全文获取类型
收费全文 | 8821篇 |
免费 | 690篇 |
国内免费 | 330篇 |
专业分类
电工技术 | 253篇 |
技术理论 | 1篇 |
综合类 | 797篇 |
化学工业 | 1963篇 |
金属工艺 | 156篇 |
机械仪表 | 196篇 |
建筑科学 | 535篇 |
矿业工程 | 210篇 |
能源动力 | 276篇 |
轻工业 | 805篇 |
水利工程 | 77篇 |
石油天然气 | 96篇 |
武器工业 | 14篇 |
无线电 | 1155篇 |
一般工业技术 | 668篇 |
冶金工业 | 358篇 |
原子能技术 | 57篇 |
自动化技术 | 2224篇 |
出版年
2024年 | 24篇 |
2023年 | 133篇 |
2022年 | 202篇 |
2021年 | 234篇 |
2020年 | 274篇 |
2019年 | 236篇 |
2018年 | 199篇 |
2017年 | 232篇 |
2016年 | 288篇 |
2015年 | 270篇 |
2014年 | 420篇 |
2013年 | 463篇 |
2012年 | 614篇 |
2011年 | 758篇 |
2010年 | 457篇 |
2009年 | 767篇 |
2008年 | 853篇 |
2007年 | 634篇 |
2006年 | 716篇 |
2005年 | 466篇 |
2004年 | 301篇 |
2003年 | 260篇 |
2002年 | 203篇 |
2001年 | 157篇 |
2000年 | 137篇 |
1999年 | 112篇 |
1998年 | 74篇 |
1997年 | 85篇 |
1996年 | 47篇 |
1995年 | 49篇 |
1994年 | 32篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1972年 | 2篇 |
1964年 | 2篇 |
1963年 | 3篇 |
1961年 | 3篇 |
1960年 | 2篇 |
1958年 | 2篇 |
1957年 | 3篇 |
1955年 | 7篇 |
排序方式: 共有9841条查询结果,搜索用时 15 毫秒
41.
针对高维数据导致的维数灾难问题,提出了一种基于面向分类准则的维数约简方法。所提准则使每个训练样本在特征空间中与同类样本尽可能接近,而与异类样本尽可能疏远。首先对每个训练样本定义同类样本加权平均距离和异类样本加权平均距离。然后基于上述两个概念分别定义总体同类距离和总体异类距离。以最小化总体同类距离和最大化总体异类距离为目的提出了面向分类的准则(Classification Oriented Criterion,COC)。最后,基于面向分类的准则推导出了一种新的维数约简方法。在公共人脸数据库ORL和Yale上的实验表明所提方法性能优于有代表性的维数约简方法。 相似文献
42.
在核电站安全级DCS设计中,为提高系统的可靠性,需保证安全级电气设备和电路之间的有效隔离,为了实现电气设备和电路的隔离,核安全相关法规标准提出了实体分隔、电气隔离等设计手段。本文通过对核电站安全级DCS隔离相关法规标准的分析,得出了电气设备和电路隔离的设计要求,提出了设计过程中应采取的方法和措施,并在此基础上给出了具体的实体分隔和电气隔离工程实现方案。该方案的工程实施结果可实现安全级DCS电气设备和电路的独立性要求,有效提高系统的可靠性,为系统的稳定运行提供重要保证和支持。 相似文献
43.
在聚乙烯醇(PVA)存在下,耐尔蓝(NB)与铈钼、钪钼杂多酸络阴离子形成离子缔合物,其最大吸收均位于585nm,表观摩尔吸光度分别为εcw=3.52×106和εSc=3.59×10_5L·molˉ1·cmˉ1,铈和钪服从比耳定律的浓度范围分别为0~0.8μg/25ml和0~2.0μg/25ml,测定极限分别为1.3ngCe/ml(n=10)和3.0ngSc/ml(n=7),对于0.02μgCe/ml或0.04μgSc/ml测定的相对标准偏差分别为2.7%(n=9)和2.8%(n=10),离子缔合物的摩尔比分别为Ce:Mo:NB=1:6:4和Sc:Mo:NB=1:12:3。本法用于地质标样分析,结果满意。 相似文献
44.
秦爱武 《网络安全技术与应用》2014,(11):168-169
随着社会科技和信息网络技术的飞速发展,慕课成为时代孕育的新时期教育模式,这种课程模式为中职学生学习提供了更大的自由空间。在中职计算机教学中,培养学生对于计算机理论知识的掌握和实际操作的技能固然重要,但对于学生综合素质的培养也是不容忽视的。为此,本文就以培养学生的创新能力和实践能力为要点,不断加强学生动手操作能力,对慕课时代下中职计算机课程知识体系的构建做进一步探讨。 相似文献
45.
Simon Piché 《Chemical engineering science》2005,60(22):6452-6461
The oxidative absorption of hydrogen sulfide (H2S) into a solution of ferric chelate of trans-1,2- diaminocyclohexanetetraacetate (CDTA) was studied in a counter-current laboratory column randomly packed with 15 mm plastic Ralu rings. The present investigation takes concern about the Kraft pulping situation where dilute H2S concentrations are omnipresent in large-volume gas effluents. A fractional two-level factorial approach was instigated to determine the significance of six operating variables, namely the solution's alkalinity (pH; 8.5-10.5), the liquid mass flow rate (L;1.73-), the solution's ionic strength (IC;0.01-), the gas mass flow rate (G;0.19-), the inlet H2S concentration (CH2S,0;70-430 ppm) and the initial ferric CDTA concentration (CFe,0;100 -). Initially, a Plackett-Burman design matrix of seven duplicated experiments revealed that pH is the leading factor controlling the H2S conversion rate while the ionic strength and ferric CDTA concentration effects remained negligible within the factorial domain. Surface response analysis based on 11 duplicated factorial experiments plus 10 central composite trials revealed that the H2S conversion significantly increases with liquid flow rate but decreases with growing H2S load up. Further examination about the influence of ferric CDTA on H2S absorption rate was set up over a broader concentration range (CFe,0;0- at pH of 9.5 and 10.5. It showed good potential at as H2S conversion increased by a significant 25% for both pH values in comparison to pure alkaline solutions containing no ferric CDTA. 相似文献
46.
A versatile electrochemical platform for characterizing the adsorption of neutral and positively charged surfactants on hydrophobic surfaces was established using methylene blue (MB) as the probe. As a rigid, planar and electroactive species, MB can intercalate inside the regular self-assembled monolayers (SAMs) of n-hexanethiol and exhibit well-defined electrochemical responses. The adsorption of surfactants on the hydrophobic SAMs through the intercalation interaction between the hydrophobic tails of surfactants and the SAMs might change the density of the SAMs and influence the electrochemical behaviors of MB, providing a simple but effective approach for characterizing surfactant adsorption on hydrophobic surfaces. As an example, the adsorptive behaviors of cetyltrimethylammonium bromide (CTAB), a positively charged surfactant, and Triton X-100, a neutral surfactant, on hydrophobic surfaces were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that these surfactants generally experienced three different adsorptive behaviors: the monomer adsorption at low concentrations, the loose monolayer adsorption at intermediate concentrations and the dense monolayer adsorption at high concentrations. In the case of CTAB, a new additional submonolayer adsorptive behavior between the monomer and the loose monolayer adsorption was observed for the first time, due to its rather long hydrophobic tail. 相似文献
47.
This paper describes a new reactive blending approach to improve the compatibility of poly(l-lactide) (PLLA) and poly(?-caprolacton) (PCL). For this purpose, the ring-opening polymerization of l-lactide (LLA) was carried out in the presence of PCL-OH (OH groups on one end). The P(CL-b-LLA) block copolymers were in situ formed during polymerization, and as a result, PLLA/P(CL-b-LLA) blends were obtained. The characterization of GPC and 1H NMR verified the synthesis of PLLA/P(CL-b-LLA) blends. Furthermore, the 13C NMR spectroscopy showed that no transesterification reaction occurred to a significant extent during LLA polymerization process. The in situ formed P(CL-b-LLA) compatibilizes the phase separated structure of PCL domains in PLLA matrix. The size of PCL domains in PLLA matrix became much smaller than that in a solution blended sample. The average sizes of PCL domains are controllable in the level of sub-micron scale. 相似文献
48.
Flavonoid pigments in chalkhill blue (Lysandra coridon Poda) and other lycaenid butterflies 总被引:1,自引:0,他引:1
Angela Wilson 《Journal of chemical ecology》1987,13(3):473-493
Nine flavonoids, namely, kaempferol, kaempferol 7-rharanoside, kaempferol 3-rhamnoside, kaempferol 3-glucoside, kaempferol 3-glucoside, 7-rhamnoside, quercetin 3-glucoside, quercetin 3,7-diglucoside, isorhamnetin 3-glucoside, and isorhamnetin 3,7-diglucoside, have been identified in the body and wings of the chalkhill blue butterflyLysandra coridon Poda. Flavonoids have also been found in 15 of a further 17 lycaenid species examined. Analysis of the two-dimensional paper chromatographic flavonoid patterns and aglycone results has shown that the flavonoid content ofL. coridon and the other lycaenids is dependent on the flavonoid content of the larval diet. Differences in the flavonoid patterns ofL. coridon and its leguminous larval food plantsHippocrepis comosa, Anthyllis vulneraria, andLotus corniculatus, indicate that the ingested flavonoids are metabolized byL. coridon or its gut flora before sequestration. Despite the presence of fiavones, glycoflavones, and isoflavones in the larval food plant species, only flavonols are sequestered by the lycaenid species examined. The relationship between lycaenid butterflies and their larval food plants, and the possible role(s) of flavonoids in lycaenids has been discussed. Interactions between ants, plants, flavonoids, and myrmecophilous lycaenids have also been considered. 相似文献
49.
50.
A micro-envioment for nerve cells and tissue growth were designed and constructed via surface modification of poly(L-lactide-co-glycolide)(PLGA)
with chitosan and hydroxyapatite(HA). The poly(L-lactide-co-glycolide)/chitosan/hydroxyapatite (PLGA/chitosan/HA) conduits
were manufactured by a combined solvent casting and particulate leaching technique. The conduits were highly porous with an
interconnected pore structure and 76.5% porosity. Micropores with 50–100 micrometer diameter were formed in the conduits.
In vivo application of PLGA/chitosan/HA conduits for reconstruction of 10 mm sciatic nerve defect was assessed by the walking
track analysis, the quantifying of the wet weight of tibialis anterior muscle and the histological assessment. The conduits
in host rats in vivo can not only be an effective in promoting regenerating of nerves but can also lead to favorable nerve
functional recovery.
Funded by the National Natural Science Foundation of China(No.50774096) 相似文献