全文获取类型
收费全文 | 29259篇 |
免费 | 4670篇 |
国内免费 | 4811篇 |
专业分类
化学 | 22431篇 |
晶体学 | 485篇 |
力学 | 1481篇 |
综合类 | 414篇 |
数学 | 3278篇 |
物理学 | 10651篇 |
出版年
2024年 | 48篇 |
2023年 | 377篇 |
2022年 | 681篇 |
2021年 | 858篇 |
2020年 | 1035篇 |
2019年 | 1065篇 |
2018年 | 924篇 |
2017年 | 848篇 |
2016年 | 1320篇 |
2015年 | 1369篇 |
2014年 | 1626篇 |
2013年 | 2210篇 |
2012年 | 2652篇 |
2011年 | 2690篇 |
2010年 | 2023篇 |
2009年 | 1960篇 |
2008年 | 2321篇 |
2007年 | 2067篇 |
2006年 | 1817篇 |
2005年 | 1526篇 |
2004年 | 1337篇 |
2003年 | 1152篇 |
2002年 | 1255篇 |
2001年 | 1019篇 |
2000年 | 799篇 |
1999年 | 640篇 |
1998年 | 417篇 |
1997年 | 394篇 |
1996年 | 346篇 |
1995年 | 292篇 |
1994年 | 274篇 |
1993年 | 236篇 |
1992年 | 226篇 |
1991年 | 169篇 |
1990年 | 160篇 |
1989年 | 124篇 |
1988年 | 79篇 |
1987年 | 69篇 |
1986年 | 62篇 |
1985年 | 61篇 |
1984年 | 45篇 |
1983年 | 33篇 |
1982年 | 23篇 |
1981年 | 22篇 |
1980年 | 11篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1974年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Jensen and Toft 8 conjectured that every 2‐edge‐connected graph without a K5‐minor has a nowhere zero 4‐flow. Walton and Welsh 19 proved that if a coloopless regular matroid M does not have a minor in {M(K3,3), M*(K5)}, then M admits a nowhere zero 4‐flow. In this note, we prove that if a coloopless regular matroid M does not have a minor in {M(K5), M*(K5)}, then M admits a nowhere zero 4‐flow. Our result implies the Jensen and Toft conjecture. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
92.
具有避难所的非自治竞争系统的持续生存和全局稳定性 总被引:2,自引:0,他引:2
考虑一个四缀块模型,其中一缀块里有三个竞争种群,另外三个分别是它们的避难所,并且种群能在竞争缀块和各自的避难所间相互扩散.在一定的条件下,我们给出了此模型的持续生存,周期性和全局稳定性. 相似文献
93.
The interactions of Cu(II) in Cu(II)-exchanged K-L gallosilicate with adsorbates containing coordinative nitrogens in ammonia, pyridine, aniline, acetonitrile and hydrazine, and with the adsorbates carbon monoxide, benzene, propanol and dimethyl sulfoxide are investigated by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. These results are compared with those in Cu(II)-exchanged K-L aluminosilicate and the differences are discussed. Adsorption of ammonia produces a complex containing four molecules of ammonia based on resolved nitrogen superhyperfine interaction. Upon equilibrium with pyridine, Cu(II) forms a complex containing four molecules of pyridine in CuK-L gallosilicate and a complex containing only three molecules of pyridine in CuK-L aluminosilicate based on resolved nitrogen superhyperfine. Upon adsorption of aniline and acetonitrile, Cu(II) forms complexes containing two molecules of each in CuK-L gallosilicate based on resolved nitrogen superhyperfine. However, no resolved nitrogen superhyperfine between hydrazine and Cu(II) is seen. Adsorption of carbon monoxide, benzene, propanol and dimethyl sulfoxide causes changes in the ESR spectrum of Cu(II), indicating migration of Cu(II) into cation positions in the main channels where adsorbate coordination can occur. Cu(II) forms complexes with one molecule of benzene and two molecules of propanol based on ESEM data in both K-L gallosilicate and K-L aluminosilicate. However, Cu(II) interacts directly with one dimethyl sulfoxide in K-L aluminosilicate but only indirectly at a longer distance with one dimethyl sulfoxide in K-L gallosilicate based on ESEM data. 相似文献
94.
95.
神经网络法计算镉(Ⅱ),羟基及碳酸根三元体系的形态分布 总被引:2,自引:0,他引:2
采用前馈线笥网络BP算法,计算了Cd62+-OH^-CO^2-3三元体系的累积稳定常数。用Hopfield反馈网络研究了体系中络合物的形态分布。溶液中溶解的CO2对lgβ1的计算结果有重要影响,对lgβ2,lgβ3,lgβ4的结果影响不大。 相似文献
96.
Tao Liu Zuxiong Xu Zhongtao Zhao Ruzhang Ma Tiandou Hu Yaning Xie Yinghuan Guo 《中国科学A辑(英文版)》1997,40(4):395-399
The role of magnetoelastic coupling effects in nanocrystalline ferromagnets is investigated by means of high-field magnetization and Doppler-broadening spectrum measurements. For the nanocrystalline Fe73 5Cu1Nb3Si13.5B9 alloy, the results show that the pinning effects resulting from the quasidislocation dipole intensely influence the movement of domain wall; by coupling with the magnetostriction the defects-induced stress fields determine the magnetic properties at the early stage of crystallization. In view of the effective anisotropy and magnetoelastic coupling energy the optimal annealing conditions of alloys are discussed. 相似文献
97.
98.
99.
High-level ab initio calculations are carried out to study the relative stability of the two hydrogen bonded structures of water-hydrogen sulfide complex, one with water as the proton donor (A) and the other with hydrogen sulfide as the proton donor (B). The results show that structure A is considerably more stable than B at the correlated level, which is in contrast with previous results obtained from Hartree-Fock calculations. 相似文献
100.
罗尔定理证明一类存在性问题 总被引:1,自引:0,他引:1
提出罗尔定理证明一类存在性问题的方法,采用拉格朗日中值定理或柯西中值定理来证明这类问题往往需要构造精巧的辅助函数,我们还指出了这种方法的一般性. 相似文献