全文获取类型
收费全文 | 31438篇 |
免费 | 5577篇 |
国内免费 | 4856篇 |
专业分类
化学 | 16183篇 |
晶体学 | 430篇 |
力学 | 1299篇 |
综合类 | 324篇 |
数学 | 2462篇 |
物理学 | 8825篇 |
无线电 | 12348篇 |
出版年
2024年 | 105篇 |
2023年 | 619篇 |
2022年 | 970篇 |
2021年 | 1165篇 |
2020年 | 1149篇 |
2019年 | 1135篇 |
2018年 | 1027篇 |
2017年 | 1085篇 |
2016年 | 1246篇 |
2015年 | 1468篇 |
2014年 | 1771篇 |
2013年 | 2324篇 |
2012年 | 2604篇 |
2011年 | 2655篇 |
2010年 | 2205篇 |
2009年 | 2346篇 |
2008年 | 2442篇 |
2007年 | 2280篇 |
2006年 | 2082篇 |
2005年 | 1731篇 |
2004年 | 1320篇 |
2003年 | 1173篇 |
2002年 | 1272篇 |
2001年 | 1088篇 |
2000年 | 936篇 |
1999年 | 676篇 |
1998年 | 424篇 |
1997年 | 375篇 |
1996年 | 322篇 |
1995年 | 296篇 |
1994年 | 249篇 |
1993年 | 215篇 |
1992年 | 199篇 |
1991年 | 157篇 |
1990年 | 131篇 |
1989年 | 104篇 |
1988年 | 91篇 |
1987年 | 69篇 |
1986年 | 64篇 |
1985年 | 53篇 |
1984年 | 45篇 |
1983年 | 35篇 |
1982年 | 29篇 |
1981年 | 31篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
Jingcheng Dong 《Archiv der Mathematik》2020,114(1):19-24
We introduce and study the notion of slightly trivial extensions of a fusion category which can be viewed as the first level of complexity of extensions. We also provide two examples of slightly trivial extensions which arise from rank 3 fusion categories. 相似文献
994.
995.
Microchimica Acta - A simple and sensitive electrochemical method was developed for the determination of trypsin by employing a specific heptapeptide (CRRRRRR) as a substrate. The positively... 相似文献
996.
997.
Gerold Jäger Changxing Dong Boris Goldengorin Paul Molitor Dirk Richter 《Journal of Heuristics》2014,20(1):107-124
We introduce a reduction technique for large instances of the traveling salesman problem (TSP). This approach is based on the observation that tours with good quality are likely to share many edges. We exploit this observation by neglecting the less important tour space defined by the shared edges, and searching the important tour subspace in more depth. More precisely, by using a basic TSP heuristic, we obtain a set of starting tours. We call the set of edges which are contained in each of these starting tours as pseudo-backbone edges. Then we compute the maximal paths consisting only of pseudo-backbone edges, and transform the TSP instance to another one with smaller size by contracting each such path to a single edge. This reduced TSP instance can be investigated more intensively, and each tour of the reduced instance can be expanded to a tour of the original instance. Combining our reduction technique with the currently leading TSP heuristic of Helsgaun, we experimentally investigate 32 difficult VLSI instances from the well-known TSP homepage. In our experimental results we set world records for seven VLSI instances, i.e., find better tours than the best tours known so far (two of these world records have since been improved upon by Keld Helsgaun and Yuichi Nagata, respectively). For the remaining instances we find tours that are equally good or only slightly worse than the world record tours. 相似文献
998.
999.
Catalytic activities of NHC‐PdCl2 species based on functionalized tetradentate imidazolium salt in three types of C‐C coupling reactions 下载免费PDF全文
A functionalized tetradentate imidazolium salt 9,10‐bis{di[2′‐(N‐ethylimidazolium‐1‐yl)ethyl]aminomethyl}anthracene tetrakis(hexafluorophosphate) ( 1 ) has been synthesized and characterized. The catalytic activity of the NHC‐PdCl2 species formed by compound 1 and PdCl2 was tested in Suzuki‐Miyaura, Heck‐Mizoroki and Sonogashira reactions. The results showed that this catalytic system was effective for above three types of C‐C coupling reactions. 相似文献
1000.