首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3438篇
  免费   199篇
  国内免费   1篇
电工技术   98篇
综合类   5篇
化学工业   851篇
金属工艺   71篇
机械仪表   110篇
建筑科学   110篇
矿业工程   8篇
能源动力   138篇
轻工业   498篇
水利工程   26篇
石油天然气   14篇
无线电   251篇
一般工业技术   815篇
冶金工业   71篇
原子能技术   19篇
自动化技术   553篇
  2023年   23篇
  2022年   26篇
  2021年   79篇
  2020年   62篇
  2019年   72篇
  2018年   138篇
  2017年   119篇
  2016年   155篇
  2015年   118篇
  2014年   161篇
  2013年   365篇
  2012年   238篇
  2011年   251篇
  2010年   208篇
  2009年   148篇
  2008年   164篇
  2007年   141篇
  2006年   119篇
  2005年   58篇
  2004年   41篇
  2003年   63篇
  2002年   52篇
  2001年   38篇
  2000年   47篇
  1999年   34篇
  1998年   34篇
  1997年   30篇
  1996年   36篇
  1995年   29篇
  1994年   36篇
  1993年   29篇
  1992年   30篇
  1991年   25篇
  1990年   22篇
  1989年   19篇
  1988年   15篇
  1985年   33篇
  1984年   36篇
  1983年   29篇
  1982年   24篇
  1981年   37篇
  1980年   34篇
  1979年   25篇
  1978年   25篇
  1977年   20篇
  1976年   22篇
  1975年   14篇
  1974年   11篇
  1973年   14篇
  1972年   15篇
排序方式: 共有3638条查询结果,搜索用时 15 毫秒
101.
The solubility of soybean oil in supercritical carbon dioxide has been determined in the pressure range of 100–300 bar and in the temperature range of 313–323 K. The obtained values (from 0.0005 to 0.02055 g L?1) have been correlated using four different empirical equations proposed correspondingly by Chrastil, del Valle and Aquilera, Adachi and Lu and Sparks et al. Since the Sparks et al. equation provided the lowest average absolute relative deviation (AARD) (10.25%) than other models in the examined experimental range, a modified equation of Sparks et al. model was developed for predicting the solubility of soybean oil in supercritical carbon dioxide as a function of temperature and density. An improved equation showed the lowest deviation (2.15%) between experimental data than the other empirical equations considered in this study. The proposed equation was also applied for correlating the solubility of linoleic acid (AARD was 2.40%).  相似文献   
102.
103.
Coastal parts of Croatia are dominated by the SW‐verging Dinaric foldbelt, to the west and SW of which is the Adriatic Basin (the stable foreland). In both areas, the stratigraphic column is dominated by a thick carbonate succession ranging from Carboniferous to Miocene. Four megasequences have been identified: (i) a pre‐platform succession ranging in age from Late Carboniferous (Middle Pennsylvanian: Moscovian) to Early Jurassic (Early Toarcian; Bru?ane and Ba?ke Ostarije Formations); (ii) an Early Jurassic to Late Cretaceous platform megasequence (Mali Alan Formation); (iii) a Paleogene to Neogene post‐platform megasequence (Ra?a Formation); and (iv) a Neogene to Quaternary (Pliocene to Holocene) megasequence (Istra and Ivana Formations). A number of organic‐rich intervals with source rock potential have been identified on‐ and offshore Croatia: Middle and Upper Carboniferous, Upper Permian, Lower and Middle Triassic, Lower and Upper Jurassic, Lower and Upper Cretaceous, Eocene, and Pliocene – Pleistocene. Traps and potential plays have been identified from seismic data in the Dinaric belt and adjacent foreland. Evaporites of Permian, Triassic and Neogene (Messinian) ages form potential regional seals, and carbonates with secondary porosity form potential reservoirs. Oil and gas shows in wells in the Croatian part of the Adriatic Basin have been recorded but no oil accumulations of commercial value have yet been discovered. In the northern Adriatic offshore Croatia, Pliocene hemi‐pelagic marlstones and shales include source rocks which produce commercial volumes of biogenic gas. The gas is reservoired in unconsolidated sands of the Pleistocene Ivana Formation.  相似文献   
104.
Geographic information systems have the potential to aid planning functions in both data processing and decision making. Because the incorporation of GIS technology into local government is at an early stage, knowledge about GIS implementation and its impact on planning activities is scarce. Using a survey of local governments in four southeastern states, this paper explores how the new technology affects planning and whether it meets the expectations of the planning agencies using it. Most of the agencies surveyed report improvements in communication of information, data accessibility, and data accuracy. They report that more current data are available, and they have confidence in analyses performed with GIS technology. Political support, staffing, length of experience with GIS technology, system sharing, data-base contents, and number and type of GIS applications all exert some influence on either planning operations or decision making. While experience with GIS emerged as the most significant factor in achieving operational benefits, using GIS technology for analytical tasks positively affected improvements in decision making.  相似文献   
105.
Supercritical (SC) CO2 extraction of dried Immortelle flowers was performed at different process parameters. The optimal extraction conditions related to the yield were determined by response surface methodology (yield 4.09% at 20 MPa and 52°C). The extracts were analyzed by GC-MS and tremetone derivatives dominated: bitalin A, 12-acetoxytremetone, gnaphaliol, 1-[2-(2-methyl-2,3-dihydroxypropyl)-2,3-dihydro-1-benzofuran-5-yl]ethanone, isobutyl bitalin A, and 1-[2-(acetylprop-1-en-2-yl)-3-hydroxy-2,3-dihydro-1-benzofuran-5-yl]ethanone. Striking differences were found among the essential oil and SC-CO2 extracts composition. The major oil compounds were γ-curcumene, α-pinene, β-selinene, α-selinene, and limonene. Mono- and sesquiterpene were found among minor constituents of the extracts. Neryl acetate was present in the extracts and essential oil.  相似文献   
106.
Polyethylene (PE) was modified and prepared as double-layer polyethylene/polycaprolactone (PE/PCL) film. Magnetite and casein were added to the PCL-coating film to improve barrier properties and prevent destruction of basic structure of primary polymer PE. Significant improvements were observed with regards to mechanical (tensile strength, elongation at break) and thermal properties, while barrier (O2 permeability) properties were slightly improved. Overall migration values into acetic acid were lower (from 1 to 4.6 mg/dm2) than the upper limit set by the legislation. Specific migration of iron in PE/PCL-Fe samples is also below (µg/L) specific migration limit value set by the legislation (mg/kg).  相似文献   
107.
Journal of Applied Electrochemistry - The consumption of critical raw materials, especially those in permanent magnets of Nd–Fe–B and Sm–Co-type, has significantly grown in the...  相似文献   
108.
12-Lipoxygenase is crucial for tumour angiogenesis. 5,6,7-Trihydroxy-2-phenyl-4H-1-benzopyran-4-one (baicalein) is a suitable inhibitor for this enzyme but is rapidly metabolised in vivo. Thus, an improvement of the metabolic stability is necessary to enhance the therapeutic efficiency. An emerging approach to enhance metabolic stability of carbon-based pharmaceuticals is the use of metabolically stable, non-toxic boron clusters, such as dicarba-closo-dodecaborane(12)s (carboranes) as phenyl mimetics. Therefore, the unsubstituted phenyl ring of baicalein was replaced by meta-carborane, resulting in borcalein, the carborane analogue of baicalein. This substitution resulted in a decreased inhibitory activity toward 12-lipoxygenase, but led to increased toxicity in melanoma (A375, B16, B16F10) and colon cancer cell lines (SW480, HCT116, CT26CL25) with decreased tumour selectivity in comparison to baicalein. Surprisingly, borcalein displays a different mechanism of cytotoxicity with increased intracellular production of reactive oxygen species (ROS), reactive nitrogen species (RNS) and nitric oxide (NO).  相似文献   
109.
110.
Despite benefiting from vast fuel reserves, combustion of low-rank coals is commonly characterized by low thermal efficiency and high pollutant emissions, partly due to high moisture content of the coals in question. Thus, removal of moisture from low-rank coals is deemed an important quality upgrading method. The paper provides an overview of the current status of low-rank coal upgrading technologies, particularly with respect to utilization of drying and dewatering procedures. In order to examine the influence of relevant parameters on the moisture removal process, a model of convective coal drying in a packed, as well as in a fluid bed combustion arrangement, is developed and presented. Product-specific data (intraparticle mass transfer, gas–solid moisture equilibrium) related to the coal variety addressed herein (lignite) are obtained through preliminary investigations. Effective thermal conductivity of the packed bed as defined by Zehner/Bauer/Schlünder is used to define heat transfer mechanisms occurring in the packed bed. Similar two-phase fluidization model has been validated for different types of biomaterials.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号