全文获取类型
收费全文 | 86988篇 |
免费 | 7095篇 |
国内免费 | 3150篇 |
专业分类
电工技术 | 4311篇 |
技术理论 | 4篇 |
综合类 | 4357篇 |
化学工业 | 15603篇 |
金属工艺 | 4369篇 |
机械仪表 | 5441篇 |
建筑科学 | 5151篇 |
矿业工程 | 1321篇 |
能源动力 | 2821篇 |
轻工业 | 6591篇 |
水利工程 | 1305篇 |
石油天然气 | 2659篇 |
武器工业 | 484篇 |
无线电 | 12294篇 |
一般工业技术 | 13386篇 |
冶金工业 | 4692篇 |
原子能技术 | 1115篇 |
自动化技术 | 11329篇 |
出版年
2024年 | 267篇 |
2023年 | 1174篇 |
2022年 | 2142篇 |
2021年 | 3123篇 |
2020年 | 2271篇 |
2019年 | 2106篇 |
2018年 | 2435篇 |
2017年 | 2560篇 |
2016年 | 2739篇 |
2015年 | 3158篇 |
2014年 | 4096篇 |
2013年 | 5397篇 |
2012年 | 5558篇 |
2011年 | 6382篇 |
2010年 | 5459篇 |
2009年 | 5164篇 |
2008年 | 5079篇 |
2007年 | 4499篇 |
2006年 | 4335篇 |
2005年 | 3736篇 |
2004年 | 2938篇 |
2003年 | 2751篇 |
2002年 | 3019篇 |
2001年 | 2554篇 |
2000年 | 2082篇 |
1999年 | 1896篇 |
1998年 | 2037篇 |
1997年 | 1514篇 |
1996年 | 1347篇 |
1995年 | 1072篇 |
1994年 | 855篇 |
1993年 | 672篇 |
1992年 | 489篇 |
1991年 | 413篇 |
1990年 | 321篇 |
1989年 | 288篇 |
1988年 | 235篇 |
1987年 | 176篇 |
1986年 | 155篇 |
1985年 | 114篇 |
1984年 | 91篇 |
1983年 | 71篇 |
1982年 | 61篇 |
1981年 | 67篇 |
1980年 | 65篇 |
1979年 | 31篇 |
1977年 | 40篇 |
1976年 | 66篇 |
1975年 | 34篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
A new prediction method with an interior light sensor for the workplane illuminance in daylighting control systems is introduced. Based on radiosity theory, the spatial distributions of daylight and electric light in the space are discussed and the prediction method is developed. An experimental verification of the technique is performed in an outdoor test-room for a double-glazed window system with a motorized venetian blind integrated between the two glazings. Electric light and daylight predictions were performed in accordance with the proposed method. The results showed that the electric light workplane illuminance can be predicted with high accuracy (±5 lux error with a linear correlation) and that the daylight workplane illuminance can be predicted within ±20 lux (with a linear correlation) for any sky conditions (overcast, clear sky, or variable) with the window system controlled to prevent direct daylight transmission. This method is useful for integrated control of motorized daylighting devices and dimmable electric lights. 相似文献
92.
Wastewater discharge from coal refining plants contains a number of biologically toxic compounds; 2000-2500 mg/l of COD of which 40% is composed of phenol, 100-400 mg/l of thiocyanate, 10-40 mg/l of cyanide, 100-250 mg/l of NH4+-N and 150-300 mg/l of total nitrogen. In order to treat this kind of high strength wastewater, we have developed a high performance biofilm process using fluidizing bio-carriers of the tube chip type. The fluidizing biofilm carriers are made of a composite of polyethylene and several inorganic materials, whose density is controlled at 0.97-0.98 g/ml. The fluidizing biofilm carriers show sound fluidization characteristics inside bioreactors. The wastewater is treated using three consecutive series reactors in oxic-anoxic-oxic arrangement. Each reactor is charged with the fluidizing biofilm carriers of 50 vol%. Furthermore, newly cultured active microorganisms for the thiocyanate biodegradation are added in the biofilm process. At total hydraulic retention time of 2.2 days, this process can achieve steady state removal efficiencies: COD, 99%; thiocyanate, 99%; NH4+-N, 99% and total nitrogen, 90%. 相似文献
93.
The optical character of waste stabilization ponds (WSPs) is of concern for several reasons. Algal photosynthesis, which produces oxygen for waste oxidation in WSPs, is influenced by attenuation of sunlight in ponds. Disinfection in WSPs is influenced by optical characteristics because solar UV exposure usually dominates inactivation. The optical nature of WSPs effluent also affects assimilation by receiving waters. Despite the importance of light behaviour in WSPs, few studies have been made of their optical characteristics. We discuss simple optical measures suitable for routine monitoring of WSPs (including at sites remote from laboratories): optical density of filtrates - an index of dissolved coloured organic (humic) matter, visual clarity - to provide an estimate of the beam attenuation coefficient (a fundamental quantity needed for optical modelling) colour (hue) - as an indicator of general WSP 'condition' and irradiance attenuation quantifying depth of light penetration. The value of optical characterisation of WSPs is illustrated with reference to optical data for WSPs in NZ (including high-rate algal ponds) treating dairy cattle wastewater versus domestic sewage. We encourage increased research on optical characteristics of WSPs and the incorporation of optical measures in monitoring and modelling of WSP performance. 相似文献
94.
Hsing-Chung Liang Wen-Chin Ho Ming-Chieh Cheng 《Reliability, IEEE Transactions on》2005,54(2):358-365
In this paper, we discuss some strategies for identifying unrepairable memories, and from that to introduce a novel theorem that can make more precise identification. A new algorithm for searching repair solutions is also proposed, which characterizes the rows, and columns of defective memory cells with revised effective coefficients. We have simulated it on many generated example maps, and compared it with the previous algorithms to verify its efficiency. It's combined with those arranged strategies of judging unrepairability to generate a complete flow. The complete algorithm has also been run on many examples with various memory sizes, defect numbers, and distribution types. The simulation results further show that identifying unrepairability in advance can help the reconfiguration procedure run much faster than searching solutions directly. 相似文献
95.
A practical resource management method that can significantly reduce cochannel interference (CCI) and improve spectrum utilisation in FH-OFDMA packet-based cellular networks is presented. The proposed method seeks an effective combination of dynamic resource allocation with fractional coding and bit loading to respectively minimise CCI and maximise system throughput for a desired performance. 相似文献
96.
Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopy was used to characterize the ferroelectric behavior of a thin poly(vinylidene fluoride–trifluoroethylene) P(VDF–TrFE) copolymer. The lab-built GIRA-FTIR apparatus allowed the heating and corona poling process to be carried out whilst collecting the GIRA spectra of the thin polymer film. The Curie transition from the ferroelectric to paraelectric phase was confirmed from the abrupt change in intensity of the 849 cm−1 band in the RA-FTIR spectrum. It was found that the Curie temperature dropped dramatically when the film thickness was lowered to below a certain critical value of approximately 100 nm. The switching of the CF2 dipoles in the ferroelectric crystals after applying the external electric field could be determined by monitoring the change in the 849 cm−1 band intensity. For the 600 nm thick P(VDF–TrFE) film, the switching of the dipoles appears to occur almost instantaneously, while the kinetics of dipole switching of the 75 nm thick film were significantly retarded. The repeated switchability of the CF2 dipoles upon the application of a bipolar cyclic electric field was also confirmed. The bistability of the film due to remnant polarization was also confirmed from the absorbance of the 849 cm−1 band after removing the applied voltage during corona poling. 相似文献
97.
Du Young Choi Long Mei Jin Dexian Wang Kyung Ho Row 《Korean Journal of Chemical Engineering》2005,22(3):465-469
High-performance frontal analysis (HPFA) was used for a protein binding study of isoflavones (daidzein, genistin, and genistein),
enantiomers of perillyl alcohol and S-ibuprofen to human serum albumin (HSA). The analyses were performed on a Develosil and
Inertsil 100-Diol-5 column (10 cm×4.6mm). Sodium phosphate solution (pH 7.4, ionic strength 0.17) was used as the mobile phase
at a flow rate of 1 ml/min. To ensure the drug to be eluted as a trapezoidal peak with a plateau, injection volumes were each
fixed up the zonal profile with an evident plateau appears. The unbound drug concentration was determined from a plateau height
of the plateau region after that experimental data were fitted by Scatchard equation. The binding constants (K) and total
binding affinities (nK) of drugs to HSA were calculated, respectively. 相似文献
98.
Y. K. Cheung W. G. Jin O. C. Zienkiewicz 《International journal for numerical methods in engineering》1991,32(1):63-78
The application of the Trefftz method for calculating wave forces on offshore structures is presented. Indirect and direct formulations using complete and non-singular systems of Trefftz functions for the Helmholtz equation are posed in this paper. An effective technique using different interpolation functions for the velocity potential and wave force are suggested to improve the computational accuracy of the wave force. The numerical examples show that the present method is highly efficient and accurate. 相似文献
99.
100.
渤中13-1油田井身结构优化研究 总被引:1,自引:0,他引:1
针对渤中 1 3- 1油田钻井过程中存在的主要问题 ,利用测井、地质、录井和钻井资料 ,对该油田的井身结构进行研究 ,设计出合理的井身结构 ,优化了套管程序 ,为进一步减少钻井过程中漏、喷、塌、卡等复杂情况的发生 ,提供了科学的理论依据 相似文献