全文获取类型
收费全文 | 9477篇 |
免费 | 1238篇 |
国内免费 | 745篇 |
专业分类
化学 | 6867篇 |
晶体学 | 125篇 |
力学 | 442篇 |
综合类 | 49篇 |
数学 | 879篇 |
物理学 | 3098篇 |
出版年
2024年 | 26篇 |
2023年 | 180篇 |
2022年 | 269篇 |
2021年 | 312篇 |
2020年 | 360篇 |
2019年 | 327篇 |
2018年 | 255篇 |
2017年 | 232篇 |
2016年 | 444篇 |
2015年 | 380篇 |
2014年 | 459篇 |
2013年 | 672篇 |
2012年 | 862篇 |
2011年 | 863篇 |
2010年 | 514篇 |
2009年 | 518篇 |
2008年 | 608篇 |
2007年 | 582篇 |
2006年 | 498篇 |
2005年 | 468篇 |
2004年 | 304篇 |
2003年 | 209篇 |
2002年 | 232篇 |
2001年 | 194篇 |
2000年 | 184篇 |
1999年 | 162篇 |
1998年 | 149篇 |
1997年 | 118篇 |
1996年 | 110篇 |
1995年 | 142篇 |
1994年 | 125篇 |
1993年 | 94篇 |
1992年 | 83篇 |
1991年 | 71篇 |
1990年 | 68篇 |
1989年 | 41篇 |
1988年 | 47篇 |
1987年 | 37篇 |
1986年 | 38篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 13篇 |
1982年 | 26篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
952.
M.R. Su Z.F. Yang B. Chen 《Communications in Nonlinear Science & Numerical Simulation》2009,14(4):1773-1780
Set pair analysis (SPA) is introduced to assess the urban ecosystems, through which the approximate degree of urban ecosystem health to the optimal set is calculated to describe the health level of the urban ecosystems by combining multiple health indices. The urban ecosystem health levels of Beijing, Dalian, Shanghai, Wuhan, Xiamen and Guangzhou from 1995 to 2003 are thereafter evaluated using SPA. The results show that the urban ecosystem health states of Xiamen and Guangzhou is the best during the study period, while the health states of the others changes over time. Particularly, the change of Beijing’s urban ecosystem health from 1992 to 2003 is analyzed in detail. 相似文献
953.
We discuss how the spectral changes of quarkonia at T
c can reflect the ‘critical’ behaviour of QCD phase transition. Starting from the temperature dependencies of the energy density
and pressure from lattice QCD calculation, we extract the temperature dependencies of the scalar and spin-2 gluon condensates
near T
c. We also parametrize these changes into the electric and magnetic condensate near T
c. While the magnetic condensate hardly changes across T
c, we find that the electric condensate increases abruptly above T
c. Similar abrupt change is also seen in the scalar condensate. Using the QCD second-order Stark effect and QCD sum rules,
we show that these sudden changes induce equally abrupt changes in the mass and width of J/ψ, both of which are larger than 100 MeV at slightly above T
c.
相似文献
954.
The relationships between the morphological characteristics and the vulnerability of atherosclerotic plaque were analyzed
theoretically and several suggestions were proposed to evaluate the plaque vulnerability. Validated by animal experiments
and clinical studies, the theoretical results were confirmed.
Supported by the National Natural Science Foundation of China (Grant Nos. 10302016 and 60402023), the National Basic Research
Program of China (973 Program)(Grant No. 2006CB503803), and the National Hi-Tech Research and Development Program of China
(863 Program) (Grant No. 2007AA02Z448) 相似文献
955.
Let X1,X2,... be a sequence of i.i.d. random variables and let X(1),X(2),... be the associatedrecord value sequence. We focus on the asymptotic distributions of sums of records, Tn=∑nk=1X(k), forX1 ∈ LN(γ). In this case, we find that 2 is a strange point for parameter γ. When γ> 2, Tn is asymptoticallynormal, while for 2 >γ> 1, we prove that Tn cannot converge in distribution to any non-degenerate lawthrough common centralizing and normalizing and log Tn is asymptotically normal. 相似文献
956.
The uniqueness of classical semicontinuous viscosity solutions of the Cauchy problem for Hamilton–Jacobi equations is established for globally Lipschitz continuous and convex Hamiltonian H=H(Du), provided the discontinuous initial value function ?(x) is continuous outside a set Γ of measure zero and satisfies
(1)
We prove that the discontinuous solutions with almost everywhere continuous initial data satisfying () become Lipschitz continuous after finite time for locally strictly convex Hamiltonians. The L1-accessibility of initial data and a comparison principle for discontinuous solutions are shown for a general Hamiltonian. The equivalence of semicontinuous viscosity solutions, bi-lateral solutions, L-solutions, minimax solutions, and L∞-solutions is clarified. To cite this article: G.-Q. Chen, B. Su, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 113–118 相似文献
957.
958.
Yin Xiangchen Lin Chunchen Zhou Zhifen Chen Wandong Zhu Shourong Lin Huakuan Su Xuncheng Chen Yunti 《Transition Metal Chemistry》1999,24(5):537-540
The hydrolysis kinetics of p-nitrophenyl acetate (NA) catalyzed by CuII, ZnII and CoII complexes of tris(2-benzimidazylmethyl)amine (NBT) have been studied. The hydrolysis rate is first-order in both metal(II) complex and NA. The second-order rate constants, kcat are 0.083, 0.241 and 0.285mol–1Ls–1 (298K, I = 0.10molL–1 KNO3, 0.02molL–1 tris buffer, 40% MeCN aqueous solution) for Zn–NBT, Co–NBT and Cu–NBT complexes, respectively. The result indicates that the hydrolytic metalloenzyme activity of different metal complexes increases with the electrophilicity of the metal ions and that the complexes, in this paper, constitute that most efficient hydrolytic metalloenzyme models reported to date. An increase in MeCN content in the solution greatly reduces the hydrolytic activity of the nucleophiles. 相似文献
959.
提出一种采用Kohonen网络算法进行12电极电容CT系统的图像重建的方法.该网络由输入和输出两层神经元组成,输入为12电极电容CT系统测量所得的66个电容值,输出对应管道介质的空间分布模式.该网络采用竞争算法无监督学习,实验结果证明,该网络有较强的抗噪声能力,可重建出较精确的介质分布图像 相似文献
960.
Consider a closed Jackson type network in which each queue has a single exponential server. Assume that N customers are moving among k queues. We establish simple closed form bounds on the network throughput (both lower and upper), which are sharper than those that are currently available. Numerical evaluation indicates that the improvements are significant. 相似文献