全文获取类型
收费全文 | 23308篇 |
免费 | 1565篇 |
国内免费 | 986篇 |
专业分类
25859篇 |
出版年
2024年 | 53篇 |
2023年 | 299篇 |
2022年 | 641篇 |
2021年 | 1026篇 |
2020年 | 689篇 |
2019年 | 920篇 |
2018年 | 924篇 |
2017年 | 717篇 |
2016年 | 998篇 |
2015年 | 1373篇 |
2014年 | 1553篇 |
2013年 | 1820篇 |
2012年 | 1999篇 |
2011年 | 1907篇 |
2010年 | 1068篇 |
2009年 | 936篇 |
2008年 | 1069篇 |
2007年 | 993篇 |
2006年 | 910篇 |
2005年 | 781篇 |
2004年 | 683篇 |
2003年 | 586篇 |
2002年 | 528篇 |
2001年 | 350篇 |
2000年 | 379篇 |
1999年 | 312篇 |
1998年 | 184篇 |
1997年 | 163篇 |
1996年 | 186篇 |
1995年 | 166篇 |
1994年 | 140篇 |
1993年 | 104篇 |
1992年 | 153篇 |
1991年 | 151篇 |
1990年 | 125篇 |
1989年 | 97篇 |
1988年 | 101篇 |
1987年 | 106篇 |
1986年 | 72篇 |
1985年 | 96篇 |
1984年 | 54篇 |
1983年 | 57篇 |
1982年 | 28篇 |
1981年 | 27篇 |
1980年 | 30篇 |
1979年 | 38篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1975年 | 29篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Low angle X-ray diffraction patterns were recorded from crab leg muscle in living resting state and in rigor (glycerol-extracted). Both resting and rigor patterns showed a series of layer-lines arising from a helical arrangement of actin subunits in the thin filaments. In the resting state, the crossover repeat of the long-pitch actin helices was 36.6 nm, and the symmetry of the genetic actin helix was an intermediate between and . When the muscle went into rigor, the crossover repeat changed to 38.3 nm and the helical symmetry to .In the living resting pattern, six other reflections were observed on the meridian and in the near-meridional region. These were indexed as orders of 2 × 38.2 nm and could be assigned to troponin molecules; the spacings and the intensity distributions of these reflections could be explained by the model proposed by Ohtsuki (1974) for the arrangement of troponin molecules in the thin filaments.The muscle in rigor gave meridional and near-meridional reflections at orders of 2 × 38.3 nm. These were identified as the same series of reflections as was assigned to troponin in the living resting pattern, but were more intense and could be seen up to higher orders. We consider that the myosin heads attached to the thin filament at regular intervals along its axis also contribute to these reflections in the rigor pattern. 相似文献
44.
45.
J. J. González-Aguilera A. Ma. Fernández-Peralta 《Plant Systematics and Evolution》1981,139(1-2):147-154
The meiotic behaviour abnormalities, fertility and size of pollen of 6 taxa ofSesamoides have been analysed. Besides diploids (2x), polyploids (4x, 6x, 8x) have been found. The chromosome base number is x = 10, but an origin from x = 5 is suggested. 相似文献
46.
Chicken brain choline acetyltransferase was purified to homogeneity using ammonium sulfate fractionation, followed by chromatography on DEAE-Sephadex (A-25), hydroxyapatite, Sephadex G-150, immunoabsorption and Sepharose-CoA columns. A purification of 3500-fold was achieved and the final preparation had a specific activity of 2:32 μmol acetylcholine formed per minute per milligram protein. The purified chicken choline acetyltransferase migrated as a single band on polyacrylamide gel electrophoresis in the presence and absence of sodium deodecyl sulfate. The native enzyme, with a molecular weight of 67,000 daltons, consists of two subunits of identical molecular weight. Chicken choline acetyltransferase has a sharp pH optimum of 7.4. It is activated by sodium chloride and potassium chloride but inhibited by cupric ion and N-ethylmaleimide. 相似文献
47.
Summary The thickness of ectoplasmic walls decreases at the contraction phase and increases at the expansion phase of each pulsation cycle. In average, 29% of material forming the walls of expanded veins is evacuated during contraction with the endoplasm streaming. 相似文献
48.
49.
一类含间隙分布时滞的种群增长模型的稳定性 总被引:4,自引:0,他引:4
本文首先利用间隙分布时滞函数来建立更为符合实际的种群增长模型,然后运用两种不同的方法,对其平衡位置的局部稳定性进行了全面的讨论,得出了局部渐近稳定的充分必要条件,在参数平面上划分出了稳定和不稳地的区域。 相似文献
50.
A disseminated infection with Penicillium marneffei, a rare human pathogen that may infect both healthy and immunocompromised patients, was diagnosed by fine needle aspiration cytology in a patient infected with the human immunodeficiency virus. The presence of yeast-form organisms with an eccentric or central dot and occasional septate and elongated forms highly suggested the diagnosis, which was confirmed on culture. Establishment of the diagnosis is important because this infection is potentially curable. 相似文献