全文获取类型
收费全文 | 5318篇 |
免费 | 345篇 |
国内免费 | 253篇 |
专业分类
电工技术 | 147篇 |
综合类 | 233篇 |
化学工业 | 1248篇 |
金属工艺 | 434篇 |
机械仪表 | 194篇 |
建筑科学 | 196篇 |
矿业工程 | 75篇 |
能源动力 | 173篇 |
轻工业 | 308篇 |
水利工程 | 22篇 |
石油天然气 | 322篇 |
武器工业 | 21篇 |
无线电 | 575篇 |
一般工业技术 | 1081篇 |
冶金工业 | 197篇 |
原子能技术 | 71篇 |
自动化技术 | 619篇 |
出版年
2024年 | 16篇 |
2023年 | 99篇 |
2022年 | 167篇 |
2021年 | 220篇 |
2020年 | 132篇 |
2019年 | 108篇 |
2018年 | 119篇 |
2017年 | 127篇 |
2016年 | 136篇 |
2015年 | 177篇 |
2014年 | 222篇 |
2013年 | 247篇 |
2012年 | 277篇 |
2011年 | 403篇 |
2010年 | 259篇 |
2009年 | 330篇 |
2008年 | 365篇 |
2007年 | 373篇 |
2006年 | 280篇 |
2005年 | 267篇 |
2004年 | 231篇 |
2003年 | 224篇 |
2002年 | 145篇 |
2001年 | 155篇 |
2000年 | 203篇 |
1999年 | 99篇 |
1998年 | 85篇 |
1997年 | 56篇 |
1996年 | 41篇 |
1995年 | 44篇 |
1994年 | 36篇 |
1993年 | 39篇 |
1992年 | 41篇 |
1991年 | 33篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 21篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 2篇 |
排序方式: 共有5916条查询结果,搜索用时 31 毫秒
991.
为满足神经受损患者下肢康复训练需要,设计了外骨骼下肢康复机器人,建立了其运动学解析关系;对患者的康复策略进行了分析选择.并对康复策略的轨迹控制方法进行了研究,详细讨论了基于固高GUC-8轴嵌入式运动控制器的主被动控制实现方法。 相似文献
992.
该文研究了在MRS培养基中添加0.05 mg/mL LA(Linoleic acid,LA)和不同浓度的乙醇时植物乳杆菌p-8的CLA(Conjugated linoleic acid,CLA)转化率和CLA合成相关酶转录水平的差异情况。结果显示,发酵液中的三种CLA异构体转化率都是在添加0.50%乙醇时最高,其中转化cis9,trans11-CLA(t9,t11-CLA)异构体最高,为2.49%,比不添加乙醇增加2.37倍。添加不同浓度乙醇的发酵液中trans10,cis12-CLA(t10,c12-CLA)转化率都是最低的。菌体中产生的CLA非常少,但规律与发酵液的基本一致。添加0.50%乙醇菌体中t9,t11-CLA转化率最高,其转化率仅为0.05%,比不添加乙醇增加了5倍。当乙醇浓度高于0.50%时,各种不同CLA异构体的转化率却都减少。结果表明CLA是在胞液内产生后再被运转到胞外的,一定浓度范围内的乙醇胁迫通过提高CLA合成相关的酶基因转录水平,进而促进了CLA的转化,可见CLA合成相关酶基因转录水平是造成CLA转化率差异的主要原因。结果为阐明植物乳杆菌p-8产CLA的分子机制和寻找有效提高CLA生成的调控手段奠定了基础。 相似文献
993.
994.
Al-Majid AM Barakat A Mabkhot YN Islam MS 《International journal of molecular sciences》2012,13(3):2727-2743
The synthesis of several novel chiral phosphoramidite ligands (L1–L8) with C2 symmetric, pseudo C2 symmetric secondary amines and chiral Brønsted acids 1a,b has been achieved. These chiral auxiliaries were obtained from commercially available d-mannitol, and secondary amines in moderate to excellent yields. Excellent diastereoselectivites of ten chiral auxiliaries were obtained. The chiral phosphoramidite ligands and chiral Brønsted acids were fully characterized by spectroscopic methods. 相似文献
995.
Amongst the four bases that form DNA, guanine is the most susceptible to oxidation, and its oxidation product, 7,8-dihydro-8-oxoguanine (8-oxoG) is the most prevalent base lesion found in DNA. Fortunately, throughout evolution cells have developed repair mechanisms, such as the 8-oxoguanine DNA glycosylases (OGG), which recognize and excise 8-oxoG from DNA thereby preventing the accumulation of deleterious mutations. OGG are divided into three subfamilies, OGG1, OGG2 and AGOG, which are all involved in the base excision repair (BER) pathway. The published structures of OGG1 and AGOG, as well as the recent availability of OGG2 structures in both apo- and liganded forms, provide an excellent opportunity to compare the structural and functional properties of the three OGG subfamilies. Among the observed differences, the three-dimensional fold varies considerably between OGG1 and OGG2 members, as the latter lack the A-domain involved in 8-oxoG binding. In addition, all three OGG subfamilies bind 8-oxoG in a different manner even though the crucial interaction between the enzyme and the protonated N7 of 8-oxoG is conserved. Finally, the three OGG subfamilies differ with respect to DNA binding properties, helix-hairpin-helix motifs, and specificity for the opposite base. 相似文献
996.
Tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL), a member of the TNF superfamily, interacts with its functional death receptors (DRs) and induces apoptosis in a wide range of cancer cell types. Therefore, TRAIL has been considered as an attractive agent for cancer therapy. However, many cancers are resistant to TRAIL-based therapies mainly due to the reduced expression of DRs and/or up-regulation of TRAIL pathway-related anti-apoptotic proteins. Compounds that revert such defects restore the sensitivity of cancer cells to TRAIL, suggesting that combined therapies could help manage neoplastic patients. In this article, we will focus on the TRAIL-sensitizing effects of natural products and synthetic compounds in colorectal cancer (CRC) cells and discuss the molecular mechanisms by which such agents enhance the response of CRC cells to TRAIL. 相似文献
997.
998.
An aerobic organocatalytic oxidative C C bond formation reaction of benzylic C H bonds with various C‐nucleophiles is described. The coupling reaction proceeds by simply stirring the substrates under elevated partial pressure of oxygen in the presence of a sulfonic acid catalyst at room temperature. Elevation of the pressure enables the reaction of a broad scope of nucleophile substrates otherwise showing poor reactivity at ambient pressure. The benzylic C H bonds of xanthene, acridanes, isochromane and related heterocycles could be functionalized with nucleophiles including ketones, 1,3‐dicarbonyl compounds and aldehydes. Electron‐rich arenes could be utilized as nucleophiles at elevated temperatures. The reactions are believed to proceed via autoxidation of the benzylic C H bonds to the hydroperoxides and subsequent nucleophilic substitution catalyzed by sulfonic acids. 相似文献
999.
Pavel Starkov Filippo Rota Jarryl M. D'Oyley Tom D. Sheppard 《Advanced Synthesis \u0026amp; Catalysis》2012,354(17):3217-3224
In the presence of a cationic gold(I) catalyst and N‐halosuccinimide, both trimethylsilyl‐protected and terminal alkynes are converted into alkynyl halides. Further experiments showed that silyl‐protected alkynes undergo electrophilic iodination and bromination under Brønsted acid catalysis, whilst terminal alkynes require a cationic gold catalyst. The former reactions probably proceed via activation of the electrophile, whilst the latter reactions proceed via a gold(I) acetylide intermediate. Gold‐catalysed halogenation was further combined with gold‐catalysed hydration and subsequent annulation to provide convenient routes to iodomethyl ketones and five‐membered aromatic heterocycles. 相似文献
1000.
Bo Jiang Mian‐Shuai Yi Man‐Su Tu Shu‐Liang Wang Shu‐Jiang Tu 《Advanced Synthesis \u0026amp; Catalysis》2012,354(13):2504-2510
Brønsted acid‐promoted divergent approaches for the synthesis of multi‐functionalized fused pyrroles with different substituted patterns (44 examples) have been established. The divergent pathways were controlled by varying the charging sequence to give a series of new fused pyrroles selectively. The direct C(sp3) S bond formation was achieved for the two‐step, one‐pot reaction. 相似文献