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   154239篇
  免费   6759篇
  国内免费   4034篇
电工技术   5184篇
技术理论   2篇
综合类   4101篇
化学工业   18437篇
金属工艺   8308篇
机械仪表   6449篇
建筑科学   5564篇
矿业工程   1519篇
能源动力   4240篇
轻工业   11735篇
水利工程   1856篇
石油天然气   2705篇
武器工业   483篇
无线电   22035篇
一般工业技术   27659篇
冶金工业   27218篇
原子能技术   2009篇
自动化技术   15528篇
  2024年   977篇
  2023年   1208篇
  2022年   2129篇
  2021年   2884篇
  2020年   2292篇
  2019年   2263篇
  2018年   2713篇
  2017年   2793篇
  2016年   2864篇
  2015年   3120篇
  2014年   4227篇
  2013年   7991篇
  2012年   6352篇
  2011年   8034篇
  2010年   6914篇
  2009年   7463篇
  2008年   7474篇
  2007年   7436篇
  2006年   6758篇
  2005年   5864篇
  2004年   4995篇
  2003年   4417篇
  2002年   3989篇
  2001年   4074篇
  2000年   3554篇
  1999年   3711篇
  1998年   9822篇
  1997年   6469篇
  1996年   5030篇
  1995年   3367篇
  1994年   2961篇
  1993年   2871篇
  1992年   1735篇
  1991年   1684篇
  1990年   1578篇
  1989年   1373篇
  1988年   1211篇
  1987年   897篇
  1986年   913篇
  1985年   929篇
  1984年   813篇
  1983年   709篇
  1982年   715篇
  1981年   682篇
  1980年   575篇
  1979年   481篇
  1978年   417篇
  1977年   538篇
  1976年   971篇
  1975年   308篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Ionic biopolymer hydrogels were prepared by the cross-linking of starches with sodium trimetaphosphate in alkaline medium at 40°C for 2 hours. The swelling capacity is relatively high — up to 310 g H20/g polymer. Salt solutions have a marked influence, and result in shrinkage but not in a total collapse. The effect of both the cross-linker and substrate concentrations on the swelling and rheological properties was investigated. The influence of temperature and NaOH concentration on the rheological behaviour suggests that they are both significant in determining the gel properties because of the readiness of the diester phosphate bonds to undergo hydrolysis. The molecular weight between two entanglement points (Me) and the effectiveness of cross-linking [ne(r)/ne(t)] were estimated from the observed Gp′ values, and those calculated from complete conversion of the cross-linker. The effectiveness of cross-linking lay between 0.2 and 2.74% for 10% wlw gels, and reached a maximum of 48.1% at the higher substrate concentration of 20% wlw. 13C-NMR signals from the anhydroglucose units became broader and decreased in intensity with rising cross-linker concentration due to the restricted motion arising from the additional bonding.  相似文献   
112.
针对复杂工业过程的控制需求,研究了一种基于多智能体系统的分布式集成智能控制系统框架,系统由人机集成单元、控制单元和虚拟仿真单元构成,每个单元由分层的Agent组构成。多个专业Agent和主管Agent组成功能Agent组,通过不同的Agent激活与后备构成Agent组的重构和控制模式的切换。采用基于PC和现场总线设备相结合的硬件结构,运用遵循职能物理代理基金会组织标准的开发工具Java智能体开发框架开发原型系统,并应用到焦炉集气管压力控制实践中。工程应用表明,所提出的集成控制系统能有效地解决焦炉集气管压力这类复杂工业对象的过程控制问题。  相似文献   
113.
Metallurgical and Materials Transactions B - The cationic effect of ferrous ions on the sulfide capacity of CaO-FetO-Al2O3-SiO2 slags was studied from the viewpoint of the ionic structure in the...  相似文献   
114.
Activity-based monitoring of cell-secreted proteases has gained significant interest due to the implication of these substances in diverse cellular functions. Here, we demonstrated a cell-based method of monitoring protease activity using fluorescent cell-permeable peptides. The activatable peptide consists of anionic (EEEE), cleavable, and cationic sequences (RRRR) that enable intracellular delivery by matrix metalloproteinase-2 (MMP2), which is secreted by living cancer cells. Compared to HT-29 cells (MMP2-negative), HT-1080 cells (MMP2-positive) showed a strong fluorescence response to the short fluorescent peptide via cell-secreted protease activation. Our approach is expected to find applications for the rapid visualization of protease activity in living cells.  相似文献   
115.
Prostate cancer is a major cause of cancer-related mortality in men in developed countries. The compound, 4-acetylantroquinonol B (4AAQB), is isolated from Antrodia cinnamomea (commonly known as Niu-Chang-Chih), which has been shown to inhibit cancer growth. However, the anticancer activity of 4AAQB has not previously been examined in prostate cancer. This study aimed to investigate the effect of 4AAQB on cancer and angiogenesis, as well as to explore its mechanism of action. Human prostate cancer cells (PC3) and human umbilical vein endothelial cells (HUVEC) were used in cell viability, cell migration, and cell cycle functional assays to evaluate the anticancer and antiangiogenic efficacy of 4AAQB in vitro. The effects of 4AAQB in vivo were determined using xenograft and angiogenesis models. The signaling events downstream of 4AAQB were also examined. The 4AAQB compound inhibited PC3 cell growth and migration, and reduced in vivo cancer growth, as shown in a subcutaneous xenograft model. Furthermore, 4AAQB inhibited HUVEC migration, tube formation, and aortic ring sprouting; it also reduced neovascularization in a Matrigel implant angiogenesis assay in vivo. The 4AAQB compound also decreased metastasis in the PC3 prostate cancer model in vivo. Serum or vascular endothelial growth factor (VEGF)-induced VEGF receptor 2 (VEGFR2), phosphoinositide 3-kinase (PI3K)/Ak strain transforming (Akt), and extracellular signal-regulated kinase ½ (ERK ½) phosphorylation were attenuated by 4AAQB in both PC3 and HUVEC. In conclusion, 4AAQB is a potential candidate for prostate cancer therapy.  相似文献   
116.
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   
117.
118.
侯民  刘战军 《钢结构》2008,23(8):70-72
针对目前高层建筑钢结构柱安装测量控制方法中存在的一些技术盲点,提出处理方法和改进建议。  相似文献   
119.
The peptidase M24 (Metallopeptidase 24, M24) superfamily is essential for plant growth, stress response, and pathogen defense. At present, there are few systematic reports on the identification and classification of members of the peptidase M24 proteins superfamily in wheat. In this work, we identified 53 putative candidate TaM24 genes. According to the protein sequences characteristics, these members can be roughly divided into three subfamilies: I, II, III. Most TaM24 genes are complex with multiple exons, and the motifs are relatively conserved in each sub-group. Through chromosome mapping analysis, we found that the 53 genes were unevenly distributed on 19 wheat chromosomes (except 3A and 3D), of which 68% were in triads. Analysis of gene duplication events showed that 62% of TaM24 genes in wheat came from fragment duplication events, and there were no tandem duplication events to amplify genes. Analysis of the promoter sequences of TaM24 genes revealed that cis-acting elements were rich in response elements to drought, osmotic stress, ABA, and MeJA. We also studied the expression of TaM24 in wheat tissues at developmental stages and abiotic stress. Then we selected TaM24-9 as the target for further analysis. The results showed that TaM24-9 genes strengthened the drought and salt tolerance of plants. Overall, our analysis showed that members of the peptidase M24 genes may participate in the abiotic stress response and provided potential gene resources for improving wheat resistance.  相似文献   
120.
Wearable and portable mobile phones play a critical role in the market,and one of the key technologies is the flexible electrode with high spe-cific capacity an...  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