全文获取类型
收费全文 | 29363篇 |
免费 | 1627篇 |
国内免费 | 3867篇 |
专业分类
化学 | 19313篇 |
晶体学 | 1057篇 |
力学 | 218篇 |
综合类 | 192篇 |
数学 | 3686篇 |
物理学 | 4081篇 |
综合类 | 6310篇 |
出版年
2024年 | 20篇 |
2023年 | 196篇 |
2022年 | 644篇 |
2021年 | 812篇 |
2020年 | 609篇 |
2019年 | 598篇 |
2018年 | 489篇 |
2017年 | 636篇 |
2016年 | 687篇 |
2015年 | 677篇 |
2014年 | 1050篇 |
2013年 | 1961篇 |
2012年 | 1572篇 |
2011年 | 1843篇 |
2010年 | 1778篇 |
2009年 | 2023篇 |
2008年 | 1945篇 |
2007年 | 2038篇 |
2006年 | 1951篇 |
2005年 | 1661篇 |
2004年 | 1608篇 |
2003年 | 1400篇 |
2002年 | 1217篇 |
2001年 | 907篇 |
2000年 | 881篇 |
1999年 | 742篇 |
1998年 | 643篇 |
1997年 | 562篇 |
1996年 | 469篇 |
1995年 | 470篇 |
1994年 | 433篇 |
1993年 | 398篇 |
1992年 | 376篇 |
1991年 | 309篇 |
1990年 | 184篇 |
1989年 | 224篇 |
1988年 | 172篇 |
1987年 | 111篇 |
1986年 | 72篇 |
1985年 | 77篇 |
1984年 | 91篇 |
1983年 | 23篇 |
1982年 | 44篇 |
1981年 | 60篇 |
1980年 | 51篇 |
1979年 | 38篇 |
1978年 | 27篇 |
1977年 | 22篇 |
1976年 | 11篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
141.
该文讨论局部可分度量空间闭s映象的分解定理, 证明了正则的Fréchet空间是局部可分度量空间的闭s映象当且仅当满足如下条件: 具有点可数的cs*网, 第一可数的闭子空间是局部可分的, 且Lindelof的闭子空间是可分的. 相似文献
142.
Using a generalization of the classical ballot theorem, Niu and Cooper [7] established a duality relation between the joint
distribution of several variables associated with the busy cycle inM/G/1 (with a modified first service) and the corresponding joint distribution of several related variables in its dualGI/M/1. In this note, we generalize this duality relation toGI/G/1 queues with modified first services; this clarifies the original result, and shows that the generalized ballot theorem
is superfluous for the duality relation. 相似文献
143.
提出了Ru(phen) 32 +-SO32 - -KClO3(phen =1 ,1 0菲咯啉 )体系化学发光法测定溶液中亚硫酸盐含量的方法 .SO32 - 浓度与化学发光强度在 1 .0× 1 0 - 6~ 1 .0× 1 0 - 3 mol/L范围内成正比 ,检出限为 2 .32× 1 0 - 6mol/L (S/N =3) ,1 .0× 1 0 - 4 mol/LSO32 - 溶液重复 6次测定结果的相对标准偏差为 3.8% .该方法成功地用于白葡萄酒中的亚硫酸盐总含量的测定 ,结果令人满意 . 相似文献
144.
Ken Tachibana Ken Takeda Masahiko Shiraishi 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(7):342
It is well-recognized that DNA methylation and histone modifications play critical roles in epigenetic regulation of gene activity through the alteration of chromatin structure. Recent studies have shown that in a subset of cancer cells, the silencing of the human E-cadherin (CDH1) gene is associated with hypermethylation of the CpG island. However, the associated molecular mechanism remains unclear. To understand the mechanism, we have investigated the alteration of CpG island methylation and histone modifications during the reactivation of the CDH1 gene by treatment with 5-aza-2′-deoxycytidine (5-aza-dC). Although the CDH1 gene expression was recovered by treatment with 5-aza-dC in a liver cancer cell line Li21, the methylation status of the entire CpG island and acetylation and methylation status of associated histones were not significantly altered. These results demonstrate that the silenced CDH1 gene can be reactivated without apparent alteration of histone modification or CpG island methylation. 相似文献
145.
Generators of some Ramanujan formulas 总被引:2,自引:0,他引:2
Jesús Guillera 《The Ramanujan Journal》2006,11(1):41-48
In this paper we prove some Ramanujan type formulas for 1/π but without using the theory of modular forms. Instead we use
the WZ—method created by H. Wilf and D. Zeilberger and find some hypergeometric functions in two variables which are second
components of WZ—pairs than can be certified using Zeilberger's EKHAD package. These certificates have an additional property
which allows us to get generalized Ramanujan's type series which are routinely proven by computer. We call these second hypergeometric
components of the WZ—pairs generators. Finding generators seems a hard task but using a kind of experimental research (explained
below), we have succeeded in finding some of them. Unfortunately we have not found yet generators for the most impressive
Ramanujan's formulas. We also prove some interesting binomial sums for the constant 1/π2. Finally we rewrite many of the obtained series using pochhammer symbols and study the rate of convergence.
2000 Mathematics Subject Classification Primary—33C20 相似文献
146.
This paper studies the tail behavior of the fundamental period in the MAP/G/1 queue. We prove that if the service time distribution
has a regularly varying tail, then the fundamental period distribution in the MAP/G/1 queue has also regularly varying tail,
and vice versa, by finding an explicit expression for the asymptotics of the tail of the fundamental period in terms of the
tail of the service time distribution. Our main result with the matrix analytic proof is a natural extension of the result
in (de Meyer and Teugels, J. Appl. Probab. 17: 802–813, 1980) on the M/G/1 queue where techniques rely heavily on analytic expressions of relevant functions.
I.-S. Wee’s research was supported by the Korea Research Foundation Grant KRF 2003-070-00008. 相似文献
147.
Karl Sigman 《Operations Research Letters》2007,35(5):581-583
In Mandelbaum and Yechiali [The conditional residual service time in the M/G/1 queue, http://www.math.tau.ac.il/∼uriy/publications (No. 30a), 1979] and in Fakinos [The expected remaining service time in a single-server queue, Oper. Res. 30 (1982) 1014-1018] a simple formula is derived for the (stationary) expected remaining service time in a M/G/1 queue, conditional on the number of customers in the system. We give a short new proof of the formula using Rate Conservation Law, and generalize to handle higher moments. 相似文献
148.
Jing Ping YANG Shi Hong CHENG Xiao Qian WANG 《数学学报(英文版)》2007,23(3):467-478
This paper investigates bivariate recursive equations on excess-of-loss reinsurance. For an insurance portfolio, under the assumptions that the individual claim severity distribution has bounded continuous density and the number of claims belongs to R1 (a, b) family, bivariate recursive equations for the joint distribution of the cedent's aggregate claims and the reinsurer's aggregate claims are obtained. 相似文献
149.
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
150.
Jun-ichi Suto 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2006,82(4):165-173
F1-Ay mice between RR (aabbCC) and C57BL/6J-Ay (AyaBBCC) have a much darker yellow coat color than do C57BL/6J-Ay. Quantitative trait locus (QTL) analysis was carried out to identify genes responsible for the darker modification of the yellow coat color (this has been traditionally termed “sable”). A significant sable QTL was identified on chromosome 1 (Dmyaq4, LOD score 15.5 for lightness, and 13.4 for color difference), in a chromosomal position similar to that of Dmyaq2, a sable QTL previously identified in C3H/HeJ. Another significant sable QTL was identified on chromosome 4 (Dmyaq5, LOD score 5.6 for lightness, and 4.3 for color difference) near the tyrosinase-related protein 1 (Tyrp1) locus. The effect of Dmyaq5 was significant only in the presence of the RR allele at Dmyaq4, suggesting that the Dmyaq4 (as well as Dmyaq2) is a novel coat color gene that may act up-stream of Tyrp1 signaling to increase eumelanin production. 相似文献