全文获取类型
收费全文 | 2862篇 |
免费 | 235篇 |
出版年
2023年 | 13篇 |
2022年 | 29篇 |
2021年 | 64篇 |
2020年 | 38篇 |
2019年 | 49篇 |
2018年 | 55篇 |
2017年 | 51篇 |
2016年 | 79篇 |
2015年 | 122篇 |
2014年 | 136篇 |
2013年 | 186篇 |
2012年 | 201篇 |
2011年 | 223篇 |
2010年 | 126篇 |
2009年 | 127篇 |
2008年 | 172篇 |
2007年 | 180篇 |
2006年 | 176篇 |
2005年 | 151篇 |
2004年 | 150篇 |
2003年 | 128篇 |
2002年 | 132篇 |
2001年 | 31篇 |
2000年 | 15篇 |
1999年 | 35篇 |
1998年 | 41篇 |
1997年 | 26篇 |
1996年 | 27篇 |
1995年 | 28篇 |
1994年 | 35篇 |
1993年 | 25篇 |
1992年 | 20篇 |
1991年 | 33篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有3097条查询结果,搜索用时 62 毫秒
191.
External sucrose, supplied by the endosperm in vivo, is the physiological source of sucrose for Ricinus communis L. seedlings. It is taken up by the cotyledons and exported via the sieve tubes to the growing hypocotyl and root. Two parallel
pathways of external sucrose to the sieve tubes, directly via the apoplasm and indirectly after transit through the mesophyll,
have already been established (G. Orlich and E. Komor, 1992). In this study, we analysed whether a symplasmic flow of sucrose
contributes to phloem loading. Uptake of external sucrose into the mesophyll and into the sieve tubes, and export of total
sucrose were measured with intact and exuding seedlings in the presence of p-chloromercuribenzenesulfonic acid (PCMBS). Sucrose uptake into the mesophyll and into the sieve tubes was inhibited by 80–90%.
Consequently, export of total sucrose slowed down. However, after the addition of PCMBS, sucrose was transiently exported
in such a high amount that could not be accounted for by the residual uptake activity nor by the amount of sucrose confined
to the sieve element-companion cell complex (seccc). From the results, we conclude that most of the sucrose exported transiently
had moved to the sieve tubes from a symplasmic domain larger than the seccc, comprising at least all the cells of the bundle
including the bundle sheath. We suggest that the symplasmic flow of sucrose observed is a mass flow driven by a turgor pressure.
As a structural prerequisite for a symplasmic flow, plasmodesmata interconnect all the cells from the bundle sheath to the
sieve tubes and also occur between the bundle sheath and the mesophyll. The phloem loading pathway of Ricinus cotyledons can thus be classified as a combination of three different routes.
Received: 17 October 1997 / Accepted: 9 March 1998 相似文献
192.
Kumud Majumder William Shawlot Gabriele Schuster Wilbur Harrison Frederick F.B. Elder Paul A. Overbeek 《Mammalian genome》1998,9(11):863-868
Mice with mutations at the downless (dl) locus have defects in hair follicle, tooth, sweat gland, preputial gland, Meibomian gland, and tail development. The dl phenotype is analogous to the human genetic disorder termed autosomal hypohidrotic (or anhidrotic) ectodermal dysplasia (HED).
On the basis of the identification of two related transgenic insertional mutations in the downless gene, yeast artificial
chromosomes (YACs) were identified that map to the critical region of mouse Chromosome (Chr) 10. To determine which of the
YACs contain the dl gene, we generated YAC transgenic mice by mouse embryo microinjections. The 200-kb YAC B25.D9 was found to rescue all of
the downless defects. In addition, the transgenic YAC rescued the dominant Sleek (Dl
slk
) allele. Since the sequences within the YAC are entirely deleted in one of the transgenic mutants, our results establish
that Sleek encodes a dominant-negative protein whose effects can be reversed by expression of extra copies of the wild-type
locus.
Received: 26 June 1998 / Accepted: 17 July 1998 相似文献
193.
The medial-Golgi Ion Pump Pmr1 Supplies the Yeast Secretory Pathway with Ca2+ and Mn2+ Required for Glycosylation, Sorting, and Endoplasmic Reticulum-Associated Protein Degradation
下载免费PDF全文
![点击此处可从《Molecular biology of the cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gabriele Dürr Jochen Strayle Richard Plemper Saskia Elbs Saskia K. Klee Patrice Catty Dieter H. Wolf Hans K. Rudolph 《Molecular biology of the cell》1998,9(5):1149-1162
The yeast Ca2+ adenosine triphosphatase Pmr1, located in medial-Golgi, has been implicated in intracellular transport of Ca2+ and Mn2+ ions. We show here that addition of Mn2+ greatly alleviates defects of pmr1 mutants in N-linked and O-linked protein glycosylation. In contrast, accurate sorting of carboxypeptidase Y (CpY) to the vacuole requires a sufficient supply of intralumenal Ca2+. Most remarkably, pmr1 mutants are also unable to degrade CpY*, a misfolded soluble endoplasmic reticulum protein, and display phenotypes similar to mutants defective in the stress response to malfolded endoplasmic reticulum proteins. Growth inhibition of pmr1 mutants on Ca2+-deficient media is overcome by expression of other Ca2+ pumps, including a SERCA-type Ca2+ adenosine triphosphatase from rabbit, or by Vps10, a sorting receptor guiding non-native luminal proteins to the vacuole. Our analysis corroborates the dual function of Pmr1 in Ca2+ and Mn2+ transport and establishes a novel role of this secretory pathway pump in endoplasmic reticulum-associated processes. 相似文献
194.
Definition of extracellular localized epitopes of Hsp70 involved in an NK immune response 总被引:10,自引:5,他引:5
下载免费PDF全文
![点击此处可从《Cell stress & chaperones》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In order to define extracellular localized epitopes of Hsp70 on human tumor cells which are accessible to the immune system, six commercially available Hsp70-specific monoclonal antibodies (mAb) with different recognition sites were examined by immunological approaches. The recognition pattern of these antibodies was analyzed on purified recombinant Hsp70 proteins (rHsp70, Hsc70, DnaK), on lysates of Hsp70-expressing colon carcinoma cells (CX+) and on lysates of M21 rat-1 cells that overexpress human Hsp70 or Hsp70 fragments: ΔBgl (del 120–428) consisting of the C-terminal part and ΔSma (del 438–618) consisting of the N-terminal part of human Hsp70. All antibodies reacted equally well with rHsp70 and cytoplasmic Hsp70 derived from human tumor cells or M21 rat-1 cells. Only one antibody (MA3–007; Hsp70, Hsc70) detects a region localized within the ATPase domain of Hsp70 (amino acid 122–264) and reacts positively with the C-terminal deletion mutant ΔSma. All other antibodies, including RPN1197 are directed against the C-terminal peptide binding domain of Hsp70 and react positively with the N-terminal deletion mutant ΔBgl. Although all six antibodies detect full-length Hsp70 protein, derived from plasma membrane fractions of CX+ tumor cells, cell surface expressed Hsp70 on viable CX+ tumor cells, as determined by flowcytometry, is only recognized with the antibodies MA3–006 (Hsp70, Hsc70; 504–617), MA3–009 (Hsp70; 504–617) and RPN1197 (Hsp70). An estimation of the ratio of membrane-bound to cytoplasmic Hsp70 molecules revealed that 15–20% of total Hsp70 molecules are expressed on the plasma membrane. This tumor-selective cell surface expression of Hsp70 correlates with an increased sensitivity to lysis mediated by non-MHC restricted natural killer (NK) cells. We demonstrate that only antibodies directed against membrane-bound Hsp70 (MA3–006, MA3–009, RPN1197) inhibit NK-killing activity against Hsp70-expressing tumor cells. Taken together our data indicate that at least the C-terminal region 504–617, that contains at least one single α-helix (amino acid 512–536), has to be localized extracellularly and might be of importance for an NK-mediated anti-tumor immune response. 相似文献
195.
Gabriele Gerlach 《Ethology : formerly Zeitschrift fur Tierpsychologie》1998,104(6):487-499
The existence of a relationship between the social ties an individual has to other family members and its further role within the family was tested in feral house mice (Mus musculus domesticus), according to the ‘Social cohesions hypothesis’. It is predicted by the hypothesis that individuals not forming strong social ties are the first who emigrate. House mice were studied using a population cage system that allowed continuous observation of individually marked animals. Data on time staying with other animals (social ties), aggressive interactions, body weight, reproduction, and emigration were collected daily. The results may be summarized as follows:
- 1 Male emigrants were less integrated in cohorts of male littermates compared with their brothers of the same age. These male cohorts appeared to protect single males from attacks by the dominant male. No difference could be observed in social ties to other family members.
- 2 After weaning, there was no difference in social ties of male and female offspring. However, after sexual maturation social ties of males decreased significantly while those of females remained almost constant.
- 3 Female emigrants showed the same intensity of social ties as their resident sisters.
- 4 No difference could be found between social ties of females becoming pregnant and their nonreproductive sisters of the same age. Reproduction or reproductive suppression could not be explained by having more or less contact with other reproductive females.
- 5 Dominant males spent least of all time with other family members.
196.
Treatment of the cell wall-less mutant CW 15 of Chlamydomonasreinhardtii with human serum leads to a marked increase of thecell volume, followed by an irreversible cytolysis. Heat-inactivatedserum as a control reveals no cytotoxic effects on CW 15. Experimentswith C4-, properdin-, C3-, and factor H-depleted sera indicatethe alternative pathway of complement as being responsible forthe serum-mediated lysis. After immunofluorescence marking aswell as electromicroscopically after negative staining the membraneattacking complex of complement, C5b-9, could be demonstratedon the surface of CW 15. These results together with the observationthat cells of the wild-type strain 11-32c of C. reinhardtiiare not lysed by active serum suggest that only protoplastsof Chlamydomonas carry surface structures capable to activatethe alternative pathway of complement. In order to find out whether other cell wall mutants of C. reinhardtii,besides CW 15, can also activate the human complement system,we tested three strains each of the three known mutant categories.Strains CW 4, CW 9, and CW 19, representing category A, andstrains CW 3, CW 10, and CW 92, representing category C, andCW 8 and CW 18, accounting for category B, were cytolysed bynormal human serum. Only one type used in our experiments, CW20 of category B, resisted serum treatment, suggesting the needto redefine this category.
1This paper is dedicated to Professor Dr. Andr? Pirson on theoccasion of his 80th birthday (Received December 1, 1989; Accepted April 5, 1990) 相似文献
197.
198.
Little is known about the associations between long-term weight change and the natural history of impaired fasting glucose (IFG) in young adults. We investigated the association between long-term body mass index (BMI) change and the risk of IFG using data of 24,930 20- to 40-year-old participants from the Vorarlberg Health Monitoring and Promotion Program (VHM&PP) cohort. Poisson models were applied to estimate the 10-year risk for new development of IFG (≥5.6 mmol/L), and persistence of IFG. Over 10 years, most men (68.2%) and women (70.0%) stayed within their initial BMI category. The risk for incident IFG was highest for men and women with persisting obesity (37.4% and 24.1%) and lowest with persisting normal weight (15.7% and 9.3%). Men transitioning from normal to overweight increased their risk of incident IFG by factor 1.45 (95%-CI: 1.31, 1.62), women by 1.70 (95%-CI: 1.50, 1.93), whereas transitioning from overweight to normal weight decreased the risk in men by 0.69 (95%-CI: 0.53, 0.90) and 0.94 (95%-CI: 0.66, 1.33) in women. Relative risks for men and women transitioning from obesity to overweight were 0.58 and 0.44, respectively. In conclusion, 10 year weight increase was associated with an increased IFG risk, weight decrease with a decreased risk of IFG in young adults. 相似文献
199.
Bruna Aparecida Souza Machado Gabriele de Abreu Barreto Aline Silva Costa Samantha Serra Costa Rejane Pina Dantas Silva Danielle Figuerêdo da Silva Hugo Neves Brand?o José Luiz Carneiro da Rocha Silmar Baptista Nunes Marcelo Andres Umsza-Guez Francine Ferreira Padilha 《PloS one》2015,10(8)
The aim of this study was to determine the best processing conditions to extract Brazilian green propolis using a supercritical extraction technology. For this purpose, the influence of different parameters was evaluated such as S/F (solvent mass in relation to solute mass), percentage of co-solvent (1 and 2% ethanol), temperature (40 and 50°C) and pressure (250, 350 and 400 bar) using supercritical carbon dioxide. The Global Yield Isotherms (GYIs) were obtained through the evaluation of the yield, and the chemical composition of the extracts was also obtained in relation to the total phenolic compounds, flavonoids, antioxidant activity and 3,5-diprenyl-4-hydroxicinnamic acid (Artepillin C) and acid 4-hydroxycinnamic (p-coumaric acid). The best results were identified at 50°C, 350 bar, 1% ethanol (co-solvent) and S/F of 110. These conditions, a content of 8.93±0.01 and 0.40±0.05 g/100 g of Artepillin C and p-coumaric acid, respectively, were identified indicating the efficiency of the extraction process. Despite of low yield of the process, the extracts obtained had high contents of relevant compounds, proving the viability of the process to obtain green propolis extracts with important biological applications due to the extracts composition. 相似文献
200.
Gabriele Anton Rory Wilson Zhong-hao Yu Cornelia Prehn Sven Zukunft Jerzy Adamski Margit Heier Christa Meisinger Werner R?misch-Margl Rui Wang-Sattler Kristian Hveem Bruce Wolfenbuttel Annette Peters Gabi Kastenmüller Melanie Waldenberger 《PloS one》2015,10(3)
Advances in the “omics” field bring about the need for a high number of good quality samples. Many omics studies take advantage of biobanked samples to meet this need. Most of the laboratory errors occur in the pre-analytical phase. Therefore evidence-based standard operating procedures for the pre-analytical phase as well as markers to distinguish between ‘good’ and ‘bad’ quality samples taking into account the desired downstream analysis are urgently needed. We studied concentration changes of metabolites in serum samples due to pre-storage handling conditions as well as due to repeated freeze-thaw cycles. We collected fasting serum samples and subjected aliquots to up to four freeze-thaw cycles and to pre-storage handling delays of 12, 24 and 36 hours at room temperature (RT) and on wet and dry ice. For each treated aliquot, we quantified 127 metabolites through a targeted metabolomics approach. We found a clear signature of degradation in samples kept at RT. Storage on wet ice led to less pronounced concentration changes. 24 metabolites showed significant concentration changes at RT. In 22 of these, changes were already visible after only 12 hours of storage delay. Especially pronounced were increases in lysophosphatidylcholines and decreases in phosphatidylcholines. We showed that the ratio between the concentrations of these molecule classes could serve as a measure to distinguish between ‘good’ and ‘bad’ quality samples in our study. In contrast, we found quite stable metabolite concentrations during up to four freeze-thaw cycles. We concluded that pre-analytical RT handling of serum samples should be strictly avoided and serum samples should always be handled on wet ice or in cooling devices after centrifugation. Moreover, serum samples should be frozen at or below -80°C as soon as possible after centrifugation. 相似文献