全文获取类型
收费全文 | 10710篇 |
免费 | 1928篇 |
国内免费 | 1317篇 |
专业分类
化学 | 7963篇 |
晶体学 | 71篇 |
力学 | 658篇 |
综合类 | 81篇 |
数学 | 1116篇 |
物理学 | 4066篇 |
出版年
2024年 | 29篇 |
2023年 | 289篇 |
2022年 | 295篇 |
2021年 | 400篇 |
2020年 | 497篇 |
2019年 | 429篇 |
2018年 | 356篇 |
2017年 | 304篇 |
2016年 | 510篇 |
2015年 | 458篇 |
2014年 | 551篇 |
2013年 | 778篇 |
2012年 | 991篇 |
2011年 | 1008篇 |
2010年 | 660篇 |
2009年 | 653篇 |
2008年 | 730篇 |
2007年 | 640篇 |
2006年 | 564篇 |
2005年 | 495篇 |
2004年 | 381篇 |
2003年 | 326篇 |
2002年 | 282篇 |
2001年 | 222篇 |
2000年 | 218篇 |
1999年 | 258篇 |
1998年 | 220篇 |
1997年 | 195篇 |
1996年 | 207篇 |
1995年 | 184篇 |
1994年 | 148篇 |
1993年 | 133篇 |
1992年 | 111篇 |
1991年 | 82篇 |
1990年 | 86篇 |
1989年 | 58篇 |
1988年 | 49篇 |
1987年 | 46篇 |
1986年 | 30篇 |
1985年 | 28篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
A high-efficiency, ultrabroadband dielectric internal reflection grating with rhombus-shaped grooves is designed by a rigorous coupled-wave analysis, and an effective method for predicting spectral bandwidths of gratings from their efficiency maps is presented. The grating can be fabricated from a single dielectric material, and its reflection diffraction efficiency of the -1st order can reach more than 0.99. More importantly, an ultrabroadband top-hat diffraction spectrum with efficiency exceeding 0.98 over 170 nm wavelength wide is achieved, which makes the gratings suitable for applications associated with broadband illumination, such as ultrashort pulses. 相似文献
992.
Hongyan Liu Riguang ZhangFangyuan Ding Ruixia YanBaojun Wang Kechang Xie 《Applied Surface Science》2011,257(22):9455-9460
A density-functional theory method has been conducted to investigate the association of C + O on (1 1 1) facets of ordered NiCo alloy and the results have been compared with those obtained on pure Ni(1 1 1) surface. In reaction of C + O, the favorable reaction path is that C adsorbed on HCP-1 site moves to the nearest Ni-Co bridge site, and associates with O migrating from FCC-1 site to result in CO adsorbed on the bridge site of Ni-Co. However, the reaction barrier is higher by 0.35 eV than that on pure Ni(1 1 1), which indicates that the incorporation of Co into the Ni crystal is not in favor of the reaction of carbon delimination. 相似文献
993.
Hongyan Liu Riguang ZhangRuixia Yan Baojun Wang Kechang Xie 《Applied Surface Science》2011,257(21):8955-8964
A density-functional theory method has been conducted to investigate the adsorption of CHx (x = 0-4) as well as the dissociation of CHx (x = 1-4) on (1 1 1) facets of ordered NiCo alloy. The results have been compared with those obtained on pure Ni (1 1 1) surface. It shows that the adsorption energies of C and CH are decreased while it is increased for CH3 on NiCo (1 1 1) compared to those on pure Ni (1 1 1). Furthermore, on NiCo (1 1 1), dissociation of CHx prefers not to the top of Ni, but to the top of Co. The rate-determining step for CH4 dissociation is considered as the first step of dehydrogenation on NiCo (1 1 1), while it is the fourth step of dehydrogenation on Ni (1 1 1). Furthermore, the activation barrier in rate-determining step is slightly higher by 0.07 eV on Ni (1 1 1) than that on NiCo (1 1 1). From above results, it is important to point out that carbon is easy to form on NiCo (1 1 1) although the adsorption energy of C atom is slightly decreased compared to that on Ni (1 1 1). 相似文献
994.
995.
We report a Kondo-effect study of electron transport through a quantum dot with embedded biaxial single-molecule magnet based on slave boson mean-field theory and non-equilibrium Green-function technique. It is found the macroscopic quantum coherence of molecule-magnet results in the Kondo peak split of differential conductance due to interaction between electron and molecular magnet. It is also demonstrated that both the peak height and position can be controlled by the sweeping magnetic field and polarization of ferromagnetic electrodes. The characteristic peak split may be used to identify the macroscopic quantum coherence and develop molecule devices. 相似文献
996.
Changfeng FangBin Cui Yuqing XuGuomin Ji Desheng Liu Shijie Xie 《Physics letters. A》2011,375(41):3618-3623
We report first-principles calculations of the current-voltage characteristic and the conductance of carbon-based molecular wires with different length capped with sulfur ends between two metallic electrodes made of different metals. The optimized molecular structure of carbon chain in the junction is presented on the structure of polyyne. The conductance of the polyyne wires shows oscillatory behavior depending on the number of carbon atoms (triple bonds). Current rectification is found and rectification direction presents inversion with the odd and even number of carbon atoms. 相似文献
997.
By using the discrete Markov chain method, Parrondo’s paradox is studied by means of theoretical analysis and computer simulation, built on the case of game AB played in alternation with modulus M=4. We find that such a case does not have a definite stationary probability distribution and that payoffs of the game depend on the parity of the initial capital. Besides, this paper reveals the phenomenon that “processing in order produces non-deterministic results, while a random process produces deterministic results”. The quantum game method is used in a further study. The results show that the explanation of the game corresponding to a stationary probability distribution is that the probability of the initial capital has reached parity. 相似文献
998.
通过电感耦合等离子体质谱(ICP-MS)对北京、太原、苏州、成都四城市40份成人血铅进行了浓度及其同位素比值的同时测定,以考查不同地区血铅的地区性特征。结果显示工业城市成都、太原血铅浓度高于非工业城市北京、苏州,说明工业污染仍是造成高血铅的重要因素;同位素测试结果显示各城市血铅同位素比值具有特征分布区域和分布特点,食源性铅可能已取代大气铅成为北京等发达城市血铅的主要来源,全球化带来的的物产多样化削弱了一些发达城市铅污染的地区特征。 相似文献
999.
By using the Hermite–Biehler theorem, we give a new proof of the real-rootedness of the coordinator polynomials of type D, which was recently established by Wang and Zhao. As a consequence, we also obtain the compatibility between the coordinator polynomials of type D and those of type C. 相似文献
1000.
The dynamic and lubrication characteristic analyses of the crankshaft–bearing system is quite a complex problem, and it is important to avoid asperity contact which may lead to bearing wear and increase of friction loss significantly in dynamic lubrication condition. In this paper, the dynamic characteristic that has an essential impact on lubrication was investigated over an inline six-cylinder engine. Multi-body dynamics method, tribology, finite element method (FEM), finite difference method (FDM) and component mode synthesis method (CMS) were combined to analyze the dynamic characteristic of crankshaft, oil leakage, oil film pressure, asperity contact pressure and friction loss. Then the orthogonal experiment that included 5 levels and 6 factors was conducted to obtain the training sample sets for neural network, and the probabilistic neural network (PNN) was employed to identify weather the asperity contact happened or not according to its nonlinear characteristic. The analyses which can provide the guidance for the design of main bearing, and avoid the asperity contact in the lubrication are significant to the design of the bearing at the development stage of the engine. 相似文献