全文获取类型
收费全文 | 3587篇 |
免费 | 109篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 82篇 |
综合类 | 22篇 |
化学工业 | 903篇 |
金属工艺 | 89篇 |
机械仪表 | 42篇 |
建筑科学 | 159篇 |
矿业工程 | 11篇 |
能源动力 | 60篇 |
轻工业 | 353篇 |
水利工程 | 26篇 |
石油天然气 | 21篇 |
无线电 | 265篇 |
一般工业技术 | 619篇 |
冶金工业 | 657篇 |
原子能技术 | 38篇 |
自动化技术 | 352篇 |
出版年
2022年 | 36篇 |
2021年 | 60篇 |
2020年 | 39篇 |
2019年 | 48篇 |
2018年 | 50篇 |
2017年 | 38篇 |
2016年 | 58篇 |
2015年 | 57篇 |
2014年 | 75篇 |
2013年 | 148篇 |
2012年 | 123篇 |
2011年 | 174篇 |
2010年 | 98篇 |
2009年 | 115篇 |
2008年 | 130篇 |
2007年 | 152篇 |
2006年 | 127篇 |
2005年 | 93篇 |
2004年 | 100篇 |
2003年 | 81篇 |
2002年 | 75篇 |
2001年 | 63篇 |
2000年 | 76篇 |
1999年 | 64篇 |
1998年 | 158篇 |
1997年 | 109篇 |
1996年 | 91篇 |
1995年 | 79篇 |
1994年 | 60篇 |
1993年 | 57篇 |
1992年 | 38篇 |
1991年 | 46篇 |
1990年 | 45篇 |
1989年 | 38篇 |
1988年 | 46篇 |
1987年 | 39篇 |
1986年 | 41篇 |
1985年 | 42篇 |
1984年 | 43篇 |
1983年 | 31篇 |
1982年 | 45篇 |
1981年 | 35篇 |
1980年 | 28篇 |
1979年 | 32篇 |
1978年 | 31篇 |
1976年 | 54篇 |
1975年 | 35篇 |
1974年 | 39篇 |
1973年 | 37篇 |
1972年 | 35篇 |
排序方式: 共有3699条查询结果,搜索用时 312 毫秒
1.
2.
Werner Hoffmann 《International journal of molecular sciences》2015,16(8):19153-19169
Gastric cancer is still a leading cause of cancer-related mortality worldwide in spite of declining incidence. Gastric cancers are, essentially, adenocarcinomas and one of the strongest risk factors is still infection with Helicobacter pylori. Within the last years, it became clear that gastric self-renewal and carcinogenesis are intimately linked, particularly during chronic inflammatory conditions. Generally, gastric cancer is now regarded as a disease resulting from dysregulated differentiation of stem and progenitor cells, mainly due to an inflammatory environment. However, the situation in the stomach is rather complex, consisting of two types of gastric units which show bidirectional self-renewal from an unexpectedly large variety of progenitor/stem cell populations. As in many other tumors, cancer stem cells have also been characterized for gastric cancer. This review focuses on the various gastric epithelial stem cells, how they contribute to self-renewal and which routes are known to gastric adenocarcinomas, including their stem cells. 相似文献
3.
Annika Jahn Anton Hoffmann Luisa Blaesing Fabian Kunde Martin Bertau Martina Bremer Steffen Fischer 《化学,工程师,技术》2020,92(11):1733-1740
The enzymatic conversion of lignins, possibly in combination with electrochemical oxidation, makes aromatics such as syringol, guaiacol, vanillin and catechol available in the qualities required by the fragrance industry. The lignins were obtained by soda digestion from wheat straw and Miscanthus, characterized and then converted with laccases. The overall yield amounted up to 9 wt % with a product spectrum confined to four substances. Catechol was the major product, with a fraction of ≈75 %. It can easily be isolated by extraction with acetone. 相似文献
4.
5.
6.
众所周如,西藏地区是研究地球深部结构和构造的窗口,是研究大陆板块学说的重要场所,也是寻找热源和其它矿产资源的有利地区.因此,世界各国地学科学家都希望在本地区进行科学研究工作,或与我国科学工作者协作共同探索这一重要地区.中国和法国的地质、地球物理科学家经商讨共同组成“中法喜马拉雅山地质研究队”,对西藏中部广大地区进行地质、地球物理的科学研究工作.深部地震探测是地球物理研究中的重要内容.中法双方共同决定,在中国西藏南部的日喀则地区至北边的那曲地区作地震探测工作.为了探测地壳上地幔的结构,1981年在西藏的南部佩枯错至普莫雍错500公里的喜马拉雅山北麓——雅鲁藏布江地区进行了人工爆炸地震探测工作.本文是中法地质研究队合作的深部地震探测资料的解释结果. 相似文献
7.
8.
An analytical solution is presented to the problem of steady groundwater flow seeping into a pumped cylindrical hole partially penetrating a homogeneous and anisotropic confined aquifer overlying a gravel substratum. Solutions are obtained for two general cases of the problem: (1) when the level of the pumped hole is below the confining layer; (2) when it is above it. The validity of the proposed theory is tested by comparing analytical predictions obtained for a few flow situations with corresponding results obtained by numerical means. The theory presented here can be utilized to convert the rate of rise of water in a pumped auger hole into directional conductivities of soil, in areas where water is found to be in a confined state overlying a gravel substratum. The study shows that the conductivity values calculated by neglecting the confining pressure of an artesian aquifer with a gravel base [i.e., by applying the existing (Boast and Kirkham in 1971), auger hole seepage theory for a phreatic aquifer with a gravel base to confined situations] may result in serious error; hence, the artesian head of an aquifer must be accounted for while computing the conductivity values. Further, it is observed that the area contributing flow to a pumped auger hole/well with a gravel base is mostly restricted to a short radial distance from the center of the hole, particularly for situations where the gravel substratum is located close to the bottom of the hole. This is in contrast to auger hole flow situations overlying an impervious substratum, where the domain contributing flow is mostly spread out to a considerable distance from the center of the hole. 相似文献
9.
W. Sjoerd Kijlstra Joop C.M.L. Daamen Jolinde M. van de Graaf Bart van der Linden Eduard K. Poels Alfred Bliek 《Applied catalysis. B, Environmental》1996,7(3-4):337-357
The effect of water on the selective catalytic reduction (SCR) of nitric oxide with ammonia over alumina supported with 2–15 wt.-% manganese oxide was investigated in the temperature range 385–600 K, with the emphasis on the low side of this temperature window. Studies on the effect of 1–5 vol.-% water vapour on the SCR reaction rate and selectivity were combined with TPD experiments to reveal the influence of water on the adsorption of the single SCR reactants. It turned out that the activity decrease due to water addition can be divided into a reversible inhibition and an irreversible deactivation. Inhibition is caused by molecular adsorption of water. TPD studies showed that water can adsorb competitively with both ammonia and nitric oxide. Additional kinetic experiments revealed that adsorbed ammonia is present in excess on the catalyst surface, even in the presence of water. Reduced nitric oxide adsorption is responsible for the observed reversible decrease in the reaction rate; the fractional reaction order changes from 0.79 in the absence of water to 1.07 in its presence. Deactivation is probably due to the dissociative adsorption of water, resulting in the formation of additional surface hydroxyls. As the amount of surface hydroxyls formed is limited to a saturation level, the deactivating effect on the catalyst is limited too. The additional hydroxyls condense and desorb in the temperature range 525–775 K, resulting in a lower degree of deactivation at higher temperature. A high temperature treatment at 775 K results in a complete regeneration. The amount of surface hydroxyls formed per unit surface area decreases at increasing MnOx-loading. The selectivity to the production of nitrogen is enhanced significantly by the presence of gas phase water. 相似文献
10.
C Müller H Dienemann H Hoffmann H Berger M Storck A Jolk FW Schildberg 《Canadian Metallurgical Quarterly》1993,118(9):543-548
The treatment of tracheo-bronchial stenosis or tracheomalacia is mainly carried out by means of resection or tracheoplastic operative strategies. Since the introduction of metal-mesh stents, a definitive endoluminal therapy has to be considered under new aspects. Six patients with malignant stenosis or tracheomalacia due to compression were treated by implantation of Palmaz- or Wallstents. Immediately after the implantation, patients were relieved from dyspnoea, the forced inspiratory volume-1 (FIV1) was normalized. All implanted stents were well tolerated, even in the long-time follow-up (19 months). Bronchoscopic control showed overgrowth of the metal meshes by respiratory epithelium. The implantation of metal-mesh stents is an adequate alternative in the treatment of malignant stenosis and tracheomalacia. 相似文献