全文获取类型
收费全文 | 90624篇 |
免费 | 6756篇 |
国内免费 | 4698篇 |
专业分类
电工技术 | 2016篇 |
技术理论 | 5篇 |
综合类 | 6841篇 |
化学工业 | 9532篇 |
金属工艺 | 20226篇 |
机械仪表 | 7722篇 |
建筑科学 | 16128篇 |
矿业工程 | 2164篇 |
能源动力 | 1666篇 |
轻工业 | 2209篇 |
水利工程 | 914篇 |
石油天然气 | 3545篇 |
武器工业 | 613篇 |
无线电 | 2342篇 |
一般工业技术 | 8342篇 |
冶金工业 | 14403篇 |
原子能技术 | 863篇 |
自动化技术 | 2547篇 |
出版年
2024年 | 231篇 |
2023年 | 1044篇 |
2022年 | 2578篇 |
2021年 | 2983篇 |
2020年 | 2795篇 |
2019年 | 2037篇 |
2018年 | 1675篇 |
2017年 | 2535篇 |
2016年 | 2811篇 |
2015年 | 3141篇 |
2014年 | 5332篇 |
2013年 | 4880篇 |
2012年 | 6330篇 |
2011年 | 7563篇 |
2010年 | 5570篇 |
2009年 | 5808篇 |
2008年 | 4750篇 |
2007年 | 6043篇 |
2006年 | 5503篇 |
2005年 | 4613篇 |
2004年 | 3772篇 |
2003年 | 3355篇 |
2002年 | 2852篇 |
2001年 | 2437篇 |
2000年 | 2122篇 |
1999年 | 1725篇 |
1998年 | 1377篇 |
1997年 | 1283篇 |
1996年 | 1097篇 |
1995年 | 847篇 |
1994年 | 728篇 |
1993年 | 503篇 |
1992年 | 447篇 |
1991年 | 305篇 |
1990年 | 272篇 |
1989年 | 202篇 |
1988年 | 147篇 |
1987年 | 82篇 |
1986年 | 45篇 |
1985年 | 47篇 |
1984年 | 37篇 |
1983年 | 25篇 |
1982年 | 30篇 |
1981年 | 21篇 |
1980年 | 47篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
为了系统地评价胸腺五肽作为辅助药物治疗各种肺癌的疗效及其对机体免疫功能的影响,利用电子检索收集有关胸腺五肽联合放疗或化疗方案治疗肺癌的临床随机对照试验文献,对符合纳入标准的文献,采用RevMan5.3 软件进行系统评价。最终共纳入文献 9 篇,总样本量 784 例。Meta 分析结果表明,胸腺五肽作为辅助药物治疗各种肺癌提高总有效率的差异无统计学意义[OR = 1.44, 95%CI(0.99, 2.10), P =0.06 > 0.05]。在对免疫功能的影响方面,胸腺五肽的使用显著增高外周血中的 CD3+ 细胞水平[OR = 5.88, 95% CI(2.34, 9.42), P =0.001],CD4+ 细胞水平也显著上升[OR =8.32, 95%CI(5.22, 11.42), P < 0.00001] , CD4+ /CD8+比值也有明显的提高[OR = 0.38, 95% CI(0.18, 0.59), P=0.0002],但 CD8+ 细胞水平的差异无统计学意义[OR =-3.12, 95% CI ( -9.02, 2.79), P >0.05]。总的来说,本研究在一定程度上反映了在辅助治疗肺癌方面,胸腺五肽能显著提高外周血中的 CD3+ 细胞水平、CD4+ 细胞水平、CD4+/CD8+ 比值。而对于治疗的有效率、CD8+ 细胞水平,差异无统计学意义。 相似文献
42.
43.
44.
热轧态中锰TRIP钢首先经650 ℃退火2 h,随后在550 ℃进行等温时效热处理,采用场发射扫描电镜(FE-SEM)研究该钢中P的偏聚和时效析出行为的变化情况。结果表明,中锰TRIP钢中P在晶界的偏聚是一种非平衡偏聚现象,临界时间约为50 h,与理论计算结果48 h较为吻合。在局部偏聚区域内,C与P存在共偏聚的关系,即P偏聚量高的地方,C含量也高。而合金元素Nb具有抑制P偏聚的效果,在20~70 h时效时间内,可以相对降低6.57%~19.5%的最大P偏聚量。根据电子背散射衍射(EBSD)菊池线分析,P偏聚量低于2.28at%时,P为固溶状态,高于2.28at.%时,P为析出状态。 相似文献
45.
Based on the phase transformation theories, especially the T0 concept of bainite transformation, alloy optimisation of bainitic steel with carbides has been carried out aiming at the produce of plastic mould with large cross-section. The effect of manganese and silicon on proeutectoid ferrite and bainite transformation is explored by dilatometric analysis, XRD and different microscopy techniques. The results show that after the alloy optimisation, the transformation of proeutectoid ferrite is suppressed and when the cooling rate is lower than 0·1°C?s??1, the new lower bainite transformation appears by decreasing carbon capacity of austenite and promoting carbide precipitation. Industrial production proves that the optimised alloy SDP1 can meet the demand for the plastic mould with the thickness of 1050?mm. 相似文献
46.
47.
《Ceramics International》2020,46(3):2868-2876
In order to improve the stability of PZT-based sensors, the mechanical, dielectric, ferroelectric and piezoelectric properties of PZT-5H under impact load were studied experimentally by using the separated Hopkinson pressure bar (SHPB) with an electrical output measurement device. At the same time, the experimental study on the material properties of PZT-5H before and after the impact was carried out. The effect of impact cracks on the output voltage of PZT-5H was also analyzed. The results show that the dynamic piezoelectric constants of PZT-5H under low stress impact (10–50 MPa) are different from those under quasi-static state, and the empirical relationship between them and the peak stress is obtained through experiments. The dielectric properties of PZT-5H did not change under low stress impact, but micro-cracks occurred in the material and dielectric loss increased at high frequencies. Under short circuit, the residual polarization intensity of PZT-5H decreases sharply due to impact load. While the impact load causes the secondary polarization and the increase of the residual polarization intensity of PZT under open circuit. When the stress is over 45 MPa, the PZT-5H breaks. The formation of cracks causes abnormal discharge voltage and gap discharge. 相似文献
48.
《Oil and Energy Trends》2019,44(8):58-60
Currency exchanges rates – updated monthly. Economic indicators of industrial production. Countries included: France, Germany, Italy, the United Kingdom, the United States, Canada, Japan (Total G-7), Eurozone and Total EU-28 (Total OECD). Updated monthly. Economic indicators of car registration in the United States, Canada, France, Germany, Italy, Poland, Spain, Turkey, the United Kingdom, Japan, Republic of Korea and Other OECD (Total OECD-30). Updated monthly. Monthly averages of crude steel production in thousand metric tons for the United States, Canada, Brazil, Mexico, Austria, Belgium, Czech Republic, France, Germany, Italy, Netherlands, Poland, Spain, Sweden, Turkey, the United Kingdom, Russia, Ukraine, South Africa, Iran, China, India, Japan, Republic of Korea, Taiwan and Australia. 相似文献
49.
Slim Salhi Jihen Mahfoudh Souhir Abid Leonard‐Ionut Atanase Marcel Popa Christelle Delaite 《Polymer International》2020,69(11):1161-1168
A series of random polyesteramides (PEAs) with a range of molar composition from 90/10 to 50/50 were synthesized by direct melt polycondensation of ε‐caprolactone and l ‐alanine. Their structure was fully characterized by Fourier transform IR and NMR spectroscopy. The resulting copolymers are completely amorphous with the exception of PEA‐90/10 which possesses a semicrystalline structure. These PEAs present increasing glass transition temperatures at increasing l ‐alanine contents and exhibit fairly good thermal stability with 10% mass loss temperatures reaching 315 °C. © 2020 Society of Industrial Chemistry 相似文献
50.
《International Journal of Hydrogen Energy》2020,45(7):4054-4064
The feasibility of microbial hydrogen consumption to mitigate the hydrogen embrittlement (HE) under different cathodic potentials was evaluated using the Devanathan-Stachurski electrochemical test and the hydrogen permeation efficiency η. The hydrogen permeation efficiency η in the presence of strain GA-1 was lower than that in sterile medium. The cathodic potential inhibited the adherence of strain GA-1 to AISI 4135 steel surface, thereby reducing the hydrogen consumption of strain GA-1. The adherent GA-1 cells were capable of consuming ‘cathodic hydrogen’ and reducing the proportions of absorbed hydrogen, indicating that it is theoretically possible to control HE by hydrogen-consuming microbes. 相似文献