全文获取类型
收费全文 | 1189篇 |
免费 | 28篇 |
国内免费 | 5篇 |
专业分类
化学 | 751篇 |
晶体学 | 6篇 |
力学 | 24篇 |
数学 | 166篇 |
物理学 | 237篇 |
综合类 | 38篇 |
出版年
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2016年 | 14篇 |
2015年 | 17篇 |
2014年 | 27篇 |
2013年 | 68篇 |
2012年 | 46篇 |
2011年 | 45篇 |
2010年 | 25篇 |
2009年 | 25篇 |
2008年 | 40篇 |
2007年 | 43篇 |
2006年 | 56篇 |
2005年 | 36篇 |
2004年 | 42篇 |
2003年 | 56篇 |
2002年 | 69篇 |
2001年 | 39篇 |
2000年 | 36篇 |
1999年 | 34篇 |
1998年 | 28篇 |
1997年 | 19篇 |
1996年 | 26篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 23篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 17篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1973年 | 12篇 |
1970年 | 9篇 |
1969年 | 11篇 |
1967年 | 5篇 |
排序方式: 共有1222条查询结果,搜索用时 15 毫秒
1.
2.
3.
Rüdiger Schultz Leen Stougie Maarten H. van der Vlerk 《Mathematical Programming》1998,83(1-3):229-252
In this paper we present a framework for solving stochastic programs with complete integer recourse and discretely distributed right-hand side vector, using Gröbner basis methods from computational algebra to solve the numerous second-stage integer programs. Using structural properties of the expected integer recourse function, we prove that under mild conditions an optimal solution is contained in a finite set. Furthermore, we present a basic scheme to enumerate this set and suggest improvements to reduce the number of function evaluations needed. 相似文献
4.
5.
6.
Palladium(II)-catalyzed oxidations constitute a paramount reaction class but have remained immature over the past few decades. Recently, this field has reappeared at the forefront of organometallic catalysis. This emerging area article outlines recent developments in palladium(II)-catalyzed oxidation chemistry with discussion of potential future growth. 相似文献
7.
The molecular structure of 4,4′-sulfanidyl-bis-thiophenol (C12H10S3) has been determined by gas electron diffraction. Assuming identical geometry and D2h local symmetry for ---SC6H4S--- moieties, the following bond lengths (rg) and bond angles were obtained: C---H = 1.101 ± 0.005, S---H = 1.388 ± 0.019, (C---C)mean = 1.400 ± 0.003, (S---C)mean = 1.778 ± 0.004 Å, Car---S---Car = 103.5 ± 1.3, C---C(S)---C = 120.4 ± 0.3, C(H)---C(H)---H = 119.1 ± 0.9 and C---S---H = 94.6 ± 3.1°. Two ratational forms were found to reproduce the experimental data, characterized by dihedral angles of the benzene rings with respect to the CarSCar plane; 1 = 67.8 ± 2.0°, 2 = 4.5 ± 7.2°, and 1 = 69.4 ± 2.0δ, 2 = −26.6 ± 7.1°. Identical signs of 1 and 2 indicate that the two benzene rings are rotated in the same direction about the respective Scentral---C axes. 相似文献
8.
9.
Jan F. Keij Jan Th . M. Jansen Frank W. Schultz Jan W. M. Visser 《Photochemistry and photobiology》1994,60(5):503-509
Abstract-During the development of a photodamage cell sorter several photosensitizers were tested for their ability to photoinactivate more than 90% of the sensitized cells after a brief irradiation with a fluence of 10 kJ/m2 . In pilot experiments, yeast cells sensitized with 10-dodecyl acridine orange (DAO) were effectively photoinactivated after receiving a fluence of 10 kJ/m2 delivered in 8 s. However, when the same fluence was delivered in 3 μ s during passage through a focused laser beam in the cell sorter, all cells survived.
Computer simulations of the relevant photophysical and chemical reactions inside the irradiated cell were used to investigate the cause of this phenomenon. The results indicated that the absence of photoinactivation by DAO, after flash irradiations, was caused by the combined effects of (1) limited oxygen diffusion into the cell and (2) a reduced number of collisions between photosensitizer triplet and oxygen molecules during the irradiation due to saturation of the intracellular photosensitizer triplet concentration. The contributions of triplet-triplet annihilation and triplet quenching by ground state photosensitizer molecules were found to be minimal and not significant. These findings indicate that Type II photosensitizers are incapable of rapid selective photoinactivation in cell sorters. 相似文献
Computer simulations of the relevant photophysical and chemical reactions inside the irradiated cell were used to investigate the cause of this phenomenon. The results indicated that the absence of photoinactivation by DAO, after flash irradiations, was caused by the combined effects of (1) limited oxygen diffusion into the cell and (2) a reduced number of collisions between photosensitizer triplet and oxygen molecules during the irradiation due to saturation of the intracellular photosensitizer triplet concentration. The contributions of triplet-triplet annihilation and triplet quenching by ground state photosensitizer molecules were found to be minimal and not significant. These findings indicate that Type II photosensitizers are incapable of rapid selective photoinactivation in cell sorters. 相似文献
10.
Studies directed at a synthesis of dihydrothiepin 1b have resulted in the elucidation of several factors which effect cyclobutene ring opening in the 3-heterobicyclo[3.2.0]hept-6-ene ring system. We report the unexpected rearrangement of 4a, 4b, 13b and 13c to the synthetically useful a-vinyl-2,5-dihydrothiophenes 7a, 7b, 15a and 15b, respectively. Conversion of 4a to 6 is suggested to occur by a 1,3-rearrangement of 4a to isomeric 3-thiabicyclo[3.2.0]hept-6-ene 19 followed by cyclobutene ring opening in 19. 相似文献