全文获取类型
收费全文 | 91326篇 |
免费 | 2187篇 |
国内免费 | 2297篇 |
专业分类
化学 | 35277篇 |
晶体学 | 1054篇 |
力学 | 7161篇 |
综合类 | 152篇 |
数学 | 33235篇 |
物理学 | 18931篇 |
出版年
2023年 | 161篇 |
2022年 | 268篇 |
2021年 | 431篇 |
2020年 | 475篇 |
2019年 | 533篇 |
2018年 | 10743篇 |
2017年 | 10629篇 |
2016年 | 6615篇 |
2015年 | 1510篇 |
2014年 | 1128篇 |
2013年 | 1376篇 |
2012年 | 5024篇 |
2011年 | 11741篇 |
2010年 | 6589篇 |
2009年 | 6935篇 |
2008年 | 7684篇 |
2007年 | 9641篇 |
2006年 | 1099篇 |
2005年 | 2043篇 |
2004年 | 2138篇 |
2003年 | 2461篇 |
2002年 | 1586篇 |
2001年 | 626篇 |
2000年 | 572篇 |
1999年 | 378篇 |
1998年 | 362篇 |
1997年 | 252篇 |
1996年 | 312篇 |
1995年 | 200篇 |
1994年 | 150篇 |
1993年 | 162篇 |
1992年 | 101篇 |
1991年 | 128篇 |
1990年 | 88篇 |
1989年 | 102篇 |
1988年 | 74篇 |
1987年 | 81篇 |
1986年 | 74篇 |
1985年 | 72篇 |
1984年 | 55篇 |
1983年 | 50篇 |
1982年 | 46篇 |
1981年 | 46篇 |
1980年 | 54篇 |
1979年 | 49篇 |
1978年 | 42篇 |
1914年 | 45篇 |
1912年 | 40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 15 毫秒
41.
42.
43.
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
44.
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
45.
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
46.
两种拔尿管方法对膀胱功能损伤的临床观察 总被引:2,自引:0,他引:2
为观察两种不同的拔尿管方法对膀胱功能损伤的差异,将80例患者随机分成两组,分别采用改良法(40例)和常规法(40例)拔除留置尿管,分析比较了两组患者排尿顺利率、逼尿肌功能恢复率及尿道刺激症、尿失禁、尿潴留。结果表明,两组患者拔管后上述指标与情况有显著性差异,P<0.05。提示改良组膀胱功能损伤明显低于对照组。改良的拔管方法是一种值得护理推广应用的好方法。 相似文献
47.
48.
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
49.
In this paper, we shall find the uniquerational price associated with the exchange option. Also, we find the decomposition of Snell envelope and value function of the American exchange option. 相似文献
50.