全文获取类型
收费全文 | 2344篇 |
免费 | 176篇 |
国内免费 | 114篇 |
专业分类
2634篇 |
出版年
2023年 | 22篇 |
2022年 | 27篇 |
2021年 | 46篇 |
2020年 | 29篇 |
2019年 | 41篇 |
2018年 | 44篇 |
2017年 | 39篇 |
2016年 | 51篇 |
2015年 | 56篇 |
2014年 | 106篇 |
2013年 | 175篇 |
2012年 | 59篇 |
2011年 | 86篇 |
2010年 | 69篇 |
2009年 | 108篇 |
2008年 | 123篇 |
2007年 | 119篇 |
2006年 | 94篇 |
2005年 | 69篇 |
2004年 | 94篇 |
2003年 | 82篇 |
2002年 | 57篇 |
2001年 | 47篇 |
2000年 | 45篇 |
1999年 | 50篇 |
1998年 | 63篇 |
1997年 | 51篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 43篇 |
1991年 | 25篇 |
1990年 | 38篇 |
1989年 | 42篇 |
1988年 | 34篇 |
1987年 | 33篇 |
1986年 | 38篇 |
1985年 | 30篇 |
1984年 | 42篇 |
1983年 | 21篇 |
1982年 | 28篇 |
1981年 | 36篇 |
1980年 | 42篇 |
1979年 | 27篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1976年 | 16篇 |
1973年 | 46篇 |
1972年 | 16篇 |
排序方式: 共有2634条查询结果,搜索用时 15 毫秒
1.
2.
Hiroyoshi Kubo 《Mycoscience》2012,53(2):147-151
Pilobolus crystallinus has three putative glyceraldehyde-3-phosphate dehydrogenase (gapdh) genes (pcgapdh1, pcgapdh2 and pcgapdh3). The results of this study demonstrate that expression of pcgapdh2 was increased by irradiation and that this increased expression was correlated with the formation of asexual reproductive
organs (trophocysts). Interestingly, expression of pcgapdh2 was restricted to trophocysts. The formation of trophocysts was likely promoted by light, and the expression of pcgapdh2 was increased as a result of trophocyst formation. This is the first report that shows the regulation of a gapdh gene in an organ-specific manner in fungi. 相似文献
3.
4.
I Gallien F Caurant M Bordes P Bustamante P Miramand B Fernandez N Quellard P Babin 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2001,130(3):389-395
Top predators from the northern sub-polar and polar areas exhibit high cadmium concentrations in their tissues. In the aim to reveal possible adverse effects, samples of five Atlantic white-sided dolphins Lagenorhyncusacutus have been collected on the occasion of the drive fishery in the Faroe Islands, for ultrastructural investigations and energy dispersive X-ray microanalyses. Cadmium concentrations were less than the limit of detection in both immature individuals and ranged from 22.7 to 31.1 μg g?1 wet weight in the mature individuals. Two individuals with the highest cadmium concentrations exhibited electron dense mineral concretions in the basal membranes of the proximal tubules. They are spherocrystals made up of numerous strata mineral deposit of calcium and phosphorus together with cadmium. Cadmium has been detected with a molar ratio of Ca:Cd of 10:1 in the middle of these concretions. To our knowledge, this is the first report of such granules in a wild vertebrate. The role of these granules in the detoxification of the metal and the possible pathological effects are considered. 相似文献
5.
Cultures of the unicellular green alga Chlamydomonas reinhardii can be synchronized by light/dark cycling not only under photoautotrophic but also under mixotrophic growth conditions. We observed that cultures synchronized in the presence of acetate continue to divide synchronously for one cell-cycle period when transferred to heterotrophic growth conditions. This finding enabled us to investigate the differential effects of light on cell growth and cell division. When cells were exposed to continuous light at the beginning of the growth period they entered the division phase earlier than dark-grown cells as a consequence of an increased growth rate. Illumination at the end of the growth period, however, caused a considerable delay in cell division and an extended growth period. The light-induced delay in cell division was also observed in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II. This finding demonstrates that cell division is directly influenced by a light/dard-responsive cell-cycle switch rather than by light/dark-dependent changes in energy metabolism. The importance of this light/dark control to the regulation of the Chlamydomonas cell cycle was investigated in comparison with other control mechanisms (size control, time control). We found that the light/dard-responsive cell-cycle switch regulates the transition from G1-to S-phase. This control mechanism is effective in cells which have attained the commitment to at least one round of DNA replication and division but have not attained the maximal cell mass which initiates cell division in the light.Abbreviations dCTP
deoxycytidine 5-triphosphate
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea 相似文献
6.
Comparison of the effect of excessive light on chlorophyll fluorescence (77K) and photon yield of O2 evolution in leaves of higher plants 总被引:10,自引:0,他引:10
High-light treatments (1750–2000 mol photons m–2 · s–1) of leaves from a number of higher-plant species invariably resulted in quenching of the maximum 77K chlorophyll fluorescence at both 692 and 734 nm (F
M, 692 and F
M, 734). The response of instantaneous fluorescence at 692 nm (F
O, 692) was complex. In leaves of some species F
O, 692 increased dramatically in others it was quenched, and in others yet it showed no marked, consistent change. Regardless of the response of F
O, 692 an apparently linear relationship was obtained between the ratio of variable to maximum fluorescence (F
V/F
M, 692) and the photon yield of O2 evolution, indicating that photoinhibition affects these two variables to approximately the same extent. Treatment of leaves in a CO2–free gas stream containing 2% O2 and 98% N2 under weak light (100 mol · m–2 · s–1) resulted in a general and fully reversible quenching of 77K fluorescence at 692 and 734 nm. In this case both F
O, 692 and F
M, 692 were invariably quenched, indicating that the quenching was caused by an increased non-radiative energy dissipation in the pigment bed. We propose that high-light treatments can have at least two different, concurrent effects on 77K fluorescence in leaves. One results from damage to the photosystem II (PSII) reaction-center complex and leads to a rise in F
O, 692; the other results from an increased non-radiative energy dissipation and leads to quenching of both F
O, 692 and F
M, 692 This general quenching had a much longer relaxation time than reported for pH-dependent quenching in algae and chloroplasts. Sun leaves, whose F
V/F
M, 692 ratios were little affected by high-light exposure in normal air, suffered pronounced photoinhibition when the exposure was made under conditions that prevent photosynthetic gas exchange (2% O2, 0% CO2). However, they were still less susceptible than shade leaves, indicating that the higher capacity for energy dissipation via photosynthesis is not the only cause of their lower susceptibility. The rate constant for recovery from photoinhibition was much higher in mature sun leaves than in mature shade leaves, indicating that differences in the capacity for continuous repair may in part account for the difference in their susceptibility to photoinhibition.Abbreviations and symbols kDa
kilodalton
- LHC-II
light-harvesting chlorophyll-protein complex
- PFD
photon flux density (photon fluence rate)
- PSI, PSII
photosystem I, II
-
F
O, F
M, F
V
instantaneous, maximum, variable fluorescence emission
-
absorptance
-
a
photon yield of O2 evolution (absorbed light)
C.I.W.-D.P.B. Publication No. 925 相似文献
7.
The amount of in-vitro translatable mRNA of the light-harvesting chlorophyll a/b-binding protein (LHCP) of photosystem II strongly increases in darkness (D) after a 5-min red-light pulse while continuous illumination of mustard seedlings with far-red (FR), red or white light leads only to a slight increase in the amount of translatable LHCP-mRNA. No increase can be observed after a long-wavelength FR (RG9-light) pulse. However, a FR pretreatment prior to the RG9-light pulse strongly increase LHCP-mRNA accumulation in subsequent D. This is not observed in the case of the mRNA for the small subunit of ribulose-1.5-bisphosphate carboxylase. The increase of LHCP-mRNA in D after a FR pretreatment can be inhibited by a reillumination of the seedlings with FR. The inhibition of LHCP-mRNA accumulation during continuous illumination with FR and the strong increase in D following a FR illumination was found to be independent of chlorophyll biosynthesis since no correlation between chlorophyll biosynthesis and translatable LHCP-mRNA levels could be detected. Even strong changes in the amount of intermediates of chlorophyll biosynthesis caused by application of levulinic acid or 5-aminolevulinic acid did not affect LHCP-mRNA levels. Therefore, we conclude that the appearance of LHCP-mRNA is inhibited during continuous illumination, even though illumination leads to a storage of a light singal which promotes accumulation of translatable LHCP-mRNA in D.Abbreviations c
continuous
- Chl
chlorophyll
- D
darkness
- FR
far-red light (3.5 W·m-2)
- LHCP
light-harvesting chlorophyll a/b-binding protein of photosystem II
- NF
Norfluration
- PChl
protochlorophyll(ide)
- Pfr
far-red absorbing form of phytochrome
- Ptot
total phytochrome
- R
red light (6.8 W·m-2)
- RG9-light
long-wavelength FR (10 W·m-2)
- SSU
small subunit of ribulose-1.5-bisphosphate carboxylase
- WL
white light
- ()
Pfr/Ptot=wavelength-dependent photoequilibrium of the phytochrome system 相似文献
8.
9.
Ted W. Simon Donald H. Edwards 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1990,166(6):745-755
The caudal photoreceptors (CPRs) of crayfish (Procambarus clarkii) can trigger walking and abdominal movements by their response to light.
相似文献
1. | In a restrained, inverted crayfish, illumination of A6 evoked a CPR discharge followed by leg movements and bursting from the abdominal tonic flexor (TF) motoneurons. Intracellular electrical stimulation of a single CPR at high frequency (80 Hz) evoked similar responses. |
2. | Responses only occurred when a single CPR axon was driven at 60 Hz or more and outlasted the stimulus. |
3. | CPR stimulation also excites the pattern-initiating network (Moore and Larimer 1987) in the abdomen. |
4. | The axon of the CPR projects from ganglion A6 to the brain. Terminal branches occur in the subesophageal ganglion and the brain. A small descending interneuron is dye-coupled to CPR in the subesophageal ganglion. |
5. | In animals with cut circumesophageal connectives, the CPRs can evoke walking and the abdominal motor pattern. |
6. | The relationship of the abdominal motor pattern to walking is altered by restraint and/or inversion. In freely moving crayfish, the cyclic abdominal motor pattern is only observed with backward walking. In restrained, inverted crayfish, the motor pattern occurs with both forward or backward walking. |
10.
Transitions in the growth limiting factor from light (I) to nitrogen (N) and vice versa caused changes in geosmin production, protein and carbohydrate content, and the synthesis of pigments such as chlorophyll a (Chl a), phycobiliproteins (PBPs), and -carotene of the cyanobacterium Oscillatoria brevis. Following IN transition the first 150h, the decrease in protein content was compensated for by an increase of carbohydrates, and thereby, a constant biomass level was maintained in this period. Thereafter, biimass dropped to 15% of its initial level. A decrease in geosmin and pigment content was observed during transition from IN-limited growth. However, geosmin increased relative to phytol (Chl a) and -carotene which may indicate that a lowered demand for phytol and -carotene during N-limited growth allows isoprenoid precursors to be directed to geosmin rather than to pigment synthesis. Synthesis of Chl a and -carotene at the expense of geosmin was suggested for the observed start of increase in geosmin production only at the time that Chl a and -carotene had reached their I-limited steady state. Transition from nitrogen to light limited growth caused an acceleration of metabolism shown by a rapid decrease in carbohydrate content accompanied by an increase in protein content. The growth rate of the organisms temporarily exceeded the dilution rate of the culture and the biomass level increased 6-fold. Due to the only modest changes in geosmin production (2-fold) compared to changes in biomass level (6-fold) during I-or N-limited growth, environmental factors seem to have limited effect on geosmin production.Abbreviations Chl a
chlorophyll a
- dry wt
dry weight;
- I-limited
light-limited
- N-limited
nitrogen-limited
- PBP
phycobiliprotein
This research was performed at the Department of Microbiology, University of Amsterdam, with finacial support provided by the Royal Norwegian Ministry of Foreign Affairs and the Royal Norwegian Council for Scientific and Industrial Research 相似文献