全文获取类型
收费全文 | 25964篇 |
免费 | 4246篇 |
国内免费 | 1191篇 |
专业分类
化学 | 3505篇 |
晶体学 | 84篇 |
力学 | 1088篇 |
综合类 | 222篇 |
数学 | 5267篇 |
物理学 | 6339篇 |
无线电 | 14896篇 |
出版年
2024年 | 84篇 |
2023年 | 304篇 |
2022年 | 517篇 |
2021年 | 659篇 |
2020年 | 748篇 |
2019年 | 654篇 |
2018年 | 659篇 |
2017年 | 945篇 |
2016年 | 1021篇 |
2015年 | 1190篇 |
2014年 | 1639篇 |
2013年 | 2040篇 |
2012年 | 1909篇 |
2011年 | 1940篇 |
2010年 | 1502篇 |
2009年 | 1519篇 |
2008年 | 1665篇 |
2007年 | 1675篇 |
2006年 | 1530篇 |
2005年 | 1296篇 |
2004年 | 1176篇 |
2003年 | 1098篇 |
2002年 | 884篇 |
2001年 | 766篇 |
2000年 | 644篇 |
1999年 | 606篇 |
1998年 | 447篇 |
1997年 | 398篇 |
1996年 | 316篇 |
1995年 | 275篇 |
1994年 | 200篇 |
1993年 | 180篇 |
1992年 | 132篇 |
1991年 | 124篇 |
1990年 | 69篇 |
1989年 | 75篇 |
1988年 | 59篇 |
1987年 | 53篇 |
1986年 | 40篇 |
1985年 | 80篇 |
1984年 | 49篇 |
1983年 | 35篇 |
1982年 | 40篇 |
1981年 | 35篇 |
1980年 | 20篇 |
1979年 | 30篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Mingxin Wang 《Journal of Mathematical Analysis and Applications》2002,274(1):424-436
This paper deals with positive solutions of degenerate and quasilinear parabolic systems not in divergence form: ut=up(Δu+av), vt=vq(Δv+bu), with null Dirichlet boundary conditions and positive initial conditions, where p, q, a and b are all positive constants. The local existence and uniqueness of classical solution are proved. Moreover, it will be proved that all solutions exist globally if and only if ab?λ12, where λ1 is the first eigenvalue of −Δ in Ω with homogeneous Dirichlet boundary condition. 相似文献
73.
对瑞利和非瑞利杂波中的单、双参数杂波图的控制虚警性能和检测性能进行了比较分析,并得到了双参数杂波图门限调整值的取值范围,得出了几点有益的结论。 相似文献
74.
75.
Let {Xk}k?1 be a strictly stationary time series. For a strictly increasing sampling function g:?→? define Yk=Xg(k) as the deterministic sub‐sampled time series. In this paper, the extreme value theory of {Yk} is studied when Xk has representation as a moving average driven by heavy‐tailed innovations. Under mild conditions, convergence results for a sequence of point processes based on {Yk} are proved and extremal properties of the deterministic sub‐sampled time series are derived. In particular, we obtain the limiting distribution of the maximum and the corresponding extremal index. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
76.
FJZ-250型高速分幅相机时间测量不确定度分析 总被引:2,自引:1,他引:1
FJZ-250型高速转镜分幅相机因转镜速度的不可重复性,光机结构的构造原理和控制系统各路高压触发时间的漂移,导致了时间测量的不确定度。为此,须对相机测量数据进行校正。阐述了校正方法、提供了逐幅校正位置误差的修正系数。若以预置转速对应的名义周期值去处理测量结果,则相机的时间测量合成小确定度将达1%,对名义周期值和名义幅间间隔时间值进行修正后,则可降至0.3%。 相似文献
77.
Jeong Ryeol Choi 《International Journal of Theoretical Physics》2004,43(4):947-958
We derived the WKB wave function for the general time-dependent quadratic Hamiltonian system using a unitary transformation method. We applied our research to sinusodially drived Caldirola–Kanai oscillator and confirmed that the time evolution of our approximated WKB wave function is similar to that of the exact one. This wave function can be used to analyze the interference between the probability amplitudes contributed by the area of overlap in phase space of quantum states. 相似文献
78.
本文把数学和管理科学有机结合,为数学应用提出问题,得出新结果,推广了J.Michel
Harrison(1985)[1]第43页的命题27,并给出了在金融中的应用. 相似文献
79.
Omer Ozturk Steven N. MacEachern 《Annals of the Institute of Statistical Mathematics》2004,56(4):701-720
We develop a method of randomizing units to treatments that relies on subjective judgement or on possible coarse modeling
to produce restrictions on the randomization. The procedure thus fits within the general framework of ranked set sampling.
However, instead of selecting a single unit from each set for full measurement, all units within a set are used. The units
within a set are assigned to different treatments. Such an assignment translates the positive dependence among units within
a set into a reduction in variation of contrasting features of the treatments.
A test for treatment versus control comparison, with controlled familywise error rate, is developed along with the associated
confidence intervals. The new procedure is shown to be superior to corresponding procedures based on completely randomized
or ranked set sample designs. The superiority appears both in asymptotic relative efficiency and in power for finite sample
sizes. Importantly, this test does not rely on perfect rankings; rather, the information in the data on the quality of rankings
is exploited to maintain the level of the test when rankings are imperfect. The asymptotic relative efficiency of the test
is not affected by estimation of the quality of rankings, and the finite sample performance is only mildly affected. 相似文献
80.
A new prediction technique is proposed for chaotic time series. The usefulness of the technique is thatit can kick off some false neighbor points which are not suitable for the local estimation of the dynamics systems. Atime-delayed embedding is used to reconstruct the underlying attractor, and the prediction model is based on the timeevolution of the topological neighboring in the phase space. We use a feedforward neural network to approximate thelocal dominant Lyapunov exponent, and choose the spatial neighbors by the Lyapunov exponent. The model is testedfor the Mackey-Glass equation and the convection amplitude of lorenz systems. The results indicate that this predictiontechnique can improve the prediction of chaotic time series. 相似文献