全文获取类型
收费全文 | 4442篇 |
免费 | 394篇 |
国内免费 | 437篇 |
出版年
2024年 | 7篇 |
2023年 | 81篇 |
2022年 | 64篇 |
2021年 | 115篇 |
2020年 | 110篇 |
2019年 | 153篇 |
2018年 | 118篇 |
2017年 | 131篇 |
2016年 | 146篇 |
2015年 | 150篇 |
2014年 | 189篇 |
2013年 | 238篇 |
2012年 | 206篇 |
2011年 | 197篇 |
2010年 | 195篇 |
2009年 | 228篇 |
2008年 | 248篇 |
2007年 | 213篇 |
2006年 | 218篇 |
2005年 | 217篇 |
2004年 | 169篇 |
2003年 | 148篇 |
2002年 | 161篇 |
2001年 | 141篇 |
2000年 | 103篇 |
1999年 | 92篇 |
1998年 | 102篇 |
1997年 | 91篇 |
1996年 | 87篇 |
1995年 | 96篇 |
1994年 | 89篇 |
1993年 | 68篇 |
1992年 | 85篇 |
1991年 | 52篇 |
1990年 | 63篇 |
1989年 | 48篇 |
1988年 | 48篇 |
1987年 | 41篇 |
1986年 | 37篇 |
1985年 | 71篇 |
1984年 | 55篇 |
1983年 | 31篇 |
1982年 | 32篇 |
1981年 | 24篇 |
1980年 | 30篇 |
1979年 | 26篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1973年 | 9篇 |
排序方式: 共有5273条查询结果,搜索用时 21 毫秒
51.
Oligodendroglial proteins labeled with radioactive amino acids were subjected to one- and two-dimensional polyacrylamide electrophoresis. Bands comigrating with myelin proteins, the basic protein (MBP), the proteolipid protein (PLP), and the Wolfgram protein (WP) doublet, were detected by Coomassie Blue staining and by autoradiography. The identity of the MBP and WP in the cellular material is evidenced by immunoblotting with specific antibodies. A comparative study of myelin samples from rat and pig CNS reveals that WP can be detected immunochemically in both species. Different protein patterns, however, are observed. Three protein bands are found with antibodies against the myelin-associated glycoprotein (MAG). The high-molecular-weight component prevails in pig myelin, whereas the medium-molecular-weight component is predominant in rat myelin. Moreover, two protein bands, of molecular weights 35,000 and 33,000 (Ol 1 and Ol 2), are present in high amounts in oligodendroglial particulate material but are not detectable in myelin. These oligodendroglial characteristic proteins are not species-specific, since they are found in preparations of cat oligodendrocytes as well. Activities of cerebroside sulfotransferase (EC 2.8.2.11) are low in freshly isolated cells and increase during the first week of culture. A reverse course of enzyme activities is observed with 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37). Values reach a minimum about day 5 in culture and recover their initial values. At day 10 they remain stable until the end of the third week of the culture period. 相似文献
52.
53.
Efficient preparation of spheroplasts fromCandida utilis, Saccharomyces cerevisiae, andSchizosaccharomyces pombe, using a purified mixture of enzymes fromTrichoderma harzianum, is described. Limitations of other methods, and differences between yeasts are demonstrated. 相似文献
54.
Koichi Negayama Takako Negayama Kiyomi Kondo 《International journal of primatology》1986,7(4):365-378
Parturitional behavior in 12 caged Macaca fuscatawas analyzed. Wild-caught mothers showed adequate maternal behaviors immediately following the neonate’s expulsion. Parity
differences existed in the behaviors; primiparae were more idiosyncratic than were multiparae. Among multiparae, those with
two or more offspring were uniformly adequate, but those with a single birth experience varied in the adequacy of the maternal
care they provided at parturition. Mothers embraced and licked their neonates and had ventroventral contact with them frequently
immediately after parturition but decreased these behaviors after expulsion of the placenta. In contrast, mothers showed allogrooming
after consuming the placenta. Placentophagy was correlated with the level of orality represented by maternal licking behaviors.
An isolation-reared primipara reacted to her newborn in a basically negative manner, although she showed little actual aggression.
She showed a rapid shift in her negative behavior during the immediate postpartum period. This mother’s newborn sought contact
with her, indicating the neonate’s active role in establishing a stable mother-neonate bond. 相似文献
55.
Conditions have been developed that induce maize (Zea mays L.) protoplasts to re-synthesize cell walls and to initiate cell divisions. Two types of embryogenic maize callus were used as a source of protoplasts: a heterogeneous callus (Type I) derived from immature embryos after three weeks in culture, and a friable, rapidly growing callus (Type II) selected from portions of the Type I callus. Many variables in the growth conditions of the donor tissue (type of medium, transfer schedule, age of callus), protoplast isolation solutions (pH, osmolarity, type and concentration of cell wall hydrolyzing enzymes, addition of polyamines) and conditions (amount of time in enzyme, amount of tissue per volume of enzyme incubation medium, agitation, preplasmolysis of source tissue, type of callus), and purification procedures (filtration and-or flotation), were found to affect both yield and viability of protoplasts (based upon fluorescein-diacetate staining). Our isolation procedure yielded high numbers of viable, uninucleated maize callus protoplasts which were densely cytoplasmic and varied in size from 20 to 50 m in diameter. Protoplasts plated in solid medium formed walls and divided several times. Of several gelling agents tested for protoplast propagation, only agarose resulted in protoplasts capable of sustained divisions leading to the formation of microcalli. Plating efficiency was established over a wide range of protoplast densities (103–107 protoplasts/ml). Highest plating efficiency (25%) was obtained at 1·106 protoplasts/ml). The resulting microcalli grew to be dense clusters of about 0.1–0.5 mm in diameter and then stopped growing. Nurse cultures of maize and carrot (Daucus carota L.), were used to establish that individual protoplasts (not contaminating cells or cell clusters) formed walls and divided. Nurse cultures also increased the efficiency of microcallus formation from protoplasts.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- MS
Murashige and Skoog (1962) salts
- MS 1D
Murashige and Skoog salts with 1 mg/l 2,4-D
- MS 2D
Murashige and Skoog salts with 2 mg/l 2,4-D
- N6
medium of Chu et al. (1975)
- NN67-mod
medium of Nitsch and Nitsch (1967) as modified in the present paper
- FDA
fluorescein diacetate
- LMP
low melting point 相似文献
56.
Are sucrosyl-oligosaccharides synthesized in mesophyll protoplasts of mature leaves of Cucumis melo?
Biosynthesis of sucrosyl-oligosaccharides (raffinose, stachyose) was traced in source leaves of Cucumis melo after 14C-photoassimilation. The main carbon compound exported was 14C-labeled stachyose. No oligosaccharide synthesis was detected in young, importing leaves. Mesophyll protoplasts, isolated from mature leaves which had previously photosynthesized 14CO2, did not contain 14C-oligosaccharides but contained [14C]-sucrose and 14C-hexoses. Isolated minor-vein-enriched fractions from the same leaves, however, showed nearly 30% of the 14C of the neutral fraction to be in oligosaccharides. Isolated, viable mesophyll protoplasts incubated with NaH14CO3 also failed to incorporate radioactivity into oligosaccharides, although sucrose and galactinol synthesis was unimpaired. Galactinolsynthase activity in leaf extracts and in mesophyll protoplasts was 16.8 mol·h-1·mg-1 protein and 13.8 mol·h-1·mg-1 protein, respectively. Galactosyltransferase (EC 2.4.1.67), which synthesizes stachyose from raffinose and galactinol, had an activity of 50 nmol·h-1·mg-1 protein in leaf extracts and was also present in the minor-vein-enriched fraction, but could not be detected in mesophyll protoplast lysates. The results indicate that mesophyll cells may not be the site of stachyose synthesis although precursor compounds like sucrose and galactinol are synthesized there.Abbreviation HPLC
high-performance liquid chromatography 相似文献
57.
The function of the syncytiotrophoblast in maternal-fetal exchange is related to the properties of its microvillous (maternal-facing) and basal (fetal-facing) plasma membranes. We have previously reported the properties of the microvillous membrane (Smith, C.H., Nelson, D.M., King, B.F., Donohue, T.M., Ruzycki, S.M. and Kelley, L.K. (1977) Am. J. Obstet. Gynecol. 128, 190–196), and now describe the purification and partial characterization of the basal plasma membrane. Sonication and incubation with EDTA were used to isolate selectively the basal cell membrane. These steps were followed by a more conventional purification by centrifugation. The trophoblast was disrupted and its microvillous membrane and cytoplasmic contents were removed by sonication. The exposed basal cell membrane was selectively released from the underlying basal lamina by sonication in the presence of EDTA and further purified by discontinuous Ficoll gradient centrifugation. The material at the 4–10% Ficoll interface consisted of smooth membrane vesicles with internal microfilaments. It was 45-fold enriched in dihydroalprenolol binding activity and 11-fold enriched in ouabain binding activity. Other enzymatic analyses, including alkaline phosphatase, cytochrome-c oxidase, cytochrome-c reductase and galactosyl transferase indicated low contamination by other organelles. This procedure yields a preparation of relatively high purity which should be suitable for investigation of transport and other functions of the basal surface membrane of trophoblast. In principle, the purification procedures used may be applicable to other transporting epithelia. 相似文献
58.
59.
Phosphoenolpyruvate carboxylase (PEPCase; EC 4.1.1.31) activity was found to be modulated by light and darkness when measured in the presence of K+, which had been added to induce swelling of guard-cell protoplasts (GCPs) from Vicia faba L., whereas no modulation was detected in the absence of K+ (PEPcase activity remained constant at 1.5±0.15 pmol PEP metabolized · GCP–1 ·h–1; subsequently, pmol GCP–1 ·h–1 will be used). The activity of PEPCase increased by 100% (from 1.5 to 3 pmol·protoplast–1·h–1) in darkness and by 200% (from 1.7 to 5 pmol·protoplast–1· h–1) in light and oscillations in activity of these magnitudes were repeated at intervals of 2 min (dark) and 2.5 min (light) for a period of 10 min during K+-induced increase in the volume of GCPs. The oscillations were reflected in changes in malate-pool sizes determined in plastids, mitochondria and the supernatant fraction (consisting of the cytosol and the vacuole). Malate probably functioned as a mitochondrial substrate, thus supplying ATP for K+ uptake and the swelling of the protoplasts. On the basis of the present paper and previous results (H. Schnabl and B. Michalke 1988, Life Sci. Adv. Plant Physiol. 7, 203–207) involving adenine nucleotidepool sizes in fractionated GCPs, a model is proposed to explain the cause-effect relationship between K+, PEPCase, the cytosolic and mitochondrial malate levels and ATP levels during the K+-induced increase of GCP volume.Abbreviations GCP
dtguard-cell protoplast
- PEP
phosphoenol-pyruvate
- PEPCase
PEP carboxylase
The authors thank Professor Hermann Schnabl, University of Stuttgart (FRG), for his assistance in applying the graph theory analysis. This work was supported by Deutsche Forschungsgemeinschaft to H.S. 相似文献
60.
Progress in leaf protoplast isolation and culture from virus-free axenic shoot cultures of Vitis vinifera L. 总被引:1,自引:0,他引:1
Theodoropoulos P. A. Roubelakis-Angelakis K. A. 《Plant Cell, Tissue and Organ Culture》1990,20(1):15-23
Axenic shoot cultures of virus-free Vitis vinifera L. cv. Soultanina were a highly efficient source for isolation of viable protoplasts. Optimum results were obtained with leaves of 50–100 mg fresh weight, leaf discs of 0.7 cm in diameter, 100 and 15 U ml-1 Cellulase R-10 and Macerozyme R-10, respectively, and 18 h reaction time in either light or in darkness. Protoplast yield was approx. 25×106 viable protoplasts per g fresh weight and their size ranged from 12 to 44 m. During a 20-day culture period, the maximum survival rate obtained was approx. 40%. A plating density of 10×105 protoplasts per ml resulted in increased survival rates. Various growth regulators and glutamine did not significantly improve survival rates of protoplasts, whereas extract from coconut added to the culture medium caused an increase in the survival rates of protoplasts. Cell elongation at a significant rate and divisions were observed. [14C]glucose uptake was studied as an index of cell membrane integrity and functioning. Uptake rate of glucose by protoplasts was linear for up to 60 min, fully inhibited by NaN3, with an optimum pH of 4.8. Protoplasts 24 h old exhibited significantly lower rates of glucose uptake. 相似文献