全文获取类型
收费全文 | 230953篇 |
免费 | 17458篇 |
国内免费 | 9134篇 |
专业分类
电工技术 | 12453篇 |
技术理论 | 24篇 |
综合类 | 14144篇 |
化学工业 | 38792篇 |
金属工艺 | 13141篇 |
机械仪表 | 14515篇 |
建筑科学 | 17563篇 |
矿业工程 | 7499篇 |
能源动力 | 6421篇 |
轻工业 | 13453篇 |
水利工程 | 3585篇 |
石油天然气 | 16618篇 |
武器工业 | 1647篇 |
无线电 | 25122篇 |
一般工业技术 | 27326篇 |
冶金工业 | 14929篇 |
原子能技术 | 2247篇 |
自动化技术 | 28066篇 |
出版年
2024年 | 993篇 |
2023年 | 3800篇 |
2022年 | 6477篇 |
2021年 | 9100篇 |
2020年 | 7077篇 |
2019年 | 6010篇 |
2018年 | 6728篇 |
2017年 | 7534篇 |
2016年 | 6747篇 |
2015年 | 8857篇 |
2014年 | 11243篇 |
2013年 | 13266篇 |
2012年 | 14204篇 |
2011年 | 15443篇 |
2010年 | 13417篇 |
2009年 | 12677篇 |
2008年 | 12342篇 |
2007年 | 11844篇 |
2006年 | 12337篇 |
2005年 | 10746篇 |
2004年 | 7260篇 |
2003年 | 6230篇 |
2002年 | 5460篇 |
2001年 | 4885篇 |
2000年 | 5432篇 |
1999年 | 6501篇 |
1998年 | 6152篇 |
1997年 | 4870篇 |
1996年 | 4446篇 |
1995年 | 3648篇 |
1994年 | 2923篇 |
1993年 | 2074篇 |
1992年 | 1549篇 |
1991年 | 1246篇 |
1990年 | 948篇 |
1989年 | 768篇 |
1988年 | 551篇 |
1987年 | 355篇 |
1986年 | 299篇 |
1985年 | 218篇 |
1984年 | 139篇 |
1983年 | 115篇 |
1982年 | 132篇 |
1981年 | 111篇 |
1980年 | 81篇 |
1979年 | 38篇 |
1978年 | 29篇 |
1977年 | 53篇 |
1976年 | 101篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
41.
新型超微晶软磁合金FePCCuMoSi微观结构缺陷的正电子湮没研究 总被引:1,自引:0,他引:1
用正电子湮没方法研究了新型超微晶软磁合金的微观结构缺陷,样品选用的是在不同温度下退火的Fe81P12C3Cu1Mo0.5Si2.5合金,结果表明,合金的微观结构构陷大小,密度随退火温度有规律地变化,这种现象可能与非晶的晶化过程有关。 相似文献
42.
利用挤压铸造制备氧化铝/锌合金复合材料,在扫描电镜(SEM)上观察复合材料的界面。结果表明,在复合材料中纤维与基体间存在致密界面层,合金元素通过适当的化学反应可改善纤维与基体间的结合;在凝固过程中,纤维/基体界面上的硅在共晶体的共生生长过程中起了领先相作用,导致复合材料的共晶转变是由铝硅共晶转变和锌铝共晶转变两者组成。 相似文献
43.
首先简单叙述了C3I系统在军事上的应用,然后针对我国各类大中型城市的交通现状及特点,涉及到城市交通管理、道路管理、车辆管理和城市交通管理指挥中心站、区域指挥站及各交叉路口控制站,提出将C3I系统体系结构运用到民用城市交通管理中去的构想。 相似文献
44.
45.
MJ Glantz PC Burger AH Friedman RA Radtke EW Massey SC Schold 《Canadian Metallurgical Quarterly》1994,44(11):2020-2027
When radiation is used to treat nervous system cancer, exposure of adjacent normal nervous system tissue is unavoidable, and radiation-induced injury may occur. Acute injury is usually mild and transient, but late forms of radiation-induced nervous system injury are usually progressive and debilitating. Treatment with corticosteroids, surgery, and antioxidants is often ineffective. We treated 11 patients with late radiation-induced nervous system injuries (eight with cerebral radionecrosis, one with a myelopathy, and two with plexopathies, all unresponsive to dexamethasone and prednisone) with full anticoagulation. Some recovery of function occurred in five of the eight patients with cerebral radionecrosis, and all the patients with myelopathy or plexopathy. Anticoagulation was continued for 3 to 6 months. In one patient with cerebral radionecrosis, symptoms recurred after discontinuation of anticoagulation and disappeared again after reinstitution of treatment. We hypothesize that anticoagulation may arrest and reverse small-vessel endothelial injury--the fundamental lesion of radiation necrosis--and produce clinical improvement in some patients. 相似文献
46.
47.
The even-flow harvest scheduling problem arises when the forestry agency has evolved into a rigid non-declining even-flow policy. In this paper, we investigate model formulation and solution strategies for the even-flow harvest scheduling problem. A multiple-objective linear programming problem is formulated for even-flow harvest scheduling problems with multiple-site classes and multiple periods. The aim of this problem is to simultaneously maximize a desired harvest-volume per hectare for each period of planning horizon and the total economic return. A block diagonal constraint structure, with many sets of network sub-problems and a set of coupling constraints, is identified in this linear programming problem. A longest path method for each of network sub-problems and a primal-dual steepest-edge algorithm for the entire problem are developed. The developed algorithm has been coded in Borland C++ and implemented on a personal computer. An illustrative example is used to display the detailed procedure for the developed algorithm and a real-world case study is used to show the trade-off between desired even-flow harvest volume policy and total economic return. Results show the potential benefits of this approach. 相似文献
48.
49.
Identification of a specific biomolecular target appropriately sensitive to a wide array of anesthetics has been elusive. At concentrations close to their respective ED50's for anesthesia in man or other species, 18 compounds, differing in potencies up to 66,000 fold, inhibited cytochrome P450 mediated metabolism of aminopyrine, a synthetic substrate, and arachidonic acid (AA), an endogenous substrate, in isolated liver microsomes. There was a highly significant correlation for both substrates between the absolute concentrations required for anesthesia (EC50) and for inhibition of P450 activity (Ki or IC50). The mean Ki/EC50 ratio was 0.97 for inhibition of aminopyrine demethylase. The mean IC50/EC50 ratios were 0.42 and 0.64 for inhibition of two AA-derived products and 2.8 for a third; a mean ratio of 1.4 for inhibition of overall AA metabolism suggests interaction of general anesthetics with a composite of P450 isozymes. The universal cytochrome P450 monooxygenases, in conjunction with other lipid oxygenases (cyclooxygenases and lipoxygenases) participate in the second messenger AA cascade. In nerve cells the sensitivity of these enzymes to hydrophobic neurodepressant drugs may underlie the state of general anesthesia: reversible disruption of intracellular and intercellular signalling without impairment of enzymes vital to cell respiration. 相似文献
50.