全文获取类型
收费全文 | 2243篇 |
免费 | 55篇 |
国内免费 | 14篇 |
专业分类
化学 | 1305篇 |
晶体学 | 13篇 |
力学 | 47篇 |
数学 | 231篇 |
物理学 | 716篇 |
出版年
2022年 | 18篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 28篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 37篇 |
2015年 | 29篇 |
2014年 | 42篇 |
2013年 | 92篇 |
2012年 | 107篇 |
2011年 | 141篇 |
2010年 | 57篇 |
2009年 | 42篇 |
2008年 | 105篇 |
2007年 | 113篇 |
2006年 | 122篇 |
2005年 | 83篇 |
2004年 | 89篇 |
2003年 | 73篇 |
2002年 | 81篇 |
2001年 | 53篇 |
2000年 | 64篇 |
1999年 | 34篇 |
1998年 | 18篇 |
1997年 | 36篇 |
1996年 | 40篇 |
1995年 | 20篇 |
1994年 | 21篇 |
1993年 | 39篇 |
1992年 | 39篇 |
1991年 | 22篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 39篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1978年 | 25篇 |
1977年 | 23篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 23篇 |
1973年 | 29篇 |
排序方式: 共有2312条查询结果,搜索用时 343 毫秒
1.
2.
We investigate optimal harvesting control in a predator–prey model in which the prey population is represented by a first-order
partial differential equation with age-structure and the predator population is represented by an ordinary differential equation
in time. The controls are the proportions of the populations to be harvested, and the objective functional represents the
profit from harvesting. The existence and uniqueness of the optimal control pair are established. 相似文献
3.
Vijaya Gracias Alan F. Gasiecki Joel D. Moore Irini Akritopoulou-Zanze Stevan W. Djuric 《Tetrahedron letters》2006,47(50):8977-8980
A general method for the preparation of diaza-spirocycles is reported. This method used an olefin metathesis in order to construct the desired spirocyclic framework. Beginning with commercially available protected amino ketones, this strategy ultimately produced pharmacologically relevant diaza-scaffolds in an efficient and high-yielding process. 相似文献
4.
Thomas Moore 《Fresenius' Journal of Analytical Chemistry》1883,22(1):247-248
Ohne Zusammenfassung 相似文献
5.
E.Ann Hallinan Clifford R. DornWilliam M. Moore Gina M. JeromePamela T. Manning Barnett S. Pitzele 《Tetrahedron letters》2003,44(39):7345-7347
Described is a method of introducing trifluoroalkyl groups at C-6 of lysine. This chemistry has the potential to introduce a variety of functionality at C-6 of lysine. 相似文献
6.
Gerald Moore. 《Mathematics of Computation》2004,73(245):211-242
We present an algorithm, based on approximation by Laguerre polynomials, for computing a point on the stable manifold of a stationary solution of an autonomous system. A superconvergence phenomenon means that the accuracy of our results is much higher than the usual spectral accuracy. Both the theory and the implementation of the method are considered. Finally, as an application of the algorithm, we describe a fully spectral approximation of homo- and heteroclinic orbits.
7.
The Bekenstein–Hawking entropy of certain black holes can be computed microscopically in string theory by mapping the elusive
problem of counting microstates of a strongly gravitating black hole to the tractable problem of counting microstates of a
weakly coupled D-brane system, which has no event horizon, and indeed comfortably fits on the head of a pin. We show here
that, contrary to widely held beliefs, the entropy of spherically symmetric black holes can easily be dwarfed by that of stationary
multi-black-hole “molecules” of the same total charge and energy. Thus, the corresponding pin-sized D-brane systems do not
even approximately count the microstates of a single black hole, but rather those of a zoo of entropically dominant multicentered
configurations.
Fourth Award in the 2007 Essay Competition of the Gravity Research Foundation. 相似文献
8.
Buffer gas beam coolers may become excellent beam preparation devices for high-resolution mass separation. The small beam
emittance provided makes efficient isobar resolution a realistic goal. In order to fulfill the needs of future facilities
providing high-intensity beams of rare isotopes, it is desirable to increase the beam intensity limit of such devices from
typically several tens of nanoamperes to microamperes. This requires the usage of high-voltage radiofrequencies in a low-pressure
gas environment. A buffer gas beam cooler, dedicated to this purpose, is under development at the NSCL. The study of voltage
breakdowns under such conditions and the design of an electrode system minimizing them is mandatory.
相似文献
9.
The cation distribution in spinel-related titanium-substituted lithium ferrite, Li0.5+0.5xFe2.5−1.5xTixO4 has been explored using interatomic potential and ab initio calculations. The results suggest that the cation distribution with Ti4+ substituting for Fe3+ on octahedral B sites and excess Li+ substituting for Fe3+ on tetrahedral A sites is stabilised by the formation of clusters of two octahedrally coordinated Ti4+ ions and one tetrahedrally coordinated Li+ ion linked through a common oxygen. 相似文献
10.