全文获取类型
收费全文 | 911篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 520篇 |
晶体学 | 14篇 |
力学 | 79篇 |
数学 | 134篇 |
物理学 | 180篇 |
出版年
2022年 | 8篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 8篇 |
2017年 | 15篇 |
2016年 | 17篇 |
2015年 | 8篇 |
2014年 | 27篇 |
2013年 | 62篇 |
2012年 | 60篇 |
2011年 | 49篇 |
2010年 | 31篇 |
2009年 | 17篇 |
2008年 | 31篇 |
2007年 | 28篇 |
2006年 | 35篇 |
2005年 | 30篇 |
2004年 | 22篇 |
2003年 | 31篇 |
2002年 | 31篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1998年 | 6篇 |
1997年 | 16篇 |
1996年 | 11篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1973年 | 16篇 |
1945年 | 6篇 |
1941年 | 11篇 |
1936年 | 9篇 |
排序方式: 共有927条查询结果,搜索用时 15 毫秒
1.
2.
3.
In this paper, we examine the orthogonal Latin squares (OLS) problem from an integer programming perspective. The OLS problem has a long history and its significance arises from both theoretical aspects and practical applications. The problem is formulated as a four-index assignment problem whose solutions correspond to OLS. This relationship is exploited by various routines (preliminary variable fixing, branching, etc) of the Branch & Cut algorithm we present. Clique, odd-hole and antiweb inequalities implement the ‘Cut’ component of the algorithm. For each cut type a polynomial-time separation algorithm is implemented. Extensive computational analysis examines multiple aspects concerning the design of our algorithm. The results illustrate clearly the improvement achieved over simple Branch & Bound. 相似文献
4.
K. Vinay Kumar Reddy B. Sreenivasa Reddy M. Sreenath Reddy Ch. Gopal Reddy P. Yadagiri Reddy K. Rama Reddy 《Radiation measurements》2003,36(1-6):419-423
Studies conducted by Atomic Minerals Directorate of Exploration and Research (AMD) of Hyderabad, India had established the presence of higher concentrations of uranium in Lambapur and Peddagattu areas of Nalgonda district, AP, India and it was estimated that it could be a viable source for commercial extraction. The envisaged extraction process involves dispersion of radioactive particulate matter into atmosphere. Environmental radioactive studies in and around proposed mining areas at this point of time will be extremely useful for establishing base line data before a large scale uranium extraction process comes into existence. To this end, Solid State Nuclear Track Detectors were installed to evaluate indoor radon and thoron concentration levels in the dwellings of the area. The geometric means of radon and thoron concentration levels were found to be (7.1±0.2)×101 and (6.7±0.3)×101 Bq/m3, respectively. Simultaneously, natural background radiation measurements were also made and these levels are found to vary from 770 to 3995 μGy/y in the spatial distribution. 相似文献
5.
6.
Surendra K Krishnaveni NS Reddy MA Nageswar YV Rao KR 《The Journal of organic chemistry》2003,68(5):2058-2059
A mild and efficient oxidation of alcohols with o-iodoxybenzoic acid (IBX) catalyzed by beta-cyclodextrin in a water/acetone mixture (86:14) has been developed. A series of alcohols were oxidized at room temperature in excellent yields. 相似文献
7.
2‐Acetyl thiophenethiocynate (ATT) was synthesized and its characterization study was carried out using elemental analysis, IR and NMR techniques. The new reagent was proposed as an extractant for the development of the extractive spectrophotometric method for determination of Pt(IV) metal. The reagent complexes with the metal to produce a yellow colored complex which was then extracted into ethyl acetate at pH 11.2–11.6 having an absorption maxima at 400 nm. The thermal study showed that the extraction reactions are exothermic in nature with the reagent, and the stoichiometric ratio of Pt(IV) to 2‐acetyl thiophenethiocynate in the organic phase was 1:2. The method permits separation and determination of platinum from real and binary mixtures. The separation of Pt(IV) from bivalent metal ions has been also studied. 相似文献
8.
The maximum number of non-vanishing and independent second order photoelastic coefficients required by the seven pentagonal
and the two icosahedral point groups 5(C5),
(S10),
(C5h
),
m2(D5h
), 52(D5), 5m(C5v
),
2m(D5d
); 235(I), 2/m
(I
h
)—that describe the quasicrystals symmetry groups in two and three dimensions—is obtained. The schemes of non-vanishing and
independent coefficients have been calculated and listed. Finally the results of this group-theoretical study are briefly
discussed. 相似文献
9.
The transport coefficients for the nine point groups
—which represent the symmetry groups of the quasicrystals in two and three dimensions—have been evaluated and tabulated in
this work, employing group-theoretical methods. 相似文献
10.