全文获取类型
收费全文 | 10362篇 |
免费 | 1084篇 |
国内免费 | 925篇 |
专业分类
化学 | 1078篇 |
晶体学 | 42篇 |
力学 | 881篇 |
综合类 | 154篇 |
数学 | 5929篇 |
物理学 | 2489篇 |
无线电 | 1798篇 |
出版年
2024年 | 23篇 |
2023年 | 123篇 |
2022年 | 224篇 |
2021年 | 210篇 |
2020年 | 323篇 |
2019年 | 299篇 |
2018年 | 260篇 |
2017年 | 329篇 |
2016年 | 343篇 |
2015年 | 277篇 |
2014年 | 471篇 |
2013年 | 797篇 |
2012年 | 581篇 |
2011年 | 614篇 |
2010年 | 523篇 |
2009年 | 745篇 |
2008年 | 714篇 |
2007年 | 650篇 |
2006年 | 714篇 |
2005年 | 593篇 |
2004年 | 434篇 |
2003年 | 442篇 |
2002年 | 365篇 |
2001年 | 289篇 |
2000年 | 277篇 |
1999年 | 286篇 |
1998年 | 265篇 |
1997年 | 206篇 |
1996年 | 184篇 |
1995年 | 108篇 |
1994年 | 92篇 |
1993年 | 70篇 |
1992年 | 69篇 |
1991年 | 61篇 |
1990年 | 49篇 |
1989年 | 57篇 |
1988年 | 37篇 |
1987年 | 32篇 |
1986年 | 30篇 |
1985年 | 32篇 |
1984年 | 29篇 |
1983年 | 13篇 |
1982年 | 25篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 19篇 |
1978年 | 18篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1972年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Monique Laurent 《Mathematical Programming》2007,109(2-3):239-261
We give a hierarchy of semidefinite upper bounds for the maximum size A(n,d) of a binary code of word length n and minimum distance at least d. At any fixed stage in the hierarchy, the bound can be computed (to an arbitrary precision) in time polynomial in n; this is based on a result of de Klerk et al. (Math Program, 2006) about the regular ∗-representation for matrix ∗-algebras.
The Delsarte bound for A(n,d) is the first bound in the hierarchy, and the new bound of Schrijver (IEEE Trans. Inform. Theory 51:2859–2866, 2005) is located
between the first and second bounds in the hierarchy. While computing the second bound involves a semidefinite program with
O(n
7) variables and thus seems out of reach for interesting values of n, Schrijver’s bound can be computed via a semidefinite program of size O(n
3), a result which uses the explicit block-diagonalization of the Terwilliger algebra. We propose two strengthenings of Schrijver’s
bound with the same computational complexity.
Supported by the Netherlands Organisation for Scientific Research grant NWO 639.032.203. 相似文献
92.
93.
V. P. Maslov 《Theoretical and Mathematical Physics》2007,150(1):102-122
From the standpoint of thermodynamic averaging of fission microprocesses, we investigate the origin of radioactive release
in an NPP after an accident or after resource depletion. The genesis of the NPP release is interpreted as a new thermodynamic
phenomenon, a zeroth-order phase transition. This problem setting results in a problem in probabilistic number theory. We
prove the corresponding theorem leading to quantization of the Zipf law for the frequency of a zeroth-order phase transition
with different values of the jump of the Gibbs thermodynamic potential. We introduce the notion of hole dimension.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 150, No. 1, pp. 118–142, January, 2007. 相似文献
94.
Piotr Biler 《Reports on Mathematical Physics》2003,52(2):205-225
We study asymptotic properties of solutions to an extension to arbitrary dimensions of the astrophysical model proposed by Chavanis et al. to explain phenomena of gravitational collapse in clouds of self-gravitating particles. In particular, we show that in the two-dimensional case the solutions can be continued to global ones, while in three space dimensions large data of negative energy blow up in a finite time. Relations between isothermal, Streater's energy-transport and the present models are also studied. 相似文献
95.
Tsuyoshi Katayama 《Queueing Systems》1992,11(3):299-306
This paper derives a conservation law for mean waiting times in a single-server multi-class service queueing system (M
X/G/1 type queue) with setup times which may be dependent on multiple customer classes and its arrival batch size by using the work decomposition property in the queueing system with vacations. 相似文献
96.
The mucosal upheaval (MU), where the mucosal wave starts and propagates upward, appears only when the vocal fold vibrates. The location of the MU histologically and the effect of changes in mean air flow rate (MFR) and vocal fold length on occurrence of the MU were studied in twelve excised canine larynges. The lower surface of the vocal fold was marked to serve as a landmark for subsequent study. Cricothyroid approximation was performed to lengthen the vocal fold. After taking high-speed pictures or recording stroboscopic images from the tracheal side, a small cut wound was made at the mark. This wound served to compare the position of the MU with the histologically identified location of the mark. The larynx was then sectioned in the frontal plane. Before lengthening the vocal fold, the MU occurred on the area where the lamina propria became thinner and where the muscular layer neared the epithelial layer. After lengthening the vocal fold, the MU actually shifted medially compared with its original position. The subglottic area surrounded by the bilateral MUs became longer and thinner. Whether or not complete glottal closure during a vibratory cycle was achieved did not alter these findings. In contrast, with a fixed vocal fold length the MU appeared more laterally as MFR increased, but, based on the relation with the mark, its location on the vocal fold did not change from its original position before increase of MFR. 相似文献
97.
98.
99.
现场抽样调查中,由于测量误差的存在,使得所测变量实测值的方差增大,通过增加每个体的测量次数可以控制测量误差,但这样每个体调查费用增大。本文对测量信度R,每个体测量次数m与相应所需的样本含量nm、调查费用Tn的关系进行了探讨,并介绍了如何根据R,及每个体测量费用占其总费用构成比C,确定最佳测量次数m值,以达到最佳控制调查费用的目的,这对我们在大型现场调查中进行经济效益分析具有重大的理论指导意义。 相似文献
100.
Youssef Saab 《Journal of Heuristics》1997,3(3):207-224
A heuristic optimization methodology, Dynamic Contraction (DC), is introduced as an approach for solving a wide variety of hard combinatorial problems. Contraction is an operation that maps an instance of a problem to a smaller instance of the same problem. DC is an iterative improvement strategy that relies on contraction as a mechanism for escaping local minima. As a byproduct of contraction, efficiency is improved due to a reduction of problem size. Effectiveness of DC is shown through simple applications to two classical combinatorial problems: The graph bisection problem and the traveling salesman problem. 相似文献