全文获取类型
收费全文 | 77825篇 |
免费 | 327篇 |
国内免费 | 378篇 |
专业分类
化学 | 23973篇 |
晶体学 | 789篇 |
力学 | 6730篇 |
数学 | 32014篇 |
物理学 | 15024篇 |
出版年
2018年 | 10436篇 |
2017年 | 10260篇 |
2016年 | 6054篇 |
2015年 | 843篇 |
2014年 | 294篇 |
2013年 | 318篇 |
2012年 | 3763篇 |
2011年 | 10474篇 |
2010年 | 5625篇 |
2009年 | 6036篇 |
2008年 | 6575篇 |
2007年 | 8738篇 |
2006年 | 205篇 |
2005年 | 1289篇 |
2004年 | 1514篇 |
2003年 | 1962篇 |
2002年 | 1009篇 |
2001年 | 245篇 |
2000年 | 287篇 |
1999年 | 152篇 |
1998年 | 191篇 |
1997年 | 143篇 |
1996年 | 197篇 |
1995年 | 114篇 |
1994年 | 78篇 |
1993年 | 92篇 |
1992年 | 52篇 |
1991年 | 63篇 |
1990年 | 49篇 |
1989年 | 58篇 |
1988年 | 58篇 |
1987年 | 60篇 |
1986年 | 57篇 |
1985年 | 46篇 |
1984年 | 43篇 |
1983年 | 39篇 |
1982年 | 41篇 |
1981年 | 38篇 |
1980年 | 46篇 |
1979年 | 45篇 |
1978年 | 34篇 |
1973年 | 25篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1910年 | 24篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
1904年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
Xun Fu Danmei Wu Xiaodong Zhou Huaqiang Shi Zhengshui Hu 《Journal of nanoparticle research》2007,9(4):675-681
Hollow spherical molybdenum disulfide has been successfully synthesized via a solvothermal method using Cyanex 301 as sulfur
source and modification agent. The hollow spheres are characterized by transmission electron microscopy, scanning electron
microscopy, X-ray diffraction and Energy-Dispersive X-ray analysis. The influences of reaction conditions are also discussed
while a mechanism is proposed to explain the formation of the peculiar morphology. 相似文献
222.
Bai-suo JIN~ 《中国科学A辑(英文版)》2007,50(9):1303-1315
In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted. 相似文献
223.
Friedrich Otto 《Semigroup Forum》2007,75(3):520-535
We consider the problem of deciding Green's relations for various types of finitely presented automatic monoids.
We establish some decidability as well as some undecidability results. 相似文献
224.
Dominique Hulin 《Geometriae Dedicata》2007,130(1):109-136
La condition pour qu’il existe des n-gones de Poncelet, inscrits dans un cercle, et circonscrits à un autre cercle, est polynomiale en les paramètres définissant ces deux cercles. Nous décomposons ces polynômes “de Poncelet” en facteurs irréductibles que nous interprétons géométriquement. 相似文献
225.
A noncooperative game governed by a distributed-parameter predator-prey system is considered, assuming that two players control
initial conditions for predator and prey, respectively. Existence of a Nash equilibrium is shown under the condition that
the desired population profiles and the environmental carrying capacity for the prey are sufficiently small. A conceptual
approximation algorithm is proposed and analyzed. Finally, numerical simulations are performed, too. 相似文献
226.
Chris Quigg 《EPJ direct》2002,4(1):1-15
We study the branching ratio, CP-violating asymmetry, forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the exclusive decay B → Kτ+τ− in the two Higgs doublet model with tree level flavor changing neutral currents (model III). We analyse the dependencies of these quantities on the neutral Higgs boson contributions and the CP parameter sinθ in the model III. We observe that to determine the neutral Higgs boson effects, the measurements of the forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the decay B → Kτ+τ− are promising. 相似文献
227.
We introduce new classes of 2-weight cyclic codes which are direct sums of 1-weight irreducible cyclic codes
相似文献
228.
A scheme for vehicle density and velocity estimation in a stretch of highway based on a modified cell transmission model [C.
F. Daganzo, Transportation Research, Part B, 28B(4),269–287, 1994. Elsevier is presented. The scheme is intended for use with on-ramp metering control algorithms, providing
local knowledge of densities and velocities that is helpful to improve on-ramp metering control performance. Estimation of
density is obtained by nonlinear estimators, while velocity estimation is obtained by gradient algorithms. There is one density–velocity
estimator for free traffic flow and other for congested traffic flow. Both estimator schemes work in parallel. The final estimation
of density and velocity results from a convex combination of the predictions of the two estimators. This combination depends
on occupancy or density measurements at the boundaries of the stretch and is produced by a fuzzy inference system. Stability
and convergence of the density and velocity estimation scheme is proved by Lyapunov based techniques. Simulation results comparing
measured and estimated traffic data are presented. They confirm good performance of the estimators.
Research sponsored by grants UNAM PAPIIT IN110403 and CONACYT 47583. 相似文献
229.
230.