全文获取类型
收费全文 | 2103篇 |
免费 | 243篇 |
国内免费 | 154篇 |
专业分类
化学 | 481篇 |
晶体学 | 5篇 |
力学 | 630篇 |
综合类 | 36篇 |
数学 | 625篇 |
物理学 | 723篇 |
出版年
2024年 | 2篇 |
2023年 | 19篇 |
2022年 | 26篇 |
2021年 | 41篇 |
2020年 | 33篇 |
2019年 | 47篇 |
2018年 | 39篇 |
2017年 | 95篇 |
2016年 | 84篇 |
2015年 | 61篇 |
2014年 | 115篇 |
2013年 | 130篇 |
2012年 | 146篇 |
2011年 | 154篇 |
2010年 | 98篇 |
2009年 | 107篇 |
2008年 | 88篇 |
2007年 | 135篇 |
2006年 | 104篇 |
2005年 | 104篇 |
2004年 | 91篇 |
2003年 | 111篇 |
2002年 | 98篇 |
2001年 | 71篇 |
2000年 | 81篇 |
1999年 | 71篇 |
1998年 | 55篇 |
1997年 | 49篇 |
1996年 | 45篇 |
1995年 | 32篇 |
1994年 | 27篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 7篇 |
1989年 | 17篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2500条查询结果,搜索用时 31 毫秒
11.
无穷区间上二阶微分方程的边值问题 总被引:5,自引:0,他引:5
刘衍胜 《应用泛函分析学报》2002,4(3):211-216
利用Schauder不动点定理讨论了一类非线性二阶微分方程在无穷区间上的边值问题无界解的存在性,部分改进了郭大钧教授最近得到的结果。 相似文献
12.
Duan-zhi ZHANG School of Mathematical Sciences Peking University Beijing China 《中国科学A辑(英文版)》2007,50(6):761-772
In this paper, we study the Maslov-type index theory for linear Hamiltonian systems with brake orbits boundary value conditions and its applications to the existence of multiple brake orbits of nonlinear Hamiltonian systems. 相似文献
13.
S. Juneja 《Queueing Systems》2007,57(2-3):115-127
Efficient estimation of tail probabilities involving heavy tailed random variables is amongst the most challenging problems
in Monte-Carlo simulation. In the last few years, applied probabilists have achieved considerable success in developing efficient
algorithms for some such simple but fundamental tail probabilities. Usually, unbiased importance sampling estimators of such
tail probabilities are developed and it is proved that these estimators are asymptotically efficient or even possess the desirable
bounded relative error property. In this paper, as an illustration, we consider a simple tail probability involving geometric
sums of heavy tailed random variables. This is useful in estimating the probability of large delays in M/G/1 queues. In this setting we develop an unbiased estimator whose relative error decreases to zero asymptotically. The key
idea is to decompose the probability of interest into a known dominant component and an unknown small component. Simulation
then focuses on estimating the latter ‘residual’ probability. Here we show that the existing conditioning methods or importance
sampling methods are not effective in estimating the residual probability while an appropriate combination of the two estimates
it with bounded relative error. As a further illustration of the proposed ideas, we apply them to develop an estimator for
the probability of large delays in stochastic activity networks that has an asymptotically zero relative error.
相似文献
14.
重离子治疗计划系统的构想 总被引:2,自引:1,他引:1
对重离子柬治癌的优势进行简要的回顾,并着重介绍了用于重离子放射治疗的治疗计划系统。治疗计划系统是一套软件系统,不同的硬件设施应有与其相匹配的软件系统,即治疗计划系统。在此基础上,针对兰州重离子加速器的特点提出一些关于治疗计划系统方面的构想。After a brief review concerning the advantages of heavy ions in radiotherapy, more interests are concentrated on treatment planning system (TPS) for heavy ion radiotherapy. Compared to the hardware devices such as accelerator and beam delivery system, the TPS is a set of software system, and different therapy facilities require their corresponding TPSs. Based on the specialities of the Heavy Ion Research Facility in Lanzhou (HIIRFL), some suggestions on the TPS for tumor therapy at HIRFL finally are given. 相似文献
15.
A stochastic version of Isaacs's (Ref. 1) game of two cars is dealt with here. In this version, the pursuer, owing to thrust and drag forces, has a variable speed, whereas the evader's speed is constant. Also, the pursuer can maneuver as long as his speed is bounded by some lower and upper limits. The probability of interception, corresponding to optimal (saddle-point) feedback strategies, is computed and serves as a reference for evaluating the performance of four different versions of the proportional navigation pursuit law as well as two other strategies. 相似文献
16.
X光底片在位相对标定 总被引:3,自引:0,他引:3
本文描述了X光底片在位相对标定技术。其原理是使X射线谱经阶梯形吸收滤片透射后,对X光底片曝光,测量底片的曝光量。文中给出了标定方法和数据处理方法,而且也给出了在X光激光实验中得到的Kodak AA5底片的特性曲线。 相似文献
17.
M. A. Macrì C. Del Gratta L. Di Donato S. Di Luzio G. L. Romani S. Della Penna A. Pasquarelli 《Il Nuovo Cimento D》1994,16(5):425-432
Summary A preliminary study is here reported on a new potential marker for biomagnetic measurements. The marker consists of superparamagnetic
polymer microspheres which were detected in the presence of external steady magnetic fields by means of an r.f.-SQUID magnetometer.
The particles were prepared in samples differing in the concentration value and immersed in a homogeneous magnetic field of
variable intensity. A simple model was taken into account for the distribution of the microspheres in the samples, so that
the theoretical values were compared to the marker field values measured by the biomagnetic sensor. The overall sensitivity
of the experimental apparatus and the minimum concentration value of the marker were then estimated. 相似文献
18.
厄米-双曲余弦-高斯光束的瞄准稳定性 总被引:1,自引:0,他引:1
用失调叠加积分的方法 ,对厄米双曲余弦高斯光束的瞄准稳定性作了研究 ,得到了厄米双曲余弦高斯光束失调因子 ηm2 的精确解析公式和近似解析公式 ,并用数值计算了相对横向偏移和相对角向偏移对失调因子ηm2 的影响以及对精确解析公式和近似解析公式的适用范围作了分析和说明。 相似文献
19.
In this paper, we give a construction of RDS in Galois ring by using some bent function, and obtain the equivalent relationship between RDS and a kind of bent function. At the same time, its existence is demonstrated. 相似文献
20.