全文获取类型
收费全文 | 112478篇 |
免费 | 19318篇 |
国内免费 | 12135篇 |
专业分类
化学 | 77488篇 |
晶体学 | 1437篇 |
力学 | 7350篇 |
综合类 | 731篇 |
数学 | 13109篇 |
物理学 | 43816篇 |
出版年
2024年 | 253篇 |
2023年 | 2229篇 |
2022年 | 2750篇 |
2021年 | 3937篇 |
2020年 | 4583篇 |
2019年 | 4444篇 |
2018年 | 3783篇 |
2017年 | 3578篇 |
2016年 | 5495篇 |
2015年 | 5235篇 |
2014年 | 6426篇 |
2013年 | 8384篇 |
2012年 | 10174篇 |
2011年 | 10706篇 |
2010年 | 7220篇 |
2009年 | 6933篇 |
2008年 | 7361篇 |
2007年 | 6705篇 |
2006年 | 6161篇 |
2005年 | 5135篇 |
2004年 | 3834篇 |
2003年 | 3008篇 |
2002年 | 2731篇 |
2001年 | 2264篇 |
2000年 | 1976篇 |
1999年 | 2237篇 |
1998年 | 2000篇 |
1997年 | 1818篇 |
1996年 | 1967篇 |
1995年 | 1569篇 |
1994年 | 1516篇 |
1993年 | 1214篇 |
1992年 | 1112篇 |
1991年 | 1019篇 |
1990年 | 823篇 |
1989年 | 589篇 |
1988年 | 477篇 |
1987年 | 392篇 |
1986年 | 387篇 |
1985年 | 330篇 |
1984年 | 244篇 |
1983年 | 158篇 |
1982年 | 144篇 |
1981年 | 108篇 |
1980年 | 77篇 |
1979年 | 46篇 |
1978年 | 34篇 |
1976年 | 37篇 |
1975年 | 35篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
941.
The binding of lomefloxacin to bovine lactoferrin (BLf) in a dilute aqueous solution was studied using fluorescence spectra. The binding constant (K) and the number of binding sites (n) were obtained by a fluorescence quenching method. The binding distance (r) and energy-transfer efficiency (E) between lomefloxacin and bovine lactoferrin were also obtained according to the mechanism of Fo?rster-type dipole-dipole nonradiative energy-transfer. The effect of lomefloxacin on the conformation of bovine lactoferrin was also analyzed by synchronous fluorescence spectroscopy. The interaction between lomefloxacin and bovine lactoferrin is strong. Lomefloxacin can affect the conformation of bovine lactoferrin to some degree. 相似文献
942.
Positive Steady States of a Prey-predator Model with Diffusion and Non-monotone Conversion Rate 总被引:1,自引:0,他引:1
Rui PENG Ming Xin WANG Wen Van CHEN 《数学学报(英文版)》2007,23(4):749-760
In this paper, we study the positive steady states of a prey-predator model with diffusion throughout and a non-monotone conversion rate under the homogeneous Dirichlet boundary condition. We obtain some results of the existence and non-existence of positive steady states. The stability and uniqueness of positive steady states are also discussed. 相似文献
943.
Optical waveguide fabrication and integration with a micro-mirror inside photosensitive glass by femtosecond laser direct writing 总被引:1,自引:0,他引:1
Z. Wang K. Sugioka Y. Hanada K. Midorikawa 《Applied Physics A: Materials Science & Processing》2007,88(4):699-704
Photosensitive glass is a potentially important material for micro-fluidic devices that can be integrated with micro-optical
components for biochemical analysis. Here, we demonstrate the fabrication of optical waveguides inside glass by femtosecond
laser direct writing. The influence of the laser parameters on the waveguide properties is investigated, and it is revealed
that the waveguide mode can be well controlled. The single mode is achieved at a low writing energy, while the multimode is
achieved with increasing energy. In spite of a longitudinally elongated elliptical shape of the cross-sectional profile, the
far-field pattern of the single-mode waveguide shows an almost symmetric profile. The measured propagation loss and the coupling
loss are evaluated to be ∼0.6 dB/cm and ∼1.6 dB at a wavelength of 632.8 nm, respectively, under the conditions of 1.0–2.0 μJ
pulse energy and 200–500 μm/s scan speed. The increased optical loss is associated with a higher waveguide mode at higher
writing energy. Furthermore, the integration of waveguides and a micromirror made of a hollow microplate inside the glass
is demonstrated to bend the laser beam at an angle of 90° in a small chip. The bending loss is estimated to be smaller than
0.3 dB.
PACS 42.62.-b; 42.82.Cr; 82.50.Pt; 42.79.Gn; 42.81.Qb 相似文献
944.
A cobalt‐containing monodentate phosphine [(μ2‐PPh2CH2PPh2‐κ2P)Co2(CO)4][μ2‐η2‐PhC≡CP(i‐Pr)2] 2f , was prepared from the reaction of (μ2‐PPh2CH2PPh2‐κ2P)Co2(CO)6 1 with PhC≡CP(i‐Pr)2. It was accompanied by an oxidized compound, [(μ2‐PPh2CH2PPh2‐κ2P)Co2(CO)4][μ2‐η2‐PhC≡CP(=O)(i‐Pr2)] 2fo during the chromatographic process. Further reaction of 2f with Mo(CO)6 resulted in the formation of a 2f ‐ligated molybdenum complex 4 , [(μ2‐PPh2CH2PPh2‐κ2P)Co2(CO)4][μ2‐η2‐PhC≡CP(i‐Pr2)‐κP]‐Mo(CO)5. 相似文献
945.
Following a previous systematic theoretical study of the ground-state properties of over 7000 nuclei from the proton drip line to the neutron drip line in the relativistic mean field model [Prog. Theor. Phys. 113 (2005) 785], which is in fair agreement with existing experimental data, we observe a few spurious shell closures, i.e. proton shell closures at Z = 58 and Z = 92. These spurious shell closures are found to persist in all the effective forces of the relativistic mean field model, e.g. TMA, NL3, PKDD and DD-ME2. 相似文献
946.
Model and empirical study on some collaboration networks 总被引:8,自引:0,他引:8
Pei-Pei Zhang Kan Chen Yue He Tao Zhou Bei-Bei Su Yingdi Jin Hui Chang Yue-Ping Zhou Li-Cheng Sun Bing-Hong Wang Da-Ren He 《Physica A》2006,360(2):599-616
In this paper we present an empirical study of a few practical systems described by cooperation networks, and propose a model to understand the results obtained. We study four non-social systems, which are the Bus Route Networks of Beijing and Yangzhou, the Travel Route Network of China, Huai-Yang recipes of Chinese cooked food, and a social system, which is the Collaboration Network of Hollywood Actors. In order to explain the results related to the degree distribution, act-degree distribution and act-size distribution (especially about the degree distribution, which may be better fitted using a stretched exponential distribution (SED)), we suggest a simple model to show a possible evolutionary mechanism for the emergence of such networks. The analytic and numerical results obtained from the model are in good agreement with the empirical results. 相似文献
947.
948.
W. Ludorf X. Z. Wang D. Bäuerle 《Applied Physics A: Materials Science & Processing》1989,49(2):221-223
Superconducting films of Bi-Sr-Ca-Cu-O on (100) MgO substrates have been fabricated by XeCl-excimer-laser sputtering from ceramic targets of Bi2.5Sr2Ca2Cu3Oy in O2 atmosphere. The films were polycrystalline with the c-axis (30.80±0.02Å) preferably oriented normal to the substrate surface. Without post-annealing the films showed metallic resistance behavior with zero resistance temperatures of up to Tc(0) }- 79 K. The critical current density of the films had values of up to jc(50K)}- 104 A/cm2. 相似文献
949.
符号几何规划的一种分解方法 总被引:1,自引:0,他引:1
针对符号几何规划提出了一种直接的分解方法,将难于求解的符号几何规划问题等价地转化为一个非线性程度很低的可分离规划,为寻求困难度高且规模较大的符号几何规划问题的求解提供了一种方法,特别是经此方法分解后的每个子问题均易于求解,最后给出了数值实例,验证了此方法的有效性. 相似文献
950.
In this paper, we discuss the dynamic behavior of networks of dynamic agents with general communication topologies. We first analyze the basic case: systems with communication topologies that have spanning trees, i.e., the systems that solve consensus problems. We establish an algebraic condition to characterize each agent's contributions to the final state. And we also study the influence of time-delays on each agent's contributions. Then, we investigate the general case: systems with weakly connected topologies. By using matrix theory, we prove that the states of internal agents will converge to a convex combination of boundary agents in the absence or presence of communication time-delays, and we also show that the coefficients of the convex combination are independent of time-delays even if the delays are time-varying. These results have broad applications in other areas, e.g., study of swarm behavior, formation control of vehicles, etc. 相似文献