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   4821篇
  免费   322篇
  国内免费   307篇
电工技术   359篇
综合类   236篇
化学工业   994篇
金属工艺   826篇
机械仪表   231篇
建筑科学   278篇
矿业工程   78篇
能源动力   161篇
轻工业   322篇
水利工程   17篇
石油天然气   180篇
武器工业   73篇
无线电   369篇
一般工业技术   620篇
冶金工业   263篇
原子能技术   61篇
自动化技术   382篇
  2024年   7篇
  2023年   54篇
  2022年   82篇
  2021年   123篇
  2020年   119篇
  2019年   101篇
  2018年   70篇
  2017年   128篇
  2016年   165篇
  2015年   156篇
  2014年   257篇
  2013年   308篇
  2012年   360篇
  2011年   475篇
  2010年   330篇
  2009年   436篇
  2008年   314篇
  2007年   366篇
  2006年   282篇
  2005年   247篇
  2004年   189篇
  2003年   179篇
  2002年   144篇
  2001年   99篇
  2000年   93篇
  1999年   66篇
  1998年   42篇
  1997年   43篇
  1996年   31篇
  1995年   29篇
  1994年   31篇
  1993年   25篇
  1992年   21篇
  1991年   22篇
  1990年   9篇
  1989年   8篇
  1988年   7篇
  1987年   4篇
  1986年   2篇
  1985年   7篇
  1984年   1篇
  1983年   3篇
  1982年   4篇
  1981年   4篇
  1979年   1篇
  1975年   1篇
  1974年   1篇
  1964年   1篇
  1959年   1篇
  1958年   2篇
排序方式: 共有5450条查询结果,搜索用时 15 毫秒
1.
Background: Within the claudin (CLDN) family, CLDN12 mRNA expression is altered in various types of cancer, but its clinicopathological relevance has yet to be established due to the absence of specific antibodies (Abs) with broad applications. Methods: We generated a monoclonal Ab (mAb) against human/mouse CLDN12 and verified its specificity. By performing immunohistochemical staining and semiquantification, we evaluated the relationship between CLDN12 expression and clinicopathological parameters in tissues from 138 cases of cervical cancer. Results: Western blot and immunohistochemical analyses revealed that the established mAb selectively recognized the CLDN12 protein. Twenty six of the 138 cases (18.8%) showed low CLDN12 expression, and the disease-specific survival (DSS) and recurrence-free survival rates were significantly decreased compared with those in the high CLDN12 expression group. We also demonstrated, via univariable and multivariable analyses, that the low CLDN12 expression represents a significant prognostic factor for the DSS of cervical cancer patients (HR 3.412, p = 0.002 and HR 2.615, p = 0.029, respectively). Conclusions: It can be concluded that a reduced CLDN12 expression predicts a poor outcome for cervical cancer. The novel anti-CLDN12 mAb could be a valuable tool to evaluate the biological relevance of the CLDN12 expression in diverse cancer types and other diseases.  相似文献   
2.
Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters.  相似文献   
3.
4.
5.
《Ceramics International》2019,45(10):12994-13003
The temperature and dc bias stability of the dielectric constant and loss tangent of CaCu3Ti4O12 samples sintered under different oxygen atmospheres are discussed. The results suggest that the metal-oxygen vacancy related defects not only provide the charge carriers for the conduction (defect doping) but also contribute to the huge permittivity in the way of defect dipoles repositioning under charge carrier hopping. The charge localization in a specific copper-oxygen vacancy defect complex is the reason of the huge and stable permittivity and low dielectric loss in the middle temperature range, 90 K-200 K (20 Hz), while the implementation of the large barrier layer height needs a contribution by the titanium oxygen vacancy related trap charges in the grain boundaries, which also lead to a second permittivity stable range in a higher temperature range 200 K–300 K.  相似文献   
6.
关于CaCu3Ti4O12陶瓷的高介电常数机理,目前广泛接受的是非本征的内阻挡层电容模型。该模型认为在多晶中元素变价、缺陷和非化学计量比等导致的半导化晶粒被绝缘晶界层,即内阻挡层所包围。其中内阻挡层的厚度对材料的介电性能影响较大,而扫描电子显微镜(SEM)测试表明样品晶界呈稀烂的果酱状,SEM难以测量晶界区域绝缘内阻挡层厚度。本文采用正电子湮没技术表征其厚度,通过对CaCu3Ti4O12陶瓷共掺不同浓度的Al、Nb(CaCu3Ti4-xAl0.5xNb0.5xO12,x=0.2%、0.5%、5.0%)改变其晶粒和晶界的微观结构,研究CaCu3Ti4O12陶瓷高介电常数机理。正电子湮没结果显示,掺杂样品符合多普勒展宽谱S参数的变化趋势与平均寿命的变化趋势一致。x=0.5%掺杂样品的介电常数最高,其平均寿命、S参数和湮没长寿命成分均最小,阻挡层最薄。实验结果验证了描述CaCu3Ti4O12陶瓷高介电常数机理的内阻挡层电容模型的预测。  相似文献   
7.
(1-x)Sr0.7Pb0.15Bi0.1TiO3-xBi4Ti3O12 ((1-x)SPBT-xBIT, x = 0-0.125) bulk ceramics were developed and calcined via the solid-state method, aimed at the application of pulsed power capacitors. The phase structures, temperature stability, hysteresis loop, and discharge properties were systematically investigated. Considering both the temperature stability and dielectric properties, 0.925SPBT-0.075BIT bulk ceramics with a capacitance variation satisfying the X7R specification were developed for pulsed power capacitors. The energy storage density was 0.252 J/cm3, and the ceramics showed high temperature stability at 80 kV/cm. The discharge current waveforms of the 0.925SPBT-0.075BIT ceramics were recorded. A high discharge power density of approximately 1.01 × 108 W/kg with an 8 Ω load resistor and short discharge period of 84 ns were achieved at 50 kV/cm. The good temperature stability properties and high power density show that the 0.925SPBT-0.075BIT ceramics are well suited for pulsed power capacitors with a wide temperature range.  相似文献   
8.
The efficient surface modification of titanium dioxide (TiO2) particles with different sizes was first carried out with “water only method” (Appl. Surf. Sci. 2018, 447, 664–672) developed in our group using 12-hydroxy stearic acid (12-HSA) as the modifier. The 12-HSA-modified TiO2 particles with different sizes were then used to explore their effect on the mechanical and thermal properties of a thermoplastic polyurethane urea (TPUU) elastomer with superior mechanical and thermal properties produced newly in our lab using nonsymmetric alicyclic diisocyanate and diamine. Orthogonal experimental results showed that the order of impact of each factor on the modification efficiency of TiO2 particles was: Temperature > time > modifier content. It was found that, in the nanometer (≤100 nm) range, smaller particles were more helpful to enhance the tensile strength of the TPUU elastomer, while larger ones to increase more significantly the elongation at break. Besides, the TiO2/polyurethane urea nanocomposites exhibited much better thermomechanical performance than the pristine TPUU elastomer, and the thermomechanical performance of the nanocomposites increased with decreasing particle size.  相似文献   
9.
Lipids play an essential role in platelet functions. It is known that polyunsaturated fatty acids play a role in increasing platelet reactivity and that the prothrombotic phenotype plays a crucial role in the occurrence of major adverse cardiovascular events. The ongoing increase in cardiovascular diseases’ incidence emphasizes the importance of research linking lipids and platelet function. In particular, the rebound phenomenon that accompanies discontinuation of clopidogrel in patients receiving dual antiplatelet therapy has been associated with changes in the lipid profile. Our many years of research underline the importance of reduced HDL values for the risk of such a rebound effect and the occurrence of thromboembolic events. Lipids are otherwise a heterogeneous group of molecules, and their signaling molecules are not deposited but formed “on-demand” in the cell. On the other hand, exosomes transmit lipid signals between cells, and the profile of such changes can be monitored by lipidomics. Changes in the lipid profile are organ-specific and may indicate new drug action targets.  相似文献   
10.
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