全文获取类型
收费全文 | 88122篇 |
免费 | 9258篇 |
国内免费 | 4866篇 |
专业分类
电工技术 | 7114篇 |
综合类 | 6151篇 |
化学工业 | 21251篇 |
金属工艺 | 11060篇 |
机械仪表 | 5517篇 |
建筑科学 | 8126篇 |
矿业工程 | 1988篇 |
能源动力 | 5433篇 |
轻工业 | 5105篇 |
水利工程 | 1503篇 |
石油天然气 | 3130篇 |
武器工业 | 1097篇 |
无线电 | 5985篇 |
一般工业技术 | 12112篇 |
冶金工业 | 3761篇 |
原子能技术 | 1028篇 |
自动化技术 | 1885篇 |
出版年
2024年 | 528篇 |
2023年 | 1749篇 |
2022年 | 2990篇 |
2021年 | 3496篇 |
2020年 | 3533篇 |
2019年 | 2959篇 |
2018年 | 2795篇 |
2017年 | 3553篇 |
2016年 | 3423篇 |
2015年 | 3508篇 |
2014年 | 4966篇 |
2013年 | 5606篇 |
2012年 | 5918篇 |
2011年 | 6326篇 |
2010年 | 4532篇 |
2009年 | 5027篇 |
2008年 | 4263篇 |
2007年 | 5345篇 |
2006年 | 5154篇 |
2005年 | 4115篇 |
2004年 | 3509篇 |
2003年 | 2904篇 |
2002年 | 2588篇 |
2001年 | 2223篇 |
2000年 | 1900篇 |
1999年 | 1586篇 |
1998年 | 1370篇 |
1997年 | 1210篇 |
1996年 | 946篇 |
1995年 | 816篇 |
1994年 | 661篇 |
1993年 | 489篇 |
1992年 | 461篇 |
1991年 | 394篇 |
1990年 | 309篇 |
1989年 | 248篇 |
1988年 | 183篇 |
1987年 | 117篇 |
1986年 | 95篇 |
1985年 | 87篇 |
1984年 | 86篇 |
1983年 | 57篇 |
1982年 | 68篇 |
1981年 | 30篇 |
1980年 | 32篇 |
1979年 | 15篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1959年 | 16篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
针对目前蒸汽吞吐产量预测模型假设条件简单、普适性差等问题,一般采用测试法和类比法综合确定海上稠油油田蒸汽吞吐初期产量。由于目前海上油田通常只开展常规测试,无法直接获得热采开发初期产量。笔者提出海上稠油油田蒸汽吞吐初期产量确定新方法,建立蒸汽吞吐相对于常规开发的初期产量倍数预测模型,通过蒸汽吞吐产量倍数,将常规测试确定的产量转化为蒸汽吞吐产量。研究表明,蒸汽吞吐初期产量倍数主要受储集层渗透率、原油黏度、注入强度、蒸汽干度等因素影响,利用正交试验设计和多元回归等方法,建立海上稠油油田蒸汽吞吐初期产量倍数与油藏地质参数及注入参数之间的非线性预测模型,该模型经实际生产数据验证,预测误差小于5%,可靠性高,能够为海上稠油油田蒸汽吞吐初期产量的确定提供依据。 相似文献
72.
The flame front deformation instability of low-velocity filtration combustion within an inert packed bed is studied based on the initial preheating non-uniformity. Based on the experimental phenomena, an initial thermal perturbation model is numerically proposed so as to predict the deformation behaviors of the flame front instabilities. The numerical prediction indicates that the assumption of an initial thermal perturbation is a feasible explanation as the cause of the flame front inclination instability. As the initial thermal perturbation increases, the phenomena of the flame front break and shrinking instabilities could easily occur at high filtration velocity or low equivalence ratio. Moreover, the evolutions of the flame front break rate and the shrinking rate are quantitatively analyzed. 相似文献
73.
Rhyzopertha dominica is a key pest of stored grain. Understanding the movement of this beetle on broad geographic scales is crucial, particularly when developing strategies to prevent the spread of phosphine resistance. We assessed population genetic structuring in this pest across Turkey, using a combination of mitochondrial (cytochrome oxidase I) and microsatellite markers. In addition, we screened samples for Wolbachia, as this endosymbiont has previously been suggested to be associated with low mitochondrial genetic diversity in this beetle. Mitochondrial genetic diversity was low, with only six haplotypes identified. The genetic diversity was, however, substantially higher than that previously found in Australia or India, suggesting that R. dominica may have originated in the Middle East. Wolbachia were detected only at a single site, indicating they are not impacting the mitochondrial genetic diversity of R. dominica across Turkey. Microsatellite markers indicated there is significant geographic genetic structuring across Turkey, even among sites less than 100 km apart, suggesting there is little movement of beetles across regions within the country. This contrasts with the significantly higher levels of gene-flow found in Australia and the United States. We suggest that the limited movement of beetles across Turkey may be due to a combination of the historically localised agricultural practices (which limits anthropogenic movement among regions), and the mountainous landscape (which limits active flight among regions). Our results demonstrate that the movement of stored product pests may differ significantly across studies conducted in different countries. As a consequence, phosphine resistance management strategies must incorporate region specific information on the extent of beetle movement. 相似文献
74.
PETROLEUM POTENTIAL, THERMAL MATURITY AND THE OIL WINDOW OF OIL SHALES AND COALS IN CENOZOIC RIFT BASINS, CENTRAL AND NORTHERN THAILAND 总被引:1,自引:0,他引:1
Oil shales and coals occur in Cenozoic rift basins in central and northern Thailand. Thermally immature outcrops of these rocks may constitute analogues for source rocks which have generated oil in several of these rift basins. A total of 56 oil shale and coal samples were collected from eight different basins and analysed in detail in this study. The samples were analysed for their content of total organic carbon (TOC) and elemental composition. Source rock quality was determined by Rock‐Eval pyrolysis. Reflected light microscopy was used to analyse the organic matter (maceral) composition of the rocks, and the thermal maturity was determined by vitrinite reflectance (VR) measurements. In addition to the 56 samples, VR measurements were carried out in three wells from two oil‐producing basins and VR gradients were constructed. Rock‐Eval screening data from one of the wells is also presented. The oil shales were deposited in freshwater (to brackish) lakes with a high preservation potential (TOC contents up to 44.18 wt%). They contain abundant lamalginite and principally algal‐derived fluorescing amorphous organic matter followed by liptodetrinite and telalginite (Botryococcus‐type). Huminite may be present in subordinate amounts. The coals are completely dominated by huminite and were formed in freshwater mires. VR values from 0.38 to 0.47%Ro show that the exposed coals are thermally immature. VR values from the associated oil shales are suppressed by 0.11 to 0.28%Ro. The oil shales have H/C ratios >1.43, and Hydrogen Index (HI) values are generally >400 mg HC/g TOC and may reach 704 mg HC/ gTOC. In general, the coals have H/C ratios between about 0.80 and 0.90, and the HI values vary considerably from approximately 50 to 300 mg HC/gTOC. The HImax of the coals, which represent the true source rock potential, range from ~160 to 310 mg HC/g TOC indicating a potential for oil/gas and oil generation. The steep VR curves from the oil‐producing basins reflect high geothermal gradients of ~62°C/km and ~92°C/km. The depth to the top oil window for the oil shales at a VR of ~0.70%Ro is determined to be between ~1100 m and 1800 m depending on the geothermal gradient. The kerogen composition of the oil shales and the high geothermal gradients result in narrow oil windows, possibly spanning only ~300 to 400 m in the warmest basins. The effective oil window of the coals is estimated to start from ~0.82 to 0.98%Ro and burial depths of ~1300 to 1400 m (~92°C/km) and ~2100 to 2300 m (~62°C/km) are necessary for efficient oil expulsion to occur. 相似文献
75.
76.
77.
Feng Juanni Guo Xuefeng Xu Chunjie Zhang Zhongming 《中国稀土学报(英文版)》2006,24(1):120-120
As-east mierostruetures and their distribution of Mg-Zn-Y ternary alloy with high magnesium, low zinc and yttrium were examined using Nikon Epiphot optical microscopy (OM), RigakuD/max-3C X- ray diffraetion (XRD), and JEOL JSM-6700F scanning electron microscopy (SEM) equipped with an energydispersive X-ray spectroscopy (EDS). In the as-east mierostructures, Yttrium and zinc tend to segregate at grain boundaries, 相似文献
78.
79.
80.