全文获取类型
收费全文 | 101456篇 |
免费 | 4537篇 |
国内免费 | 3985篇 |
专业分类
化学 | 41445篇 |
晶体学 | 1091篇 |
力学 | 8074篇 |
综合类 | 299篇 |
数学 | 34940篇 |
物理学 | 24129篇 |
出版年
2024年 | 50篇 |
2023年 | 392篇 |
2022年 | 514篇 |
2021年 | 762篇 |
2020年 | 861篇 |
2019年 | 915篇 |
2018年 | 11060篇 |
2017年 | 10844篇 |
2016年 | 7125篇 |
2015年 | 1986篇 |
2014年 | 1783篇 |
2013年 | 2213篇 |
2012年 | 5846篇 |
2011年 | 12606篇 |
2010年 | 7294篇 |
2009年 | 7694篇 |
2008年 | 8375篇 |
2007年 | 10304篇 |
2006年 | 1769篇 |
2005年 | 2618篇 |
2004年 | 2589篇 |
2003年 | 2817篇 |
2002年 | 2035篇 |
2001年 | 1032篇 |
2000年 | 972篇 |
1999年 | 692篇 |
1998年 | 570篇 |
1997年 | 456篇 |
1996年 | 519篇 |
1995年 | 351篇 |
1994年 | 279篇 |
1993年 | 249篇 |
1992年 | 211篇 |
1991年 | 173篇 |
1990年 | 161篇 |
1989年 | 150篇 |
1988年 | 123篇 |
1987年 | 105篇 |
1986年 | 109篇 |
1985年 | 99篇 |
1984年 | 62篇 |
1983年 | 57篇 |
1982年 | 49篇 |
1981年 | 45篇 |
1980年 | 60篇 |
1979年 | 51篇 |
1978年 | 48篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
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
62.
63.
Graham Smith 《The Journal of the Operational Research Society》1989,40(9):761-770
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation. 相似文献
64.
就一般非完整约束系统,从约束方程满足的变分恒等式出发,利用增广位形流形上的向量场定义三类非自由变分,即非完整变分:vakonomic变分、Hlder变分、Suslov变分,并讨论它们之间的关系以及它们成为自由变分的充要条件.利用非完整变分以及相应的积分变分原理建立两类动力学方程:vakonomic方程和Routh方程或Chaplygin方程.通过vakonomic方程分别与Routh方程和Chaplygin方程比较,得到它们具有共同解的两类充分必要条件.这些条件并不是约束的可积性条件.
关键词:
非完整约束
非完整变分
Chetaev条件
vakonomic动力学 相似文献
65.
66.
J Ashenfelter 《Pramana》2002,59(5):713-717
The ESTU began operation in 1988 and achieved the design voltage of 20 MV in 1990. Since that time, improvements to the gas
handling system, negative ion injector, accelerator terminal and control system have greatly increased its capability and
reliability. Today, the ESTU can efficiently produce an extensive assortment of stable ions at wide-ranging energies in support
of low-energy nuclear physics. 相似文献
67.
A pressure sensitive paint (PSP) measurement has been known as a pressure field measurement technique based on the oxygen quenching phenomenon of luminescence of specific luminophores. A PSP measurement was applied for pressure field measurement in a low-solidity circular cascade diffuser of a single-stage transonic centrifugal compressor with 5 in pressure ratio for HFC134a gas. The oxygen concentration was about 500 ppm. Ru (bath-phen) was adsorbed on a silica-gel thinlayer chromatography sheet, and the sheet was pasted onto the side-wall between the cascade vanes. A drastic change in luminescent intensity was recognized during a surge condition. Also the pressure variations based on luminescent intensity agreed well with the pressure fluctuations measured using a semiconductor pressure sensor with high-frequency-response. It was shown that a PSP measurement worked well to investigate the unsteady pressure fields in a circular cascade diffuser of a transonic centrifugal compressor. Moreover, the time response of PSP becomes clear as a problem to be overcome for the present. 相似文献
68.
69.
Dual fractional cutting plane algorithms, in which cutting planes are used to iteratively tighten a linear relaxation of an integer program,
are well-known and form the basis of the highly successful branch-and-cut method. It is rather less well-known that various primal cutting plane algorithms were developed in the 1960s, for example by Young. In a primal algorithm, the main role of the cutting
planes is to enable a feasible solution to the original problem to be improved. Research on these algorithms has been almost
non-existent.
In this paper we argue for a re-examination of these primal methods. We describe a new primal algorithm for pure 0-1 problems based on strong valid inequalities and give some encouraging computational results. Possible extensions to the case of general
mixed-integer programs are also discussed. 相似文献
70.
Chong-Guang Cao Zhong-Peng Yang Xian Zhang 《Journal of Applied Mathematics and Computing》2002,10(1-2):101-109
We extend two inequalities involving Hadamard products of positive definite Hermitian matrices to positive semi-definite Hermitian matrices. Simultaneously, we also show the sufficient conditions for equalities to hold. Moreover, some other matrix inequalities are also obtained. Our results and methods are different from those which are obtained by S. Liu in [J. Math. Anal. Appl. 243:458–463(2000)] and B.-Y. Wang et al. in [Lin. Alg. Appl. 302–303: 163–172(1999)]. 相似文献