全文获取类型
收费全文 | 3889篇 |
免费 | 29篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 20篇 |
化学工业 | 277篇 |
金属工艺 | 23篇 |
机械仪表 | 29篇 |
建筑科学 | 90篇 |
矿业工程 | 3篇 |
能源动力 | 32篇 |
轻工业 | 93篇 |
水利工程 | 12篇 |
石油天然气 | 5篇 |
无线电 | 138篇 |
一般工业技术 | 223篇 |
冶金工业 | 2762篇 |
原子能技术 | 11篇 |
自动化技术 | 202篇 |
出版年
2018年 | 16篇 |
2017年 | 17篇 |
2016年 | 20篇 |
2015年 | 17篇 |
2014年 | 28篇 |
2013年 | 84篇 |
2012年 | 42篇 |
2011年 | 54篇 |
2010年 | 56篇 |
2009年 | 40篇 |
2008年 | 55篇 |
2007年 | 55篇 |
2006年 | 50篇 |
2005年 | 38篇 |
2004年 | 47篇 |
2003年 | 48篇 |
2002年 | 37篇 |
2001年 | 32篇 |
2000年 | 29篇 |
1999年 | 106篇 |
1998年 | 647篇 |
1997年 | 443篇 |
1996年 | 292篇 |
1995年 | 166篇 |
1994年 | 131篇 |
1993年 | 159篇 |
1992年 | 48篇 |
1991年 | 39篇 |
1990年 | 53篇 |
1989年 | 41篇 |
1988年 | 54篇 |
1987年 | 41篇 |
1986年 | 44篇 |
1985年 | 45篇 |
1984年 | 40篇 |
1983年 | 44篇 |
1982年 | 42篇 |
1981年 | 49篇 |
1980年 | 27篇 |
1979年 | 32篇 |
1978年 | 26篇 |
1977年 | 78篇 |
1976年 | 150篇 |
1975年 | 29篇 |
1974年 | 23篇 |
1973年 | 27篇 |
1972年 | 25篇 |
1970年 | 21篇 |
1963年 | 17篇 |
1955年 | 16篇 |
排序方式: 共有3920条查询结果,搜索用时 15 毫秒
1.
2.
Math1 is essential for genesis of cerebellar granule neurons 总被引:1,自引:0,他引:1
N Ben-Arie HJ Bellen DL Armstrong AE McCall PR Gordadze Q Guo MM Matzuk HY Zoghbi 《Canadian Metallurgical Quarterly》1997,390(6656):169-172
3.
Use of an intravascular T1 contrast agent to improve MR cine myocardial-blood pool definition in man
The feasibility of improving myocardial/blood pool contrast in MR cine images through use of an intravascular contrast agent (Ferumoxtran, Advanced Magnetics, Inc., Cambridge, MA) was tested in four subjects. The contrast-to-noise ratio (CNR) demonstrated a trend toward improvement in the short axis and improved significantly in the long axis cine by an average of 128% (P < .05). Image intensity gradients at the myocardial/blood pool interface increased significantly in both the short and long axis (P < .01). It is expected that larger image intensity gradients at the endocardial border should improve the capabilities of automated segmentation algorithms, reducing the uncertainty and need for manual editing. 相似文献
4.
BB Horswell CL Castiglione AE Poole LA Assael 《Canadian Metallurgical Quarterly》1993,51(2):145-9; discussion 149-50
The double-reversing Z-plasty of Furlow for closure of the soft palate was used in 34 children with various types of cleft palate. Mean age at repair was 12.8 months. Intraoperative experience was favorable, with acceptable operating time and blood loss. Length of hospitalization averaged 1.9 days. Postoperatively, two children experienced temporary stridor, which resolved within 24 to 48 hours. One child had dehiscence of the hard palate (Von Lagenbeck repair) 4 weeks postoperatively, and three children developed small oronasal fistulae. Early speech evaluation demonstrated adequate soft palate mobility in 33 of 34 patients, with observable velopharyngeal function. Twelve children had mild velar compromise, with eight exhibiting slight nasal air escape. 相似文献
5.
AE Speckens AM Van Hemert JH Bolk HG Rooijmans MW Hengeveld 《Canadian Metallurgical Quarterly》1996,26(4):745-752
BACKGROUND: Measurement of intracardiac hemodynamic parameters has been limited to brief periods in the acute care setting. We developed and evaluated an implantable hemodynamic monitor that is capable of measuring chronic right ventricular oxygen saturation and pulmonary artery pressure. METHODS AND RESULTS: The device consists of an electronic controller placed subcutaneously and two transvenous leads placed in the right ventricle (reflectance oximeter) and pulmonary artery (variable capacitance pressure sensor). Implantation was performed in 10 patients with severe left ventricular dysfunction. Average implant pulmonary artery pressures were systolic, 52 +/- 16 mm Hg; diastolic, 29 +/- 11 mm Hg; and mean, 40 +/- 12 mm Hg. The mean right ventricular oxygen saturation at implant was 51%. Provocative maneuvers, including postural changes, sublingual nitroglycerin, and bicycle exercise, demonstrated expected changes in measured oxygen saturation and pulmonary artery pressures over time. At follow-up of 0.5 to 15.5 months, there were no significant differences between pulmonary artery pressures or oxygen saturation values transmitted from the device and simultaneous measurement with balloon flotation catheters. Four of the pulmonary artery leads dislodged and three demonstrated sensor drift, whereas two of the oxygen saturation sensors failed. Four patients died and four received transplants. Pathological study did not demonstrate injury to the right ventricular outflow tract or pulmonic valve. CONCLUSIONS: Chronic measurement of hemodynamic parameters in the outpatient setting with implantable sensor technology appears to be feasible. The devices are well tolerated without significant untoward effects, and the sensors generally function well over time, providing reliable information. Clinical usefulness remains to be established. 相似文献
6.
This paper presents the results of a study in the design of a neural network based adaptive robotic control scheme. The neural network used here is a two hidden layer feedforward network and the learning scheme is the well-known backpropagation algorithm. The neural network essentially provides the inverse of the plant and acts in conjunction with a standard PD controller in the feedback loop. The objective of the controller is to accurately control the end position of a single link manipulator in the presence of large payload variations, variations in the link length and also variations in the damping constant. Based on results of this study, guidelines are presented in selecting the number of neurons in the hidden layers and also the parameters for the learning scheme used for training the network. Results also indicate that increasing the number of neurons in the hidden layer will improve the convergence speed of learning scheme up to a certain limit beyond which the addition of neurons will cause oscillations and instability. Guidelines for selecting the proper learning rate, momentum and fast backpropagation constant that ensure stability and convergence are presented. Also, a relationship between the r.m.s. error and the number of iterations used in training the neural network is established. 相似文献
7.
Paul I. Dalven James R. Hildebrandt Abraham Shamir Anthony J. Laccetti Leonard T. Hodgins Harry P. Gregor 《应用聚合物科学杂志》1985,30(3):1113-1132
Various high molecular weight copolymers of acrylonitrile and a vinyl comonomer containing an aryl amine, a pyridine, or an aliphatic hydroxyl group were synthesized via slurry polymerization techniques so as to contain from 1 to 15 mol % functional comonomer. The comonomer content was quantitated by ultraviolet absorbance, base titration of acid polymer salts, and/or relative chemical reactivity with trichloro-s-triazine. Thin films were cast from copolymer solutions, coagulated into unsupported ultrafiltration membrances, and characterized with respect to both water permeability and pore size distribution. Analysis by size exclusion chromatography of the membrane permeate of a pool of dextran fractions yielded a continuous distribution curve for membrane pore size over the range 1.5 to 70 nm. The ultrafiltration membranes were used for protein immobilization after appropriate chemical activation. The three distinct types of functional copolymers gave comparable results for α-chymotrypsin, with protein weight loadings of 6–12% and 40–65% retention of enzymatic specific activity. 相似文献
8.
This paper deals with the time-optimal control problem for a class of control systems which includes controlled mechanical systems with possible dissipation terms. The Lie algebras associated with such mechanical systems have certain special properties. These properties are explored and used in conjunction with the Pontryagin maximum principle to determine the structure of singular extremals and, in particular, time-optimal trajectories. The theory is illustrated by an application to a time-optimal problem for a class of underwater vehicles. 相似文献
9.
10.