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   16909篇
  免费   1384篇
  国内免费   720篇
电工技术   903篇
技术理论   3篇
综合类   1143篇
化学工业   2944篇
金属工艺   827篇
机械仪表   931篇
建筑科学   1378篇
矿业工程   447篇
能源动力   493篇
轻工业   961篇
水利工程   280篇
石油天然气   1097篇
武器工业   109篇
无线电   2016篇
一般工业技术   2407篇
冶金工业   748篇
原子能技术   180篇
自动化技术   2146篇
  2024年   45篇
  2023年   267篇
  2022年   380篇
  2021年   641篇
  2020年   444篇
  2019年   432篇
  2018年   478篇
  2017年   476篇
  2016年   433篇
  2015年   597篇
  2014年   768篇
  2013年   880篇
  2012年   1024篇
  2011年   1112篇
  2010年   992篇
  2009年   990篇
  2008年   941篇
  2007年   895篇
  2006年   945篇
  2005年   831篇
  2004年   553篇
  2003年   543篇
  2002年   475篇
  2001年   411篇
  2000年   450篇
  1999年   464篇
  1998年   414篇
  1997年   395篇
  1996年   361篇
  1995年   326篇
  1994年   234篇
  1993年   189篇
  1992年   150篇
  1991年   85篇
  1990年   101篇
  1989年   104篇
  1988年   66篇
  1987年   30篇
  1986年   25篇
  1985年   18篇
  1984年   11篇
  1983年   7篇
  1982年   13篇
  1981年   4篇
  1980年   8篇
  1979年   1篇
  1978年   1篇
  1976年   2篇
  1959年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Integrated lectin affinity microfluidic chip for glycoform separation   总被引:1,自引:0,他引:1  
Mao X  Luo Y  Dai Z  Wang K  Du Y  Lin B 《Analytical chemistry》2004,76(23):6941-6947
Lectin affinity chromatography was miniaturized into a microfluidic format, which results in improvement of performance, as compared to the conventional method. A lectin affinity monolith column was prepared in the microchannel of a microfluidic chip. The porous monolith was fabricated by UV-initiated polymerization of ethylene dimethacrylate (EDMA) and glycidyl methacrylate (GMA) in the presence of porogeneities, followed by immobilization of pisum sativum agglutinin (PSA) on the monolith matrix. Using electroosmosis as the driven force, lectin affinity chromatographies of three kinds of glycoprotein, turkey ovalbumin (TO), chicken ovalbumin (CO), and ovomucoid (OM), were carried out on the microfluidic system. All the glycoproteins were successfully separated into several fractions with different affinities toward the immobilized PSA. The integrated system reduces the time required for the lectin affinity chromatography reaction to approximately 3%, thus, the overall analysis time from 4 h to 400 s. Only 300 pg of glycoprotein is required for the whole separation process. Moreover, troublesome operations for lectin affinity chromatography are simplified.  相似文献   
992.
Solvent extraction of cesium ions from aqueous solution to hydrophobic ionic liquids without the introduction of an organophilic anion in the aqueous phase was demonstrated using calix[4]arene-bis(tert-octylbenzo-crown-6) (BOBCalixC6) as an extractant. The selectivity of this extraction process toward cesium ions and the use of a sacrificial cation exchanger (NaBPh(4)) to control loss of imidazolium cation to the aqueous solutions by ion exchange have been investigated.  相似文献   
993.
Kano H  Nomura D  Shibuya H 《Applied optics》2004,43(12):2409-2411
We report an experimental result that shows the excitation of surface plasmon polaritons by use of a zeroth-order Bessel beam. From the viewpoint of energy efficiency, the zeroth order Bessel beam is ideal for the local excitation of surface plasmon polaritons on a metal film. We introduce an optical setup using an axicon element in order to carry out the excitation.  相似文献   
994.
The NaCl/water solutions of commercial poly(vinyl alcohol) (a-PVA) with the degrees of polymerization and saponification of 1730 and 99.39%, respectively were gel-spun into methanol (–30°C) and then the removed NaCl dry-filaments were drawn at 200°C. The draw ratio showed the maximum at NaCl concentration C N = 3 wt% (polymer concentration C P = 150 kg/m3). The Young's modulus and strength at break were 95 and 6 GPa ( = 19). In the case of DMSO system (C P = 170 kg/m3), the Young's modulus was 52 GPa ( = 25) and the strength at break was 3.3 GPa. Under a polarized microscope, the fine lateral structure was observed for the DMSO system, but not for the NaCl system, that is, the smooth structure was recognized. The smooth structure, like a Netlon packing net for oranges, might be considered to result in heightening of mechanical properties.  相似文献   
995.
异常挖掘是数据挖掘的重要研究内容之一,对于不完全数据会面对双重的困难.首先将用于缺失数据填充的EM算法和MI算法推广到混合缺失情形,并根据Weisberg的不完全数据填充理论,提出了RE算法,然后通过将聚类分析与向前搜索算法结合起来,获得了比单纯的向前搜索法更优越的算法.最后,在上述填充算法的基础上探讨了不完全数据的异常挖掘.理论和实例分析均表明,基于不完全数据的异常挖掘算法是有效可行的.  相似文献   
996.
An important characteristic of virtual assembly is interaction.Traditional direct manipulation in virtual assembly relies on dynamic collision detection,which is very time-consuming and even impossible in desktop virtual assembly environment.Feature-matching is a critical process in harmonious virtual assembly,and is the premise of assembly constraint sensing.This paper puts forward an active object-based feature-matching perception mechanism and a feature-matching interactive computing process,both of which make the direct manipulation in virtual assembly break away from collision detection.They also help to enhance virtual environment understandability of user intention and promote interaction performance.Experimentl results show that this perception mechanism can ensure that users achieve real-time direct manipulation in desktop virtual environment.  相似文献   
997.
The aim of this work was to estimate absorbed doses received by a victim of the radiation accident with a 60Co source in Henan province, China. With a Monte Carlo stochastic simulation method, an estimation method for doses to the radiation accident victim was made. It utilised a mathematical model of adult man (MIRD) and a relative applied computer program was developed. By means of the simulated conditions of the accident, the absorbed doses to the victim's main organ and total body doses were estimated. The results estimated by our Monte Carlo method are close to those of experimental simulation measurement of the accident. With its convenience and rapidity, this method will be valuable for radiation dose reconstruction for victims in radiation accidents.  相似文献   
998.
A data anomaly was observed that affected the uniformity and reproducibility of fluorescent signal across DNA microarrays. Results from experimental sets designed to identify potential causes (from microarray production to array scanning) indicated that the anomaly was linked to a batch process; further work allowed us to localize the effect to the posthybridization array stringency washes. Ozone levels were monitored and highly correlated with the batch effect. Controlled exposures of microarrays to ozone confirmed this factor as the root cause, and we present data that show susceptibility of a class of cyanine dyes (e.g., Cy5, Alexa 647) to ozone levels as low as 5-10 ppb for periods as short as 10-30 s. Other cyanine dyes (e.g., Cy3, Alexa 555) were not significantly affected until higher ozone levels (> 100 ppb). To address this environmental effect, laboratory ozone levels should be kept below 2 ppb (e.g., with filters in HVAC) to achieve high quality microarray data.  相似文献   
999.
Sun J  Zhang R  Wang Q  Chai L  Pang D  Dai J  Zhang Z  Torizuka K  Nakagawa T  Sugaya T 《Applied optics》2001,40(21):3539-3541
We present a novel high-power, self-starting mode-locked Ti:sapphire laser with a semiconductor saturable-absorber mirror as the starter element. This laser, whose slope efficiency is 22%, generates pulses with an average power as high as 1.7 W and a pulse width as short as 16 fs. The self-starting process is also investigated.  相似文献   
1000.
板仓坝王宅     
黄琪  戴志中 《华中建筑》2001,19(6):87-89
传统居民留给我们丰富的建筑文化传统与建筑经验,具有极大的参考价值和借鉴意义,然而在今天,它却正在悄悄走向衰败。该文期望通过对自贡板仓坝王宅的现状考察,唤起人们对这一古老居民的关注与保护。  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