全文获取类型
收费全文 | 31275篇 |
免费 | 2676篇 |
国内免费 | 1359篇 |
专业分类
电工技术 | 1792篇 |
技术理论 | 5篇 |
综合类 | 1862篇 |
化学工业 | 5426篇 |
金属工艺 | 1444篇 |
机械仪表 | 1842篇 |
建筑科学 | 2298篇 |
矿业工程 | 916篇 |
能源动力 | 794篇 |
轻工业 | 2318篇 |
水利工程 | 546篇 |
石油天然气 | 1669篇 |
武器工业 | 241篇 |
无线电 | 3871篇 |
一般工业技术 | 3966篇 |
冶金工业 | 1486篇 |
原子能技术 | 292篇 |
自动化技术 | 4542篇 |
出版年
2024年 | 136篇 |
2023年 | 576篇 |
2022年 | 1045篇 |
2021年 | 1420篇 |
2020年 | 1046篇 |
2019年 | 874篇 |
2018年 | 962篇 |
2017年 | 1049篇 |
2016年 | 967篇 |
2015年 | 1302篇 |
2014年 | 1573篇 |
2013年 | 1977篇 |
2012年 | 1970篇 |
2011年 | 2179篇 |
2010年 | 1777篇 |
2009年 | 1700篇 |
2008年 | 1692篇 |
2007年 | 1573篇 |
2006年 | 1651篇 |
2005年 | 1413篇 |
2004年 | 920篇 |
2003年 | 850篇 |
2002年 | 727篇 |
2001年 | 622篇 |
2000年 | 709篇 |
1999年 | 759篇 |
1998年 | 667篇 |
1997年 | 564篇 |
1996年 | 536篇 |
1995年 | 389篇 |
1994年 | 354篇 |
1993年 | 260篇 |
1992年 | 216篇 |
1991年 | 161篇 |
1990年 | 146篇 |
1989年 | 109篇 |
1988年 | 87篇 |
1987年 | 60篇 |
1986年 | 47篇 |
1985年 | 43篇 |
1984年 | 30篇 |
1983年 | 20篇 |
1982年 | 35篇 |
1981年 | 24篇 |
1980年 | 17篇 |
1979年 | 11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 8 毫秒
71.
Y. Liu W. Zhu O. K. Tan X. Yao Y. Shen 《Journal of Materials Science: Materials in Electronics》1996,7(4):279-282
A low-temperature plasma-enhanced chemical vapour deposition (PECVD) technique has been employed to produce ultrafine tin oxide powders. The structural features and phase transition of this material have been characterized using differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction, infrared spectroscopy (IR) and transmission electron microscopy (TEM). The oxygen absorption behaviour and gassensing properties have been investigated by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and electrical measurements. Thick film gas sensors made from such ultrafine SnO2 powders yield better sensitivities than those of normal undoped SnO2 gas sensors. A gas-sensing reaction mechanism is also proposed. 相似文献
72.
The human chromosome 9 displays the highest degree of structural variability. Four different types of variants are described including pericentric inversion, extra G-positive band in the q arm, additional G-positive band in the p arm and duplication of band 9q21-q22. It is important to demonstrate inheritance from a phenotypically normal individual in order to differentiate between a variant chromosome and an abnormal chromosome. 相似文献
73.
Cytological identification of soybean mitotic metaphase chromosomes (2n = 40) has been severely limited by their small size and uniform karyomorphology. We have developed fluorescent in situ hybridization (FISH), PCR-primed in situ labelling (PCR-PRINS) procedures, and molecular probes for routine cytological identification and for the physical mapping of soybean somatic chromosomes. Chromosome preparation has been achieved by modifications of previous protocols and through the preparation of root-tip protoplasts prior to chromosome spreading. Initially our probe selection focused on highly repeated DNAs that provide very intense localized hybridization signals. Repetitive gene probes that have proven valuable include the rDNA loci (5S and 45S) which are chromosome specific. We have also developed satellite DNA probes for two different sequence families: the SB92 and the STR120 satellites. Both of these are tandemly arranged at multiple chromosomal loci. By using different cloned examples of each family, we have been able to selectively label unique subsets of soybean chromosomes. Double hybridization with biotin and digoxigenin labeled probes has allowed us to determine the chromosomal overlap between different probes. In addition, we have joined portions of the metaphase chromosome painting patterns with the genetic map by single-copy FISH and PCR-PRINS detection of the RFLP loci G8.15, G17.3, and A199a and A199b. Total genomic DNA in situ hybridization (GISH) patterns were also used to characterize the soybean chromosomes. 相似文献
74.
Compressive and tribological properties of Al2O3 fibre and hexagonal BN particle hybrid reinforced Al-Si alloys 总被引:6,自引:0,他引:6
Al2O3 fibre-hexagonal BN particle hybrid reinforced aluminium-silicon alloys were fabricated by centrifugal force infiltration route. Hardness test and ultimate compressive test results are reported. The wear and friction properties of hybrid MMCs was investigated by means of a block-on-ring (bearing steel) type wear rig in a dry sliding condition. It is shown that the hardness and ultimate compressive strength of hybrid MMCs was evidently decreased with the addition of hexagonal BN particles, however, the wear rate and coefficient of friction of hybrid MMCs was improved simultaneously with increase of BN particle volume fraction, especially for the higher applied loads in the test. 相似文献
75.
76.
77.
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
78.
79.
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
80.
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