全文获取类型
收费全文 | 75792篇 |
免费 | 4818篇 |
国内免费 | 3962篇 |
专业分类
化学 | 41586篇 |
晶体学 | 403篇 |
力学 | 6464篇 |
综合类 | 1208篇 |
数学 | 17053篇 |
物理学 | 17858篇 |
出版年
2024年 | 94篇 |
2023年 | 580篇 |
2022年 | 1088篇 |
2021年 | 2446篇 |
2020年 | 1758篇 |
2019年 | 1808篇 |
2018年 | 1490篇 |
2017年 | 1811篇 |
2016年 | 2341篇 |
2015年 | 2001篇 |
2014年 | 2762篇 |
2013年 | 4913篇 |
2012年 | 3623篇 |
2011年 | 3602篇 |
2010年 | 3256篇 |
2009年 | 4156篇 |
2008年 | 4210篇 |
2007年 | 4699篇 |
2006年 | 3789篇 |
2005年 | 3051篇 |
2004年 | 2880篇 |
2003年 | 2643篇 |
2002年 | 4803篇 |
2001年 | 2281篇 |
2000年 | 1807篇 |
1999年 | 1569篇 |
1998年 | 1525篇 |
1997年 | 1227篇 |
1996年 | 1213篇 |
1995年 | 1094篇 |
1994年 | 1047篇 |
1993年 | 972篇 |
1992年 | 905篇 |
1991年 | 691篇 |
1990年 | 596篇 |
1989年 | 435篇 |
1988年 | 466篇 |
1987年 | 326篇 |
1986年 | 321篇 |
1985年 | 453篇 |
1984年 | 342篇 |
1983年 | 196篇 |
1982年 | 385篇 |
1981年 | 516篇 |
1980年 | 465篇 |
1979年 | 525篇 |
1978年 | 399篇 |
1977年 | 294篇 |
1976年 | 260篇 |
1973年 | 157篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
101.
102.
103.
Copper bromide was used as a catalyst for the addition of pyrroles to enones. When both the reactants were used in equimolar amounts, mono and dialkylated products were obtained. However, the use of excess enone furnished only dialkylated products. Thus, copper bromide was shown to be an efficient catalyst for the dialkylation of pyrroles. 相似文献
104.
In this study, the nonlinear dynamic responses of a string are simulated using the Cellular Automata method based on the reflection rule. In the case of nonlinear systems, the velocity of wave propagation is not constant and depends on the amplitude. A new treatment of the dynamic time step is proposed for the Cellular Automata method considering the effect of the propagation velocity. As numerical examples, first, the dynamic responses of a string with linear characteristic are simulated using the Cellular Automata method. A typical resonance curve can be obtained. Second, the dynamic responses of a string with nonlinear characteristic are simulated using the proposed method. Some characteristic types of vibration can be obtained. It is concluded that the linear and nonlinear dynamic responses of a string may be obtained by simulation using the Cellular Automata method. 相似文献
105.
F. Balibrea 《Topology and its Applications》2006,153(12):2092-2095
Recently, Forti, Paganoni and Smítal constructed an example of a triangular map of the unite square, F(x,y)=(f(x),g(x,y)), possessing periodic orbits of all periods and such that no infinite ω-limit set of F contains a periodic point. In this note we show that the above quoted map F has a homoclinic orbit. As a consequence, we answer in the negative the problem presented by A.N. Sharkovsky in the eighties whether, for a triangular map of the square, existence of a homoclinic orbit implies the existence of an infinite ω-limit set containing a periodic point. It is well known that, for a continuous map of the interval, the answer is positive. 相似文献
106.
The diffusion of the anti-microbial chlorhexidine digluconate (CHG) has been studied in C. albicans biofilms by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). C. albicans has been shown to become resistant to common anti-microbial agents, including CHG, when growing as a biofilm. Mass transport resistance within biofilms has commonly been suggested as a resistance mechanism, but measurement of transport for most anti-microbial agents in biofilms has proven extremely difficult because of the heterogeneity of the biofilms and the difficulty in detecting these agents within an intact biofilm. In this study, TOF-SIMS has been used to study the transport of CHG and glucose in a frozen hydrated biofilm. The TOF-SIMS images reveal a progression of CHG from the top of the biofilm to its base with time. Images suggest that there are channels within the biofilm and show preferential binding of CHG to cellular components of the biofilm. Additionally, both living and dead cells can be identified in the TOF-SIMS images by the sequestration of K+ and the presence of cell markers. This study demonstrates that TOF-SIMS has the unique potential to simultaneously observe the presence of an antimicrobial agent, concentration of nutrients, and the viability of the cell population. 相似文献
107.
108.
M. Brando N. Büttgen V. Fritsch J. Hemberger H. Kaps H.-A. Krug von Nidda M. Nicklas K. Pucher W. Trinkl A. Loidl E.W. Scheidt M. Klemm S. Horn 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):289-298
We present susceptibility, microwave resistivity, NMR and heat-capacity results for Li1-xZnx(V1-yTiy)2O4 with 0 ?
x
? 0.3 and 0 ?
y
? 0.3. For all doping levels the susceptibility curves can be fitted with a Curie-Weiss law. The paramagnetic Curie-Weiss temperatures
remain negative with an average value close to that of the pure compound Θ≈ - 36 K. Spin-glass anomalies are observed in the susceptibility, heat-capacity and NMR measurements for both type of dopants.
From the temperature dependence of the spin-lattice relaxation rate we found critical-dynamic behavior in the Zn doped compounds
at the freezing temperatures. For the Ti-doped samples two successive freezing transitions into disordered low-temperature
states can be detected. The temperature dependence of the heat capacity for Zn-doped compounds does not resemble that of canonical
spin glasses and only a small fraction of the total vanadium entropy is frozen at the spin-glass transitions. For pure LiV2O4 the spin-glass transition is completely suppressed. The temperature dependence of the heat capacity for LiV2O4 can be described using a nuclear Schottky contribution and the non-Fermi liquid model, appropriate for a system close to
a spin-glass quantum critical point. Finally an (
x
/
y
,
T
)-phase diagram for the low-doping regime is presented.
Received 16 March 2001 and Received in final form 30 October 2001 相似文献
109.
110.