全文获取类型
收费全文 | 1371篇 |
免费 | 93篇 |
国内免费 | 1篇 |
出版年
2021年 | 18篇 |
2020年 | 9篇 |
2019年 | 19篇 |
2018年 | 21篇 |
2017年 | 20篇 |
2016年 | 29篇 |
2015年 | 61篇 |
2014年 | 61篇 |
2013年 | 58篇 |
2012年 | 79篇 |
2011年 | 87篇 |
2010年 | 51篇 |
2009年 | 39篇 |
2008年 | 71篇 |
2007年 | 54篇 |
2006年 | 60篇 |
2005年 | 44篇 |
2004年 | 49篇 |
2003年 | 43篇 |
2002年 | 50篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 18篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 30篇 |
1986年 | 12篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 17篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1974年 | 9篇 |
1972年 | 8篇 |
1971年 | 12篇 |
1970年 | 9篇 |
1968年 | 8篇 |
1966年 | 12篇 |
排序方式: 共有1465条查询结果,搜索用时 109 毫秒
1.
Denise Risch Nicholas J. Gales Jason Gedamke Lars Kindermann Douglas P. Nowacek Andrew J. Read Ursula Siebert Ilse C. Van Opzeeland Sofie M. Van Parijs Ari S. Friedlaender 《Biology letters》2014,10(4)
For decades, the bio-duck sound has been recorded in the Southern Ocean, but the animal producing it has remained a mystery. Heard mainly during austral winter in the Southern Ocean, this ubiquitous sound has been recorded in Antarctic waters and contemporaneously off the Australian west coast. Here, we present conclusive evidence that the bio-duck sound is produced by Antarctic minke whales (Balaenoptera bonaerensis). We analysed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species. This finding allows the interpretation of a wealth of long-term acoustic recordings for this previously acoustically concealed species, which will improve our understanding of the distribution, abundance and behaviour of Antarctic minke whales. This is critical information for a species that inhabits a difficult to access sea-ice environment that is changing rapidly in some regions and has been the subject of contentious lethal sampling efforts and ongoing international legal action. 相似文献
2.
3.
4.
Ohne Zusammenfassung 相似文献
5.
N C Leal A T De Sá C A Solari S J Da Silva E Hofer 《Memórias do Instituto Oswaldo Cruz》1987,82(1):43-49
From 13,196 faecal cultures made in Recife-Pernambuco during the period from 1978 to 1980, 1,720 strains of Salmonella were isolated. Serological typing on 1,387 of the isolates recognized 63 serotypes, 73.18% of which belonged to group B. The prevalent serotypes adding up to 1,231 strains (88.75% of the total of the isolates) were: S. typhimurium, S. saint-paul, S. poona, S. derby, S. agona, S. newport, S. oranienburg, S. infantis, S. tshiongwe and S. ndolo. 相似文献
6.
Calli of P. argentatum were grown on a newly designed liquid nutrient flow-through system which facilitated the subculturing of calli and delayed
browning for 6 weeks. Friable calli were obtained on half-strength Gamborg B5-medium supplemented with 0.05 mgl−1 2,4-dichlorophenoxyacetic acid. Shoots developed on media supplemented with 0.2 mgl−1 benzylaminopurine but lacking 2,4-dichlorophenocyacetic acid. 相似文献
7.
A cyclic-3',5'-GMP-dependent protein kinase was purified 7400-fold from the reproductive tract of female ascarids to a specific activity of 718 nmol min-1 mg-1 (histone as substrate). The yield of the preparation was 25%. The enzyme protein obtained was homogeneous as judged by isoelectrofocusing and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The native enzyme behaved as a dimer of two 82-kDa subunits in gel permeation chromatography on Superose 12. The protein kinase was inactive in the absence of cyclic purine nucleotides. Half-maximum velocity was obtained in the presence of 18 nM cGMP, whereas 400-fold higher concentrations of cAMP were required for the same activity. The enzyme underwent autophosphorylation in first-order kinetics (rate constant 0.054 min-1), leading to maximum incorporation of 0.96 phosphate per subunit. The autophosphorylation led to a 4-fold increase in Vmax, while the Km remained almost unchanged. In an extract from the reproductive tract, cGMP-stimulated phosphorylation was primarily observed in five proteins (molecular masses of 66, 60, 43, 30, and 25 kDa). These proteins also incorporated phosphate when isolated reproductive tracts were incubated in the presence of [32P]phosphate. The phosphate content in cellular proteins was enhanced when the incubation was performed in the presence of 10(-4) M of either octyl-cAMP or octyl-cGMP. In addition to the proteins mentioned above, however, six more electrophoretic bands containing radioactive phosphate were identified after in situ labeling of reproductive tracts with radioactive phosphate. 相似文献
8.
The effects of solar and artifical ultraviolet radiation on the marine cryptoflagellate, Cryptomonas maculata, were studied. Even after short exposure to UV the accessory photosynthetic pigment phycoerythrin is bleached; likewise the fluorescence undergoes significant changes both in amplitude and in the maximal peak wavelength. In parallel, the photosynthetic oxygen production decreases rapidly during exposure. Gel electrophoresis and FPLC of membrane proteins show a significant decrease in chromoproteins after 2 h UV, which is confirmed by fluorescence excitation and emission spectra of the FPLC fractions.Abbreviations APS
ammonium persulfate
- DCMU
3-(3,4dichlorophenyl)1,1-dimethylurea; Emulphogen, polyoxyethylene 10 tridecyl ether
- FPLC
fast protein liquid chromatography
- PMSF
phenylmethylsulfonyl fluoride
- SDS
sodium dodecylsulfate
- SDS PAGE
sodium dodecylsulfate polyacrylamide gel electrophoresis
- TEMED
NN NNtetramethylethylene diamine
- UV-A
wavelength range between 320 nm and 400 nm
- UV-B
wavelength range between 280 nm and 320 nm
Dedicated to the 60th birthday of Professor Dr. W. Wehrmeyer 相似文献
9.
In Avena coleoptile segments a decrease of cytoplasmic pH activates energy-dependent H+ extrusion into the apoplast, thereby triggering extension growth. This sequence of events cannot be inhibited by cycloheximide and is induced by the following conditions and compounds. (i) A short anaerobic treatment of coleoptile segments results in the formation of lactic acid and an intracellular decrease of pH. For a period of 20 min after transfer to normal air, the growth rate is up to six times higher than the rate before anaerobiosis. (ii) Similarly, incubation of segments with CN– (0.1 mM) in the presence of oxygen causes and accumulation of lactic acid and a fall in cell-sap pH. After removing CN– a growth burst occurs. (iii) Higher concentrations of permeable acids (10 mM in buffer pH 5.8) induce extension growth. This growth is O2-dependent and therefore differs from the acid growth, which can be triggered under anaerobic conditions by acid buffers of pH5 via the direct increase of cell-wall plasticity. (iv) A short application of CO2-saturated buffer (pH 5.8) causes CO2-induced elongation growth; after a 3-min pulse the growth rate is enhanced for about 15 min. (v) Lipophilic esters of acetic acid or propionic acid, such as naphthylacetate, naphthylpropionate, phenylacetate, benzylacetate induce elongation growth. These compounds, when taken up into the cell, are hydrolized by esterases; the acids released lower the cytoplasmic pH (shown by the pH indicator, fluorescein). The highest esterase activity was found in a microsomal membrane fraction of coleoptiles. While the carboxyester-induced extension growth is completely inhibited under anoxia, the initial acidification of the bathing solution can still be observed. This decrease in external pH is obviously the result of ester hydrolysis, caused by damaged cells, and is not the result of pH changes within the cell-wall compartment. It is suggested that a fast uptake of carboxyesters and the shift in equilibrium caused by their internal hydrolysis leads to a continuous formation of acids which lowers the cytoplasmic pH and activates the ATP-dependent H+ extrusion. In most experiments fusicoccin (a diacetic acid ester) acts similarly to naphthylacetate and the other carboxyesters, although quantitative differences exist. Therefore, it is possible that fusicoccin is effective partly on the basis of its ester characteristic. The effects observed are discussed with regard to the very narrow pH optimum of plasma-membrane H+-ATPases exhibiting their highest levels of activity at pH 6.5 (Hager and Biber 1984, Z. Naturforsch. C 39, 927–937).Abbreviations CHM
cycloheximide
- DMO
dimethadione (5.5-dimethyl-2,4-oxazolidinedione)
- FC
fusicoccin
- IAA
indole-3-acetic acid
- Mes
2-(N-morpholino)ethanesulfonic acid
- NA
(or )-naphthylacetate (acetic acid-1(or-2-)naphthylester)
- NAA
(or )-naphthaleneacetic acid
- PA
phenylacetate (acetic acid phenylester) 相似文献
10.
Ilse B. Barthelmess 《Molecular & general genetics : MGG》1984,194(1-2):318-321
Summary A lethal allele at the putative regulatory locus, cpc-1, of cross-pathway control in Neurospora crassa was discovered by genetic analysis. cpc-1
j-5 is viable only in the presence of a second mutation, slo, causing slow growth. The detection of a lethal allele at a regulatory locus is a rare event and points to the physiological importance of the regulatory circuit concerned, namely the cross-pathway or general control of amino acid biosynthetic enzymes in lower eukaryotes. 相似文献