全文获取类型
收费全文 | 2815篇 |
免费 | 328篇 |
国内免费 | 249篇 |
专业分类
化学 | 866篇 |
晶体学 | 4篇 |
力学 | 209篇 |
综合类 | 59篇 |
数学 | 1566篇 |
物理学 | 688篇 |
出版年
2024年 | 8篇 |
2023年 | 24篇 |
2022年 | 121篇 |
2021年 | 123篇 |
2020年 | 124篇 |
2019年 | 96篇 |
2018年 | 76篇 |
2017年 | 100篇 |
2016年 | 79篇 |
2015年 | 102篇 |
2014年 | 130篇 |
2013年 | 192篇 |
2012年 | 119篇 |
2011年 | 158篇 |
2010年 | 131篇 |
2009年 | 194篇 |
2008年 | 155篇 |
2007年 | 147篇 |
2006年 | 161篇 |
2005年 | 135篇 |
2004年 | 120篇 |
2003年 | 124篇 |
2002年 | 80篇 |
2001年 | 73篇 |
2000年 | 67篇 |
1999年 | 67篇 |
1998年 | 78篇 |
1997年 | 64篇 |
1996年 | 49篇 |
1995年 | 31篇 |
1994年 | 30篇 |
1993年 | 19篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 19篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1974年 | 12篇 |
1973年 | 21篇 |
排序方式: 共有3392条查询结果,搜索用时 0 毫秒
991.
A systematic approach evaluating template-directed ligation reactions has now resulted in a simple outline for a two-stage replication cycle. This cycle builds on an efficient method for reading the information encoded in DNA into an amplified translation product. It is further demonstrated that the translation product strand is capable of catalyzing the synthesis of the original DNA strand. We propose that this cycle represents just one of many possible solutions; other chemical ligation or polymerization reactions could be accommodated with different templates. In that context, a new template, derived by modest changes to the DNA backbone, has been developed and has been shown to hybridize under reaction conditions different than those accessible to DNA. Therefore, the conceptual groundwork has been laid for extending this approach to encoding and reading stored information in molecules other than the natural biopolymers at the densities found in biology. 相似文献
992.
William G. Lyon Darrell W. Osborne Howard E. Flotow 《The Journal of chemical thermodynamics》1975,7(12):1189-1194
The heat capacity of a sample of Cs2CrO4 was determined in the temperature range 5 to 350 K by aneroid adiabatic calorimetry. The heat capacity at constant pressure Cpo(298.15 K), the entropy So(298.15 K), the enthalpy {Ho(298.15 K) - Ho(0)} and the function were found to be (146.06 ± 0.15) J K?1 mol?1, (228.59 ± 0.23) J K?1 mol?1, (30161 ± 30) J mol?1, and (127.43 ± 0.13) J K?1 mol?1, respectively. The heat capacity Cpo(298.15 K) and entropy So(298.15 K) and entropy So(298.15 K) of Rb2CrO4 are estimated to be (146.0 ± 1.0) J K?1 mol?1 and (217.6 ± 3.0) J K?1 mol?1, respectively. 相似文献
993.
韩英 《新疆大学学报(理工版)》2009,26(3):281-283
图G=(V,E)称为L-可染的,如果对给定的列表L={L(v):v∈V(G)),存在图G的一个正常染色c,满足c(v)∈L(v).如果对任何|L(v)|≥南的列表,图G都是L-可染的,则称图G为k-可选的.本文我们证明了平面图不含4圈,5圈,7圈和三角形距离小于2是3-可选的. 相似文献
994.
以碳纤维、石墨为导电相材料, 掺入粉煤灰和硅灰制备导电混凝土, 研究了粉煤灰、硅灰的掺量对导电混凝土抗冻融性能的影响, 定义了压阻效应稳定性的指标, 探究了压阻效应稳定性随冻融循环的变化规律, 建立了导电混凝土在冻融循环下的电阻率演化模型和压阻效应稳定性模型. 研究结果表明: 在导电混凝土中加入粉煤灰、硅灰可有效提高其抗冻融能力; 当粉煤灰、硅灰总掺量相同时, 较高掺量的粉煤灰可以提升导电混凝土压阻效应的稳定性. 相似文献
995.
Zr-4合金的低周疲劳行为 总被引:3,自引:0,他引:3
研究了620℃×1h再结晶状态Zr-4合金在室温(RT)、400℃和600℃下对称拉-压低周疲劳行为,不同温度下Zr-4合金的循环应力-应变曲线均位于单调拉伸曲线上方,表现为循环硬化特征。疲劳寿命曲线测试结果表明,随着试验温度升高,疲劳寿命降低,特别在低应变幅区域。断口分析表明:RT下Zr-4断口形貌以浅的韧窝和辉纹为主;400 ℃下出现了许多二次裂纹;600℃下则为规则排列的“之”字形裂纹.分别采用Coffin-Manson法和循环滞回能法估算了Zr-4的疲劳寿命。 相似文献
996.
扰动系统在奇异闭轨附近的后继函数对于判断奇异闭轨分支出极限环的个数、极限环的稳定性和相对位置具有极其重要的作用。通过对Dulac映射及正则映射的光滑性的研究得到结论:具有奇异闭轨的Ck系统在小扰动下奇异闭轨附近的的后继函数为Ck-1的。所得结果简洁,可为以后相关研究工 相似文献
997.
Reassignment of the “Forbidden” character in the Ã1B3u-X̃1Ag transitions of pyrazine-d0, 15N and d4
Contours of bands polarized in the plane of the pyrazine (1,4-diazine) molecule are analyzed in greater detail than before (J. Mol. Spectrosc.11, 257 (1963); 21, 66 (1966)). Largely on the basis of simulations of the pyrazine-15N and d4 bands, it is concluded that the vibronic transition moment lies not along the line of the nitrogen atoms but perpendicular to that line. The reassignment requires the vibration responsible for the bands to be ν10a and the electronic transition(s) which loans intensity to be 1B2u. It is confirmed from the derived changes of inertial constants that the two nitrogen atoms lie closer together in the ecited state than in the ground state. 相似文献
998.
Circadian rhythms occur in nearly all living organisms with a period close to 24 h. These rhythms constitute an important class of biological oscillators which present the characteristic of being naturally subjected to forcing by light-dark (LD) cycles. In order to investigate the conditions in which such a forcing might lead to chaos, we consider a model for a circadian limit cycle oscillator and assess its dynamic behavior when a light-sensitive parameter is periodically forced by LD cycles. We determine as a function of the forcing period and of the amplitude of the light-induced changes in the light-sensitive parameter the occurrence of various modes of dynamic behavior such as quasi-periodicity, entrainment, period-doubling and chaos. The type of oscillatory behavior markedly depends on the forcing waveform; thus the domain of entrainment grows at the expense of the domain of chaos as the forcing function progressively goes from a square wave to a sine wave. Also studied is the dependence of the phase of periodic or aperiodic oscillations on the amplitude of the light-induced changes in the control parameter. The results are discussed with respect to the main physiological role of circadian rhythms which is to allow organisms to adapt to their periodically varying environment by entrainment to the natural LD cycle. 相似文献
999.
A. I. Pavlov 《Mathematical Notes》1997,62(6):739-746
Let Λ be an arbitrary set of positive integers andS
n
(Λ) the set of all permutations of degreen for which the lengths of all cycles belong to the set Λ. In the paper the asymptotics of the ratio |S
n
(Λ)|/n! asn→∞ is studied in the following cases: 1) Λ is the union of finitely many arithmetic progressions, 2) Λ consists of all positive
integers that are not divisible by any number from a given finite set of pairwise coprime positive integers. Here |S
n
(Λ)| stands for the number of elements in the finite setS
n
(Λ).
Translated fromMatematicheskie Zametki, Vol. 62, No. 6, pp. 881–891, December, 1997.
Translated by A. I. Shtern 相似文献
1000.
ONGENERALIZEDLIENARDEQUATIONANDTHEUNIQUENESSOFLIMITCYCLESINGAUSS-TYPE PREDATOR-PREY SYSTEMShaoMinghua(邵明华)(HangzhouTeachers'C... 相似文献