全文获取类型
收费全文 | 10012篇 |
免费 | 760篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 137篇 |
综合类 | 26篇 |
化学工业 | 2510篇 |
金属工艺 | 207篇 |
机械仪表 | 228篇 |
建筑科学 | 486篇 |
矿业工程 | 43篇 |
能源动力 | 163篇 |
轻工业 | 1700篇 |
水利工程 | 59篇 |
石油天然气 | 17篇 |
无线电 | 718篇 |
一般工业技术 | 2657篇 |
冶金工业 | 293篇 |
原子能技术 | 76篇 |
自动化技术 | 1454篇 |
出版年
2023年 | 144篇 |
2022年 | 187篇 |
2021年 | 383篇 |
2020年 | 204篇 |
2019年 | 218篇 |
2018年 | 371篇 |
2017年 | 380篇 |
2016年 | 431篇 |
2015年 | 327篇 |
2014年 | 405篇 |
2013年 | 757篇 |
2012年 | 531篇 |
2011年 | 639篇 |
2010年 | 539篇 |
2009年 | 511篇 |
2008年 | 556篇 |
2007年 | 500篇 |
2006年 | 372篇 |
2005年 | 302篇 |
2004年 | 234篇 |
2003年 | 246篇 |
2002年 | 227篇 |
2001年 | 190篇 |
2000年 | 147篇 |
1999年 | 133篇 |
1998年 | 126篇 |
1997年 | 115篇 |
1996年 | 100篇 |
1995年 | 64篇 |
1994年 | 76篇 |
1993年 | 62篇 |
1992年 | 48篇 |
1991年 | 53篇 |
1990年 | 34篇 |
1989年 | 37篇 |
1988年 | 31篇 |
1987年 | 37篇 |
1986年 | 48篇 |
1985年 | 105篇 |
1984年 | 66篇 |
1983年 | 52篇 |
1982年 | 51篇 |
1981年 | 42篇 |
1980年 | 49篇 |
1979年 | 34篇 |
1978年 | 40篇 |
1976年 | 29篇 |
1973年 | 30篇 |
1943年 | 26篇 |
1925年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
E. Michaelsen K. Jäger D. Roschkowski L. Doktorski M. Arens 《Pattern Recognition and Image Analysis》2012,22(1):44-53
Computer vision is an ever more important means for the navigation of UAVs. Here we propose a landmark recognition system
looking for salient man-made infrastructure. An object-oriented structural system is preferred since it can utilize known
properties of these objects such as part-of hierarchies, mutual geometric constraints of parts, generalization etc. The structure,
available for use as landmark, will vary strongly with the region the UAV is supposed to navigate in. The structural knowledge
can lose its meaning in two ways: 1) If the area contains a lot of non-intended structure fulfilling the demands modeled the
system will start hallucinating lots of landmarks anywhere. 2) If the landmarks in the area do not fulfill the demands modeled
they will not be detected. Up to a certain degree these semantics—or lack of meaning—can be investigated mathematically using
probabilistic models. But the results from this are very optimistic. In reality the meaning breaks down much earlier. This
contribution reports on an example: Testing a system, designed for a central European country (Germany), for use elsewhere
(e.g., Russia or Turkey). 相似文献
992.
Hanna-Liisa Kangas Jussi Lintunen Johanna Pohjola Lauri Hetemäki Jussi Uusivuori 《Energy Economics》2011,33(6):1165-1176
Increasing scarcity of oil reserves and the high CO2 emissions from using oil have contributed to the development of renewable biofuels. Pulp and paper mill integrated forest biorefineries offer one important means to increase biofuel production. This study analyzes the effects of policies to support biofuel production in the pulp and paper sector. We study the relative effectiveness of three biofuel supporting policy instruments, namely production subsidy, input subsidy and investment subsidy. We present a partial equilibrium pulp and paper market model with a biorefinery investment option. A numerical model is used to evaluate the impacts of policy instruments on wood prices, as well as input choices and investment strategies of pulp and paper industries. The data represent the Finnish pulp and paper sector. We evaluate the values and direct costs of the policy instruments in a situation of exogenous biofuel production targets. The direct costs of input and investment subsidies are higher than those of a production subsidy. With all the policy instruments, Finnish pulp and paper mills would invest in wood-gasifying technology, instead of black liquor based one. The number of biorefinery units is dependent on the subsidy type — investment and input subsidies are likely to result in more numerous but smaller biofuel production units than a production subsidy. With all the policy instruments the demand for wood increases in Finland leading to higher wood prices. This, in turn, could reflect negatively on the profitability of the pulp and paper industries. To a significant degree, the model and the results can be generalized to other countries and markets where integrated pulp and paper mills are operating. 相似文献
993.
994.
CIB working commission W23A on loadbearing walls has submitted proposals for a code dealing with the risk of progressive collapse of structures. The proposals have been forwarded to the international joint committee now preparing a model code on structural safety in general, and they are presented here with explanatory comments. 相似文献
995.
Tilman Esslinger Immanuel Bloch Theodor W. Hänsch 《Journal of Modern Optics》2013,60(14-15):2725-2732
Abstract We probe the spatial coherence properties of a magnetically trapped Bose gas. Two matter wave beams are extracted from two spatially separated regions of the trap and overlap outside the trapping region. The visibility of the resulting interference pattern measures the phase coherence between the regions of extraction. By varying the spatial separation between the two regions the first-order spatial correlation function of the trapped Bose gas can be measured. The location of the minima of the interference pattern is reproducible, which experimentally confirms that the trapped Bose-Einstein condensate is not fragmented into individual condensates. 相似文献
996.
997.
Heta Vuontisjärvi Marja Keinänen Pekka J. Vuorinen Kimmo Peltonen 《Polycyclic Aromatic Compounds》2013,33(4-5):333-342
Fish exposed to polycyclic aromatic hydrocarbons (PAHs) accumulate only a small amount of PAH in their tissues. Hydrophobic PAHs are readily transformed into hydrophilic metabolites and excreted in bile. Bile samples of five fish species were collected from the Baltic Sea and analyzed using two methods: high-performance liquid chromatography (HPLC) with fluorescence detection and a fixed wavelength fluorescence method. With the HPLC method PAH compounds were quantitated after hydrolysis, and with the fluorescence method without enzyme-assisted hydrolysis. In HPLC analysis the major metabolite in all fish species, 1-hydroxypyrene, was the only metabolite detected in perch and salmon samples. 1-Hydroxyphenanthrene was detected in a few flounder and in most eelpouts. The correlation between the two methods for pyrene-type metabolites was good (r2 = 0.773). 相似文献
998.
999.
Dr.‐Ing. Wilfried Rähse 《化学,工程师,技术》2013,85(6):886-900
In the last fifty years, powder and granular detergents have been significantly improved in performance and ecology: more concentrated (less chemicals), biodegradable surfactants, no phosphates, reduced water and energy consumption. The use of optimized enzymes and bleaching boosters enables lowered wash temperatures and the removal of natural stains. The production of solid detergents runs either in spray towers without and with compaction step, or in a non‐tower agglomeration plant. The latest generation of granulation with an integrated mill for simultaneous drying and grinding allows the production of spherical particles, which can be adjusted (small or large, heavy or light). Future formulations will enable lower washing temperatures. 相似文献
1000.