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   55460篇
  免费   5111篇
  国内免费   2658篇
电工技术   3499篇
技术理论   8篇
综合类   3627篇
化学工业   9419篇
金属工艺   2933篇
机械仪表   3273篇
建筑科学   3982篇
矿业工程   1505篇
能源动力   1754篇
轻工业   3486篇
水利工程   1096篇
石油天然气   2830篇
武器工业   646篇
无线电   6944篇
一般工业技术   6767篇
冶金工业   2902篇
原子能技术   697篇
自动化技术   7861篇
  2024年   255篇
  2023年   908篇
  2022年   1803篇
  2021年   2461篇
  2020年   1819篇
  2019年   1522篇
  2018年   1695篇
  2017年   1804篇
  2016年   1624篇
  2015年   2279篇
  2014年   2702篇
  2013年   3432篇
  2012年   3571篇
  2011年   3783篇
  2010年   3321篇
  2009年   3228篇
  2008年   3109篇
  2007年   2944篇
  2006年   2973篇
  2005年   2468篇
  2004年   1854篇
  2003年   1616篇
  2002年   1671篇
  2001年   1530篇
  2000年   1316篇
  1999年   1330篇
  1998年   1159篇
  1997年   989篇
  1996年   799篇
  1995年   670篇
  1994年   495篇
  1993年   429篇
  1992年   329篇
  1991年   266篇
  1990年   183篇
  1989年   179篇
  1988年   144篇
  1987年   86篇
  1986年   88篇
  1985年   77篇
  1984年   33篇
  1983年   27篇
  1982年   37篇
  1981年   34篇
  1980年   23篇
  1979年   21篇
  1977年   16篇
  1976年   19篇
  1974年   13篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
准噶尔盆地三台-北三台地区第三系勘探潜力分析   总被引:1,自引:0,他引:1  
从沉积及储层组合、油气运移系统等方面全面剖析了准噶尔盆地三台-北三台地区第三系油气成藏条件,建立了成藏模式,对未钻探区勘探潜力进行了预测;通过分析,认为该区第三系储层物性主体差,断裂更多地表现为封闭性,导致沟通深部油气源的运移体系不畅,致使第三系圈闭不能有效捕获和储集油气。圈闭又比较匮乏,主体勘探潜力不大。北25井西背斜紧邻多期活动的甘诃子北断裂,第三系可能发育较好的储层,相对有利,北25井西背斜应是钻探第三系的首选目标。  相似文献   
132.
Measurement-based TFRC: improving TFRC in heterogeneous mobile networks   总被引:1,自引:0,他引:1  
As a well-known multimedia stream transport protocol, TFRC provides smooth transfer rate under stable network conditions, and achieves good fairness to TCP. However, it is not flexible in heterogeneous mobile networks because the available bandwidth varies rapidly. This paper proposes a measurement based TFRC (MBTFRC) protocol, which uses passive bandwidth measurements at the receiver to improve the flexibility of TFRC. In addition, a window-based EWMA filter with two weights is used to achieve stability and fairness simultaneously. Simulation results verify the flexibility, stability and fairness of MBTFRC.  相似文献   
133.
Ri-Chao Zhang  Yi Xu  Ai Lu  Kemei Cheng  Yigang Huang  Zhong-Ming Li   《Polymer》2008,49(10):2604-2613
The crystalline morphology of poly(phenylene sulfide) (PPS) isothermally crystallized from the melt under shear has been observed by polarized optical microscope (POM) equipped with a CSS450 hot-stage. The shish–kebab-like fibrillar crystal structure is formed at a higher shear rate or for a longer shear time, which is ascribed to the tight aggregation of numerous oriented nuclei in the direction of shear. The crystallization induction time of PPS decreases with the shear time, indicating that the shear accelerates the formation of stable crystal nuclei. Under shear, the increase of spherulite growth rate results from highly oriented chains. The melting behavior of shear-induced crystallized PPS performed by differential scanning calorimetry (DSC) shows multiple melting peaks. The lower melting peak corresponds to melting of imperfect crystal, and the degree of crystal perfection decreases as the shear rate increases. The higher melting peak is related to the orientation of molecular chains. These oriented molecular chains form the orientation nuclei which have higher thermal stability than the kebab-like lamellae that are developed later. A new model based on the above observation has been proposed to explain the mechanism of shish–kebab-like fibrillar crystal formation under shear flow.  相似文献   
134.
Di Zhou  Xiulin Zhu  Jian Zhu  Zhenping Cheng 《Polymer》2008,49(13-14):3048-3053
A novel monomer containing pyridylazo-2-naphthoxyl group, 1-(1-(4-vinylbenzyloxy)naphthalen-2-yl)-2-(pyridin-2-yl)diazene (VBNPA), was successfully synthesized and copolymerized with styrene (St) in N,N-dimethyl formamide (DMF) via reversible addition–fragmentation chain transfer (RAFT) polymerization using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) as RAFT agent. The polymerization behavior exhibited “living”/controlled characters. The obtained copolymer, poly(St-co-VBNPA), with pre-determinable molecular weight and narrow molecular weight distribution can be used as a carrier in metal ion detection and analysis via pre-concentration technique. The copolymer–metal ion (copper (Cu) and europium (Eu)) complexes were prepared and characterized.  相似文献   
135.
程蔚萍 《自动化仪表》2007,28(Z1):113-114
通过对超超临界参数对热电偶保护套管材质影响的分析和研究,从既要确保机组安全经济运行,又要具有先进自动化水平的角度,报告了1000MW机组超超临界参数介质测温热电偶套管材质选择、插入深度、安装方式及工厂加工方案,提出了现阶段1000MW机组热电偶保护套管材质选型方案的建议。  相似文献   
136.
土体中毛细水压力的研究   总被引:1,自引:0,他引:1  
该文从毛细水产生负孔隙水压力概念入手 ,对较难确定的孔隙水压力系数以及较抽象的地下连续墙时效稳定分析等问题进行了定量计算 ,以期对工程实践有一定的指导作用  相似文献   
137.
2005年初,水电十四局承担了漫湾二期水电站和小湾水电站蜗壳的制造任务。蜗壳钢材选用国产600 MPa级别高强钢,为了全面综合地考核该级别钢种的材料强度和安全裕度,检验模拟大型蜗壳焊接制造工艺的可靠性。对国产的WDB620高强钢进行了可焊性和制造工艺性试验研究,并在国内首次设计、制造模拟压力容器并对其进行水压试验和爆破试验。研究成果通过中国水电集团公司鉴定,结论为该课题研究成果达到国内选进水平。  相似文献   
138.
Three kinds of carboxymethyl chitosan/β-cyclodextrin microspheres loaded with theophylline were prepared by spray drying intended for pulmonary delivery. Mucociliotoxicity, permeation rate, and drug release characteristics of the product were investigated. The microspheres obtained by spray drying were found to be spherical with smooth or wrinkled surfaces. The mean particle size was between 3.39 and 6.06 µm. The microspheres demonstrated high product yield (43.7-50.2%), high drug loading (13.7-38.1%), and high encapsulation efficiency (86.9-92.8%). FT-IR indicated that there were interactions of theophylline with carboxymethyl chitosan matrix. Further studies on mucociliotoxicity and permeation confirmed that microspheres had better adaptability and high permeation rate. In vitro drug release from the microspheres was not related to the drug/polymer ratios.  相似文献   
139.
In this study, crisp and fuzzy multiple-goal optimization approaches are respectively introduced to design an optimal biocompatible solvent to a two-stage extractive fermentation with cell recycling for ethanol production. When designing a biocompatible solvent for the extractive fermentation process, many issues, such as extractive efficiency, conversion, amount of solvent utilized and so on, have to be considered. An interactive multiple-goal design procedure is introduced to determine a trade-off result in order to satisfy such contradicted goals. Both approaches could be iterated to solve the interactive multiple-goal design problem in order to yield a trade-off result. However, the crisp optimization design is a tedious task that requires the designer to provide various pairs of the upper bounds for the design problem to obtain the corresponding solution. The fuzzy optimization approach is able to be trade-off several goals simultaneously and to yield the overall satisfactory grade for the product/process design problem.  相似文献   
140.
The deposition morphology of Brownian/non-Brownian particles within a constricted tube is investigated by applying the Brownian dynamics simulation method in the present paper. Two different geometric structures, the parabolic constricted tube (PCT) and the sinusoidal constricted tube (SCT), are adopted. The effect of various types of the total interaction energy curves of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and of the shadow area cast by those deposited particles, on the particles’ collection efficiencies are also examined. For the PCT structure, under the same interaction energy curve, it is found that the non-Brownian particles always own a higher collection efficiency than that of the Brownian particles. Since the deposition location moves closer to the constriction part of the tube, the collection efficiencies of the Brownian/non-Brownian particles increase with the decrease of flow velocity. The SCT behaves differently, it is found that the collection efficiencies of non-Brownian particles are only slightly higher than those of Brownian particles when SCT is adopted. The steep slope of the tube wall near the constriction part of SCT dominates the whole deposition process of Brownian/non-Brownian particles. In comparison with the available experimental data, it is found that the present method can give a good simulation result.  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