全文获取类型
收费全文 | 3606篇 |
免费 | 265篇 |
国内免费 | 5篇 |
出版年
2023年 | 22篇 |
2022年 | 44篇 |
2021年 | 56篇 |
2020年 | 52篇 |
2019年 | 52篇 |
2018年 | 59篇 |
2017年 | 53篇 |
2016年 | 91篇 |
2015年 | 166篇 |
2014年 | 205篇 |
2013年 | 268篇 |
2012年 | 284篇 |
2011年 | 260篇 |
2010年 | 188篇 |
2009年 | 151篇 |
2008年 | 238篇 |
2007年 | 232篇 |
2006年 | 175篇 |
2005年 | 182篇 |
2004年 | 193篇 |
2003年 | 182篇 |
2002年 | 137篇 |
2001年 | 44篇 |
2000年 | 18篇 |
1999年 | 36篇 |
1998年 | 42篇 |
1997年 | 29篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 28篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 21篇 |
1990年 | 21篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 19篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 10篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 6篇 |
排序方式: 共有3876条查询结果,搜索用时 31 毫秒
241.
A new multicolor-FISH approach for the characterization of marker chromosomes: centromere-specific multicolor-FISH (cenM-FISH) 总被引:6,自引:0,他引:6
Nietzel A Rocchi M Starke H Heller A Fiedler W Wlodarska I Loncarevic IF Beensen V Claussen U Liehr T 《Human genetics》2001,108(3):199-204
Centromere-specific multi-color FISH (cenM-FISH) is a new multicolor FISH technique that allows the simultaneous characterization of all human centromeres by using labeled centromeric satellite DNA as probes. This approach allows the rapid identification of all human centromeres by their individual pseudo-coloring in one single step and is therefore a powerful tool in molecular cytogenetics. CenM-FISH fills a gap in multicolor karyotyping using WCP probes and distinguishes all centromeric regions apart from the evolutionary highly conserved regions on the chromosomes 13 and 21. The usefulness of the cenM-FISH technique for the characterization of small supernumerary marker chromosomes with no (or nearly no) euchromatin and restricted amounts of available sample material is demonstrated in prenatal, postnatal, and tumor cytogenetic cases. In addition, rarely described markers with the involvement of heterochromatic material inserted into homogeneously staining regions could be identified and characterized by using the cenM-FISH technique. 相似文献
242.
DNases were shown to be present in the extracellular fraction of Frankia strains R43 and CcI3. In spite of this, DNA was found in both the extracellular and cell wall fractions of these strains,
and it was shown that extracellular DNA was resistant to the DNases secreted into the culture medium of both Frankia strains. Furthermore, Southern blot analysis under high stringency conditions revealed the chromosomal origin of the cell
wall-adsorbed DNA (CW-DNA). Mobility gel band shift assays suggested that the extracellular DNA and the CW-DNA are engaged
in complexes with other molecules, most likely proteins, which are probably responsible for the enzymatic resistance observed
against extracellular DNase activities. In addition, it was shown that lysis of a small proportion of the cells in the exponential
growth phase may account for the DNA being released into the supernatant and adsorbed to the cell wall.
Received: 21 July 2000 / Accepted: 21 August 2000 相似文献
243.
Frankia KB5 Possesses a Hydrogenase Immunologically Related to Membrane-Bound [NiFe]-Hydrogenases 总被引:1,自引:0,他引:1
The immunological relationship of the hydrogenase in Frankia KB5 to hydrogenases in other microorganisms was investigated using antisera raised against holo-[NiFe]-hydrogenases isolated
from Alcaligenes latus, Azotobacter vinelandii, Ralstonia eutropha, and the small and large hydrogenase subunits from Bradyrhizobium japonicum. The antisera raised against the A. latus, R. eutropha, and B. japonicum (large subunit) polypeptides were found to recognize two polypeptides, corresponding to the unprocessed and processed forms
of the hydrogenase subunit in Frankia KB5. None of the antisera, including the antibodies produced against the small hydrogenase subunit isolated from B. japonicum, recognized any polypeptide related to the small hydrogenase subunit in Frankia KB5. An immunogold localization study of the intracellular distribution of hydrogenase in Frankia KB5, with the cryo-section technique, showed that labeling in the membrane of both hyphae and vesicles was positively correlated
with hydrogenase activity.
Received: 6 November 2000 / Accepted: 18 December 2000 相似文献
244.
Karelson E Bogdanovic N Garlind A Winblad B Zilmer K Kullisaar T Vihalemm T Kairane C Zilmer M 《Neurochemical research》2001,26(4):353-361
The markers of oxidative stress were measured in four cerebrocortical regions of Alzheimer's disease (AD) and age-matched control brains. In controls the levels of diene conjugates (DC) and lipid peroxides (LOOH) were significantly higher in the sensory postcentral and occipital primary cortex than in the temporal inferior or frontal inferior cortex. The antioxidant capacity (AOC) was highest in the temporal, and GSH in the frontal inferior cortex. The highest activity of superoxide dismutase (SOD) and catalase (CAT) was found in the occipital primary cortex. Compared with controls, significantly higher level of DC and LOOH and attenuated AOC were evident in AD temporal inferior cortex. In AD frontal inferior cortex moderate increase in LOOH was associated with positive correlation between SOD activity and counts of senile plaques. Our data suggest that in AD cerebral cortex, the oxidative stress is expressed in the reducing sequence: temporal inferior cortex > frontal inferior cortex > sensory postcentral cortex occipital primary cortex, corresponding to the histopathological spreading of AD from the associative to primary cortical areas. 相似文献
245.
Anita Löfgren 《Pal?ontologische Zeitschrift》1998,72(3-4):337-350
The Lower Ordovician conodont species first described asScolopodusl peselephantis Lindström 1955, has a seximembrate apparatus of laterally compressed, variously curved and flexed coniform elements. These are very small and invariably striated or multicostate. The taxon is reassigned toDecoriconus Cooper 1975, a genus hitherto known by species from Upper Ordovician and Silurian strata. These younger species share several characteristic morphological features with the older species investigated in this work. When studied in detail, it was discovered thatD. peselephantis was the first species in a lineage which also included two successive new species. Of these,D. mercurius n. sp. occurs in the middle Arenig, whileD. pesequus n. sp. ranges from the late middle Arenig and at least through the Llanvirn, possibly even into the Caradoc. These new species, which were previously included intoS.? peselephantis, are described and their geographic distribution investigated. In addition, a probable homeomorphic form ofD. peselephantis, Toxotodus? gabriellae n. sp., is diagnosed. 相似文献
246.
Identification of Highly Attenuated Mutants of Simian Immunodeficiency Virus 总被引:16,自引:11,他引:5 下载免费PDF全文
Ronald C. Desrosiers Jeffrey D. Lifson James S. Gibbs Susan C. Czajak Anita Y. M. Howe Larry O. Arthur R. Paul Johnson 《Journal of virology》1998,72(2):1431-1437
Deletion mutants of the pathogenic clone of simian immunodeficiency virus isolate 239 (SIVmac239) were derived that are missing nef, vpr, and upstream sequences (US) in the U3 region of the LTR (SIVmac239Δ3), nef, vpx, and US (SIVmac239Δ3x), and nef, vpr, vpx, and US (SIVmac239Δ4). These multiply deleted derivatives replicated well in the continuously growing CEMx174 cell line and were infectious for rhesus monkeys. However, on the basis of virus load measurements, strength of antibody responses, and lack of disease progression, these mutants were highly attenuated. Measurements of cell-associated viral load agreed well with assays of plasma viral RNA load and with the strengths of the antibody responses; thus, these measurements likely reflected the extent of viral replication in vivo. A derivative of SIVmac239 lacking vif sequences (SIVmac239Δvif) could be consistently grown only in a vif-complementing cell line. This Δvif virus appeared to be very weakly infectious for rhesus monkeys on the basis of sensitive antibody tests only. The weak antibody responses elicited by SIVmac239Δvif were apparently in response to low levels of replicating virus since they were not elicited by heat-inactivated virus and the anti-SIV antibody responses persisted for greater than 1 year. These results, and the results of previous studies, allow a rank ordering of the relative virulence of nine mutant strains of SIVmac according to the following order: Δvpr > Δvpx > ΔvprΔvpx Δnef > Δ3 > Δ3x ≥ Δ4 > Δvif > Δ5. The results also demonstrate that almost any desired level of attenuation can be achieved, ranging from still pathogenic in a significant proportion of animals (Δvpr and Δvpx) to not detectably infectious (Δ5), simply by varying the number and location of deletions in these five loci. 相似文献
247.
248.
Nader Rahimi Eric Tremblay Laura McAdam Anita Roberts Bruce Elliott 《In vitro cellular & developmental biology. Animal》1998,34(5):412-420
Summary We have developed an in vitro system to examine the influence of adipocytes, a major mammary stromal cell type, on the growth of a murine mammary carcinoma,
SP1. Previously, we have shown that 3T3-L1 adipocytes release a mitogenic factor, hepatocyte growth factor, which strongly
stimulates proliferation of SP1 cells. We now show that 3T3-L1 pre-adipocytes secrete active inhibitory molecules which inhibit
DNA synthesis in SP1 cells. In addition, latent inhibitory activity is present in conditioned media (CM) from both pre-adipocytes
and adipocytes, and is activated following acid treatment. CM also inhibited DNA synthesis in Mv1Lu wild type epithelial cells,
but not DR27 mutant epithelial cells which lack TGF-β type II receptor. Inhibitory activity of CMs was partially abrogated
by neutralizing anti-TGF-β1 and anti-TGF-β2 antibodies, and was removed following ultrafiltration through membranes of 10
000 Mr but not 30 000 Mr pore size. These results show that the inhibitory effect on DNA synthesis is mediated by TGF-β1-like and TGF-β2-like molecules.
In addition, acid-treated CM as well as purified TGF-β inhibited differentiation of pre-adipocytes. Untreated pre-adipocyte
CM, but not mature adipocyte CM, spontaneously inhibited adipocyte differentiation. Together, these findings indicate that
pre-adipocytes spontaneously activate their own secreted TGF-β, whereas mature adipocytes do not, and suggest that activation
of TGF-β has a potent negative regulatory effect on adipocyte differentiation and tumor growth. Thus, TGF-β may be an important
modulator of tumor growth and adipocyte differentiation via both paracrine and autocrine mechanisms. These findings emphasize
the importance of adipocyte-tumor interactions in the regulation of tumor microenvironment. 相似文献
249.
Identification of an integral membrane 80 kDa protein of Saccharomyces cerevisiae induced in response to dehydration 下载免费PDF全文
Using SDS-PAGE gels we observed the induced synthesis of a protein with a molecular mass of 80 kDa when cells of strains of Saccharomyces cerevisiae were subjected to dehydration. Physiological analysis showed that this protein is not present during growth on glucose but was found in derepressed cells from stationary phase. Furthermore, its synthesis was induced when cells were grown on medium containing α-methyl-glucoside as carbon source. However, the 80 kDa protein was not found in cells of mutants unable to transport trehalose. This protein was localized in the cytoplasmic membrane and showed trehalose-binding activity, determined by its partial purification on a trehalose–Sepharose 6B affinity column. The possible involvement of the 80 kDa protein with the trehalose transport system is discussed. 相似文献
250.
Petter Angell Olsen Anita Solhaug James Alexander Booth Monika Gelazauskaite Stefan Krauss 《DNA Repair》2009,8(3):298-308
Single-stranded oligonucleotides (ssODNs) and zinc-finger nucleases (ZFNs) are two approaches that are being pursued to achieve sequence specific genome modification. ZFNs induce high rates of homologous recombination (HR) between the target sequence and a given donor by introducing site-specific genomic double-strand breaks (DSBs). The mode of action that is used by ssODNs remains largely unknown, but may involve genomic integration of the ssODNs. In this work, cellular responses following ssODN and ZFN mediated correction of a genomic reporter gene have been investigated in human cells. Comparison of the cell cycle distribution of corrected cells following ssODN or ZFN exposure, established that ssODN corrected cells were arrested in the late S and G2/M cell cycle phases, while ZFN corrected cells displayed normal cell cycle profiles. We demonstrate that after ssODN mediated gene correction, phosphorylation of the damage sensor protein H2AX could be observed in 5.8% and 29% of the corrected cells, using a single copy and a multi copy reporter, respectively. When using the ZFN strategy in a single copy reporter only 1.5% of the corrected cells were positive for γ-H2AX staining. By direct detection of genomic DSBs we establish that the observed cell cycle arrest following ssODN mediated gene correction could be associated with the presence of unrepaired genomic DSBs. Lastly, we establish that although a mutant cellular mismatch repair (MMR) system as expected enhanced ssODN mediated gene correction, the capacity of the ssODN corrected cells to proliferate was not influenced by the MMR system. In conclusion gene correction by means of the ssODN strategy leads to activation of DNA damage signalling and cell cycle arrest due to formation of unrepaired genomic DSBs in a high proportion of the corrected cells. On the contrary, cells corrected using ZFNs displayed normal cell cycle distribution and lower rates of DNA damage. 相似文献