全文获取类型
收费全文 | 107769篇 |
免费 | 8818篇 |
国内免费 | 4524篇 |
专业分类
电工技术 | 6959篇 |
技术理论 | 22篇 |
综合类 | 17615篇 |
化学工业 | 9563篇 |
金属工艺 | 3674篇 |
机械仪表 | 5764篇 |
建筑科学 | 18272篇 |
矿业工程 | 5733篇 |
能源动力 | 2778篇 |
轻工业 | 6296篇 |
水利工程 | 6984篇 |
石油天然气 | 4537篇 |
武器工业 | 689篇 |
无线电 | 7358篇 |
一般工业技术 | 7172篇 |
冶金工业 | 5180篇 |
原子能技术 | 874篇 |
自动化技术 | 11641篇 |
出版年
2024年 | 156篇 |
2023年 | 1045篇 |
2022年 | 1765篇 |
2021年 | 2319篇 |
2020年 | 2231篇 |
2019年 | 1897篇 |
2018年 | 1801篇 |
2017年 | 2336篇 |
2016年 | 2844篇 |
2015年 | 3432篇 |
2014年 | 7407篇 |
2013年 | 5575篇 |
2012年 | 7365篇 |
2011年 | 7988篇 |
2010年 | 6380篇 |
2009年 | 7079篇 |
2008年 | 6325篇 |
2007年 | 8331篇 |
2006年 | 7682篇 |
2005年 | 6611篇 |
2004年 | 5454篇 |
2003年 | 4756篇 |
2002年 | 3881篇 |
2001年 | 3272篇 |
2000年 | 2722篇 |
1999年 | 2032篇 |
1998年 | 1375篇 |
1997年 | 1129篇 |
1996年 | 1043篇 |
1995年 | 906篇 |
1994年 | 749篇 |
1993年 | 604篇 |
1992年 | 491篇 |
1991年 | 330篇 |
1990年 | 324篇 |
1989年 | 304篇 |
1988年 | 238篇 |
1987年 | 166篇 |
1986年 | 124篇 |
1985年 | 94篇 |
1984年 | 89篇 |
1983年 | 46篇 |
1982年 | 36篇 |
1981年 | 58篇 |
1980年 | 42篇 |
1979年 | 40篇 |
1978年 | 26篇 |
1977年 | 23篇 |
1976年 | 22篇 |
1975年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Clive Bell 《Papers in Regional Science》2022,101(2):373-397
The effects of a rural roads programme depend on labour mobility, how the programme is financed, and agglomeration economies. If financed by a rural poll tax and cross-price effects and agglomeration economies are sufficiently small, the wage will rise, with some return migration. Taxes on trade act as countervailing distortions, yielding urban households some relief. Rural-urban commuting promotes the exploitation of agglomeration economies; taxes on international trade are then inferior to a poll tax. The change in the value, at producer prices, of the rural sector's net supply vector can be a poor measure of the programme's social profitability. 相似文献
3.
Christian Soize Roger Ghanem 《International journal for numerical methods in engineering》2022,123(1):268-290
The probabilistic learning on manifolds (PLoM) introduced in 2016 has solved difficult supervised problems for the “small data” limit where the number N of points in the training set is small. Many extensions have since been proposed, making it possible to deal with increasingly complex cases. However, the performance limit has been observed and explained for applications for which N is very small and for which the dimension of the diffusion-map basis is close to N. For these cases, we propose a novel extension based on the introduction of a partition in independent random vectors. We take advantage of this development to present improvements of the PLoM such as a simplified algorithm for constructing the diffusion-map basis and a new mathematical result for quantifying the concentration of the probability measure in terms of a probability upper bound. The analysis of the efficiency of this extension is presented through two applications. 相似文献
4.
5.
为应对"三软"煤层综放沿空掘巷围岩稳定性差的问题,通过数值模拟分析、揭示"三软"煤层中锚杆、锚索载荷变化规律及其与围岩变形相互作用关系,为"三软"煤层沿空掘巷锚网支护参数优化提供理论依据,改善了巷道支护状况,降低相邻工作面间保护煤柱压煤率,提高矿井经济效益和社会效益。 相似文献
6.
为了解汉江上游干支流沉积物细菌多样性以及确定性过程和随机性过程在沉积物细菌群落构建过程中的相对重要性,基于Illumina高通量测序技术,分析了环境因子对细菌群落组成的影响,采用非度量多维尺度(NMDS)排序探究了季节之间沉积物细菌群落的差异,并结合中性群落模型和标准化随机率量化了确定性过程和随机过程对群落构建的影响。结果表明:汉江上游及其支流细菌群落主要由变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、蓝藻门(Cyanophyta)、浮霉菌门(Planctomycetes)和酸杆菌门(Acidobacteria)等组成;细菌群落在不同季节有显著差异;地理距离和环境因子对细菌群落结构影响较小,确定性过程并未在细菌群落组成中起到主导作用;随机过程很大程度上影响了群落在秋季和春季的组成,是沉积物细菌群落构建的主导因素。 相似文献
7.
Abdellatif GHEDIRA 《粮油食品科技》2022,30(1):79-82
The International Olive Council(IOC) is an international intergovernmental organization dedicated to olive oil and table olives, aiming at modernizing olive production, coordinating olive policies, improving the regulation of international trade, defending the quality of the olive sector and promoting olive oil and table olives to increase their consumption. The IOC grants recognition of laboratories and tasting panels in annual trials when they meet the conditions given in the decisions adopting the IOC certificate for laboratories for the physico–chemical testing of olive oil and laboratories for the sensory analysis of virgin olive oils. The IOC establishes analysis methods applying to olive oils and olive pomace oils for purity, quality and organoleptic assessment. The IOC elaborates guides of storage conditions for olive oils and olive pomace oils, of managing virgin olive oil tasting panels and of sensory testing laboratories. In future works, the IOC includes activities to identify analytical criteria for detecting fraud and guaranteeing the quality of olive oils and olive pomace oils. 相似文献
8.
东北亚地区至少发育9个大型草原石林,属花岗岩石林的一种,是东北亚早白垩世巨量伸展和第四系冰川、风化作用的共同产物,主要特点是发育密集的近水平节理。本文通过整理岩浆岩专题填图和构造研究发现,这些石林的主体是早白垩世东北亚地区巨量伸展过程中形成众多的不对称花岗岩穹隆或同减薄岩体,岩体边部发育韧性剪切带,核部发布近水平岩浆流动面理,伸展和岩浆多期侵位导致与成矿密切相关的岩浆热液大量上涌,岩体抬升至地表,沿岩浆面理发育密集的近水平节理和部分垂直节理,后期沿这些构造面理发生的物理风化和化学作用(包括风蚀、冰川以及盐风化等)造就了千奇百怪的形态。草原石林是花岗岩地貌中的“另类”,不仅具有指示东北亚地区花岗岩形成时代(早白垩世)的特点,也是寻找晚中生代中国北方大规模成矿的良好标志体,而且风化形成的千姿百态的景色极具观赏价值,可以作为整个蒙古草原地区和大兴安岭南段地区特色的地学科普和生态旅游资源。 相似文献
9.
Corey R. Nelson Tyler Mrozowich Sean M. Park Simmone Dsouza Amy Henrickson Justin R. J. Vigar Hans-Joachim Wieden Raymond J. Owens Borries Demeler Trushar R. Patel 《International journal of molecular sciences》2021,22(1)
Rift Valley fever virus (RVFV) is a mosquito-transmitted virus from the Bunyaviridae family that causes high rates of mortality and morbidity in humans and ruminant animals. Previous studies indicated that DEAD-box helicase 17 (DDX17) restricts RVFV replication by recognizing two primary non-coding RNAs in the S-segment of the genome: the intergenic region (IGR) and 5′ non-coding region (NCR). However, we lack molecular insights into the direct binding of DDX17 with RVFV non-coding RNAs and information on the unwinding of both non-coding RNAs by DDX17. Therefore, we performed an extensive biophysical analysis of the DDX17 helicase domain (DDX17135–555) and RVFV non-coding RNAs, IGR and 5’ NCR. The homogeneity studies using analytical ultracentrifugation indicated that DDX17135–555, IGR, and 5’ NCR are pure. Next, we performed small-angle X-ray scattering (SAXS) experiments, which suggested that DDX17 and both RNAs are homogenous as well. SAXS analysis also demonstrated that DDX17 is globular to an extent, whereas the RNAs adopt an extended conformation in solution. Subsequently, microscale thermophoresis (MST) experiments were performed to investigate the direct binding of DDX17 to the non-coding RNAs. The MST experiments demonstrated that DDX17 binds with the IGR and 5’ NCR with a dissociation constant of 5.77 ± 0.15 µM and 9.85 ± 0.11 µM, respectively. As DDX17135–555 is an RNA helicase, we next determined if it could unwind IGR and NCR. We developed a helicase assay using MST and fluorescently-labeled oligos, which suggested DDX17135–555 can unwind both RNAs. Overall, our study provides direct evidence of DDX17135–555 interacting with and unwinding RVFV non-coding regions. 相似文献
10.