全文获取类型
收费全文 | 7421篇 |
免费 | 1057篇 |
国内免费 | 6篇 |
专业分类
8484篇 |
出版年
2021年 | 69篇 |
2018年 | 67篇 |
2016年 | 111篇 |
2015年 | 196篇 |
2014年 | 206篇 |
2013年 | 291篇 |
2012年 | 344篇 |
2011年 | 334篇 |
2010年 | 211篇 |
2009年 | 213篇 |
2008年 | 280篇 |
2007年 | 310篇 |
2006年 | 393篇 |
2005年 | 347篇 |
2004年 | 337篇 |
2003年 | 354篇 |
2002年 | 351篇 |
2001年 | 195篇 |
2000年 | 140篇 |
1999年 | 144篇 |
1998年 | 91篇 |
1997年 | 89篇 |
1996年 | 84篇 |
1995年 | 72篇 |
1994年 | 80篇 |
1993年 | 68篇 |
1992年 | 90篇 |
1991年 | 99篇 |
1990年 | 99篇 |
1989年 | 80篇 |
1988年 | 78篇 |
1987年 | 88篇 |
1986年 | 98篇 |
1985年 | 94篇 |
1984年 | 101篇 |
1983年 | 97篇 |
1982年 | 76篇 |
1981年 | 93篇 |
1980年 | 82篇 |
1979年 | 103篇 |
1978年 | 81篇 |
1977年 | 76篇 |
1976年 | 77篇 |
1975年 | 64篇 |
1974年 | 71篇 |
1973年 | 91篇 |
1972年 | 72篇 |
1971年 | 70篇 |
1970年 | 61篇 |
1969年 | 63篇 |
排序方式: 共有8484条查询结果,搜索用时 15 毫秒
11.
12.
Summary The carbon cycle of a loblolly pine plantation in North Carolina was examined during its 12th through 16th years from planting. Net primary production during the study period averaged 2056 g C m-2 year-1. With autotrophic respiration equal to 2068 g C, the calculated gross production was 4124 g C m-2 year-1. Heterotrophic respiration of 694 g C m-2 year-1 resulted in net ecosystem production of 1362 g C m-2 year-1. In carbon cycle comparisons between forest ecosystems, autotrophic respiration rates were found to be closely coupled to regional temperature. 相似文献
13.
William A. Wells 《The Journal of cell biology》2003,162(2):168-169
14.
Sixin Jiang Brigitte Heller Vincent S. Tagliabracci Lanmin Zhai Jose M. Irimia Anna A. DePaoli-Roach Clark D. Wells Alexander V. Skurat Peter J. Roach 《The Journal of biological chemistry》2010,285(45):34960-34971
Stbd1 is a protein of previously unknown function that is most prevalent in liver and muscle, the major sites for storage of the energy reserve glycogen. The protein is predicted to contain a hydrophobic N terminus and a C-terminal CBM20 glycan binding domain. Here, we show that Stbd1 binds to glycogen in vitro and that endogenous Stbd1 locates to perinuclear compartments in cultured mouse FL83B or Rat1 cells. When overexpressed in COSM9 cells, Stbd1 concentrated at enlarged perinuclear structures, co-localized with glycogen, the late endosomal/lysosomal marker LAMP1 and the autophagy protein GABARAPL1. Mutant Stbd1 lacking the N-terminal hydrophobic segment had a diffuse distribution throughout the cell. Point mutations in the CBM20 domain did not change the perinuclear localization of Stbd1, but glycogen was no longer concentrated in this compartment. Stable overexpression of glycogen synthase in Rat1WT4 cells resulted in accumulation of glycogen as massive perinuclear deposits, where a large fraction of the detectable Stbd1 co-localized. Starvation of Rat1WT4 cells for glucose resulted in dissipation of the massive glycogen stores into numerous and much smaller glycogen deposits that retained Stbd1. In vitro, in cells, and in animal models, Stbd1 consistently tracked with glycogen. We conclude that Stbd1 is involved in glycogen metabolism by binding to glycogen and anchoring it to membranes, thereby affecting its cellular localization and its intracellular trafficking to lysosomes. 相似文献
15.
Summary Pollen mother cells at early meiotic prophase fromFritillaria lanceolata, F. mutica, Tulbaghia violacea, the lily “Formobel”,Triticum aegilopoides, T. dicoccoides, T. aestivum and synaptic and asynaptic forms ofT. durum were studied in thin sections with the electron microscope (a) in relation to distribution of nuclear pores (b) in respect
of fine structure of the pore complex in those of the first four. The pores were distributed in random clusters during leptotene
to pachytene in all plants, except in the two forms ofT. durum where there were either no pores or so few that they were not detectable. Probably correlated with this, the two membranes
of the nuclear envelope were often widely separated and frequently sacculated. No pores were seen at leptotene in the part
of the envelope to which, in theFritillarias and lily, the nucleolus was adpressed at this time. Evidence supporting a recent model which proposes that annuli are composed
of three rings of eight granular subunits was obtained. These subunits as well as a dense central element, observed in most
pores, were composed of filaments about 3 nm in diameter and evidently protein in character. There was evidence of a continuity
between filaments in the central element and those in the rings of subunits which encircle the pore aperture at both the nuclear
and cytoplasmic sides of the pore. In profiles of pores knobbed filaments were sometimes seen extending laterally from the
pore wall into the perinuclear space at two sides. Questions concerning the role of the annulus are discussed.
The author wish to thank Mr. R. F. Scott for construction to the model. 相似文献
16.
17.
Globin synthesis on reticulocyte membrane-bound ribosomes 总被引:1,自引:0,他引:1
W R Woodward S D Adamson H M McQueen J W Larson S M Estvanik P Wilairat E Herbert 《The Journal of biological chemistry》1973,248(5):1556-1561
18.
Abstract— When day-old chicks were injected intraperitoneally with 1.62mmoles of l -phenylalanine, they developed a condition resembling narcosis. Simultaneously, whole brain levels of phenylalanine were 2–4 μmol/g, whereas those in control brain were 0.06 μmol/g. Examination of some glycolytic intermediates in the brain revealed significant decreases in fructose-1,6-diphosphate, l -α-glycerol phosphate and lactate, in comparison to the levels of these compounds in the saline-injected control animals. Levels of glucose and glucose-6-phosphate either increased or did not change, whereas levels of glycogen did not differ significantly. Phosphocreatine increased reciprocally with the decrease in inorganic phosphate. The levels of adenine nucleotide (energy charge) were not affected. Utilization of cerebral high-energy phosphates was depressed by 50–70 per cent when determined as a function of metabolic rate in the brain at 15- and 30-s periods of ischaemia according to the ‘closed-system’ technique. Explanations for these data have been examined, such as toxicity of phenylacetate and inhibition of glycolytic enzymes by phenylpyruvate and l -phenylalanine and their relevance to this study is discussed. 相似文献
19.
D A Hartman S R Kuo T R Broker L T Chow R D Wells 《The Journal of biological chemistry》1992,267(8):5488-5494
A conformational distortion in the DNA duplex at the regulatory region of human papillomavirus type-11 next to an intermolecular triplex, formed with a synthetic oligonucleotide, was investigated with several chemical probes. The sequence targeted for triplex formation borders on the binding sites for the regulatory proteins encoded by the viral E2 open reading frame. Dimethyl sulfate, diethyl pyrocarbonate, and OsO4 all react to a greater extent with nucleotides in the duplex that are immediately adjacent to the triplex as compared to other bases throughout the duplex. This hypermodification was observed on both the polypurine and polypyrimidine strands of the duplex DNA. Similar hyperreactivity of bases flanking a triplex also was seen when the contiguous target polypurine tract was effectively extended by mutating interrupting pyrimidines in the human papillomavirus type-11 sequence to purines. We propose that this hyperreactivity is due to a structural distortion caused by the junction between the triplex and the duplex tracts. 相似文献
20.
Preparation of isolated biomolecules for SFM observations: T4 bacteriophage as a test sample. 总被引:2,自引:1,他引:1
The T4 bacteriophage has been used to investigate protocols for the preparation of samples for scanning force microscopy in air, in order to obtaining reproducible images. The resolution of images and the distribution of bacteriophages on the substrate depends on the buffer type, its concentration, the surface treatment of substrate, and the method of deposition. The best imaging conditions for the phages require dilution in a volatile buffer at low ionic strength and adsorption onto hydrophilic surfaces. When imaging with the scanning force microscopy the quality of the images is influenced by the vertical and lateral forces applied on the sample and by the tip geometry. 相似文献