全文获取类型
收费全文 | 32748篇 |
免费 | 6035篇 |
国内免费 | 3943篇 |
专业分类
化学 | 23210篇 |
晶体学 | 469篇 |
力学 | 1934篇 |
综合类 | 166篇 |
数学 | 3211篇 |
物理学 | 13736篇 |
出版年
2024年 | 141篇 |
2023年 | 710篇 |
2022年 | 1275篇 |
2021年 | 1391篇 |
2020年 | 1444篇 |
2019年 | 1429篇 |
2018年 | 1220篇 |
2017年 | 1136篇 |
2016年 | 1657篇 |
2015年 | 1613篇 |
2014年 | 2049篇 |
2013年 | 2555篇 |
2012年 | 3010篇 |
2011年 | 3052篇 |
2010年 | 2071篇 |
2009年 | 1965篇 |
2008年 | 2174篇 |
2007年 | 1912篇 |
2006年 | 1779篇 |
2005年 | 1415篇 |
2004年 | 1069篇 |
2003年 | 840篇 |
2002年 | 825篇 |
2001年 | 676篇 |
2000年 | 553篇 |
1999年 | 643篇 |
1998年 | 544篇 |
1997年 | 526篇 |
1996年 | 506篇 |
1995年 | 449篇 |
1994年 | 357篇 |
1993年 | 296篇 |
1992年 | 290篇 |
1991年 | 237篇 |
1990年 | 208篇 |
1989年 | 161篇 |
1988年 | 96篇 |
1987年 | 84篇 |
1986年 | 108篇 |
1985年 | 75篇 |
1984年 | 43篇 |
1983年 | 49篇 |
1982年 | 35篇 |
1981年 | 28篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1961年 | 1篇 |
1957年 | 5篇 |
1923年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Positron-lifetime experiments have been carried out on two undoped n-type liquid encapsulated Czochralski (LEC)-grown InP samples with different stoichiometric compositions in the temperature range 10-300 K. For temperatures below 120 K for P-rich InP and 100 K for In-rich InP, the positron average lifetime began to increase rapidly and then leveled off, which was associated with the charge state change of hydrogen indium vacancy complexes from (VInH4)+ to (VInH4)0. This phenomenon was more obvious in P-rich samples that have a higher concentration of VInH4. The transformation temperature of approximately 120 K suggests that the complex VInH4 is a donor defect and that the ionization energy is about 0.01 eV. The ionization of neutral VInH4 accounted for the decrease of the positron average lifetime when the sample was illuminated with a photon energy of 1.32 eV at 70 K. These results provide evidence for hydrogen complex defects in undoped LEC InP. 相似文献
42.
Hongyong Zhao 《Journal of Mathematical Analysis and Applications》2003,282(2):437-443
The paper is devoted to the invariant set and periodic attractor for nonautonomous functional differential systems. Some sufficient criteria of the invariant set and periodic attractor are derived. Particularly, we have provided an estimate on existence range of periodic attractor by using the properties of nonnegative matrices and differential inequality technique. 相似文献
43.
A new method based on anion exchange resin separation and graphite furnace atomic absorption spectrometry (GFAAS) detection
is proposed for the determination of inorganic tin species. The result showed that Sn(IV) was quantitatively retained on the
resin when [HCl] = 9.0 mol · L−1, but Sn(II) could not be adsorbed on the resin under the same condition. Thus, a separation of Sn(II) and Sn(IV) has been
realized. When the concentration of NaOH solution was between 2.0–7.0 mol · L−1, Sn(IV) that adsorbed on the resin could be eluated from the resin completely. Meanwhile, under the atmosphere and the nitrogen
states, the translation between Sn(II) and Sn(IV) was investigated. Under the optimal conditions, the detection limit of Sn(IV)
is 0.40 μg · L−1 with RSD of 2.3% (n = 5, c = 2.0 μg · L−1). The proposed method was applied to the speciation analysis of tin in different water samples and the recovery of total
Sn was in the range of 98.7–101.7%. In order to verify the accuracy of the method, a certified reference water sample was
analyzed and the results obtained were in good agreement with the certified value. 相似文献
44.
Ji-hong SU & Yi-cai ZHAO LMAM Department of Mathematics Jinan University Guangzhou China 《中国科学A辑(英文版)》2007,50(4):495-502
Let X be a smooth projective variety of dimension 2k-1 (k≥3) over the complex number field. Assume that fR: X→Y is a small contraction such that every irreducible component Ei of the exceptional locus of fR is a smooth subvariety of dimension k. It is shown that each Ei is isomorphic to the k-dimensional projective space Pk, the k-dimensional hyperquadric surface Qk in Pk 1, or a linear Pk-1-bundle over a smooth curve. 相似文献
45.
In this paper, we establish a theorem on the distribution of primes in quadratic progressions on average. 相似文献
46.
In this paper, we consider a queueing system in which there are two exponential servers, each having his own queue, and arriving
customers will join the shorter queue. Based on the results given in Flatto and McKean, we rewrite the formula for the probability
that there are exactlyk customers in each queue, wherek = 0, 1,…. This enables us to present an algorithm for computing these probabilities and then to find the joint distribution
of the queue lengths in the system. A program and numerical examples are given. 相似文献
47.
为解决高等师范院校物理专业学生的知识结构和实际能力与社会需要明显不相适应的矛盾,我们对四年制物理专业的课程结构进行了全面改革。改革后,毕业生不仅能胜任普通中学或职业中学(职业中专)的教学,而且有能力参与厂矿企业的技术工作,具有更广泛的适应性和更强的竞争力。 相似文献
48.
用漫反射红外光谱和光声红外光谱研究了金属羰基化合物(CpFe(CO)2)2Cp=η^5-C5H5与酸性,中性和碱性Al2O3及TiO2的相互作用,结果表明,在Al2O3表面生成的洗生物种类及浓度与Al2O3的酸碱度明显相关,在酸性Al2O3表面,主要存在衍生物(CpFe(CO)2Fe-H-Fe(CO2Cp)^+及少量的CpFe(CO)2(-O-);在中性Al2O3表面存在的CpFe(CO)2(-O 相似文献
49.
建立了一个把增强颗粒球和基体空心球嵌入等效复合介质空腔中的“双层嵌套模型”,研究了颗粒增强材料自高温冷却下来时,不同相中热应力的分布特点。推出了热应力在弹性和弹塑性状态的各种表达式。研究表明,随着温度降低,增强体受到压应力,基体材料中存在的静水应力为拉应力。温度继续下降,将出现自增强颗粒与基体界面向外扩展的屈服区。随增强相体积分数增大,增强颗粒受到的压应力和基体中的静水拉应力减小,增强颗粒与基体界面屈服的起始温差增大,而基体材料全面屈服的温差却减小。 相似文献
50.
苯并噻唑重氮氨基偶氮苯与汞(Ⅱ)的显色反应及其应用 总被引:26,自引:2,他引:24
报道了新试剂苯并噻唑重氮氨基偶氮苯的合成及其与汞(Ⅱ)的显色反应,在TritonX-100存在下弱碱性介质中,试剂与汞形成2:1的橙红色络合物,最大吸收波长位于520nm处,表观摩尔吸光系数为1.51×10^5L.mol^-1.cm^-1。汞量在0~1.2mg/L范围内遵守比尔定律,直接应用于废水中微量汞的测定,结果满意。 相似文献