全文获取类型
收费全文 | 27354篇 |
免费 | 3801篇 |
国内免费 | 4889篇 |
专业分类
化学 | 15387篇 |
晶体学 | 260篇 |
力学 | 2805篇 |
综合类 | 105篇 |
数学 | 6803篇 |
物理学 | 10684篇 |
出版年
2024年 | 70篇 |
2023年 | 817篇 |
2022年 | 980篇 |
2021年 | 1110篇 |
2020年 | 1289篇 |
2019年 | 903篇 |
2018年 | 1092篇 |
2017年 | 1193篇 |
2016年 | 1361篇 |
2015年 | 1450篇 |
2014年 | 1861篇 |
2013年 | 2494篇 |
2012年 | 2416篇 |
2011年 | 2392篇 |
2010年 | 1925篇 |
2009年 | 1931篇 |
2008年 | 1580篇 |
2007年 | 1622篇 |
2006年 | 1558篇 |
2005年 | 1083篇 |
2004年 | 801篇 |
2003年 | 728篇 |
2002年 | 642篇 |
2001年 | 630篇 |
2000年 | 459篇 |
1999年 | 583篇 |
1998年 | 429篇 |
1997年 | 382篇 |
1996年 | 301篇 |
1995年 | 241篇 |
1994年 | 194篇 |
1993年 | 171篇 |
1992年 | 220篇 |
1991年 | 134篇 |
1990年 | 125篇 |
1989年 | 162篇 |
1988年 | 388篇 |
1987年 | 71篇 |
1986年 | 63篇 |
1985年 | 53篇 |
1984年 | 34篇 |
1983年 | 25篇 |
1982年 | 35篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1971年 | 4篇 |
1959年 | 3篇 |
1957年 | 7篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The ρ-T curves in our single phase HgBa2Ca2Cu3O8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ0exp(−Ueff/κBT). It can be transformed to another form d(lnρ)/d(1/T)=−Ueff+TdUeff/dT, then this becomes a plot of the activation energy Ueff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems. 相似文献
92.
《European Journal of Operational Research》2005,161(1):191-202
In this paper we consider a single item lot-sizing problem with backlogging on a single machine at a finite production rate. The objective is to minimize the total cost of setup, stockholding and backlogging to satisfy a sequence of discrete demands. Both varying demands over a finite planning horizon and fixed demands at regular intervals over an infinite planning horizon are considered. We have characterized the structure of an optimal production schedule for both cases. As a consequence of this characterization, a dynamic programming algorithm is proposed for the computation of an optimal production schedule for the varying demands case and a simpler one for the fixed demands case. 相似文献
93.
本文引入并研究一类新的广义集值强非线性拟变分不等式,讨论这类广义集值强非线性拟变分不等式解的存在性以及由算法所构造的迭代序列的收敛性.我们的结果改进和发展了Noor,Siddiqi和Ansari等人近期的一些主要结果. 相似文献
94.
《Journal of Electrostatics》2007,65(9):582-592
The spatial sensitivity, spatial filtering effect, temporal frequency response characteristics and bandwidth are important parameters influencing the accuracy and response speed of a ring-shaped electrostatic inductive sensor. In this paper, the charge induced on the ring-shaped sensor with different geometric sizes from a single particle having a unity charge was modeled mathematically. And from the numerical solution obtained using the finite element analysis software ANSYS, the spatial sensitivity of the sensor was derived. The effect of the geometric size of the sensor on the spatial sensitivity was also investigated, and its spatial filtering fundamental theory and spatial filtering effect were also analyzed quantitatively. The temporal frequency response characteristics of the sensor were also derived. The experimental results on a gravity-fed conveyor were presented. The theoretical and experimental results obtained demonstrate that the ring-shaped sensor acts as a low-pass filter in the spatial frequency domain and its spatial frequency characteristics are closely related to the radial position of the charged particle and the axial length of the electrode. The measurement system, including the probe and signal conditioning circuit, acts as a band-pass filter, and the radial position, the axial length of the electrode, particle velocity and particle size have important effects on the temporal frequency characteristics of the measurement system. 相似文献
95.
Wang Dunhui Huang Songling Han Zhida Su Zhenghua Wang Yi Du Youwei 《Solid State Communications》2004,131(2):97-99
A series of Gd(1−x)Bx alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd(1−x)Bx alloys may be utilized as refrigerant in household magnetic refrigeration. 相似文献
96.
其中m,P,q>1.利用试验函数方法,首先推导一些积分不等式,然后对方程组爆破解的生命跨度 [0,T)给出估计. 相似文献
97.
Observation of spontaneous pattern with six-fold symmetry in disk-shaped ZnO complex microstructures
L.W. Yang Y.J. Gao X.L. Wu Y.M. Yang G.S. Huang Z.Y. Zhang P.K. Chu 《Applied Physics A: Materials Science & Processing》2007,89(1):173-176
Using a simple vapor phase transport technique, we have fabricated unique complex disk-shaped ZnO microstructures comprising
a small disk coaxially grown on a large one and observed spatially perfect six-fold symmetric patterns. The observed results
can be explained based on the spontaneous nanoindentation (NI) effect under the geometric constraints and the explanation
can be extended to fathom the growth mechanism of other highly symmetrical ZnO nanostructures. Our results indicate that NI
not only can elucidate the mechanical properties of surfaces and thin films but also is an effective approach to fabricate
ordered nanostructures with high precision on the location of the building blocks.
PACS 81.16.Rf; 81.07.-b; 81.05.Dz 相似文献
98.
J. Xu J. Mei X.H. Huang X. Li Z. Li W. Li K. Chen 《Applied Physics A: Materials Science & Processing》2005,80(1):123-126
The effect of nitrogen surface doping on the electron field emission characteristics of hydrogenated amorphous carbon films was studied. It was found that the emission threshold electric field decreased after nitrogen surface doping which indicated the reduction of the emission barrier at the film surface. It was demonstrated that this improvement arose from the decrease of the effective work function due to the formation of a dipole layer induced by chemical termination and chemical structural change on the film surface. PACS 52.75.Xx; 73.30 +y; 73.61.Jc 相似文献
99.
The purpose of this work is to investigate the weakened Ambrosetti–Prodi type multiplicity results for weak doubly periodic solutions of damped beam equations. By using the topological degree theory, the author obtains a result which is similar to the result for damped wave equations in the literature. 相似文献
100.
Q.-Y. Shao A.-D. Li J.-B. Cheng H.-Q. Ling D. Wu Z.-G. Liu N.-B. Ming C. Wang H.-W. Zhou B.-Y. Nguyen 《Applied Physics A: Materials Science & Processing》2005,81(6):1181-1185
LaAlO3 (LAO) gate dielectric films were deposited on Si substrates by low-pressure metalorganic chemical vapor deposition. The interfacial structure and composition distribution were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectroscopy (SIMS), and Auger-electron spectroscopy (AES). HRTEM confirms that there exists an interfacial layer between LAO and Si in most samples. AES, SIMS, and XPS analyses indicate that the interfacial layer is compositionally graded La–Al silicate and the Al element is severely deficient close to the Si surface. Electrical properties of LAO films were evaluated. No evident difference in electrical properties between samples with and without native SiO2 layers was observed. The electrical properties are discussed in terms of LAO growth mechanisms, in relation to the interfacial structure. PACS 73.40.Qv; 81.15.Gh; 77.55.+f; 68.35.-p 相似文献