全文获取类型
收费全文 | 638篇 |
免费 | 53篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 5篇 |
综合类 | 35篇 |
化学工业 | 295篇 |
金属工艺 | 4篇 |
机械仪表 | 13篇 |
建筑科学 | 34篇 |
矿业工程 | 7篇 |
能源动力 | 3篇 |
轻工业 | 209篇 |
水利工程 | 3篇 |
石油天然气 | 11篇 |
武器工业 | 2篇 |
无线电 | 14篇 |
一般工业技术 | 44篇 |
冶金工业 | 2篇 |
原子能技术 | 1篇 |
自动化技术 | 25篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 26篇 |
2021年 | 24篇 |
2020年 | 10篇 |
2019年 | 24篇 |
2018年 | 29篇 |
2017年 | 14篇 |
2016年 | 29篇 |
2015年 | 25篇 |
2014年 | 20篇 |
2013年 | 39篇 |
2012年 | 41篇 |
2011年 | 34篇 |
2010年 | 30篇 |
2009年 | 26篇 |
2008年 | 41篇 |
2007年 | 29篇 |
2006年 | 26篇 |
2005年 | 34篇 |
2004年 | 23篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 19篇 |
2000年 | 8篇 |
1999年 | 13篇 |
1998年 | 1篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 12篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1980年 | 1篇 |
排序方式: 共有707条查询结果,搜索用时 0 毫秒
21.
22.
On the basis of energy conservation law and surface pressure isotherm, the conformation energy changes of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) in pure phospholipid monolayer at the air/water interface during compression are derived. The optimized conformations of phospholipids at absolute freedom state are simulated by Gaussian 98 software. Based on following assumptions: (1)the conformation energy change is mainly caused by the rotation of one special bond; (2)the atoms of glycerol near the water surface are active; (3)the rotation is motivated by hydrogen-bond action; (4)the rotation of bond is inertial, one simplified track of conformational change is suggested and the conformations of DPPC and DPPG at different states are determined by the plots of conformation energy change vs. dihedral angle. The thickness of the simulated phospholipid monolayer is consistent with published experimental result. According to molecular areas at different states, the molecular orientations in the compressing process are also developed. 相似文献
23.
Cunshan Zhou Haile Ma Qingzhi Ding Lin Lin Xiaojie Yu Lin Luo Chunhua Dai Abu El-Gasim A. Yagoub 《Food and Bioproducts Processing》2013,91(4):665-671
The impact of ultrasound pretreatment of corn gluten meal (CGM) protein and neutrase on the ACE (angiotensin converting enzyme) inhibitory activity of hydrolysate was studied. The UV–vis differential spectra and fluorescence spectra of the CGM protein and neutrase were determined. The neutrase activity and the ACE inhibitory activity of the CGM protein hydrolysates were analyzed. The highest ACE inhibitory activity was obtained at 10 min hydrolysis when the CGM protein was pretreated at 20 kHz for 10–30 min and at a power of 1000 W. The neutrase activity and ACE inhibitory activity were at their maxima at sonication of 250 W and sonication time of 15 min. The fluorescence and UV differential spectra of the proteins of CGM and neutrase reflected molecular unfolding due to sonication. Sonication of the protein substrate and the enzyme before hydrolysis may be an effective way to enhance the ACE inhibition attributes of the hydrolysate. 相似文献
24.
引 言炉内受热面结渣被认为是电站锅炉中最难以处理的一个问题 ,特别在我国长时间内煤粉锅炉作为主要的能源供应手段 .近年来 ,国内有许多电站采用混煤燃烧的方法以适应不同的要求 ,如减少结渣和SOx 的排放 .然而 ,实际上如果混煤中设计使用的煤和实际使用的煤特性不一样 ,混煤燃烧可能会导致严重的结渣 .对单一煤种燃烧过程中的矿物质行为已经有了广泛研究[1~ 4 ] ,但对混煤很少有研究[5,6] .本文主要研究混煤燃烧后矿物质行为特性的变化 ,并用XRD分析矿物质形态随温度的变化 ,从矿物学的观点来解释混合煤灰熔融特性 ,以揭示混煤结… 相似文献
25.
26.
Chiaki Nakano Dr. Tsutomu Hoshino Prof. Dr. 《Chembiochem : a European journal of chemical biology》2009,10(12):2060-2071
The Rv3377c gene from the Mycobacterium tuberculosis H37 genome is specifically limited to those Mycobacterium species that cause tuberculosis. We have demonstrated that the gene product of Rv3377c is a diterpene cyclase that catalyzes the formation of tuberculosinol from geranylgeranyl diphosphate (GGPP). However, the characteristics of this enzyme had not previously been studied in detail with homogeneously purified enzyme. The purified enzyme catalyzed the synthesis of tuberculosinyl diphosphate from GGPP, but it did not bring about the synthesis of tuberculosinol. Optimal conditions for the highest activity were found to be as follows: pH 7.5, 30 °C, MgII (0.1 mM ), and Triton X‐100 (0.1 %). Under these conditions, the kinetic values of KM and kcat were determined to be 11.7±1.9 μM for GGPP and 12.7±0.7 min?1, respectively, whereas the specific activity was 186 nmol min?1 mg?1. The enzyme activity was inhibited at substrate concentrations higher than 50 μM . The catalytic activity was strongly inhibited by 15‐aza‐dihydrogeranylgeraniol and 5‐isopropyl‐N,N,N,2‐tetramethyl‐4‐(piperidine‐1‐carbonyloxy)benzenaminium chloride (Amo‐1618). The DXDTT293–297 motif, corresponding to the DXDDTA motif conserved among terpene cyclases, was mutated in order to investigate its function. The middle D295 was found to be the most crucial entity for the catalysis. D293 and two threonine residues function synergistically to enhance the acidity of D295, possibly through hydrogen‐bonding networks. The Rv3377c enzyme could also react with (14R/S)‐14,15‐oxidoGGPP to generate 3α‐ and 3β‐hydroxytuberculosinyl diphosphate. Conformational analyses were carried out with deuterium‐labeled GGPP and oxidoGGPP. We found that GGPP and (14R)‐oxidoGGPP adopted a chair/chair conformation, but (14S)‐oxidoGGPP adopted a boat/chair conformation. Interestingly, the conformations of oxidoGGPP for the A‐ring formation are the opposite of those of oxidosqualene when it is used as a substrate by squalene cyclases for the biosynthesis of hopene and tetrahymanol. (3R)‐Oxidosqualene is folded in a boat conformation, whereas (3S)‐2,3‐oxidosqualene folds into a chair conformation, for the formation of the A‐rings of the hopene and tetrahymanol skeletons, respectively. 相似文献
27.
Ruopei Xu Yue Qiu Siyi Tang Cheng Yang Yu Dai Dajie Zhang Yue Gao Kexiong Gao Longbo Luo Xiangyang Liu 《大分子材料与工程》2021,306(5):2000814
High performance fibers with high strength and toughness have great potential in composites, but contradiction between tensile strength and elongation at break makes the preparation to become a current challenge. Herein, an asymmetric structure of more flexible diamine, 3,4′-diaminodiphenyl ether (3,4′-ODA), is introduced into heterocyclic aramid (PBIA) fibers to replace rigid symmetric p-phenylenediamine (PDA). By studying the properties of copolymer (mPEBA) fibers with different ratios of diamine, it is found that the mPEBA fiber reached the optimal mechanical properties with the 30% content of 3,4′-ODA. Compared with homopolymerized heterocyclic aramid fibers, the tensile strength and elongation at break of mPEBA fiber are improved by 26.2% and 38.7%, respectively. Results of X-ray diffraction show that the introduction of 3,4′-ODA structure can increase stretchability of mPEBA fibers, improving the orientation degree during hot-drawing. Molecular dynamics simulations confirm that 3,4′-ODA structure undergoes a conformation transformation to form a straightened chain during hot-drawing, while symmetrical 4,4′-diaminodiphenyl ether (4,4′-ODA) cannot form the same conformation. The misplaced-nunchaku structure is formed based on the special meta-para position of 3,4′-ODA, achieving the synergy of high strength and high toughness. 相似文献
28.
29.
30.
潘春宇 《食品与生物技术学报》2000,19(4):418-421
分析了服装内空间的三重涵义及服装形态与内空间的关系 .比较了立体性服装与平面性服装在空间观念上的差异 .指出 :内空间设计是服装艺术的真正核心 ,也是未来服装设计发展的方向 . 相似文献