首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1616篇
  免费   32篇
  国内免费   3篇
电工技术   23篇
综合类   2篇
化学工业   168篇
金属工艺   19篇
机械仪表   12篇
建筑科学   23篇
矿业工程   2篇
能源动力   21篇
轻工业   97篇
水利工程   9篇
石油天然气   4篇
无线电   107篇
一般工业技术   99篇
冶金工业   963篇
原子能技术   6篇
自动化技术   96篇
  2023年   3篇
  2022年   9篇
  2021年   9篇
  2020年   7篇
  2019年   18篇
  2018年   21篇
  2017年   20篇
  2016年   8篇
  2015年   18篇
  2014年   31篇
  2013年   47篇
  2012年   23篇
  2011年   32篇
  2010年   26篇
  2009年   46篇
  2008年   27篇
  2007年   25篇
  2006年   26篇
  2005年   21篇
  2004年   21篇
  2003年   25篇
  2002年   36篇
  2001年   31篇
  2000年   16篇
  1999年   38篇
  1998年   338篇
  1997年   195篇
  1996年   117篇
  1995年   59篇
  1994年   55篇
  1993年   64篇
  1992年   12篇
  1991年   13篇
  1990年   10篇
  1989年   19篇
  1988年   13篇
  1987年   9篇
  1986年   7篇
  1985年   7篇
  1984年   4篇
  1983年   4篇
  1982年   9篇
  1981年   14篇
  1980年   6篇
  1979年   6篇
  1978年   4篇
  1977年   34篇
  1976年   62篇
  1975年   3篇
  1972年   2篇
排序方式: 共有1651条查询结果,搜索用时 0 毫秒
81.
The aerosol optical depth data obtained by two methods are compared. The first method uses solar radiance measurements with the spectroradiometer Optronic OL752 installed inside the Santa Cruz de Tenerife Harbour (28.48 N, 16.24 W). The second one takes the solar radiation scattered by the atmosphere using the Advanced Very High Resolution Radiometer (AVHRR) radiometer channels on board the NOAA meteorological satellites. A 91 per cent correlation between the two procedures was obtained for channel 1 (630nm).  相似文献   
82.
The contributions of 23 insertion, deletion, or missense mutations within an 81-bp fragment of rpoB, the gene encoding the beta-subunit of the DNA-dependent RNA polymerase of Mycobacterium tuberculosis, to the development of resistance to rifamycins (rifampin, rifabutin, rifapentine, and KRM-1648) in 29 rifampin-resistant clinical isolates were defined. Specific mutant rpoB alleles led to the development of cross-resistance to all rifamycins tested, while a subset of mutations were associated with resistance to rifampin and rifapentine but not to KRM-1648 or rifabutin. To further study the impact of specific rpoB mutant alleles on the development of rifamycin resistance, mutations were incorporated into the rpoB gene of M. tuberculosis H37Rv, contained on a mycobacterial shuttle plasmid, by in vitro mutagenesis. Recombinant M. tuberculosis clones containing plasmids with specific mutations in either codon 531 or 526 of rpoB exhibited high-level resistance to all rifamycins tested, whereas clones containing a plasmid with a mutation in codon 516 exhibited high-level resistance to rifampin and rifapentine but were susceptible to both rifabutin and KRM-1648. These results provided additional proof of the association of specific rpoB mutations with the development of rifamycin resistance and corroborate previous reports of the usefulness of rpoB genotyping for predicting rifamycin-resistant phenotypes.  相似文献   
83.
The subcellular events responsible for release of mediators by mast cells may help to clarify roles for mast cells in health and disease. In this study we show that the granule-associated protease chymase is also within cytoplasmic vesicles in appropriately stimulated rat peritoneal mast cells. Rat peritoneal mast cells were recovered before or 1-10 sec after exposure to the secretogogue compound 48/80 (10 micrograms/ml) and then were examined by radioimmunoassay to quantify histamine release or were processed, using routine methods for postembedding immunoelectron microscopy, to identify the subcellular localization of chymase. In comparison to unstimulated cells, compound 48/80 stimulated cells in two independent experiments showed an increase (15%, 28%) in the surface area of the cell and a decrease (12%, 6%) in the surface area of the total granule compartment before degranulation channel formation. These global cellular changes occurred in a background of transient but significant (p < 0.01) increases in the area and number of chymase-immunoreactive vesicles per microns2 cytoplasm. These changes were detectable at 5 or 7 sec after stimulation with compound 48/80 but returned to near prestimulation levels by 9 or 10 sec after addition of compound 48/80 (total cumulative histamine release was 28% by 8 sec and 47% by 14 sec). These observations suggest that vesicles participate in the early stages of regulated secretion of chymase from rat peritoneal mast cells.  相似文献   
84.
85.
The scaphoid test described by Watson has generally been accepted as the definitive test for scaphoid instability and uses pressure against the scaphoid tubercle as the wrist moves from ulnar to radial deviation for the evaluation. This article describes a stress test done with the wrist in neutral position, which actively provokes scaphoid instability. Variations in stability can be used to grade scaphoid laxity.  相似文献   
86.
Treatments of Chinese hamster V79 cells during one cell cycle with a new type of topoisomerase II inhibitor, ICRF-193, which does not accumulate cleavable topoisomerase-DNA complexes induced both chromosome- and chromatid-type aberrations with high frequencies. Furthermore, ICRF-193 synergistically enhanced the yield of UVB-induced chromatid-type aberrations, chromatid exchanges in particular. Treated with ICRF-193 for the last 3 h before harvest, cells showed frequent incidence of chromatid-type aberrations and synergistic enhancement of UVB-induced chromatid-type aberrations, chromatid exchanges in particular. These results suggest that spontaneous and UVB-induced lesions might be ultimately transformed into chromatid-type aberrations by topoisomerase II-dependent checkpoint process(es) in the G2 phase of the cell cycle.  相似文献   
87.
Abstract

Power scheduling of distributed storage devices and renewable energy resources in microgrids is crucial for their reliable and optimal operation. Conventionally, the power scheduling problem is solved with a centralized energy management control, which has access to all the information from the overall system. This type of control has limitations related to computational burden, communication latencies, and missing information. Therefore, the primary objective of this paper is to propose a distributed energy management strategy, to reduce the operational cost of microgrids, and to enhance the computation time. The strategy is formulated based on the model predictive control method since it allows the control action in the current time-step to be optimized while taking into account the future time-steps. Outputs of the energy management system are the optimal power references generated for all energy resources based on the system’s demand, constraints, and objective functions. To illustrate the effectiveness of the distributed model predictive control, the proposed algorithm is validated through simulation, on a microgrid candidate via MATLAB/Simulink, and controller hardware-in-the-loop experiment on a LabVIEW platform using National Instruments control devices (myRIO). The results will show the computation time in the distributed IEM method is improved compared to centralized IEM. Additionally, the results will show the robustness of the distributed IEM in the plug and play scenario.  相似文献   
88.
EuQoS is the acronym for "end-to-end quality of service support over heterogeneous networks", which is a European research project aimed at building an entire QoS framework, addressing all the relevant network layers, protocols, and technologies. This framework, which includes the most common access networks (xDSL, UMTS, WiFi, and LAN) is being prototyped and tested in a multidomain scenario throughout Europe, composing what we call the EuQoS system. In this article we present the novel QoS routing mechanisms that are being developed and evaluated in the framework of this project. The preliminary performance results validate the design choices of the EuQoS system, and confirm the potential impact this project is likely to have in the near future  相似文献   
89.
We address restoration of eutrophic lakes and reservoirs through the formulation of dynamic optimization problems subject to complex PDAE systems representing biogeochemical processes in the water bodies. The model includes phytoplankton, zooplankton, fish, nutrients, DO, particulate and dissolved carbon dynamics. The PDAE has been transformed into an ordinary differential algebraic equation system by spatial discretization into two water layers. An optimal control problem for the implementation of three different restoration techniques and their combinations has been formulated within a control vector parameterization approach. Numerical results for the different problems provide optimal profiles for tributary deviation flowrate through a nearby wetland, aeration rates and fish removal rates, as restoration strategies.  相似文献   
90.
An efficient protocol for the rapid room temperature deacetylation of carbohydrate derivatives using CuFe2O4 nanoparticles as an inexpensive and reusable catalyst is presented. After separation of the catalyst with an external magnet, the reaction products are easily obtained in good purity and excellent yields.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号