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   39871篇
  免费   2622篇
  国内免费   963篇
电工技术   1530篇
技术理论   4篇
综合类   1564篇
化学工业   6099篇
金属工艺   1550篇
机械仪表   1724篇
建筑科学   1698篇
矿业工程   766篇
能源动力   1211篇
轻工业   2242篇
水利工程   453篇
石油天然气   1019篇
武器工业   146篇
无线电   5486篇
一般工业技术   5106篇
冶金工业   7438篇
原子能技术   400篇
自动化技术   5020篇
  2024年   247篇
  2023年   485篇
  2022年   878篇
  2021年   1206篇
  2020年   950篇
  2019年   811篇
  2018年   924篇
  2017年   972篇
  2016年   881篇
  2015年   1084篇
  2014年   1425篇
  2013年   2125篇
  2012年   1989篇
  2011年   2309篇
  2010年   1835篇
  2009年   1879篇
  2008年   1929篇
  2007年   1739篇
  2006年   1566篇
  2005年   1254篇
  2004年   1111篇
  2003年   1201篇
  2002年   1398篇
  2001年   1177篇
  2000年   817篇
  1999年   848篇
  1998年   2406篇
  1997年   1540篇
  1996年   1105篇
  1995年   768篇
  1994年   645篇
  1993年   620篇
  1992年   276篇
  1991年   275篇
  1990年   278篇
  1989年   256篇
  1988年   226篇
  1987年   206篇
  1986年   190篇
  1985年   169篇
  1984年   110篇
  1983年   83篇
  1982年   91篇
  1981年   84篇
  1980年   109篇
  1979年   51篇
  1978年   72篇
  1977年   181篇
  1976年   353篇
  1975年   50篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Guan  ChunYi  Shang  XiongJun  Xie  YanQiong  Yang  Chang  Zhang  Sai  Liu  Si  Xiao  FuLiang 《中国科学:技术科学(英文版)》2020,63(11):2369-2374
Science China Technological Sciences - Previous studies have shown that EMIC waves occur preferentially in the afternoon sector of the magnetosphere. Here we report obliquely propagating H+ and He+...  相似文献   
13.
为了解决倾斜矿体开采中斜天井掘进问题,我院新开发了我国第一代斜天井钻机产品。本文较详细地介绍了其设计思想,并对工业试验情况进行了分析。经过三个阶段的反复试验和改进后,使该设备具有优良的技术性能和使用效果。  相似文献   
14.
近些年砂金生产企业相继出现重大投资失误,造成严重经济损失,这都是因为地质资源不可靠所造成的。造成地质资源不可靠的原因既有技术方面的,也有人为方面的.对这两方面的原因进行了分析、阐述,并针对性地提出了改进措施:修改现行砂金矿勘探技术规范、实行小规模试验性开采、业主提前介入监督。  相似文献   
15.
Plant materials with cellular structure, like fruits and vegetables, are often viewed as porous media in terms of model building of the drying process, on the basis of a hypothesis that all of the moisture of a plant tissue is trapped in a continuous and connected pore network system. However, most of the moisture in the plant tissue is contained naturally in enclosed cells. In the course of drying, the trapped moisture has to cross the cell membranes and then migrates in the extracellular space. Based on this concept, a pore network model for isothermal drying of plant materials was developed in which two stages of moisture movement—transmembrane transfer and extracellular transfer in the pore network—were considered. Finally, the isothermal convective air-drying processes of a potato slice were simulated. The calculated results were validated by the experiments conducted under the simulation conditions.  相似文献   
16.
An intramolecular palladium(II)‐catalyzed dearomative arylation reaction of indoles via C H bond functionalization was developed, providing access to structurally novel spiroindolenines with moderate to good yields. A one‐pot process for the synthesis of spiroindoline derivatives was also realized.

  相似文献   

17.
Massive commodity transactions lead to enormous virtual water and water pollution transfer; this phenomenon will be intensified within the process of Regional Comprehensive Economic Partnership (RCEP) enforcement. This study applied multi-regional input–output and scenario simulation approach to reveal the virtual water elements flow, while exploring the trade structure optimisation roadmap for China. Results unveiled that China was a virtual water net exporter (9.17 billion tons), also the largest importer of water pollutants (N 622456 tons and P 136110 tons) among RCEP countries in 2015. In order to alleviate the water pressure in China, the textiles and other manufacturing industries should be limited, while the service industry is encouraged. Optimal scenario can realize 29.8% water conservation and 8% water pollutants reduction and also achieve a 36.5 million dollars trade volume increase. This research improves trade-off balance between water environment and economy at multi-regional level and accelerates green trade in economic partnerships globally.  相似文献   
18.
本实验旨在优化氧化锆珠破壁方法,以期筛选出较佳的破壁条件,提高蛋白得率。实验在菌体重量、研磨buffer和研磨时间这3方面对该破壁方法进行了优化,并通过SDS-PAGE来分析其破壁效果。在优化后的条件下,同时对6株乳酸菌进行破壁处理并通过SDS-PAGE来分析其破壁效果。结果表明:在菌体重量、研磨buffer、锆珠三者的加入比例(W/V/W)为0.013 g∶300μL∶1 g的条件下,研磨15 min,提取的蛋白图谱条带清晰,丰度高;RIPA、PBS、PENP、GUS作为研磨buffer时,提取的蛋白图谱条带清晰且丰度高,而8 mol/L尿素作为研磨buffer时,图谱条带模糊且丰度低;6株乳酸菌经该方法破壁处理后,蛋白图谱条带均具有较高的丰度和清晰度。因此,对于乳酸菌的破壁,氧化锆珠破壁法具有快速、高效的优点。   相似文献   
19.
Pancreatic cancer (PC) is a devastating malignant tumor of gastrointestinal (GI) tumors characterized by late diagnosis, low treatment success and poor prognosis. The most common pathological type of PC is pancreatic ductal adenocarcinoma (PDAC), which accounts for approximately 95% of PC. PDAC is primarily driven by the Kirsten rat sarcoma virus (KRAS) oncogene. Ferroptosis was originally described as ras-dependent cell death but is now defined as a regulated cell death caused by iron accumulation and lipid peroxidation. Recent studies have revealed that ferroptosis plays an important role in the development and therapeutic response of tumors, especially PDAC. As the non-apoptotic cell death, ferroptosis may minimize the emergence of drug resistance for clinical trials of PDAC. This article reviews what has been learned in recent years about the mechanisms of ferroptosis in PDAC, introduces the association between ferroptosis and the KRAS target, and summarizes several potential strategies that are capable of triggering ferroptosis to suppress PDAC progression.  相似文献   
20.
Asthma is a chronic respiratory disease with symptoms such as expiratory airflow narrowing and airway hyperresponsiveness (AHR). Millions of people suffer from asthma and are at risk of life-threatening conditions. Lactoferrin (LF) is a glycoprotein with multiple physiological functions, including antioxidant, anti-inflammatory, antimicrobial, and antitumoral activities. LF has been shown to function in immunoregulatory activities in ovalbumin (OVA)-induced delayed type hypersensitivity (DTH) in mice. Hence, the purpose of this study was to investigate the roles of LF in AHR and the functions of dendritic cells (DCs) and Th2-related responses in asthma. Twenty 8-week-old male BALB/c mice were divided into normal control (NC), ovalbumin (OVA)-sensitized, and OVA-sensitized with low dose of LF (100 mg/kg) or high dose of LF (300 mg/kg) treatment groups. The mice were challenged by intranasal instillation with 5% OVA on the 21st to 27th day after the start of the sensitization period. The AHR, cytokines in bronchoalveolar lavage fluid, and pulmonary histology of each mouse were measured. Serum OVA-specific IgE and IgG1 and OVA-specific splenocyte responses were further detected. The results showed that LF exhibited protective effects in ameliorating AHR, as well as lung inflammation and damage, in reducing the expression of Th2 cytokines and the secretion of allergen-specific antibodies, in influencing the functions of DCs, and in decreasing the level of Th2 immune responses in a BALB/c mouse model of OVA-induced allergic asthma. Importantly, we demonstrated that LF has practical application in reducing DC-induced Th2 cell responses in asthma. In conclusion, LF exhibits anti-inflammation and immunoregulation activities in OVA-induced allergic asthma. These results suggest that LF may act as a supplement to prevent asthma-induced lung injury and provide an additional agent for reducing asthma severity.  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