全文获取类型
收费全文 | 1301篇 |
免费 | 136篇 |
出版年
2021年 | 16篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 16篇 |
2016年 | 31篇 |
2015年 | 49篇 |
2014年 | 50篇 |
2013年 | 70篇 |
2012年 | 81篇 |
2011年 | 87篇 |
2010年 | 51篇 |
2009年 | 54篇 |
2008年 | 78篇 |
2007年 | 72篇 |
2006年 | 81篇 |
2005年 | 80篇 |
2004年 | 61篇 |
2003年 | 59篇 |
2002年 | 61篇 |
2001年 | 23篇 |
2000年 | 31篇 |
1999年 | 34篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 21篇 |
1995年 | 9篇 |
1994年 | 18篇 |
1993年 | 24篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 18篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 13篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1969年 | 6篇 |
排序方式: 共有1437条查询结果,搜索用时 31 毫秒
991.
Peter Haase 《Oecologia》1986,68(3):456-458
Summary The annual leaf area production of the subalpine composite shrubsOlearia ilicifolia andSenecio bennettii is related to the environmental temperatures experienced at the time of leaf primordia initiation in the previous growing season. The sensitive period occurs 3–9 weeks after bud break when the new resting bud is formed in the growing shoot apex. The initiation periods ofOlearia andSenecio do not coincide and, therefore, the annual variation of leaf area increment follows a different pattern in the two species. A minimum annual increment of 20 cm2 inOlearia and 40–45 cm2 inSenecio seems to represent a probable lower limit; lower temperatures are unlikely to be experienced during primordia formation as these would delay bud break. 相似文献
992.
The localization of Na+-cotransport proteins in cortex and outer medulla of rat kidney was investigated with five monoclonal antibodies. Recently, it was found that these antibodies altered Na+-D-glucose cotransport and/or Na+-dependent high affinity phlorizin binding in pig kidney cortex and that three of these antibodies interacted also with Na+-cotransporters for lactate, L-alanine and/or L-glutamate (Koepsell, H., K. Korn, A. Raszeja-Specht, S. Bernotat-Danielowski, D. Ollig, J. Biol. Chem. 263, 18,419-18,429 (1988]. In pig and rat the monoclonal antibodies bind to two brush-border membrane polypeptides with identical molecular weights and isoelectric points of 75,000 and pI 5.5, and 47,000 and pI 5.4. These polypeptides have been previously identified as components of the porcine renal Na+-D-glucose cotransporter (Neeb, M., U. Kunz, H. Koepsell, J. Biol. Chem. 262, 10,718-10,727 (1987] and may also be part of other Na+-cotransporters. The electron microscopic localization of antibody binding was demonstrated by protein A-gold labeling on ultrathin plastic sections. Three antibodies bound to brush-border membranes of proximal convoluted and straight tubules. In the proximal convoluted tubules all antibodies reacted with apical endocytic vacuoles, apical dense tubules and lysosomes. Since dense tubules are supposed to originate from endocytic vacuoles and to fuse with brush-border membranes the data suggest recycling of Na+-cotransporters in the proximal convoluted tubule. In the outer medulla two antibodies bound to apical membranes of descending thin limbs (DTL) of short loops of Henle and to apical and basal membranes of DTL of long loops of Henle. Three antibodies bound to apical membranes of collecting ducts. These data indicate that Na+-cotransporters or homologous proteins exist beyond the proximal tubule. 相似文献
993.
994.
Peter Eckes Petra Schmitt Winfried Daub Friedrich Wengenmayer 《Molecular & general genetics : MGG》1989,217(2-3):263-268
Summary We have obtained transgenic tobacco plants overexpressing the enzyme glutamine synthetase (GS) by fusing an alfalfa GS gene
to the cauliflower mosaic virus 35S promotor and integrating it intoNicotiana tabacum var. W38 plants byAgrobacterium tumefaciens mediated gene transfer. The amount of RNA specific to alfalfa GS was about 10 times higher in transgenic tobacco plants than
in alfalfa. The alfalfa GS produced by these transgenic plants was identified by Western blotting and represented 5% of total
soluble protein in the transformed plants, amounting to a 5-fold increase in specific GS activity and in a 20-fold increase
in resistance to the GS inhibitorl-phosphinothricin in vitro. Tissue from GS overproducing plants showed a sevenfold lower amount of free NH3. The amino acid composition of the plant tissue was not altered significantly by GS overproduction. GS overproducing plants
were fertile and grew normally. These data show that a high level of expression of a key metabolic enzyme such as glutamine
synthetase does not interfere with growth and fertility of plants. 相似文献
995.
The turnover number for band 3-mediated sulfate transport in phosphatidylcholine bilayers 总被引:2,自引:0,他引:2
The anion transport system of the human erythrocyte membrane was reconstituted in unilamellar phosphatidylcholine vesicles, and a vesicle subpopulation of a narrow size distribution was isolated from the sample by gel filtration. In this subpopulation, the turnover number of the transport protein (the band 3 protein) for sulfate transport was determined. It was found that, in the reconstituted system, the protein transports sulfate 5-10 times faster than in the human erythrocyte membrane. 相似文献
996.
To examine the stereoselectivity of biliary excretion, the optically pure enantiomers of ketoprofen (KT), ibuprofen (IBU), and flurbiprofen (FLU) were intravenously administered to normal and bile duct-cannulated rats at 10 mg/kg. The recovery of total KT in bile was significantly higher after administration of (S)-KT than after (R)-KT [90.1 ± 3.5% vs 68.8 ± 8.2%, n =3, P < 0.05]. In normal rats the terminal half-life of (R)-KT was significantly shorter than that of (S)-KT after administration of (R)-KT (2.2 ± 0.6 h vs 14.3 ± 4.9 h, n = 3, P < 0.05). The terminal half-life of both enantiomers was significantly shorter in rats with continuous bile drainage as compared to normal rats. No significant differences in pharmacokinetic parameters could be found between both enantiomers in bile duct-cannulated animals. The total amount of IBU in bile was slightly higher after administration of (S)-IBU than after (R)-IBU administration. The percentage of (R)-IBU after (R)-IBU administration, however, was very low [(R)-IBU: 1.5 ± 0.9%, (S)-IBU: 23.4 ± 5.8%]. In normal rats the clearance of (R)-IBU was significantly higher as compared to (S)-IBU. Differences in pharmacokinetic parameters between normal and bile duct-cannulated rats were not statistically significant due to high interindividual variability. The total recovery of FLU, which was excreted in bile to a lower extent than either KT or IBU, also tended to be greater after S-enantiomer administration. Only small amounts of (S)-FLU could be recovered in bile after (R)-FLU administration. The pharmacokinetic parameters did not differ significantly between (R)- and (S)-FLU or between normal and bile duct-cannulated rats due to its low inversion rate and low excretion via bile. © 1993 Wiley-Liss, Inc. 相似文献
997.
Engel G. Vrieling Arie Draaijer Wilhelmus J. M. van Zeijl Louis Peperzak Winfried W. C. Gieskes Marten Veenhuis 《Journal of phycology》1993,29(2):180-188
Two different fluorescein isothiocyanate (FITC) conjugates were used to analyze the effect of labeling intensity on the flow cytometric appearance of marine dinoflagellates labeled with antibodies that specifically recognized the outer cell wall. Location of the labeling was revealed by epifluorescence and real-time confocal laser scanning microscopy using an anti-rabbit IgG/FITC-conjugated secondary antiserum. Flow cytometric measurements showed that cells of Prorocentrum species labeled this way could not always be distinguished from unlabeled cells. The labeling intensity increased several times when a biotinylated anti-rabbit IgG secondary antiserum was used in combination with a streptavidin/FITC conjugate. Flow cytometry indicated that the labeling intensity had increased 50%, which resulted in an improved separation of clusters of labeled and unlabeled cells. 相似文献
998.
R. Bordel E. Haase 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1993,163(3):219-224
The influence of flight and flight duration on 13 blood parameters was studied in homing pigeons which returned after 2–22 h of flight from release sites 113–620 km away. The haematocrit value decreased from 54.4% in controls to 51.0% in the flown birds. A lowered haematocrit overproportionately improves blood flow. The plasma concentrations of glucose and l(+)-lactate did not differ between experimental and control birds. This is compatible with the idea that carbohydrates are utilized as fuel mainly in the initial phase of flight. Plasma free fatty acid levels were significantly increased during flight and triglyceride concentrations gradually decreased with progressive flight duration. These findings support the view that lipids are the main energy source during flight. Plasma uric acid concentrations were increased two- to fourfold in flown birds. Urea levels gradually rose with flight duration to 400% of controls. Plasma protein concentration was lowered in flown pigeons. These results hint to an increased protein degradation during flight. Na+, K+, Ca2+, and Mg2+ levels in the plasma of the flown pigeons were not significantly different from control values. This finding together with the urea/uric acid ratio indicates that no severe dehydration occurred in our pigeons during free-range flight.Abbreviations FA
fatty acids
- FFA
free fatty acids 相似文献
999.
Martin Müller Conrad Flössel Michael Haase Thomas Luther Sybille Albrecht Peter Paul Nawroth Youming Zhang 《Virchows Archiv. B, Cell pathology including molecular pathology》1993,64(1):265-269
Expression of tissue factor (TF), the cellular receptor of clotting factor VII/VIIa, is a feature of certain malignant tumours.
The TF gene has been classified as an immediate early gene responsive to serum and cytokines. Thus, the regulation of TF gene
expression seems to play a role in cell growth. Recently, we have shown that constitutive TF expression in MCF-7 breast cancer
cells is modulated by such growth factors as EGF, TGFα, and IL-1. The present study deals with the immunocytochemically detectable
cellular distribution of TF in human breast cancer cell lines MCF-7 and MaTu stimulated by EGF and TGFα. In MCF-7 cells growing
logarithmically, stimulation led to a significant increase of TF mRNA after 2 h (in situ hybridization, Northern blot) and
to maximum TF expression after 6 h (immunohistochemistry). When decorated by monoclonal antibodies, TF protein showed a pronounced
localization at ruffled membrane areas, cell edges, and processes of spreading cells after 6 and 20 h. In more flattened cells
TF was concentrated in peripheric lamellae and microspikes communicating with neighbouring cells. After epithelial colony
pattern had established, TF was predominantly accumulated at the intercellular boundaries. The vary same distribution patterns
as seen in MCF-7 cells were true for the stimulated MaTu cell line. The dynamics and cellular distribution patterns of stimulated
TF expression support the hypothesis that TF could be of importance for morphogenic events associated with the growth and
differentiation of breast cancer cells in culture. 相似文献
1000.
Evidence for effect of random genetic drift on G+C content after lateral transfer of fucose pathway genes to Escherichia coli K-12 总被引:4,自引:0,他引:4
The cps cluster of Escherichia coli K-12 comprises genes involved in
synthesis of capsular polysaccharide colanic acid. Part of the E. coli K-12
cps region has been cloned and sequenced and compared to its Salmonella
enterica LT2 counterpart. The cps genes from the two organisms are
homologous; in the case of the LT2 genes, with G+C content of 0.61 and
codons characteristic of high G+C species, it seems clear that they have
been acquired relatively recently by lateral transfer from a high G+C
species. The K-12 form of these cps genes is closely related to those of
LT2 so must derive from the same high G+C species, but it appears to have
transferred much earlier such that random genetic drift has brought P3 (the
corrected G+C content of codon base 3) down from 0.77 to 0.64, more than
halfway to the E. coli average of 0.57. We estimate, using an equation
developed by Sueoka, that the lateral transfer to E. coli took place
approximately 45 million years ago. This is the first report we are aware
of demonstrating the expected adjustment of P3 after lateral transfer
between species with different G+C content DNA.
相似文献