全文获取类型
收费全文 | 68944篇 |
免费 | 8260篇 |
国内免费 | 4337篇 |
专业分类
电工技术 | 18615篇 |
技术理论 | 4篇 |
综合类 | 7125篇 |
化学工业 | 4040篇 |
金属工艺 | 4473篇 |
机械仪表 | 4232篇 |
建筑科学 | 6178篇 |
矿业工程 | 1781篇 |
能源动力 | 1797篇 |
轻工业 | 1337篇 |
水利工程 | 1754篇 |
石油天然气 | 1679篇 |
武器工业 | 703篇 |
无线电 | 9214篇 |
一般工业技术 | 4834篇 |
冶金工业 | 4656篇 |
原子能技术 | 844篇 |
自动化技术 | 8275篇 |
出版年
2024年 | 150篇 |
2023年 | 948篇 |
2022年 | 1685篇 |
2021年 | 1997篇 |
2020年 | 2299篇 |
2019年 | 1894篇 |
2018年 | 1625篇 |
2017年 | 2437篇 |
2016年 | 2730篇 |
2015年 | 2911篇 |
2014年 | 4737篇 |
2013年 | 3987篇 |
2012年 | 5444篇 |
2011年 | 5826篇 |
2010年 | 4419篇 |
2009年 | 4613篇 |
2008年 | 4180篇 |
2007年 | 5171篇 |
2006年 | 4375篇 |
2005年 | 3615篇 |
2004年 | 2957篇 |
2003年 | 2422篇 |
2002年 | 2003篇 |
2001年 | 1864篇 |
2000年 | 1527篇 |
1999年 | 1222篇 |
1998年 | 898篇 |
1997年 | 744篇 |
1996年 | 611篇 |
1995年 | 505篇 |
1994年 | 399篇 |
1993年 | 286篇 |
1992年 | 267篇 |
1991年 | 181篇 |
1990年 | 141篇 |
1989年 | 139篇 |
1988年 | 89篇 |
1987年 | 54篇 |
1986年 | 30篇 |
1985年 | 33篇 |
1984年 | 30篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1964年 | 2篇 |
1961年 | 2篇 |
1959年 | 3篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
近年来,通过优化飞行程序降低机场飞机噪声影响成为机场环境保护的重要研究方向。文章首先建立了基于飞机“噪声-功率-距离”数据的噪声计算模型,介绍了平均飞行航迹以及连续爬升运行(Continuous Climb Opera-tion, CCO)离场程序的相关理论,最后以大型国际机场为实例,使用飞机平均飞行航迹进行噪声预测,运用综合噪声模型计算出噪声影响面积并绘制噪声影响等值线图,比较了CCO离场相对常规的标准仪表离场(Standard Instru-ment Departure, SID)的降噪效果。结果表明,CCO离场程序可有效降低机场噪声影响,在高噪声级影响区域的降噪效果更佳。 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(52):22203-22214
The gas purging states affect electricity output and energy storage capacity of unitized regenerative fuel cells. In this study, a model of unitized regenerative fuel cell is established. Cell voltages and operating temperatures influences on the dynamic distribution of thermal fluid during purging process and the discharge of residual liquid water in electrolytic cell mode are investigated. The motivation of the present study is better understanding the gas purging characteristics and its effect on reaction behaviors of unitized regenerative fuel cells. Simulation results reveal a significant influence of purging gas temperature on the water flooding and a great effect of operating voltage on the water diffusion. The operating temperature of electrolytic cell model almost has little effect on purging results at different cell temperature and the same purging gas temperature. When the purging gas temperature is changed, higher temperatures of cell and purging gas facilitate liquid water discharging out from the cell regions. In cell water flooding situation, when having large liquid content, the purging gas has little effects on the water expelling process. 相似文献
5.
《International Journal of Hydrogen Energy》2022,47(78):33272-33281
According to the International Energy Agency, only a small part of the full potential of biomass energy is currently used in the world. The annual amount of agricultural waste in the Russian Federation is estimated at about 152 million tons, and the energy potential of animal waste is 201 PJ/year. Anaerobic digestion is an efficient method of converting organic waste into renewable energy sources. Previously, the positive effect of pretreatment of various organic feedstocks in vortex layer apparatus (VLA) on the characteristics of anaerobic digestion and energy efficiency was shown. Currently, there is a significant interest in the world in obtaining biohydrogen from organic waste using the dark fermentation (DF) process. During pretreatment in the VLA, the iron working bodies are abraded and iron particles are introduced into the feedstock of the DF reactor. This may have a positive effect on the production rate and yield of hydrogen, which has not been previously studied. This work is aimed at evaluating the possibility of using the VLA as a method for pretreatment of a dark fermentation feedstock for the intensification of biohydrogen production. To achieve this goal, an experimental setup was constructed. It consisted of a 45 L DF reactor, a VLA and a process control system to collect data on the DF process parameters every 5 min. At a hydraulic retention time in the DF reactor of 24 h and in the VLA of 30 s, the hydrogen content in the biogas increased from 51.1% to 52.2%. At the same time, the pH increased from 3.85 to 4.8–4.9, and the hydrogen production rate increased by 16% to 1.941 L/(L day). The hydrogen yield was 80.9 ml/g VS. Thus, pretreatment of the feedstock in VLA can be an effective way to intensify the DF process; however, further study of the VLA operating modes is required in order to optimize the concentrations of iron particles introduced into the feedstock for the most efficient continuous production of dark fermentative biohydrogen. 相似文献
6.
《Mechatronics》2022
This paper considers the shared path following control of an unmanned ground vehicle by a single person. A passive measure of human intent is used to blend the human and machine inputs in a mixed initiative approach. The blending law is combined with saturated super-twisting sliding mode speed and heading controllers, so that exogenous disturbances can be counteracted via equivalent control. It is proven that when the proposed blending law is used, the combined control signals from both the human and automatic controller respect the actuator magnitude constraints of the machine. To demonstrate the approach, shared control experiments are performed using an unmanned ground vehicle, which follows a lawn mower pattern shaped path. 相似文献
7.
Prashant Thapliyal Alok S. Kandari Vijendra Lingwal N.S. Panwar G. Mohan Rao 《Ceramics International》2021,47(9):12066-12071
(Ta2O5)1-x- (TiO2)x (TTOx) thin films, with x = 0, 0.03, 0.06, 0.08, and 0.11, were deposited using magnetron direct current (DC) sputtering method onto the P/boron-silicon (1 0 0) substrates by varying areas of Tantalum and Titanium metallic targets, in oxygen environment at ambient temperature. The as-deposited thin films were annealed at temperatures ranging from 500 to 800 °C. Generally, the formation of the Ta2O5 structure was observed from the X-ray diffraction measurements of the annealed films. The capacitance of prepared metal– oxide– semiconductor (MOS) structures of Ag/TTOx/p-Si was measured at 1 MHz. The dielectric constant of the deposited films was observed altering with varying composition and annealing temperature, showing the highest value 71, at 1 MHz, for the TTOx films, x = 0.06, annealed at 700 °C. With increasing annealing temperature, from 700 to 800 °C, the leakage current density was observed, generally decreasing, from 10?5 to 10?8 A cm?2, for the prepared compositions. Among the prepared compositions, films with x = 0.06, annealed at 800 °C, having the observed value of dielectric constant 48, at 1 MHz; and the leakage current density 2.7 × 10?8 A cm?2, at the electric field of 3.5 × 105 V cm?1, show preferred potential as a dielectric for high-density silicon memory devices. 相似文献
8.
9.
Dr. Barbara Wienen-Schmidt Matthias Oebbeke Dr. Khang Ngo Prof. Dr. Andreas Heine Prof. Dr. Gerhard Klebe 《ChemMedChem》2021,16(1):292-300
In lead optimization, protein crystallography is an indispensable tool to analyze drug binding. Binding modes and non-covalent interaction inventories are essential to design follow-up synthesis candidates. Two protocols are commonly applied to produce protein–ligand complexes: cocrystallization and soaking. Because of its time and cost effectiveness, soaking is the more popular method. Taking eight ligand hinge binders of protein kinase A, we demonstrate that cocrystallization is superior. Particularly for flexible proteins, such as kinases, and larger ligands cocrystallization captures more reliable the correct binding pose and induced protein adaptations. The geometrical discrepancies between soaking and cocrystallization appear smaller for fragment-sized ligands. For larger flexible ligands that trigger conformational changes of the protein, soaking can be misleading and underestimates the number of possible polar interactions due to inadequate, highly impaired positions of protein amino-acid side and main chain atoms. Thus, if applicable cocrystallization should be the gold standard to study protein–ligand complexes. 相似文献
10.
Mit Rita Goswami Prayas Singh Pankaj Chamoli Sumit Bhardwaj Kuldeep Kumar Raina Ravi Kumar Shukla 《应用聚合物科学杂志》2021,138(43):51260
ZnO rice like nonarchitects are grafted on the graphene carbon core via a rapid microwave synthesis route. The prepared grafted systems are characterized via XRD, SEM, RAMAN, and XPS to examined the structural and morphological parameters. Zinc oxide grafted graphene sheets (ZnO-G) are further doped in β-phase of polyvinylidene fluoride (PVDF) to prepare the polymer nanocomposites (PNCs) via mixed solvent approach (THF/DMF). β-phase confirmation of PVDF PNCs is done by FTIR studies. It is observed that ZnO-G filler enhances the β-phase content in the PNCs. Non-doped PVDF and PNCs are further studied for rheological behavior under the shear rate of 1–100 s−1. Doping of ZnO-G dopant to the PVDF matrix changes its discontinuous shear thickening (DST) behavior to continues shear thickening behavior (CST). Hydrocluster formation and their interaction with the dopant could be the reason for this striking DST to CST behavioral change. Strain amplitude sweep (10−3% -10%) oscillatory test reveals that the PNCs shows extended linear viscoelastic region with high elastic modulus and lower viscous modulus. Effective shear thickening behavior and strong elastic strength of these PNCs present their candidature for various fields including mechanical and soft body armor applications. 相似文献