全文获取类型
收费全文 | 7278篇 |
免费 | 193篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 113篇 |
综合类 | 12篇 |
化学工业 | 1078篇 |
金属工艺 | 112篇 |
机械仪表 | 135篇 |
建筑科学 | 285篇 |
矿业工程 | 18篇 |
能源动力 | 161篇 |
轻工业 | 661篇 |
水利工程 | 96篇 |
石油天然气 | 6篇 |
无线电 | 682篇 |
一般工业技术 | 1028篇 |
冶金工业 | 2104篇 |
原子能技术 | 61篇 |
自动化技术 | 930篇 |
出版年
2023年 | 26篇 |
2022年 | 72篇 |
2021年 | 115篇 |
2020年 | 57篇 |
2019年 | 88篇 |
2018年 | 118篇 |
2017年 | 99篇 |
2016年 | 120篇 |
2015年 | 95篇 |
2014年 | 162篇 |
2013年 | 273篇 |
2012年 | 278篇 |
2011年 | 345篇 |
2010年 | 241篇 |
2009年 | 241篇 |
2008年 | 260篇 |
2007年 | 283篇 |
2006年 | 198篇 |
2005年 | 202篇 |
2004年 | 193篇 |
2003年 | 177篇 |
2002年 | 166篇 |
2001年 | 109篇 |
2000年 | 111篇 |
1999年 | 162篇 |
1998年 | 692篇 |
1997年 | 459篇 |
1996年 | 316篇 |
1995年 | 192篇 |
1994年 | 188篇 |
1993年 | 186篇 |
1992年 | 79篇 |
1991年 | 73篇 |
1990年 | 84篇 |
1989年 | 72篇 |
1988年 | 86篇 |
1987年 | 55篇 |
1986年 | 56篇 |
1985年 | 76篇 |
1984年 | 52篇 |
1983年 | 39篇 |
1982年 | 46篇 |
1981年 | 46篇 |
1980年 | 42篇 |
1979年 | 47篇 |
1978年 | 41篇 |
1977年 | 52篇 |
1976年 | 78篇 |
1975年 | 34篇 |
1974年 | 25篇 |
排序方式: 共有7482条查询结果,搜索用时 15 毫秒
1.
2.
Bart Van der Bruggen 《Membrane Technology》2003,2003(2):6-9
As the requirement for fresh water increases worldwide, there is a need for more and more plants that are able to treat non-conventional water sources. Sea water has become an important source of fresh water in many arid regions. This feature provides an overview of recent process improvements in sea water desalination using reverse osmosis, multi-stage flash, multi-effect distillation and electrodialysis. Areas discussed include the use of alternative energy sources (wind energy, solar energy and nuclear energy) for reverse osmosis or distillation processes, and the impact of the different desalination process on the environment. Also covered are the implementation of hybrid processes in sea water desalination, and the pretreatment of desalination plants by pressure-driven membrane processes. 相似文献
3.
An experimental technique together with a numerical model is proposed with which the diffusion coefficient and the sorption isotherm of water in paint can be measured. Inside a closed vessel, paint films are on stainless-steel plates. Water is present as water vapour in the air and in the paint. After blowing dry or wet air through the vessel for some time, the situation moves to a new equilibrium. The relative humidity of the air inside the vessel is measured as a function of time. From fitting the theoretical/numerical model against the experimental values, follow the diffusion coefficient and the sorption isotherm of water in the paint. The results show large scattering. When the independently measured sorption isotherm is used as an input parameter in the model, the fitting procedure gives much smaller scattering for the diffusion coefficient. 相似文献
4.
Robben J.; der Schueren J.Van; Verhasselt P.; Aert R.; Volckaert G. 《Protein engineering, design & selection : PEDS》1995,8(2):159-165
The deletion of nine residues from the C-terminus of the bacterialchloramphenicol acetyltransferase (CAT) results in depositionof the mutant protein in cytoplasmic inclusion bodies and lossof chloramphenicol resistance in Escherichia coli. This foldingdefect is relieved by C-terminal fusion of the polypeptide withas few as two residues. Based on these observations, efficientpositive selection for the cloning of DNA fragments has beendemonstrated. The cloning vector encodes a C-terminally truncatedCAT protein. Restriction sites in front of the stop codon allowthe insertion of target DNA, resulting in the production ofproperly folded CAT fusion proteins and regained chloramphenicolresistance. The positive selection of recombinants is accomplishedby growth of transformants on chloramphenicol-containing agarplates. The method appears particularly convenient for the cloningof DNA fragments amplified by the PCR because minimal informationto restore CAT folding can be included in the primers. The cloningof random sequences shows that the folding defect can be relievedby fusion to a wide variety of peptides, providing great flexibilityto the positive selection system. This vector may also contributeto the determination of the role of the C-terminus in CAT folding. 相似文献
5.
van der Steen J.-L.P.J. Esseni D. Palestri P. Selmi L. Hueting R.J.E. 《Electron Devices, IEEE Transactions on》2007,54(8):1843-1851
This paper investigates the validity of the parabolic effective mass approximation (EMA), which is almost universally used to describe the size and bias-induced quantization in n-MOSFETs. In particular, we compare the EMA results with a full-band quantization approach based on the linear combination of bulk bands (LCBB) and study the most relevant quantities for the modeling of the mobility and of the on-current of the devices, namely, the minima of the 2-D subbands, the transport masses, and the electron density of states. Our study deals with both silicon and germanium n-MOSFETs with different crystal orientations and shows that, in most cases, the validity of the EMA is quite satisfactory. The LCBB approach is then used to calculate the values of the effective masses that help improve the EMA accuracy. There are crystal orientations, however, where the 2-D energy dispersion obtained by the LCBB method exhibits features that are difficult to reproduce with the EMA model. 相似文献
6.
Ohne Zusammenfassung 相似文献
7.
van der Wielen P.C.J.M. Steennis E.F. Wouters P.A.A.F. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2003,10(4):678-688
On-line partial discharge (PD) detection of three-phase belted medium voltage cable connections results in a number of interpretation differences as compared to off-line measurements where only one phase is energized. The induced currents and charges in the phase conductors and earth screen upon a PD not only depend on the discharge site, but also become phase angle dependent. Furthermore, simulations show that the PD distribution itself varies with the amount of eccentricity of the rotating electric field and may differ from the off-line distributions obtained with a linear field. Finally, the PD propagation in a multi-conductor cable also alters the signals measured at the cable terminals. In this paper, induced charges and PD distributions are studied by means of computer simulation. The cable propagation characteristics are verified by measurements. 相似文献
8.
Cross-Layer Packetization and Retransmission Strategies for Delay-Sensitive Wireless Multimedia Transmission 总被引:1,自引:0,他引:1
Existing wireless networks provide dynamically varying resources with only limited support for the quality of service required by the bandwidth-intense, loss-tolerant and delay-sensitive multimedia applications. This variability of resources does not significantly impact delay insensitive data transmission (e.g., file transfers), but has considerable consequences for multimedia applications. Recently, the research focus has been to adapt existing algorithms and protocols at the lower layers of the protocol stack to better support multimedia transmission applications and conversely, to modify application layer solutions to cope with the varying wireless networks resources. In this paper, we show that significant improvements in wireless multimedia performance can be obtained by deploying a joint application-layer adaptive packetization and prioritized scheduling and MAC-layer retransmission strategy. We deploy a state-of-the-art wavelet coder for the compression of the video data that enables on-the-fly adaptation to changing channel conditions and inherent prioritization of the video bitstream. We pose the cross-layer problem as a distortion minimization given delay constraints and derive analytical solutions by modifying existing joint source-channel coding theory aimed at fulfilling rate, rather than delay, constraints. We also propose real-time algorithms that explicitly consider the available information about previously transmitted packets. The obtained results show significant improvements in terms of video quality as opposed to ad-hoc optimizations currently deployed, while the complexity associated with performing this optimization in real time, i.e., at transmission time, is limited 相似文献
9.
Gert van der Horn Johan H. Huijsing 《Analog Integrated Circuits and Signal Processing》1997,14(3):207-222
In many applications electronic sensors are used toimprove performance and reliability of measurement systems. Suchsensors should provide a correct transfer from the physical signalto be measured to the electrical output signal. One importantstep to achieve this, is to calibrate each sensor by applyingdifferent reference input signals and adjusting the sensor transferaccordingly. Besides expensive reference equipment the calibrationprocess takes much time and attention per individual sensor,which means a considerable increase in sensor production costs.By including at the sensor or sensor interface chip a programmablecalibration facility the calibration of such smart sensors caneasily be automated and can be executed for a batch of sensorsat a time, thus minimizing the calibration time and costs. Thispaper presents a calibration method and options for integrationin the smart sensor concept, in hardware as well as in software.An advantage of the proposed method is that it does not needa large matrix of calibration data, which needs to be storedin a look-up table or converted into a correction formula, butinstead it uses a step-by-step approach to correct the sensortransfer at each calibration measurement until the error is sufficientlysmall. 相似文献
10.
Knippels G.M.H. van der Meer A.F.G. Oepts D. van Amersfoort P.W. 《Quantum Electronics, IEEE Journal of》1997,33(1):10-17
We have investigated the optical output of the free-electron laser for infrared experiments (FELIX) when it is driven by an electron beam with a ramped energy. We show that the applied slow ramp on the electron beam energy leads to a frequency chirp on each picosecond optical pulse. Typical values for the chirp are 0.2% frequency sweep across a 1.5-ps-long optical pulse. The optical pulses were analyzed with a double-grating pair and with a second-order autocorrelator. The pulse duration was reduced in the double-grating pair by 20%. A linear dependence of the chirp on the cavity desynchronization was measured 相似文献