全文获取类型
收费全文 | 8687篇 |
免费 | 1286篇 |
国内免费 | 907篇 |
专业分类
化学 | 4622篇 |
晶体学 | 72篇 |
力学 | 405篇 |
综合类 | 41篇 |
数学 | 640篇 |
物理学 | 2952篇 |
无线电 | 2148篇 |
出版年
2024年 | 19篇 |
2023年 | 209篇 |
2022年 | 188篇 |
2021年 | 239篇 |
2020年 | 309篇 |
2019年 | 263篇 |
2018年 | 231篇 |
2017年 | 232篇 |
2016年 | 346篇 |
2015年 | 362篇 |
2014年 | 420篇 |
2013年 | 576篇 |
2012年 | 637篇 |
2011年 | 684篇 |
2010年 | 487篇 |
2009年 | 517篇 |
2008年 | 522篇 |
2007年 | 470篇 |
2006年 | 455篇 |
2005年 | 443篇 |
2004年 | 341篇 |
2003年 | 271篇 |
2002年 | 282篇 |
2001年 | 207篇 |
2000年 | 233篇 |
1999年 | 229篇 |
1998年 | 193篇 |
1997年 | 165篇 |
1996年 | 200篇 |
1995年 | 159篇 |
1994年 | 154篇 |
1993年 | 138篇 |
1992年 | 136篇 |
1991年 | 106篇 |
1990年 | 71篇 |
1989年 | 82篇 |
1988年 | 57篇 |
1987年 | 48篇 |
1986年 | 42篇 |
1985年 | 39篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1970年 | 6篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
922.
923.
924.
Hung-Yan Gu Chiu-Yu Tseng Lin-Shan Lee 《Signal Processing, IEEE Transactions on》1991,39(8):1743-1752
Hidden Markov models (HMMs) with bounded state durations (HMM/BSD) are proposed to explicitly model the state durations of HMMs and more accurately consider the temporal structures existing in speech signals in a simple, direct, but effective way. A series of experiments have been conducted for speaker dependent applications using 408 highly confusing first-tone Mandarin syllables as the example vocabulary. It was found that in the discrete case the recognition rate of HMM/BSD (78.5%) is 9.0%, 6.3%, and 1.9% higher than the conventional HMMs and HMMs with Poisson and gamma distribution state durations, respectively. In the continuous case (partitioned Gaussian mixture modeling), the recognition rates of HMM/BSD (88.3% with 1 mixture, 88.8% with 3 mixtures, and 89.4% with 5 mixtures) are 6.3%, 5.0%, and 5.5% higher than those of the conventional HMMs, and 5.9% (with 1 mixture), 3.9% (with 3 mixtures) and 3.1% (with 1 mixture), 1.8% (with 3 mixtures) higher than HMMs with Poisson and gamma distributed state durations, respectively 相似文献
925.
对1.5μm波导型声光TE-TM模式转换光滤波器进行了研究。采用了可降低驱动功率的表面声波导结构。在1.5 ̄1.6μm波段实现了可调滤光,通带宽度小于2nm,达到97¥以上转换率所需的射频驱动功率约80mW(19dBm),器件总插入损耗约9dB。 相似文献
926.
927.
GGG晶体板状激光器特性的研究 总被引:1,自引:0,他引:1
测试GGG晶体板条的激光性能,并在高功率泵浦下对板条的热聚焦效应进行了研究. 相似文献
928.
发光效率是彩色AC PDP的一个重要性能指标。为正确测试该参数,针对器件特有的性能,用不同方法测试其功耗和光通量,计算得发光效率,分析讨论不同方法测得的数值,对其中有的方法测试值予以修正,最后提出一种简易可行的测试方法。 相似文献
929.
J R Gu H Q Jiang L P He D Z Li X M Zhou W L Dai L F Qian Y Q Chen C Schweinfest T Papas 《Science in China. Series B, Chemistry, life sciences & earth sciences》1991,34(11):1312-1318
From a subtracting cDNA library constructed from normal liver versus human primary hepatic cancer (PHC) a cDNA clone pG8 was isolated. Using it as a probe, RNA extracted from one human liver and 9 PHC samples were analyzed by Northern hybridization. As expected, its mRNA was highly expressed in liver; however, the expression was strikingly suppressed in PHC. Only weak signal was observed in 2 out of 9 PHC, while no signal was detectable in the other 7 samples. Utilizing pG8 as a probe, DNA from the same PHC specimens was analyzed after MspI digestion and Southern hybridization. Deletion of DNA fragment was observed in 4 out of 9 samples. In further study of cancer and non-cancerous liver from other 7 PHC patients, similar deletion of DNA fragments in cancer was observed in 4 out of 7 samples. After sequencing of the clone of 572 bp, it was unexpectedly found that pG8 was completely homologous to the coding sequence of transthyretin, TTR gene, as TTR (or prealbumin) gene has been known to be linked to a hereditary disorder, familial amyloidosis (FAP), and related to thyroxine transport and binding to retinol-RBP (the retinol binding protein) complex. This is the first report of a study on TTR in human primary hepatic cancer. Since TTR gene was strikingly suppressed in mRNA expression and possibly defective in its gene structure, it was strongly implicated that TTR might be an important gene marker or a candidate of anti-oncogene for human PHC. The biological activity of TTR gene is under study. 相似文献
930.
一类新的k-次增生型变分包含解的存在性及其具有混合误差项的Ishikawa迭代逼近 总被引:1,自引:0,他引:1
在实自反Banach空间中,引入和研究了一类新的k-次增生型变分包含问题,证明了这类变分包含解的存在性、唯一性及其具有混合误差项的Ishikawa迭代程序的收敛性.本文结果本质地改进、发展和统一了张石生和曾六川等人的一系列相关结果. 相似文献