全文获取类型
收费全文 | 36543篇 |
免费 | 6332篇 |
国内免费 | 5125篇 |
专业分类
化学 | 26522篇 |
晶体学 | 484篇 |
力学 | 2142篇 |
综合类 | 449篇 |
数学 | 4600篇 |
物理学 | 13803篇 |
出版年
2024年 | 102篇 |
2023年 | 687篇 |
2022年 | 1256篇 |
2021年 | 1308篇 |
2020年 | 1479篇 |
2019年 | 1477篇 |
2018年 | 1232篇 |
2017年 | 1122篇 |
2016年 | 1708篇 |
2015年 | 1744篇 |
2014年 | 2174篇 |
2013年 | 2714篇 |
2012年 | 3199篇 |
2011年 | 3299篇 |
2010年 | 2415篇 |
2009年 | 2282篇 |
2008年 | 2503篇 |
2007年 | 2272篇 |
2006年 | 2098篇 |
2005年 | 1807篇 |
2004年 | 1457篇 |
2003年 | 1194篇 |
2002年 | 1305篇 |
2001年 | 1117篇 |
2000年 | 819篇 |
1999年 | 738篇 |
1998年 | 601篇 |
1997年 | 569篇 |
1996年 | 546篇 |
1995年 | 456篇 |
1994年 | 421篇 |
1993年 | 331篇 |
1992年 | 251篇 |
1991年 | 257篇 |
1990年 | 198篇 |
1989年 | 170篇 |
1988年 | 142篇 |
1987年 | 103篇 |
1986年 | 79篇 |
1985年 | 77篇 |
1984年 | 73篇 |
1983年 | 49篇 |
1982年 | 47篇 |
1981年 | 32篇 |
1980年 | 29篇 |
1979年 | 8篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1959年 | 5篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
Chunxia Zhao Guowang Xu Xianzhe Shi Jianmei Ma Yan Zhang Shen Lv Qianfeng Weng Qing Yang 《Analytical sciences》2004,20(7):1001-1005
Fluorescent-based single-strand conformation polymorphism (F-SSCP) analysis with capillary electrophoresis (CE) is the most common method for the detection of mutation because of its high sensitivity and resolution. In this study, we prepared an inexpensive linear polyacrylamide (LPA), and successfully applied it to CE-SSCP analysis and tandem CE-SSCP/heteroduplex analysis (HA) of the P53 gene on an ABI capillary genetic analyzer. A comparison of the sieving capabilities of a homemade LPA and commercial polydimethylacrylamide (PDMA) demonstrates that the homemade LPA has a higher resolution, a shorter analysis time, and is more suitable for tandem SSCP/HA than commercial PDMA. To show the usefulness, mutations of P53 gene exon 7 - 8 in 37 tumor samples were investigated by using homemade LPA. The results indicate that 10 mutations were found in 9 of 37 cases; the majority of P53 mutations were missense mutations, and 70% were located in exon 7, which plays an important role in neoplastic progression in human tumorigenesis. 相似文献
12.
本文首先提出逆(反)对策这一新问题,给出了数学模型;探讨了“奇门遁甲”预测理论(术)中的数学问题;通过系统分析“专门遁甲”预测过程,可知它的预测过程隐含着一个特殊的逆(反)对策问题;最后指出逆(反)对策问题的广泛存在并给出案例分析. 相似文献
13.
14.
15.
This paper investigates mutual influence of duct and room acoustics in the whole fan-duct-plenum-room integrations. Applying the parametric design language of finite element software ANSYS (APDL), dimensional and positional influence on system acoustics has been studied. Models with different room dimensions, duct lengths, duct cross-sections, duct locations, duct discharges and duct elbow were constructed, and their characteristics were compared qualitatively. Results show that small rooms, short ducts, large duct cross-sections and bell mouth duct discharges help to increase room sound pressure levels (SPLs); SPLs in ducts and plenums are sensitive to duct dimensions and duct discharge types but insensitive to duct locations and room dimensions; duct elbows have relatively indistinct acoustic influence in each component. Based on the calculation results, a semi-experimental method was proposed for simply and approximately evaluating indoor acoustic spectra of fan-duct-plenum-room integrations, then an example was used to demonstrate the prediction process. Finally, by adopting several ideal models, sound field constitutions, duct and room wall admittances and duct end reflection were explored quantitatively. This study may give a detailed understanding of fan-duct-plenum-room acoustics for researchers, also it might provide a new, simple and approximate prediction method for professionals to evaluate and improve fan-ducted acoustics. 相似文献
16.
The plastic deformation field near the horizontal surface of a half space of perfectly plastic material associated with an indenting rotating rigid tooth is studied using slip line theory. The tooth is one of many on a roll surface and indents first into the half-space material and then rotates about the roll center. A slip line field is proposed for the deforming plastic region and a solution scheme is outlined. The emphasis is on determining the shape of the deforming region, especially that of the free surface. The study has a potential application in roughness transfer in metal forming processing. 相似文献
17.
We describe a scheme of stochastic implementations of quantum teleportation and entanglement swapping in terms of neutral kaons. In this scheme, the kaon whose state is to be teleported collides with one of the two entangled kaons in an Einstein–Podolsky–Rosen state. Subsequent detection of the outgoing particles of the collision completes the two-qubit projection on Alice side. There appear novel features, which connects quantum information science with fundamental laws of particle physics. 相似文献
18.
Z.G. Xiao R.J. HuH.Y. Wu G.M. JinZ.Y. Li L.M. DuanH.W. Wang B.G. ZhangS.F. Wang Z.Y. WeiH.S. Xu Y.T. ZhuS.L. Li F. FuX.H. Yuan Z.Q. Feng 《Physics letters. [Part B]》2006
The inclusive reduced velocity correlation functions of the intermediate mass fragments were measured in the reactions of 36Ar + 112,124Sn at 35 MeV/u. The anti-correlation is observed to be stronger in 36Ar + 124Sn system than that in 36Ar + 112Sn. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three body Coulomb repulsive trajectory model is employed to calculate the emission time scale of the IMFs for the two systems. The time scale is 150 fm/c in 36Ar + 112Sn and 120 fm/c in the 36Ar + 124Sn, respectively. 相似文献
19.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
20.
时间分辨红外发射光谱法对自由基反应的研究 总被引:2,自引:0,他引:2
在过去的 15年中 ,傅立叶变换红外发射光谱法广泛应用于研究气相自由基反应 .Sloan首先研究了O(1D)的反应 ,随后Leone和Hancock研究了O(3 P)的反应 .此后 ,孔繁敖和朱起鹤等研究了小自由基 ,包括CH、CH2 、CH3 、C2 H3 、C2 H5、C2 H、C3 H3 和C3 H5与O2 、NO、N2 O、NO2 等分子的反应。在红外光谱中观察到各个反应的初生产物和初步反应通道 ,和从头算的理论研究结合起来 ,这些反应的机理已基本弄清 . 相似文献