全文获取类型
收费全文 | 133354篇 |
免费 | 11885篇 |
国内免费 | 6764篇 |
专业分类
电工技术 | 2836篇 |
技术理论 | 1篇 |
综合类 | 7627篇 |
化学工业 | 46565篇 |
金属工艺 | 7852篇 |
机械仪表 | 4493篇 |
建筑科学 | 3533篇 |
矿业工程 | 3214篇 |
能源动力 | 3191篇 |
轻工业 | 24687篇 |
水利工程 | 1222篇 |
石油天然气 | 6061篇 |
武器工业 | 663篇 |
无线电 | 9394篇 |
一般工业技术 | 13420篇 |
冶金工业 | 5078篇 |
原子能技术 | 1486篇 |
自动化技术 | 10680篇 |
出版年
2024年 | 470篇 |
2023年 | 2149篇 |
2022年 | 3731篇 |
2021年 | 5131篇 |
2020年 | 4173篇 |
2019年 | 3990篇 |
2018年 | 3488篇 |
2017年 | 4330篇 |
2016年 | 4651篇 |
2015年 | 4670篇 |
2014年 | 6926篇 |
2013年 | 7870篇 |
2012年 | 9129篇 |
2011年 | 10503篇 |
2010年 | 7682篇 |
2009年 | 8313篇 |
2008年 | 7244篇 |
2007年 | 8801篇 |
2006年 | 8002篇 |
2005年 | 6720篇 |
2004年 | 5402篇 |
2003年 | 4739篇 |
2002年 | 3966篇 |
2001年 | 3169篇 |
2000年 | 3020篇 |
1999年 | 2508篇 |
1998年 | 2039篇 |
1997年 | 1566篇 |
1996年 | 1434篇 |
1995年 | 1147篇 |
1994年 | 1065篇 |
1993年 | 842篇 |
1992年 | 656篇 |
1991年 | 536篇 |
1990年 | 399篇 |
1989年 | 294篇 |
1988年 | 193篇 |
1987年 | 198篇 |
1986年 | 180篇 |
1985年 | 132篇 |
1984年 | 113篇 |
1983年 | 77篇 |
1982年 | 71篇 |
1981年 | 44篇 |
1980年 | 70篇 |
1979年 | 40篇 |
1978年 | 21篇 |
1977年 | 26篇 |
1976年 | 21篇 |
1974年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers (HCTs) during direct shear of infilled joints under constant normal stiffness (CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using three-dimensional (3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients (JRCs) of 8–10 and 18–20 with the ratios of infill thickness to asperity height (t/a) equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness. 相似文献
113.
114.
Peng Jiang Jiafeng Lu Kun Li Xiquan Chen Ruiqi Dan 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(5):381-386
AbstractPreparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe3O4/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe3O4/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe3O4 nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe3O4 nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe3O4/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has been enhanced. 相似文献
115.
116.
117.
Eicosapentaenoic acid (EPA) production by an oleaginous fungus Mortierella alpina expressing heterologous the Δ17‐desaturase gene under ordinary temperature
下载免费PDF全文
![点击此处可从《European Journal of Lipid Science and Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
118.
Rice straw is the most abundant agricultural residue on a global scale and is widely available as feedstock for cellulosic fuel production. However, it is highly recalcitrant to biochemical deconstruction and also generates inhibitors that affect enzymatic saccharification. Rice straw from eastern Arkansas was subjected to dilute acid pretreatment (160 °C, 48 min and 1.0% sulfuric acid) and solid-state fermentation with two lignocellulolytic fungi, Trametes hirsuta and Myrothecium roridum, and their saccharification efficacies were compared. T. hirsuta and M. roridum were tested separately; pretreatment of rice straw with either strain for seven days resulted in 19 and 70% enrichment of its holocellulose content, respectively. However, liquid chromatography analysis of the alkali extracts showed significant differences in cell wall degradation by T. hirsuta and M. roridum. T. hirsuta removed 15% more phenolic compounds and 38% more glucan than M. roridum, while M. roridum removed 77% more xylan than T. hirsuta. Fungal and dilute acid pretreated biomass was then hydrolyzed using Accellerase® 1500, a saccharification cocktail. Saccharification efficiency of M. roridum was 37% higher than that of dilute acid pretreatment of rice straw, requiring 8% lower enzyme loading and 50% shorter enzymatic hydrolysis duration. Alkali extraction of fungal pretreated biomass also yielded 10–15 g kg−1 of acid precipitable polymeric lignin (APPL), which is a valuable co-product for biorefineries. In comparison to dilute acid pretreatment, fungal pretreatment could be a cost-effective alternative for the degradation of recalcitrant biomass, such as rice straw. 相似文献
119.
Tomasz Wasiewicz Paulina Szyszka Miroslawa Cichorek Zorica Janjetovic Robert C. Tuckey Andrzej T. Slominski Michal A. Zmijewski 《International journal of molecular sciences》2015,16(4):6645-6667
Deregulated melanogenesis is involved in melanomagenesis and melanoma progression and resistance to therapy. Vitamin D analogs have anti-melanoma activity. While the hypercalcaemic effect of the active form of Vitamin D (1,25(OH)2D3) limits its therapeutic use, novel Vitamin D analogs with a modified side chain demonstrate low calcaemic activity. We therefore examined the effect of secosteroidal analogs, both classic (1,25(OH)2D3 and 25(OH)D3), and novel relatively non-calcemic ones (20(OH)D3, calcipotriol, 21(OH)pD, pD and 20(OH)pL), on proliferation, colony formation in monolayer and soft-agar, and mRNA and protein expression by melanoma cells. Murine B16-F10 and hamster Bomirski Ab cell lines were shown to be effective models to study how melanogenesis affects anti-melanoma treatment. Novel Vitamin D analogs with a short side-chain and lumisterol-like 20(OH)pL efficiently inhibited rodent melanoma growth. Moderate pigmentation sensitized rodent melanoma cells towards Vitamin D analogs, and altered expression of key genes involved in Vitamin D signaling, which was opposite to the effect on heavily pigmented cells. Interestingly, melanogenesis inhibited ligand-induced Vitamin D receptor translocation and ligand-induced expression of VDR and CYP24A1 genes. These findings indicate that melanogenesis can affect the anti-melanoma activity of Vitamin D analogs in a complex manner. 相似文献
120.
Hashim A.
Hashim 《国际强度与非线性控制杂志
》2020,30(10):3848-3870
》2020,30(10):3848-3870
This paper introduces two novel nonlinear stochastic attitude estimators developed on the Special Orthogonal Group with the tracking error of the normalized Euclidean distance meeting predefined transient and steady‐state characteristics. The tracking error is confined to initially start within a predetermined large set such that the transient performance is guaranteed to obey dynamically reducing boundaries and decrease smoothly and asymptotically to the origin in probability from almost any initial condition. The proposed estimators produce accurate attitude estimates with remarkable convergence properties using measurements obtained from low‐cost inertial measurement units. The estimators proposed in continuous form are complemented by their discrete versions for the implementation purposes. The simulation results illustrate the effectiveness and robustness of the proposed estimators against uncertain measurements and large initialization error, whether in continuous or discrete form. 相似文献