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71.
Shells of probable former living communities ofDreissena polymorpha were found within sediments of the shallow polytrophic to hypertrophic hard water Lake Breitling (Havel-Lake system, Germany).
Corresponding sediments have been deposited between approximately 1940 and 1970 and reflect increasing eutrophication and
heavy metal pollution of the Lake during this period (Schettler, 1992). Single shells from various sediment depths were analysed
by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) along a line on the outer part of the shell. The
response of these freshwater mussels to increasing heavy metal pollution is clearly reflected in the distribution of Pb, Cu,
Cd and Zn within their valves. In general, Cd, Cu, Pb and Zn contents are lower, and the distribution more even, in the outer
parts of the deepest (oldest) shells compared to shells from higher in the cored sediments. Notably higher contents of Cu,
Pb and Zn were recorded from the central (umbonal) part of the more recent shells, but this behaviour is not recorded for
Cd. Metabolic changes brought on by worsening environmental conditions are proposed to explain this phenomena. Acidity produced
during anaerobic metabolism can be neutralised by dissolution of the carbonate part of the shell. Copper, Zn and Pb, which
show an affinity for the organic component of the shell, may thus accumulate by repeated dissolution and reprecipitation of
the shell during the lifetime of an individual organism. Cadmium, which is bound mainly in the aragonite of the shells, is
released during the dissolution of carbonate and is not concentrated in the umbonal area of the shell. 相似文献
72.
Helen E. Chadd Ian R. Joint Nicholas H. Mann Noel G. Carr 《FEMS microbiology ecology》1996,21(2):69-76
Abstract: Laboratory cultures of marine Synechococcus sp. WH 7803 were grown under conditions of restricted iron availability. The culture medium was adjusted to restrict iron availability: (i) by adding the iron chelator EDDA; (ii) by omitting iron; and (iii) by omitting both iron and EDTA. An adaptive response was observed to these iron-restricted conditions, including a decrease in cellular phycoerythrin and synthesis of a 36 kDa polypeptide in [35 S]methionine radiolabelled whole cell lysates separated by SDS-PAGE. The polypeptide was synthesized within 48 h of transferring exponential phase cells to the iron-restricted medium. The protein was localized to the cell membranes and not the cytoplasmic fraction. 相似文献
73.
Ronald W. Wilen Ping Fu Albert J. Robertson Suzanne R. Abrams Nicholas H. Low Lawrence V. Gusta 《Planta》1996,200(1):138-143
The application of abscisic acid (ABA), either as a racemic mixture or as optically resolved isomers, increases freezing tolerance in a bromegrass (Bromus inermis Leyss) cell culture and induces the accumulation of several heat-stable proteins. Two stereoisomers of an ABA analog, 23 dihydroacetylenic abscisyl alcohol (DHA), were used to study the role of ABA-induced processes in the acquisition of freezing tolerance in these cells. Freezing tolerance was unchanged in the presence of (–) DHA (LT50 -9°C), and no increase in heat-stable protein accumulation was detected; however, the (+) enantiomer increased the freezing tolerance (LT50 -13°C) and induced the accumulation of these polypeptides. All three forms of ABA increased freezing tolerance in the bromegrass cells, although (–) ABA was less effective than either (+) or (±) ABA when added at equal concentrations. Cells pretreated with 20 or 50 M (–) DHA displayed lower levels of freezing tolerance following the addition of 2.5, 7.5 or 25 M (±) ABA. Full freezing tolerance could be restored by increasing the concentration of (±) ABA to > 25 M. Pretreatment of cells with (–) DHA (20 or 50 M) had no effect on freezing tolerance when 25 M (+) ABA was added. The induction of freezing tolerance by 25 M (–) ABA was completely inhibited by the presence of 20 M (–) DHA. The accumulation of ABA-responsive heat-stable proteins was inhibited by pretreatment with 20 M (–) DHA in cells treated with 2.5 or 7.5M (+) ABA, and in cells treated with 25 M (–) ABA. The accumulation of these polypeptides was restored when (±) or (+) ABA was added at a concentration of 25 M. The analysis of proteins which cross-reacted with a dehydrin antibody revealed a similar inhibitory pattern as seen with the other ABA-responsive proteins. The effects of the various isomers of ABA and DHA on cell osmolarity and sucrose uptake was also investigated. In both cases, (±) and (+) ABA had pronounced effects on the parameters measured, whereas (–) ABA treated cells gave substantially different results. In both sucrose uptake and cell osmolarity, DHA had no significant effect on the results obtained following (±) or (+) ABA treatment. Maximum freezing tolerance was only observed in cells when both heat-stable protein accumulation and sucrose uptake were observed.Abbreviations ABA
abscisic acid
- DHA
2,3 dihydroacetylenicabscisyl alcohols
- DMSO
dimethyl sulfoxide
- LT50
temperature at which 50% of cells are killed
The authors would like to acknowledge the technical assistance of Angela Bollman, Bruce Ewan and Angela Shaw. This work was supported by grants from the Natural Science and Engineering Research Council of Canada to L.V.G. and N.H.L., and a grant from the University of Saskatchewan to R.W.W. 相似文献
74.
Tonti-Filippini N 《Bioethics》1996,10(4):334-340
The Health Care Ethics Consultant marks a stage in the development of ethics consultancy. Ethics consultancy is a manifestation of a newly secularized society in which a new discipline has developed to fill a gap created by the combination of the diminishing influence of traditional moral authorities and the growth of new problems associated with the development of new technology and changes in society and culture. The stated primary objective of the book is to focus attention on an immediate practical problem: the role and responsibilities, the education and training, and the certification and accreditation of health ethics consultants. An edited collection of articles, the book originated as a research project financed by the Social Sciences and Humanities Research Council of Canada, undertaken by a Strategic Research Network which included faculty members from Dalhousie University, McGill University, the University of Toronto, McMaster University and the University of Calgary. 相似文献
75.
Nicholas C. Nicolaides Fabio Palombo Kenneth W. Kinzler Bert Vogelstein Josef Jiricny 《Genomics》1996,31(3):395
Defects in mismatch repair genes cause the genetic instability characteristic of hereditary nonpolyposis colorectal cancer and a subset of sporadic colon tumors. The newest member of the mismatch repair gene family,GTBP, has recently been identified as a partial cDNA. Here, we describe the isolation of its 5′ terminus, allowing definition of the entire coding region. Several polymorphisms within the 5′ end were identified and are presented. 相似文献
76.
Nienow AW Langheinrich C Stevenson NC Emery AN Clayton TM Slater NK 《Cytotechnology》1996,22(1-3):87-94
Because of concern for cell damage, very low agitation energy inputs have been used in industrial animal cell bioreactors, typical values being two orders of magnitude less than those found in bacterial fermentations. Aeration rates are also very small. As a result, such bioreactors might be both poorly mixed and also unable to provide the higher oxygen up-take rates demanded by more intensive operation. This paper reports experimental studies both of K
L
a and of mixing (via pH measurements) in bioreactors up to 8 m3 at Wellcome and of scaled down models of such reactors at Birmingham. Alongside these physical measurements, sensitivity of certain cell lines to continuously controlled dO2 has been studied and the oxygen up-take rates measured in representative growth conditions. An analysis of characteristic times and mixing theory, together with other recent work showing that more vigorous agitation and aeration can be used especially in the presence of Pluronic F-68, indicates ways of improving their performance. pH gradients offer a special challenge. 相似文献
77.
The ability of bacterial cultures to degrade diethanolamine under anoxic conditions with nitrate as an electron acceptor was investigated. A mixed culture capable of anaerobic degradation of diethanolamine was obtained from river sediments by enrichment culture. From this a single bacterial strain was isolated which could use diethanolamine, monoethanolamine, triethanolamine and N-methyl diethanolamine as its sole carbon and energy sources either aerobically or anaerobically. Growth on diethanolamine was faster in the absence of oxygen. The accumulation of possible metabolites in the culture medium was determined as was the ability to grow on certain putative intermediates in the degradation of diethanolamine. A possible pathway for the degradation of ethanolamines by this organism is suggested. 相似文献
78.
Nicholas A. Ashbaugh Anthony A. Echelle Alice F. Echelle 《Journal of fish biology》1994,45(2):291-302
Starch gel electrophoresis of proteins was used to study geographic variation at 26 gene loci in the Red River pupfish ( Cyprinodon rubrofluviatílís ), a species restricted to west Texas and Oklahoma. Marked differences were detected between populations in the Red and Brazos river drainages, with fixed or nearly fixed differences occurring at five gene loci. In addition, mean heterozygosity was uniformly high for the Red River form ( = 0·076–0·101) while samples of the Brazos River form were genetically depauperate ( =0·00–0·017). Introduced populations in the South Canadian and Colorado river drainages appear to have been derived from the Red River drainage. The presence of alleles diagnostic of the Red and Brazos river forms supports the suggestion from previous work that they may represent cryptic species. Regardless of taxonomy, however, the presence of two genetically distinct forms must be taken into consideration by those concerned with maintenance of biotic diversity. 相似文献
79.
Peter H. Quail Winslow R. Briggs Joanne Chory Roger P. Hangarter Nicholas P. Harberd Richard E. Kendrick Maarten Koornneef Brian Parks Robert A. Sharrock Eberhard Schäfer William F. Thompson Garry C. Whitelam 《Plant Molecular Biology Reporter》1994,12(2):S50-S56
These recommendations for genes encoding phytochromes were developed independently by Quail et al., but are broadly consistent
with the Commission's guidelines. Their original article, kindly provided in advance of publication, appeared as a Letter
to the Editor inPlant Cell (6:468–471, 1994) and is published with permission of the American Society of Plant Physiologists. 相似文献
80.
A cDNA encoding the mature, chloroplast-localized carbonic anhydrase in pea has been expressed inE. coli. The enzyme is fully active and yields of up to 20% of the total soluble protein can be obtained from the bacteria. This expression system was used to monitor the effects of site-directed mutagenesis of seven residues found within conserved regions in the pea carbonic anhydrase amino acid sequence. The effects of these modifications are discussed with respect to the potential of various amino acids to act as sites for zinc coordination or intramolecular proton shuttles. 相似文献