全文获取类型
收费全文 | 1205篇 |
免费 | 33篇 |
国内免费 | 32篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 18篇 |
2020年 | 33篇 |
2019年 | 40篇 |
2018年 | 26篇 |
2017年 | 22篇 |
2016年 | 19篇 |
2015年 | 23篇 |
2014年 | 50篇 |
2013年 | 56篇 |
2012年 | 41篇 |
2011年 | 47篇 |
2010年 | 48篇 |
2009年 | 53篇 |
2008年 | 36篇 |
2007年 | 40篇 |
2006年 | 54篇 |
2005年 | 44篇 |
2004年 | 49篇 |
2003年 | 37篇 |
2002年 | 39篇 |
2001年 | 31篇 |
2000年 | 28篇 |
1999年 | 40篇 |
1998年 | 31篇 |
1997年 | 21篇 |
1996年 | 22篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 16篇 |
1984年 | 23篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 4篇 |
排序方式: 共有1270条查询结果,搜索用时 15 毫秒
31.
Edward J. Kendall Kutty K. Kartha Javed A. Qureshi Paul Chermak 《Plant cell reports》1993,12(2):89-94
Spring wheat (Triticum aestivum L.) zygotic embryos were successfully cryopreserved, without the addition of exogenous cryoprotectants, using only an abscisic acid (ABA) pretreatment. Optimum survival was obtained when embryos were cultured in vitro for 10 days on semisolid Murashige and Skoog (MS) nutrient medium supplemented with 0.5 mg/L (±) ABA prior to cryopreservation. The embryos resumed growth within three days when returned to MS medium devoid of ABA but containing 2mg/L 2,4-dichlorophenoxyacetic acid. The embryogenic calli produced from these embryos exhibited normal plant regeneration on auxin-free media. Changes in dw/fw ratio, as well as the esterified fatty acid and sucrose concentrations correlated positively with the development of tolerance to cryopreservation.NRCC Publication No. 33519 相似文献
32.
R. Honegger 《Plant biology (Stuttgart, Germany)》2003,5(3):324-330
Abstract: Lichen-forming ascomycetes and their green algal photobionts completely die off within approximately 3 years of storage at room temperature. Macroscopically this is recognizable as a colour change, the green shades of the chlorophylls being lost. In fluorescent light microscopy preparations an increase in fungal autofluorescence and a significant decrease in chlorophyll autofluorescence in the Trebouxia cells was observed. In transmission electron microscopy preparations of Xanthoria parietina and its green algal photobiont, Trebouxia arboricola, the fungal membrane systems were found to be largely broken down whereas the shrivelled algal protoplast failed to rehydrate after storage at room temperature. When stored in the desiccated state at - 20 °C, both partners of the symbiosis stayed fully viable for up to 13 years, their colouration and chlorophyll fluorescence being unchanged. Viability was measured as ascospore ejection and germination rates in Xanthoria parietina, soredium germination rates in Xanthoria fallax, Hypogymnia physodes and Parmelia sulcata, and autospore formation rate in Trebouxia cells (green algal photobiont), which had been isolated from the thalli after rehydration. Thallus fragments of Xanthoria parietina were shown to grow normally after one week of storage in LN2 without any cryoprotectant. In the desiccated state deep-frozen samples can be repeatedly brought to room temperature and back to - 20 °C without any loss of viability. Cryopreservation is therefore a suitable mode of long-term storage of viable lichen thalli for experimental studies or transplant experiments. 相似文献
33.
猪精子中与卵透明带糖蛋白ZP3结合的蛋白质 总被引:3,自引:0,他引:3
依次经PSL-Sepharose亲和层析柱和纤维素CM-52离子交换层析柱,从猪精子的CHAPS抽提液分离得4个蛋白质组分。用固相透明带精蛋白结合试验(IZPGBA)检测;表明精子蛋白SP1和SP2具有结合透明带糖蛋白ZP3的活性,SP2并显示凝集血球的活性。精子蛋白SP1与卵预温育明显抑制精卵结合,抑制活性与加入的精子蛋白的浓度呈正相关。用生物素标记的ZP3和蛋白质印迹技术,证明SP1中的68kD精子蛋白与ZP3结合,提示68kD精子蛋白参与精卵结合。 相似文献
34.
肌肽对绵羊精子无氧酵解的影响 总被引:3,自引:0,他引:3
在无氧条件下,绵羊精子通过酵解途径获得能量,代谢结果产生大量乳酸,本实验通过测定精子悬液中果糖摄取以及乳酸生成量,研究肌肽、棉酚对绵羊精子酵解途径的影响,结果表明:4mM肌肽对绵羊精子酵解有显著增强作用,并能刺激精子对果糖的摄取。12μM棉酚对绵羊精子无明显抑制,棉酚能部分抑制肌肽对精子的酵解作用。 相似文献
35.
Channel catfish leucocytes cryopreserved with glycerol or dimethyl sulphoxide (DMSO) had significantly higher ( P <0.05) viability and recovery rates than did cells cryopreserved with methanol. After 7 days of frozen storage, a 24 to 27% reduction of viability was observed for cells cryopreserved with glycerol; a 25 to 43% reduction for cells frozen with DMSO, and a 67 to 100% reduction for cells frozen with methanol. The concentration of cryoprotectants affected the viability of cryopreserved cells significantly ( p <0.05). The viability reduction was 36% for cells frozen with 5% of cryoprotectants, 30% for cells frozen with 10% of cryoprotectants, and 49% for cells frozen with 15% of cryoprotectants. The viability of cells frozen at the slower rate (-2.7°C min−1 ) was significantly higher ( p <0.05) than that of cells frozen at the faster rate (-45°C min−1 ). Best results were obtained for cells cryopreserved with 10% of glycerol or DMSO and frozen at the slower rate. The chromosomes prepared from cells cryopreserved using this procedure were identical to those prepared from fresh cells, and to those reported in the literature for channel Catfish. 相似文献
36.
Ex situ conservation of plant germplasm using biotechnology 总被引:6,自引:0,他引:6
Conservation of plant genetic resources attracts more and more public interest as the only way to guarantee adequate food supplies for future human generations. However, the conservation and subsequent use of such resources are complicated by cultural, economical, technical and political issues. Over the last 30 years, there have been significant increases in the number of plant collections and in accessions in ex situ storage centres throughout the World. The present review is of these ex situ collections and the contribution biotechnology has made and can make to conservation of plant germplasm. The applications and limitations of the new, molecular approaches to germplasm characterization are discussed.
In vitro slow growth is used routinely for conserving germplasm of plants such as banana, plantain, cassava and potato. More recently, cryopreservation procedures have become more accessible for long-term storage. New cryopreservation techniques, such as encapsulation-dehydration, vitrification and desiccation, lengthen the list of plant species that can not only tolerate low temperatures but also give normal growth on recovery. Extensive research is still needed if these techniques are to be fully exploited.V.M. Villalobos is with the Food and Agriculture Organization of the United Nations, Viale delle Terme di Caracalia, 00100 Rome, Italy. F. Engelmann is with the International Plant Genetic Resources Institute (IPGRI), Via delle Sette Chiese 142, 00145 Rome, Italy. 相似文献
37.
38.
Roger A. Williamson James K. Koehler W. Dianne Smith Laurence E. Karp 《Molecular reproduction and development》1984,10(3):319-325
We studied six men whose spermatozoa were immotile and possessed a variety of sperm tail structural abnormalities by electron microscopy. The semen of all six subjects had a normal percentage of oval forms and sperm undergoing capacitation and acrosome reaction. Despite the absence of motility, when incubated sperm from these subjects was added to a microdrop of medium containing zona pellucida-free hamster ova, sperm penetration or entry into the cytoplasm of from 1–9% of the eggs was evident with phase contrast microscopy. This latter finding suggests that, at least in this system, oocytes actively facilitate sperm incorporation. Penetration was absent when sperm of fertile men were rendered immotile, though still viable, by heat treatment. 相似文献
39.
D. L. Garner L. A. Johnson S. Lake N. Chaney D. Stephenson D. Pinkel B. L. Gledhill 《Molecular reproduction and development》1984,10(4):339-351
The morphological and ultrastructural changes that occur during preparation of porcine, bovine, and murine spermatozoa for flow cytometric quantification of the relative DNA content of the X- and Y-chromosome-bearing sperm populations were examined. Ejaculated spermatozoa from the boar and bull were washed using a series of dimethyl sulfoxide (DMSO) solutions prior to fixation, whereas the epididymal mouse spermatozoa were washed only in phosphate-buffered saline (PBS). Spermatozoa from all three species were then fixed in ethanol and processed for fluorochrome staining by a treatment regimen consisting of sulfhydryl reduction and proteolysis. The processed sperm nuclei were stained for DNA with the fluorochrome, 4′-6-diamidino-2-phenylindole (DAPI) before quantification by flow cytometry. Scanning and transmission electron micrographs of sperm heads taken at various steps of the preparation and staining procedures show 1) that the rigorous washing procedure disrupted the plasma and outer acrosomal membranes, 2) that ethanol fixation resulted in removal of the outer membranes and disintegration of the nuclear envelope, and 3) that thiol and proteolysis treatment removed the remaining cellular organelles including the tail and rapidly induced partial decondensation of the tightly packed chromatin. Sequential micrographs showed that the nuclear matrix of all three species increased in thickness about twofold during the preparation and staining. Consequently, the harsh procedures currently used for quantitative staining of DNA for high-resolution flow cytometric analyses destroy most cellular organelles and thereby prevent simultaneous characterization of DNA content and other sperm cell constituents. 相似文献
40.
M. Jose Comez-L Pilar Lopez Jose V. Castell 《In vitro cellular & developmental biology. Plant》1984,20(11):826-832
Summary The present study was undertaken to define the conditions for optimal cryopreservation of hepatocytes. Two different freezing
procedures were analyzed: a slow freezing rate (SFR) (−2° C/min down to −30°C and then quick freezing to −196° C) and a fast
freezing rate (FFR) (direct freezing of tubes to −196° C: −39° C/min). Cells were frozen in fetal bovine serum containing
10% Dimethyl sulfoxide (DMSO). After rapid thawing at 37° C, followed by dilution and removal of the cryoprotectant, cells
were plated and several parameters were followed as criteria for optimal cryopreservation of cells. The FFR cells showed no
apparent ultrastructural damage after 24 h of culture. Plating efficiency and spreading were similar as controls. Gluconeogenesis
from pyruvate and fructose, tyrosine amino transferase induction by glucagon and dexamethasone, urea production, and plasma
protein synthesis of FFR cells were similar to those found in control cultures. The FFR procedure, in comparison to the SFR
method, seemed to render the best preserved hepatocytes.
The financial support for this work was from Fondo de Investigaciones Sanitarias de la Seguridad Social, Grants 41/82 and
48/82. 相似文献