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   12611篇
  免费   29篇
  国内免费   207篇
系统科学   1198篇
丛书文集   218篇
教育与普及   256篇
理论与方法论   50篇
现状及发展   106篇
研究方法   15篇
综合类   11004篇
  2023年   1篇
  2020年   13篇
  2019年   2篇
  2018年   2篇
  2017年   66篇
  2016年   75篇
  2015年   88篇
  2014年   30篇
  2013年   24篇
  2012年   32篇
  2011年   700篇
  2010年   202篇
  2009年   437篇
  2008年   172篇
  2007年   181篇
  2006年   110篇
  2005年   258篇
  2004年   1631篇
  2003年   1225篇
  2002年   1021篇
  2001年   566篇
  2000年   305篇
  1999年   430篇
  1998年   667篇
  1997年   750篇
  1996年   207篇
  1995年   132篇
  1994年   389篇
  1993年   821篇
  1992年   562篇
  1991年   539篇
  1990年   466篇
  1989年   274篇
  1988年   168篇
  1987年   172篇
  1986年   82篇
  1985年   31篇
  1984年   10篇
  1983年   1篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1974年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
反相高效液相色谱法快速测定靛蓝中残留苯胺   总被引:6,自引:2,他引:6  
建立了用反相高效液相色谱测定靛蓝中残留痕量苯胺含量的方法.用YWG C18(5μm,300mm×5mmID) 柱,V甲醇∶V水=70∶30的溶液为流动相,柱温30℃时于285nm波长处以外标法测定.结果表明苯胺在6.92× 10-8~3.59×10-4g/mL范围内,浓度与峰面积有良好的线性关系(r=0.9997).苯胺的回收率为98.34%~ 98.36%,相对标准偏差为1.84%~3.03%(n=5).检测限为2.02×10-9g/mL(S/N=3).实验表明该法简便、快 速,应用于实际靛蓝样品中残留痕量苯胺的测定,取得了很好的结果.  相似文献   
102.
研究了具有周期外力的非线性系统的解产生不同的次谐波分枝的参数范围,并且指出了无穷多次谐波分枝是如何与smale马蹄型混沌解共存的.  相似文献   
103.
The reliability of capacity of signalized intersections in mixed traffic conditions involving vehicles, bicycles, and pedestrians was investigated to complete the conventional, deterministic capacity calculations. Simulations using VISSIM provided estimates of capacity distributions, and demonstrated the effects of the analysis intervals on the distributions. With the random vehicle arrivals taken into account, a capacity reliability assessment method was given as a function. Assessments were also performed...  相似文献   
104.
Fused deposition modelling (FDM) is a filament based rapid prototyping system which offers the possibility of introducing new composite material for the FDM process as long as the new material can be made in feedstock filament form. Swinburne has been undertaking extensive research in development of new composite materials involving acrylonitrile-butadiene-styrene (ABS) and other materials including metals. In order to predict the behaviour of new ABS based composite materials in the course of FDM process, it is necessary to investigate the flow of the composite material in liquefier head. No such study is available considering the geometry of the liquefier head. This paper presents 2-D and 3-D numerical analysis of melt flow behaviour of a representative ABS-iron composite through the 90-degree bent tube of the liquefier head of the fused deposition modelling process using ANSYS FLOTRAN and CFX finite element packages. Main flow parameters including temperature, velocity, and pressure drop have been investigated. Filaments of the filled ABS have been fabricated and characterized to verify the possibility of prototyping using the new material on the current FDM machine. Results provide promising information in developing the melt flow modelling of metal-plastic composites and in optimising the FDM parameters for better part quality with such composites.  相似文献   
105.
A NAM Representation Method for Data Compression of Binary Images   总被引:1,自引:0,他引:1  
A representation method using the non-symmetry and anti-packing model (NAM) for data compression of binary images is presented.The NAM representation algorithm is compared with the popular linear quadtree and run length encoding algorithms.Theoretical and experimental results show that the algorithm has a higher compression ratio for both lossy and lossless cases of binary images and better reconstructed quality for the lossy case.  相似文献   
106.
The housing market, an important component of the urban economy, is closely integrated with urban development. Urban development attracts labor inflows which then increase the housing demand in the cities. Urban dwellers’ willingness-to-pay (WTP) for housing, as part of their living costs, depends on their incomes they can earn in the cities and the quality of life (QOL) they want to enjoy. Urban wage growth and quality of life improvements are always accompanied by increased demand and increased WTP. This ...  相似文献   
107.
Content addressable storage (CAS) is a promising technology for improving storage efficiency as well as access throughput.Currently,many CAS products are implemented on the block level,which results in loss of file information.Thus,some sophisticated optimizations cannot be achieved,such as accurate fileprefetching.This paper presents a file-aware block-level storage system combined with the CAS function.In contrast with some existing file-level CAS,this system is transparent to upper-level applications,including the operating system and the file system.These features are achieved by using smart-disk technologies to help the storage system to learn the file-system layout.A prototype was implemented on an open-source virtual machine (VM) with the guest operating system being Windows XP.Tests show that this combination significantly reduces the size of the VM image file and improves the storage performance by discarding unused blocks and using a simple file-level prefetching strategy.  相似文献   
108.
This paper shows that the protocol presented by Goyal et al.can be further simplified for a one-way function,with the simplified protocol being more practical for the decisional Diffie-Hellman assumption.Goyal et al.provided a general transformation from any honest verifier statistical zero-knowledge argument to a concurrent statistical zero-knowledge argument.Their transformation relies only on the existence of one-way functions.For the simplified transformation,the witness indistinguishable proof of kn...  相似文献   
109.
Erns is a highly glycosylated envelope protein of classical swine fever virus (CSFV) with RNase activity. Erns can induce neutralizing antibodies and provide immune protection against CSFV infection. In this study, the RNase domain of the Erns was produced in Escherichia coli. Its reactivity with CSFV-positive sera and its ability to induce antibodies and to provide protective immunity were then investigated. The serological tests showed that the prokaryotically expressed RNase domain of the Erns retained i...  相似文献   
110.
The patternless casting manufacturing (PCM) technique, which adopts a new concept of double scanning method, combines the principle of discreteness and deposition with resin-bonded sand technique. This paper is to evaluate the dimensional accuracy of sand mould on PCM. The two important factors-the liquid penetration rule in the space of particles and the shape and dimension of the agglomeration unit body, which influence the process parameters such as scanning speed, layer thickness, liquid flux on dimension accuracy, and surface qualities, were investigated systematically, thus the theoretical basis for these parameters was provided. Experiments on rapid manufacturing of sand mould were carried out, and the results of the free penetration and the constraint penetration well verified the relationship of the two factors and the process parameters.  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