全文获取类型
收费全文 | 8307篇 |
免费 | 726篇 |
国内免费 | 15篇 |
专业分类
9048篇 |
出版年
2023年 | 43篇 |
2022年 | 128篇 |
2021年 | 207篇 |
2020年 | 120篇 |
2019年 | 141篇 |
2018年 | 185篇 |
2017年 | 161篇 |
2016年 | 264篇 |
2015年 | 434篇 |
2014年 | 472篇 |
2013年 | 554篇 |
2012年 | 665篇 |
2011年 | 593篇 |
2010年 | 419篇 |
2009年 | 337篇 |
2008年 | 454篇 |
2007年 | 440篇 |
2006年 | 412篇 |
2005年 | 355篇 |
2004年 | 367篇 |
2003年 | 338篇 |
2002年 | 305篇 |
2001年 | 139篇 |
2000年 | 134篇 |
1999年 | 121篇 |
1998年 | 77篇 |
1997年 | 52篇 |
1996年 | 49篇 |
1995年 | 47篇 |
1994年 | 46篇 |
1993年 | 46篇 |
1992年 | 75篇 |
1991年 | 61篇 |
1990年 | 54篇 |
1989年 | 47篇 |
1988年 | 42篇 |
1987年 | 39篇 |
1986年 | 48篇 |
1985年 | 36篇 |
1984年 | 42篇 |
1983年 | 32篇 |
1979年 | 29篇 |
1977年 | 27篇 |
1976年 | 20篇 |
1972年 | 24篇 |
1970年 | 29篇 |
1969年 | 32篇 |
1968年 | 28篇 |
1967年 | 22篇 |
1965年 | 23篇 |
排序方式: 共有9048条查询结果,搜索用时 0 毫秒
11.
L. J. Cox Betty Caicedo V. Vanos Eva Heck Sophie Hofstaetter J. L. Cordier 《World journal of microbiology & biotechnology》1987,3(2):143-153
Summary A catalogue of indigenous fermented beverages produced by different ethnic groups in Ecuador has been compiled and the microflora of selected examples examined. A diversity of fermentation substrates was encountered depending on the climatic zone. The fermentations are typicallyLactobacillus spp.—yeast fermentations except for one which includes a mould fermentation by a mixed starter ofMoniha sitophila, Rhizopus stolonifer and aFusarium sp. A discussion is made of the role of these beverages in the human ecology of certain regions.
Resumen Se ha confeccionado un catálogo de bebidas indígenas ecuatorianas producidas por distintos grupos étnicos, examinándose la microflora de algunos ejemplos seleccionados. Las fermentaciones son generalmente del tipoLactobacillus sp.—levaduras, excepto en un caso que incluye una fermentación fúngica iniciada de forma mixta porM. sitophila, R. stolonifer y unFusarium sp. Se discute el papel de estas bebidas en la ecologia humana de ciertas regiones.
Résumé Un catalogue des boissons fermentées indigènes produites par divers groupes ethniques de l'Equateur a été compilé et les micro-flores des exemples sélectionnés ont été éxaminés. Les substrats de fermentation varient d'une région climatique à l'autre. Les fermentations sont généralement du typeLactobacillus sp — levures, sauf dans un cas qui comporte une fermentation par des moisissures, avec un mélange initial deMoniha sitophila, Rhizopus stolonifer et une espèce deFusarium. Le rôle de ces boissons dans l'écologie humaine de certaines régions est discuté.相似文献
12.
13.
14.
Identification of regulatory elements within the minimal promoter region of the human endogenous ERV9 proviruses: accurate transcription initiation is controlled by an Inr-like element. 下载免费PDF全文
G La Mantia B Majello A Di Cristofano M Strazzullo G Minchiotti L Lania 《Nucleic acids research》1992,20(16):4129-4136
15.
G Milazzo G L La Rosa R Catalfamo R Vigneri A Belfiore 《Journal of cellular biochemistry》1992,49(3):231-238
The well-known mitogenic effects of TSH observed in vivo on the thyroid are not always reproducible of human thyroid cells in vitro where conflicting results have been obtained. In order to clarify this issue, we have used primary cultures of human thyroid cells obtained from normal tissue and maintained in serum-free medium for several days. In this in vitro model we have studied the effect of TSH on growth by measuring three different parameters: [3H]-thymidine incorporation, cell counts, and DNA measurement. Monolayer cultures were plated at both low and high cell density (2 x 10(4) and 8 x 10(4) cells/25 mm well, respectively). Although at either cell density cultures were equally able to functionally respond to TSH in terms of cAMP accumulation a significant growth response to TSH was observed only in low density cultures. In high density cultures TSH had an antimitogenic effect. Moreover, TSH potentiated the mitogenic effect of insulin only in low density cultures. In contrast to TSH, FCS induced a similar proliferative response at both high and low cell density. Following TSH stimulation, cAMP content was always increased, paralleling the effect of growth in low density but not in high density cultures. The cAMP analogues dibutyryl-cAMP and 8-bromo-cAMP, as well as cholera toxin and forskolin, did not mimic the mitogenic effect of TSH but had an antiproliferative effect. In addition, these agents blunted the proliferative effect of insulin. These data suggest that in thyroid cells TSH is able to elicit both a mitogenic and an antimitogenic effect depending on the environmental conditions such as cell density.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
16.
17.
I A Malanicheva L I Koz'mian Iu V Dudnik M Iu Novozhenov A V La?ko N P Potapova 《Antibiotiki i khimioterapii͡a》1991,36(5):5-8
Strain 344 synthesizing an antibiotic complex was isolated after fusion of the protoplasts of Streptomyces monomycini producing monomycin and Streptomyces kanamyceticus producing kanamycin. The major component of the complex was identified with albofungin and the minor one was suggested to be chloralbofungin. In the cultures of strain 344 variants forming monomycin were detected. After regeneration of the protoplasts of the parent strains there were isolated no stable clones synthesizing antibiotics differing from monomycin and kanamycin. 相似文献
18.
M. V. Martinez-Toledo J. Gonzalez-Lopez V. Salmeron T. De La Rubia F. Ballesteros A. Ramos-Cormenzana 《Folia microbiologica》1986,31(2):154-163
Batch cultures ofA. vinelandii in ammonium phosphate-limited and N-free phosphate-limited media were compared with control cultures (N-free phosphate-sufficient media). The effects of phosphate limitation on growth were determined by viable cells counts. Under phosphate-limitation conditions, growth inhibition and decreased viability were observed. Intracellular levels of RNA, poly-3-hydroxybutyrate, phosphate and oxygen uptake were significantly affected by phosphate limitation. When phosphate-limited cultures were examined microscopically, pleomorphism was more marked than in control cultures. Also phosphate-limited cells showed an increase in resistance to UV irradiation, mechanical disruption, desiceation and the combined action of ethylenediaminetetraacetie acid and lysozyme. 相似文献
19.
V La Grutta M Sabatino G Gravante V Savatteri 《Archives internationales de physiologie et de biochimie》1986,94(5):295-303
The effects of caudate and septal stimulation on hippocampal activity were studied. Sodium penicillin was intravenously injected in order to induce a steady rate of interictal epileptic activity. Penicillin injection caused significant reduction of the rate of occurrence and duration of hippocampal rhythmic slow activity (RSA). Spontaneous RSA as well as RSA-eliciting caudate and septal stimulation induced a marked inhibition on frequency of epileptiform complexes. Lesions of the medial septal nucleus made it impossible to record RSA or to observe any sort of influence on hippocampal epileptiform activity by caudate stimulation. This result suggests that the septum is important for RSA genesis in the striato-hippocampal pathway or in the reciprocal septo-hippocampal connections. 相似文献
20.
U Pande G N La Mar J T Lecomte F Ascoli M Brunori K M Smith R K Pandey D W Parish V Thanabal 《Biochemistry》1986,25(19):5638-5646
The 1H NMR characteristics of the high-spin metmyoglobin from the mollusc Aplysia limacina have been investigated and compared with those of the myoglobin (Mb) from sperm whale. Aplysia metMb exhibits a normal acid----alkaline transition with pK approximately 7.8. In the acidic form, the heme methyl and meso proton resonances have been assigned by 1H NMR using samples reconstituted with selectively deuterated hemins and in the latter case by 2H NMR as well. On the basis of the methyl peak intensities and shift pattern, heme rotational disorder could be established in Aplysia Mb; approximately 20% of the protein exhibits a reversed heme orientation compared to that found in single crystals. Three meso proton resonances have been detected in the upfield region between -16 and -35 ppm, showing that the chemical shift of such protons can serve as a diagnostic probe for a pentacoordinated active site in hemoproteins, as previously shown to be the case in model compounds. The temperature dependence of the chemical shift of the meso proton signals deviates strongly from the T-1 Curie behavior, reflecting the presence of a thermally accessible Kramers doublet with significant S = 3/2 character. Nuclear Overhauser effect, NOE, measurements on Aplysia metMb have provided the assignment of individual heme alpha-propionate resonances and were used to infer spatial proximity among heme side chains. The hyperfine shift values for assigned resonances, the NOE connectivities, and the NOE magnitudes were combined to reach a qualitative picture of the rotational mobility and the orientation of the vinyl and propionate side chains of Aplysia metMb relative to sperm whale MbH2O.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献