全文获取类型
收费全文 | 70369篇 |
免费 | 7773篇 |
国内免费 | 5808篇 |
专业分类
电工技术 | 6302篇 |
技术理论 | 1篇 |
综合类 | 6790篇 |
化学工业 | 8463篇 |
金属工艺 | 4679篇 |
机械仪表 | 4829篇 |
建筑科学 | 4997篇 |
矿业工程 | 2189篇 |
能源动力 | 1566篇 |
轻工业 | 7838篇 |
水利工程 | 2319篇 |
石油天然气 | 2582篇 |
武器工业 | 848篇 |
无线电 | 7683篇 |
一般工业技术 | 6651篇 |
冶金工业 | 3858篇 |
原子能技术 | 1461篇 |
自动化技术 | 10894篇 |
出版年
2024年 | 359篇 |
2023年 | 1076篇 |
2022年 | 2679篇 |
2021年 | 3507篇 |
2020年 | 2519篇 |
2019年 | 1737篇 |
2018年 | 1905篇 |
2017年 | 2175篇 |
2016年 | 1950篇 |
2015年 | 3013篇 |
2014年 | 3840篇 |
2013年 | 4664篇 |
2012年 | 5721篇 |
2011年 | 6119篇 |
2010年 | 5645篇 |
2009年 | 5518篇 |
2008年 | 5499篇 |
2007年 | 5434篇 |
2006年 | 4694篇 |
2005年 | 3607篇 |
2004年 | 2608篇 |
2003年 | 1886篇 |
2002年 | 1667篇 |
2001年 | 1616篇 |
2000年 | 1204篇 |
1999年 | 627篇 |
1998年 | 597篇 |
1997年 | 446篇 |
1996年 | 307篇 |
1995年 | 225篇 |
1994年 | 172篇 |
1993年 | 148篇 |
1992年 | 76篇 |
1991年 | 64篇 |
1990年 | 71篇 |
1989年 | 73篇 |
1988年 | 39篇 |
1987年 | 43篇 |
1986年 | 31篇 |
1985年 | 34篇 |
1984年 | 34篇 |
1983年 | 30篇 |
1982年 | 22篇 |
1981年 | 56篇 |
1980年 | 35篇 |
1979年 | 26篇 |
1978年 | 14篇 |
1977年 | 28篇 |
1976年 | 32篇 |
1959年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Recent years have witnessed a rapid growth of interest in the study of the dynamic behavior of replenishment rules of bullwhip effect. We prove that bullwhip effect and butterfly effect share a same the self-oscillation amplifying mechanism that is the ordering decisions the supplier self-oscillation amplify the perturbations brought by the errors in the processing of retailers' demand information. This results as an explicit self-similar structure of the sensitivity of the system to the initial values duty to the nonlinear mechanism. In this paper, the causes process of the bullwhip effect is described as the internal nonlinear mechanism and study on the complexity of bullwhip effect for order-up-to policy under demand signal processing. The methodology is based on fractal and chaotic theory and allows important insights to be gained about the complexity behavior of bullwhip effect. 相似文献
72.
73.
74.
76.
A mechanical model is presented in this paper to describe the initiating and propagating of brittle cracks. Two criteria have been deduced from the model to determine the effects of such factors as local stress state, surface and grain boundary energies as well as local grain boundary orientation on the initiating and propagating of both intergranular and transgranular brittle cracks. By which the role of adding B in Ni3Al base alloys to improve their ductility,temper and hydrogen embrittlements in steels and other alloys as well as the random feature of brittle crack initiation could be explained 相似文献
77.
We discuss circuit parameters that limit the precision of basic dynamic current-memory cells. In addition to analyzing current-copying errors caused by the finite output conductances of the current sources and by the clock-feedthrough (CFT) of the feedback switches, we analyze the noise performance of the basic memory cell. To reduce CFT and noise, we propose a novel circuit based on Miller capacitance-enhancement. Measurement results of memory cells integrated in a 1-μm CMOS process confirm the theoretical findings; with our CFT and noise reduction technique based on Miller enhanced capacitance and dummy switches, we achieve a dynamic range of 11 b at clock frequencies greater than 100 kHz 相似文献
78.
B Antonsson DB Kassel G Di Paolo R Lutjens BM Riederer G Grenningloh 《Canadian Metallurgical Quarterly》1998,273(14):8439-8446
SCG10 is a neuron-specific, membrane-associated protein that is highly concentrated in growth cones of developing neurons. Previous studies have suggested that it is a regulator of microtubule dynamics and that it may influence microtubule polymerization in growth cones. Here, we demonstrate that in vivo, SCG10 exists in both phosphorylated and unphosphorylated forms. By two-dimensional gel electrophoresis, two phosphoisoforms were detected in neonatal rat brain. Using in vitro phosphorylated recombinant protein, four phosphorylation sites were identified in the SCG10 sequence. Ser-50 and Ser-97 were the target sites for protein kinase A, Ser-62 and Ser-73 for mitogen-activated protein kinase and Ser-73 for cyclin-dependent kinase. We also show that overexpression of SCG10 induces a disruption of the microtubule network in COS-7 cells. By expressing different phosphorylation site mutants, we have dissected the roles of the individual phosphorylation sites in regulating its microtubule-destabilizing activity. We show that nonphosphorylatable mutants have increased activity, whereas mutants in which phosphorylation is mimicked by serine-to-aspartate substitutions have decreased activity. These data suggest that the microtubule-destabilizing activity of SCG10 is regulated by phosphorylation, and that SCG10 may link signal transduction of growth or guidance cues involving serine/threonine protein kinases to alterations of microtubule dynamics in the growth cone. 相似文献
79.
80.
L Giorgi A Di Filippo A Franchini L Rizzo S Benvenuti M Conti GP Novelli 《Canadian Metallurgical Quarterly》1994,60(1-2):43-47
OBJECTIVE: The reflex response to orotracheal intubation provokes an increase of arterial pressure accompanied by an increase of chorioides volume and a consequent ocular hypertone. There are several methods to reduce the reflex response due to intubation. One of the most effective is topical anaesthesia of larynx and trachea. Experiments were directed to evaluate the efficacy of topical anaesthesia to reduce the intraocular hypertone due to orotracheal intubation. DESIGN: A prospective randomized mask study was conduct on patients undergoing ophthalmologic (anterior segment) surgery at the Eye Clinic of Florence University. METHODS: Intraocular pressure was measured by a Goldman tonometer at four times: T0 = basal, T1 = 2' minutes after induction of general anaesthesia, T2 = 2' minutes after laryngoscopy, T3 = 2' minutes after orotracheal intubation. At the same moments, systolic blood pressure, heart rate, rate pressure pro duct were measured. Patients were randomly divided in two groups: Group L (n = 10) in which was evaluated the efficacy of laryngotracheal topical spray of lidocaine 4% (2 ml) and Group F (n = 10) in which saline was used instead of anesthetic. The filling of the LTA kit (Abbott) was made by a person not involved in the experiments. DATA ANALYSIS: Student's t test for unpaired data. RESULTS: Topical anaesthesia reduces the increase of intraocular pressure, hypertension and rate pressure product due to intubation. The intraocular pressure reduces to 13% less than basal value in Group L and increase to 50% more than basal value in Group F. CONCLUSION: The topical anaesthesia of larynx and trachea is effective to reduce the intraocular hypertension due to the reflex response evoked by orotracheal intubation. 相似文献