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   1996篇
  免费   96篇
电工技术   25篇
综合类   25篇
化学工业   588篇
金属工艺   58篇
机械仪表   36篇
建筑科学   152篇
矿业工程   8篇
能源动力   50篇
轻工业   232篇
水利工程   13篇
石油天然气   2篇
无线电   115篇
一般工业技术   363篇
冶金工业   131篇
原子能技术   19篇
自动化技术   275篇
  2023年   22篇
  2022年   42篇
  2021年   74篇
  2020年   32篇
  2019年   42篇
  2018年   49篇
  2017年   37篇
  2016年   62篇
  2015年   66篇
  2014年   81篇
  2013年   86篇
  2012年   119篇
  2011年   129篇
  2010年   117篇
  2009年   84篇
  2008年   90篇
  2007年   78篇
  2006年   78篇
  2005年   58篇
  2004年   52篇
  2003年   30篇
  2002年   47篇
  2001年   34篇
  2000年   30篇
  1999年   30篇
  1998年   36篇
  1997年   31篇
  1996年   19篇
  1995年   29篇
  1994年   21篇
  1993年   15篇
  1992年   20篇
  1991年   14篇
  1990年   16篇
  1989年   16篇
  1987年   15篇
  1985年   12篇
  1984年   18篇
  1983年   9篇
  1982年   10篇
  1981年   13篇
  1980年   11篇
  1979年   10篇
  1978年   22篇
  1977年   13篇
  1976年   10篇
  1975年   9篇
  1974年   21篇
  1969年   12篇
  1968年   10篇
排序方式: 共有2092条查询结果,搜索用时 15 毫秒
71.
Fingolimod, an oral sphingosine 1-phosphate (S1P) receptor modulator, is approved for the treatment of relapsing forms of multiple sclerosis (MS). The interference with S1P signaling leads to retention particularly of chemokine receptor-7 (CCR7) expressing T cells in lymph nodes. The immunological basis of varicella zoster virus (VZV) infections during fingolimod treatment is unclear. Here, we studied the dynamics of systemic and intrathecal immune responses associated with symptomatic VZV reactivation including cessation of fingolimod and initiation of antiviral therapy. Key features in peripheral blood were an about two-fold increase of VZV-specific IgG at diagnosis of VZV reactivation as compared to the previous months, a relative enrichment of effector CD4+ T cells (36% versus mean 12% in controls), and an accelerated reconstitution of absolute lymphocytes counts including a normalized CD4+/CD8+ ratio and reappearance of CCR7+ T cells. In cerebrospinal fluid (CSF) the lymphocytic pleocytosis and CD4+/CD8+ ratios at diagnosis of reactivation and after nine days of fingolimod discontinuation remained unchanged. During this time CCR7+ T cells were not observed in CSF. Further research into fingolimod-associated VZV reactivation and immune reconstitution is mandatory to prevent morbidity and mortality associated with this potentially life-threatening condition.  相似文献   
72.
A quasi-one-dimensional model of the process of continuous sedimentation in clarifier-thickeners (settlers) with variable cross-sectional area is presented. The partial differential equation (PDE) model extends the settler model advanced by Bürger et al. (2013 Bürger, R., Diehl, S., Farås, S., Nopens, I., and Torfs, E. (2013). A consistent modelling methodology for secondary settling tanks: A reliable numerical method, Water Sci. Technol. 68(1), 192208.[Crossref], [PubMed], [Web of Science ®] [Google Scholar]), which assumes a constant cross section. A reliable numerical method that handles the special features of the nonlinear PDE is presented along with an advantageous time-step condition for continuous and batch sedimentation under the condition of a variable cross-sectional area. Simulations of continuous sedimentation show the effect of change of cross-sectional area in the concentration inside the vessel and in the underflow. Simulations of batch settling in cones illustrate the versatility of the numerical scheme to include a vertex, where the area shrinks to zero.  相似文献   
73.
On‐line liquid chromatography‐gas chromatography (LC‐GC) has been applied to the detection of vegetable oils in milk fat using β‐sitosterol as marker. The method involves transesterification of the fat, pre‐separation of the sterol fraction from other lipid constituents and on‐line transfer to the capillary GC system. The on‐line approach avoids time‐consuming sample preparation steps prior to GC analysis. The suitability of this analytical approach was tested with model mixtures of milk fat with cotton and rapeseed oil. The method allows the detection of adulterations at low levels. Simultaneous quantification of cholesterol in milk fat is also possible. Considering the rapid sample preparation, the described method can be applied for screening of large sample numbers.  相似文献   
74.
The potential of two hydrolytic enzymes, namely a lipase from Thermomyces lanuginosus (TlL) and a cutinase from Humicola insolens (HiC) for hydrolysis of the phthalic acid backbone based polyester coatings was assessed. Two phthalic acid/trimethylolpropane based model substrates resembling the structure of the polyester backbone of coatings were synthesized. Out of both enzymes, only the cutinase was able to hydrolyze both model substrates while the larger substrate was hydrolyzed at a lower rate. The cutinase was also able to hydrolyze a coating (alkyd resin) both in suspension and as dried film. LC–MS analysis of the hydrolysis products released from the coating revealed the presence of oleic acid, its monoglyceride, phthalic acid and 2-((3-((2-((2,3-dihydroxypropoxy)carbonyl)benzoyl)oxy)-2-hydroxypropoxy)carbonyl)benzoic acid. These results indicate that the enzyme was able to hydrolyze the polyester backbone as well as to release fatty acid side chains. Consequently, enzymatic hydrolysis has a potential for the removal of coatings, their recycling or their functionalization.  相似文献   
75.
The fatigue behavior of lead zirconate stannate titanate (PZST) ceramics prepared by spark plasma sintering (SPS) was investigated. Polarization and strain hysteresis loops were monitored. The material shows a high resistance to fatigue because of bipolar electric cycling. Both maximum strain and switchable polarization first show a fatigue stage 0 to 105 cycles and then a fatigue-free period up to 108 cycles. The maximum losses of maximum strain and switchable polarization are 18% and 10% of their initial values, respectively. The dominant fatigue mechanism is assigned to the pinning of domain walls by charged defects.  相似文献   
76.
Different routes for immobilization of TiO2 on conducting substrates were compared to find active and stable photocatalysts, which could either be operated in open circuit (photocatalysis) or with applied electric potential (photoelectrocatalysis). The advantage of applying an electric potential was investigated. Polarization curves and photoelectrochemical degradation reactions served to characterize catalysts and to find a way of predicting the optimum synthesis conditions. The difference between front side (EE) and back side (SE) illumination is discussed as a function of layer thickness, as well as the influence of oxidizable substance concentration on photocurrents. Stability of catalysts was investigated in repetitive degradation experiments.  相似文献   
77.
Polycrystalline Fe7.5Al7Cr is a ferritic light weight steel that shows a strong anisotropic dissolution behaviour. This electrochemical phenomenon was investigated by use of a scanning droplet cell (SDC). The crystallographic orientation of the single grains was determined by electron back scatter diffraction (EBSD). The fraction of grains with a near 〈1 1 1〉 orientation (<10°) was 1.88 times higher than that of the near 〈0 0 1〉 orientation prior to annealing and 3.58 times higher after annealing. Voltammograms were performed on single grains with low index planes. The critical current density was 53% higher on 〈0 0 1〉 grains as compared to 〈1 1 1〉 grains. These results are used to discuss the electrochemical behaviour of the polycrystalline FeAlCr.  相似文献   
78.
This paper presents a novel fiber spraying process for the manufacturing of short fiber bundle-reinforced Nextel™ 610/Al2O3-ZrO2 oxide fiber composites (SF-OFC) and its characterization. First, the influence of varying fiber lengths (7, 14, and 28 mm, continuous fibers) and fiber orientations (unidirectional 0°, quasi-isotropic, ±45°) was investigated using hand-laid SF-OFC. Due to the weak matrix, the hand-laid material exhibited a strongly fiber-dominated material behavior, that is, variations in fiber length and orientation had a strong influence on the material properties. Second, the automated sprayed SF-OFC, however, exhibited a random orientation of the fiber bundles, which resulted in in-plane isotropic material properties. Average bending strengths of up to 177 MPa, strains of .39%, and a quasi-ductile fracture behavior were achieved. The strain was, therefore, in the range of fabric-reinforced OFC. While the bending strength of the SF-OFC was somewhat lower than that of fabric-reinforced OFC with the fiber orientation parallel to the loading direction, it was more than two times higher than the strength in 45° direction relative to the fabric reinforcement. Combined with good drapability and lower material costs compared to fabric-reinforced OFC, SF-OFC is, therefore, a promising material for industrial applications.  相似文献   
79.
80.
Analogues of the anticancer natural product oximidine II were prepared and evaluated for cytotoxicity. One analogue of oximidine II that carries a C15 allylic amide side chain as well as two analogues with C15 vinyl sulfone side chains were found to lack cytotoxicity against the cancer cell line SK‐Mel‐5, thereby confirming the necessity of the C15 enamide side chain of oximidine II for cytotoxicity. Four analogues, designed by comparative molecular similarity index analysis (CoMSIA), that feature a less complex macrolactone scaffold were prepared and tested. The two analogues carrying a C15 vinyl sulfone group and the two analogues with a C15 oximidine II enamide side chain showed weak cytotoxicity against the SK‐Mel‐5 cell line and other cell lines, indicating that the designed simplified macrocycles cannot replace the oximidine II macrocycle.  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