polygonaquinones A and B, a novel homoisoflavanone, a new gentrogenin glycoside and 13 known compounds were isolated and characterized. The structures of the new compounds were determined as two homologous series of three 2,5-dihydroxy-3-methyl-6-alkyl-1,4-benzoquinones and three 2-hydroxy-3-methyl-6-alkyl-1,4-benzoquinones, with chain lengths C21 to C23, and 4',5,7-trihydroxy-6,8-dimethylhomoisoflavanone and gentrogenin 3-O-beta-D-glucopyranosyl(1-->2)-[beta-D-xylopyranosyl(1-->3)] -beta-D-glucopyranosyl(1-->4)-beta-D-galactopyranoside. 相似文献
146.
The aim of the present study was to determine the afferent connections of the nucleus accumbens in snakes, in particular its catecholaminergic input. For that purpose, in vitro and in vivo applications of retrograde tracers in the nucleus accumbens of Elaphe guttata were combined with tyrosine hydroxylase (TH) immunohistochemistry. Both techniques revealed telencephalic inputs to the nucleus accumbens originating from the diagonal band of Broca, ventral pallidum, amygdaloid complex, and dorsal cortex. Major diencephalic inputs arise from the dorsomedial thalamic nucleus and the hypothalamus. In the brainstem, a few retrogradely labeled cells were observed in the raphe nucleus and the locus coeruleus. Considerably more cells were found in the midbrain tegmentum. Within the confines of the locus coeruleus and, in particular, the midbrain tegmentum, retrogradely labeled cells stained also for TH suggesting that those areas constitute the major catecholaminergic input to the nucleus accumbens of snakes. The experimental approach used in the present study, in particular the in vitro technique, seems to be very suited for studying the development of basal ganglia organization of reptiles in the near future. 相似文献
147.
A new minimum zone method for evaluating flatness errors 总被引:1,自引:0,他引:1
A new minimum zone method for flatnes error analyis is proposed in this article. Based on the criteria for the minimum zone solution and strict rules for data exchange, a simple and rapid algorithm, called the control plane rotation scheme, is developed for the flatness analysis of a flat surface. Experimental work was performed, and some examples are given in terms of the minimum zone and least-squares solutions. 相似文献
149.
金属-橡胶硫化粘接过程中分子取向行为的间接证据 总被引:2,自引:1,他引:1
对金属-橡胶热硫化粘接复合体的剥离行为进行了研究,同一粘接试样的双向180°剥离试验显示出了巨大的差异。本文分析了弹性材料在硫化过程中的分子行为,并提出了相应的新假设,认为这是由于金属-橡胶在硫化粘接过程中分子取向交联行为所致。这种双向180°剥离破坏现象可被看作是金属-橡胶硫化粘接过程中分子取向行为的间接证据。 相似文献
150.
By using a mRNA differential display technique to search for salicylate suppressible genes, we identified a cDNA in human foreskin fibroblasts, which by GenBankTM DNA data base search shows sequence homology to the recently reported cullin/Cdc53 (CUL) family genes, especially CUL-3. We have cloned the full-length human CUL-3 (Hs-CUL-3) cDNA. It encodes a 768-amino acid polypeptide and has a predicted molecular weight of 88,939. The amino acid sequence of Hs-CUL-3 shows 46% homology to that of its Caenorhabditis elegans ortholog, Ce-CUL-3, and 27 and 23% to that of Hs-CUL-1 and Hs-CUL-2, respectively. Northern blot analysis showed that phorbol 12-myristate 13-acetate increased the expression of Hs-CUL-3 mRNA in a concentration- and time-dependent manner, and this increase was inhibited by sodium salicylate. Hs-CUL-3 widely expressed in human tissues and its expression in cultured COLO205 colon cancer cells was increased when compared with that in normal colon cells. It is likely that Hs-CUL-3 is involved in cell proliferation control. 相似文献