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   3065篇
  免费   90篇
  国内免费   17篇
电工技术   44篇
综合类   1篇
化学工业   841篇
金属工艺   117篇
机械仪表   71篇
建筑科学   59篇
矿业工程   15篇
能源动力   140篇
轻工业   181篇
水利工程   16篇
石油天然气   8篇
无线电   285篇
一般工业技术   759篇
冶金工业   265篇
原子能技术   75篇
自动化技术   295篇
  2023年   40篇
  2022年   76篇
  2021年   106篇
  2020年   79篇
  2019年   65篇
  2018年   104篇
  2017年   97篇
  2016年   116篇
  2015年   61篇
  2014年   87篇
  2013年   206篇
  2012年   133篇
  2011年   173篇
  2010年   129篇
  2009年   148篇
  2008年   150篇
  2007年   149篇
  2006年   102篇
  2005年   81篇
  2004年   68篇
  2003年   63篇
  2002年   79篇
  2001年   58篇
  2000年   44篇
  1999年   46篇
  1998年   84篇
  1997年   45篇
  1996年   65篇
  1995年   53篇
  1994年   28篇
  1993年   36篇
  1992年   29篇
  1991年   30篇
  1990年   32篇
  1989年   29篇
  1988年   27篇
  1987年   32篇
  1986年   22篇
  1985年   22篇
  1984年   18篇
  1983年   16篇
  1982年   18篇
  1981年   27篇
  1980年   17篇
  1979年   8篇
  1978年   9篇
  1977年   10篇
  1976年   11篇
  1975年   7篇
  1973年   10篇
排序方式: 共有3172条查询结果,搜索用时 15 毫秒
61.
Breast cancer is one of the most common types of cancer among women globally. It is caused by mutations in the estrogen/progesterone receptors and conventional treatment methods are commonly utilized. About 70–80 percent of individuals with the early-stage non-metastatic disease may be cured. Conventional treatment is far less than the optimal ratio, as demonstrated through the high mortality rate of women with this cancer. However, conventional treatment methods like surgery, radiotherapy, and chemotherapy are not as effective as expected and lead to concerns about low bioavailability, low cellular uptake, emerging resistance, and adverse toxicities. A nanomedicine-based approach is a promising alternative for breast cancer treatment. The present era is witnessing rapid advancements in nanomedicine as a platform for investigating novel therapeutic applications and modern intelligent healthcare management strategies. This paper focuses on nanomedicine-based therapeutic interventions that are becoming more widely accepted for improving treatment effectiveness and reducing undesired side effects in breast cancer patients. By evaluating the state-of-the-art tools and taking the challenges involved into consideration, various aspects of the proposed nano-enabled therapeutic approaches have been discussed in this review.  相似文献   
62.
Heat transfer to constant-property, fully developed, laminar flows in circular-segment ducts with uniform wall temperature (T) has been analyzed. Besides representing a compact surface, the segment duct geometry models the flow cross section of a circular tube with a straight-tape insert. Two variations in the T thermal boundary condition are considered: constant axial and circumferential wall temperature, and constant temperature on the curved surface but an adiabatic flat wall. These two conditions model the extremes of the fin effects of a straight-tape insert, i.e., 100% and zero fin efficiencies, respectively. Numerical solutions, obtained by using finite difference techniques, are presented for both the velocity and temperature fields. The isothermal friction factors are in excellent agreement with analytical solutions reported in the literature. The Nusselt number results for the two thermal boundary conditions are presented for different segment shapes, 0° ≤, 6 ≤, 90°, and they represent the lower limits of the heat transfer enhancement due to twisted-tape inserts.  相似文献   
63.
Microorganisms play a vital role in understanding the ecological system. The motions of micororganisms are self‐propelled while the impact of thermophoresis and Brownian motion property of nanoparticle shows more challenges in biotechnological and medical applications. The present problem is based on the understanding of double‐dispensed bioconvection for a Casson nanofluid flow over a stretching sheet. Suction phenomenon is introduced at the surface of the stretching sheet along with the convective boundary condition. The convection and movement of the microorganisms are assisted by an applied magnetic field, nonlinear thermal radiation, and first‐order chemical reaction. The governing equations are highly coupled and thus we used the spectral quasilinearization method to solve the governing equations. The study of the residual errors on the systemic parameters had given a confidence with the present results. The final outcomes are displayed through graphs and tables. The thermal dispersion coefficient shows a positive response in the temperature while a similar response is observed for the concentration with solutal dispersion coefficient. The response is reversible for the heat transfer rate at the surface with thermal dispersion coefficient. The density of the motile microorganism at the surface decreases with increase in the Casson number, thermal dispersion coefficient, and solute dispersion coefficient, while an opposite phenomenon was observed with increase in the density ratio of the motile microorganism.  相似文献   
64.
Chemically controlled co-precipitation method has been adopted for the fabrication of pure and different wt% Zr doped CdO photocatalysts. Conventionally, the crystallite size and crystalline phase of CdO are in the midst of the parameters involved in the control of the photocatalytic activity. Aiming utterly at the size effect that modifies other attributes which are important to assess the photocatalytic activity of nanometric CdO, it was explored to synthesize CdO nanoparticles with controlled size, highly comparable morphology and analogous phase. The crystal structure and the crystallite size were estimated from the X-ray diffraction patterns and were confirmed through transmission electron microscope. The degree of crystallinity varied on Zr doping and the calculated crystallite sizes were in the range of 16–81 nm. The dopant ion Zr4+ have been detected through X-ray photoelectron spectroscopy (XPS) analysis signifying the dopant to substitute for cadmium (Cd2+) in the lattice of CdO. Particle size dependent optical band gaps calculated in the range 2.02–2.57 eV informed the viability of the materials to initiate photocatalytic reaction in the visible light region. Lesser recombination rate of the generated electrons and holes under light irradiation produced low intense photoluminescence peaks that displayed the appropriateness as photocatalysts. Zr4+ doping resulted in the enhancement of photocatalytic activity, evaluated by monitoring the degradation of methylene blue solution. 0.5 wt% Zr doped CdO nanoarticles calcined at 400 °C exhibited the highest photocatalytic activity with better percentage of color abatement (80.95%). The pseudo-first-order reaction rate became faster on Zr doping such that the rate constant is ~?0.4–0.5 h?1 for Zr doped CdO while that for pure CdO is ~?0.3 h?1.  相似文献   
65.
66.
The potential large-scale production of fullerene C60 and its widespread use in consumer products may translate into occupational and public exposure and in long-term environmental exposure. To assess the risk and fate of C60 in the environment, it is important to understand its solvate formation in common industrial solvents as the solvates may affect various properties of C60 including reactivity and toxicity, particularly when solvates occur in C60 clusters. In this study, the solubility measurements in mixed solvent system can provide useful information about solvate formation. The solubility of C60 was measured in pure toluene, tetrahydrofuran, ethanol, and acetonitrile to be 3000, 11, 1.4, and 0.04 mg/L, respectively. Additionally, the solubility of C60 was measured in mixtures of toluene-acetonitrile, toluene-ethanol, toluene-tetrahydrofuran, and acetonitrile-tetrahydrofuran. The solubility data were modeled with some accuracy using Wohl's equation. The estimated crystal energy term for C60 in tetrahydrofuran was different than that in the other solvents, indicating that the C60 solid phase in equilibrium with tetrahydrofuran solution may be a solvated crystal.  相似文献   
67.
68.
The expression of the NMDA subtype of glutamate receptors was investigated by Western blot analysis and RT-PCR in cultured chick Bergmann and Müller glial cells. Using subunit-specific antibodies directed to the carboxy terminus of the rat NMDAR2A/B we detected the expression of the NMDAR2 subunit in both kinds of culture. The functional subunit of the NMDA receptor, NMDAR1, was detected by means of RT-PCR. These results, together with our previous functional characterization of NMDA receptors in radial glia, provide conclusive evidence for the expression of functional NMDA receptor/channels in Bergmann and Muller glia cells. Our findings strengthen the notion of a modulatory role of glial cells in synaptic transmission.  相似文献   
69.
The room-temperature fracture-resistance behavior ( R -curve) of unidirectional silicon-carbide-fiber-reinforced zircon-matrix composites has been studied experimentally and numerically. The composites showed strong rising R -curve behavior from experimental results that used in situ crack-length measurements taken via optical microscopy as well as the compliance method. A numerical calculation, based on the available models, then was performed to determine the bridging-stress function from the experimental R -curve. In addition, the effect of the residual stress and constituent properties on the bridging-stress function also has been considered in the numerical calculations. These results have indicated that the bridging-stress function, which controls the fracture resistance of ceramic composites, can be obtained from the carefully measured R -curve.  相似文献   
70.
Poly(vinyl alcohol) (PVA)‐amino acid (AA) biocomposite membranes are prepared by blending PVA with AAs such as glycine, lysine (LY), and phenyl alanine followed by in situ crosslinking with citric acid (CA) and explored as a new class of biocomposite membrane electrolytes for direct methanol fuel cells (DMFCs). CA crosslinks with PVA through esterification offers adequate chemical, thermal, and morphological stability thereby produces methanol‐obstructing close‐packed polymeric network. These biocomposite membranes are characterized in terms of mechanical, thermal, sorption, and proton‐conducting properties. Hydrophilic nature of AA zwitterions significantly facilitates proton conduction and CA crosslinking mitigates methanol crossover through establishing appropriate balance between hydrophilic/hydrophobic domains. The rational design of membrane microstructure with proper arrangement of hydrophobic/hydrophilic domains is a key to enhance electrochemical selectivity of PVA‐AA/CA biocomposite membranes. Biocomposite membrane comprising LY exhibits nearly threefold higher electrochemical selectivity in relation to PVA/CA blend membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43514.  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