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   25378篇
  免费   1920篇
  国内免费   860篇
电工技术   1325篇
技术理论   1篇
综合类   1379篇
化学工业   4538篇
金属工艺   1319篇
机械仪表   1321篇
建筑科学   1876篇
矿业工程   578篇
能源动力   886篇
轻工业   1663篇
水利工程   340篇
石油天然气   1342篇
武器工业   118篇
无线电   3113篇
一般工业技术   3262篇
冶金工业   1475篇
原子能技术   314篇
自动化技术   3308篇
  2024年   84篇
  2023年   410篇
  2022年   702篇
  2021年   1035篇
  2020年   724篇
  2019年   679篇
  2018年   697篇
  2017年   811篇
  2016年   762篇
  2015年   928篇
  2014年   1243篇
  2013年   1593篇
  2012年   1582篇
  2011年   1741篇
  2010年   1404篇
  2009年   1456篇
  2008年   1351篇
  2007年   1244篇
  2006年   1352篇
  2005年   1171篇
  2004年   845篇
  2003年   762篇
  2002年   766篇
  2001年   543篇
  2000年   525篇
  1999年   602篇
  1998年   572篇
  1997年   462篇
  1996年   448篇
  1995年   346篇
  1994年   280篇
  1993年   191篇
  1992年   175篇
  1991年   118篇
  1990年   95篇
  1989年   73篇
  1988年   88篇
  1987年   51篇
  1986年   46篇
  1985年   28篇
  1984年   35篇
  1983年   21篇
  1982年   27篇
  1981年   13篇
  1980年   11篇
  1979年   17篇
  1976年   10篇
  1975年   5篇
  1974年   4篇
  1965年   5篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
随着我国光伏产业的大起大落,对于相关技术的研究以及专利申请数量也潜移默化地发生了改变。切割废砂浆的综合回收利用对减少环境污染、提高资源利用具有重要意义,更重要的是可以缓解我国太阳能多晶硅的紧缺、减少多晶硅的进口量。文章从国内专利申请情况分析了硅晶切割废砂浆回收处理工艺的发展。  相似文献   
952.
The Bi2O3–B2O3–ZnO–SiO2 (BB35SZ) glass effects on the sintering behavior and magnetic properties of Bi–Zn co‐doped Co2Y ferrites were investigated in developing low‐temperature‐fired ferrites. The results indicate that BB35SZ glass can be used as a sintering aid to reduce the densification temperature of Co2Y ferrites from 1300°C to 900°C. The 2(Ba0.9Bi0.1O)·2(Zn0.4Co0.4Cu0.2O)·6(Fe1.97Zn0.03O3) ferrite with 4 wt% BB35SZ glass can be densified below 900°C, exhibiting an initial permeability of 3.4 and quality factor of 55. This process provides a promising candidate for multilayer chip magnetic devices for microwave applications.  相似文献   
953.
Novel low temperature firing microwave dielectric ceramic LiCa3MgV3O12 (LCMV) with garnet structure was fabricated by the conventional solid‐state reaction method. The phase purity, microstructure, and microwave dielectric properties were investigated. The densification temperature for the LCMV ceramic is 900°C. LCMV ceramic possessed εr = 10.5, Qu × = 74 700 GHz, and τf = ?61 ppm/°C. Furthermore, 0.90LiCa3MgV3O12–0.10CaTiO3 ceramic sintered at 925°C for 4 h exhibited good properties of εr = 12.4, Qu × = 57 600 GHz, and τf = 2.7 ppm/°C. The LCMV ceramic could be compatible with Ag electrode, which makes it a promising ceramic for LTCC technology application.  相似文献   
954.
The thermal and thermo-oxidative degradation behaviors of styrene-butadiene-styrene (SBS) star block copolymer were reported using thermogravimetric analysis (TGA). TGA coupled with Fourier Transform Infrared spectroscopy was used to characterize the degradation volatile of SBS in air atmosphere. The thermal degradation kinetics of SBS in nitrogen and air atmospheres was studied in three steps: (1) the activation energies E α were estimated by iterative method; (2) the proper form of f(α) was deduced by Popescu method; (3) the results obtained by above steps were used in determination pre-exponential factor A.  相似文献   
955.
Extensive laboratory investigations and mill scale trials confirmed the applicability of ultrafiltrated high molecular weight Ca-ligno-sulfonates in adhesive composition with phenolic resin for insulation board manufacture based on mineral wool. Insulation materials produced with adhesive components with a formulation of lignosulfonate/PF resin between 10/90 and 30/70 have appropriate technical and commercial properties.  相似文献   
956.
Vinyl ester (VE) resins are widely used as thermoset adhesives in structural joints and composites, but complete curing under environmental conditions is not produced. The existing literature dealing with the effect of post-curing on the structure, viscoelastic, mechanical, and adhesion properties of VE resin is scarce. Therefore, in this study, VE resin was subjected to different post-curing temperatures (50–140 °C) for one hour, and the changes in structure and properties were assessed. The degree of cross-linking of the VE resin depended on the post-curing temperature and cure started to be completed above 100 °C, a temperature close to the glass transition temperature (115 °C) of the completely cross-linked polymer. Furthermore, gel formation in VE resin was evidenced for post-curing temperature below 100 °C. In order to fully cross-link the VE resin, post-curing at 140 °C for one hour was necessary, and it was evidenced by an increase in the glass transition temperature and in the mechanical properties; an increase in adhesion to cold rolled steel was obtained although the shear strength was lower than in the joint produced with the non-post-cured VE resin.  相似文献   
957.
Tight junctions (TJs) are a mode of cell-to-cell adhesion in epithelial or endothelial cells, and serve as a physical barrier to maintenance of homeostasis in body by controlling paracellular transport. Claudins are the most important molecules of the TJs, but paradoxically these proteins are frequently over-expressed in cancers and their overexpression is implicated in the invasive potential of cancer. Hence, we investigated the effects of flavonoids extracted from Orostachys japonicus A. Berger (FEOJ) on TJs and the expression of claudins as well as cancer invasion along with in LnCaP human prostate cancer. FEOJ suppressed cancer cell motility and invasiveness at the concentrations where FEOJ did not show anti-proliferative activity. FEOJ increased transepithelial electrical resistance (TER) associated with tightening TJs, and suppressed expression of claudin proteins. Furthermore, FEOJ suppressed the activities of MMP-2 and -9 in a dose-dependent manner, which came from the activation of tissue inhibitor of metalloproteinases (TIMPs) by FEOJ. FEOJ suppressed migration and invasion by suppressing PI3K/Akt signaling pathway. Taken together, this study suggest that FEOJ suppresses cancer migration and invasion by tightening TJs through the suppression of claudin expression, and by suppressing MMPs in LnCaP human prostate cancer cells, which at least in part results from the suppression of PI3K/Akt signaling pathway.  相似文献   
958.
Caffeic acid phenethyl ester (CAPE) is a bioactive component extracted from honeybee hive propolis. Our observations indicated that CAPE treatment suppressed cell proliferation and colony formation of TW2.6 human oral squamous cell carcinoma (OSCC) cells dose-dependently. CAPE treatment decreased G1 phase cell population, increased G2/M phase cell population, and induced apoptosis in TW2.6 cells. Treatment with CAPE decreased protein abundance of Akt, Akt1, Akt2, Akt3, phospho-Akt Ser473, phospho-Akt Thr 308, GSK3β, FOXO1, FOXO3a, phospho-FOXO1 Thr24, phospho-FoxO3a Thr32, NF-κB, phospho-NF-κB Ser536, Rb, phospho-Rb Ser807/811, Skp2, and cyclin D1, but increased cell cycle inhibitor p27Kip. Overexpression of Akt1 or Akt2 in TW2.6 cells rescued growth inhibition caused by CAPE treatment. Co-treating TW2.6 cells with CAPE and 5-fluorouracil, a commonly used chemotherapeutic drug for oral cancers, exhibited additive cell proliferation inhibition. Our study suggested that administration of CAPE is a potential adjuvant therapy for patients with OSCC oral cancer.  相似文献   
959.
It has been confirmed that alternatively activated macrophages (M2) participate in tissue remodeling and fibrosis occurrence, but the effect of M2 on peritoneal fibrosis related to peritoneal dialysis (PD) hasn’t been elucidated. This study was therefore conducted to assess the association between M2 and peritoneal fibrosis related to PD. In this study, peritoneal fibrosis was induced by intraperitoneal (i.p.) injection of Lactate-4.25% dialysate (100 mL/kg) to C57BL/6J mice for 28 days, and liposome-encapsulated clodronate (LC, the specific scavenger of macrophages) was used to treat the peritoneal fibrosis mice model by i.p. injection at day 18 and day 21. All animals were sacrificed at day 29. Parietal peritonea were stained with Masson’s trichrome, and the expression of type I collagen (Col-I), fibronectin, mannose receptor (CD206), transforming growth factor beta (TGF-β), chemokine receptor 7 (CCR7), chitinase 3-like 3 (Ym-1) and arginase-1 (Arg-1) was determined by Western blotting, immunofluorescence and quantitative real-time PCR. Our results revealed that peritoneal thickness, Col-I, fibronectin, CD206, TGF-β, Ym-1 and Arg-1 were upregulated in the peritoneal fibrosis mice model, and all of these indexes were downregulated in those treated with LC. Additionally, there was no difference in the level of CCR7 between the model and treatment group. Our study indicated that peritoneal M2 played an important role in the process of peritoneal fibrosis related to PD and might be a potential target for intervention therapy of peritoneal fibrosis.  相似文献   
960.
Low‐molecular‐weight copolymers of styrene and vinylbenzyl ammonium salts (oligomeric surfactant) were used to modify montmorillonite (MMT). The oligomeric‐modified MMT showed good thermal stability, which made it suitable to be used for preparing polycarbonate(PC)/MMT nanocomposites at high temperature. A different series of PC/MMT nanocomposites had been prepared by melt processing using a twin screw extruder. The effect of oligomeric surfactant structure and clay loading on the morphology, mechanical property, thermal stability, and color appearance of the nanocomposites were explored. The results of X‐ray diffraction and transmission electron microscopy analyses indicated that the PC/MMT nanocomposites had partially exfoliated structures. The PC/MMT nanocomposites were found to retain light colored, which was important for optical application. Compared to neat PC, the nanocomposites showed better properties of thermal stability and heat insulation. The mechanical properties of the nanocomposites are significantly enhanced by incorporating clay into the PC matrix. The tensile strength of nanocomposites with 2 wt% clay content was up to 55 MPa, which was much higher than that of the neat PC (37 MPa). The maximum tensile modulus value was 19% higher than that of neat PC. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers  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