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   1709篇
  免费   52篇
  国内免费   5篇
电工技术   28篇
综合类   1篇
化学工业   433篇
金属工艺   27篇
机械仪表   29篇
建筑科学   48篇
矿业工程   7篇
能源动力   29篇
轻工业   84篇
水利工程   11篇
石油天然气   2篇
武器工业   1篇
无线电   132篇
一般工业技术   279篇
冶金工业   364篇
原子能技术   13篇
自动化技术   278篇
  2022年   38篇
  2021年   31篇
  2020年   19篇
  2019年   19篇
  2018年   24篇
  2017年   25篇
  2016年   31篇
  2015年   22篇
  2014年   37篇
  2013年   105篇
  2012年   66篇
  2011年   75篇
  2010年   48篇
  2009年   56篇
  2008年   40篇
  2007年   40篇
  2006年   63篇
  2005年   62篇
  2004年   65篇
  2003年   55篇
  2002年   41篇
  2001年   27篇
  2000年   32篇
  1999年   22篇
  1998年   48篇
  1997年   49篇
  1996年   40篇
  1995年   25篇
  1994年   26篇
  1993年   23篇
  1992年   29篇
  1990年   17篇
  1989年   22篇
  1988年   23篇
  1987年   13篇
  1986年   19篇
  1985年   16篇
  1984年   14篇
  1983年   14篇
  1982年   20篇
  1981年   15篇
  1980年   16篇
  1979年   16篇
  1978年   24篇
  1977年   22篇
  1976年   27篇
  1975年   16篇
  1974年   22篇
  1973年   16篇
  1971年   14篇
排序方式: 共有1766条查询结果,搜索用时 15 毫秒
21.
Hepatocellular carcinoma (HCC), the most common malignant tumor in the liver, grows and metastasizes rapidly. Despite advances in treatment modalities, the five-year survival rate of HCC remains less than 30%. We sought genetic mutations that may affect the oncogenic properties of HCC, using The Cancer Genome Atlas (TCGA) data analysis. We found that the GNAQ T96S mutation (threonine 96 to serine alteration of the Gαq protein) was present in 12 out of 373 HCC patients (3.2%). To examine the effect of the GNAQ T96S mutation on HCC, we transfected the SK-Hep-1 cell line with the wild-type or the mutant GNAQ T96S expression vector. Transfection with the wild-type GNAQ expression vector enhanced anchorage-independent growth, migration, and the MAPK pathways in the SK-Hep-1 cells compared to control vector transfection. Moreover, cell proliferation, anchorage-independent growth, migration, and the MAPK pathways were further enhanced in the SK-Hep-1 cells transfected with the GNAQ T96S expression vector compared to the wild-type GNAQ-transfected cells. In silico structural analysis shows that the substitution of the GNAQ amino acid threonine 96 with a serine may destabilize the interaction between the regulator of G protein signaling (RGS) protein and GNAQ. This may reduce the inhibitory effect of RGS on GNAQ signaling, enhancing the GNAQ signaling pathway. Single nucleotide polymorphism (SNP) genotyping analysis for Korean HCC patients shows that the GNAQ T96S mutation was found in only one of the 456 patients (0.22%). Our data suggest that the GNAQ T96S hotspot mutation may play an oncogenic role in HCC by potentiating the GNAQ signal transduction pathway.  相似文献   
22.
Peter  Eugene  Subash  T. D.  Subha  T. D.  Nazim  Alsufiyan 《SILICON》2021,13(12):4285-4291
Silicon - This work fully depends on the silicon nanoparticles. It is represented as SiNPs. This depends on the transparent LEDs color converters. The spectrum obtained is fully white, so it is...  相似文献   
23.
24.
Eugene V. Vega  Ki Yong Lee 《Fuel》2007,86(4):512-519
This work investigates the electric field effect on nitrogen oxide (NO) pollutant formation and emission composition of premixed flames in order to provide better insight on the mechanism of controlling the combustion process by electro-physical means. The present study aims to investigate experimentally the effect of radial DC electric field on premixed laminar methane flame. The electric field effect on flame shape, emission composition and NO emission index of flame is investigated experimentally under the action of direct-current electric field under varying equivalence ratio and level of oxygen enrichment. The results show that ionic wind effects cause the distortion in flame shape. The ionic wind effects diminish with increasing flow rate and level of oxygen enrichment. Minimal effects on NO are measured for flames under the influence of electric field and vanished as the level of oxygen enrichment is increased. This was well supported by the temperature profile measurement in the post flame gas showing no field-induced modification also. It seemed that the action of an electric field on a flame with a geometry that remains practically undeformed produces very minimal effect on pollutant emission.  相似文献   
25.
Paper I provides the underlying theoretical framework for the SCOPE dynamic model of emulsion copolymerization. The present paper compares the model predictions for styrenemethyl methacrylate copolymerizations with experimental measurements made at a variety of polymerization conditions. The SCOPE model predicts conversion–time profiles reasonably well over wide ranges of initiator concentration, monomer concentration and monomer composition. In addition, the model accurately predicts number average molecular weights and copolymer compositions over the entire range of monomer composition. Like previous investigations of this system, the present study suggests that free radical desorption from polymer particles plays a dominant role on the copolymerization kinetics: Simple case II Smith-Ewart kinetics do not apply. The model for this system was applied to understand how changing reaction conditions could effect polymer properties such as particle size and molecular weight distributions. The power of the SCOPE model is illustrated by using it to predict conversion profiles, temperature profiles and copolymer properties for some large-scale versions of these recipes.  相似文献   
26.
We have measured leakage current in a silicon substrate-based nanopore membrane device immersed in an aqueous environment which typically shows the current level of few nA. This current level is compared with the measured current density (400 nA/cm2 at 1 V) from the pristine Si wafer (p-type, 1016/cm3 boron doping) indicating that the exposed Si surface in a nanopore membrane device acts as an electrochemical reaction site. The leakage current is drastically reduced from >10 nA to <100 pA at 1 V by the deposition of a dielectric layer to the Si-based nanopore membrane device. We also noted that the root-mean-square noise of the ionic current is also reduced from 38 to 28 pA in correlation with the reduction of leakage current, indicating that electrochemical reaction provides one of the major sources of noise.  相似文献   
27.
The extrudate swell effect has not received sufficient attention in modeling the film blowing process. This effect is addressed in this paper, and as an ab initio study, only viscous fluids were considered. The problem region was separated into two zones; the extrudate swell zone and the film blowing zone. The annular extrudate swell problem was solved using a finite element method. The film blowing process was modeled following Pearson and Petrie's (4) work. Although only viscous fluids were considered, the simulation results show a remarkable difference when swelling was included in the modeling. Viscoelastic fluids, which are more realistic for polymer melts, were not investigated here because of the so called high Weisenberg number problem. This is an open area still under investigation.  相似文献   
28.
The solubility and activity–composition relations of chromium oxide in melts of the systems CaO–CrO x –SiO2 and CaO–Al2O3–CrO x –SiO2 have been determined at 1500°C by equilibrating melts with Pt–Cr alloys at known oxygen pressures. It is shown that the increase in the concentration of divalent chromium ions, as the oxygen pressure and the basicity of melt decrease, results in a dramatic increase in the solubility of chromium oxide in the liquid phase. An increase in the Al2O3 content of the melt leads to a decrease in the solubility of chromium oxide over the whole composition range studied. The activity coefficient of CrO has been found to increase with increasing melt basicity and decreasing oxygen pressure whereas the activity coefficient of CrO1.5 decreases sharply with increasing melt basicity for siliceous melts but levels off at a basicity ratio (wt% CaO/wt% SiO2) of about 0.7. An increase in the Al2O3 content of the melts results in an increase in the activity coefficient of CrO.  相似文献   
29.
Most heterogeneous catalysts are either supported on some kind of porous material or the catalyst itself is porous. To satisfy practical constraints such as pressure drop, handling, and separation from products, these catalysts are generally pelletized. Very often the overall chemical reaction rates within these catalyst pellets are determined by a complicated interaction of internal and external transport effects with the intrinsic kinetic rate at the active surface.  相似文献   
30.
(Z, Z)-6,9-Heneicosadien-11-one (Z6Z9-11-one-21Hy) was identified as the major sex pheromone component of the painted apple moth (PAM), Teia anartoides (Lepidoptera: Lymantriidae), on the basis of (1) comparative gas chromatographic-electroantennographic detection (GC-EAD) analyses, GC-mass spectrometry (MS), high-performance liquid chromatography (HPLC)-MS, and HPLC-UV/visible spectroscopy of pheromone gland extracts and authentic standards; (2) GC-EAD analyses of effluvia of calling females; and (3) wind tunnel and field trapping experiments with a synthetic standard. In field experiments in Australia, synthetic Z6Z9-11-one-21Hy as a single component attracted male moths. Wind tunnel experiments suggested that a 4-component blend consisting of Z6Z9-11-one-21Hy, (6Z,9R,10S)-cis-9,10-epoxy-heneicosene (Z6-9R10S-epo-21Hy), (E, E)-7,9-heneicosadien-6,11-dione (E7E9-6,11-dione-21Hy), and 6-hydroxy-(E, E)-7,9-heneicosadien-11-one (E7E9-6-ol-11-one-21Hy) (all present in pheromone gland extracts) might induce more males to orient toward, approach, and contact the source than did Z6Z9-11-one-21Hy as a single component. Additional experiments are needed to determine conclusively whether or not Z6-9R10S-epo-21Hy, E7E9-6,11-dione-21Hy, and E7E9-6-ol-11-one-21Hy might be minor sex pheromone components of PAM. Moreover, attractiveness of synthetic pheromone and virgin PAM females needs to be compared to determine whether synthetic pheromone could replace PAM females as trap baits in the program to monitor eradication of exotic PAM in New Zealand.  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