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   144384篇
  免费   5174篇
  国内免费   2832篇
电工技术   4566篇
技术理论   2篇
综合类   2188篇
化学工业   17068篇
金属工艺   7909篇
机械仪表   5601篇
建筑科学   4928篇
矿业工程   1185篇
能源动力   4216篇
轻工业   9017篇
水利工程   1374篇
石油天然气   2433篇
武器工业   293篇
无线电   21339篇
一般工业技术   28116篇
冶金工业   27985篇
原子能技术   1943篇
自动化技术   12227篇
  2024年   700篇
  2023年   1098篇
  2022年   1863篇
  2021年   2427篇
  2020年   1903篇
  2019年   1764篇
  2018年   2370篇
  2017年   2483篇
  2016年   2356篇
  2015年   2437篇
  2014年   3406篇
  2013年   7164篇
  2012年   4937篇
  2011年   6417篇
  2010年   5271篇
  2009年   6046篇
  2008年   6102篇
  2007年   6072篇
  2006年   5715篇
  2005年   4998篇
  2004年   4372篇
  2003年   4170篇
  2002年   3754篇
  2001年   3972篇
  2000年   3723篇
  1999年   4139篇
  1998年   10624篇
  1997年   7059篇
  1996年   5550篇
  1995年   3811篇
  1994年   3279篇
  1993年   3114篇
  1992年   1962篇
  1991年   1855篇
  1990年   1734篇
  1989年   1517篇
  1988年   1317篇
  1987年   956篇
  1986年   960篇
  1985年   987篇
  1984年   860篇
  1983年   752篇
  1982年   746篇
  1981年   705篇
  1980年   598篇
  1979年   500篇
  1978年   440篇
  1977年   557篇
  1976年   969篇
  1975年   310篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
The mobilization and translocation of carbohydrates and mineral nutrients from vegetative plant parts to grains are pivotal for grain filling, often involving a whole plant senescence process. Loss of greenness is a hallmark of leaf senescence. However, the relationship between crop yield and senescence has been controversial for many years. Here, in this study, the overexpression and RNA interference lines of gene of OsNYC3 (Non-Yellow Coloring 3), a chlorophyll catabolism gene, were investigated. Furthermore, exogenous phytohormones were applied, and a treatment of alternate wetting and moderate drying (AWMD) was introduced to regulate the processes of leaf senescence. The results indicated that the delayed senescence of the “STAY-GREEN” trait of rice is undesirable for the process of grain filling, and it would cause a lower ratio of grain filling and lower grain weight of inferior grains, because of unused assimilates in the stems and leaves. Through the overexpression of OsNYC3, application of exogenous chemicals of abscisic acid (ABA), and water management of AWMD, leaf photosynthesis was less influenced, a high ratio of carbohydrate assimilates was partitioned to grains other than leaves and stems as labeled by 13C, grain filling was improved, especially for inferior spikelets, and activities of starch-synthesizing enzymes were enhanced. However, application of ethephon not only accelerated leaf senescence, but also caused seed abortion and grain weight reduction. Thus, plant senescence needs to be finely adjusted in order to make a contribution to crop productivity.  相似文献   
63.
64.
张立国  程瑶  金梅  王娜 《计量学报》2021,42(4):515-520
室内场景的语义分割一直是深度学习语义分割领域的一个重要方向.室内语义分割主要存在的问题有语义类别多、很多物体类会有相互遮挡、某些类之间相似性较高等.针对这些问题,提出了一种用于室内场景语义分割的方法.该方法在BiSeNet(bilateral segmentation network)的网络结构基础上,引入了一个空洞金...  相似文献   
65.
Adenosine A2A receptors (A2AR) control fear memory and the underlying processes of synaptic plasticity in the amygdala. In other brain regions, A2AR activation is ensured by ATP-derived extracellular adenosine formed by ecto-5′-nucleotidase or CD73. We now tested whether CD73 is also responsible to provide for the activation of A2AR in controlling fear memory and amygdala long-term potentiation (LTP). The bilateral intracerebroventricular injection of the CD73 inhibitor αβ-methylene ADP (AOPCP, 1 nmol/ventricle/day) phenocopied the effect of the A2AR blockade by decreasing the expression of fear memory, an effect disappearing in CD73-knockout (KO) mice and in forebrain neuronal A2AR-KO mice. In the presence of PPADS (20 μM) to eliminate any modification of ATP/ADP-mediated P2 receptor effects, both AOPCP (100 μM) and the A2AR antagonist, SCH58261 (50 nM), decreased LTP magnitude in synapses of projection from the external capsula into the lateral amygdala, an effect eliminated in slices from both forebrain neuronal A2AR-KO mice and CD73-KO mice. These data indicate a key role of CD73 in the process of A2AR-mediated control of fear memory and underlying synaptic plasticity processes in the amygdala, paving the way to envisage CD73 as a new therapeutic target to interfere with abnormal fear-like emotional processing.  相似文献   
66.
67.
68.
The extracellular circulating microRNA (miR)-200 regulates epithelial-mesenchymal transition and, thus, plays an essential role in the metastatic cascade and has shown itself to be a promising prognostic and predictive biomarker in metastatic breast cancer (MBC). Expression levels of the plasma miR-200 family were analyzed in relationship to systemic treatment, circulating tumor cells (CTC) count, progression-free survival (PFS), and overall survival (OS). Expression of miR-200a, miR-200b, miR-200c, miR-141, and miR-429, and CTC status (CTC-positive ≥ 5 CTC/7.5 mL) was assessed in 47 patients at baseline (BL), after the first completed cycle of a new line of systemic therapy (1C), and upon the progression of disease (PD). MiR-200a, miR-200b, and miR-141 expression was reduced at 1C compared to BL. Upon PD, all miR-200s were upregulated compared to 1C. At all timepoints, the levels of miR-200s were elevated in CTC-positive versus CTC-negative patients. Further, heightened miR-200s expression and positive CTC status were associated with poorer OS at BL and 1C. In MBC patients, circulating miR-200 family members decreased after one cycle of a new line of systemic therapy, were elevated during PD, and were indicative of CTC status. Notably, increased levels of miR-200s and elevated CTC count correlated with poorer OS and PFS. As such, both are promising biomarkers for optimizing the clinical management of MBC.  相似文献   
69.
The ADP/ATP carrier (AAC) plays a central role in oxidative metabolism by exchanging ATP and ADP across the inner mitochondrial membrane. Previous experiments have shown the involvement of the matrix loops of AAC in its function, yet potential mechanisms remain largely elusive. One obstacle is the limited information on the structural dynamics of the matrix loops. In the current work, unbiased all-atom molecular dynamics (MD) simulations were carried out on c-state wild-type AAC and mutants. Our results reveal that: (1) two ends of a matrix loop are tethered through interactions between the residue of triplet 38 (Q38, D143 and Q240) located at the C-end of the odd-numbered helix and residues of the [YF]xG motif located before the N-end of the short matrix helix in the same domain; (2) the initial progression direction of a matrix loop is determined by interactions between the negatively charged residue of the [DE]G motif located at the C-end of the short matrix helix and the capping arginine (R30, R139 and R236) in the previous domain; (3) the two chemically similar residues D and E in the highly conserved [DE]G motif are actually quite different; (4) the N-end of the M3 loop is clamped by the [DE]G motif and the capping arginine of domain 2 from the two sides, which strengthens interactions between domain 2 and domain 3; and (5) a highly asymmetric stable core exists within domains 2 and 3 at the m-gate level. Moreover, our results help explain almost all extremely conserved residues within the matrix loops of the ADP/ATP carriers from a structural point of view. Taken together, the current work highlights asymmetry in the three matrix loops and implies a close relationship between asymmetry and ADP/ATP transport.  相似文献   
70.
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