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   1992篇
  免费   96篇
  国内免费   6篇
电工技术   22篇
综合类   5篇
化学工业   501篇
金属工艺   30篇
机械仪表   39篇
建筑科学   120篇
矿业工程   32篇
能源动力   37篇
轻工业   155篇
水利工程   29篇
石油天然气   4篇
无线电   135篇
一般工业技术   325篇
冶金工业   147篇
原子能技术   5篇
自动化技术   508篇
  2023年   20篇
  2022年   32篇
  2021年   59篇
  2020年   28篇
  2019年   26篇
  2018年   59篇
  2017年   51篇
  2016年   79篇
  2015年   69篇
  2014年   81篇
  2013年   95篇
  2012年   112篇
  2011年   135篇
  2010年   79篇
  2009年   117篇
  2008年   103篇
  2007年   89篇
  2006年   100篇
  2005年   69篇
  2004年   64篇
  2003年   49篇
  2002年   54篇
  2001年   31篇
  2000年   29篇
  1999年   36篇
  1998年   32篇
  1997年   36篇
  1996年   38篇
  1995年   38篇
  1994年   30篇
  1993年   20篇
  1992年   15篇
  1991年   17篇
  1990年   15篇
  1989年   6篇
  1988年   9篇
  1987年   14篇
  1985年   14篇
  1984年   14篇
  1983年   12篇
  1982年   5篇
  1981年   9篇
  1980年   9篇
  1979年   8篇
  1978年   11篇
  1977年   6篇
  1976年   14篇
  1975年   9篇
  1973年   4篇
  1971年   6篇
排序方式: 共有2094条查询结果,搜索用时 31 毫秒
111.
Acute transplant rejection is the leading cause of graft loss in the first months after kidney transplantation. Lipoxygenase products mediate pro- and anti-inflammatory actions and thus we aimed to correlate the histological reports of renal transplant biopsies with urinary lipoxygenase products concentrations to evaluate their role as a diagnostic marker. This study included a total of 34 kidney transplant recipients: 17 with an acute transplant rejection and 17 controls. LTE4, LTB4, 12-HETE and 15-HETE concentrations were measured by enzyme immunoassay. Urinary lipoxygenase product concentrations were not significantly changed during an acute allograft rejection. Nevertheless, LTB4 concentrations correlated significantly with the body temperature (P ≤ 0.05) 3 months after transplantation, and 12- and 15-HETE concentrations correlated significantly with renal function (P ≤ 0.05) 2 weeks after transplantation. In conclusion, our data show a correlation for LTB4 with the body temperature 3 months after transplantation and urinary 12- and 15-HETE concentrations correlate positively with elevated serum creatinine concentrations but do not predict acute allograft rejection.  相似文献   
112.
In order to distinguish between aerobic biodegradation of synthetic polymers in fresh and seawater, polyethylene glycols (PEGs) were systematically and comparatively investigated in inocula from municipal wastewater and seawater aquarium filters for the first time. The molecular weight (MW) of the PEGs, (HO(CH(2)CH(2)O)(n)H, n=3-1350) as representatives of water-soluble polymers, ranged from 250 to 57,800Da. The biodegradation was observed by removal of dissolved organic carbon and carbon dioxide production by applying standardized ISO and OECD test methods. Specific analyses using liquid chromatography mass spectrometry (LC-MS) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) were performed. All PEGs selected were completely biodegradable in freshwater media within 65d. PEGs with an MW up to 14,600Da have a similar degradation pathway which is characterized by gradual splitting of C(2)-units off the chain resulting in formation of short-chain PEGs. In artificial seawater media, full biodegradation of PEGs up to 7400Da required more time than in freshwater. PEGs with MW 10,300 and 14,600Da were only partially degraded whereas PEGs with MW 26,600 and 57,800Da were not degraded for a period of 135d. The biodegradation pathway of PEG 250 and PEG 970 in seawater is similar to that for freshwater. For PEGs having an MW from 2000 to 10,300Da, the degradation pathway in seawater differs from the pathway of the shorter PEGs.  相似文献   
113.
Synthesis and Properties of Liquid Crystalline Derivatives of Rhodanine Substituted benzylidene-rhodanines 3 – 8 were prepared both by condensation of 1 a – f with suitable aldehydes and by acylation of 2a – g with substituted benzoyl chlorides or cinnamoyl chlorid. The mesomorphic properties of the compounds are discussed in respect to molecular structure with the aid of i.r.-, Raman- and u.v./vis-spectra of 3d , 3k , 4 , 5 , 6g , 8a . We have investigated the dielectric and electrooptic behaviour of 31 .  相似文献   
114.
115.
Continuous casting of steel free of surface cracks is still one of the major quality challenges in the whole steel production. The key roles for the phenomenon of surface cracking are played by the critical strain and the temperature-dependent material’s phenomena. The new In-Situ Characterization Bending (IMC-B) method will enable the investigation of the critical strains with respect to the cracking under the main continuous casting boundaries. This publication presents potential and interesting results of the IMC-B experiment.  相似文献   
116.
Different acid solids loaded with 1 wt.% of Pt have been studied in n-heptane hydroisomerization in order to determine the influence of porosity and acidity (considered measured by the activity) on selectivities. The open solids like Y and β zeolites and a pillared clay present different activities towards n-C7 conversion but similar selectivities. Consequently, acidity seems to be a less important parameter in n-C7 isomerization than porosity. Very different results were obtained as a function of the solid structure and so n-heptane hydroconversion appears to be a simple and rapid method to obtain data concerning the porosity of unknown zeolite structures. The highest content of multibranched isomers was obtained on open solids but the value predicted by the thermodynamic was never reached due to the fact that cracking of multibranched isomers is initiated quickly.  相似文献   
117.
The aim of this paper is investigating the microstructural characteristics of asphalt mixture under different compaction powers. In order to achieve this aim, a test track was built to provide asphalt mixture specimens and X-ray computed tomography (XCT) device was used to scan the internal structure. The aggregate particles and air-voids were extracted using Digital Image Processing (DIP), so the relationship between compaction and air-voids was determined at first, and then, the effect of aggregate particles on the morphology of air-voids can be evaluated, finally, fatigue properties of asphalt mixture with different air-void ratio were measured by indirect tensile fatigue test as well. The research results release the distribution of microstructures in asphalt pavement. 3D fractal dimension is an effective indicator to quantize the complexity of aggregate particles and air-voids; suffering the same compaction power, aggregates cause different constitutions of air-voids in asphalt mixture; investigation in this paper can present the essential relationship between microstructures and fatigue properties.  相似文献   
118.
The synthesis and structural characterization of Co-(dN)25-Cbl (Cbl: cobalamin; dN: deoxynucleotide) and Co-(dN)39-Cbl, which are organometallic DNA–B12 conjugates with single DNA strands consisting of 25 and 39 deoxynucleotides, respectively, and binding studies of these two DNA–Cbl conjugates to three homologous human Cbl transporting proteins, transcobalamin (TC), intrinsic factor (IF), and haptocorrin (HC), are reported. This investigation tests the suitability of such DNA–Cbls for the task of eventual in vivo oligonucleotide delivery. The binding of DNA–Cbl to TC, IF, and HC was investigated in competition with either a fluorescent Cbl derivative and Co-(dN)25-Cbl, or radiolabeled vitamin B12 (57Co-CNCbl) and Co-(dN)25-Cbl or Co-(dN)39-Cbl. Binding of the new DNA–Cbl conjugates was fast and tight with TC, but poorer with HC and IF, which extends a similar original finding with the simpler DNA–Cbl, Co-(dN)18-Cbl. The contrasting affinities of TC versus IF and HC for the DNA–Cbl conjugates are rationalized herein by a stepwise mechanism of Cbl binding. Critical contributions to overall affinity result from gradual conformational adaptations of the Cbl-binding proteins to the DNA–Cbl, which is first bound to the respective β domains. This transition is fast with TC, but slow with IF and HC, with which weaker binding results. The invariably tight interaction of the DNA–Cbl conjugates with TC makes the Cbl moiety a potential natural vector for the specific delivery of oligonucleotide loads from the blood into cells.  相似文献   
119.
120.
This paper examines the performance of cascade‐aerated facultative ponds in a waste stabilisation pond (WSP) installation in the United Kingdom. The pond system is privately owned and treats wastewater from a conference centre with a population equivalent between 20 and 40. A snapshot analysis investigates the removal efficiency of BOD, COD, SS, FC and nutrients. Further, the oxygen supply through ‘flow form’ cascades is examined, and the DO concentrations, surface loads and retention times are discussed. The results show a very high removal of BOD, COD and SS; and nutrient removal is satisfactory. An unusual finding is that the FC removal efficiency is almost two log units better than for a common maturation pond. This is possibly attributable to the high cascade flow, where wastewater is exposed to the damaging effects of sunlight (photo‐oxidation).  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