全文获取类型
收费全文 | 7644篇 |
免费 | 342篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 213篇 |
综合类 | 20篇 |
化学工业 | 1635篇 |
金属工艺 | 160篇 |
机械仪表 | 183篇 |
建筑科学 | 237篇 |
矿业工程 | 8篇 |
能源动力 | 511篇 |
轻工业 | 758篇 |
水利工程 | 89篇 |
石油天然气 | 153篇 |
武器工业 | 4篇 |
无线电 | 940篇 |
一般工业技术 | 1346篇 |
冶金工业 | 451篇 |
原子能技术 | 77篇 |
自动化技术 | 1249篇 |
出版年
2024年 | 17篇 |
2023年 | 178篇 |
2022年 | 422篇 |
2021年 | 524篇 |
2020年 | 372篇 |
2019年 | 373篇 |
2018年 | 480篇 |
2017年 | 336篇 |
2016年 | 378篇 |
2015年 | 232篇 |
2014年 | 357篇 |
2013年 | 589篇 |
2012年 | 389篇 |
2011年 | 441篇 |
2010年 | 280篇 |
2009年 | 240篇 |
2008年 | 226篇 |
2007年 | 206篇 |
2006年 | 172篇 |
2005年 | 153篇 |
2004年 | 124篇 |
2003年 | 102篇 |
2002年 | 117篇 |
2001年 | 62篇 |
2000年 | 65篇 |
1999年 | 76篇 |
1998年 | 123篇 |
1997年 | 107篇 |
1996年 | 72篇 |
1995年 | 78篇 |
1994年 | 52篇 |
1993年 | 51篇 |
1992年 | 40篇 |
1991年 | 23篇 |
1990年 | 28篇 |
1989年 | 42篇 |
1988年 | 46篇 |
1987年 | 28篇 |
1986年 | 28篇 |
1985年 | 42篇 |
1984年 | 49篇 |
1983年 | 41篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 21篇 |
1976年 | 30篇 |
1974年 | 16篇 |
排序方式: 共有8034条查询结果,搜索用时 0 毫秒
941.
942.
943.
A real-time image processor which is capable of video compression using either the sequency-ordered Walsh-Hadamard transform (WHT)W, or the discrete cosine transform (DCT), is considered. The processing is done on an intraframe basis in (8 X 8) data blocks. The (WHT)W coefficients are computed directly, and then used to obtain the DCT coefficients. This is achieved via an (8 X 8) transformation matrix which is orthonormal, and has a block-diagonal structure. As such, it results in substantial savings in the number of multiplications and additions required to obtain the DCT, relative to its direct computation. Some aspects of a hardware implementation of the processor are also included. 相似文献
944.
CF Wu B Haider SS Ahmed HA Oldewurtel MM Lyons TJ Regan 《Canadian Metallurgical Quarterly》1977,55(1):200-205
The effects of chronic tolbutamide treatment were examined in a diabetic animal model in which abnormal myocardial function and composition have previously been demonstrated. Eight diabetic dogs were given tolbutamide 250 mg/day orally and compared with seven untreated diabetics, five healthy dogs receiving tolbutamide, and eight normal controls. After one year, resting hemodynamic studies in the intact anesthetized state showed that treated diabetic dogs had a significantly higher left ventricular end-diastolic pressure of 12.1+/-1.3 mm Hg associated with normal end-diastolic volume, compared to 6.1+/-0.8 mm Hg in untreated diabetics (P less than 0.01) and 6.3+/-0.5 in normals. Stroke work and ejection fraction were similar to normals. Acute volume expansion revealed a larger rise of left ventricular end-diastolic pressure in treated and untreated diabetics than normals, without a significant stroke volume response in treated diabetics. Enhanced stiffness of myocardium appeared to be related to interstitial accumulation of periodic acid-Schiff staining material, further intensified in treated diabetics by triglyceride accumulation observed on electron microscopy and by chemical analysis. Thus treatment of diabetes with tolbutamide, despite improved glucose tolerance, effected further reduction of left ventricular function and altered morphology of myocardium. 相似文献
945.
Rose D.R.; Phipps J.; Michniewicz J.; Birnbaum G.I.; Ahmed F.R.; Muir A.; Anderson W.F.; Narang S. 《Protein engineering, design & selection : PEDS》1988,2(4):277-282
The polypeptide produced by expressing a chemically synthesizedgene coding for the amino-acid sequence of T4-lysozyme has beencrystallized and subjected to X-ray diffraction. The crystalstructure has been refined to a standard R-factor of 0.191 fordata between 8 and 2 ? resolution. The refined model is essentiallythe same as the well-known structure of wild-type T4-lysozymedetermined previously by Matthews et al. (1987). Some smallchanges in the C-terminal region, which is important in maintainingthe folded structure, have been noted. In addition to confirmingthat the synthetic gene product is very close to the wild type,this structure provides a benchmark for protein engineeringexperiments on the folding and the catalytic activity of thismolecule by the method of gene synthesis. 相似文献
946.
Hypothalamic and pituitary insulin-like growth factor II (IGF-II) peptide concentrations are differentially regulated by factors associated with metabolism such as insulin and glucoprivation. However, the effects of other metabolic stressors such as food restriction or exercise on hypothalamic IGF-II concentrations remain largely to be explored. In order to assess whether metabolic stress alters central nervous system IGF-II secretion, peptide analysis was conducted in rats exhibiting activity-based anorexia (ABA) compared to exercised-matched, body weight-matched or ad libitum fed controls. Further, the possibility of serotonergic control of IGF-II secretion was examined by determining IGF-II response to fluoxetine (FLX) injections (15 mg/kg body wt., i.p.). While ABA and body weight loss altered peripheral IGF-II concentrations compared to ad libitum fed or exercised controls, these treatments had no effect on hypothalamic or posterior pituitary IGF-II content. However, FLX administration increased IGF-II concentrations in the ventromedial hypothalamus and decreased IGF-II content in the lateral hypothalamus compared to vehicle injected. Anterior pituitary levels of IGF-II were also decreased by FLX. These data suggest that a serotonergic influence on CNS IGF-II exists and that IGF-II secretion may be altered by factors affecting serotonin metabolism or efficacy. 相似文献
947.
Hamed El-Shattawy Alaa Kassem Sanaa Omar Ahmed Sami Alaa-El-Din Yassin 《Drug development and industrial pharmacy》1994,20(5):901-909
A formula containing Compactrol, Ac-Di-Sol, Aerosil 200 and talc was used to prepare directly-compressed tablets of indomethacin and its sodium and meglumine salts. The prepared tablets were evaluated for uniformity of weight and thickness, hardness, friability and content uniformity. Each batch was then divided into two, one was coated with an opaque non-enteric film coat and evaluated for coat thickness uniformity. The dissolution rates of the uncoated and coated tablets and the effect of shelf-storage, at room temperature for 11 months, on drug contents were also studied. Indomethacin meglumine tablets showed the least relative standard deviation of weight and thickness. They exhibited acceptable uniformity of content and coat thickness, and the highest hardness-friability ratio. Also exhibited, uncoated and coated, the best in-vitro release of its drug contents and the maximal stability. 相似文献
948.
949.
A Ahmed 《Canadian Metallurgical Quarterly》1993,43(9):185-187
950.
Analysis of self-dual excited synchronous machine. II. Smallperturbation model and dynamic behaviour
For Part I, see ibid., vol.3, no.2, June 1988, pp.305-314. Having developed the general mathematical model of an isolated self-dual excited synchronous machine in part I, the author derives the small displacement equations for the two alternative excitation systems. A novel analytical method is developed for the small displacement model of the self-dual excited synchronous machine that requires less CPU time than previously. This method is general and take into account the variation of the firing angle and the automatic feedback control circuit during small disturbances. The coefficients of the characteristic equation and the eigenvalues are calculated to study the dynamic stability of the system. The effects of the ratio of the two field currents, the inertia constant, the power factor, and the gain and time constant of the feedback control circuit on the dynamic stability of the system are investigated. The results obtained show that the self-dual excited synchronous machine with the two field windings having MMF ratios between 0.75 and 1.5 presume better dynamic stability bounds than the conventional self-excited synchronous machine. In the range where the other proposed excitation system can be compared with the conventional machine, it has been found that the developed system has the same dynamic stability response with the advantage that the effect of automatic voltage regulator is implicitly included with a smaller time constant. Including the change of the firing angle during the small disturbance, a pronounced effect on the dynamic stability of the system results 相似文献