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   25299篇
  免费   2206篇
  国内免费   831篇
电工技术   1359篇
技术理论   1篇
综合类   1383篇
化学工业   4511篇
金属工艺   1329篇
机械仪表   1390篇
建筑科学   1869篇
矿业工程   578篇
能源动力   923篇
轻工业   1649篇
水利工程   342篇
石油天然气   1349篇
武器工业   118篇
无线电   3176篇
一般工业技术   3264篇
冶金工业   1441篇
原子能技术   347篇
自动化技术   3307篇
  2024年   247篇
  2023年   437篇
  2022年   716篇
  2021年   1041篇
  2020年   737篇
  2019年   678篇
  2018年   723篇
  2017年   828篇
  2016年   777篇
  2015年   941篇
  2014年   1251篇
  2013年   1594篇
  2012年   1574篇
  2011年   1723篇
  2010年   1397篇
  2009年   1443篇
  2008年   1342篇
  2007年   1238篇
  2006年   1349篇
  2005年   1163篇
  2004年   841篇
  2003年   758篇
  2002年   759篇
  2001年   541篇
  2000年   522篇
  1999年   601篇
  1998年   572篇
  1997年   462篇
  1996年   446篇
  1995年   345篇
  1994年   280篇
  1993年   191篇
  1992年   174篇
  1991年   117篇
  1990年   92篇
  1989年   72篇
  1988年   89篇
  1987年   48篇
  1986年   44篇
  1985年   25篇
  1984年   33篇
  1983年   19篇
  1982年   27篇
  1981年   12篇
  1980年   10篇
  1979年   15篇
  1977年   4篇
  1976年   9篇
  1975年   4篇
  1965年   5篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Distribution of polychlorinated biphenyls in the Newark Bay Estuary   总被引:2,自引:0,他引:2  
As part of the NJ Toxics Reduction Workplan for NY/NJ Harbor, ambient water samples were collected at 15 locations along the tidal portions of the Hackensack, Passaic, Raritan, Rahway and Elizabeth Rivers, and in Newark Bay, the Arthur Kill, and Kill van Kull. A Trace Organics Platform Sampler was used to collect a total of 73 dissolved phase and 73 suspended sediment phase samples between June 2000 and May 2002. These samples were analyzed for spatial and wet versus dry weather trends in the 114 polychlorinated biphenyls (PCBs; modified USEPA Method 1668A). Mean total PCB concentrations at the sampling locations ranged between 3.45 and 56 ng/L. PCB homolog groups distribution patterns at the sampling locations are presented.  相似文献   
102.
103.
104.
Jin  Qiangguo  Chen  Qi  Meng  Zhaopeng  Wang  Bing  Su  Ran 《Neural Processing Letters》2020,52(2):1005-1022
Neural Processing Letters - Segmentation of retinal vessels in fundus images plays a very important role in diagnosing relevant diseases. In this paper, we have constructed automated segmentation...  相似文献   
105.
Unstable and low-abundance protein complexes represent a large family of transient protein complexes that are difficult to characterize, even by means of high-resolution NMR spectroscopy. A method to assign the NMR signals of these unstable complexes through a combination of selective isotope labeling of amino acids in a protein and site-specific labeling the protein with a paramagnetic tag is presented herein. By using this method, the resonances of unstable thioester intermediate complex (lifetime <5 h and highest concentration ≈20 μm ) generated by Staphylococcus aureus sortase A and its peptide substrate under a real-time reaction have been assigned.  相似文献   
106.
107.
Host Defense Peptides (HDPs) have gained considerable interest due to the omnipresent threat of bacterial infection as a serious public health concern. However, development of HDPs is impeded by several drawbacks, such as poor selectivity, susceptibility to proteolytic degradation, low-to-moderate activity and requiring complex syntheses. Herein we report a class of lipo-linear α/urea-γ-AApeptides with a hybrid backbone and low molecular weight. The heterogeneous backbone not only enhances chemodiversity, but also shows effective antimicrobial activity against Gram-positive bacteria and is capable of disrupting bacterial membranes and killing bacteria rapidly. Given their low molecular weight and ease of access via facile synthesis, they could be practical antibiotic agents.  相似文献   
108.
When air is injected into silicone oil contained in a horizontal Hele-Shaw cell, a single air bubble forms and grows showing various interesting phenomena. In this study the effects of the bubble front velocity, air injection velocity at a nozzle, fluid properties and cell depth on the stability of the growing bubble were investigated experimentally. By using the modified capillary number involving the aspect ratio, we obtained the onset conditions of the unstable bubble. Also, the bubble width was analyzed both quantitatively and qualitatively. Before the bubble experiences splitting, the bubble front velocity is almost proportional to the air injection velocity. Therefore the latter velocity may be used in a practical sense.  相似文献   
109.
Photo-assisted one-step electrodeposition has been applied to help in forming smooth and dense CuInSe2 films. The difference in surface morphology and crystalline quality between CuInSe2 films with various photo-assistance has been investigated. In the photo-assisted electrodeposition process, the many kinds of lamps providing maximum light intensity at about 380 to 620 nm were used as light source to be irradiated onto the surface of Mo-coated soda-lime glass substrates. The results suggested effects of photo-assistance including activating surface diffusion and growing high-crystalline quality films with reduced defects during electrodeposition.  相似文献   
110.
Structural motifs for the BC2N superlattices were identified from a systematic search based on a greedy algorithm. Using a tree data structure, we have retrieved seven structural models for c-BC2N 1 × 1 × 1 lattice which were identified previously by Sun et al. [Phys. Rev. B 64, 094108 (2001)]. Furthermore, the atomic structures with the maximum number of C–C bonds for c-BC2N 2 × 2 × 2, 3 × 3 × 3, and 4 × 4 × 4 superlattices were found by imposing the greedy algorithm in the tree data structure. This new structural motif has not been previously proposed in the literature. A total of up to 512 atoms in the c-BC2N superlattice are taken into consideration. The atoms in these superlattices are in diamond-like structural form. Furthermore, the C atoms, as well as B and N atoms, form the octahedral motif separately. The octahedral structure consisting of C is bounded with {111} facets, and each facet is interfaced to a neighboring octahedral structure consisting of B and N atoms. The electronic and mechanical properties of newly identified low energy structures were analyzed.  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