全文获取类型
收费全文 | 487307篇 |
免费 | 15506篇 |
国内免费 | 6963篇 |
专业分类
电工技术 | 13908篇 |
技术理论 | 9篇 |
综合类 | 11192篇 |
化学工业 | 76870篇 |
金属工艺 | 23627篇 |
机械仪表 | 20553篇 |
建筑科学 | 17451篇 |
矿业工程 | 5951篇 |
能源动力 | 9868篇 |
轻工业 | 37796篇 |
水利工程 | 6964篇 |
石油天然气 | 14620篇 |
武器工业 | 1092篇 |
无线电 | 51207篇 |
一般工业技术 | 86975篇 |
冶金工业 | 58740篇 |
原子能技术 | 10320篇 |
自动化技术 | 62633篇 |
出版年
2022年 | 6010篇 |
2021年 | 8403篇 |
2020年 | 6249篇 |
2019年 | 6172篇 |
2018年 | 22411篇 |
2017年 | 21849篇 |
2016年 | 18557篇 |
2015年 | 8707篇 |
2014年 | 11720篇 |
2013年 | 19656篇 |
2012年 | 19022篇 |
2011年 | 27618篇 |
2010年 | 23326篇 |
2009年 | 21370篇 |
2008年 | 22689篇 |
2007年 | 23225篇 |
2006年 | 14524篇 |
2005年 | 13459篇 |
2004年 | 11553篇 |
2003年 | 11254篇 |
2002年 | 10799篇 |
2001年 | 9836篇 |
2000年 | 9351篇 |
1999年 | 8710篇 |
1998年 | 15285篇 |
1997年 | 11154篇 |
1996年 | 8792篇 |
1995年 | 6996篇 |
1994年 | 6123篇 |
1993年 | 5795篇 |
1992年 | 4790篇 |
1991年 | 4386篇 |
1990年 | 4565篇 |
1989年 | 4340篇 |
1988年 | 4095篇 |
1987年 | 3608篇 |
1986年 | 3578篇 |
1985年 | 3978篇 |
1984年 | 3820篇 |
1983年 | 3449篇 |
1982年 | 3292篇 |
1981年 | 3377篇 |
1980年 | 3248篇 |
1979年 | 3265篇 |
1978年 | 3338篇 |
1977年 | 3574篇 |
1976年 | 4447篇 |
1975年 | 2959篇 |
1974年 | 2823篇 |
1973年 | 2957篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The tracer methods developed to assess exfiltration from sewers in the European project APUSS (assessment of the performance of sewer systems) have a high degree of freedom with regard to the choice of tracer and the dosing strategy. These can lead to very different degrees of uncertainty in the measured exfiltration ratio. In this study, we demonstrate how to select an optimal experimental design using decision analysis, which accounts for this uncertainty and its associated costs. Although the results are site-specific, we can conclude generally that, when NaCl is used as the tracer, the accuracy of the exfiltration estimate is most sensitive to the amount of tracer used and the starting time of the experiment. 相似文献
3.
A GIS-based one-dimensional flood simulation model is presented and applied to the centre of the city of N?mes (Gard, France), for mapping flow depths or velocities in the streets network. The geometry of the one-dimensional elements is derived from the Digital Elevation Model (DEM). The flow is routed from one element to the next using the kinematic wave approximation. At the crossroads, the flows in the downstream branches are computed using a conceptual scheme. This scheme was previously designed to fit Y-shaped pipes junctions, and has been modified here to fit X-shaped crossroads. The results were compared with the results of a two-dimensional hydrodynamic model based on the full shallow water equations. The comparison shows that good agreements can be found in the steepest streets of the study zone, but differences may be important in the other streets. Some reasons that can explain the differences between the two models are given and some research possibilities are proposed. 相似文献
4.
Observer-based estimators (OBE) were used for estimation of state variables and kinetic parameters in an anaerobic digestion (AD) process. A simplified first-order model with time-varying kinetic parameters was used to design an OBE for kinetic parameter estimation. This approach was validated on a laboratory-scale anaerobic reactor equipped with a multiwavelength fluorometer for on-line measurements of COD and VFA concentrations in the reactor effluent. The proposed estimators provide continuous adjustment of kinetic parameters and can be used for predictions of state variables between samples acquisition and during sensor failure. 相似文献
5.
The proliferation of both online and bricks and mortar outlet stores underscores the observation that secondary markets are readily accessible to retailers of short-life-cycle products. These secondary markets provide recourse channels for retailers to sell excess inventory of out-of-favor items at reduced prices when overstocking occurs in a primary market. We study the problem of determining when a retailer should terminate its primary selling season by selling remaining inventory on a secondary market. The retailer has a single opportunity to procure prior to a primary selling season consisting of multiple periods. Demand in each period is random, but correlated. At the end of each period, any remaining inventory incurs a holding cost. Then, based upon the current level of inventory and the cumulative demand-to-date, the retailer decides either to terminate the primary selling season by selling all or part of the remaining inventory on a secondary market, or to extend the current primary selling season by another period. We develop structural properties of the optimal policy for determining when to terminate the primary selling season, and we develop corresponding implications for procurement. 相似文献
6.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit. 相似文献
7.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
8.
The tensile elastic modulus (E), yield stress (σY) and microhardness (MH) of neat and binary and ternary blends of glassy semicrystalline ethylene–vinyl alcohol copolymer (EVOH), a glassy amorphous polyamide and a semicrystalline nylon‐containing ionomer covering a broad range of properties were examined. The tests were carried out on dry and water‐equilibrated samples to produce stiffer and softer materials, respectively. From the results, more accurate linear correlations were found to describe adequately the microhardness, modulus and yield stress of these strongly self‐associated polymers through hydrogen bonding. Copyright © 2003 Society of Chemical Industry 相似文献
9.
The objective of this study was to compare methane production and characteristics of digested material in anaerobic digestion concepts according to the Animal By-Products Regulation (ABP-Regulation) of the EC (hygienisation of biowaste for 1 hour at 70 degrees C, particle size < 12 mm) and Finnish national regulations (treatment temperature 55 degrees C, feeding interval 24 h, hydraulic retention time (HRT) 20 d, particle size < 40 mm) and with small variations in treatment methods for treating manure and biowaste. Moreover, the survival of three different salmonella bacteria in these processes was studied. Hygienisation of biowaste prior to digestion at 35 degrees C enhanced methane production by 14-18% compared to similar treatment without hygienisation. The differences in treatment temperature, HRT and hygienisation of biowaste prior to digestion did not significantly affect the characteristics of digested material. The concepts according to the ABP-Regulation and Finnish national regulations were effective in destroying salmonella bacteria to an undetectable level. 相似文献
10.
杨宇 《中国室内装饰装修天地》2006,(7):54-61
华风气象影视大楼总面积4万平方米,根据空间功能不同分为办公大楼和商务写字楼两部分,办公大楼是集演播室、制作机房、办公室为一体的九层综合性建筑。设计师杨宇在刚接触到这个项目的时候,面对的是一个既成事实的建筑。 相似文献