全文获取类型
收费全文 | 4638篇 |
免费 | 363篇 |
国内免费 | 3篇 |
出版年
2023年 | 12篇 |
2022年 | 42篇 |
2021年 | 78篇 |
2020年 | 48篇 |
2019年 | 60篇 |
2018年 | 62篇 |
2017年 | 72篇 |
2016年 | 131篇 |
2015年 | 212篇 |
2014年 | 217篇 |
2013年 | 299篇 |
2012年 | 384篇 |
2011年 | 378篇 |
2010年 | 256篇 |
2009年 | 225篇 |
2008年 | 294篇 |
2007年 | 322篇 |
2006年 | 296篇 |
2005年 | 248篇 |
2004年 | 265篇 |
2003年 | 235篇 |
2002年 | 215篇 |
2001年 | 44篇 |
2000年 | 38篇 |
1999年 | 56篇 |
1998年 | 69篇 |
1997年 | 45篇 |
1996年 | 40篇 |
1995年 | 47篇 |
1994年 | 39篇 |
1993年 | 35篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 20篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1972年 | 6篇 |
1966年 | 4篇 |
排序方式: 共有5004条查询结果,搜索用时 15 毫秒
11.
Embryogenic suspension cultures of Abies alba were established using an embryogenic suspensor mass culture originating from the zygotic embryo in immature seed explants (Schuller et al. 1989). Protoplasts were isolated from the suspension material. The protoplasts were immobilized in alginate layers in order to follow the development of single protoplasts. During the first days of protoplast culture a modified Kao and Michayluk (1975) medium proved to be necessary for subsequent divisions. The formation of proembryos succeeded within 2–3 weeks when subcultured with a modified Schenk and Hildebrandt (1972) liquid medium. Light, enhanced sugar concentration, and the addition of abscisic acid led to the formation of slightly green torpedo-shaped somatic embryos after 6–8 weeks from protoplast isolation.Abbreviations ABA
abscisic acid
- BAP
N6-benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- ESM
Embryonal suspensor mass (Gupta and Durzan 1986)
- KM
Kao and Michayluk (1975)
- LP
(von Arnold and Eriksson 1977)
- MES
2-(N-morpholino)ethane-sulfonic acid
- NAA
1-naphthalene-acetic acid (sodium salt)
- PVP
polyvinylpyrrolidone
- SH
Schenk and Hildebrandt (1972)
- Tween 80
polyoxyethylene-sorbitan-monooleate 相似文献
12.
A unifying approach described by a random birth and death process which includes both environmental and demographic noise is introduced. It is shown that both of these noise sources play an essential role in extinction processes in general. The probability distribution of the lifetime of a population is determined and its dependence on the parameters of the model is discussed. Finally a population divided into subpopulations is modeled. The lifetime of this ensemble of subpopulations is compared to the lifetime of one large population. 相似文献
13.
A detailed study of the regulation and evolution of the two classes of patatin genes in Solanum tuberosum L. 总被引:4,自引:0,他引:4
Xiang-Yun Liu Mario Rocha-Sosa Sabine Hummel Lothar Willmitzer Wolf B. Frommer 《Plant molecular biology》1991,17(6):1139-1154
The class-specific expression of patatin genes was investigated by analysing four new patatin genes. A class I patatin gene from cv. Berolina as well as a class I and two class II patatin genes from the monohaploid cultivar AM 80/5793 were isolated and partially sequenced. Sequence comparison indicates rearrangements as the major source for the generation of diversity between the different members of the classes. The expression of single genes was studied in potato plants transformed with chimaeric genes where the putative patatin promoters were fused to the GUS reporter gene. A detailed histochemical analysis reveals that both class I genes are expressed as the previously described class I patatin gene B33 from cv. Berolina [1], i.e. in the starch-containing cells of potato tubers and in sucrose-induced leaves. The class II gene pgT12 shows the same pattern as the previously described class II gene pgT2 [2], i.e. expression in root tips and in the vascular tissue of tubers, whereas no activity was detectable for pgT4. Thus the expression pattern of both classes of genes seems to be stable at least within or even between different cultivars. 相似文献
14.
Oliver Selberg Sabine Schlaak Hans J. Balks Alexander von zur Mühlen Manfred J. Müller 《European journal of applied physiology and occupational physiology》1991,63(6):417-423
The contribution of insulin (3.6 pmol.kg body mass-1.min-1) to adrenaline-induced (0.164 nmol.kg fat free mass-1.min-1) thermogenesis was studied in ten postabsorptive healthy volunteers using two sequential protocols. Variables considered were oxygen consumption as well as carbon dioxide production, heart rate, blood pressure, plasma concentrations of glucose, insulin, glycerol, free fatty acids, beta-HO-butyrate and lactate. Adrenaline increased plasma concentrations of glucose, glycerol, free fatty acids, and beta-HO-butyrate, and heart rate and metabolic rate during normo-insulinaemia [61.3 (SEM 6.6) pmol.l-1]. Similar effects were observed during hyperinsulinaemia [167.9 (SEM 18.7) pmol.l-1], but the effect of adrenaline on oxygen consumption was reduced. On average, metabolic rate increased by 12.9% during normo-insulinaemia and by 8.9% during hyperinsulinaemia. We concluded that relative hyperinsulinaemia resulted in decreased adrenaline-induced thermogenesis and therefore increased whole body anabolism. 相似文献
15.
Katrin Kausch Clemens R. Müller Tiemo Grimm Kenneth Ricker Marcella Rietschel Sabine Rudnik-Schöneborn Klaus Zerres 《Human genetics》1991,86(3):317-318
Summary Two recent articles have reported the linkage of a gene for recessive spinal muscular atrophy (SMA) on the chromosome region 5q11.2–13.3. Our data show no linkage of the dominantly inherited forms of SMA to this chromosome region. 相似文献
16.
Volker Schirrmacher Sabine Leidig Andreas Griesbach 《Cancer immunology, immunotherapy : CII》1991,33(5):299-306
Summary Tumour-specific cytotoxic T lymphocytes (CTL) are usually obtained after immunization in vivo and restimulation of immune cells in vitro. We here describe the generation of syngeneic tumour-specific CTL within no more than 9 days by priming and restimulation in vivo. This is achieved only if the correct sites are used both for primary immunization (ear pinna) and for restimulation (peritoneal cavity). The kinetics of immune T cell induction and of the secondary response in vivo will be reported. While a secondary CTL response could be generated in the peritoneal cavity, this was not possible in the spleen, no matter which routes of antigen restimulation were used. Upon transfer of immune spleen cells into the peritoneal cavity but not into the spleen, a secondary response could be generated upon in situ restimulation, indicating the importance of the correct microenvironment for this type of response. The peritoneal effector cells were true T cells and recognized a tumour-associated antigen in association with the Kd major histocompatibility (MHC class I) antigen. Finally the activated tumour-specific peritoneal exudate cells were able to transfer protective immunity without exogenous interleukin-2 into normal syngeneic mice. 相似文献
17.
Mycobacterium tuberculosis H37Ra,M. smegmatisATCC 607,M. smegmatis MC2155,M. aurum A +,M. aurum A11, and one representative strain ofM. flavescens were transformed by electroporation with plasmid pMY10 and cosmid pDC100. Plasmid pMY 10 contained the origin of replication of pAL5000, the origin of replication of pBR322, a kanamycin resistance gene, and the origin of transfer of the Inc plasmid RK2; the cosmid pDC100 contained the pHC79 SS cosmid, the origin of replication of pAL5000, and a kanamycin resistance gene. The efficiency of transformation varied with the recipient cells used and was in decreasing order: 7×105 forM. smegmatis MC2155, 6×103 forM. tuberculosis H37Ra, 103 forM. aurum, 50 forM. smegmatis ATCC 607, and 5 forM. flavescens. A rapid protocol for plasmid extraction from mycobacteria was developed.The satisfactory transformation of the nonvirulentM. tuberculosis strain H37Ra was of interest for future studies on cloning of virulence genes, while the satisfactory transformation ofM. aurum was of interest for future studies on the genetics of drug resistance because these bacteria are sensitive to drugs specifically used in the treatment of tuberculosis and leprosy. However, neither vector was stably maintained inM. smegmatis, indicating that further investigations are still necessary to resolve this difficulty. 相似文献
18.
A 5.1-kb plasmid, designated pSCS12, isolated from a naturally occurring Staphylococcus sciuri conferred resistance to chloramphenicol (CmR) and streptomycin (SmR). Restriction endonuclease analyses of pSCS12 revealed partial structural homologies to the CmR-plasmids pC221 from S. aureus and pSCS1 from S. intermedius, to the SmR-plasmids pSAI-1 from S. hyicus and pS194 from S. aureus, as well as to the CmR/SmR plasmid pSK68 from S. aureus. Southern-blot hybridization with specific CmR- and SmR-gene probes confirmed these similarities and allowed the mapping of the CmR- and SmR-determinants in the S. sciuri plasmid pSCS12. These observations lead to the suggestion that CmR/SmR-plasmids, such as pSCS12, may have evolved from CmR- and SmR-plasmids by interplasmidic recombination. 相似文献
19.
Daniel Chappard Christian Alexandre Sabine Palle George Riffat 《Biotechnic & histochemistry》1986,61(2):93-96
Polyester fibers are not dissolved by either glycol methacrylate or methyl methacrylate. Commercial polyester wadding is consequently an advantageous material to use in getting precise orientation of tissue specimens during embedding in methacrylate. 相似文献
20.
Daniel Chappard Christian Alexandre Sabine Palle Georges Riffat 《Biotechnic & histochemistry》1986,61(3):145-149
A one-step clearing and embedding procedure for alizarin red S stained skeletons is described. Embryos are fixed in formalin, skinned and eviscerated. After staining in a 10 mg/liter solution of alizarin red S in 5% aqueous KOH, specimens are dehydrated in a graded series of acetone-polyester monomer solutions. Finally, the specimens are embedded at room temperature in the polyester resin. A special reusable metallic mold is described for embedment of large fetuses. Specimens previously cleared in glycerol can be processed with this method. 相似文献