全文获取类型
收费全文 | 28291篇 |
免费 | 2214篇 |
国内免费 | 1837篇 |
专业分类
化学 | 1128篇 |
晶体学 | 20篇 |
力学 | 1247篇 |
综合类 | 345篇 |
数学 | 5997篇 |
物理学 | 3615篇 |
综合类 | 19990篇 |
出版年
2024年 | 152篇 |
2023年 | 370篇 |
2022年 | 614篇 |
2021年 | 679篇 |
2020年 | 577篇 |
2019年 | 600篇 |
2018年 | 602篇 |
2017年 | 829篇 |
2016年 | 904篇 |
2015年 | 939篇 |
2014年 | 1482篇 |
2013年 | 1476篇 |
2012年 | 1625篇 |
2011年 | 1773篇 |
2010年 | 1363篇 |
2009年 | 1729篇 |
2008年 | 1706篇 |
2007年 | 2184篇 |
2006年 | 1970篇 |
2005年 | 1589篇 |
2004年 | 1407篇 |
2003年 | 1149篇 |
2002年 | 1041篇 |
2001年 | 858篇 |
2000年 | 733篇 |
1999年 | 641篇 |
1998年 | 558篇 |
1997年 | 492篇 |
1996年 | 390篇 |
1995年 | 326篇 |
1994年 | 238篇 |
1993年 | 235篇 |
1992年 | 194篇 |
1991年 | 153篇 |
1990年 | 155篇 |
1989年 | 123篇 |
1988年 | 127篇 |
1987年 | 85篇 |
1986年 | 57篇 |
1985年 | 53篇 |
1984年 | 40篇 |
1983年 | 11篇 |
1982年 | 27篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1959年 | 5篇 |
1955年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
对美国HONEYWELL公司S9000DCS系统软件和系统数据进行了结构分析,着重研究并总结出S9000历史数据库的数据结构,开发出TSR型实用软件,实现了S9000汉化报表生成,同时也拓宽了S9000在工业生产中的实际应用范围。 相似文献
82.
从系统论的观点来看,学生的卫生保健工作可作为教育系统的一个子系统。本文利用系统、信息庥和控制论的方法,首先试图分析该子系统的功能和各种相互依赖作用的关系,然后提出建立学生卫生保健工作信息管理的初步方案,高等教育的总目标就是培养德、智、体全面发展的高级人才,当然卫生保健工作的优化目标必须从属于该总目标。 相似文献
83.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help. 相似文献
84.
戴伏生 《数学的实践与认识》2006,36(2):186-192
经典的D IJKSTRA和BELLM AN-F LOYD通信网络路由算法,只能根据特定网络参数得到最佳路由,却无法获得网络存在的全部可用路由,而通信网理论研究及网络管理等方面,往往需要获得节点之间的全部可用路由.研究出一种路由新算法,遵循逻辑代数运算规则、采用关联矩阵中行与行之间整合与删除方式计算,N个节点的网络只需N-1次整合及删除运算,就能得到源节点到任意节点两点之间全部路由结果.详细论证了算法的正确性与合理性,简介了算法的并行运算可行性及与经典路由算法的兼容性等问题.通过算例详细说明算法的计算过程,并验证其正确性. 相似文献
85.
Chen Hao 《中国科学A辑(英文版)》2006,49(5):715-720
In this paper, for the the primes p such that 3 is a divisor of p − 1, we prove a result which reduces the computation of the linear complexity of a sequence over GF(p
m) (any positive integer m) with the period 3n (n and p
m − 1 are coprime) to the computation of the linear complexities of three sequences with the period n. Combined with some known algorithms such as generalized Games-Chan algorithm, Berlekamp-Massey algorithm and Xiao-Wei-Lam-Imamura
algorithm, we can determine the linear complexity of any sequence over GF(p
m) with the period 3n (n and p
m
− 1 are coprime) more efficiently. 相似文献
86.
87.
Temperature effects on deposition rate of silicon nitride films were characterized by building a neural network prediction model. The silicon nitride films were deposited by using a plasma enhanced chemical vapor deposition system and process parameter effects were systematically characterized by 26−1 fractional factorial experiment. The process parameters involved include a radio frequency power, pressure, temperature, SiH4, N2, and NH3 flow rates. The prediction performance of generalized regression neural network was drastically improved by optimizing multi-valued training factors using a genetic algorithm. Several 3D plots were generated to investigate parameter effects at various temperatures. Predicted variations were experimentally validated. The temperature effect on the deposition rate was a complex function of parameters but N2 flow rate. Larger decreases in the deposition rate with the temperature were only noticed at lower SiH4 (or higher NH3) flow rates. Typical effects of SiH4 or NH3 flow rate were only observed at higher or lower temperatures. A comparison with the refractive index model facilitated a selective choice of either SiH4 or NH3 for process optimization. 相似文献
88.
E. Mathieu Y. Foucher P. Dellamonica J. P. Daures 《Methodology and Computing in Applied Probability》2007,9(3):389-397
In AIDS control, physicians have a growing need to use pragmatically useful and interpretable tools in their daily medical
taking care of patients. Semi-Markov process seems to be well adapted to model the evolution of HIV-1 infected patients. In
this study, we introduce and define a non homogeneous semi-Markov (NHSM) model in continuous time. Then the problem of finding
the equations that describe the biological evolution of patient is studied and the interval transition probabilities are computed.
A parametric approach is used and the maximum likelihood estimators of the process are given. A Monte Carlo algorithm is presented
for realizing non homogeneous semi-Markov trajectories. As results, interval transition probabilities are computed for distinct
times and follow-up has an impact on the evolution of patients.
相似文献
89.
A. V. Kel’manov L. V. Mikhailova 《Computational Mathematics and Mathematical Physics》2006,46(1):165-181
The problem of joint a posteriori detection of reference fragments in a quasi-periodic sequence and its partition into segments containing series of recurring fragments from the reference tuple is solved. It is assumed that (i) an ordered reference tuple of sequences to be detected is given, (ii) the number of desired fragments is known, (iii) the index of the sequence term corresponding to the beginning of a fragment is a deterministic (not random) value, and (iv) a sequence distorted by an additive uncorrelated Gaussian noise is available for observation. It is established that the problem consists in testing a set of hypotheses about the mean of a random Gaussian vector. The cardinality of the set grows exponentially as the vector dimension (i.e., the sequence length) increases. An efficient a posteriori algorithm producing a maximum-likelihood optimal solution to the problem is substantiated. Time and space complexity bounds related to the parameters of the problem are derived. The results of numerical simulation are presented. 相似文献
90.
利用普通幂级数发生函数方法,通过对发生函数进行xD算子,得到和式∑k=0^nμ^kf(k)的计算公式,并计算该类和式+ 相似文献