全文获取类型
收费全文 | 1249篇 |
免费 | 93篇 |
国内免费 | 1篇 |
出版年
2021年 | 19篇 |
2020年 | 8篇 |
2019年 | 19篇 |
2018年 | 22篇 |
2017年 | 22篇 |
2016年 | 34篇 |
2015年 | 61篇 |
2014年 | 65篇 |
2013年 | 61篇 |
2012年 | 78篇 |
2011年 | 88篇 |
2010年 | 60篇 |
2009年 | 55篇 |
2008年 | 77篇 |
2007年 | 59篇 |
2006年 | 68篇 |
2005年 | 40篇 |
2004年 | 51篇 |
2003年 | 35篇 |
2002年 | 49篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1972年 | 6篇 |
1970年 | 7篇 |
1967年 | 5篇 |
1966年 | 11篇 |
1957年 | 6篇 |
1954年 | 5篇 |
排序方式: 共有1343条查询结果,搜索用时 15 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.
The measurement of the ATP content of fresh semen is as accurate as the estimation of sperm motility by conventional methods in discriminating between semen of fertile versus subfertile men. The ATP content of frozen thawed donor semen is correlated with the probability of conception per cycle of insemination. Exact quantification of cytotoxic sperm antibodies in serum is possible with the adenosine-triphosphate-release-cytotoxicity test, since measurement is free of the bias of microscopic examination. The procedure has been simplified by testing only one serum dilution and calculating the ‘sperm toxicity index’. 相似文献
4.
5.
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
6.
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
7.
Crude extracts from human cells were microinjected into the cytoplasm of cultured fibroblasts from 9 excision-deficient xeroderma pigmentosum (XP) complementation groups. The level of UV-induced unscheduled DNA synthesis (UDS) was measured to determine the effect of the extract on the repair capacity of the injected cells. With a sensitive UDS assay procedure a (transient) increase in UV-induced UDS level was found in fibroblasts from all complementation groups after injection of extracts from repair-proficient (HeLa) or complementing XP cells (except in the case of XP-G), but not after introduction of extracts from cells belonging to the same complementation group. This indicates that the phenotypic correction is exerted by complementation-group-specific factors in the extract, a conclusion that is in agreement with the observation that different levels of correction are found for different complementation groups. The XP-G-correcting factor was shown to be sensitive to proteolytic degradation, suggesting that it is a protein like the XP-A factor. 相似文献
8.
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
9.
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
10.
Microinjection of human cell extracts corrects xeroderma pigmentosum defect 总被引:8,自引:0,他引:8 下载免费PDF全文
Cultured fibroblasts of patients with the DNA repair syndrome xeroderma pigmentosum (XP) were injected with crude cell extracts from various human cells. Injected fibroblasts were then assayed for unscheduled DNA synthesis (UDS) to see whether the injected extract could complement their deficiency in the removal of u.v.-induced thymidine dimers from their DNA. Microinjection of extracts from repair-proficient cells (such as HeLa, placenta) and from cells belonging to XP complementation group C resulted in a temporary correction of the DNA repair defect in XP-A cells but not in cells from complementation groups C, D or F. Extracts prepared from XP-A cells were unable to correct the XP-A repair defect. The UDS of phenotypically corrected XP-A cells is u.v.-specific and can reach the level of normal cells. The XP-A correcting factor was found to be sensitive to the action of proteinase K, suggesting that it is a protein. It is present in normal cells in high amounts, it is stable on storage and can still be detected in the injected cells 8 h after injection. The microinjection assay described in this paper provides a useful tool for the purification of the XP-A (and possibly other) factor(s) involved in DNA repair. 相似文献