全文获取类型
收费全文 | 34630篇 |
免费 | 4240篇 |
国内免费 | 2878篇 |
专业分类
化学 | 17687篇 |
晶体学 | 309篇 |
力学 | 1525篇 |
综合类 | 109篇 |
数学 | 2923篇 |
物理学 | 8990篇 |
综合类 | 10205篇 |
出版年
2024年 | 108篇 |
2023年 | 620篇 |
2022年 | 961篇 |
2021年 | 1056篇 |
2020年 | 1093篇 |
2019年 | 1023篇 |
2018年 | 877篇 |
2017年 | 797篇 |
2016年 | 1265篇 |
2015年 | 1294篇 |
2014年 | 1639篇 |
2013年 | 2020篇 |
2012年 | 2628篇 |
2011年 | 2735篇 |
2010年 | 1869篇 |
2009年 | 1808篇 |
2008年 | 2019篇 |
2007年 | 1860篇 |
2006年 | 1686篇 |
2005年 | 1488篇 |
2004年 | 1127篇 |
2003年 | 850篇 |
2002年 | 854篇 |
2001年 | 704篇 |
2000年 | 712篇 |
1999年 | 1048篇 |
1998年 | 965篇 |
1997年 | 964篇 |
1996年 | 935篇 |
1995年 | 783篇 |
1994年 | 685篇 |
1993年 | 533篇 |
1992年 | 531篇 |
1991年 | 482篇 |
1990年 | 376篇 |
1989年 | 372篇 |
1988年 | 276篇 |
1987年 | 231篇 |
1986年 | 152篇 |
1985年 | 99篇 |
1984年 | 53篇 |
1983年 | 44篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
101.
New Kamenev-type oscillation criteria for second-order nonlinear differential equations with damping 总被引:1,自引:0,他引:1
Yuan Gong Sun 《Journal of Mathematical Analysis and Applications》2004,291(1):341-351
Some new oscillation criteria are established for the nonlinear damped differential equation (r(t)y′)′+p(t)y′+q(t)f(y)=0 that are different from most known ones in the sense that they are based on a class of new functions Φ(t,s,r) defined in the sequel. Our results are sharper than some previous results which can be seen by the examples at the end of this paper. 相似文献
102.
In 1934, Romanoff proved that there are a positive proportion natural numbers which can be expressed as the sum of a prime and a power of 2. In this paper, a quantitative version of this theorem is given. We show that the proportion is larger than 0.0868 and for a positive proportion of odd integers the number of such representations is between 1 and 16. 相似文献
103.
This paper has demonstrated that the Schwartz alternating process must converge if D-N alternating process has converged. Its technique is that the overlapping regions in Schwartz alternating process are considered as independent domains, then Schwartz alternating process could be transformed into D-N alter-nating process. Finally the convergence estimation of Schwartz alternating process could be obtained. The results show that its convergence rate is same as that of D-N alternating process. 相似文献
104.
105.
106.
This paper uses the method of linear approximation for impulsive systems and gets a theorem which guarantees a fishery modei to be asymptotically stable at its equilibrium point and gives the ecological explanation. 相似文献
107.
108.
A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.
相似文献109.
110.
Positron-lifetime experiments have been carried out on two undoped n-type liquid encapsulated Czochralski (LEC)-grown InP samples with different stoichiometric compositions in the temperature range 10-300 K. For temperatures below 120 K for P-rich InP and 100 K for In-rich InP, the positron average lifetime began to increase rapidly and then leveled off, which was associated with the charge state change of hydrogen indium vacancy complexes from (VInH4)+ to (VInH4)0. This phenomenon was more obvious in P-rich samples that have a higher concentration of VInH4. The transformation temperature of approximately 120 K suggests that the complex VInH4 is a donor defect and that the ionization energy is about 0.01 eV. The ionization of neutral VInH4 accounted for the decrease of the positron average lifetime when the sample was illuminated with a photon energy of 1.32 eV at 70 K. These results provide evidence for hydrogen complex defects in undoped LEC InP. 相似文献