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   2046篇
  免费   135篇
  国内免费   109篇
系统科学   71篇
丛书文集   49篇
教育与普及   18篇
理论与方法论   8篇
现状及发展   9篇
综合类   2134篇
自然研究   1篇
  2024年   3篇
  2023年   21篇
  2022年   38篇
  2021年   50篇
  2020年   53篇
  2019年   51篇
  2018年   45篇
  2017年   66篇
  2016年   61篇
  2015年   95篇
  2014年   163篇
  2013年   116篇
  2012年   151篇
  2011年   156篇
  2010年   86篇
  2009年   106篇
  2008年   93篇
  2007年   103篇
  2006年   127篇
  2005年   108篇
  2004年   83篇
  2003年   75篇
  2002年   68篇
  2001年   58篇
  2000年   38篇
  1999年   48篇
  1998年   26篇
  1997年   38篇
  1996年   22篇
  1995年   28篇
  1994年   24篇
  1993年   13篇
  1992年   12篇
  1991年   16篇
  1990年   16篇
  1989年   19篇
  1988年   4篇
  1987年   5篇
  1986年   2篇
  1985年   3篇
排序方式: 共有2290条查询结果,搜索用时 156 毫秒
61.
鉴于聚合物改性沥青可以明显改善沥青混凝土路面的低温和高温性能,延长道路使用寿命,因此聚合物改性沥青已经成为全球沥青路面的首选。本次高速公路项目的路面上面层组成配合比设计就添加和利用了石灰岩集料和SBS改性沥青(基质沥青为韩国SK重交沥青AH-70)来进行配合比筛选和设计,并得出最佳沥青用量和沥青混凝土密度,总结SBS改性沥青混凝土相比于普通沥青混凝土具有更好性能。  相似文献   
62.
The number of equivalent keys in multivariate cryptosystem is closely related to the scheme security. This study analyzes the structure of the private key space in some multivariate schemes.The result gives the lower bounds on the number of equivalent keys of some variants of the hidden field equation (HFE) scheme including plus, minus-plus, embedding, and internal perturbation. This method estimates the number of invertible transformations which maintain the form of the central map invariant. Furthermore,a formal proof shows that the two modifications of fixing and embedding are equivalent in security analyses of multivariate schemes. Also this paper corrects previous proofs in Wolf’s work on the number of equivalent keys in HFEv,the unbalanced oil and vinegar (UOV) scheme, and the stepwise triangular systems (STS).  相似文献   
63.
在希尔伯特空间中,通过构造非扩张映射的迭代序列,证明了一个非扩张映射的强收敛定理,该结果是先前文献相应结果的改进和推广.  相似文献   
64.
The potential of genetically modified organisms(GMOs) to increase allergenicity or predispositions to allergies has attracted much attention.An approach that will properly and holistically evaluate the allergenicity of GMOs is yet to be found.Here,85 transgenes that have been reported in both international and domestic studies during recent years are summarized case by case;49 of the transformed genes were from plant sources and 36 were from animal sources.EVALLERTM,a web server for the in silico assessment of potential protein allergenicity,was used to evaluate the potential of the transgenic proteins as allergens.The biomedical journals listed in Highwire(http://highwire.stanford.edu/) were searched and reviewed to decipher whether any of the transformed genes were linked to allergenicity or human health.The EVALLER analysis identified 5 allergenic genes,whilst our literature review found 11 genes that were either related to allergic cases or to clinical adverse events;all 16 of these genes have been used in GMOs.The analysis pathway that we have developed can help guide the selection of genes to be used in genetic modification.The pathway also provides a paradigm for allergenicity analysis of transgene candidates.  相似文献   
65.
Graphene attracts more and more scientists and researchers owing to its superior electronic,thermal,and mechanical properties.For material scientists,graphene is a kind of versatile building blocks,and considerable progress has been made in recent years.Graphene-based hybrid materials have been prepared by incorporating inorganic species and/or cross-linking of organic species through covalent and/or noncovalent interactions.The graphene-based hybrid materials show improved or excellent performance in various fields.In this review,we summarize the synthesis of graphene and graphene-based hybrid materials,and their applications in energy storage and conversion.  相似文献   
66.
A flexible electronic shogging system was presented based on rotary type servo motor,which aimed to improve the dynamic response of the shogging drive and decrease the impact of the guide bar during the higher speed running of warp-knitting machine.In this system,the speed control mode,faster response servo motor,no-flat modified trapezoid motion law,and its electronic cam were chosen;the realization standard and method were also introduced in details.The speed response curves of loaded motor indicated that the system could satisfy the technology requirements of high-speed warpknitting machine which run at the speed of 1000 r/min in the experiments,and the vibration curves showed that the guide bar had weaker mechanical impact and higher dynamic response characteristics.The results indicated that the flexible electronic shogging system designed following the previous step was successful,and the design principle of the electronic shogging was testified validly.  相似文献   
67.
The aim of this work is to evaluate the feasibility of applying the technology of oxidation-reduction potential(ORP)control on the municipal wastewater treatment system for nitrogen and phosphorus removal.Meanwhile the relation between the optimal ORP(ORP opt)and influent C/N ratio was evaluated,in which the influent chemical oxygen demand(COD)concentration was stabilized at(290±10)mg/L,the influent total phosphorus(TP)concentration was stabilized at(7.0±0.5)mg/L.The results indicated that:(1)the ORP in the second anoxic zone had effect on nitrogen and phosphorus removal capability,and the average percentages of phosphorus uptake in ANO2zone(ηa)increased with increasing ORP,i.e.,increasing from 12.0%at-143 mV to22.0%,30.0%,37.0%,and 45.0%at-123,-111,-105 and-95 mV,respectively;(2)the ORP opt as function of influent C/N ratio could be calculated by the equation:y=252.73e(-x/3.39)-131.01;the maximum percentage of phosphorus uptake in ANO2as function of the ORP opt could be calculated by the equation:y=-0.49 e(x/15.58)+1.51.The ORP opt was the important process control parameter that must be optimized for operation of enhanced biological phosphorus removal(EBPR)system.Moreover,ORP sensor is very simple,and the industrial applications of this strategy is practical.  相似文献   
68.
研究了一种新型的具有大各向异性的改性PbTiO3 陶瓷材料的性能随着材料制备中铅过量的变化而变化的关系 ,其中包括材料的机电耦合系数、机械品质因素、介电损耗等 .研究结果表明当铅过量为 1%~ 2 % (摩尔百分比 )时 ,材料的性能达到较佳 .通过分析认为 :当铅不足时 ,主要是由其它的B位掺杂离子取代A位的铅 ,从而造成配方B位离子的重新排列 ,材料的性能因而有所下降 ;当铅过量时 ,铅离子将取代A位的钙 ,部分钙离子将进入晶界 ,从而降低了材料的性能  相似文献   
69.
With Co/GCE in 0.005 mol Tris/L/0.05 mol/L NaCl solution (pH 7.1), a sensitive reductive peak of adriamgcin (ADM) was obtained by the linear scan voltammetry. The peak potential is ?0.62 V (vs. SCE). The peak current is proportional to the concentration of ADM. The electrochemical behavior of the system was studied by the linear-sweep and cyclic voltammetry. The experiments showed that the reduction at Co/GCE is a quasi-reversible process with adsorption. According to Laviron’s theory, the electrode reaction rate constant k0 and the electron transfer coefficient a are determined to be 2.15 s-1 and 0.62, respectively. The composition of the surface, valence state of elements and depth distribution of elements on the surfaces of Co/GCE were determined by the X-ray photoelectron spectroscopy and Auger electron spectroscopy. The experiments showed that Co was surely implanted into the surface of GCE. The implanted Co element in the form of Co-C catalyzed the reduction of ADM.  相似文献   
70.
关于内部收益率与现金流量模式关系的分析   总被引:1,自引:1,他引:0  
研究了内部收益率与现金流量模式的关系。 通过对折现率与现金流量结构间的相互关系的分析,探讨内部收益率的存在性与现金流量模式的关系,给出净现值法与内部收益率法具有一致性的条件;在定义修正内部收益率的基础上,给出其计算公式,并将内部收益率法的应用范围推广。  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