全文获取类型
收费全文 | 345544篇 |
免费 | 8712篇 |
国内免费 | 3516篇 |
专业分类
化学 | 193280篇 |
晶体学 | 4790篇 |
力学 | 14696篇 |
综合类 | 116篇 |
数学 | 39820篇 |
物理学 | 105070篇 |
出版年
2021年 | 2810篇 |
2020年 | 3131篇 |
2019年 | 3084篇 |
2018年 | 2924篇 |
2017年 | 2718篇 |
2016年 | 5290篇 |
2015年 | 4603篇 |
2014年 | 6033篇 |
2013年 | 16209篇 |
2012年 | 13658篇 |
2011年 | 16338篇 |
2010年 | 10139篇 |
2009年 | 10003篇 |
2008年 | 14345篇 |
2007年 | 14433篇 |
2006年 | 13882篇 |
2005年 | 12603篇 |
2004年 | 11152篇 |
2003年 | 9713篇 |
2002年 | 9544篇 |
2001年 | 10631篇 |
2000年 | 8239篇 |
1999年 | 6680篇 |
1998年 | 5343篇 |
1997年 | 5203篇 |
1996年 | 5289篇 |
1995年 | 4761篇 |
1994年 | 4488篇 |
1993年 | 4212篇 |
1992年 | 4693篇 |
1991年 | 4522篇 |
1990年 | 4216篇 |
1989年 | 3990篇 |
1988年 | 4237篇 |
1987年 | 3898篇 |
1986年 | 3772篇 |
1985年 | 5418篇 |
1984年 | 5456篇 |
1983年 | 4429篇 |
1982年 | 4799篇 |
1981年 | 4820篇 |
1980年 | 4563篇 |
1979年 | 4684篇 |
1978年 | 4684篇 |
1977年 | 4655篇 |
1976年 | 4615篇 |
1975年 | 4524篇 |
1974年 | 4360篇 |
1973年 | 4531篇 |
1972年 | 2579篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
201.
R. J. Vanderbei 《Mathematical Programming》1989,43(1-3):31-44
The affine-scaling modification of Karmarkar's algorithm is extended to solve problems with free variables. This extended primal algorithm is used to prove two important results. First the geometrically elegant feasibility algorithm proposed by Chandru and Kochar is the same algorithm as the one obtained by appending a single column of residuals to the constraint matrix. Second the dual algorithm as first described by Adler et al., is the same as the extended primal algorithm applied to the dual. 相似文献
202.
J Szeman H Ueda J Szejtli E Fenyvesi Y Machida T Nagai 《Chemical & pharmaceutical bulletin》1987,35(1):282-288
203.
通过反应磁控溅射过程中的等离子体发射光谱,研究了制备ZnO薄膜的沉积温度、氧气流量比例R=O2/(O2+Ar)对Zn和O原子发射光谱的影响,并结合ZnO薄膜的结构和物理性能,探讨了沉积温度在ZnO薄膜生长中的作用.研究结果显示:当R≥0.75%时, Zn的溅射产额随R的增加基本呈线性下降规律.当R介于10%—50%时,氧含量的变化相对平缓,有利于ZnO薄膜生长的稳定性控制.Zn原子发射光谱强度随沉积温度的变化可以分为三个阶段.当沉积温度低于250℃时,发射光谱强
关键词:
ZnO
薄膜生长
反应磁控溅射
等离子体发射光谱 相似文献
204.
文章提出了大学研究性物理实验与创新心理品质培养的主题,介绍了大学研究性物理实验的特点,论述了大学研究性物理实验对大学生创新心理品质的影响。 相似文献
205.
A piecewise linearization method based on the linearization of nonlinear ordinary differential equations in small intervals, that provides piecewise analytical solutions in each interval and smooth solutions everywhere, is developed for the study of the limit cycles of smooth and non-smooth, conservative and non-conservative, nonlinear oscillators. It is shown that this method provides nonlinear maps for the displacement and velocity which depend on the previous values through the nonlinearity and its partial derivatives with respect to time, displacement and velocity, and yields non-standard finite difference formulae. It is also shown by means of five examples that the piecewise linearization method presented here is more robust and yields more accurate (in terms of displacement, energy and frequency) solutions than the harmonic balance procedure, the method of slowly varying amplitude and phase, and other non-standard finite difference equations. 相似文献
206.
I. J. Tchoupaeva 《Journal of Mathematical Sciences》2006,135(5):3409-3419
Some geometric theorems can be stated in coordinate-free form as polynomials in Grassman algebra and can be proven by the anticommutative Gröbner basis method. In this article, we analyze some properties of both sets of hypotheses and conclusions of the theorem. 相似文献
207.
The consequences of Ge deposition on Br-terminated Si(1 0 0) were studied with scanning tunneling microscopy at ambient temperature after annealing at 650 K. One monolayer of Br was sufficient to prevent the formation of Ge huts beyond the critical thickness of 3 ML. This is possible because Br acts as a surfactant whose presence lowered the diffusivity of Ge adatoms. Hindered mobility was manifest at low coverage through the formation of short Ge chains. Further deposition resulted in the extension and connection of the Ge chains and gave rise to the buildup of incomplete layers. The deposition of 7 ML of Ge resulted in a rough surface characterized by irregularly shaped clusters. A short 800 K anneal desorbed the Br and allowed Ge atoms to reorganize into the more energetically favorable “hut” structures produced by conventional Ge overlayer growth on Si(1 0 0). 相似文献
208.
J. Carlos Díaz-Ramos Ramón Vázquez-Lorenzo 《Differential Geometry and its Applications》2006,24(4):433-442
Explicit examples of Osserman 4-manifolds with exactly two distinct eigenvalues of the Jacobi operators, α and β=4α≠0, are given. The former has multiplicity two and is a double root of the minimal polynomial of the Jacobi operators. 相似文献
209.
R. J. Hinde 《Few-Body Systems》2006,38(2-4):187-191
We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2-H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set
for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster
theory and find that a fully iterative treatment of connected triples may be required to estimate the H2-H2 vibrational coupling accurately using coupled cluster theory. 相似文献
210.
Neodymium-substituted Bi4Ti3O12 (BNdT) thin films were prepared by a chemical solution deposition technique on platinum- coated silicon substrates. All of
the samples were annealed at the relatively low temperature of 600 °C by a rapid thermal annealing process in different atmospheres,
such as O2, air, and nitrogen, and vacuum. Irrespective of different annealing atmospheres, all of the BNdT thin films exhibit good
ferroelectric properties, such as a saturated hysteresis loop, good fatigue endurance, and low leakage current density. A
large remanent polarization (Pr) of ∼48 μC/cm2 with an electric field of 240 kV/cm was observed from the BNdT thin film annealed in O2 atmosphere. The BNdT thin films annealed in nitrogen and vacuum, at reduced oxygen partial pressures, exhibit smaller Pr than that annealed in oxygen. The difference of Pr of the BNdT thin films annealed in different atmospheres may originate from differences in the grain sizes and the number
of oxygen vacancies.
PACS 77.55.+f; 77.80.-e; 77.80.Fm; 81.15.-z 相似文献