全文获取类型
收费全文 | 133996篇 |
免费 | 6946篇 |
国内免费 | 5098篇 |
专业分类
化学 | 49001篇 |
晶体学 | 1125篇 |
力学 | 8776篇 |
综合类 | 241篇 |
数学 | 35819篇 |
物理学 | 28202篇 |
无线电 | 22876篇 |
出版年
2024年 | 171篇 |
2023年 | 1148篇 |
2022年 | 1366篇 |
2021年 | 1808篇 |
2020年 | 1797篇 |
2019年 | 1605篇 |
2018年 | 12885篇 |
2017年 | 12478篇 |
2016年 | 8629篇 |
2015年 | 2903篇 |
2014年 | 2808篇 |
2013年 | 3502篇 |
2012年 | 7989篇 |
2011年 | 15195篇 |
2010年 | 9411篇 |
2009年 | 9352篇 |
2008年 | 9994篇 |
2007年 | 12091篇 |
2006年 | 2755篇 |
2005年 | 3766篇 |
2004年 | 3441篇 |
2003年 | 3507篇 |
2002年 | 2290篇 |
2001年 | 1316篇 |
2000年 | 1324篇 |
1999年 | 1331篇 |
1998年 | 1224篇 |
1997年 | 1078篇 |
1996年 | 1188篇 |
1995年 | 972篇 |
1994年 | 857篇 |
1993年 | 770篇 |
1992年 | 674篇 |
1991年 | 549篇 |
1990年 | 464篇 |
1989年 | 356篇 |
1988年 | 326篇 |
1987年 | 293篇 |
1986年 | 223篇 |
1985年 | 228篇 |
1984年 | 194篇 |
1983年 | 167篇 |
1982年 | 139篇 |
1981年 | 104篇 |
1980年 | 104篇 |
1979年 | 82篇 |
1978年 | 64篇 |
1976年 | 47篇 |
1975年 | 52篇 |
1914年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
113.
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
114.
铝互连线的电迁移问题历来是微电子产业的研究热点,其面临的电迁移可靠性挑战也是芯片制造业最持久和最重要的挑战之一.从20世纪90年代开始,超深亚微米(特征尺寸≤0.18 μm)铝互连技术面临了更加复杂的电迁移可靠性问题.从电迁移理论出发,分析概括了铝互连电迁移问题的研究方法,总结了上世纪至今关于铝互连电迁移问题的主要经验;最后结合已知的结论和目前芯片制造业现状,分析了当前超深亚微米铝互连线电迁移可靠性挑战的原因和表现形式,提出了解决这些问题的总方向.
关键词:
电迁移
铝互连
微结构 相似文献
115.
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
116.
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
117.
运用层析法、结晶法从狭苞橐吾全草中分离得到艾里莫芬烷型倍半萜8β-hydroxyeremophil-7(11)-ene-12,8α(4β,6α)-diolide化合物,并通过质谱、核磁共振氢谱和碳谱、氢核-氢核相关谱、异核多量子相干谱和异核多键相干谱进行结构鉴定.其单晶经X射线衍射测试表明,其晶体属正交晶系,空间群为P212121,晶胞参数为: a=6.8519(5),b=10.7191(8),c=18.5942(14)A,V=1365.67(18) A3,Z=4,Dc=1.354 mg/m3.F(000)=592,μ=0.101 mm-1 相似文献
118.
Wu Hongyi 《高校应用数学学报(英文版)》2006,21(1):96-106
A family of Said-Bézier type generalized Ball (SBGB) bases and surfaces with a parameter H over triangular domain is introduced, which unifies Bézier surface and Said-Ball surface and includes several intermediate
surfaces. To convert different bases and surfaces, the dual functionals of bases are presented. As an application of dual
functionals, the subdivision formulas for surfaces are established. 相似文献
119.
120.
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