全文获取类型
收费全文 | 907篇 |
免费 | 16篇 |
国内免费 | 11篇 |
专业分类
化学 | 551篇 |
晶体学 | 26篇 |
力学 | 47篇 |
数学 | 192篇 |
物理学 | 118篇 |
出版年
2023年 | 8篇 |
2022年 | 14篇 |
2021年 | 24篇 |
2020年 | 22篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 10篇 |
2016年 | 38篇 |
2015年 | 14篇 |
2014年 | 35篇 |
2013年 | 66篇 |
2012年 | 44篇 |
2011年 | 44篇 |
2010年 | 35篇 |
2009年 | 44篇 |
2008年 | 60篇 |
2007年 | 39篇 |
2006年 | 42篇 |
2005年 | 30篇 |
2004年 | 30篇 |
2003年 | 30篇 |
2002年 | 39篇 |
2001年 | 12篇 |
2000年 | 19篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1965年 | 2篇 |
1916年 | 4篇 |
排序方式: 共有934条查询结果,搜索用时 31 毫秒
71.
Daniel Francisco Palacios Juan A. Alfonso Haydn Barros John J. LaBrecque Karla Prez Marian R. Lossada 《Radiation measurements》2008,43(1):77-84
A semi-empirical method to determine radionuclide concentrations in large environmental samples without the use of reference material and avoiding the typical complexity of Monte-Carlo codes is proposed. The calculation of full-energy peak efficiencies was carried out from a relative efficiency curve (obtained from the gamma spectra data), and the geometric (simulated by Monte-Carlo), absorption, sample and intrinsic efficiencies for energies between 130 and 3000 keV. The absorption and sample efficiencies were determined from the mass absorption coefficients, whereas the intrinsic efficiency was approximated by an empirical function. The deviations between calculated and experimental efficiencies for a reference material in most cases are less than 10%. Radionuclide activities in marine sediment samples calculated by the proposed method and by the experimental comparative method were not significantly different. This new method can be used for routine environmental monitoring when uncertainties up to 10% are acceptable. 相似文献
72.
Marian E. Robbins 《Integral Equations and Operator Theory》2002,43(4):480-487
Given a large weighted Hardy space we show there exists a composition operatorC
with that maps from that space into the unweighted Dirichlet space and lies in every Schatten p-class for 0<p<. This is in contrast to the situation in which the image space is a smaller weighted Dirichlet space. It is known that in that case it is not possible to find such a composition operator that is bounded.This research was supported in part by a summer stipend from Bellarmine College. 相似文献
73.
74.
Nuclear substructures associated with apoptosis in HeLa cells have been examined using light-microscopic morphometry, trichrome staining, spectral imaging and transmission electron microscopy. This detailed analysis reveals several sites where alterations in the normal cellular ultrastructure occur during apoptotic progression. To correlate these ultrastructural changes with the underlying molecular processes, we have characterized and quantified apoptotic cell morphology with and without inhibition of two caspases, which are key effectors of the apoptotic program. Using this analysis, early apoptotic events included: (a) the segregation of nucleolar components, a diminished granular component, and a reduction in number but increase in size of fibrillar centers, (b) an increase in the number of cytoplasmic ribosomes and (c) a very minimal increase in the amount of peripherally condensed DNA. Apoptosis progressed with: (a) an increase in the number of perichromatin granules and perichromatin fibrils, (b) a reduction in number of interchromatin granule centers concomitant with an increase in their size, (c) partial digestion and circumferential condensation of the DNA at the nuclear membrane and (d) rounding of the cytoplasm with an increase in organellar density and shrinkage in cell size. Endstage apoptotic cells showed: (a) one (or two) very large pools of incompletely digested DNA, (b) one (or two) very large interchromatin granule centers, (c) an increased number of perichromatin granules which were distanced from DNA and often closely apposed to the nucleolus, (d) formation of unusually condensed, highly coiled perinucleolar bodies and (e) blebbing of highly dense cytoplasm.In HeLa cells treated with UV and inhibitors of caspase 1 and 3, the length of time from early apoptosis to the formation of apoptotic bodies was greatly extended. Inhibiting caspase activity: (a) prevented the pooling of DNA, (b) retarded the formation of large interchromatin granule centers, (c) increased the number of perichromatin granules, (d) produced disassembly of the nucleolus, (e) prevented the formation of highly coiled perinucleolar bodies, and (f) caused vacuolization in the cell center and a unipolar blebbing of the cytoplasm.Spectral imaging in conjunction with serial section electron microscopy confirmed the staining specificities of the condensed DNA, of the large condensed interchromatin granule centers, and of the nucleoli. The results indicate that the interface between the components of the chromatin domain and the interchromatin space is a critical site of caspase activity in apoptosis, and precedes other events such as internucleosomal DNA degradation. 相似文献
75.
Robert C. Moore Marian Borkowski Michael G. Bronikowski Jianfeng Chen Oleg S. Pokrovsky Yuanxian Xia Gregory R. Choppin 《Journal of solution chemistry》1999,28(5):521-531
The stability constants of NpO
2
+
, UO
2
2+
Am3+, and Th4+ with acetate and lactate anions has been measured in 0.3–5.0m NaCl media at 25°C by the solvent extraction technique. For the 1:1 complexation, the values of the stability constants increased in the order: NpO
2
+
< Am3+ <
2
2+
< Th4+, in accordance with the actinide charge density and reflecting the strongly ionic bonding of the complexes. The Pitzer ionic interaction parameters were calculated and used to estimate the thermodynamic stability constants at I = 0. Because our data were collected mainly in the high ionic strength region values of (1) were estimated from values reported in the literature. For all stability constants the Pitzer model gives an excellent representation of the data using three interaction parameters (0), (1), and COn leave from Institute of 相似文献
76.
Marian Vâ jâ itu Alexandru Zaharescu 《Proceedings of the American Mathematical Society》1999,127(8):2225-2232
For given elements and belonging to the ring of integers of a number field we consider the set of all tuples in for which divides for any and prove under some reasonable assumptions that the set of solutions is finite.
77.
78.
79.
We study the behaviour of Koszul cohomology under restriction to a divisor, extending previous results of M. Green. Using our result we compare Greens canonical conjecture to the gonality conjecture of Green-Lazarsfeld.Revised version: 15 May 2003Acknowledgements. M. Aprodu was financed by a EC-Marie Curie Fellowship, contract no. HPMF-CT-2000-00895. We would like to thank the referee for some useful remarks on the first version of this paper. 相似文献
80.
We have performed systematic studies of intensity-related dynamics of the pulse repetition and carrier-envelope offset frequencies in mode-locked Ti:sapphire lasers. We compared the results far two laser systems that have different intracavity dispersion-compensation schemes. We found that the carrier-envelope phase noise and its dynamic response depend critically on the mode-locking conditions. An intensity-related shift of the laser spectrum was found to be instrumental in interpretations. 相似文献