全文获取类型
收费全文 | 45653篇 |
免费 | 3711篇 |
国内免费 | 7篇 |
专业分类
49371篇 |
出版年
2023年 | 242篇 |
2021年 | 377篇 |
2020年 | 316篇 |
2019年 | 321篇 |
2018年 | 909篇 |
2017年 | 941篇 |
2016年 | 1014篇 |
2015年 | 876篇 |
2014年 | 1047篇 |
2013年 | 1853篇 |
2012年 | 3138篇 |
2011年 | 3488篇 |
2010年 | 1773篇 |
2009年 | 1142篇 |
2008年 | 2869篇 |
2007年 | 2944篇 |
2006年 | 2713篇 |
2005年 | 2432篇 |
2004年 | 2328篇 |
2003年 | 2170篇 |
2002年 | 2191篇 |
2001年 | 1495篇 |
2000年 | 1739篇 |
1999年 | 907篇 |
1998年 | 431篇 |
1997年 | 351篇 |
1996年 | 415篇 |
1995年 | 357篇 |
1994年 | 381篇 |
1993年 | 343篇 |
1992年 | 386篇 |
1991年 | 325篇 |
1990年 | 298篇 |
1989年 | 268篇 |
1988年 | 268篇 |
1987年 | 265篇 |
1986年 | 242篇 |
1985年 | 320篇 |
1984年 | 388篇 |
1983年 | 341篇 |
1982年 | 317篇 |
1981年 | 293篇 |
1980年 | 265篇 |
1979年 | 270篇 |
1978年 | 280篇 |
1977年 | 258篇 |
1976年 | 243篇 |
1975年 | 296篇 |
1974年 | 226篇 |
1973年 | 208篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
62.
Paola A Gilardoni Stefan Schuck Ruth Jüngling Björn Rotter Ian T Baldwin Gustavo Bonaventure 《BMC plant biology》2010,10(1):66
Background
Plants trigger and tailor defense responses after perception of the oral secretions (OS) of attacking specialist lepidopteran larvae. Fatty acid-amino acid conjugates (FACs) in the OS of the Manduca sexta larvae are necessary and sufficient to elicit the herbivory-specific responses in Nicotiana attenuata, an annual wild tobacco species. How FACs are perceived and activate signal transduction mechanisms is unknown. 相似文献63.
Tor Strömgren 《Coral reefs (Online)》1987,6(1):43-47
Series of apices of Acropora pulchra from an intertidal reef at Phuket, Thailand, were grown at different depths in the sea, and the length growth was monitored at 12–24 h intervals with laser diffraction. The growth rates of actively growing apices were normally distributed and showed a high variability, with an average coefficient of variation of 58%. There was a highly significant difference in average growth rate between adjacent colonies. A significant linear relationship was found between irradiance and length growth, with a saturating level at 300–400 Wm-2. At 1000 Wm-2 length growth was significantly reduced. Under normal daylight conditions, day and night growth rates were equal. 相似文献
64.
C Haux A Larsson M L Sj?beck G Lithner 《Comparative biochemistry and physiology. A, Comparative physiology》1987,86(4):729-732
Intra-lake variations in physiological parameters, representing haematology, plasma ion composition and carbohydrate metabolism, were investigated in perch (Perca fluviatilis), inhabiting a comparatively unpolluted lake. Provided the perch were subjected to a standardized procedure for capture, handling, recovery after capture, and sampling, only few and minor differences were observed in 21 parameters investigated when 3 groups were compared to a control group of perch. It is concluded that the experimental design used is suitable for the examination of the physiological status of perch in the field. 相似文献
65.
Summary The replication model for sister chromatid exchange (SCE), when introduced in 1980 by Painter, was claimed to be consistent with the one hit property of SCE. However, the argument offered in favour of the one hit property was based on a defective dose-response function, as shown in this paper, since dose as the independent parameter of any dose-response function was not included in the considerations. This missing part of the model's dose-response function is added and, by using Bessel functions, a formula for the complete dose-response function is presented. A re-examination of the newly derived function shows that, in the model, linearity holds only under certain restricted circumstances. 相似文献
66.
Bernd Höffken Reinhard Ködding Alexander von zur Mühlen Tainer Hehrmann Rolf-Dieter Hesch 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,539(1):114-124
The nature of the conversion of thyroxine (T4) to triiodothyronine (T3) and reverse triiodothyronine (rT3) was investigated in rat liver homogenate and microsomes. A 6-fold rise of T3 and 2.5-fold rise of rT3 levels determined by specific radioimmunoassays was observed over 6 h after the addition of T4. An enzymic process is suggested that converts T4 to T3 and rT3. For T3 the optimal pH is 6 and for rT3, 9.5. The converting activity for both T3 and rT3 is temperature dependent and can be suppressed by heat, H2O2, merthiolate and by 5-propyl-2-thiouracil. rT3 and to a lesser degree iodide, were able to inhibit the production of T3 in a dose related fashion. Therefore the pH dependendy, rT3 and iodide may regulate the availability of T3 or rT3 depending on the metabolic requirements of thyroid hormones. 相似文献
67.
Uta Kühne Branka Filjak Hans Kröger 《Biochimica et Biophysica Acta (BBA)/General Subjects》1975,399(1):42-49
An injection of cortisone acetate at a dose of 5 mg/100 g body weight concomitant with dibutryl cyclic AMP prevents the increase in the activity of rat liver cytosol serine aminotransferase (L-serine: pyruvate aminotransferase, EC 2.6.1.51) elicited by the nucleotide with a lag of about 2 h. If the glucocorticoid is given 2 h prior to the nucleotide inducer, the lag disappears. The inhibitory effect of cortisone acetate gradually decays and is no longer detectable 12 h following its administration. Theophylline, insulin and glucose at doses which affect significantly the level of tyrosine aminotransferase, have no effect on the level of serine aminotransferase and on the cortisone inhibition. The inhibitory effect of the glucocorticoid on the dibutyryl cyclic AMP-mediated increase in serine aminotransferase diminishes with the age of animals. Increase in the enzyme activity by a single dose of glucagon can also be inhibited by cortisone acetate and actinomycin D as in the case with dibutyrl cyclic AMP as an inducer. The possibility of the existence of a specific inhibitory factor which is formed in response to cortisone acetate is discussed. 相似文献
68.
Andrea Schrödel 《当今生物学》2007,37(5):289-289
69.
The influence of moulded hay (Alternaria alternata, Epicoccum nigrum, Mucor racemosus, Ulocladium chartarum) and the efficiency of Vitamin B1 substitution to cope these effects on rumen protozoa was investigated using the longterm rumen simulation technique (RUSITEC) for about 25 days. Moulded hay affected medium-sized protozoa to a different extent (Alternaria alternata: ?16 %, Epicoccum nigrum: ?27 %, Mucor racemosus: ?9 %, Ulocladium chartarum: +2 %). The vitamin B1 substitution had positive effects during the feeding of Mucor racemosus and Ulocladium chartarum. 相似文献
70.
The protolytic reactions of PSII membrane fragments were analyzed by measurements of absorption changes of the water soluble indicator dye bromocresol purple induced by a train of 10 s flashes in dark-adapted samples. It was found that: a) in the first flash a rapid H+-release takes place followed by a slower H+-uptake. The deprotonation is insensitive to DCMU but is completely eliminated by linolenic acid treatment of the samples; b) the extent of the H+-uptake in the first flash depends on the redox potential of the suspension. In this time domain no H+-uptake is observed in the subsequent flashes; c) the extent of the H+-release as a function of the flash number in the sequence exhibits a characteristic oscillation pattern. Multiphasic release kinetics are observed. The oscillation pattern can be satisfactorily described by a 1, 0, 1, 2 stoichiometry for the redox transitions Si Si+1 (i=0, 1, 2, 3) in the water oxidizing enzyme system Y. The H+-uptake after the first flash is assumed to be a consequence of the very fast reduction of oxidized Q400(Fe3+) formed due to dark incubation with K3[Fe(CN)6]. The possible participation of component Z in the deprotonation reactions at the PSII donor side is discussed.Abbreviations A
protonizable group at the PSII acceptor side
- BCP
Bromocresol Purple
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- FWHM
Full Width at Half Maximum
- QA, QB
primary and secondary plastoquinone at PSII acceptor side
- Q400
redox group at PSII-acceptor side (high spin Fe2+)
- P680
Photoactive chlorophyll of PSII reaction center
- Si
redox states of the catalytic site of water oxidation
- Z
redox component connecting the catalytic site of water oxidation with the reaction center 相似文献