全文获取类型
收费全文 | 49881篇 |
免费 | 5603篇 |
国内免费 | 3074篇 |
专业分类
电工技术 | 3876篇 |
技术理论 | 2篇 |
综合类 | 3889篇 |
化学工业 | 7402篇 |
金属工艺 | 2722篇 |
机械仪表 | 3265篇 |
建筑科学 | 4181篇 |
矿业工程 | 1480篇 |
能源动力 | 1483篇 |
轻工业 | 3424篇 |
水利工程 | 1271篇 |
石油天然气 | 2312篇 |
武器工业 | 497篇 |
无线电 | 6364篇 |
一般工业技术 | 5689篇 |
冶金工业 | 2066篇 |
原子能技术 | 814篇 |
自动化技术 | 7821篇 |
出版年
2024年 | 284篇 |
2023年 | 878篇 |
2022年 | 1671篇 |
2021年 | 2437篇 |
2020年 | 1776篇 |
2019年 | 1542篇 |
2018年 | 1605篇 |
2017年 | 1710篇 |
2016年 | 1541篇 |
2015年 | 2109篇 |
2014年 | 2739篇 |
2013年 | 3026篇 |
2012年 | 3431篇 |
2011年 | 3764篇 |
2010年 | 3525篇 |
2009年 | 3223篇 |
2008年 | 3057篇 |
2007年 | 2919篇 |
2006年 | 2774篇 |
2005年 | 2203篇 |
2004年 | 1728篇 |
2003年 | 1776篇 |
2002年 | 2025篇 |
2001年 | 1699篇 |
2000年 | 1165篇 |
1999年 | 965篇 |
1998年 | 621篇 |
1997年 | 479篇 |
1996年 | 389篇 |
1995年 | 312篇 |
1994年 | 250篇 |
1993年 | 217篇 |
1992年 | 164篇 |
1991年 | 106篇 |
1990年 | 103篇 |
1989年 | 84篇 |
1988年 | 78篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1976年 | 3篇 |
1959年 | 10篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
分析了OSI参考模型和B-ISDN协议参考模型之间的关系,为B-ISDN与以OSI为标准的数据网的互联打下了基础。 相似文献
92.
本文首先简述D>0.06mm泥沙的粒析沉降特性及其粒径偏粗的原因。继之对悬沙中粒径大于0.06mm的粒析级配组成机理,及级配组成不同对标准粒径Db与粒析粒径DL关系的影响进行了详细研究。在以上研究工作的基础上,开展了Db与DL的比较试验,得出了粗、中、细型悬沙的Db~DL关系和对DL的改正方法。 相似文献
93.
1MotivationsIncreasingdensityofVLSIchipsmakesthecostoftestingveryexpensive.Designfortestabilitycantemperthisproblemdrastically.Therearetwokindsofsolutions:(i)localsolutionl3'2]withlowcomputingcomplexity,whichcannotalwaysgetsatisfactoryresults;(ii)globa.lsolutionwithprohibitivecomputingcomplekityl1'5].T.H.Chen'andM.A.Breuer[1lpresentedanILPmodeltoplacetestpointsglobally.Becauseofitscomputingcomplealty,[1lcanonlydealwithsmallormediumscalecircuits.SCOAPisusedin[1],whichisnotaveryaccuratet… 相似文献
94.
95.
96.
Microfibre reinforced cement composites reinforced with high volume fractions of carbon, steel and polypropylene fibres were tested in uniaxial tension. Composites investigated included those with only one type of fibre (mono-fibre composites) and those with two or more types of fibres (hybrid-fibre composites) in the same mix. Considerable strengthening, toughening and stiffening of the host matrix due to microfibre reinforcement were observed. In the hybrid-fibre composites, different fibres appear to act as additive phases; i.e., they maintain their individual reinforcing capabilities. The composites were also impact tested in uniaxial tension using a newly designed instrumented impact machine. When compared with static test results, considerable sensitivity to stress rate was noted; composites were found to be stronger and tougher under impact and the improvements were more pronounced at higher fibre volume fractions. The potential of these composites for use in thin sheet products and other similar applications is recognized, and the need for continued research is stressed. 相似文献
97.
Voigt线型及其精确快速算法 总被引:1,自引:1,他引:0
通过把上半复平面分为4个区,并在每一区利用不同近似,建立了一种精确快速计算Voigt函数、修正的Voigt函数和Voigt函数偏导数的算法,其最大相对误差小于5×10-4.该算法是Line-by-Line大气透过率/辐射强度计算及其相关应用的有效算法. 相似文献
98.
The effects of chronic injection of U50,488H (trans-3,4-dichloro-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeacetamidel++ +), a selective kappa opioid agonist, on the properties of the binding sites of tritiated U69593 [(5 alpha,7 alpha,8 beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro (4,5)dec-8-yl)benzeneacetamide], another selective kappa opioid agonist, and mechanical responses to U50,488H of the heart were studied. Rats received injection twice a day with U50,488H for 4 days. Binding studies on the crude membrane homogenates revealed that there was no change in maximum binding, but a significant increase in Kd after the treatment, indicating that the number of kappa binding sites remained unchanged whereas the affinity of the binding sites to kappa-agonist decreased. The study on the mechanical responses to U50,488H in the isolated perfused heart preparation showed that although the agonist at 10(-6) M caused MR2266 reversible reductions in heart rate and force of contraction as well as ventricular ectopic beat in the heart of rats in the control group, its effects were absent in the U50,488H-treated group, indicating the development of tolerance to the mechanical effects of U50,488H on the heart. The results indicate that the development of tolerance to the mechanical effects of a kappa-agonist after chronic treatment with the agonist was not accompanied by down-regulation, but only a slight and significant reduction in affinity of kappa binding sites in the rat heart. 相似文献
99.
A novel recursive procedure for extracting discriminant features, termed recursive cluster-based linear discriminant (RCLD), is proposed in this paper. Compared to the traditional Fisher linear discriminant (FLD) and its variations, RCLD has a number of advantages. First of all, it relaxes the constraint on the total number of features that can be extracted. Second, it fully exploits all information available for discrimination. In addition, RCLD is able to cope with multimodal distributions, which overcomes an inherent problem of conventional FLDs, which assumes uni-modal class distributions. Extensive experiments have been carried out on various types of face recognition problems for Yale, Olivetti Research Laboratory, and JAFFE databases to evaluate and compare the performance of the proposed algorithm with other feature extraction methods. The resulting improvement of performances by the new feature extraction scheme is significant. 相似文献
100.
准噶尔盆地腹部普遍发育深层(大于4000m)超压系统,很多钻井都钻遇超压。通过对超压段钻井、地质、测井、地震特征系统研究发现,超压段泥浆密度大幅增加,具有高声波时差、低电阻率以及地震低速的超压响应特征。利用Dix公式计算地震层速度和利用Fillippone公式计算地层压力,得到超压数据体。准噶尔盆地腹部超压在白垩系及其以下沉积地层中均有分布,超压层的深度范围不同。分1井西凹陷边缘以及昌吉凹陷西南有空层现象。超压顶面分布的层位由北往南、从东到西逐渐变浅,从三叠系顶部到白垩系底部。深部超压对油气分布和富集有着重要的控制作用,准噶尔盆地腹部超压层分布的研究将对本区油气勘探起积极的推动作用。 相似文献