全文获取类型
收费全文 | 49419篇 |
免费 | 4038篇 |
国内免费 | 7篇 |
出版年
2023年 | 235篇 |
2021年 | 384篇 |
2020年 | 338篇 |
2019年 | 327篇 |
2018年 | 957篇 |
2017年 | 971篇 |
2016年 | 1056篇 |
2015年 | 977篇 |
2014年 | 1171篇 |
2013年 | 2013篇 |
2012年 | 3387篇 |
2011年 | 3719篇 |
2010年 | 1942篇 |
2009年 | 1295篇 |
2008年 | 3094篇 |
2007年 | 3182篇 |
2006年 | 2961篇 |
2005年 | 2672篇 |
2004年 | 2531篇 |
2003年 | 2390篇 |
2002年 | 2389篇 |
2001年 | 1576篇 |
2000年 | 1790篇 |
1999年 | 978篇 |
1998年 | 513篇 |
1997年 | 395篇 |
1996年 | 459篇 |
1995年 | 420篇 |
1994年 | 440篇 |
1993年 | 404篇 |
1992年 | 414篇 |
1991年 | 345篇 |
1990年 | 324篇 |
1989年 | 284篇 |
1988年 | 290篇 |
1987年 | 288篇 |
1986年 | 250篇 |
1985年 | 345篇 |
1984年 | 416篇 |
1983年 | 367篇 |
1982年 | 344篇 |
1981年 | 327篇 |
1980年 | 303篇 |
1979年 | 290篇 |
1978年 | 297篇 |
1977年 | 273篇 |
1976年 | 257篇 |
1975年 | 310篇 |
1974年 | 248篇 |
1973年 | 220篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
81.
Oat (Avena sativa L.) mesophyll protoplasts were recently demonstrated to be capable of dedifferentiation, repeated divisions, and colony formation. Since the development of oat mesophyll protoplasts is decisively influenced by the nature of the used feeder culture (species, variety and concentration), we conducted a systematic study of this parameter. Generally, graminaceous feeders promoted protoplast proliferation, while dicot species repressed protoplast divisions. The beneficial effect of those feeders that promote divisions was counterbalanced by a factor that causes necrosis. The correct balance between promotion of divisions or necrosis depended on the nature of the feeder and its plating density. 相似文献
82.
Band 3 protein extracted from human erythrocyte membranes by Triton X-100 was recombined with the major classes of phospholipid occurring in the erythrocyte membrane. The resulting vesicle systems were characterized with respect to recoveries, phospholipid composition, protein content and vesicle size as well as capacity and activation energy of sulfate transport. Transport was classified into band-3-specific fluxes and unspecific permeability by inhibitors. Transport numbers (sulfate ions per band 3 per minute) served as a measure of functional recovery after reconstitution. The transport properties of band 3 proved to be insensitive to replacement of phosphatidylcholine by phosphatidylethanolamine, while sphingomyelin and phosphatidylserine gradually inactivated band-3-specific anion transport when present at mole fractions exceeding 30 mol%. The activation energy of transport remained unaltered in spite of the decrease in transport numbers. The results, which are discussed in terms of requirements of band 3 protein function with respect to the fluidity and surface charge of its lipid environment, provide a new piece of evidence that the transport function of band 3 protein depends on the properties of its lipid environment just as the catalytic properties of some other membrane enzymes. The well-established species differences in anion transport (Gruber, W. and Deuticke, B. (1973) J. Membrane Biol. 13, 19–36) may to some extent reflect this lipid dependence. 相似文献
83.
Paola A Gilardoni Stefan Schuck Ruth Jüngling Björn Rotter Ian T Baldwin Gustavo Bonaventure 《BMC plant biology》2010,10(1):66
Background
Plants trigger and tailor defense responses after perception of the oral secretions (OS) of attacking specialist lepidopteran larvae. Fatty acid-amino acid conjugates (FACs) in the OS of the Manduca sexta larvae are necessary and sufficient to elicit the herbivory-specific responses in Nicotiana attenuata, an annual wild tobacco species. How FACs are perceived and activate signal transduction mechanisms is unknown. 相似文献84.
Walter Döpp 《Planta》1932,17(1):86-152
Ohne ZusammenfassungMit 2 Textabbildungen und Tafel I–X. 相似文献
85.
Polytene salivary gland nuclei of Chironomus pallidivittatus were transplanted into oocytes of Xenopus laevis which were then cultured in vitro for 18 h. The giant chromosomes and nucleoli as well as the entire nuclei enlarged considerably
in volume during this time. The polyteny and specific chromomere pattern of the chromosomes were maintained, and the puffing
of the salivary gland-specific Balbiani rings was not noticeably changed. — Polytene nuclei from differentiated insect cells
transplanted into Xenopus oocytes thus appear suited for exposing giant chromosomes in vivo to purified factors such as regulatory molecules.
This paper is dedicated to Professor Wolfgang Beermann on the occasion of his 60th birthday 相似文献
86.
Tor Strömgren 《Coral reefs (Online)》1987,6(1):43-47
Series of apices of Acropora pulchra from an intertidal reef at Phuket, Thailand, were grown at different depths in the sea, and the length growth was monitored at 12–24 h intervals with laser diffraction. The growth rates of actively growing apices were normally distributed and showed a high variability, with an average coefficient of variation of 58%. There was a highly significant difference in average growth rate between adjacent colonies. A significant linear relationship was found between irradiance and length growth, with a saturating level at 300–400 Wm-2. At 1000 Wm-2 length growth was significantly reduced. Under normal daylight conditions, day and night growth rates were equal. 相似文献
87.
Interaction of extracellular Pseudomonas lipase with alginate and its potential use in biotechnology
Jost Wingender Silke Volz Ulrich K. Winkler 《Applied microbiology and biotechnology》1987,27(2):139-145
Summary Extracellular Pseudomonas lipase is able to interact directly or indirectly with alginate as deduced from the following results: (i) During adsorption chromatography of exolipase the enzyme adsorbed quantitatively to glass beads in the absence of alginate, but not after its preincubation in the presence of the polysaccharide; pretreatment of glass beads with alginate did not prevent enzyme adsorption. (ii) In the presence of alginate exolipase was much more resistant to heat inactivation than in its absence. (iii) In the presence of alginate the increase in exolipase activity caused by the non-ionic detergent Triton X-100 was drastically reduced. (iv) Exolipase could be rapidly and almost completely harvested from cell-free culture fluid of P. aeruginosa 5940 by ethanolic coprecipitation with alginate. After dissolving the coprecipitate in detergent-containing buffer exolipase and polysaccharide could be easily separated by ion-exchange chromatography on DEAE-Sephadex A-25. The coprecipitation method was also successfully applied to exolipases produced by Pseudomonas sp., Chromobacierium viscosum and Rhizopus delamar, thus suggesting potential use of this method in biotechnology. 相似文献
88.
89.
Summary The replication model for sister chromatid exchange (SCE), when introduced in 1980 by Painter, was claimed to be consistent with the one hit property of SCE. However, the argument offered in favour of the one hit property was based on a defective dose-response function, as shown in this paper, since dose as the independent parameter of any dose-response function was not included in the considerations. This missing part of the model's dose-response function is added and, by using Bessel functions, a formula for the complete dose-response function is presented. A re-examination of the newly derived function shows that, in the model, linearity holds only under certain restricted circumstances. 相似文献
90.
Bernd Höffken Reinhard Ködding Alexander von zur Mühlen Tainer Hehrmann Rolf-Dieter Hesch 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,539(1):114-124
The nature of the conversion of thyroxine (T4) to triiodothyronine (T3) and reverse triiodothyronine (rT3) was investigated in rat liver homogenate and microsomes. A 6-fold rise of T3 and 2.5-fold rise of rT3 levels determined by specific radioimmunoassays was observed over 6 h after the addition of T4. An enzymic process is suggested that converts T4 to T3 and rT3. For T3 the optimal pH is 6 and for rT3, 9.5. The converting activity for both T3 and rT3 is temperature dependent and can be suppressed by heat, H2O2, merthiolate and by 5-propyl-2-thiouracil. rT3 and to a lesser degree iodide, were able to inhibit the production of T3 in a dose related fashion. Therefore the pH dependendy, rT3 and iodide may regulate the availability of T3 or rT3 depending on the metabolic requirements of thyroid hormones. 相似文献