全文获取类型
收费全文 | 89717篇 |
免费 | 13662篇 |
国内免费 | 8519篇 |
专业分类
化学 | 60222篇 |
晶体学 | 881篇 |
力学 | 5825篇 |
综合类 | 586篇 |
数学 | 11007篇 |
物理学 | 33377篇 |
出版年
2024年 | 284篇 |
2023年 | 1757篇 |
2022年 | 2963篇 |
2021年 | 3053篇 |
2020年 | 3279篇 |
2019年 | 3178篇 |
2018年 | 2960篇 |
2017年 | 2596篇 |
2016年 | 3935篇 |
2015年 | 3958篇 |
2014年 | 4746篇 |
2013年 | 6337篇 |
2012年 | 7670篇 |
2011年 | 7842篇 |
2010年 | 5301篇 |
2009年 | 5200篇 |
2008年 | 5494篇 |
2007年 | 4882篇 |
2006年 | 4665篇 |
2005年 | 3966篇 |
2004年 | 3127篇 |
2003年 | 2371篇 |
2002年 | 2181篇 |
2001年 | 1899篇 |
2000年 | 1739篇 |
1999年 | 1973篇 |
1998年 | 1610篇 |
1997年 | 1472篇 |
1996年 | 1535篇 |
1995年 | 1325篇 |
1994年 | 1228篇 |
1993年 | 1094篇 |
1992年 | 926篇 |
1991年 | 840篇 |
1990年 | 698篇 |
1989年 | 583篇 |
1988年 | 453篇 |
1987年 | 422篇 |
1986年 | 366篇 |
1985年 | 353篇 |
1984年 | 254篇 |
1983年 | 209篇 |
1982年 | 177篇 |
1981年 | 138篇 |
1980年 | 111篇 |
1978年 | 69篇 |
1977年 | 67篇 |
1976年 | 67篇 |
1975年 | 72篇 |
1973年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
The effects of toxicants on the populations for ann-dimensional food chain model in a polluted environment are studied. The thresholds between persistence and extinction of the populations are obtained as functions of model parameters and a time-varying chemical concentration. 相似文献
242.
本研究应用聚类分析的方法,对人离休髁突×片进行数字图像技术处理所获得的影像密度数值做了详细分析,取得人髁突不同区的骨密度分布及不同年龄阶段髁突密度变化的情况。该方法避免了人为因素的影响,其结果较客观地反映了髁突的骨质密度;为研究病理状态时髁突骨密度的改变提供参考。 相似文献
243.
The Existence of Solutions to Sturm-Liouville Boundary Value Problems with Laplacian-like Operator 总被引:2,自引:0,他引:2
Wei-ping Sun Wei-gao GeDepartment of Applied Mathematics Beijing Institute of Technology Beijing China 《应用数学学报(英文版)》2002,18(2):341-348
Abstract The existence of infinitely many solutions to Sturm-Liouville boundary value problem with aLaplacian-like operator is studied by applying generalized polar coordinates. 相似文献
244.
M.-K. Chen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):13-18
We examine the influence of relativistic and QED effects on the existence of the 1,3P
o
H- resonances between n
= 2 and 3 hydrogen thresholds, the relativistic and QED corrections and the coupling effects between the high singlet and triplet
states are considered as first-order perturbations. We firstly obtain accurate non-relativistic resonant energies and widths
of fifteen 1P
o
resonances, and fifteen 3P
o
resonances. The fifteen 1P
o
resonances are classified to be
3
(2, 0)
-
n
( 4 ?
n
? 12) and
3
(1, 1)
+
n
( 3 ?
n
? 8). The fifteen 3P
o
resonances are classified to be
3
(2, 0)
+
n
( 3 ?
n
? 12) and
3
(1, 1)
-
n
( 4 ?
n
? 8). We found there exist six Feshbach resonances for
3
(2, 0)
-
n
(1P
o
) series, four Feshbach resonances for
3
(1, 1)
+
n
(1P
o
) series, seven Feshbach resonances for
3
(2, 0)
+
n
(3P
o
) series, and three Feshbach resonances for
3
(1, 1)
-
n
(1P
o
) series.
Received 22 February 2002 Published online 24 September 2002 相似文献
245.
246.
Browder-Petryshyn 型的严格伪压缩映射的粘滞迭代逼近方法 总被引:1,自引:0,他引:1
主要研究Browder-Petryshyn型的严格伪压缩映射的粘滞迭代逼近过程,证明了Browder-Petryshyn型的严格伪压缩映射的不动点集F(T)是闭凸集.在q-一致光滑且一致凸的Banach空间中,对于严格伪压缩映射T,利用徐洪坤在2004年引进的粘滞迭代得到的序列弱收敛于T的某个不动点.同时证明了Hilbert空间中Browder-Petryshyn型的严格伪压缩映射的相应迭代序列强收敛到T的某个不动点,其结果推广与改进了徐洪坤2004年的相应结果. 相似文献
247.
A novel type of corner reflector for the reflection of surface plasmon polariton (SPP) is proposed. The reflector consists
of two layers of compensatory media whose permittivity and permeability take opposite signs to that of the corresponding layer
of the SP waveguide. By rigorously solving Maxwell's equations, the reflected SPP is proved to exist. The transverse wave
vector of the reflected SPP is always antiparallel to that of the incident SPP and no phase retardation is introduced. 相似文献
248.
Hong-Chao Ma 《Applied Surface Science》2006,252(24):8593-8597
In this paper, we found that boron deposited on the surface of support when sodium borohydride used as reducing agent during the preparation of Pt/C catalyst. The deposition of boron markedly reduces particle size of Pt, raises electrochemical active surface (EAS) area of catalyst and electrochemical activity for hydrogen evolution or oxygen reduction reaction (ORR) compared with which prepared using other reducing agents (hydrogen and formaldehyde). 相似文献
249.
Yi Jiang Chuan-Lei Jia Xue-Lin Wang Ke-Ming Wang Hong-Ji Ma 《Applied Surface Science》2006,253(5):2674-2677
A planar optical waveguide has been formed in a LiB3O5 crystal using 6.0 MeV Cu+-ions with a dose of 1 × 1015 ions/cm2 at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE0 and TM0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change. 相似文献