全文获取类型
收费全文 | 2505篇 |
免费 | 272篇 |
国内免费 | 149篇 |
专业分类
电工技术 | 113篇 |
综合类 | 261篇 |
化学工业 | 324篇 |
金属工艺 | 29篇 |
机械仪表 | 94篇 |
建筑科学 | 67篇 |
矿业工程 | 25篇 |
能源动力 | 88篇 |
轻工业 | 31篇 |
水利工程 | 116篇 |
石油天然气 | 32篇 |
武器工业 | 16篇 |
无线电 | 908篇 |
一般工业技术 | 247篇 |
冶金工业 | 125篇 |
原子能技术 | 52篇 |
自动化技术 | 398篇 |
出版年
2024年 | 8篇 |
2023年 | 51篇 |
2022年 | 88篇 |
2021年 | 120篇 |
2020年 | 90篇 |
2019年 | 68篇 |
2018年 | 64篇 |
2017年 | 87篇 |
2016年 | 96篇 |
2015年 | 116篇 |
2014年 | 151篇 |
2013年 | 152篇 |
2012年 | 161篇 |
2011年 | 165篇 |
2010年 | 140篇 |
2009年 | 164篇 |
2008年 | 167篇 |
2007年 | 185篇 |
2006年 | 162篇 |
2005年 | 129篇 |
2004年 | 100篇 |
2003年 | 89篇 |
2002年 | 74篇 |
2001年 | 60篇 |
2000年 | 39篇 |
1999年 | 25篇 |
1998年 | 35篇 |
1997年 | 27篇 |
1996年 | 21篇 |
1995年 | 28篇 |
1994年 | 18篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1964年 | 2篇 |
1961年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有2926条查询结果,搜索用时 15 毫秒
991.
The paper describes a novel technique for estimating the sampled impulse-response of a time-varying channel, where the latter involves an HF radio link with two independent Rayleigh fading sky waves. The channel estimator operates on the sampled demodulated baseband signal in the receiver of a synchronous serial data-transmission system, which transmits a 16-level quadrature amplitude modulated signal at 9600 bit/s over the HF radio link. By making a more effective use of the available prior knowledge of the channel the estimator obtains a more accurate estimate of the sampled impulse-response of the channel than that given by more conventional techniques. Results of computer simulation tests are presented to compare the performance of the new estimator with that of an arrangement previously described. 相似文献
992.
袁立新 《计算机与应用化学》2002,19(4):503-505
指出了在DOS平台下“辅助化学实验测量系统-CACE”的局限性,介绍了在Windows平台下的多通道化学实验测量与处理系统的实现方法,并说明了改进后的系统对测量数值与处理数据可同时进行,另外系统还可实现非线性电压的测量。 相似文献
993.
V. A. Bazhenov E. S. Dekhtyaryuk L. Yu. Nemchinova V. V. Obrashevskaya 《Strength of Materials》2008,40(2):269-274
We examine the possibility of stabilizing dynamic states, caused by deterministic periodic parametric loading, by means of
surplus excitation, which is an exponentially correlated random process. The range of correlation radius values for which
random excitation has a stabilizing effect on dynamic state has been determined.
__________
Translated from Problemy Prochnosti, No. 2, pp. 141–148, March–April, 2008. 相似文献
994.
The critical flow principle is a useful approach for the hydraulic analysis of round-crested weirs due to their single head-discharge relationships. The hydraulics of circular-crested weirs is examined using simplified models incorporating streamline curvature effects, comparing their predictions with experimental data. A generalized one-dimensional model based on the critical flow in curvilinear motion has been developed. The discharge coefficient increases with the specific energy normalized with the radius of curvature, E/R, when streamline curvature effects are included. The relative flow depth at the crest decreases as E/R increases. The flow at the weir crest is only critical for a normalized specific energy value of E/R ≈ 0.5–0.6. For larger heads, the flow at the weir crest has been found to be supercritical. 相似文献
995.
Crown ethers are of enormous interest and importance in chemistry, biochemistry, materials science, catalysis, separation, transport and encapsulated processes, as well as in the design and synthesis of various synthetic systems with specific properties, diverse capabilities, and programmable functions. Classical crown ethers are macrocyclic polyethers that contain 3-20 oxygen atoms separated from each other by two or more carbon atoms. They are exceptionally versatile in selectively binding a range of metal ions and a variety of organic neutral and ionic species. Crown ethers are currently being studied and used in a variety of applications beyond their traditional place in chemistry. This review presents additional applications and the ever-increasing biomedical potentials of these intriguing compounds, with particular emphasis on the prospects of their relevance as anticancer agents. We believe that further research in this direction should be encouraged, as crown compounds could either induce toxicities that are different from those of conventional antitumor drugs, or complement drugs in current use, thereby providing a valuable adjunct to therapy. 相似文献
996.
Zoheir Kordrostami Mohammad Hossein Sheikhi Reza Mohammadzadegan 《Fullerenes, Nanotubes and Carbon Nanostructures》2008,16(1):66-77
Reviewing experimental results and based on the physical reasoning, we present a basic circuit model for Multiwall carbon nanotubes (MWCNTs), which can simulate different experimental results. Investigation of different results confirms the severe effects of fabrication process (nanotube and contacts) on electronic properties of the MWCNTs. The circuit model has been developed to show the performance improvements of a CNT interconnect when the single-wall carbon nanotube (SWCNT) is replaced by an MWCNT. To calculate the current-voltage characteristic and the switching delay of MWCNTs, we have simulated their DC and AC properties, respectively, using the developed transmission line models. Based on the physical models, the elements of the circuit model can be changed so that the simulation and the practical measurements for an MWCNT can correspond. Switching Delays of the MWCNTs and SWCNTs are calculated and compared for different cases. 相似文献
997.
An 80-nm gate length metamorphic high electron mobility transistor (mHEMT) on a GaAs substrate with high indium composite compound-channels In0.7Ga0.3As/In0.6Ga0.4As and an optimized grade buffer scheme is presented. High 2-DEG Hall mobility values of 10200 cm2/(V· s) and a sheet density of 3.5 × 1012 cm-2 at 300 K have been achieved. The device's T-shaped gate was made by utilizing a simple three layers electron beam resist, instead of employing a passivation layer for the T-share gate, which is beneficial to decreasing parasitic capacitance and parasitic resistance of the gate and simplifying the device manufacturing process. The ohmic contact resistance Rc is 0.2 Ω ·mm when using the same metal system with the gate (Pt/Ti/Pt/Au), which reduces the manufacturing cycle of the device. The mHEMT device demonstrates excellent DC and RF characteristics. The peak extrinsic transconductance of 1.1 S/mm and the maximum drain current density of 0.86 A/mm are obtained. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) are 246 and 301 GHz, respectively. 相似文献
998.
999.
Richard Copas 《Landscape Research》1997,22(1):115-131
Recent river landscape assessments of the eastern part of the Thames catchment have enabled a better understanding of their landscape status and value. These rivers have formed the focal point for human settlement and have been extensively affected by their use. Flood defence through channelization and surfacing of the watercourses has been highly detrimental to their landscape quality. Flooding has itself been exacerbated by catchment urbanization and by land drainage systems. The issues affecting the landscape planning and design of river systems are examined and suggestions made as to how they can be addressed. 相似文献
1000.
Gilbert D Funk K Dekowski B Lechler R Keller S Möhrlen F Frings S Hagen V 《Chembiochem : a European journal of chemical biology》2007,8(1):89-97
The vanilloid capsaicin, N-(4-hydroxy-3-methoxybenzyl)-8-methylnon-6-enamide, is the pungent ingredient of chili peppers and is used in pain research as an activating ligand of heat-sensitive transduction channels in nociceptive neurons. Here we describe the synthesis and application of two capsaicin derivatives modified at the hydroxy function of the vanillyl motif: alpha-carboxy-4,5-dimethoxy-2-nitrobenzyl-caged (CDMNB-caged) capsaicin and {7-[bis(carboxymethyl)amino]coumarin-4-yl}methoxycarbonyl-caged (BCMACMOC-caged) capsaicin. These compounds show dramatically reduced pungency, but release active capsaicin upon irradiation with UV light. CDMNB-caged capsaicin can be used to perform concentration-jump experiments, while BCMACMOC-caged capsaicin is membrane-impermeant and can be applied selectively to the intracellular or extracellular sides of a plasma membrane. Both compounds can serve as valuable research tools in pain physiology. 相似文献