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排序方式: 共有698条查询结果,搜索用时 15 毫秒
1.
W P Fung-Leung M W Schilham A Rahemtulla T M Kündig M Vollenweider J Potter W van Ewijk T W Mak 《Cell》1991,65(3):443-449
A mutant mouse strain without CD8 (Lyt-2 and Lyt-3) expression on the cell surface has been generated by disrupting the Lyt-2 gene using embryonic stem cell technology. In these mice, CD8+ T lymphocytes are not present in peripheral lymphoid organs, but the CD4+ T lymphocyte population seems to be unaltered. Cytotoxic response of T lymphocytes from these mice against alloantigens and viral antigens is dramatically decreased. Proliferative response against alloantigens and in vivo help to B lymphocytes, however, are not affected. These data suggest that CD8 is necessary for the maturation and positive selection of class I MHC restricted cytotoxic T lymphocytes but is not required on any of the intermediate thymocyte populations (CD8+CD4-TcR- or CD4+CD8+TcRlow) during the development of functional class II MHC restricted helper T cells. 相似文献
2.
E Benedikt A Gossauer H P K?st W Miki K Yamaguchi 《European journal of biochemistry》1988,175(3):643-648
The ovaries of the marine snail Turbo cornutus contain a number of pigments. So far, the presence of carotenoids and a chromoprotein with a bile pigment, called turboverdin (= 3(2)-hydroxy-mesobiliverdin IX alpha), as its prosthetic group are known. The present work describes the isolation and structure elucidation of two further bile pigments, biliverdin IX delta and neobiliverdin IX delta. This is the first report of naturally occurring bile pigments with IX delta structure. 相似文献
3.
Kost Benedikt; Galli Alessandro; Potrykus Ingo; Neuhaus Gunther 《Journal of experimental botany》1995,46(9):1157-1167
An efficient system has been established that allows well controlledDNA microinjection into tobacco (Nicotiana tabacum) mesophyllprotoplasts with partially regenerated cell walls and subsequentanalysis of transient as well as stable expression of injectedreporter genes in particular targeted cells or derived clones.The system represents an effective tool to study parametersimportant for the successful transformation of plant cells bymicroinjection and other techniques. Protoplasts were immobilizedin a very thin layer of medium solidified with agarose or alginate.DNA microinjection was routinely monitored by coinjecting FITC-dextranand aimed at the cytoplasm of target cells. The injection procedurewas optimized for efficient delivery of injection solution intothis compartment. Cells were found to be at the optimal stagefor microinjection about 24 h after immobilization in solidmedium. Embedded cells could be kept at this stage for up to4 d by incubating them at 4 C in the dark. Within 1 h successfuldelivery of injection, solution was routinely possible into2040 cells. Following cytoplasmic coinjection of FITC-dextran and pSHI913,a plasmid containing the neo (neomycin phosphotransferase II)gene, stably transformed, paromomycin-resistant clones couldbe recovered through selection. Transgenic tobacco lines havebeen established from such clones. Injection solutions containingpSHI913 at a concentration of either 50 µg ml1or 1 mg ml1 have been tested. With 1 mg ml1 plasmidDNA the percentage of resistant clones per successfully injectedcell was determined to be about 3.5 times higher. Incubationof embedded protoplasts at 4C before microinjection was foundto reduce the percentage of resistant clones obtained per injectedcell Protoplasts were immobilized above a grid pattern and the locationof injected cells was recorded by Polaroid photography. Thefate of particular targeted cells could be observed. Isolationand individual culture of clones derived from injected cellswas possible. Following cytoplasmic coinjection of FITC-dextranand 1 mg ml1 plasmid DNA on average about 20% of thetargeted cells developed into microcalli and roughly 50% ofthese calli were stably transformed. Transient expression ofthe firefly luciferase gene (Luc) was nondestructively analysed24 h after injection of pAMLuc. Approximately 50% of the injectedcells that were alive at this time point expressed the Luc genetransiently. Apparently, stable integration of the injectedgenes occurred in essentially all transiently expressing cellsthat developed into clones. Key words: DNA microinjection, firefly luciferase, FITCdextran, Nicotiana tabacum, protoplast transformation 相似文献
4.
Hilary Woodcock Pierre Vollenweider Rolf Dubs Rose-Marie Hofer 《Trees - Structure and Function》1995,9(5):279-288
One of the first symptoms expressed by declining trees is reduced growth in stem diameter and length increment. The possibility of a relationship between length increment and crown thinning in beech (Fagus sylvatica L.) was investigated by developing a computer model to simulate first order branching patterns of the apical 2 m of monopodially branching beech trees, 70–100 years old, for a range of length increment rates. The model was based on values for branching angle, main axis and branch length increment, number of branches produced per year and branch mortality rates for six healthy and declining trees. Shoot growth rates in the apical 2 m of the sample trees ranged from about 5 cm/year (decline class 3) to 43 cm/ year (healthy). Simulations of branching patterns in the apical 2 m of trees growing at different rates indicated that, when growth rate exceeded about 20 cm/year, total first order branch length and area explored were independent of growth rate. When growth rates fell below this value there was a reduction in total area explored and first order branch length due primarily to the formation of fewer branches. More acute branching angles contributed to a reduction in the area explored. Growth rate-related crown thinning could increase the risk of bark necrosis and secondary pathogen infection during dry and/or hot spells. 相似文献
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Heterogeneity of expression and secretion of native and mutant [AspB10]insulin in AtT20 cells 总被引:2,自引:0,他引:2
S Ferber D J Gross L Villa-Komaroff F Danehy F Vollenweider K Meyer M R Loeken C R Kahn P A Halban 《Molecular endocrinology (Baltimore, Md.)》1991,5(3):319-326
AtT20 (pituitary corticotroph) cells were transfected with either the native or a mutant [AspB10]rat insulin II gene, using a plasmid containing the insulin gene and a neomycin resistance gene under the control of independent constitutive promoters. The cellular immunoreactive insulin (IRI) content ranged from 0.8-440 ng/10(6) cells, with the highest value similar to that found for a rat insulinoma cell line (RIN) and corresponding to approximately 1% that of native pancreatic B-cells. There was a direct correlation between insulin mRNA levels and IRI content and no correlation between mRNA levels and rat insulin II gene copy number. Furthermore, in some lines the insulin II transgene was lost even though the gene encoding neomycin resistance was retained. IRI release was stimulated up to 4-fold by isobutylmethylxanthine in all lines transfected with the native rat insulin II gene, and HPLC analysis showed most IRI as fully processed insulin, with less than 5% as proinsulin. These cells, thus, directed most proinsulin to secretory granules for conversion and regulated release regardless of the absolute amount of IRI expressed. One of the lines transfected with the AspB10 mutant gene (line AA9) released nearly 50% of IRI as proinsulin under basal conditions, with stimulation of insulin, but not proinsulin, release by isobutylmethylxanthine. This confirmed our previous finding of partial diversion of this mutant proinsulin from the regulated to the constitutive pathway. A second line (IC6) expressing the same mutant gene at much higher levels appeared to direct all mutant proinsulin to the regulated pathway, suggesting that for this particular mutant proinsulin, the secretory pathway employed by the transfected cells can be affected by the amount of proinsulin synthesized. 相似文献
7.
Benedikt Buchspies Martin Kaltschmitt Martin Junginger 《Global Change Biology Bioenergy》2020,12(10):789-805
The shift from straw incorporation to biofuel production entails emissions from production, changes in soil organic carbon (SOC) and through the provision of (co‐)products and entailed displacement effects. This paper analyses changes in greenhouse gas (GHG) emissions arising from the shift from straw incorporation to biomethane and bioethanol production. The biomethane concept comprises comminution, anaerobic digestion and amine washing. It additionally provides an organic fertilizer. Bioethanol production comprises energetic use of lignin, steam explosion, enzymatic hydrolysis and co‐fermentation. Additionally, feed is provided. A detailed consequential GHG balance with in‐depth focus on the time dependency of emissions is conducted: (a) the change in the atmospheric load of emissions arising from the change in the temporal occurrence of emissions comparing two steady states (before the shift and once a new steady state has established); and (b) the annual change in overall emissions over time starting from the shift are assessed. The shift from straw incorporation to biomethane production results in net changes in GHG emissions of (a) ?979 (?436 to ?1,654) and (b) ?955 (?220 to ?1,623) kg CO2‐eq. per tdry matter straw converted to biomethane (minimum and maximum). The shift to bioethanol production results in net changes of (a) ?409 (?107 to ?610) and (b) ?361 (57 to ?603) kg CO2‐eq. per tdry matter straw converted to bioethanol. If the atmospheric load of emissions arising from different timing of emissions is neglected in case (a), the change in GHG emissions differs by up to 54%. Case (b) reveals carbon payback times of 0 (0–49) and 19 (1–100) years in case of biomethane and bioethanol production, respectively. These results demonstrate that the detailed inclusion of temporal aspects into GHG balances is required to get a comprehensive understanding of changes in GHG emissions induced by the introduction of advanced biofuels from agricultural residues. 相似文献
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10.
Frances M. Cowan Sibongile Mtetwa Calum Davey Elizabeth Fearon Jeffrey Dirawo Ramona Wong-Gruenwald Theresa Ndikudze Samson Chidiya Clemens Benedikt Joanna Busza James R. Hargreaves 《PloS one》2013,8(10)