全文获取类型
收费全文 | 2302篇 |
免费 | 110篇 |
国内免费 | 1篇 |
专业分类
2413篇 |
出版年
2021年 | 30篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 30篇 |
2016年 | 39篇 |
2015年 | 52篇 |
2014年 | 69篇 |
2013年 | 174篇 |
2012年 | 124篇 |
2011年 | 136篇 |
2010年 | 79篇 |
2009年 | 63篇 |
2008年 | 120篇 |
2007年 | 126篇 |
2006年 | 120篇 |
2005年 | 133篇 |
2004年 | 109篇 |
2003年 | 121篇 |
2002年 | 148篇 |
2001年 | 25篇 |
2000年 | 17篇 |
1999年 | 35篇 |
1998年 | 44篇 |
1997年 | 21篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 33篇 |
1993年 | 21篇 |
1992年 | 15篇 |
1991年 | 23篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 20篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 16篇 |
1984年 | 24篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 27篇 |
1980年 | 22篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 16篇 |
1975年 | 13篇 |
1974年 | 14篇 |
1973年 | 9篇 |
1972年 | 11篇 |
排序方式: 共有2413条查询结果,搜索用时 15 毫秒
31.
Production of (R)-3-Chloro-1,2-Propanediol from Prochiral 1,3-Dichloro-2-Propanol by Corynebacterium sp. Strain N-1074 总被引:2,自引:1,他引:1 下载免费PDF全文
The production of (R)-3-chloro-1,2-propanediol [(R)-MCP] from prochiral 1,3-dichloro-2-propanol (DCP) was examined with a bacterial strain identified as a Corynebacterium strain. The addition of glycerol as a carbon source or some chlorinated alcohols to a medium was effective for the induction of activity catalyzing the transformation of DCP into MCP. The optimum pH for (R)-MCP production by the resting cell reaction was around 8.0. The optical purity of (R)-MCP formed was improved by keeping the level of DCP in the reaction mixture at a low concentration. (R)-MCP was obtained from 77.5 mM DCP with a 97.3% molar conversion yield and an 83.8% enantiomeric excess of its optical purity by periodic feeding of the substrate. 相似文献
32.
Cells of Nitella flexilis were made inexcitable by treatmentwith 10 mM KCl for more than 24 h. A Ca2+-sensitive photoproteinaequorin was injected into the cytoplasm of such cells. Forvacuolar per fusion, the central part of an aequorin-loadedcell was immersed in silicone oil, and both cell ends bathedin the perfusion medium were cut off. A large light emissionfrom aequorin was observed when the vacuole was perfused witha hypotonic medium whose osmotic pressure was adjusted to halfof the osmotic pressure of the cell sap. This shows that hydrationof the cytoplasm triggers release of Ca2+ from internal stores,since influx of Ca2+ from silicone oil is excluded. Hydration of cells was induced in another way. Cells were firstdehydrated by transferring them from 10 mM KCl solution to thatwith 250 mM sorbitol added. This procedure did not affect thecytoplasmic streaming. When cells were rehydrated by transferringthem to 10 mM KCl solution, cytoplasmic streaming was eitherstopped or slowed down in a few seconds. A quick light emissionfrom aequorin was observed in the rehydration, evidence thatcytoplasmic streaming was inhibited by an increase in the cytoplasmicCa2+ concentration. Both streaming cessation and aequorin lightemission were observed even in KCl-treated cells which werefurther treated with 5 mM EGTA. Thus, the increase in Ca2+ isconcluded to be caused by the release of Ca2+ from internalstores. These results support our previous hypothesis [Tazawa et al.(1994) Plant Cell Physiol. 35:63] that, in Nitella flexilis,the increase in the concentration of Ca2+ in the cytoplasm whichoccurs on the endoosmotic side of the cell during transcellularosmosis is caused by hydration of the cytoplasm. (Received June 6, 1994; Accepted December 26, 1994) 相似文献
33.
High level of GUS gene expression driven by pollen-specific promoters in electroporated lily pollen protoplasts 总被引:8,自引:0,他引:8
Gene constructs that contained the -glucuronidase (GUS) gene under the control of a pollen-specific Zm13 promoter from maize and a LAT52 promoter from tomato were introduced by electroporation into pollen protoplasts isolated from bicellular pollen grains of Lilium longiflorum. After 20 h in culture, the pollen protoplasts exhibited the apparent expression of GUS in a fluorometric assay. The GUS activity induced under the control of the Zm13 promoter was over 10 000 times higher than activity in the control (with no DNA or without electroporation). By contrast, the GUS gene was nearly silent in the lily microspore protoplasts and generative cell protoplasts. The GUS activity driven by the Zm13 and LAT52 promoters was also detected by a cytochemical assay. The frequency of blue-staining pollen protoplasts was about 70% in the case of the Zm13 promoter. The efficiency of gene transfer by electroporation was much higher than by particle bombardment. This protoplast-specific electroporation system is suitable for rapid and reliable examination of pollen-specific promoters, being as good as the particle bombardment system. 相似文献
34.
Mitsuyo Okazaki Makoto Kinoshita Chikayuki Naito Ichiro Hara 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1984,336(1)
A simple and rapid method for apolipoprotein analysis in serum high-density lipoproteins (HDL) has been developed using high-performance liquid chromatography (HPLC) with sodium phosphate buffer (pH 7.0) containing 0.1% sodium dodecyl sulphate (SDS) as eluent. In contrast to the use of urea solution as an eluent, apolipoproteins can be analysed by applying an incubation mixure of HDL and the eluent buffer. A TSK-GEL column of G3000SW was found to be more profitable than G2000SW or G4000SW for analysis of HDL apolipoproteins. Elution patterns monitored by absorbance at 280 nm using a G3000SW column can give precise quantitative as well as qualitative information about apolipoproteins of molecular weight between 104 and 105. HPLC patterns of HDL apolipoproteins were compared between individual human subjects with various diseases. Elution profiles for lipid components in an incubation mixture were also examined. 相似文献
35.
36.
Prof. Dr. Ichiro Ichihara Martin Kallio Lauri J. Pelliniemi 《Cell and tissue research》1978,192(3):381-390
Summary The ducts of the rat ventral prostate have been studied by light and electron microscopy for elucidation of their role in prostatic function. The epithelium of the main duct consists of simple columnar cells and polymorphic basal cells. The columnar cells show no indication of secretory activity. The basal cells contain bundles of filaments of 5–6 nm thickness and numerous pinocytotic vesicles. The ducts are surrounded by layers of circular smooth muscle cells interspersed with nerve axons. On ultrastructural grounds the ducts do not appear to secrete material into the seminal fluid, but apparently the muscular coat actively helps drain the gland during ejaculation. 相似文献
37.
Ichiro Azuma Mikio Yamawaki Kosei Yasumoto Yuichi Yamamura 《Cancer immunology, immunotherapy : CII》1978,4(2):95-100
Summary The antitumor activity of the cell wall skeleton preparations of four species of Nocardia, N. brasiliensis strain 146, N. coeliaca strain 122, N. polychromogenes strain 6, and N. rubra, which showed potent adjuvant activity on the induction of cell-mediated cytotoxicity in allogeneic mice, was examined with the aid of EL-4 leukemia, melanoma B16, and MH-134 hepatoma in syngeneic mice. Preliminary clinical trials were performed and the results suggest that the cell wall skeleton of N. rubra, upon intrapleural injection, may be useful as an immunotherapeutic agent for patients with malignant pleurisy. The chemical properties of these cell wall skeleton preparations are described. 相似文献
38.
Summmary Electric characteristics of internodalChara australis cells, from which the tonoplast had been removed by vacuolar perfusion with media containing EGTA, were studied in relation to intracellular concentrations of ATP and Mg2+ using the ordinary microelectrode method and the open-vacuole method developed by Tazawa, Kikuyama and Nakagawa (1975.Plant Cell Physiol.
16:611). The concentration of ATP was decreased by introducing hexokinase and glucose into the cell and that of Mg2+ by introducing EDTA or CyDTA. The membrane potential decrease and the membrane resistance increase were both significant when the ATP or Mg2+ concentration was decreased. An ATP-dependent membrane potential was also found in other species of Characeae,Nitella axillaris andN. pulchella. Excitability of the membrane was also completely lost by reducing the ATP or Mg2+ concentration. Both membrane potential and excitability were recovered by introducing ATP or Mg2+ into ATP- or Mg2+-depleted cells.The time course of membrane potential recovery was followed by the open-vacuole method. Recovery began as soon as intracellular perfusion with medium containing ATP and Mg2+ was started. Reversible transition of the membrane potential between polarized and pepolarized levels by controlling the intracellular concentration of ATP or Mg2+ could be repeated many times by the open-vacuole method, when the excitability was suppressed by addition of Pb2+ to the external medium.The ineffectiveness of an ATP analog, AMP-PNP, and the synergism of ATP and Mg2+ in maintaining the membrane potential and excitability strongly suggest that ATP act via its hydrolysis by Mg2+-activated ATPase. The passive nature of the membrane, as judged from responses of the membrane potential to changes of the external K+ concentration, was not altered by lowering the ATP concentration in the cell. The mechanism of membrane potential generation dependent on ATP is discussed on the basic of an electrogenic ion pump. Involvement of the membrane potential generated by the ion pump in the action potential is also discussed. 相似文献
39.
Chara cells without tonoplasts, prepared by replacing the cellsap with EGTA-containing media, showed essentially the samepattern of light-induced changes in membrane potential and membraneresistance as normal cells although the concentrations of ionsand ATP in the cytoplasm decreased considerably (1/31/10)after loss of the tonoplast. Removal of the tonoplast reducedthe rate of photosynthetic O2 evolution to about 50% of thatof normal cells but did not affect the magnitude of light-inducedpotential change. Not a full but a certain level of electronflow seems necessary to activate the putative electrogenic H+-pump.
1 Present address: Department of Botany, Faculty of Science,University of Tokyo, Japan.
2 Present address: Niigata College of Pharmacy, Niigata 950-21,Japan. (Received September 4, 1978; ) 相似文献
40.