全文获取类型
收费全文 | 226081篇 |
免费 | 4221篇 |
国内免费 | 851篇 |
专业分类
电工技术 | 3990篇 |
综合类 | 539篇 |
化学工业 | 33462篇 |
金属工艺 | 8840篇 |
机械仪表 | 6739篇 |
建筑科学 | 5607篇 |
矿业工程 | 1496篇 |
能源动力 | 5607篇 |
轻工业 | 21003篇 |
水利工程 | 2561篇 |
石油天然气 | 4208篇 |
武器工业 | 38篇 |
无线电 | 24595篇 |
一般工业技术 | 44696篇 |
冶金工业 | 43392篇 |
原子能技术 | 5241篇 |
自动化技术 | 19139篇 |
出版年
2021年 | 2250篇 |
2020年 | 1684篇 |
2019年 | 1990篇 |
2018年 | 3431篇 |
2017年 | 3411篇 |
2016年 | 3617篇 |
2015年 | 2598篇 |
2014年 | 3986篇 |
2013年 | 10607篇 |
2012年 | 6304篇 |
2011年 | 8326篇 |
2010年 | 6716篇 |
2009年 | 7410篇 |
2008年 | 7635篇 |
2007年 | 7632篇 |
2006年 | 6413篇 |
2005年 | 5926篇 |
2004年 | 5479篇 |
2003年 | 5355篇 |
2002年 | 4949篇 |
2001年 | 4985篇 |
2000年 | 4889篇 |
1999年 | 5127篇 |
1998年 | 13228篇 |
1997年 | 9238篇 |
1996年 | 7187篇 |
1995年 | 5180篇 |
1994年 | 4678篇 |
1993年 | 4444篇 |
1992年 | 3376篇 |
1991年 | 3221篇 |
1990年 | 3006篇 |
1989年 | 3088篇 |
1988年 | 2956篇 |
1987年 | 2534篇 |
1986年 | 2419篇 |
1985年 | 2901篇 |
1984年 | 2672篇 |
1983年 | 2489篇 |
1982年 | 2201篇 |
1981年 | 2355篇 |
1980年 | 2184篇 |
1979年 | 2233篇 |
1978年 | 2214篇 |
1977年 | 2564篇 |
1976年 | 3611篇 |
1975年 | 1906篇 |
1974年 | 1840篇 |
1973年 | 1874篇 |
1972年 | 1483篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
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
93.
94.
95.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
96.
97.
Iryna Smokovych Manja Krüger Michael Scheffler 《Journal of the European Ceramic Society》2019,39(13):3634-3642
Silica-based coating systems were developed using polymer derived ceramics (PDCs) technology. Ceramic composites on the base of a SiO2 and SiNO matrix and homogeneously distributed Mo5SiB2, SiB6, Si and B fillers were manufactured. The coating systems have low porosity and provide a high oxidation resistance up to 100 h at 800 °C and 1100 °C in air. The influence of temperature and atmosphere of pyrolysis on the polymer precursor, the volume fraction of filler materials on the chemical composition of compacts as well as their high-temperature oxidation protection was investigated. 相似文献
98.
Parsania P. H. Sankhavara Dharmesh B. Chopda Jalpa Patel Jignesh P. 《Polymer Bulletin》2020,77(6):3111-3128
Polymer Bulletin - Jute and glass composites of epoxy resin of (2E, 6E)-bis(4-hydroxybenzylidene)cyclohexanone (EBHBC) were prepared by compressing molding technique using three different hardeners... 相似文献
99.
Nathan M. Wilbur Antin M. O'Sullivan Kerry T. B. MacQuarrie Tommi Linnansaari R. Allen Curry 《河流研究与利用》2020,36(5):769-783
Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems. 相似文献
100.