全文获取类型
收费全文 | 18882篇 |
免费 | 1281篇 |
国内免费 | 169篇 |
专业分类
电工技术 | 283篇 |
综合类 | 77篇 |
化学工业 | 4616篇 |
金属工艺 | 469篇 |
机械仪表 | 646篇 |
建筑科学 | 631篇 |
矿业工程 | 50篇 |
能源动力 | 1233篇 |
轻工业 | 1746篇 |
水利工程 | 241篇 |
石油天然气 | 265篇 |
武器工业 | 4篇 |
无线电 | 2006篇 |
一般工业技术 | 3735篇 |
冶金工业 | 1037篇 |
原子能技术 | 157篇 |
自动化技术 | 3136篇 |
出版年
2024年 | 83篇 |
2023年 | 373篇 |
2022年 | 843篇 |
2021年 | 1284篇 |
2020年 | 980篇 |
2019年 | 1076篇 |
2018年 | 1206篇 |
2017年 | 1078篇 |
2016年 | 1075篇 |
2015年 | 652篇 |
2014年 | 977篇 |
2013年 | 1788篇 |
2012年 | 1162篇 |
2011年 | 1245篇 |
2010年 | 868篇 |
2009年 | 753篇 |
2008年 | 574篇 |
2007年 | 495篇 |
2006年 | 421篇 |
2005年 | 277篇 |
2004年 | 243篇 |
2003年 | 231篇 |
2002年 | 182篇 |
2001年 | 142篇 |
2000年 | 142篇 |
1999年 | 139篇 |
1998年 | 290篇 |
1997年 | 236篇 |
1996年 | 192篇 |
1995年 | 139篇 |
1994年 | 110篇 |
1993年 | 113篇 |
1992年 | 80篇 |
1991年 | 80篇 |
1990年 | 74篇 |
1989年 | 64篇 |
1988年 | 49篇 |
1987年 | 53篇 |
1986年 | 68篇 |
1985年 | 57篇 |
1984年 | 53篇 |
1983年 | 54篇 |
1982年 | 35篇 |
1981年 | 32篇 |
1980年 | 29篇 |
1979年 | 24篇 |
1978年 | 32篇 |
1977年 | 35篇 |
1976年 | 47篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Solutions, within the framework of linear uncoupled thermoelasticity, are presented for certain problems of flexure of composite laminates. Benchmark numerical results, useful for the validation or otherwise of approximate laminate models, are tabulated. Finally, these results are used to examine the accuracy of the classical lamination theory based on Kirchhoff's hypothesis. 相似文献
92.
93.
Anmar W. Sabri Zainab H. Ali Serwan F. Shawkat Lamia A. Thejar Thaer I. Kassim Khalid A. Rasheed 《河流研究与利用》1993,8(3):237-250
The influences of the Samarra impoundment on the ecology of the downstream sector of the river Tigris are investigated. Zooplankton were collected monthly from July 1987 to July 1988. It was found that zooplankton were most abundant during high river discharges in March. During the month of low river discharge, September, the zooplankton population was greatly reduced immediately below the barrage and remained so to the last downstream station. Several factors seem to explain such differences. The high discharge from the impoundment was found to be the dominating factor and may flush the small backwaters in which zooplankton were abundant, thus increasing the population in the river. Zooplankton species vary in their ability to sustain populations in the river, variations which are due mainly to species-specific characteristics. 相似文献
94.
Second-law-based thermodynamic analysis of two-stage and mechanical-subcooling refrigeration cycles 总被引:1,自引:0,他引:1
Thermodynamic analysis of HFC-134a vapor-compression refrigeration cycles is investigated by both the first and second laws of thermodynamics. Second-law analysis is carried out for both two-stage and mechanical-subcooling refrigeration cycles. The analysis is performed on each of the system components to determine their individual contribution to the overall system irreversible losses. It is found that most of the losses are due to a low compressor efficiency. Irreversibilities of expansion valves and condenser are also significant. In addition, it is shown that the optimum inter-stage pressure for two-stage and mechanical-subcooling refrigeration systems is very close to the saturation pressure corresponding to the arithmetic mean of the refrigerant condensation and evaporation temperatures. These results are compared with the existing practice in the industry. Furthermore, theoretical results of a two-stage refrigeration system performance are also compared with experimental values for a CFC-22 system. 相似文献
95.
Nanotechnology research is booming worldwide, having an impact on multiple sectors and with a general belief that medical
and biological applications will form the greatest area of expansion over the next decade, driven by an attempt to bring radical
solutions to areas of unmet medical need. What is true in the USA is also being fulfilled in Europe, though generally at a
significantly lower investment level, even for ’large’ capital infrastructure and interdisciplinary centres. Against this,
the UK and its European partners are following the maxim ’small is beautiful’ and are attempting to identify and grow academic
research and commercial businesses in areas that traditional nanotechnology developments out of engineering or physics find
challenging. Thus, University College London and Imperial College, in a major joint project linked to other centres of excellence
both in the UK and in the rest of Europe, are building upon their internationally competitive medical and hard-matter research
activities to focus on and develop nanotechnology as a major sector of research activity. The two universities together form
one of the largest centres of biomedical research outside the USA. A novel approach to commercialisation has been taken, exemplified
by the establishment with government and private equity funds of a ‘Bionanotechnology Centre’ — this will act as a portal
for UK industry to access specialist skills to solve issues relating to developing nanotechnology-based medical applications,
for example, for environmental screening, diagnostics and therapy. This paper reviews our academic and business strategy with
examples from our current research portfolio, biased towards medicine as the London Centre for Nanotechnology’s most rapidly
growing area. 相似文献
96.
KS Min AR Khan MK Kwon YJ Jung Z Yun Y Kiso 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(8):909-915
The performance of a laboratory‐scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food‐waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food‐waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2 °C, and mesophilic: 35 ± 2 °C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food‐waste increased up to 920 mg dm?3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm?3) were found due to the conversion of VFA into biogas in the case of 25 wt % food‐waste, which increased significantly at HRT of 3–5 days. In terms of biogas composition (CO2 and CH4), the organic matter was converted into CO2 through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3–7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food‐waste content in the mixture. Yet, the higher concentration of food‐waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFAproduced g?1 VSfed day?1) was achieved in the 10 wt % food‐waste at ambient temperature and at a 5‐day HRT. Copyright © 2005 Society of Chemical Industry 相似文献
97.
Kazi Md. Shorowordi Md. Mohar Ali Bepari 《Journal of Materials Engineering and Performance》2002,11(6):625-630
Carbon (0.13%) steel samples containing about 0.48% molybdenum (Mo) singly and in combination with nickel (Ni) were carburized in a natural Titas gas atmosphere at a temperature of 1223 K (950 °C) and at a pressure of about 0.10 MPa (15 psia) for time periods ranging from 1–4 h followed by slow cooling in the furnace. Their microstructure was studied by optical microscopy. The austenite grain size of the case and the case depths were determined. It was found that Mo and Ni alone and in combination decrease the thickness of the cementite network near the surface of the carburized case of the steels. However, Ni is found to be more effective than Mo in decreasing the thickness of cementite network. Both Mo and Ni enhance the formation of Widmanstätten cementite plates at the grain boundary and within the grains near the surface of the carburized steels. However, Ni alone is more effective than Mo in the formation of Widmanstätten cementite plates. In the presence of Ni, Mo is much more effective in the formation of Widmanstätten cementite plates than Mo in absence of Ni. It was also revealed that both Mo and Ni increased the case depth. Ni is more effective than Mo in increasing the case depth. The combined effect of Mo and Ni is much greater than that of either Mo or Ni alone in increasing case depth. Mo as Mo carbide (Mo2C) particles refined the austenite grain size of the carburized case. Ni in solution was not found to have any effect in restricting grain growth of austenite, but the presence of Ni enhances the austenite grain size refining effect of Mo in the carburized case. 相似文献
98.
Presented here is a computerized capacity planning system for the IBM Microcomputer family. The system maintains the profile of the job shop in a data base along with data pertinent to various products that can be manufactured in the shop. Projected orders for the planning period are input to the system with their associated quantities and delivery dates. The system uses the forward and backward loading rules in generating capacity loading scenarios. User selects the best course of action which may satisfy delivery dates subject to the limitations of the work centers. Efficiency figures are provided to aid the user in his/her decision. 相似文献
99.
100.