全文获取类型
收费全文 | 27374篇 |
免费 | 2508篇 |
国内免费 | 948篇 |
专业分类
电工技术 | 1242篇 |
综合类 | 1603篇 |
化学工业 | 5662篇 |
金属工艺 | 1071篇 |
机械仪表 | 1144篇 |
建筑科学 | 1493篇 |
矿业工程 | 430篇 |
能源动力 | 737篇 |
轻工业 | 4029篇 |
水利工程 | 534篇 |
石油天然气 | 749篇 |
武器工业 | 136篇 |
无线电 | 2462篇 |
一般工业技术 | 3265篇 |
冶金工业 | 1276篇 |
原子能技术 | 245篇 |
自动化技术 | 4752篇 |
出版年
2024年 | 87篇 |
2023年 | 362篇 |
2022年 | 865篇 |
2021年 | 1197篇 |
2020年 | 920篇 |
2019年 | 787篇 |
2018年 | 866篇 |
2017年 | 929篇 |
2016年 | 911篇 |
2015年 | 1216篇 |
2014年 | 1662篇 |
2013年 | 2080篇 |
2012年 | 2301篇 |
2011年 | 2484篇 |
2010年 | 2053篇 |
2009年 | 1981篇 |
2008年 | 1813篇 |
2007年 | 1724篇 |
2006年 | 1366篇 |
2005年 | 1020篇 |
2004年 | 718篇 |
2003年 | 530篇 |
2002年 | 478篇 |
2001年 | 313篇 |
2000年 | 253篇 |
1999年 | 214篇 |
1998年 | 299篇 |
1997年 | 197篇 |
1996年 | 162篇 |
1995年 | 138篇 |
1994年 | 103篇 |
1993年 | 104篇 |
1992年 | 67篇 |
1991年 | 64篇 |
1990年 | 61篇 |
1989年 | 64篇 |
1988年 | 42篇 |
1987年 | 58篇 |
1986年 | 50篇 |
1985年 | 46篇 |
1984年 | 41篇 |
1983年 | 25篇 |
1982年 | 20篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 30篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
31.
32.
Daniela M. Nevskaia Maria Luisa Rojas Cervantes Antonio Guerrero Ruíz Juan de Dios Lpez Gonzlez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):249-256
Adsorption of Triton X-100 on various silica substrates has been investigated. A number of solids, including a natural quartz, this quartz washed with HCl acid and subsequently heated at 1273 K; two aerosils and one Kieselgel silicas were studied. These solids exhibit surface areas in the range of 5 to 430 m2 g?1. All the Triton adsorption isotherms display an S-shape at the adsorption temperatures studied (298 and 308 K). It has been found that the pretreatments of natural quartz (by water washing, impurities removed by acid and/or high temperature calcination) affect considerably the amounts of TX-100 adsorbed. Measurements of surface composition have been made by X-ray photoelectron spectroscopy (XPS) with particular emphasis on the presence of impurities and on the number of OH groups at the surface of the samples. The nature of the surface hydroxyl has also been studied by infrared spectroscopy. Furthermore, the specific number of hydroxyl groups on the surface of the silica samples has been determined by thermogravimetric analysis. Finally an attempt to correlate solid surface characteristics with adsorption isotherms has been developed. 相似文献
33.
DH Kang CL Coe DO McCarthy NN Jarjour EA Kelly RR Rodriguez WW Busse 《Canadian Metallurgical Quarterly》1997,17(8):481-487
T cell cytokines play an important role in mediating airway inflammation in asthma. The predominance of a Th2 cytokine profile, particularly interleukin (IL)-4 and IL-5, is associated with the pathogenesis and course of asthma. The aim of this study was to test the hypothesis that a stressful life event alters the pattern of cytokine release in asthmatic individuals. Thirteen healthy controls and 21 asthmatic adolescents gave blood samples three times over a semester: midsemester, during the week of final examinations, and 2-3 weeks after examinations. Interferon-gamma (IFN-gamma), IL-2, IL-4, and IL-5 were measured from supernatants of cells stimulated with PHA/PMA for 24 h. Cells from asthmatic subjects released significantly more IL-5 during the examination and postexamination periods, whereas cells from healthy controls released significantly more IL-2 during the midsemester and examination periods, thereby indicating a bias for a Th2-like pattern in asthmatics and a Th1-like pattern in healthy controls. IL-4 and IL-5 production showed a marked decrease during and after examinations in healthy controls, whereas this decline was absent in asthmatics. The ratios of IFN-gamma:IL-4 and IFN-gamma:IL-5 also revealed significant changes in the profile of cytokine release across the semester. These results indicate differential cytokine responses in asthmatics that may become pronounced during periods of cellular activation. 相似文献
34.
本文对分布式数据库的设计方法、分割与分配技术作了一些探讨,并就分布式数据库的发展方向进行了初步分析。 相似文献
35.
Head and eye movements were simultaneously recorded during locomotory and pecking behavior of 4 pigeons, which were trained to traverse a conditioning chamber, with a pecking key and a food dispenser at each end. Each trial involved key pecking, walking, and feeding. Head movements were registered with a skull-mounted miniature accelerometer, and eye movements were recorded with implanted electrooculogram (EOG) electrodes. An almost perfect temporal coordination between head and eye movements was observed during both walking and feeding bouts. During walking, head movements primarily provide retinal image stability, and eye movements support visual scanning. During feeding, head movements mainly subserve the grasping of food items, and eye movements maintain visual fixation on them. Because the eyes are reflexively closed during the middle phase of pecks, the head and eye movements are then under ballistic control. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
36.
37.
Murad Nour Mohammad Belfiore Jean Claude Guisantes George Rodriguez 《Wireless Personal Communications》2002,20(2):145-161
In DS-WCDMA mobile systems such the UMTS, asynchronous cell site operation,assigning different long spreading code to each cell, yields the advantageof flexible system deployment. We can design an indoor system basedon an outdoor one. However, in general, much longer search time isrequired in asynchronous operation than in synchronous. This paperproposes three techniques to take decisions about synchronizationbased on observation of correlated signals. Classical decision criterialike maximum and threshold criterion are presented. A new decisioncriteria that we call Threshold&Max combined decision criteriais analyzed. The results of this new introduced technique is comparedwith the classical ones. 相似文献
38.
39.
高粘稠性搅拌型刺梨酸奶的研制 总被引:2,自引:0,他引:2
以新鲜优质牛奶为原料,添加刺梨果浆,将保加利亚乳杆菌及嗜热链球菌以1:2混合作为发酵剂发酵,研制出具有刺梨风味的高粘稠性搅拌型酸奶。 相似文献
40.