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   1849篇
  免费   139篇
  国内免费   15篇
电工技术   33篇
综合类   28篇
化学工业   351篇
金属工艺   17篇
机械仪表   42篇
建筑科学   80篇
矿业工程   5篇
能源动力   58篇
轻工业   144篇
水利工程   10篇
石油天然气   8篇
无线电   338篇
一般工业技术   347篇
冶金工业   233篇
原子能技术   7篇
自动化技术   302篇
  2023年   10篇
  2022年   31篇
  2021年   53篇
  2020年   37篇
  2019年   44篇
  2018年   64篇
  2017年   44篇
  2016年   72篇
  2015年   45篇
  2014年   60篇
  2013年   114篇
  2012年   81篇
  2011年   101篇
  2010年   81篇
  2009年   98篇
  2008年   101篇
  2007年   73篇
  2006年   81篇
  2005年   59篇
  2004年   62篇
  2003年   68篇
  2002年   49篇
  2001年   35篇
  2000年   46篇
  1999年   59篇
  1998年   74篇
  1997年   56篇
  1996年   47篇
  1995年   30篇
  1994年   29篇
  1993年   23篇
  1992年   11篇
  1991年   18篇
  1990年   15篇
  1989年   7篇
  1988年   18篇
  1987年   13篇
  1986年   5篇
  1985年   10篇
  1984年   10篇
  1983年   3篇
  1982年   8篇
  1981年   11篇
  1979年   3篇
  1978年   3篇
  1977年   12篇
  1976年   10篇
  1974年   3篇
  1972年   3篇
  1971年   2篇
排序方式: 共有2003条查询结果,搜索用时 15 毫秒
91.
This study investigated the physicochemical properties of ternary mixtures of palm mid-fraction (PMF):refined bleached deodorized palm kernel oil (RBDPKO):refined bleached deodorized palm stearin (RBDPS) for cocoa butter substitute (CBS). Fatty acid constituents, triacylglycerol constituents, solid fat contents (SFCs), melting behavior, polymorphism and crystal morphology were determined using gas chromatography (GC), high-performance liquid chromatography (HPLC), differential scanning calorimetry (DSC), pulsed nuclear magnetic resonance (p-NMR), X-ray diffraction (XRD) and polarized light microscopy (PLM), respectively. Eight blends of various ratios of ternary mixtures were investigated based on the previously studied binary fat mixtures. The composition of palmitic (P) and oleic (O), POP, and crystal morphology (size and shape) of the PMF/RBDPKO/RBDPS [14.9/59.6/25.5 (%w/w)] mixture were comparable to cocoa butter (CB), while its melting profile (18.5 and 37 °C), SFC at 20 °C and polymorphism were different from CB. The iso-solid diagrams of the mixture displayed a monotectic effect at 20–25 °C. Therefore, the 14.9/59.6/25.5 PMF/RBDPKO/RBDPS mixture could be used as a CBS in confectionery fillings because of the crystal morphology and monotectic behaviors comparable to those of CB.  相似文献   
92.
93.
The new amphiphilic BODPY‐porphyrin conjugate BZnPP and its precursor BZnPH were synthesised, and their linear and two‐photon photophysical properties, together with their cellular uptake and photo‐cytotoxicity, were studied. This amphiphilic conjugate consists of a hydrophobic BODIPY moiety and a hydrophilic tetra(ethylene glycol) chain bridging a cationic triphenylphosphonium group to an amphiphilic porphyrin ZnP through acetylide linkers at its meso positions. A large two‐photon absorption cross‐section (σ=1725 GM) and a high singlet oxygen quantum yield (0.52) were recorded. Intense linear‐ and two‐photon‐induced red emissions were also observed for both BZnPP and BZnPH. Further in vitro studies showed that BZnPP exhibited very efficient cellular uptake and strong photocytotoxic but weak dark cytotoxic properties towards human breast carcinoma MCF‐7 cells. In summary, the two‐photon‐induced emission and the potent photo‐cytotoxicity of BZnPP make it an efficacious dual‐purpose tumour‐imaging and photodynamic therapeutic agent in the tissue‐transparent spectral windows.  相似文献   
94.
均一粒径液滴喷雾干燥塔(MDSD)在生产均匀尺寸颗粒产品中发挥着较大优势,进一步优化其干燥过程操作尤为重要。集成离散相(DPM)和反应工程法(REA)干燥方法,通过耦合分散室和主干燥室模型,本研究开发了完整的MDSD三维计算流体力学模型。并系统探究了在干燥过程中分散气旋流、热空气旋流以及二者共同旋流对颗粒运动和最终干燥效果的影响。模拟结果表明,在30°入射角下加入旋流效果最优。同时引入分散室和干燥室旋流后发现,同向旋流比反向旋流带来的干燥效果提升2%,更比无旋流操作下的干燥效果提升30%。欲达到同样的干燥效果,引入同向旋流,塔身可缩短近12%。  相似文献   
95.
A specially designed electro-cross-flow nanofiltration (NF) membrane system was used for this investigation. To enhance the rejection of arsenic ionic species like H2AsO4, a NF membrane having a negative surface charge was fabricated via the interfacial polymerization process. The membrane was characterized by SEM, AFM, surface charge density, molecular weight cut-off (MWCO), total and skin thickness and pure water flux. The parameters that affected the rejections of As(III) and As(V) were studied; they included the initial arsenic concentration, the applied potential, pH of the feed, the cross-flow filtration pressure and the presence of different salts in the feed. Among those parameters, the pH of the feed greatly affected As(V) rejection; As(V) ([As(V)]o = 1000 ppb) rejection was increased from 72.3 to 98.5% when pH of the feed was changed from 3.0 to 10.0. This might be due to the fact that higher pH enhanced the formation of negative divalent anion like HAsO42− which should be rejected more effectively by the negative surface charge of the NF membrane. Beside the effect of the negative surface charge of the membrane, applied potential increased the As(V) rejection by 48.2% when the applied potential was increased from 0 to 2.0 V for a feed containing 1000 ppb initially. For the same change of applied potential rejection of As(III) was increased from 52.3 to 70.4%; this might be the result of the formation of anionic species like H2AsO3 from the neutral molecule of H3AsO3 by the applied potential.  相似文献   
96.
A series of polymer–clay nanocomposite (PCN) materials consisting of 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene–4,4′‐oxydiphthalic anhydride (BATB–ODPA) polyimide (PI) and layered montmorillonite (MMT) clay were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. The synthesized PCN materials were subsequently characterized by Fourier‐Transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of material composition on thermal stability, mechanical strength, molecular permeability and optical clarity of bulk PI and PCN materials in the form of membranes were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), molecular permeability analysis (GPA) and ultraviolet‐visible (UV/VIS) transmission spectra, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1072–1079, 2004  相似文献   
97.
In this investigation, we propose and experimentally demonstrate the remodulation technique using DPSK format in both downlink and uplink traffics with high extinction ratio (ER) in colorless WDM-PON; together with a simple self-restored architecture against fiber fault. Error free operation was achieved in a 20-km-reach 10-Gb/s WDM-PON without dispersion compensation. Comparison with other wavelength remodulation schemes for WDM-PONs is also performed, showing the proposed scheme can be a potential candidate for next generation wavelength reuse WDM-PONs. In addition, the performance of self-protection has also been discussed and analyzed.  相似文献   
98.
Inaccurate early project cost estimates can eliminate investment benefits. This study focuses on assisting estimators who are attempting to enhance the accuracy and reliability of engineering project cost in the pre-conceptual stage. This aim has recently garnered the attention of the transportation communities. Data from the Texas Department of Transportation (TxDOT) were utilized to develop an alternative approach that aids decision makers in terms of probability and confidence level. The proposed procedure comprises heuristic and practical simulation models that can be employed to calculate the probabilistic costs of highway bridge replacement projects. The simulation models utilize independent, correlated, and Latin Hypercube sampling approaches that incorporate major work items, roll-up work items, and project-level engineering contingencies. Cumulative distribution functions (CDFs) are then developed as a user-friendly chart for decision makers and these CDFs can be used to assess project risks during the pre-conceptual stage. Trial runs using these estimating procedures generate reliable pre-conceptual estimates. Additionally, these procedures can be extended to other project types along with programming techniques for developing an engineering project cost decision support system.  相似文献   
99.
Distrust hinders disputing parties and mediators from achieving mediation success. Mediators therefore often use different trust-building tactics to generate some degree of trust in themselves and in the mediation process. This paper reports a study that identified the trust-building tactics used by construction mediators and examined the efficacy of these tactics with respect to their outcomes. Three study stages were designed. With reference to the mediation model of Sloan (1998), trust-building tactics and outcomes were first identified in Stage I. Next, the data were collected from accredited mediators with a questionnaire survey in Stage II. The collected data were then validated via reliability assessments in Stage III. With the use of multiple regression analyses, the efficacy of the trust-building tactics was examined by relating these tactics to their outcomes. The findings of this study suggest that the trust-building tactics used in Step 4 (i.e., explore interests) of Sloan’s (1998) mediation model are influential in developing trust among disputing parties and that they can also act as a time-saving tool in the mediation process. Furthermore, it was found that mediators can earn trust by adopting the trust-building tactics used in Step 3 (i.e., issues and trust) of Sloan’s (1998) model. These tactics can also serve to improve the relationships between the disputing parties. The results show that the trust-building tactics used in the final step (i.e., solutions) of Sloan’s (1998) model seem to have low efficacy in developing trust among disputing parties.  相似文献   
100.
Highly efficient blue electrophosphorescent organic light‐emitting diodes incorporating a bipolar host, 2,7‐bis(diphenylphosphoryl)‐9‐[4‐(N,N‐diphenylamino)phenyl]‐9‐phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6‐difluoro‐phenyl)pyridinato‐N,C]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron‐donating (p‐type) triphenylamine group and an electron‐accepting (n‐type) 2,7‐bis(diphenyl‐phosphoryl)fluorene segment linked through the sp3‐hybridized C9 position of the fluorene unit. The lack of conjugation between these p‐ and n‐type groups endows POAPF with a triplet energy gap (ET) of 2.75 eV, which is sufficiently high to confine the triplet excitons on the blue‐emitting guest. In addition, the built‐in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF‐based device doped with 7 wt% FIrpic exhibits a very low turn‐on voltage (2.5 V) and high electroluminescence efficiencies (20.6% and 36.7 lm W?1). Even at the practical brightnesses of 100 and 1000 cd m?2, the efficiencies remain high (20.2%/33.8 lm W?1 and 18.8%/24.3 lm W?1, respectively), making POAPF a promising material for use in low‐power‐consumption devices for next‐generation flat‐panel displays and light sources.  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