全文获取类型
收费全文 | 58898篇 |
免费 | 4327篇 |
国内免费 | 140篇 |
出版年
2021年 | 407篇 |
2020年 | 366篇 |
2019年 | 397篇 |
2018年 | 976篇 |
2017年 | 915篇 |
2016年 | 1400篇 |
2015年 | 2201篇 |
2014年 | 2354篇 |
2013年 | 3030篇 |
2012年 | 3720篇 |
2011年 | 3491篇 |
2010年 | 2153篇 |
2009年 | 1632篇 |
2008年 | 2902篇 |
2007年 | 2894篇 |
2006年 | 2868篇 |
2005年 | 2662篇 |
2004年 | 2583篇 |
2003年 | 2405篇 |
2002年 | 2385篇 |
2001年 | 1607篇 |
2000年 | 1704篇 |
1999年 | 1353篇 |
1998年 | 517篇 |
1997年 | 432篇 |
1996年 | 404篇 |
1995年 | 377篇 |
1994年 | 395篇 |
1993年 | 359篇 |
1992年 | 836篇 |
1991年 | 801篇 |
1990年 | 787篇 |
1989年 | 736篇 |
1988年 | 696篇 |
1987年 | 621篇 |
1986年 | 606篇 |
1985年 | 556篇 |
1984年 | 497篇 |
1983年 | 456篇 |
1982年 | 397篇 |
1981年 | 394篇 |
1979年 | 513篇 |
1978年 | 391篇 |
1977年 | 332篇 |
1975年 | 386篇 |
1974年 | 377篇 |
1973年 | 347篇 |
1972年 | 363篇 |
1971年 | 326篇 |
1968年 | 314篇 |
排序方式: 共有10000条查询结果,搜索用时 27 毫秒
151.
R Larisch K Kley S Nikolaus W Sitte M Franz H Hautzel W Tress H-W Müller 《Hormones et métabolisme》2004,36(9):650-653
Previous studies on hypothyroid subjects have indicated serious psychiatric symptoms affecting the patients' quality of life. The present prospective cross-sectional study's aim was to examine these symptoms in thyroid patients with different functional states. A total of 254 patients (age: 56 +/- 14 years [mean +/- standard deviation], 181 female, 73 male) referred to a hospital for radioiodine treatment of hyperthyroidism or for follow-up of differentiated thyroid cancer, respectively, were included. All patients underwent the twelve-item general health questionnaire, which is an instrument for detecting mood disturbances. Euthyroid and hyperthyroid patients did not differ significantly in their general health questionnaire score (11 +/- 5 vs. 11 +/- 7), nor did subclinical hyperthyroid (11 +/- 6) or subclinical hypothyroid subjects (12 +/- 5). In contrast, hypothyroid patients showed a significantly higher mean score (17 +/- 7, p < 0.001, ANOVA). Binary logistic regression revealed that hypothyroidism increases age and gender-adjusted risk for critical mood deterioration by seven-fold. Thus, hypothyroidism represents a widely underestimated functional condition that may severely affect mental health. 相似文献
152.
153.
154.
B Griefahn C Künemund M Blaszkewicz K Golka P Mehnert G Degen 《Bioelectromagnetics》2001,22(8):581-588
The present study investigated the hypothesis that a strong extremely low frequency magnetic field partially suppresses the synthesis of melatonin and subsequently elevates the core body temperature. Seven healthy young men (16-22 years) took part in a control and in an exposure session. Three men experienced first the control and then the exposure session, four men experienced the sessions in reverse order. Control sessions were performed as constant routines, where the participants spent 24 hour periods continuously in bed while air temperature was 18 degrees C, illumination less than 30 lux, and the sound pressure level 50 dBA. The exposure sessions differed from that protocol only between 6 pm and 2 am when a strong extremely low frequency magnetic field was continuously applied (16.7 Hz, 0.2 mT). Assuming that the participants were unable to perceive the field consciously, they were blind against the actual condition. Salivary melatonin levels were determined hourly; body core temperatures and heart rates were registered continuously throughout. Neither of these parameters revealed alterations that can be related to the influence of the magnetic field. The present results, taken together with other investigations using that particular field, lead to the hypothesis that the effects most likely, occur, only after repetitive exposures to intermittent fields. 相似文献
155.
Reconstitution and crystallisation experiments with isolated split proteins from Bacillus stearothermophilus ribosomes 总被引:1,自引:0,他引:1
H S Gewitz C Glotz P Goischke B Romberg J Müssig A Yonath H G Wittmann 《Biochemistry international》1987,15(5):887-895
Six proteins (B-L1, B-L6, B-L10, B-L11, B-L12 and B-L16) were removed from 50S ribosomal subunits of Bacillus stearothermophilus by treatment with ethanol and ammonium chloride. The proteins were isolated in a pure form, and one of them (B-L6) was crystallized. Five of the six proteins (in various combinations) were added back to the core particles, resulting in 50S subunits lacking one protein. The biological activities of these ribosomal particles as determined in the poly(U)-system varied over a wide range, depending on the protein which was omitted. The particles lacking one protein provide useful tools for heavy-atom derivation necessary for our crystallographic studies on the 50S subunits of Bacillus stearothermophilus. 相似文献
156.
Absorbance changes associated with the oxidation and reduction of cytochrome f belong to the classical observations about the interaction of the two photosystems. A complex induction pattern of cytochrome f oxidation results, if both photosystems are excited simultaneously. This indicates a light-modulated regulation of the photosynthetic electron transport, which we examined for intact biological systems of decreasing complexity. The ferredoxin-NADP+-oxidoreductase (FNR) is suggested to be activated by light and inactivated in the dark. This is pointed out by the kinetics of variable fluorescence and by the influence of different artificial electron acceptors on the cytochrome f kinetics. The photoreduction of NADP+ by carefully prepared thylakoids demonstrates the activation process directly.This work was supported by the Deutsche Forschungsgemeinschaft. 相似文献
157.
Yongru Sun Berthold M. Heil Günter Kahl Hans Willy Kohlenbach 《Plant Cell, Tissue and Organ Culture》1987,8(1):91-100
Calli were initiated from flower buds, gynoecia and inflorescence segments of Haworthia magnifica v. Poelln. and subcultured on solid medium. Two liquid culture steps were necessary to prepare the calli for the isolation of protoplasts capable of sustained cell divisions. Plants were regenerated from protoplast-derived calli. The influence of both the osmolality of the culture media and exudates on the viability of protoplasts and protoplast-derived cell colonies is briefly discussed. 相似文献
158.
The translational diffusion of pyrene, pyrene butyric acid and pyrene decanoic acid has been determined in phosphatidylcholine bilayers of different chain length and under pressure up to 200 bars. In the liquid crystalline phase and at a given temperature the diffusion decreases with increasing chain length. At a constant reduced temperature, T
red (about 10 K above the transition temperature), long chain lipids exhibit the fastest diffusion which is in disagreement with hydrodynamic models but favours free volume models for diffusion in lipid bilayers. The volume of activation, V
act, calculated from the decrease of the diffusion coefficient with pressure, ln D/P, depends on lipid chain length. V
act decreases with decreasing lipid chain length at a given temperature, T=65°C, and increases at the reduced temperature. These results are again in agreement with the dependence of the diffusion on lipid chain length and therefore with the free volume model.Abbreviations DLPC
Dilauroylphosphatidylcholine
- DMPC
Dimyristoylphosphatidylcholine
- DPPC
Dipalmitoylphosphatidylcholine
- DSPC
Distearoylphosphatidylcholine
- LUV
Large unilamellar vesicles
- SUV
Small unilamellar vesicles
- Tris
Tris(hydroxymethyl)aminomethan 相似文献
159.
W. L. C. Vaz J. Stümpel D. Hallmann A. Gambacorta M. De Rosa 《European biophysics journal : EBJ》1987,15(2):111-115
Fluorescence recovery after photobleaching was used to investigate the translational diffusion of a fluorescent derivative of a membrane-spanning lipid in L
phase multibilayers of 1-palmitoyl-2-oleoylphosphatidylcholine prepared in water and in glycerol. The translational diffusion coefficient in hydrated bilayers (D
w) ranged between 2 and 5x10–8 cm2/s and in glycerinated bilayers (D
g) the range was between 3 and 24×10–10 cm2/s between 10° and 40°C. These results are discussed in terms of models for diffusion in membranes. 相似文献
160.
Fluorescence polarization measurements with the probe 1,6-diphenyl-1,3,5-hexatriene (DPH) were performed to detect changes in the fluidity of plasma membranes from T-lymphocytes stimulated with mitogens. When the cells were incubated with succinyl-concanavalin A an increase in fluorescence polarization was observed. This, however, could be shown to be due to the interaction of the mitogen with the label DPH and did not reflect changes in the plasma membrane. In purified plasma membranes a decrease rather than an increase of fluorescence polarization was observed. 相似文献