全文获取类型
收费全文 | 79747篇 |
免费 | 14962篇 |
国内免费 | 1065篇 |
专业分类
电工技术 | 2332篇 |
技术理论 | 4篇 |
综合类 | 1642篇 |
化学工业 | 23657篇 |
金属工艺 | 2053篇 |
机械仪表 | 2673篇 |
建筑科学 | 3630篇 |
矿业工程 | 771篇 |
能源动力 | 2252篇 |
轻工业 | 9442篇 |
水利工程 | 757篇 |
石油天然气 | 1094篇 |
武器工业 | 150篇 |
无线电 | 13369篇 |
一般工业技术 | 17009篇 |
冶金工业 | 4447篇 |
原子能技术 | 476篇 |
自动化技术 | 10016篇 |
出版年
2024年 | 113篇 |
2023年 | 549篇 |
2022年 | 1005篇 |
2021年 | 1584篇 |
2020年 | 2423篇 |
2019年 | 3919篇 |
2018年 | 3988篇 |
2017年 | 4349篇 |
2016年 | 4713篇 |
2015年 | 4970篇 |
2014年 | 5326篇 |
2013年 | 7159篇 |
2012年 | 4898篇 |
2011年 | 4961篇 |
2010年 | 4662篇 |
2009年 | 4619篇 |
2008年 | 4248篇 |
2007年 | 3895篇 |
2006年 | 3459篇 |
2005年 | 2830篇 |
2004年 | 2637篇 |
2003年 | 2706篇 |
2002年 | 2825篇 |
2001年 | 2431篇 |
2000年 | 2012篇 |
1999年 | 1284篇 |
1998年 | 1470篇 |
1997年 | 1031篇 |
1996年 | 803篇 |
1995年 | 628篇 |
1994年 | 525篇 |
1993年 | 482篇 |
1992年 | 340篇 |
1991年 | 311篇 |
1990年 | 301篇 |
1989年 | 248篇 |
1988年 | 222篇 |
1987年 | 211篇 |
1986年 | 192篇 |
1985年 | 162篇 |
1984年 | 143篇 |
1983年 | 97篇 |
1982年 | 80篇 |
1981年 | 100篇 |
1980年 | 104篇 |
1979年 | 70篇 |
1978年 | 88篇 |
1977年 | 101篇 |
1976年 | 119篇 |
1975年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
As technology evolves, it is now feasible to implement sophisticated adaptive routing schemes on networks which support different kinds of services with heterogeneous bandwidth characteristics. Adaptive routing can increase the network throughput by routing calls to less congested paths. It can also be used to bypass transmission facility failures. In this paper, we analyze and compare two adaptive routing schemes. The first is called theMaximum mean time to blocking (MTB) routing which is based on themean time to blocking measure of a link. This measure captures the traffic rates, bandwidth characteristic and link capacity information and reflects more accurately the congestion status of different paths. The second is theM
2 routing, which is a modification of the least loaded routing (LLR). Aggregation of link status information can significantly reduce signalling traffic. We show in this paper that with properly designed aggregation, the aggregatedM
2 and MTB routings can have performance that approach that of the non-aggregated schemes. The use of complete sharing and restricted access policies together with trunk reservation control in multirate loss networks are also studied. 相似文献
112.
本项预测采用概率方法,即首先根据广东省水利部门提出的55座土坝和59个重点的座标(见附图),进行概率地震危险性分析,给出它们在一定预测年限T(取50年和100年)的地震烈度Ⅰ的超越概率;其次根据近年我国发生的几次强震时处于不同烈度区内的土坝和堤防的震害资料,形成表示土坝和土堤地震易损性的震害概率矩阵;然后,根据上述两方面结果用概率公式评价各土坝和堤围点在预测年限内各震害等级的超越概率,并取10%超越概率为标准,估计震害等级。结果表明,珠江三角洲土工构筑物的地震危害性南部高于北部。 相似文献
113.
114.
Abstract: Environmental justice advocates have recently focused attention on cumulative exposure in minority neighborhoods due to multiple sources of pollution. This article uses U.S. EPA's National Air Toxics Assessment (NATA) for 1996 to examine environmental inequality in California, a state that has been a recent innovator in environmental justice policy. We first estimate potential lifetime cancer risks from mobile and stationary sources. We then consider the distribution of these risks using both simple comparisons and a multivariate model in which we control for income, land use, and other explanatory factors, as well as spatial correlation. We find large racial disparities in California's “riskscape” as well as inequalities by other factors and suggest several implications for environmental and land use policy. 相似文献
115.
116.
郝永明古建园林绘画作品另辟蹊径,难能可贵。郝永明的画,不仅给我国美术宝库增加了一份积累,也给古建园林艺术增添了珍贵的资料。 相似文献
117.
Fanggao Chang Tao Li Yongxia Ge Zhenping Chen Zhongshi Liu Xiping Jing 《Journal of Materials Science》2007,42(17):7109-7115
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x
Ho
x
)TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x
Ho
x
)TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The
local electron density and defect concentration estimated using positron annihilation technique conforms well to the features
found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model. 相似文献
118.
Hyeong Soo Chang 《Automatic Control, IEEE Transactions on》2005,50(9):1413-1418
This note considers finite-step approximations for solving an infinite-horizon controlled Markov set-chain problem with finite state and action spaces. We develop a value-iteration type algorithm based on the optimality equation developed by Kurano et al. and analyze an error bound relative to the optimal value that satisfies the optimality equation from the successive approximation. We further analyze an error bound of the approximate control policy defined from a finite-step approximate value by applying the value-iteration type algorithm. 相似文献
119.
Christina Dirk‐Faitakis D Grant Allen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(7):737-745
This paper describes the development and simulation of an unsteady state biofilter model used to predict dynamic behaviour of cyclically‐operated biofilters and compares it with experimental results obtained from three, parallel, bench‐scale biofilters treating both periodically fluctuating concentrations and constant concentrations of an α‐pinene‐laden gas stream. The dynamic model, using kinetic parameters estimated from the constant concentration biofilter, was able to predict the performance of cyclic biofilters operating at short cycle periods (ie, in the order of minutes and hours). Steady state kinetic data from a constant concentration biofilter can be used to predict unsteady state biofilter operation. At a 24 h cycle period, the dynamic model compared well with experimental results. For long cycle periods (ie, hours and days), removal efficiency decreased after periods of non‐loading: the longer the period of non‐loading, the poorer the biofilter's performance at the re‐commencement of pollutant loading. At longer time scales the model did not effectively predict transient behaviour, as adsorption and changes in kinetic parameters were not accounted for. Modelling results showed that similar biofiltration performance for the cyclic and constant concentration biofiltration of α‐pinene is expected for biofilters operating solely in the first order kinetics regime. Poorer performance for cyclic biofilters following Monod kinetics spanning the entire kinetics range is expected as the cycle amplitude increases. The most important parameters affecting the performance of a cyclically‐operated biofilter with short cycle periods are: amplitude of cyclic fluctuations, Cg, max/Cg, relative value of the half‐saturation constant in the Monod expression, Ks, and effective diffusivity of α‐pinene in the biofilm, De. Copyright © 2005 Society of Chemical Industry 相似文献
120.
RM Martín‐Aranda E Ortega‐Cantero ML Rojas‐Cervantes MA Vicente‐Rodríguez MA Baares‐Muoz 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(2):234-238
α,β‐Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline‐promoted clays (Li+‐ and Cs+‐exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent‐free procedure, α,β‐unsaturated nitriles have been produced in very high yields (97%) when the Cs+‐saponite is used as catalyst. Copyright © 2004 Society of Chemical Industry 相似文献