全文获取类型
收费全文 | 7250篇 |
免费 | 218篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 61篇 |
综合类 | 2篇 |
化学工业 | 853篇 |
金属工艺 | 77篇 |
机械仪表 | 92篇 |
建筑科学 | 82篇 |
矿业工程 | 4篇 |
能源动力 | 123篇 |
轻工业 | 576篇 |
水利工程 | 26篇 |
石油天然气 | 19篇 |
无线电 | 193篇 |
一般工业技术 | 570篇 |
冶金工业 | 4495篇 |
原子能技术 | 18篇 |
自动化技术 | 283篇 |
出版年
2024年 | 11篇 |
2023年 | 34篇 |
2022年 | 91篇 |
2021年 | 123篇 |
2020年 | 89篇 |
2019年 | 113篇 |
2018年 | 113篇 |
2017年 | 125篇 |
2016年 | 120篇 |
2015年 | 88篇 |
2014年 | 150篇 |
2013年 | 209篇 |
2012年 | 198篇 |
2011年 | 205篇 |
2010年 | 164篇 |
2009年 | 187篇 |
2008年 | 152篇 |
2007年 | 155篇 |
2006年 | 115篇 |
2005年 | 86篇 |
2004年 | 67篇 |
2003年 | 74篇 |
2002年 | 50篇 |
2001年 | 47篇 |
2000年 | 31篇 |
1999年 | 177篇 |
1998年 | 1492篇 |
1997年 | 850篇 |
1996年 | 554篇 |
1995年 | 288篇 |
1994年 | 259篇 |
1993年 | 279篇 |
1992年 | 44篇 |
1991年 | 55篇 |
1990年 | 54篇 |
1989年 | 59篇 |
1988年 | 73篇 |
1987年 | 34篇 |
1986年 | 35篇 |
1985年 | 30篇 |
1984年 | 6篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 19篇 |
1980年 | 39篇 |
1978年 | 4篇 |
1977年 | 88篇 |
1976年 | 197篇 |
1975年 | 6篇 |
1974年 | 3篇 |
排序方式: 共有7474条查询结果,搜索用时 15 毫秒
81.
In this paper the design of pole placement feedback controllers for interval plants is addressed within an Interval Analysis framework. Three main topics connected by the concept of interval Diophantine equation are treated: a relatively straightforward investigation about robust coprimeness of interval polynomials, a reliable computing approach for the design of pole placement controllers in the presence of inaccuracies of interval type, and the design of robust controllers with regional pole placement specifications. After explicitly characterizing a convex subset of robust controllers, the problem of designing non-fragile controllers is formulated as a design centering problem, which is then solved by a global optimization algorithm. Numerical examples illustrate the main characteristics of the approach proposed.This paper has been partially supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnológico–Brazil. 相似文献
82.
Optimal Locations of Groundwater Extractions in Coastal Aquifers 总被引:1,自引:0,他引:1
A regional water supply management model for coastal aquifers was developed. One of its outcomes is the definition of the
optimized locations for groundwater withdrawal. Such a tool permits the analysis of alternative plans for groundwater extraction
and the sustainable use of water resources in a coastal aquifer subject to saltwater intrusion. The principal components are
the evolutionary optimization and the analytical/numerical simulation models. The optimization technique looks for the best
well locations taking into consideration the economic results and the satisfaction of the societal water demand. However these
two concerns are conditioned by trying to control the saltwater intrusion, i.e., preserving the environmental equilibrium.
The simulation model uses the governing mathematical equations for groundwater movement to find the interface between freshwater
and saltwater. Because of the non-linearity in the system and the possibility of a jumping interface, a security distance
was defined. This is a controlling variable which can be set by the decision makers. The model was applied to a typical case
with interesting results. For example, diagrams showing the relationship between the location of the wells and the security
distance(s) are of importance to the managers. It was also crucial to have an understanding of the tradeoffs between groundwater
withdrawals, positions of the wells from the coast line, and the security distance. The model was also applied to a real case
in order to relate the extractions, distances and artificial recharge (not presented in this paper). 相似文献
83.
84.
85.
86.
The cytoskeletal components of hamster oocytes, zygotes, and spontaneously activated parthogenotes were examined after immunocytochemical labeling. Microtubules were found only in the anastral, tangentially arranged second meiotic spindle of unfertilized oocytes. Taxol treatment of unfertilized oocytes greatly augmented astral microtubules in both the metaphase II spindle and the cortex. Disruption of the meiotic spindle microtubules with nocodazole resulted in cortical chromosomal scattering. During hamster sperm incorporation and pronuclear formation, no sperm aster was detected in association with the male DNA. Instead, a large overlapping array of microtubules assembled in the cortex. By mitosis, this interphase array disassembled and an anastral metaphase spindle formed. Microtubule and chromatin configurations were also imaged in hamster oocytes injected with human sperm. Astral microtubules were absent from the sperm centrosome. The implications of these results are discussed in relation to the hamster oocyte penetration assay, a test commonly used by in vitro fertilization clinics to demonstrate the fertilizing ability of human sperm. We conclude that since hamsters and humans follow different methods of centrosome inheritance, maternal and paternal, respectively, the hamster may be an inappropriate model for exploring microtubule and centrosomal defects in humans or for assaying postinsemination forms of human male fertility defects. 相似文献
87.
AP West PJ Bjorkman DA Dougherty HA Lester 《Canadian Metallurgical Quarterly》1997,272(41):25468-25473
To provide material suitable for structural studies of the nicotinic acetylcholine receptor, we have expressed and purified the NH2-terminal extracellular domain of the mouse muscle alpha subunit. Several constructs were initially investigated using Xenopus oocytes as a convenient small scale expression system. A fusion protein (alpha210GPI) consisting of the 210 NH2-terminal amino acids of the alpha subunit and a glycosylphosphatidylinositol anchorage sequence conferred surface alpha-bungarotoxin binding in oocytes. Coexpression of alpha210GPI with an analogous construct made from the delta subunit showed no evidence of heterodimer formation. The alpha210GPI protein was chosen for large scale expression in transfected Chinese hamster ovary cells. The alpha210GPI protein was cleaved from these cells and purified on an immunoaffinity column. Gel and column chromatography show that the purified protein is processed as expected and exists as a monomer. The purified protein also retains the two distinct, conformation-specific binding sites expected for the correctly folded alpha subunit. Circular dichroism studies of alpha210GPI suggest that this region of the receptor includes considerable beta-sheet secondary structure, with a small proportion of alpha-helix. 相似文献
88.
89.
90.