全文获取类型
收费全文 | 23889篇 |
免费 | 963篇 |
国内免费 | 319篇 |
专业分类
电工技术 | 481篇 |
综合类 | 543篇 |
化学工业 | 4618篇 |
金属工艺 | 562篇 |
机械仪表 | 809篇 |
建筑科学 | 941篇 |
矿业工程 | 182篇 |
能源动力 | 630篇 |
轻工业 | 2524篇 |
水利工程 | 276篇 |
石油天然气 | 185篇 |
武器工业 | 27篇 |
无线电 | 2594篇 |
一般工业技术 | 3236篇 |
冶金工业 | 4188篇 |
原子能技术 | 196篇 |
自动化技术 | 3179篇 |
出版年
2023年 | 149篇 |
2022年 | 560篇 |
2021年 | 684篇 |
2020年 | 357篇 |
2019年 | 412篇 |
2018年 | 467篇 |
2017年 | 444篇 |
2016年 | 503篇 |
2015年 | 427篇 |
2014年 | 636篇 |
2013年 | 1198篇 |
2012年 | 940篇 |
2011年 | 1158篇 |
2010年 | 883篇 |
2009年 | 950篇 |
2008年 | 924篇 |
2007年 | 938篇 |
2006年 | 788篇 |
2005年 | 683篇 |
2004年 | 739篇 |
2003年 | 948篇 |
2002年 | 1235篇 |
2001年 | 1045篇 |
2000年 | 618篇 |
1999年 | 572篇 |
1998年 | 1509篇 |
1997年 | 963篇 |
1996年 | 714篇 |
1995年 | 463篇 |
1994年 | 360篇 |
1993年 | 389篇 |
1992年 | 207篇 |
1991年 | 164篇 |
1990年 | 154篇 |
1989年 | 157篇 |
1988年 | 141篇 |
1987年 | 115篇 |
1986年 | 123篇 |
1985年 | 164篇 |
1984年 | 91篇 |
1983年 | 97篇 |
1982年 | 91篇 |
1981年 | 113篇 |
1980年 | 103篇 |
1979年 | 66篇 |
1978年 | 51篇 |
1977年 | 107篇 |
1976年 | 205篇 |
1975年 | 51篇 |
1973年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
De RG Moio L Napolitano F Grasso F Gubitosi L Bordi A 《Journal of chemical ecology》2002,28(2):269-281
Goat feeding preferences for straw pellets flavored with ryegrass (Lolium perenne, cv. Belida) or white clover (Trifolium repens, cv. Huia) aromatic extracts, obtained by means of a cold aromatic extraction method, were assessed with cafeteria trials. Prior to the trials, odor differences between the two plant species, the two aromatic extracts, and the straw pellets sprayed with the two aromatic extracts were verified using sensory analysis performed by 30 human panelists. Since odor differences observed among fresh samples were still detectable in aromatic extracts and moistened pellets, the extraction method was considered effective in reproducing plant odors. Straw pellets sprayed with either distilled water (W) or ryegrass (R) or clover (C) aromatic extracts were used to assess flavor preferences of 12 female Rossa Mediterranea goats. Sprayed pellet preference was evaluated in two sessions conducted in two consecutive weeks. Each session consisted of three two-choice presentations performed on three consecutive days. In both sessions, food intake, proportion of food intake, time spent feeding, and proportion of time spent feeding were significantly affected by pellet type (0.05 > P > 0.001). In particular, straw pellets sprayed with ryegrass extract were highly selected compared to those sprayed with clover (0.01 > P > 0.001) or water (0.01 > P > 0.001). In addition, in the second session, the clover extract was preferred to distilled water (0.05 > P > 0.01). The results of this study gave two main indications: first, goat selectivity for ryegrass against clover was consistent even when straw pellets sprayed with odors of these plants were offered, and secondly, the addition of aromatic extracts to straw pellets increased the preference for pellets. 相似文献
992.
Os-catalyzed dihydroxylation will find more widespread application if truly heterogeneous catalysts are available which use O2 or H2O2 as terminal oxidants. This paper discusses and critically evaluates the concepts by which Os can be anchored on solid supports. New methods are also available for reoxidation of hexavalent to octavalent Os. 相似文献
993.
以葡萄糖为辅助底物发酵生产1,3-丙二醇的研究 总被引:16,自引:0,他引:16
采用Klebsiellapneumoniae对葡萄糖作为辅助底物发酵生产 1 ,3 丙二醇进行了研究。结果表明葡萄糖单独作为底物发酵时不生成 1 ,3 丙二醇。以葡萄糖和甘油为混合底物时 ,则可以显著提高菌体浓度 ,但是 1 ,3 丙二醇浓度和甘油到 1 ,3 丙二醇转化率没有提高。在甘油为底物的批式发酵过程中 ,通过流加葡萄糖作为辅助底物可以提高甘油到 1 ,3 丙二醇的摩尔转化率 ,同时可缩短发酵时间。通过选择合适的葡萄糖流加速率 ,较以甘油为单一底物的发酵结果 ,1 ,3 丙二醇的摩尔转化率最高可达0 649,提高了 53 4% ;生产强度为 1 0 0 5g/ (L·h) ,提高了 1 39 9%。 相似文献
994.
1,3-丙二醇发酵过程中底物抑制及其对策的研究 总被引:14,自引:1,他引:14
研究了底物甘油浓度对Klebsiellapneumoniae发酵生产 1 ,3 丙二醇的影响 ,并通过实验确定了最佳的初始甘油浓度和甘油开始对产物生成产生抑制作用的浓度。针对底物抑制现象 ,提出了菌种驯化和流加甘油发酵两种解决途径。结果表明 :采用原始菌株发酵 ,适宜的甘油初始浓度为 642 .4mmol/L ,此时 1 ,3 丙二醇浓度和转化率分别可达 2 60mmol/L和 0 .492mol/mol;在较高甘油初始浓度 (789mmol/L)的情况下 ,经驯化培养获得的耐底物抑制菌株 ,可将最终 1 ,3 丙二醇浓度和转化率分别提高到 30 0 .9mmol/L和 0 .530mol/mol;采用流加甘油发酵工艺 ,1 ,3 丙二醇浓度和转化率分别可提高到 397.7mmol/L和 0 .62 5mol/mol。 相似文献
995.
996.
997.
发展加氢工艺技术优产润滑油基础油 总被引:2,自引:0,他引:2
论述了润滑油基础油的生产消费情况 ,分析了加氢工艺技术与传统工艺的区别。介绍了加氢处理、催化脱蜡和异构脱蜡 3种加氢工艺的特点及其专利技术和应用情况。着重对异构脱蜡工艺进行了介绍 ,指出了发展异构脱蜡工艺的必要性 相似文献
998.
Several polyimide resins were tested as possible scratch resistant coatings for aluminosilicate glass centrifuge tubes. Tubes with siloxane pretreatments provided the best adhesion between the polyimide and glass surface. Resins synthesized with an alkoxysilane group incorporated into the polyimide chain also showed improved adhesion, but the results were not as significant as when the pretreatment was used. Elastic recovery and effective Young's modulus of the polyimide coatings were calculated from nano-scratching. The results indicate that polyimides with a lower modulus, and higher elastic recovery, protected the glass surface best, exhibiting compression of the coating layer. An example was poly-4-4'-oxydiphenylene pyromellitimide (PMDA-ODA), whereas the coatings with a high effective Young's modulus and low elastic recovery ruptured. An example of a failed coating was poly-4,4'-carbonyldiphenylene 3,3',4,4'-biphenylenetetracarboximide (BPDA-DABP) which had low amount of elastic recovery, high effective Young's modulus and a large amount of flaking during macroscratch testing. 相似文献
999.
Dufour Gland Contents of Ants of the Cataglyphis bicolor Group 总被引:1,自引:0,他引:1
The species of desert-dwelling ants of the Cataglyphis bicolor (Hymenoptera: Formicidae) group are difficult to distinguish by morphological features. Analysis of the secretion from the Dufour glands of workers of a number of colonies was undertaken to see if it provided a clear test of species. Linked 6c-ms showed in all samples straight and branched-chain alkanes, linear alkenes, ketones, aldehydes, acetates, and a group of C22 to C28 esters not previously identified in this genus. Contents of the Dufour glands of C. savignyi from Tunisia and Egypt were similar, and comprised straight and branched-chain alkanes, alkenes and small amounts of esters. C. bicolor from Tunisia contained compounds similar to C. savignyi but was distinguished from the latter by larger amounts of the esters. The major compound in the glands of C. viaticus was tridecane, in contrast to the pentadecane of other species. It also contained a branched alkane, 3-methyltridecane as a major component. Branched-chain esters and a wide variety of acetates were also found in this species. C. diehlii had a limited range of compounds, with branched alkanes almost completely absent and high proportions of pentadecene and dodecyl acetate. C. bombycinus, a sympatric species, but recognized as not belonging to the bicolor group by its different mandibular gland substances, was notable in having butanoate esters in its Dufour glands. Despite these differences among species, both the great variability of individuals from a single colony and the among between conspecific colonies make species diagnosis from a few individuals difficult, in contrast with postpharyngeal glands, which, as recently reported, give a clearer indication of species. 相似文献
1000.
The influence of convective heat transfer on constant current density anodizing of aluminium in sulfuric acid has been examined in a wall-jet electrode reactor. The uniformity of the anodic film thickness is related to the local electrode temperature distribution, which is dependent on the convection. The higher the local temperature, the greater the local oxide thickness. An increased local temperature enhances local field assisted oxide dissolution at the pore bases, and consequently acts to increase the local current density. At relatively high current densities, local features develop on the electrode surface, accompanied by high initial, local temperature rises. The relevance of such local features, limiting useful oxide growth, is considered further. 相似文献