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   23755篇
  免费   2403篇
  国内免费   1021篇
电工技术   1387篇
综合类   1133篇
化学工业   3909篇
金属工艺   1592篇
机械仪表   1778篇
建筑科学   1432篇
矿业工程   668篇
能源动力   871篇
轻工业   1658篇
水利工程   369篇
石油天然气   1073篇
武器工业   138篇
无线电   3179篇
一般工业技术   3783篇
冶金工业   1275篇
原子能技术   228篇
自动化技术   2706篇
  2024年   115篇
  2023年   508篇
  2022年   848篇
  2021年   1356篇
  2020年   960篇
  2019年   768篇
  2018年   915篇
  2017年   865篇
  2016年   878篇
  2015年   1000篇
  2014年   1215篇
  2013年   1439篇
  2012年   1585篇
  2011年   1749篇
  2010年   1476篇
  2009年   1431篇
  2008年   1291篇
  2007年   1062篇
  2006年   1017篇
  2005年   885篇
  2004年   689篇
  2003年   669篇
  2002年   609篇
  2001年   514篇
  2000年   481篇
  1999年   490篇
  1998年   464篇
  1997年   371篇
  1996年   336篇
  1995年   270篇
  1994年   213篇
  1993年   144篇
  1992年   113篇
  1991年   79篇
  1990年   77篇
  1989年   64篇
  1988年   43篇
  1987年   33篇
  1986年   34篇
  1985年   22篇
  1984年   14篇
  1983年   9篇
  1982年   8篇
  1981年   15篇
  1980年   13篇
  1979年   5篇
  1978年   6篇
  1977年   6篇
  1976年   10篇
  1959年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
燕麦为西藏自治区典型牧草之一,由于种植区地域辽阔,灌溉试验结果受限,西藏燕麦主要种植区的灌溉定额尚不明确。本文在西藏燕麦主要种植区内选取28个典型站点进行资料收集,遵循农业气候相似原则进行区域划分,基于水量平衡法揭示了西藏燕麦主要种植区灌溉定额的空间分布特征,并根据统计学原理分析了其影响因素。研究表明:燕麦主要种植区的灌溉定额呈由西藏中部至东部呈现先递增后递减的趋势,50%水文年下的燕麦灌溉定额在56~265 mm之间变化。降雨量是影响研究区内燕麦灌溉定额的主要因素(R2为0.515),ET0次之(R2为0.152);其它气象因素中,日照时数对研究区燕麦灌溉定额影响较大(R2为0.462),且呈正相关关系;相对湿度对燕麦灌溉定额影响较小。西藏燕麦主要种植区的灌溉定额及其空间分布可为西藏自治区灌溉用水管理提供支撑。  相似文献   
2.
The effects of high-pressure-modified soy 11S globulin (0.1, 200, and 400 MPa) on the gel properties, water-holding capacity, and water mobility of pork batter were investigated. The high-pressure-modified soy 11S globulin significantly increased (P < 0.05) the emulsion stability, cooking yield, hardness, springiness, chewiness, resilience, cohesiveness, the a* and b* values, and the G′ and G′′ values of pork batter at 80 °C, compared with those of 0.1 MPa-modified globulin. In contrast, the centrifugal loss and initial relaxation time of T2b, T21, and T22 significantly decreased (P < 0.05). Meanwhile, the microstructure was denser, and the voids were smaller and more uniform compared with those of 0.1 MPa-modified globulin. In addition, the sample with 11S globulin modified at 400 MPa had the best water-holding capacity, gel structure, and gel properties among the samples. Overall, the use of high-pressure-modified soy 11S globulin improved the gel properties and water-holding capacity of pork batter, especially under 400 MPa.  相似文献   
3.
In this work, we developed a novel system of isovalent Zr4+ and donor Nb5+ co-doped CaCu3Ti4O12 (CCTO) ceramics to enhance dielectric response. The influences of Zr4+ and Nb5+ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr4+ and Nb5+ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu3Ti3.8-xZrxNb0.2O12 (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr4+ and Nb5+ ions than that of single-doped with Zr4+ or Nb5+ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~105) at a frequency range of 102–105 Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr4+ and Nb5+ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus.  相似文献   
4.
Neoantigen vaccines and adoptive dendritic cell (DC) transfer are major clinical approaches to initiate personalized immunity in cancer patients. However, the immunization efficacy is largely limited by the in vivo trajectory including neoantigens’ access to resident DCs and DCs’ access to lymph nodes (LNs). Herein, an innovative strategy is proposed to improve personalized immunization through neoantigen-loaded nanovaccines synergized with adoptive DC transfer. It is found that it enables selective delivery of neoantigens to resident DCs and macrophages by coating cancer cell membranes onto neoantigen-loaded nanoparticles. In addition, the nanovaccines promote the secretion of chemokine C-C motif ligand 2 (CCL2), CCL3, and C-X-C motif ligand 10 from macrophages, thus potentiating the access of transferred DCs to LNs. This immunization strategy enables coordinated delivery of identified neoantigens and autologous tumor lysate-derived undefined antigens, leading to initiation of antitumor T cell immunity in a personalized manner. It significantly inhibits tumor growth in prophylactic and established mouse tumor models. The findings provide a new vision for potentiating adoptive cell transfer by nanovaccines, which may open the door to a transformative possibility for improving personalized immunization.  相似文献   
5.
The confinement of CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) in a stabilized inorganic glass matrix is a new strategy for improving their long-term stability and promoting their applications in the optoelectronic field. Here, in situ nanocrystallization strategy is developed to precipitate CsPbBr3?xIx NCs with arbitrary I/Br ratio among an elaborately designed GeS2–Sb2S3-based chalcogenide glass matrix. Spherical CsPbBr3?xIx NCs are homogeneously distributed in the glass matrix after thermal treatment. The photoluminescence (PL) spectra show that the emission peaks of CsPbBr3?xIx NCs can be tuned from 570 nm to 722 nm with the replacement of Br by I. The fs transient absorption (TA) spectra reveal that there exists some structural defects in the NCs, leading to short PL decay life. This work would shed light on confining CsPbX3 NCs into glassy matrices, facilitating their future applications in photoelectronic fields.  相似文献   
6.
Tian  Dating  Zhou  Yuchi  An  Kai  Kang  Huiting 《Polymer Bulletin》2020,77(4):1847-1868
Polymer Bulletin - Preparation of konjac glucomannan-grafted poly(trimethyl allyl ammonium chloride) (KGM-g-PTMAAC) was carried out using KGM as polysaccharide matrix and TMAAC as cationic...  相似文献   
7.
The Journal of Supercomputing - Spark is one of the most widely used systems for the distributed processing of big data. Its performance bottlenecks are mainly due to the network I/O, disk I/O, and...  相似文献   
8.
Wireless Personal Communications - In recent years, many wireless communication services have become indispensable for our daily life, such as voice telephoning and the internet surfing. However,...  相似文献   
9.
Engineering novel Sn-based bimetallic materials could provide intriguing catalytic properties to boost the electrochemical CO2 reduction. Herein, the first synthesis of homogeneous Sn1−xBix alloy nanoparticles (x up to 0.20) with native Bi-doped amorphous SnOx shells for efficient CO2 reduction is reported. The Bi-SnOx nanoshells boost the production of formate with high Faradaic efficiencies (>90%) over a wide potential window (−0.67 to −0.92 V vs RHE) with low overpotentials, outperforming current tin oxide catalysts. The state-of-the-art Bi-SnOx nanoshells derived from Sn0.80Bi0.20 alloy nanoparticles exhibit a great partial current density of 74.6 mA cm−2 and high Faradaic efficiency of 95.8%. The detailed electrocatalytic analyses and corresponding density functional theory calculations simultaneously reveal that the incorporation of Bi atoms into Sn species facilitates formate production by suppressing the formation of H2 and CO.  相似文献   
10.
Bacteria with antibiotic-resistant could seriously threaten to human health, increasing the treatment cost for infections and negatively affecting treatment outcomes. Stress adaptation is one possible mechanism for the acquisition or enhancement of antibiotic resistance in bacteria as a result of cross-protection. In this study, the effects of acid, salt, and cold stress on the antibiotic resistance of Salmonella Enteritidis, Listeria monocytogenes, and Escherichia coli O157:H7 were investigated using the disc diffusion method. For S. Enteritidis, acidic growth conditions increased resistance to ciprofloxacin and erythromycin (p < .05), and addition of 4% NaCl to growth media decreased resistance to chloramphenicol (p < .05). Irrespective of pH and the NaCl concentration of the growth medium, refrigerated E. coli O157:H7 showed increased resistance to amoxycillin, ciprofloxacin, gentamicin, streptomycin, and erythromycin (p < .05). Acid-adapted L. monocytogenes showed decreased the resistance to amoxycillin, ampicillin, chloramphenicol, ciprofloxacin, erythromycin, gentamicin, streptomycin, and tetracycline (p < .05). In conclusion, prolonged exposure of foodborne pathogens to acid, salt, and cold stress alters their antibiotic resistance. However, the effect of acid, salt, and cold stress on bacterial antibiotic resistance depend on both the bacterial species and the specific antibiotic. Therefore, multiple factors need to be considered for a foodborne antimicrobial resistant risk assessment.  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