全文获取类型
收费全文 | 20908篇 |
免费 | 1532篇 |
国内免费 | 843篇 |
专业分类
电工技术 | 1089篇 |
技术理论 | 4篇 |
综合类 | 1127篇 |
化学工业 | 3763篇 |
金属工艺 | 934篇 |
机械仪表 | 1228篇 |
建筑科学 | 1463篇 |
矿业工程 | 547篇 |
能源动力 | 588篇 |
轻工业 | 1206篇 |
水利工程 | 343篇 |
石油天然气 | 1195篇 |
武器工业 | 137篇 |
无线电 | 2714篇 |
一般工业技术 | 2735篇 |
冶金工业 | 1066篇 |
原子能技术 | 196篇 |
自动化技术 | 2948篇 |
出版年
2024年 | 76篇 |
2023年 | 329篇 |
2022年 | 572篇 |
2021年 | 825篇 |
2020年 | 598篇 |
2019年 | 537篇 |
2018年 | 617篇 |
2017年 | 628篇 |
2016年 | 587篇 |
2015年 | 742篇 |
2014年 | 952篇 |
2013年 | 1283篇 |
2012年 | 1214篇 |
2011年 | 1332篇 |
2010年 | 1039篇 |
2009年 | 1065篇 |
2008年 | 1071篇 |
2007年 | 1020篇 |
2006年 | 1069篇 |
2005年 | 950篇 |
2004年 | 648篇 |
2003年 | 621篇 |
2002年 | 551篇 |
2001年 | 461篇 |
2000年 | 558篇 |
1999年 | 616篇 |
1998年 | 558篇 |
1997年 | 480篇 |
1996年 | 461篇 |
1995年 | 337篇 |
1994年 | 315篇 |
1993年 | 226篇 |
1992年 | 175篇 |
1991年 | 144篇 |
1990年 | 127篇 |
1989年 | 100篇 |
1988年 | 79篇 |
1987年 | 54篇 |
1986年 | 46篇 |
1985年 | 38篇 |
1984年 | 22篇 |
1983年 | 18篇 |
1982年 | 31篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 1 毫秒
91.
92.
本文介绍以PC-1500(A)型袖珍计算机为主体的地面放射性总量数据采集及处理系统的方案、硬件、软件及应用。 相似文献
93.
本文在全面阐述鞍山市水资源现状的基础上,系统地分析了鞍山市供水系统存在的问题,并针对鞍山实际情况,提出了保障鞍山市城市饮水安全的相关研究及对策。 相似文献
94.
95.
酶促合成生物柴油反应动力学 总被引:1,自引:0,他引:1
以Candidasp.99-125脂肪酶为催化剂,甘油三油酸酯和甲醇为底物,采用有序机制模型对酶促合成生物柴油的酯交换反应动力学进行了研究,并与经典乒乓机制模型进行了比较。研究结果表明,反应初速率的实验值与有序机制模型方程的计算值吻合很好。对于固定化Candidasp.99-125脂肪酶催化合成生物柴油的酯交换反应机理进行研究,采用有序机制模型比经典乒乓机制模型更为精确。反应过程中,醇抑制为竞争性抑制,在甘油三油酸酯浓度较小的范围内,醇抑制作用较为显著,醇浓度越低反应初速率越快。该有序机制模型可用来预测生物柴油的生产批次或连续反应器中酯交换反应的速率,确定最佳底物油脂和醇的浓度。 相似文献
96.
The purpose of these experiments was to determine whether the exposure of rats at night to pulsed DC magnetic fields (MF) would influence the nocturnal production and secretion of melatonin, as indicated by pineal N-acetyltransferase (NAT) activity (the rate limiting enzyme in melatonin production) and pineal and serum melatonin levels. By using a computer-driven exposure system, 15 experiments were conducted. MF exposure onset was always during the night, with the duration of exposure varying from 15 to 120 min. A variety of field strengths, ranging from 50 to 500 microT (0.5 to 5.0 G) were used with the bulk of the studies being conducted using a 100 microT (1.0 G) field. During the interval of DC MF exposure, the field was turned on and off at 1-s intervals with a rise/fall time constant of 5 ms. Because the studies were performed during the night, all procedures were carried out under weak red light (intensity of <5 microW/cm2). At the conclusion of each study, a blood sample and the pineal gland were collected for analysis of serum melatonin titers and pineal NAT and melatonin levels. The outcome of individual studies varied. Of the 23 cases in which pineal NAT activity, pineal melatonin, and serum melatonin levels were measured, the following results were obtained; in 5 cases (21.7%) pineal NAT activity was depressed, in 2 cases (8.7%) studies pineal melatonin levels were lowered, and in 10 cases (43.5%) serum melatonin concentrations were reduced. Never was there a measured rise in any of the end points that were considered in this study. The magnitudes of the reductions were not correlated with field strength (i.e., no dose-response relationships were apparent), and likewise the reductions could not be correlated with the season of the year (experiments conducted at 12-month intervals under identical exposure conditions yielded different results). Duration of exposure also seemed not to be a factor in the degree of melatonin suppression. The inconsistency of the results does not permit the conclusion that pineal melatonin production or release are routinely influenced by pulsed DC MF exposure. In the current series of studies, a suppression of serum melatonin sometimes occurred in the absence of any apparent change in the synthesis of this indoleamine within the pineal gland (no alteration in either pineal NAT activity or pineal melatonin levels). Because melatonin is a direct free radical scavenger, the drop in serum melatonin could theoretically be explained by an increased uptake of melatonin by tissues that were experiencing augmented levels of free radicals as a consequence of MF exposure. This hypothetical possibly requires additional experimental documentation. 相似文献
97.
制备低硫可膨胀石墨的研究 总被引:18,自引:3,他引:15
研究了以过二硫酸铵作氧化剂低硫可膨胀石墨的制备,找到了在较低温度下,制备低硫可膨胀石墨的最佳条件。即过二硫酸铵和石墨的重量比为15%;反应温度为55℃;反应时间为40min;硫酸浓度为98%;硫酸与石墨的重量比为4∶1,草酸和硝酸(浓度为65%)的重量比为7.5%时,所制得的可膨胀石墨含硫量为0.65%,膨胀容积为200mL/g可膨胀石墨。并且,其终端产品柔性石墨具有优良的力学性能和抗氧化性能。 相似文献
98.
Low cardiac output after open heart operations in neonates and infants carries a high mortality. Delayed sternal closure may be life-saving but may prolong hospital stay and increase costs. To circumvent these issues, we shaped homograft bone and interposed it between the sternal edges to allow primary wound closure in 2 pediatric patients. Midterm results are satisfactory. 相似文献
99.
100.
水下成像的现状和发展动向 总被引:5,自引:0,他引:5
本文以下水成像在军事,海洋开发工程应用为基础,论述了水下观测和成像中采用微光电视摄像机和激光器件及其系统的技术现状和发展动向。 相似文献