全文获取类型
收费全文 | 39152篇 |
免费 | 1491篇 |
国内免费 | 61篇 |
专业分类
电工技术 | 406篇 |
综合类 | 30篇 |
化学工业 | 7456篇 |
金属工艺 | 941篇 |
机械仪表 | 799篇 |
建筑科学 | 2045篇 |
矿业工程 | 198篇 |
能源动力 | 1126篇 |
轻工业 | 3088篇 |
水利工程 | 450篇 |
石油天然气 | 120篇 |
武器工业 | 5篇 |
无线电 | 2754篇 |
一般工业技术 | 6521篇 |
冶金工业 | 7587篇 |
原子能技术 | 302篇 |
自动化技术 | 6876篇 |
出版年
2023年 | 209篇 |
2022年 | 368篇 |
2021年 | 718篇 |
2020年 | 481篇 |
2019年 | 647篇 |
2018年 | 806篇 |
2017年 | 721篇 |
2016年 | 868篇 |
2015年 | 776篇 |
2014年 | 1086篇 |
2013年 | 2520篇 |
2012年 | 1744篇 |
2011年 | 2189篇 |
2010年 | 1737篇 |
2009年 | 1641篇 |
2008年 | 1884篇 |
2007年 | 1873篇 |
2006年 | 1693篇 |
2005年 | 1503篇 |
2004年 | 1241篇 |
2003年 | 1186篇 |
2002年 | 1107篇 |
2001年 | 758篇 |
2000年 | 616篇 |
1999年 | 650篇 |
1998年 | 861篇 |
1997年 | 742篇 |
1996年 | 687篇 |
1995年 | 650篇 |
1994年 | 599篇 |
1993年 | 610篇 |
1992年 | 543篇 |
1991年 | 329篇 |
1990年 | 450篇 |
1989年 | 430篇 |
1988年 | 344篇 |
1987年 | 386篇 |
1986年 | 346篇 |
1985年 | 451篇 |
1984年 | 446篇 |
1983年 | 345篇 |
1982年 | 323篇 |
1981年 | 313篇 |
1980年 | 299篇 |
1979年 | 295篇 |
1978年 | 274篇 |
1977年 | 284篇 |
1976年 | 278篇 |
1975年 | 217篇 |
1974年 | 201篇 |
排序方式: 共有10000条查询结果,搜索用时 881 毫秒
951.
Testing a MODIS Global Disturbance Index across North America 总被引:4,自引:0,他引:4
David J. Mildrexler Maosheng Zhao Steven W. Running 《Remote sensing of environment》2009,113(10):2103-3566
Large-scale ecosystem disturbances (LSEDs) have major impacts on the global carbon cycle as large pulses of CO2 and other trace gases from terrestrial biomass loss are emitted to the atmosphere during disturbance events. The high temporal and spatial variability of the atmospheric emissions combined with the lack of a proven methodology to monitor LSEDs at the global scale make the timing, location and extent of vegetation disturbance a significant uncertainty in understanding the global carbon cycle. The MODIS Global Disturbance Index (MGDI) algorithm is designed for large-scale, regular, disturbance mapping using Aqua/Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature (LST) and Aqua/MODIS Enhanced Vegetation Index (EVI) data. The MGDI uses annual maximum composite LST data to detect fundamental changes in land-surface energy partitioning, while avoiding the high natural variability associated with tracking LST at daily, weekly, or seasonal time frames. Here we apply the full Aqua/MODIS dataset through 2006 to the improved MGDI algorithm across the woody ecosystems of North America and test the algorithm by comparison with confirmed, historical wildfire events and the windfall areas of documented major hurricanes. The MGDI accurately detects the location and extent of wildfire throughout North America and detects high and moderate severity impacts in the windfall area of major hurricanes. We also find detections associated with clear-cut logging and land-clearing on the forest-agricultural interface. The MGDI indicates that 1.5% (195,580 km2) of the woody ecosystems within North America was disturbed in 2005 and 0.5% (67,451 km2) was disturbed in 2006. The interannual variability is supported by wildfire detections and official burned area statistics. 相似文献
952.
Stuart D.C. Walsh Martin O. Saar Peter Bailey David J. Lilja 《Computers & Geosciences》2009,35(12):2353-2364
Many complex natural systems studied in the geosciences are characterized by simple local-scale interactions that result in complex emergent behavior. Simulations of these systems, often implemented in parallel using standard central processing unit (CPU) clusters, may be better suited to parallel processing environments with large numbers of simple processors. Such an environment is found in graphics processing units (GPUs) on graphics cards.This paper discusses GPU implementations of three example applications from computational fluid dynamics, seismic wave propagation, and rock magnetism. These candidate applications involve important numerical modeling techniques, widely employed in physical system simulations, that are themselves examples of distinct computing classes identified as fundamental to scientific and engineering computing. The presented numerical methods (and respective computing classes they belong to) are: (1) a lattice-Boltzmann code for geofluid dynamics (structured grid class); (2) a spectral-finite-element code for seismic wave propagation simulations (sparse linear algebra class); and (3) a least-squares minimization code for interpreting magnetic force microscopy data (dense linear algebra class). Significant performance increases (between 10× and 30× in most cases) are seen in all three applications, demonstrating the power of GPU implementations for these types of simulations and, more generally, their associated computing classes. 相似文献
953.
Although function points (FP) are considered superior to source lines of code (SLOC) for estimating software size and monitoring developer productivity, practitioners still commonly use SLOC. One reason for this is that individuals who fill different roles on a development team, such as managers and developers, may perceive the benefits of FP differently. We conducted a survey to determine whether a perception gap exists between managers and developers for FP and SLOC across several desirable properties of software measures. Results suggest managers and developers perceive the benefits of FP differently and indicate that developers better understand the benefits of using FP than managers. 相似文献
954.
955.
Nicolás Peña David Scarlatti Aníbal Ollero 《Journal of Intelligent and Robotic Systems》2009,54(1-3):39-59
The System Wide Information Management (SWIM) approach has been conceived to overcome the capacity and flexibility limitations of the current ATM systems. On the other hand the commercial applications of Unmanned Aerial Vehicles (UAVs) require the integration of these vehicles in the ATM. From this perspective, the unavoidable modernization of the ATM is seen as an opportunity to integrate the UAVs with the rest of the air traffic. This paper is devoted to study the feasibility and impact of the aggregation of UAVs on the future ATM supported by a SWIM inspired architecture. Departing from the existing technical documents that describe the fundamentals of SWIM we have explored the compatibility with a potential UAVs integration and also explored how the UAVs could help to improve the future ATM system. We will use the weather application as an example in both cases. 相似文献
956.
Donato Di Paola David Naso Biagio Turchiano Grazia Cicirelli Arcangelo Distante 《Journal of Intelligent and Robotic Systems》2009,56(5):513-541
This paper focuses on the control system for an autonomous robot for the surveillance of indoor environments. Our approach
proposes a matrix-based formalism which allows us to merge in a single framework discrete-event supervisory control, conflict
resolution and reactive control. As a consequence, the robot is able to autonomously handle high level tasks as well as low-level
behaviors, solving control and decision-making issues simultaneously. Moreover, the matrix-based controller is modular and
can be easily reconfigured if mission characteristics or robot hardware configuration change. An illustrative example and
a report on experimental investigations are provided to illustrate the main features of the proposed approach. 相似文献
957.
Detection of sulfur dioxide (SO2) at high temperature (600–750 °C) in the presence of some interferents found in combustion exhausts (NO2, NO, CO2, CO, and hydrocarbon (C3H6)) is described. The detection scheme involves use of a catalytic filter in front of a non-Nernstian (mixed-potential) sensing element. The catalytic filter was a Ni:Cr powder bed operating at 850 °C, and the sensing elements were pairs of platinum (Pt) and oxide (Ba-promoted copper chromite ((Ba,Cu)xCryOz) or Sr-modified lanthanum ferrite (LSF)) electrodes on yttria-stabilized zirconia. The Ni:Cr powder bed was capable of reducing the sensing element response to NO2, NO, CO, and C3H6, but the presence of NO2 or NO (“NOx”, at 100 ppm by volume) still interfered with the SO2 response of the Pt–(Ba,Cu)xCryOz sensing element at 600 °C, causing approximately a 7 mV (20%) reduction in the response to 120 ppm SO2 and a response equivalent to about 20 ppm SO2 in the absence of SO2. The Pt–LSF sensing element, operated at 750 °C, did not suffer from this NOx interference but at the cost of a reduced SO2 response magnitude (120 ppm SO2 yielded 10 mV, in contrast to 30 mV for the Pt-(Ba,Cu)xCryOz sensing element). The powder bed and Pt–LSF sensing element were operated continuously over approximately 350 h, and the response to SO2 drifted downward by about 7%, with most of this change occurring during the initial 100 h of operation. 相似文献
958.
David Longinotti 《Minds and Machines》2009,19(4):495-506
Computationalism, a specie of functionalism, posits that a mental state like pain is realized by a ‘core’ computational state
within a particular causal network of such states. This entails that what is realized by the core state is contingent on events
remote in space and time, which puts computationalism at odds with the locality principle of physics. If computationalism
is amended to respect locality, then it posits that a type of phenomenal experience is determined by a single type of computational
state. But a computational state, considered by itself, is of no determinate type—it has no particular symbolic content, since
it could be embedded in any of an infinite number of algorithms. Hence, if locality is respected, then the type of experience
that is realized by a computational state, or whether any experience at all is realized, is under-determined by the computational
nature of the state. Accordingly, Block’s absent and inverted qualia arguments against functionalism find support in the locality
principle of physics. If computationalism denies locality to avoid this problem, then it cannot be considered a physicalist
theory since it would entail a commitment to phenomena, like teleological causation and action-at-a-distance, that have long
been rejected by modern science. The remaining theoretical alternative is to accept the locality principle for macro events
and deny that formal, computational operations are sufficient to realize a phenomenal mental state. 相似文献
959.
A formalism to describe design patterns based on role concepts 总被引:1,自引:0,他引:1
960.
Magnetic materials used in cored microinductors to supersede ferrite in the 0.5-10 MHz frequency range are investigated in
this article. The performance of electrodeposited nickel–iron, cobalt–iron–copper alloys and the commercial alloy Vitrovac
6025 have been assessed through their inclusion within a custom-made solenoid microinductor. Although the present inductor
achieves 77% power efficiency at 500 KHz for 24.7 W/cm3 power density, an optimized process predicts a power efficiency of
97% for 30.83 W/cm3 power density. The main issues regarding microinductor design and performance are discussed. 相似文献