全文获取类型
收费全文 | 34963篇 |
免费 | 5791篇 |
国内免费 | 4339篇 |
专业分类
化学 | 25562篇 |
晶体学 | 355篇 |
力学 | 2257篇 |
综合类 | 355篇 |
数学 | 3916篇 |
物理学 | 12648篇 |
出版年
2024年 | 112篇 |
2023年 | 695篇 |
2022年 | 1180篇 |
2021年 | 1289篇 |
2020年 | 1461篇 |
2019年 | 1481篇 |
2018年 | 1185篇 |
2017年 | 1009篇 |
2016年 | 1708篇 |
2015年 | 1778篇 |
2014年 | 1988篇 |
2013年 | 2530篇 |
2012年 | 3026篇 |
2011年 | 3143篇 |
2010年 | 2128篇 |
2009年 | 2011篇 |
2008年 | 2149篇 |
2007年 | 1934篇 |
2006年 | 1815篇 |
2005年 | 1563篇 |
2004年 | 1382篇 |
2003年 | 1168篇 |
2002年 | 1243篇 |
2001年 | 1117篇 |
2000年 | 834篇 |
1999年 | 761篇 |
1998年 | 568篇 |
1997年 | 488篇 |
1996年 | 470篇 |
1995年 | 441篇 |
1994年 | 380篇 |
1993年 | 303篇 |
1992年 | 327篇 |
1991年 | 294篇 |
1990年 | 255篇 |
1989年 | 192篇 |
1988年 | 126篇 |
1987年 | 110篇 |
1986年 | 101篇 |
1985年 | 96篇 |
1984年 | 60篇 |
1983年 | 52篇 |
1982年 | 39篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1969年 | 4篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献
23.
Xiaodong Hu 《应用数学学报(英文版)》1993,9(2):97-103
Since the point-to-set maps were introduced by Zangwill[1] in the study of conceptual algorithms, various sufficient conditions for the algorithms to be of global convergence have been established. In this paper, the relations among all these conditions are illustrated by a unified approach; still more, unlike the sufficient conditions previously given in the literature, a new necessary condition is put forward at the end of the paper, so that it implies more applications. 相似文献
24.
HUYUDA MENGZHIQING 《高校应用数学学报(英文版)》1998,13(4):473-477
In this paper, the existence theorem of the cone-weak subdiflerential of set-valued mapping in locally convex topological vector space is proved. 相似文献
25.
The micro element content of food is an important quality index due to the action of these elements on human health. In this
article, we discuss how to ensure the reliability of analytical data on micro elements in order to truly represent the condition
of food. Sampling, treatment of the analytical sample, selection of the analytical method, standard solution, and certified
reference material, blank test, calibration of the instrument and equipment, application of the quality control chart, assessment
of the final analytical result, and quality assurance system are briefly described.
Received: 5 July 2001 Accepted: 19 November 2001 相似文献
26.
J Z Hu R J Pugmire A M Orendt D M Grant C Ye 《Solid state nuclear magnetic resonance》1992,1(4):185-195
Taking advantage of the long 13C T1 values generally encountered in solids, selective saturation and inversion of more than one resonance in 13C CP/MAS experiments can be achieved by sequentially applying several DANTE pulse sequences centered at different transmitter frequency offsets. A new selective saturation pulse sequence is introduced composed of a series of 90 degrees DANTE sequences separated by interrupted decoupling periods during which the selected resonance is destroyed. Applications of this method, including the simplification of the measurement of the principal values of the 13C chemical shift tensor under slow MAS conditions, are described. The determination of the aromaticity of coal using a relatively slow MAS rate is also described. 相似文献
27.
28.
For approximate wave functions, we prove the theorem that there is a one‐to‐one correspondence between the constraints of normalization and of the Fermi–Coulomb and Coulomb hole charge sum rules at each electron position. This correspondence is surprising in light of the fact that normalization depends on the probability of finding an electron at some position. In contrast, the Fermi–Coulomb hole sum rule depends on the probability of two electrons staying apart because of correlations due to the Pauli exclusion principle and Coulomb repulsion, while the Coulomb hole sum rule depends on Coulomb repulsion. We demonstrate the theorem for the ground state of the He atom by the use of two different approximate wave functions that are functionals rather than functions. The first of these wave function functionals is constructed to satisfy the constraint of normalization, and the second that of the Coulomb hole sum rule for each electron position. Each is then shown to satisfy the other corresponding sum rule. The significance of the theorem for the construction of approximate “exchange‐correlation” and “correlation” energy functionals of density functional theory is also discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
29.
30.
应用七级目测法对浙江中部地区27个夏熟作物田样点的杂草进行了优势等级调查,将所得数据转换成重要值,以杂草在27个样点中的重要值为运算指标,应用主成分分析法和图论聚类中的最小生成树法,对24种杂草的生态学相似性进行了比较,指出了长期使用单一的除草剂导致农田杂草种群迅速更迭的原因:杂草对除草剂的敏感性差异及不同杂草间的生态学特性的差异。 相似文献