全文获取类型
收费全文 | 7692篇 |
免费 | 533篇 |
国内免费 | 2篇 |
出版年
2023年 | 39篇 |
2022年 | 27篇 |
2021年 | 159篇 |
2020年 | 90篇 |
2019年 | 133篇 |
2018年 | 161篇 |
2017年 | 144篇 |
2016年 | 244篇 |
2015年 | 357篇 |
2014年 | 409篇 |
2013年 | 528篇 |
2012年 | 610篇 |
2011年 | 587篇 |
2010年 | 422篇 |
2009年 | 325篇 |
2008年 | 451篇 |
2007年 | 442篇 |
2006年 | 464篇 |
2005年 | 400篇 |
2004年 | 404篇 |
2003年 | 357篇 |
2002年 | 339篇 |
2001年 | 84篇 |
2000年 | 61篇 |
1999年 | 73篇 |
1998年 | 76篇 |
1997年 | 86篇 |
1996年 | 55篇 |
1995年 | 40篇 |
1994年 | 52篇 |
1993年 | 46篇 |
1992年 | 37篇 |
1991年 | 36篇 |
1990年 | 33篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 22篇 |
1986年 | 24篇 |
1985年 | 33篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 37篇 |
1981年 | 29篇 |
1980年 | 26篇 |
1979年 | 18篇 |
1977年 | 17篇 |
1976年 | 12篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1973年 | 17篇 |
排序方式: 共有8227条查询结果,搜索用时 296 毫秒
71.
ABA and Low Temperature Induce Freezing Tolerance via Distinct Regulatory Pathways in Wheat 总被引:1,自引:0,他引:1
Dallaire Sylvain; Houde Mario; Gagne Yves; Saini Hargurdeep S.; Boileau Serge; Chevrier Normand; Sarhan Fathey 《Plant & cell physiology》1994,35(1):1-9
The role of ABA in the induction of freezing tolerance was investigatedin two wheat (T. aestivum L.) cultivars, Glenlea (spring var)and Fredrick (winter var). Exogenous application of ABA (5x105M for 5 days at 24°C) increased the freezing tolerance ofintact plants by only 3°C (LT50) in both cultivars. Maximalfreezing tolerance (LT50 of 9°C for Glenlea and 17°Cfor Fredrick) could only be obtained with a low temperaturetreatment (6/2°C; day/night) for 40 days. These resultsshow that exogenously applied ABA cannot substitute for lowtemperature requirementto induce freezing tolerance in intactwheat plants. Furthermore, there was no increase in the endogenousABA level of wheat plants during low temperature acclimation,suggesting the absence of an essential role for ABA in the developmentof freezing tolerance in intact plants. On the other hand, ABAapplication (5x105 M for 5 days at 24°C) to embryogenicwheat calli resulted in an increase of freezing tolerance similarto that achieved by low temperature. However, as in intact plants,there was no increase in the endogenous ABA level during lowtemperature acclimation of calli. These results indicate thatthe induction of freezing tolerance by low temperature is notassociated with an increase in ABA content. Using an antibodyspecific to a protein family associated with the developmentof freezing tolerance, we demonstrated that the induction offreezing tolerance by ABA in embryogenic wheat calli was correlatedwith the accumulation of a new 32 kDa protein. This proteinis specifically induced by ABA but shares a common antigenicitywith those induced by low temperature. These results suggestthat ABA induces freezing tolerance in wheat calli via a regulatorymechanism different from that of low temperature. (Received June 15, 1993; Accepted September 16, 1993) 相似文献
72.
Study of the influence of plasmids on the arbitrary primer polymerase chain reaction fingerprint of Escherichia coli strains 总被引:4,自引:0,他引:4
Abdesslam Elaichouni John van Emmelo Geert Claeys Gerda Verschraegen Rita Verhelst Mario Vaneechoutte 《FEMS microbiology letters》1994,115(2-3):335-339
Abstract To study the effect of plasmids on the arbitrary primer-polymerase chain reaction fingerprint of bacterial strains, the Escherichia coli strains DH5, Top10, and W3110 were transformed with plasmids of different sizes: respectively, pUC19, pCEP and two clinically important plasmids carrying resistance to several antibiotics. Total DNA, i.e. both chromosomal and plasmid DNA, was prepared from transformed cells by boiling the cell suspensions and by phenol-chloroform extraction; chromosomal DNA was prepared by the same methods from the non-transformed, plasmid-free strains; plasmid DNA of pUC19 was purchased; plasmid DNA of pCEP was purified from the transformed strains by caesium chloride density gradient centrifugation. Arbitrarily primed polymerase chain reaction was carried out for all of these preparations. Amplification carried out independently with three different primers resulted in similar patterns for the chromosomal preparations whether or not plasmid was present. Amplification of plasmid DNA gave different patterns, characterized by fragments larger than those obtained when total or chromosomal DNA were used as the target. These data illustrate that the plasmids studied here do not influence the chromosomal arbitrarily primed PCR fingerprint, although plasmids alone are amplified in the absence of chromosomal DNA. Experiments comparing different relative concentrations of plasmid and chromosomal DNA indicate that under natural conditions the amount of chromosomal DNA per cell is sufficient to inhibit observable amplification of the plasmid(s) present. 相似文献
73.
Acetaldehyde production in Saccharomyces cerevisiae wine yeasts 总被引:1,自引:0,他引:1
Patrizia Romano Giovanna Suzzi Luca Turbanti Mario Polsinelli 《FEMS microbiology letters》1994,118(3):213-218
Abstract Eighty-six strains of Saccharomyces cerevisiae were investigated for their ability to produce acetaldehyde in synthetic medium and in grape must. Acetaldehyde production did not differ significantly between the two media, ranging from a few mg/l to about 60 mg/l, and was found to be a strain characteristic. The fermentation temperature of 30°C considerably increased the acetaldehyde produced. This study allowed us to assign the strains to different phenotypes: low, medium and high acetaldehyde producers. The low and high phenotypes differed considerably also in the production of acetic acid, acetoin and higher alcohols and can be useful for studying acetaldehyde production in S. cerevisiae , both from the technological and genetic point of view. 相似文献
74.
Mario Herrera-Marschitz C. Fabián Loidl Zhi-Bing You Kurt Andersson Rodolfo Silveira William T. O'Connor Michel Goiny 《Molecular neurobiology》1994,9(1-3):171-182
The neurocircuitries of the basal ganglia are studied with in vivo microdialysis, with special consideration to dopamine transmission and its interaction with other neurotransmitter systems. The aim is to develop experimental models to study the pathophysiology and therapy of neurodegenerative disorders of the basal ganglia, as well as to develop models to study the short- and long-term consequences of perinatal asphyctic lesions. A main goal of these studies is to find and to characterize new treatments for these disorders. 相似文献
75.
76.
Peter E. Andreotti Dee Linder Diana M. Hartmann Ian A. Cree Mario Pazzagli Howard W. Bruckner 《Luminescence》1994,9(6):373-378
The BATLE LE TCA-100 tumour chemosensitivity assay has been used to evaluate chemotherapeutic drug sensitivity of cultured tumour cell lines. Studies were performed using test drug concentrations calibrated to discriminate sensitivity and resistance of clinical specimens. Strong sensitivity which appeared to be inconsistent with clinical experience was detected for some drugs and cell lines. Findings of strong sensitivity were consistent with basic differences between sensitivity testing cultured cell lines and clinical specimens. Results with cell lines frequently may not apply directly to clinical applications. Characterization of differences between cell lines and clinical specimens may assist in application of cell line findings to clinical trials. 相似文献
77.
Deimination of Human Myelin Basic Protein by a Peptidylarginine Deiminase from Bovine Brain 总被引:6,自引:1,他引:5
Abstract: A peptidylarginine deiminase (PAD; EC 3.5.3.15) has been isolated from bovine brain and some of its characteristics have been studied. The enzyme showed an absolute requirement for Ca2+, a temperature optimum at ~50°C, and two Kmvalues when benzoylarginine ethyl ester was used as substrate, 0.78 mMand 11.2 mM.The higher Kmhas not been reported previously. Protein substrates for the enzyme included polyarginine and myelin basic protein but not histones. Because one of the components of MBP contains six citrullinyl residues per mole, enzymic deimination appeared to be a likely mechanism. When the most cationic component (C-1) was subjected to PAD in solution, 17 of the 19 arginyl residues were modified. From sequence analyses we concluded that the nature of the amino acid residues adjacent to the deiminated arginine were not modifiers of the reaction as arginyl residues in a variety of environments were deiminated. This deimination was reflected in a large increase in random structure, as measured by [θ]200. At 5°C, the [θ]200of the deiminated protein was -70 × 103 compared with -30 × 103 deg cm2/dmol for the native protein. When the temperature was increased to 70°C, the [θ]200 was -44 × 103 for the deiminated protein and -20 × 107 deg cm2/ dmol for the native C-1. When plotted as a function of temperature, [θ]200 decreased linearly from 5°C to 50°C for both proteins and did not change from 50°C to 70°C. PAD provides a mechanism for deimination of arginyl residues of myelin basic protein. The selective deimination of the six arginyl residues that are consistently found deiminated in C-8 may be determined by the orientation of the protein in the membrane and/or the more complex lipid composition of myelin may affect the selectivity of the deimination. 相似文献
78.
Kinetics of microbial growth with mixtures of carbon sources 总被引:11,自引:0,他引:11
79.
Enhanced Growth and Activity of a Biocontrol Bacterium Genetically Engineered To Utilize Salicylate 总被引:2,自引:1,他引:1 下载免费PDF全文
Stephen F. Colbert Mavis Hendson Mario Ferri Milton N. Schroth 《Applied microbiology》1993,59(7):2071-2076
Plasmid NAH7 was transferred from Pseudomonas putida PpG7 to P. putida R20 [R20(NAH7)], an antagonist of Pythium ultimum. The plasmid did not affect growth or survival of R20(NAH7) and was stably maintained under nonselective conditions in broth and soil and on sugar beet seeds. Plasmid NAH7 conferred to R20(NAH7) the ability to utilize salicylate in culture, agricultural field soil, and on sugar beet seeds. The metabolic activity of R20(NAH7), but not the wild-type R20, was greatly increased in soil by amendment with salicylate (250 μg/g) as measured by induced respiration. Population densities of R20(NAH7) were also enhanced in salicylate-amended soil, increasing from approximately 1 × 105 CFU/g to approximately 3 × 108 CFU/g after 35 h of incubation. In contrast, population densities of R20(NAH7) in nonamended soil were approximately 3 × 106 CFU/g of soil after 35 h of incubation. The concentration of salicylate in soil affected the rate and extent of population increase by R20(NAH7). At 50 to 250 μg of salicylate per g of soil, population densities of R20(NAH7) increased to approximately 108 CFU/g of soil by 48 h of incubation, with the fastest increase at 100 μg/g. A lag phase of approximately 24 h occurred before the population density increased in the presence of salicylate at 500 μg/g; at 1,000 μg/g, population densities of R20(NAH7) declined over the time period of the experiment. Population densities of R20(NAH7) on sugar beet seeds in soils amended with 100 μg of salicylate per g were not increased while ample carbon was present in the spermosphere. However, after carbon from the seed had been utilized, population densities of R20(NAH7) decreased significantly less (P = 0.005) on sugar beet seeds in soil amended with salicylate than in nonamended soil. 相似文献
80.
Cameron L. Rutt W. Justin Cooper Christian B. Andretti Thiago V. V. Costa Philip C Stouffer Claudeir F. Vargas David A. Luther Mario Cohn-Haft 《Diversity & distributions》2023,29(4):466-477