全文获取类型
收费全文 | 15037篇 |
免费 | 1077篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 103篇 |
综合类 | 7篇 |
化学工业 | 2816篇 |
金属工艺 | 191篇 |
机械仪表 | 365篇 |
建筑科学 | 472篇 |
矿业工程 | 25篇 |
能源动力 | 296篇 |
轻工业 | 2223篇 |
水利工程 | 88篇 |
石油天然气 | 40篇 |
无线电 | 917篇 |
一般工业技术 | 2179篇 |
冶金工业 | 4554篇 |
原子能技术 | 47篇 |
自动化技术 | 1806篇 |
出版年
2024年 | 33篇 |
2023年 | 155篇 |
2022年 | 146篇 |
2021年 | 355篇 |
2020年 | 308篇 |
2019年 | 319篇 |
2018年 | 421篇 |
2017年 | 416篇 |
2016年 | 532篇 |
2015年 | 471篇 |
2014年 | 623篇 |
2013年 | 1121篇 |
2012年 | 988篇 |
2011年 | 789篇 |
2010年 | 596篇 |
2009年 | 599篇 |
2008年 | 619篇 |
2007年 | 532篇 |
2006年 | 490篇 |
2005年 | 318篇 |
2004年 | 297篇 |
2003年 | 251篇 |
2002年 | 244篇 |
2001年 | 159篇 |
2000年 | 153篇 |
1999年 | 253篇 |
1998年 | 1416篇 |
1997年 | 869篇 |
1996年 | 588篇 |
1995年 | 347篇 |
1994年 | 256篇 |
1993年 | 295篇 |
1992年 | 64篇 |
1991年 | 87篇 |
1990年 | 66篇 |
1989年 | 80篇 |
1988年 | 76篇 |
1987年 | 51篇 |
1986年 | 59篇 |
1985年 | 62篇 |
1984年 | 27篇 |
1983年 | 25篇 |
1982年 | 34篇 |
1981年 | 34篇 |
1980年 | 52篇 |
1979年 | 30篇 |
1978年 | 20篇 |
1977年 | 87篇 |
1976年 | 191篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Although the good appearance and biocompatibility of dental porcelains, failures are still of considerable concern because of the limited properties to all ceramic system. Physical properties that might be considered ideal include high strength, resistance to abrasion, and resistance to the hostile oral environment. Porcelain has been considered by many of its physical characteristic are similar to those of enamel. In 1983 a new modality of treatment, the etched porcelain restoration was introduced by Simonsen and Calamia. Numerous investigations have shown the strength of the etched porcelain bonded to composite resin and also the clinical success of this porcelain to be used as laminated veneers and etched inlays and onlays. 相似文献
92.
AJ Dorta M Ferra R Bu-Colfiu L García M Gil X Escobar G Martín NA Díaz OM Perez MT Interián 《Canadian Metallurgical Quarterly》1993,10(10):490-491
It is essential to know how the immune system acts in different neurological diseases, some of them non very well known or of unknown etiology at all. It was applied Reiber and Felgenhauer's formula in 56 patients with different diseases. IgA, IgM, IgG and albumin were quantified in sera and cerebrospinal fluid by simple immunodiffusion. It was observed more frequent IgG local synthesis and IgA in this sample. 相似文献
93.
WA Schumacher CL Heran TE Steinbacher S Youssef ML Ogletree 《Canadian Metallurgical Quarterly》1993,22(4):526-533
We determined the effects of aspirin and a novel thromboxane A2/prostaglandin endoperoxide (TP)-receptor antagonist, BMS-180291, on thrombosis and bleeding times in skin and mesenteric arteries. In anesthetized rats, occlusive thrombosis was induced in the carotid artery by topical application of ferrous chloride and in the vena cava by blood flow stasis combined with either infusion of thromboplastin or hypotonic saline. Aspirin (1, 10, and 50 mg/kg) did not reduce arterial or venous thrombus weight significantly. BMS 180,291 (150 micrograms/kg/min) decreased arterial thrombus weight and hypotonic saline-induced caval thrombus weight by 58 and 57%, respectively. BMS-180291 lacked antithrombotic activity at a lower dose (50 micrograms/kg/min) and failed to inhibit thromboplastin-induced caval thrombosis. BMS-180291 (150 micrograms/kg/min) significantly reduced arterial thrombus weight by 40% when plasma epinephrine concentration was increased to 5 ng/ml. BMS-180291 and aspirin produced increases of only < or = 30% in bleeding times. These results demonstrate that BMS-180291 has antithrombotic activity in experimental aspirin-resistant arterial and venous thrombosis. Both aspirin and BMS-180291 have only modest effects on small artery hemostasis in rats. 相似文献
94.
Four cannulated cows in a 4 x 4 Latin square design were used to study the effects of supplemental dietary fatty acids from roasted soybeans combined with tallow or partially hydrogenated fats, varying in esterification and fatty acid chain length, on nutrient digestion and lactation performance. Diets were formulated to contain (DM basis) 48% forage in addition to 1.5% fatty acids from roasted soybeans and 2.5% fatty acids from tallow, partially hydrogenated tallow triglycerides, partially hydrogenated tallow fatty acids, or a blend of 30% tallow and 70% hydrogenated fatty acids that were rich in palmitic acid. Apparent total tract digestibilities of OM, N, and NDF were similar among diets. Supplemental fat as fatty acids, compared with triglycerides, increased digestibilities of total fatty acids and C18:1 in the small intestine, perhaps indicating that lipolysis was rate-limiting. Fatty acids also increased milk fat percentage and efficiency of 4% FCM production. Although intake of C16 fatty acids was higher for cows fed the fat rich in palmitic acid than for those fed the tallow fatty acids, total duodenal flows of C16 fatty acids were similar, and digestibility in the small intestine was unaffected. Dry matter intake, 4% FCM production, and milk protein percentage were similar among treatments. 相似文献
95.
The goal of this research was to examine the accuracy of three methods used to indicate the hip joint center (HJC) in seated steady-state cycling. Two of the methods have been used in previous studies of cycling biomechanics and included tracking a marker placed over the superior aspect of the greater trochanter, a location that estimates the center of rotation of the hip joint, and assuming that the hip is fixed. The third method was new and utilized an anthropometric relationship to determine the hip joint location from a marker placed over the anterior-superior iliac spine. To perform a comparative analysis of errors inherent in the three methods, a standard method which located the true hip joint center was developed. The standard method involved establishing a pelvis-fixed coordinate system using a triad of video markers attached to an intracortical pin. Three-dimensional motion analysis quantified the true hip joint center position coordinates. To provide data for the comparative analysis, the intracortical pin was anchored to a single subject who pedaled at nine cadence-workrate combinations while data for all four methods were simultaneously recorded. At all cadence-workrate combinations the new method was more accurate than the trochanter method with movement errors lower by a factor of 2 in the vertical direction and a factor of 3 in the horizontal direction. Relative to the errors introduced by the fixed hip assumption, the new method was also generally more accurate by at least a factor of 2 in the horizontal direction and had comparable accuracy in the vertical direction. For computed kinetic quantities, the new method most accurately indicated hip joint force power but the fixed hip method most accurately indicated the work produced by the hip joint force over the crank cycle. 相似文献
96.
José Martínez-Aroza Ramón Román-Roldán 《Multidimensional Systems and Signal Processing》1995,6(1):7-35
A multiresolution analysis of digital gray-level images is presented. A gray-level multi-scale framework is determined from two main assumptions: the gray scale is binary at the finest spatial resolution, and the gray levels of composed regions are obtained additively. In order to interrelate the gray-level histograms of the same image at different resolutions, probabilistic linear models are developed, which are then applied for estimation. Linear-optimization theory is used as a way of constructing such models. A general procedure for image processing is sketched, based on gray-level estimation. A versatile algorithm for nonlinear filtering is derived. Some examples of prospective applications are given.This work was partially supported by grant TIC91-646 from the DGYCIT of the Spanish Government. 相似文献
97.
Urinary tract infections (UTIs) are common conditions in clinical practice. For uncomplicated UTIs, the causative organisms and their antimicrobial susceptibility profiles are generally predictable, and empiric short course (3 day) antibiotic therapy after an abbreviated laboratory workup is advocated. Acute pyelonephritis requires a 2 week antibiotic course, often with initial parenteral therapy. Women with frequent recurrences of UTIs may require intermittent self-treatment or continuous or postcoital antibiotic prophylaxis. Catheter-associated UTIs generally only require treatment if the patient shows signs of systemic infection. Treatment of asymptomatic bacteriuria is only recommended in certain circumstances. Careful consideration of the clinical circumstances, the patient's known or predicted urinary tract anatomy, and the antibiotic susceptibility of the bacterial pathogen(s) are critical factors in the choice of appropriate therapy for urinary tract infections. 相似文献
98.
Thompson Robert J.; Gil Karen M.; Burbach Daniel J.; Keith Barbara R.; Kinney Thomas R. 《Canadian Metallurgical Quarterly》1993,61(3):468
In this study, 64% of children aged 7–12 yrs with sickle cell disease were found to have a parent-reported behavior problem, and 50% met the criteria for a Diagnostic and Statistical Manual of Mental Disorders-III-Revised (DSM-III-R) diagnosis based on a structured clinical interview of the child. Internalizing types of behavior problems and diagnoses were the most frequent. Support was provided for a transactional stress and coping model in delineating the processes associated with child adjustment. In particular, maternal anxiety accounted for 16–33% of the variance in mother-reported internalizing and externalizing behavior problems, respectively, and child pain-coping strategies accounted for 21% of the variance in child-reported adjustment problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
99.
100.