全文获取类型
收费全文 | 5893篇 |
免费 | 455篇 |
国内免费 | 2篇 |
专业分类
6350篇 |
出版年
2023年 | 19篇 |
2022年 | 40篇 |
2021年 | 70篇 |
2020年 | 52篇 |
2019年 | 54篇 |
2018年 | 85篇 |
2017年 | 73篇 |
2016年 | 118篇 |
2015年 | 189篇 |
2014年 | 262篇 |
2013年 | 347篇 |
2012年 | 353篇 |
2011年 | 389篇 |
2010年 | 263篇 |
2009年 | 255篇 |
2008年 | 347篇 |
2007年 | 366篇 |
2006年 | 343篇 |
2005年 | 348篇 |
2004年 | 310篇 |
2003年 | 292篇 |
2002年 | 310篇 |
2001年 | 68篇 |
2000年 | 61篇 |
1999年 | 87篇 |
1998年 | 115篇 |
1997年 | 88篇 |
1996年 | 78篇 |
1995年 | 59篇 |
1994年 | 63篇 |
1993年 | 66篇 |
1992年 | 49篇 |
1991年 | 58篇 |
1990年 | 40篇 |
1989年 | 58篇 |
1988年 | 46篇 |
1987年 | 32篇 |
1986年 | 42篇 |
1985年 | 34篇 |
1984年 | 31篇 |
1983年 | 24篇 |
1982年 | 52篇 |
1981年 | 34篇 |
1980年 | 33篇 |
1979年 | 23篇 |
1978年 | 16篇 |
1977年 | 23篇 |
1976年 | 16篇 |
1975年 | 21篇 |
1974年 | 15篇 |
排序方式: 共有6350条查询结果,搜索用时 0 毫秒
41.
Glycine metabolism by plant mitochondria 总被引:3,自引:0,他引:3
David J. Oliver Michel Neuburger Jacques Bourguignon Roland Douce 《Physiologia plantarum》1990,80(3):487-491
42.
Birgit Conrad Regina S. Savchenko Roland Breves Jürgen Hofemeister 《Molecular & general genetics : MGG》1996,250(2):230-236
The adaptation and application of theEscherichia coli T7 RNA polymerase system for regulated and promoter-specific gene expression inBacillus subtilis is reported. The expression cassette used inBacillus subtilis was tightly regulated and T7 RNA polymerase (T7 RNAP) appeared 30 min after induction. The efficiency of T7 promoter-specific gene expression inB. subtilis was studied using one secretory and two cytosolic proteins of heterologous origin. The accumulation ofE. coli -galactosidase, as well as a 1,4--glucosidase fromThermoanaerobacter brockii inB. subtilis after T7 RNAP induction was strongly enhanced by rifampicin inhibition of host RNAP activity. The-amylase ofThermoactinomyces vulgaris, a secretory protein, was found to accumulate in the culture supernatant up to levels of about 70 mg/l 10–20 h after T7 RNAP induction, but was also deposited in cellular fractions. The addition of rifampicin inhibited-amylase secretion, but unexpectedly, after a short period, also prevented its further (intra)cellular accumulation 相似文献
43.
Summary Many plant cell walls are constructed according to a helicoidal pattern that is analog to a cholesteric liquid crystal order. This raises the question whether the wall assembly passes through a true but temporary liquid crystal state. The paper focuses on experiments performed from aqueous suspensions of extracted quince slime, i.e., a cellulose/glucuronoxylan wall composite that presents a helicoidal order when observed in situ, within the enlarged periplasm of the seed epidermal cells. Experiments carried out in acellular conditions showed that a spontaneous reassociation into a helicoidal order can be obtained from totally dispersed suspensions. The ultrastructural aspect of the reassembled mucilage suspension was different according to the resin used (LR White or nanoplast, a water-soluble melamin resin). It was always typically polydomain, and when an order was visible it was cholesteric-like and similar to the in situ native organization. Transition states with many imperfections expressed the difficulty of the system to reassemble in the absence of constraining surfaces. The possible intervention of glucuronoxylan (GX) in the ordered assembly of the microfibrils was checked by: (1) progressive extraction of GX by trifluoroacetic acid (TFA). The extraction was associated to a control of the fraction by analysis of uronic acid contents and observation at the electron microscope level. Extraction of GX provoked the formation of a flocculent mass, the flocculation being more intense when the TFA was more concentrated; (2) progressive change of pH in order to analyze the influence of pH on flocculation. Low pH (ca. pH 3) led also to a flocculation of the suspension, but the floc was reversibly lost after dialysis against distilled water. The results indicate the antifloc role of the GX due to the anionic charges carried by the side-chains. However, the function of GX as helper twisting agent in the cholesteric-like reassembly must not be ruled out. 相似文献
44.
Nathalie Leduc Victor Alejandro Iglesias Roland Bilang Andreas Gisel Ingo Potrykus Christof Sautter 《Sexual plant reproduction》1994,7(2):135-143
Direct gene transfer to floral meristems could contribute to cell-fate mapping, to the study of flower-specific genes and promoters, and to the production of transgenic gametes via the transformation of sporogenic tissues. Despite the wide potential of its applications, direct gene transfer to floral meristems has not been achieved so far because of the lack of suitable technology. We show in this paper that ballistic micro-targeting is the technique of choice for this purpose, and in this way, we were able to transfer genes efficiently into excised wheat immature spikes. Particle size was adjusted for optimal penetration into the L1 and L2 cell layers of the spikes with limited cell damage. Spikes at different developmental stages were shot either with a plasmid containing two genes involved in anthocyanin biosynthesis or with a plasmid bearing the uidA (-glucuronidase) gene. The transient expression of these marker genes was observed in the different developmental stages tested and in cells of both the L1 and the L2 layers. The transient expression of the uidA gene was significantly increased when the sucrose concentration in the culture medium was increased from 0.06 to 0.52 M. At the highest concentration, 100% of the targeted spikes expressed the uidA gene, with an average of 69 blue cells per spike. Twelve days after microtargeting, multicellular sectors showing transgene expression and containing up to 17 cells were found in 85% of the shot immature inflorescences. This indicated that targeted cells survived particle bombardment. Sectors were found in primordia of both vegetative and reproductive organs. 相似文献
45.
Modification of sialic acids by 9-O-acetylation is detected in human leucocytes using the lectin property of influenza C virus 总被引:1,自引:0,他引:1
Zimmer Gert; Suguri Toshiaki; Reuter Gerd; Yu Robert K.; Schauer Roland; Herrler Georg 《Glycobiology》1994,4(3):343-349
Influenza C virus spike glycoprotein HEF specifically recognizesglycoconjugates containing 9-O-acetyl-N-acetylneuraminic acid.The same protein also contains an esterase activity. Takingadvantage of these two properties, influenza C virus was usedas a very sensitive probe for the detection of traces of 9-O-acetyl-N-acetylneuraminicacid in human leucocytes. The binding of influenza C virus toleucocyte glycoproteins and gangliosides separated by sodiumdodecyl sulphatepolyacrylamide gel electrophoresis andthin-layer chromatography, respectively, was assayed using achromogenic esterase substrate. In this way, glycoproteins ofB-lymphocytes and T-lymphocytes were found to contain 9-O-acetylatedsialic acids. Of the various 9-O-acetylated gangliosides detected,one had the characteristics of 9-O-acetylated GD3. The identificationof 9-O-acetylated sialic acids on distinct glycoproteins andglycolipids should be helpful in assigning a physiological roleto this sugar. O-acetylation gangliosides influenza C virus lymphocytes sialic acids 相似文献
46.
Maryvonne Le Coniat Elisabeth Traiffort Martial Ruat Jean-Michel Arrang Roland Berger 《Human genetics》1994,94(2):186-188
We have assigned the human histamine H1-receptor gene to chromosome 3 by Southern blot analysis of a chromosome mapping panel constructed from humanhamster somatic cell hybrids. This assignment was confirmed by in situ hybridization on metaphase chromosomes and involved bands 3p14–p21. 相似文献
47.
The variation pattern in the perennial Hordeum brachyantherum complex and in the annual H. depressum are described. The diploid form of H. brachyantherum s. lat., endemic to California in USA, previously recognized as a separate species is here treated as a subspecies ( H. brachyantherum ssp. californicum ). Despite its restricted distribution it shows a considerable variation and overlap in morphology with the tetraploid ssp. brachyantherum , and no unambiguous determination based on morphology between the two tax a is possible. The tetraploid cytotype has a large distribution area in western North America and easternmost Asia and a very wide morphological variation. It has also a small disjunct distribution area in easternmost Canada. A single hexaploid population from California is referred to ssp. brachyantherum . 相似文献
48.
Per Mrin Roland Rosmond Bengt-ke Bengtsson Carola Gustafsson Gran Holm Per Bjmtorp 《Obesity (Silver Spring, Md.)》1994,2(3):263-270
Visceral obese men were characterized by a decreased total GH secretion and diminished peak amplitude, size, and number. T-substitution was followed by elevation of IGF-I levels. The IGF-I increase correlated with the elevation of T-concentration, and was most pronounced in men with the lowest concentrations of free T from the outset. There were no detectable changes in total quantity, amplitude, size or number of peaks of GH secretion. Glucose, cholesterol and triglycerides as well as diastolic blood pressure decreased. There were no changes in thyroid or hematology variables. Visceral obesity in men has been reported to be characterized by low testosterone (T) and insulin-like growth factor I (IGF-I) concentrations, the latter suggesting a relative growth hormone (GH) deficiency. Since T and GH-secretions are interrelated, men with visceral obesity were substituted with T for 14 days, and diurnal secretion pattern of GH as well as IGF-I concentrations, and metabolic variables were followed. T-substitution of visceral obese men is followed by an elevation of IGF-I concentrations. It is suggested that this might be due either to minor, non-detectable increases in GH secretion, or to direct effects of T on IGF-I concentrations. The regulatory mechanisms by which T-administration are leading to metabolic and anthropometric improvements, might be direct effects of T, with or without mediation via GH secretion. 相似文献
49.
Roland Rost 《Journal of Ornithology》1993,134(1):93-95
Summary A pair of Marsh Tits ( white/blue; yellow/green), which has been caught for bioacoustical investigations in May 1984, was released at the same place 15 months later (August 1985). Although their territory had been occupied by another Marsh Tit pair, the released birds reconquered it after violent skirmishes within one day. In 1986 White/Blue and Yellow/Green raised successfully eight young. Because its female partner died probably during winter 1986/87, in 1987, 1988 and 1989 Yellow/Green was observed raising young together with a female (Blue) ringed in autumn 1986 as a this year's bird. On the 15th of January 1990 I saw Yellow/Green (at least seven years and eight months old) for the last time. Although White/Blue and Yellow/Green were kept in captivity for 15 months, they obviously were able to maintain themselves free living after they had been released again. Thus, small passerines — when housed in accordance with their species specific claims and handled properly — are definitely able to survive in the wild even if they had lived in captivity for longer periods. 相似文献
50.
Joseph H. Sellin Roland DeSoignie Susan Burlingame 《The Journal of membrane biology》1993,136(2):147-158
Short-chain fatty acids (SCFAs) are the predominant luminal anion in the mammalian colon. Although they are rapidly absorbed
in vivo, little is known about the mechanisms of transepithelial transport in vitro. Previous studies have suggested that
SCFA transport may be linked to Na absorption or an anion exchange mechanism. We compared the transport of propionate under
short-circuit conditions in rabbit proximal and distal colon to determine whether there were segmental differences, how SCFAs
may be linked to either Na absorption or anion transport, and whether SCFAs, as weak electrolytes, may be affected by transepithelial
pH gradients. In distal colon, propionate transport was not significantly altered by stimulation of electrogenic Na absorption,
epinephrine or Cl removal. However, a modest transepithelial pH gradient (luminal 6.8/serosal 7.4) stimulated propionate absorption.
In proximal colon, propionate transport was significantly altered by manuevers that either stimulated (lowered [Na] in the
bathing media) or inhibited (theophylline) apical Na−H exchange. Neither Cl removal, nor the anion exchange inhibitor DIDS,
nor a transepithelial bicarbonate gradient, altered propionate transport. A transepithelial pH gradient inhibited propionate
secretion, but not in a manner entirely consistent with the effect of pH on the distribution of a weak electrolyte. These
results suggest that there is significant segmental heterogeneity in colonic SCFA transport; that transepithelial propionate
fluxes are altered by changes in pH or electroneutral Na absorption (Na−H exchange), but not by chloride removal, bicarbonate
gradients or electrogenic Na absorption. Regulation of SCFA transport may be an important factor in the physiology of colonic
fluid balance. 相似文献