全文获取类型
收费全文 | 196531篇 |
免费 | 9514篇 |
国内免费 | 7123篇 |
专业分类
化学 | 94814篇 |
晶体学 | 2343篇 |
力学 | 13446篇 |
综合类 | 427篇 |
数学 | 46022篇 |
物理学 | 56116篇 |
出版年
2023年 | 1161篇 |
2022年 | 2512篇 |
2021年 | 2740篇 |
2020年 | 3171篇 |
2019年 | 3333篇 |
2018年 | 13519篇 |
2017年 | 13248篇 |
2016年 | 10289篇 |
2015年 | 4125篇 |
2014年 | 4904篇 |
2013年 | 6778篇 |
2012年 | 10778篇 |
2011年 | 17609篇 |
2010年 | 11159篇 |
2009年 | 11442篇 |
2008年 | 12322篇 |
2007年 | 14055篇 |
2006年 | 5279篇 |
2005年 | 5685篇 |
2004年 | 5259篇 |
2003年 | 5221篇 |
2002年 | 4379篇 |
2001年 | 3202篇 |
2000年 | 2681篇 |
1999年 | 2237篇 |
1998年 | 2128篇 |
1997年 | 1885篇 |
1996年 | 1912篇 |
1995年 | 1530篇 |
1994年 | 1523篇 |
1993年 | 1414篇 |
1992年 | 1343篇 |
1991年 | 1373篇 |
1990年 | 1325篇 |
1989年 | 1235篇 |
1988年 | 1062篇 |
1987年 | 1077篇 |
1986年 | 1025篇 |
1985年 | 1046篇 |
1984年 | 1001篇 |
1983年 | 901篇 |
1982年 | 874篇 |
1979年 | 854篇 |
1978年 | 852篇 |
1977年 | 827篇 |
1976年 | 944篇 |
1975年 | 839篇 |
1974年 | 858篇 |
1973年 | 875篇 |
1972年 | 773篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
Chee Sing Yap 《The Journal of the Operational Research Society》1989,40(7):649-658
This paper describes three case studies which investigated issues relating to the implementation and management of advanced information technology. The benefits derived from information technology were found to vary from one organization to another. These studies provide further evidence to support earlier research findings that senior management has an important role to play in the effective exploitation of information technology, and that the investment approach taken by an organization has a significant effect on the development of computer-based information systems. The effectiveness of a system depends not only on applying the appropriate technology, but also on how successfully technical and behavioural issues are resolved. 相似文献
153.
A convenient method is proposed for the synthesis of all the individual methyl ethers of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside based on the partial methylation of 2-acetamido-2-deoxy-α-D-glucopyranoside with dimethyl sulfate in an alkaline medium followed by preparative liquid column chromatography on silica gel of the resulting mixture of methyl ethers. 相似文献
154.
采用顶部籽晶提拉法(TSSG)生长出Yb:KY(WO4)2(Yb:KYW)激光晶体.对预烧后的原料及晶体进行了XRD分析,结果表明,分别在920℃和600℃预烧8h后的熔质和助熔剂基本上形成一相,抑止了实验中的挥发问题;所生长的晶体为β-Yb:KYW,计算其晶格常数为a=1.063nm,b=1.034nm,c=0.755nm,β=130.75°.测得不同厚度样品的吸收光谱,结果表明样品在933nm和981nm有较强的吸收峰,计算出主峰981nm的吸收截面σ关键词:
Yb:KYW
TSSG法
晶体结构
光谱参数 相似文献
155.
采用Agilent 81910A光子全参量测试仪,首次实验研究了InP/In1-xGaxAs1-yPy-MQW(Multiple-Quantum-Well,MQW)材料与衬底间因应力而产生的M-Z型光调制器的PDL影响以及由此引起的由差分群时延(Differential Group Delay,DGD)表征的偏振模色散(Polarization Mode Dispersion,PMD).研究结果表明,半导体MQW光调制器的PDL与DGD是一致的.因此在半导体光器件的制作过程中,应尽可能地减小衬底与波导芯层之间的因残存应力的存在造成对光器件的高速性能的不利影响. 相似文献
156.
157.
The main result of the paper is a theorem, using which a new proof of Roth’s theorem is obtained, a new solvability criterion
for the matrix equation AX-YB = C is proved, a formula for a particular solution of the latter is derived, and the least of
the orders of square nonsingular matrices containing a given rectangular matrix as a submatrix is determined. Bibliography:
5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 323, 2005, pp. 15–23. 相似文献
158.
M I Salema A P B Póvoa A Q Novais 《The Journal of the Operational Research Society》2006,57(6):615-629
In this paper, an MILP formulation is proposed for the design of a reverse logistics network based on a warehouse location–allocation model, which optimizes, simultaneously, the forward and reverse networks. A single product model with unlimited capacity is first defined. Subsequently, the model is extended to a multi-product capacitated recovery network model, where capacity limitations and a multi-product system can be considered. The proposed model is compared to published work in the field, where different model assumptions have been proposed. Two cases are described so as to gain a better insight into the model and allow a comparative analysis. 相似文献
159.
The quantum states are presented in these processions of fabricating poly-Si films. Amorphous silicon films prepared by PECVD has been crystallized by conventional furnace annealing (FA) and rapid thermal annealing (RTA), respectively. It is found that the thin films grain size present quantum states with the increasing of the gas flow ratios of SiH4, H2 mixture, substrate temperatures, frequency power, annealing temperature and time. 相似文献
160.
Yu. I. Matveev 《Polymer Science Series A》2006,48(11):1185-1189
An expression for the ratio of the glass transition temperature to the melting temperature, T g/T m, was derived with allowance for fluctuations of the packing factor in the amorphous state. This relationship made it possible to describe the actual range of variation in T g/T m depending on a change in the packing factor in the crystalline state k o, cr. The proposed approach forms the basis for the method of determination of increments in the packing ratio k o, cr and formulation of the principles of selection of experimental data for calculations. The glass transition temperatures in polyethylene depending on the type of unit cell were calculated. 相似文献