全文获取类型
收费全文 | 4771篇 |
免费 | 448篇 |
国内免费 | 1篇 |
出版年
2023年 | 20篇 |
2022年 | 50篇 |
2021年 | 84篇 |
2020年 | 60篇 |
2019年 | 70篇 |
2018年 | 66篇 |
2017年 | 69篇 |
2016年 | 139篇 |
2015年 | 217篇 |
2014年 | 239篇 |
2013年 | 324篇 |
2012年 | 434篇 |
2011年 | 379篇 |
2010年 | 265篇 |
2009年 | 246篇 |
2008年 | 310篇 |
2007年 | 314篇 |
2006年 | 306篇 |
2005年 | 295篇 |
2004年 | 277篇 |
2003年 | 264篇 |
2002年 | 282篇 |
2001年 | 53篇 |
2000年 | 29篇 |
1999年 | 52篇 |
1998年 | 79篇 |
1997年 | 43篇 |
1996年 | 38篇 |
1995年 | 37篇 |
1994年 | 26篇 |
1993年 | 31篇 |
1992年 | 22篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1965年 | 3篇 |
排序方式: 共有5220条查询结果,搜索用时 31 毫秒
41.
Ulrich Flögel Thoralf Niendorf Nathalie Serkowa Annette Brand Joachim Henke Dieter Leibfritz 《Neurochemical research》1995,20(7):793-802
Diffusion-weighted in vivo1H-NMR spectroscopy of F98 glioma cells embedded in basement membrane gel threads showed that the initial cell swelling to about 180% of the original volume induced under hypotonic stress was followed by a regulatory volume decrease to nearly 100% of the control volume in Dulbecco's modified Eagle's medium (DMEM) but only to 130% in Krebs-Henseleit buffer (KHB, containing only glucose as a substrate) after 7 h. The initial cell shrinkage to approx. 70% induced by the hypertonic stress was compensated by a regulatory volume increase which after 7 h reached almost 100% of the control value in KHB and 75% in DMEM.1H-,13C-and31P-NMR spectroscopy of perchloric acid extracts showed that these volume regulatory processes were accompanied by pronounced changes in the content of organic osmolytes. Adaptation of intra- to extracellular osmolarity was preferentially mediated by a decrease in the cytosolic taurine level under hypotonic stress and by an intracellular accumulation of amino acids under hypertonic stress. If these solutes were not available in sufficient quantities (as in KHB), the osmolarity of the cytosol was increasingly modified by biosynthesis of products and intermediates of essential metabolic pathways, such as alanine, glutamate and glycerophosphocholine in addition to ethanolamine. The cellular nucleoside triphosphate level measured by in vivo31P-NMR spectroscopy indicated that the energy state of the cells was more easily sustained under hypotonic than hypertonic conditions.To whom to address reprint requests. 相似文献
42.
A new monoclonal antibody (3D3) generated with human respiratory mucins and directed against Lewis determinants 总被引:1,自引:1,他引:0
Nathalie Emery; Palfa Shirley B.; Place Graham; Oriol Rafael; Hall Roderick L.; Roussel Philippe; Lhermitte Michel 《Glycobiology》1995,5(6):563-570
We have prepared a monoclonal antibody (MAb), 3D3, raised againstpurified human respiratory mucins. This antibody recognizedmucins and proteolytically derived glycopeptides. The epitoperecognized by the antibody was destroyed by -L-fucosidase, indicatingthat it was present on the carbohydrate moieties. Structuralspecificity was determined by adsorption on a variety of synthetic,insolubilized oligosaccharides. Several lines of evidence indicatethat the 3D3 MAb reacted strongly with the Lewis (Leb) antigen,but also recognized Lea and Ley determinants. This antibodymight be useful to study mucin secretion. human bronchial mucins Lewis b 相似文献
43.
Cytokinesis, cell expansion, and the potential for cytokinin-autonomous growth in tobacco pith
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Turgeon R 《Plant physiology》1982,70(4):1071-1074
Pith tissue from Nicotiana tabacum L. cv `Maryland Mammoth' or `Wisconsin 38' was isolated, free of vascular tissue, and cultured on a medium containing auxin but no cytokinin. Explants from the apical 1 cm of stem, within the pith rib meristem, initiated callus growth with 100% efficiency. Macroscopically visible callus was evident 5 days after the tissue was isolated, and the cultures grew persistently in the absence of cytokinin. Heat treatment, sometimes used to initiate cytokinin habituation, was not required. Explants from tissue basipetal to the pith rib meristem declined in the frequency of habituation with increasing distance from the shoot apex. Although pith tissue which was growing, in vivo, was more prone than mature tissue to establish cytokinin-habituated callus, the basipetal decline in habituation frequency extended well beyond the zone of cell expansion. Explants from mature pith 40 centimeters or more from the shoot apex grew in the absence of cytokinin with 18% frequency, although the response required at least 2 weeks of culture. Further analysis demonstrated that tissue near the periphery of mature pith was more prone to cytokinin-habituation than tissue from the pith center. 相似文献
44.
Quantitative Analysis of Photosynthate Unloading in Developing Seeds of Phaseolus vulgaris L. : I. The Use of Steady-State Labeling
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The pathway and kinetics of photosynthate unloading in developing seeds of bean (Phaseolus vulgaris L.) were investigated using steady-state labeling with 14CO2. The continuous assimilation of 14CO2 at constant specific activity produced stable tracer fluxes that facilitated straightforward analyses of photosynthate import and unloading in developing seeds. The kinetics of tracer equilibration within intact seeds were compatible with a symplastic route of photosynthate unloading in the seed coat. The import and partitioning of tracer within seeds were partially disrupted by the surgical excision of the distal halves of seeds as practiced during the preparation of “empty” seed coats for perfusion. 相似文献
45.
Danielle-Julie Carrier Nathalie Chauret Michael Mancini Pierre Coulombe Ronald Neufeld Martin Weber Jean Archambault 《Plant cell reports》1991,10(5):256-259
Ginkgo biloba cells were cultured in two 500 mL shake flasks and in 2 L and 6 L immobilization bioreactors using MS medium supplemented with 1 mg.L–1 NAA, 0.1 mg.L–1 K and 30 g.L–1 sucrose. Specific growth rates were 0.06 d–1, 0.11 d–1 and 0.07 d–1 for the 2 L and 6 L bioreactors and shake flask cultures, respectively. Extracellular phosphate, nitrate, ammonium and carbohydrate uptake rates of the bio reactor cultures were approximately 17 to 39% slower than those of shake flask cultures. The specific oxygen uptake and carbon dioxide transfer rates of immobilized Ginkgo biloba cells ranged from 0.027 to 0.041 mmol O2.g–1.d.w.hr–1 (maximum uptake at 14 days) and 0.020 to 0.057 mmol CO2g. –1.d.w.hr–1 (maximum production at 14 days). Extracts from the biomass of the two immobilized and shake flask suspension cultures were analysed for ginkgolide A by GC-MS. Yields of 7, 17, 19 and 7 ng.g. –1d.w. of ginkgolide A were determined for shake flask 1, shake flask 2 and the 2 L and 6 L immobilized cultures, respectively. Traces of ginkgolide B were detected with the signal to noise ratio, however, being too low for positive confirmation of this last product.Abbreviations CTR
Carbon dioxide transfer rate
- DO
Dissolved oxygen
- g.d.w.
Gram dry weight
- GA
Ginkgolide A
- GB
Ginkgolide B
- GC
Gas chromatography
- GC-MS
Gas chromatography-mass spectrometry
- HPLC
High performance liquid chromatography
- K
Kinetin
- MS
Murashige and Skoog salt medium
- N1K1MS
Complete Murashige and Skoog medium supplemented with 1 mg.L–1 NAA, 0.1 mg.L–1 K and 30g.L–1 sucrose
- NAA
Naphthaleneacetic acid
- OTR
Oxygen transfer rate
- PAF
Platelet Aggregating Factor
- qCO2
Specific carbon dioxide production rate
- qO2
Specific oxygen uptake rate
- u
Specific growth rate 相似文献
46.
McQueen Donald J. Johannes Mark R. S. Lafontaine Nathalie R. Young Andrew S. Longbotham Eric Lean David R. S. 《Hydrobiologia》1990,(1):337-341
We used two analyses to test the hypothesis that planktivore abundances contribute to the residual variations of Secchi depth
or chlorophyll-a plotted with respect to mean summer epilimnetic total phosphorus. The first analysis involved 15 lake years of data from
six lakes. The data set comprised mark-recapture assessments of piscivore and planktivore numbers and estimates of mean summer
chlorophyll-a, total phosphorus and Secchi depth. We found that residual chlorophyll-a variation was not significantly (p>0.05) correlated with planktivore densities, but that planktivore densities did contribute (p<0.02) to the residual variation of Secchi depth on mean total phosphorus. The second analysis included all of the data used
in the first plus an additional 13 lake years of data from the literature. These data showed that the percentage of the total
fish community comprising planktivores did not significantly (p>0.05) contribute to the residual variation in chlorophyll-a with respect to mean summer total phosphorus. Together, our results suggest that planktivore abundance has a significant
cascading impact on water clarity, but no long term statistically significant impact on mean summer chlorophyll-a concentration. 相似文献
47.
A Meisels M Roy M Fortier C Morin M Casas-Cordero K V Shah H Turgeon 《Acta cytologica》1981,25(1):7-16
We report on 162 cases of human papillomavirus (HPV) infection of the cervix seen in a two-year period in which the cell sample showed such marked atypia that errors of interpretation could easily have been made. These atypical condylomata are difficult to diagnose cytologically as well as histologically because they mimic dysplasia or carcinoma in situ and, on smears, even invasive squamous carcinoma. HPV particles associated with fibrillar material were found within nuclei of these lesions; their nature was further proved by the immunoperoxidase test. This new form of HPV infection of the cervix showed a 9.1% rate of progression to more advanced cervical lesions. The cytologic finding of atypical condylomata is an indication for colposcopy, confirmative biopsy and appropriate treatment. 相似文献
48.
Persistence of conidia of the entomopathogenic fungus Paecilomyces fumosoroseus exposed to artificial and solar radiation at a constant temperature was studied by monitoring the ability to germinate and to form colonies (colony - forming units , CFUs) . The photic effect of radiation on each of these variables was modelled by a decreasing function of UVB irradiation ( in J m 2) . Germination ability was represented by a logistic function and viability (log CFU) by an infinitely decreasing function . Experiments carried out under artificial conditions , at three different UVB irradiances ( from 0 . 3 to 1 . 6 W m 2) , similar to those observed in nature , confirmed the adequacy of the predictor variable and of the functions chosen for describing these data . The proposed models appeared to be irradiance independent . Under solar radiation , the models were able to describe data collected on three different summer days in France (48 o 51 N , 2 o 06 E) . However , it took a greater amount of solar UVB radiation to produce the same effect as that achieved indoors . This could be explained by differences in radiation spectra . For each model , one set of parameters was sufficient for representing all three sets of data: this constitutes an initial validation of the models proposed . 相似文献
49.
A checklist of identified oribatid mite taxa from riverine freshwater environments from six islands in Polynesia (New Caledonia, Tahiti, Moorea, Rurutu, Tubuai, Raiatea) is presented; 18 species, 16 genera and eight families were recorded. Trhypochthoniellus longisetus (Berlese, 1904) and Trimalaconothrus albulus Hammer, 1972 prevailed on distribution. Fortuynia smiti
sp. n. (Fortuyniidae) is described from New Caledonia. The new speciesis morphologically most similar to Fortuynia marina Hammen, 1960 from New Guinea, but it differs from the latter by the longer notogastral setae dm, lm, c2, p1, epimeral setae 3b and adanal setae ad1 and the presence of prodorsal lateral ridges. 相似文献
50.