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   61268篇
  免费   5010篇
  国内免费   2414篇
电工技术   3746篇
技术理论   4篇
综合类   3971篇
化学工业   9829篇
金属工艺   3403篇
机械仪表   4022篇
建筑科学   4589篇
矿业工程   1843篇
能源动力   1796篇
轻工业   3964篇
水利工程   1050篇
石油天然气   3975篇
武器工业   524篇
无线电   6740篇
一般工业技术   7389篇
冶金工业   3777篇
原子能技术   697篇
自动化技术   7373篇
  2025年   11篇
  2024年   1228篇
  2023年   1274篇
  2022年   1851篇
  2021年   2574篇
  2020年   2203篇
  2019年   1797篇
  2018年   1800篇
  2017年   1982篇
  2016年   1764篇
  2015年   2319篇
  2014年   2996篇
  2013年   3320篇
  2012年   3591篇
  2011年   4043篇
  2010年   3502篇
  2009年   3278篇
  2008年   3216篇
  2007年   2976篇
  2006年   3069篇
  2005年   2561篇
  2004年   1840篇
  2003年   1626篇
  2002年   1608篇
  2001年   1390篇
  2000年   1294篇
  1999年   1567篇
  1998年   1605篇
  1997年   1349篇
  1996年   1127篇
  1995年   890篇
  1994年   720篇
  1993年   551篇
  1992年   428篇
  1991年   278篇
  1990年   226篇
  1989年   178篇
  1988年   135篇
  1987年   87篇
  1986年   81篇
  1985年   60篇
  1984年   35篇
  1983年   36篇
  1982年   41篇
  1981年   31篇
  1980年   23篇
  1979年   6篇
  1977年   33篇
  1976年   70篇
  1975年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
设计HSE管理     
何云 《化工设计》2006,16(2):33-37
论述设计HSE管理,重点探讨HAZOP审查、布置图HSE审查和HACON施工危害研究,以确保工程设计能满足装置的安全操作和可维护性,防止环境污染,降低施工期的风险。  相似文献   
122.
SOC软硬件划分系统中的关键算法   总被引:1,自引:0,他引:1  
设计并实现了SOC软硬件划分系统,搭建了软硬件协同设计的平台并描述了软硬件协同设计的流程。运用多目标遗传算法对目标系统的价格、功耗、速度进行优化,采用了基于Pareto支配的适应值赋值、精英保持和密度计算截断操作的方法进行多目标寻优。针对单任务图描述多CPU系统结构的不足,提出采用多任务图来描述的方法,并提出了MTLS性能评估算法,验证系统软硬件划分的优劣。在对比实验中将NSGA2算法运用到本系统中,结果证明论文的多目标寻优算法获得的非支配解80%比NSGA2的非支配解优。  相似文献   
123.
Single-event effects(SEEs) induced by medium-energy protons in a 28 nm system-on-chip(So C) were investigated at the China Institute of Atomic Energy. An on-chip memory block was irradiated with 90 MeV and70 MeV protons, respectively. Single-bit upset and multicell upset events were observed, and an uppermost number of nine upset cells were discovered in the 90 MeV proton irradiation test. The results indicate that the SEE sensitivities of the 28 nm SoC to the 90 MeV and 70 MeV protons were similar. Cosmic Ray Effects on Micro-Electronics Monte Carlo simulations were analyzed, and it demonstrates that protons can induce effects in a 28 nm SoC if their energies are greater than 1.4 MeV and that the lowest corresponding linear energy transfer was 0.142 MeV cm~2 mg~(-1). The similarities and discrepancies of the SEEs induced by the 90 MeV and 70 MeV protons were analyzed.  相似文献   
124.
125.
In this study, corrosion behaviour of double-phase Al1.3CrFeNi chemically complex alloy was investigated, including hot corrosion and electrochemical corrosion. Hot corrosion behaviour of Al1.3CrFeNi alloy was explored in molten 75 wt-% Na2SO4?+?25 wt-% NaCl salt. The result revealed that the corrosion kinetic curve of Al1.3CrFeNi alloy followed the exponential rate rule through mass loss measurement. In addition, it prevented that the formed corrosion layer had obvious stratification including external granular Al2O3 and inner porous Cr2O3 when corrosion time was up to 100?h. Besides, it should be noted that the Al1.3CrFeNi alloy was sensitive to the molten salt containing chlorine, which makes the alloy surface leave voids and bring about acceleration of corrosion. Meanwhile, electrochemical corrosion resistance of Al1.3CrFeNi alloy in NaCl solution with different concentrations (0.6, 1.0 and 2.0?mol?L?1) was investigated at room temperature. The results revealed that Al1.3CrFeNi alloy showed superior corrosion resistance in NaCl solution due to the existence of Al and Cr which aid the formation of protective oxide layer.  相似文献   
126.
TCH4 is a xyloglucan endotransglucosylase/hydrolase (XTH) family member. Extensive studies have shown that XTHs are very important in cell wall homeostasis for plant growth and development. Boron (B), as an essential micronutrient for plants, plays an essential role in the cross-linking of cell wall pectin. However, the effect of B on cell wall organization is unclear. This study aimed to explore the mechanism of plant adaption to B stress by investigating the role of TCH4 in cell wall homeostasis. We conducted both plate and hydroponic cultures of wild-type Col-0 and overexpression and gene knockout lines of XTH22/TCH4 to analyze the phenotype, components, and characteristics of the cell wall using immunofluorescence, atomic force microscopy (AFM), and transmission electron microscopy (TEM). B deficiency induces the expression of TCH4. The overexpression lines of TCH4 presented more sensitivity to B deficiency than the wild-type Col-0, while the knockout lines of TCH4 were more resistant to low B stress. Up-regulation of TCH4 influenced the ratio of chelator-soluble pectin to alkali-soluble pectin and decreased the degree of methylesterification of pectin under B-deficient conditions. Moreover, we found that B deficiency disturbed the arrangement of cellulose, enlarged the gap between cellulose microfibrils, and decreased the mechanical strength of the cell wall, leading to the formation of a thickened and deformed triangular region of the cell wall. These symptoms were more profound in the TCH4 overexpression lines. Consistently, compared with Col-0, the O2 and MDA contents in the TCH4 overexpression lines increased under B-deficient conditions. This study identified the B-deficiency-induced TCH4 gene, which regulates cell wall homeostasis to influence plant growth under B-deficient conditions.  相似文献   
127.
孔系位置度是机械行业比较常见的一种位置公差,其测量一般用坐标法。但因检测设备、人员、及数理知识等原因的限制,目前这种测量方法在我厂还无法开展。经过实际工作的不断实践,探索出一种简单、易行且准确的测量方法。  相似文献   
128.
Pannexins (PANX) were cloned based on their sequence homology to innexins (Inx), invertebrate gap junction proteins. Although there is no sequence homology between PANX and connexins (Cx), these proteins exhibit similar configurations. The PANX family has three members, PANX1, PANX2 and PANX3. Among them, PANX1 has been the most extensively studied. The PANX1 channels are activated by many factors, including high extracellular K+ ([K+]e), high intracellular Ca2+ ([Ca2+]i), Src family kinase (SFK)-mediated phosphorylation, caspase cleavage and mechanical stimuli. However, the mechanisms mediating this mechanosensitivity of PANX1 remain unknown. Both force-from-lipids and force-from-filaments models are proposed to explain the gating mechanisms of PANX1 channel mechanosensitivity. Finally, both the physiological and pathological roles of mechanosensitive PANX1 are discussed.  相似文献   
129.
近红外光热转换材料在光热治疗、光驱动智能器件等医学和能源领域受到广泛重视.本文以商业化芳香小分子为单体,通过一步简单的交联聚合方法制得了四种共轭多孔聚合物,并首次系统研究了它们的光热转换性能.结果表明,它们均具有灵敏的近红外光热响应性,且材料的光热转换效率与单体结构中共轭苯环数有很大关系,其中两种聚合物的光热转换效率可...  相似文献   
130.
Adipocytic tumors are the most common subtype of soft tissue tumors. In current clinical practice, distinguishing benign lipomas from well-differentiated liposarcomas (WDLPS), as well as dedifferentiated liposarcomas (DDLPS) from their morphologic mimics, remains a significant diagnostic challenge. This is especially so when examining small biopsy samples and without the aid of additional ancillary tests. Recognizing the important role that microRNAs (miRNAs) play in tumorigenesis and their potential utility in tumor classification, we analyzed routine clinical tissue samples of benign and malignant lipomatous tumors, as well as other sarcoma mimics, to identify distinguishing miRNA-based signatures that can aid in the differential diagnosis of these entities. We discovered a 6-miRNA signature that separated lipomas from WDLPS with high confidence (AUC of 0.963), as well as a separate 6-miRNA signature that distinguished DDLPS from their more aggressive histologic mimics (AUC of 0.740). Functional enrichment analysis unveiled possible mechanistic involvement of these predictive miRNAs in adipocytic cancer-related biological processes and pathways such as PI3K/AKT/mTOR and MAPK signaling, further supporting the relevance of these miRNAs as biomarkers for adipocytic tumors. Our results demonstrate that miRNA expression profiling may potentially be used as an adjunctive tool for the diagnosis of benign and malignant adipocytic tumors. Further validation studies are warranted.  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