全文获取类型
收费全文 | 48118篇 |
免费 | 9912篇 |
国内免费 | 17928篇 |
专业分类
化学 | 34413篇 |
晶体学 | 2283篇 |
力学 | 3954篇 |
综合类 | 2044篇 |
数学 | 7934篇 |
物理学 | 25330篇 |
出版年
2024年 | 134篇 |
2023年 | 503篇 |
2022年 | 1861篇 |
2021年 | 1776篇 |
2020年 | 1691篇 |
2019年 | 1658篇 |
2018年 | 1522篇 |
2017年 | 2411篇 |
2016年 | 1639篇 |
2015年 | 2512篇 |
2014年 | 3034篇 |
2013年 | 4034篇 |
2012年 | 3896篇 |
2011年 | 4114篇 |
2010年 | 4304篇 |
2009年 | 4451篇 |
2008年 | 5040篇 |
2007年 | 4430篇 |
2006年 | 4389篇 |
2005年 | 3844篇 |
2004年 | 2926篇 |
2003年 | 2098篇 |
2002年 | 2079篇 |
2001年 | 2132篇 |
2000年 | 2225篇 |
1999年 | 1276篇 |
1998年 | 680篇 |
1997年 | 553篇 |
1996年 | 501篇 |
1995年 | 444篇 |
1994年 | 522篇 |
1993年 | 481篇 |
1992年 | 412篇 |
1991年 | 294篇 |
1990年 | 284篇 |
1989年 | 323篇 |
1988年 | 259篇 |
1987年 | 210篇 |
1986年 | 164篇 |
1985年 | 128篇 |
1984年 | 121篇 |
1983年 | 134篇 |
1982年 | 113篇 |
1981年 | 97篇 |
1980年 | 70篇 |
1979年 | 63篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1971年 | 17篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
51.
52.
In this paper,we consider a delayed diffusive SVEIR model with general inci-dence.We first establish the threshold dynamics of this model.Using a Nonstandard Fi... 相似文献
53.
The authors introduce a notion of a weak graph map homotopy (they call it
M-homotopy), discuss its properties and applications. They prove that the weak graph
map homotopy equivalence between graphs coincides with the graph homotopy equivalence
defined by Yau et al in 2001. The difference between them is that the weak graph map
homotopy transformation is defined in terms of maps, while the graph homotopy transformation is defined by means of combinatorial operations. They discuss its advantages over
the graph homotopy transformation. As its applications, they investigate the mapping
class group of a graph and the 1-order MP-homotopy group of a pointed simple graph.
Moreover, they show that the 1-order MP-homotopy group of a pointed simple graph is
invariant up to the weak graph map homotopy equivalence. 相似文献
54.
对给定的简单图$H_1,H_2,\ldots,H_c$, 我们将使完全图$K_n$的任意边分解$\{G_i\}^c_{i=1}$都存在至少一个$G_i$有子图同构于$H_i$的最小正整数$n$称为多染色拉姆齐数 $R(H_1,H_2,\ldots,$ $H_c)$. 对正整数$m,n_1,n_2,\ldots,n_c$, 令$\Sigma=\sum_{i=1}^{c}(n_i-1)$. 在文献中,我们已经获得了$R(K_{1,n_1},\ldots,K_{1,n_c},P_m)$ 的一些界和精确值.Wang推测若$\Sigma\not\equiv 0\pmod{m-1}$且$\Sigma+1\ge (m-3)^2$, 则有$R(K_{1,n_1},\ldots, K_{1,n_c}, P_m)=\Sigma+m-1.$ 本文中, 我们给出了一个新的下界并给出$R(K_{1,n_1},\ldots,K_{1,n_c},P_m)$在$m\leq\Sigma$, $\Sigma\equiv k\pmod{m-1}$且$2\leq k \leq m-2$情况下的部分精确值. 这些结果部分证实了Wang的猜想. 相似文献
55.
The determination of 241Am in the environment is of importance in monitoring its release and assessing its environmental impact and radiological risk. This paper aims to give an overview about the recent developments and the state-of-art analytical methods for 241Am determination in environmental samples. Thorough discussions are given in this paper covering a wide range of aspects, including sample pre-treatment and pre-concentration methods, chemical separation techniques, source preparation, radiometric and mass spectrometric measurement techniques, speciation analyses, and tracer applications. The paper focuses on some hyphenated separation methods based on different chromatographic resins, which have been developed to achieve high analytical efficiency and sample throughput for the determination of 241Am. The performances of different radiometric and mass spectrometric measurement techniques for 241Am are evaluated and compared. Tracer applications of 241Am in the environment, including speciation analyses of 241Am, and applications in nuclear forensics are also discussed. 相似文献
56.
57.
在碱性介质中,Mn(Ⅱ)对催化KIO4氧化镁试剂Ⅰ(对硝基苯偶氮间苯二酚)的褪色反应有显著作用。据此建立了测定痕量Mn(Ⅱ)的流动注射停流-催化光度法。优化了流动注射条件,Mn(Ⅱ)在2~10μg/L,10~160μg/L,160~1000μg/L范围内符合比尔定律,采样频率6样/h,检出限0.12μg/L,相对标准偏差(RSD)4.9%(n=6)。用于环境水样中Mn(Ⅱ)的检测,回收率为95.5%~102%。 相似文献
58.
59.
ZHANG Shun-Li 《理论物理通讯》2006,45(6):969-978
The generalized conditional symmetry is developed to study the variable
separation for equations of type uxt=A(u,ux)uxx+B(u,ux). Complete classification of those equations which admit derivative-dependent functional separable solutions is obtained and some of their
exact separable solutions are constructed. 相似文献
60.
As a key factor leading to the pressure-dependent R1-line-shift reversal and R1-state lifetime, at 10 K, the pressure-dependent variation of mixing-degree of |t22(3T1)e4T2〉
and |t232
E〉base-wavefunctions in the wavefunction of R1 state of
LLGG:Cr3+ has been calculated and analyzed. From this, the physical origin of the pressure-dependent R1-line-shift reversal has been revealed. Furthermore, by using
the pressure-dependent values of the
sum of all square mixing-coefficients
of |t22(3T1)e4T2〉in the wavefunction of R1 state, the lifetimes of R1 state
of LLGG:Cr3+ at various pressures have been calculated, which
are in good agreement with observed results. The quantum anticrossing
effect between
t232E and t22(3T1)e4T2
levels due to both spin-orbital interaction and electron-phonon interaction is remarkable, which is related to the admixture of
|t22(3T1)e4T2〉and |t232
E〉as well as the low-high crystal-field transition. 相似文献